Monday, January 11, 2010
Wednesday, December 23, 2009
Suturing and Such
And 5 months later I am back...
The new topic is:
SUTURING
This week the suture technique is:
Simple Interrupted Suturing
Text on this type of suturing will be available later in the week.
Later,
Hannah M. Loveland
"Future MD, PhD, FACS, ABS"
The new topic is:
SUTURING
This week the suture technique is:
Simple Interrupted Suturing
Text on this type of suturing will be available later in the week.
Later,
Hannah M. Loveland
"Future MD, PhD, FACS, ABS"
Sunday, July 5, 2009
Taking a Break
I will be taking a hiatus from posting on here
I need to help someone
I do not have the time
But I will resume sometime this month
Till We Meet Again,
Hannah Marie
"Future RNFA, ARNP, PhD, MBChB"
I need to help someone
I do not have the time
But I will resume sometime this month
Till We Meet Again,
Hannah Marie
"Future RNFA, ARNP, PhD, MBChB"
Monday, June 22, 2009
Diffusion MRI
PROCEDURE OF THE DAY
Diffusion MRI
Diffusion MRI is a magnetic resonance imaging (MRI) method that produces in vivo images of biological tissues weighted with the local microstructural characteristics of water diffusion. The field of diffusion MRI can best be understood in terms of two distinct classes of application - Diffusion Weighted MRI and Diffusion Tensor MRI.
In Diffusion Weighted Imaging (DWI), each image voxel (three dimensional pixel) has an image intensity that reflects a single best measurement of the rate of water diffusion at that location. This measurement is far more sensitive to early changes after a stroke than more traditional MRI measurements such as T1 or T2 relaxation rates. DWI is most applicable when the tissue of interest is dominated by isotropic water movement - the diffusion rate appears to be the same when measured along any axis.
Diffusion Tensor Imaging (DTI) is important when a tissue - such as the neural axons of white matter in the brain or muscle fibers in the heart - has an internal fibrous structure analogous to the anisotropy of some crystals. The result is that water will diffuse more rapidly in the direction aligned with the internal structure and more slowly as it moves perpendicular to the preferred direction. This also means that the measured rate of diffusion will differ depending on the direction from which an observer is looking. In DTI, each voxel therefore has one or more pairs of parameters: a rate of diffusion and a preferred direction of diffusion - described in terms of three dimensional space - for which that parameter is valid. The properties of each voxel of a single DTI image is usually calculated by vector or tensor math from six or more different diffusion weighted acquisitions, each obtained with a different orientation of the diffusion sensitizing gradients. In some methods, hundreds of measurements - each making up a complete image - are made to generate a single resulting calculated image data set. The higher information content of a DTI voxel makes it extremely sensitive to subtle pathology in the brain. In addition the directional information can be exploited at a higher level of structure to select and follow neural tracts through the brain - a process called tractography. [1][2]
A more precise statement of the image acquisition process is that, the image-intensities at each position are attenuated, depending on the strength (b-value) and direction of the so-called magnetic diffusion gradient, as well as on the local microstructure in which the water molecules diffuse. The more attenuated the image is at a given position, the more diffusion there is in the direction of the diffusion gradient. In order to measure the tissue's complete diffusion profile, one needs to repeat the MR scans, applying different directions (and possibly strengths) of the diffusion gradient for each scan.
Traditionally, in diffusion-weighted imaging (DWI), three gradient-directions are applied, sufficient to estimate the trace of the diffusion tensor or 'average diffusivity', a putative measure of edema. Clinically, trace-weighted images have proven to be very useful to diagnose vascular strokes in the brain, by early detection (within a couple of minutes) of the hypoxic edema.
More extended diffusion tensor imaging (DTI) scans derive neural tract directional information from the data using 3D or multidimensional vector algorithms based on three, six, or more gradient directions, sufficient to compute the diffusion tensor. The diffusion model is a rather simple model of the diffusion process, assuming homogeneity and linearity of the diffusion within each image-voxel. From the diffusion tensor, diffusion anisotropy measures such as the Fractional Anisotropy (FA), can be computed. Moreover, the principal direction of the diffusion tensor can be used to infer the white-matter connectivity of the brain (i.e. tractography; trying to see which part of the brain is connected to which other part).
Recently, more advanced models of the diffusion process have been proposed that aim to overcome the weaknesses of the diffusion tensor model. Amongst others, these include q-space imaging and generalized diffusion tensor imaging.
Bloch-Torrey Equation
In 1956, H.C. Torrey mathematically showed how the Bloch equation for magnetization would change with the addition of diffusion.[3] Torrey modified Bloch's original description of transverse magnetization to include diffusion terms and the application of a spatially varying gradient. The Bloch-Torrey equation neglecting relaxation is:
\frac{dM_+}{dt}=-j \gamma \vec r \cdot \vec G M_+ + \vec \nabla^T \cdot \vec {\vec D} \cdot \vec \nabla M_+
For the simplest case where the diffusion is isotropic the diffusion tensor is
\vec {\vec D} = D \cdot \vec I = D \cdot \begin{bmatrix} 1 & 0 & 0 \\ 0 & 1 & 0 \\ 0 & 0 & 1 \end{bmatrix},
which means that the Bloch-Torrey equation will have the solution
M_+(\vec r,t)=M_0e^{-\frac{1}{3}D\gamma ^2G^2t^3}e^{-j\gamma \vec r \cdot \int_0^tdt' \vec G(t')}.
This demonstrates a cubic dependence of transverse magnetization on time. Anisotropic diffusion will have a similar solution method, but with a more complex diffusion tensor.
Diffusion-weighted imaging
Diffusion-weighted imaging is an MRI method that produces in vivo magnetic resonance images of biological tissues weighted with the local characteristics of water diffusion.
DWI is a modification of regular MRI techniques, and is an approach which utilizes the measurement of Brownian motion of molecules. Regular MRI acquisition utilizes the behaviour of protons in water to generate contrast between clinically relevant features of a particular subject. The versatile nature of MRI is due to this capability of producing contrast, called weighting. In a typical T1-weighted image, water molecules in a sample are excited with the imposition of a strong magnetic field. This causes many of the protons in water molecules to precess simultaneously, producing signals in MRI. In T2-weighted images, contrast is produced by measuring the loss of coherence or synchrony between the water protons. When water is in an environment where it can freely tumble, relaxation tends to take longer. In certain clinical situations, this can generate contrast between an area of pathology and the surrounding healthy tissue.
In diffusion-weighted images, instead of a homogeneous magnetic field, the homogeneity is varied linearly by a pulsed field gradient. Since precession is proportional to the magnet strength, the protons begin to precess at different rates, resulting in dispersion of the phase and signal loss. Another gradient pulse is applied in the same direction but with opposite magnitude to refocus or rephase the spins. The refocusing will not be perfect for protons that have moved during the time interval between the pulses, and the signal measured by the MRI machine is reduced. This reduction in signal due to the application of the pulse gradient can be related to the amount of diffusion that is occurring through the following equation:
\frac{S}{S_0} = e^{-\gamma^2 G^2 \delta^2 \left( \Delta - \delta /3 \right) D} = e^{-b D}\,
where S0 is the signal intensity without the diffusion weighting, S is the signal with the gradient, γ is the gyromagnetic ratio, G is the strength of the gradient pulse, δ is the duration of the pulse, Δ is the time between the two pulses, and finally, D is the diffusion constant.
By rearranging the formula to isolate the diffusion-coefficient, it is possible to obtain an idea of the properties of diffusion occurring within a particular voxel (volume picture element). These values, called apparent diffusion coefficient (ADC) can then be mapped as an image, using diffusion as the contrast.
The first successful clinical application of DWI was in imaging the brain following stroke in adults. Areas which were injured during a stroke showed up "darker" on an ADC map compared to healthy tissue. At about the same time as it became evident to researchers that DWI could be used to assess the severity of injury in adult stroke patients, they also noticed that ADC values varied depending on which way the pulse gradient was applied. This orientation-dependent contrast is generated by diffusion anisotropy, meaning that the diffusion in parts of the brain has directionality. This may be useful for determining structures in the brain which could restrict the flow of water in one direction, such as the myelinated axons of nerve cells (which is affected by multiple sclerosis). However, in imaging the brain following a stroke, it may actually prevent the injury from being seen. To compensate for this, it is necessary to apply a mathematical operator, called a tensor, to fully characterize the motion of water in all directions. This tensor is called a diffusion tensor: \bar{D} = \begin{vmatrix} D_{xx} & D_{xy} & D_{xz} \\ D_{xy} & D_{yy} & D_{yz} \\ D_{xz} & D_{yz} & D_{zz} \end{vmatrix}
Diffusion-weighted images are very useful to diagnose vascular strokes in the brain. Diffusion tensor imaging is being developed for studying the diseases of the white matter of the brain as well as for studies of other body tissues (see below).
Diffusion Anisotropy indices
There are various coefficients used for estimating the anisotropy from the diffusion matrix. Here is a list of a few of them:
Fractional Anisotropy (FA)
\sqrt{3[(\lambda_1-\langle\lambda\rangle)^2+(\lambda_2-\langle\lambda\rangle)^2+(\lambda_3-\langle\lambda\rangle)^2] \over 2(\lambda_1^2+\lambda_2^2+\lambda_3^2)}
Diffusion tensor imaging
Diffusion tensor imaging (DTI) is a magnetic resonance imaging (MRI) technique that enables the measurement of the restricted diffusion of water in tissue in order to produce neural tract images instead of using this data solely for the purpose of assigning contrast or colors to pixels in a cross sectional image. It also provides useful structural information about muscle - including heart muscle, as well as other tissues such as the prostate. [4]
History
In 1990, Michael Moseley reported that water diffusion in white matter was anisotropic - the effect of diffusion on proton relaxation varied depending on the orientation of tracts relative to the orientation of the diffusion gradient applied by the imaging scanner. He also pointed out that this should best be described by a tensor.[5] Aaron Filler and colleagues reported in 1991 on the use of MRI for tract tracing in the brain using a contrast agent method but pointed out that Moseley's report on polarized water diffusion along nerves would affect the development of tract tracing.[6] A few months after submitting that report, in 1991, the first successful use of diffusion anisotropy data to carry out the tracing of neural tracts curving through the brain without contrast agents was accomplished.[7][1][8] Filler and colleagues identified both vector and tensor based methods in the patents, but the data for these initial images was obtained using the following sets of vector formulas:
(\text{vector length})^2 = BX^2 + BY^2 + BZ^2 \,
\text{diffusion vector angle between }BX\text{ and }BY = \arctan \frac{BY}{BX}
\text{diffusion vector angle between }BX\text{ and }BZ = \arctan \frac{BZ}{BX}
\text{diffusion vector angle between }BY\text{ and }BZ = \arctan \frac{BY}{BZ}
The first DTI image showing neural tracts curving through the brain in Macaca fascicularis (Filler et al. 1992)[8]
The use of mixed contributions from gradients in the three primary orthogonal axes in order to generate an infinite number of differently oriented gradients for tensor analysis was also identified in 1992 as the basis for accomplishing tensor descriptions of water diffusion in MRI voxels.[9][10][11] Both vector and tensor methods provide a "rotationally invariant" measurement - the magnitude will be the same no matter how the tract is oriented relative to the gradient axes - and both provide a three dimensional direction in space, however the tensor method is more efficient and accurate for carrying out tractography.[1]
The use of electromagnetic data acquisitions from six or more directions to construct a tensor ellipsoid was known from other fields at the time,[12] as was the use of the tensor ellipsoid to describe diffusion. [13] The invention of DTI therefore involved two aspects - 1) the application of known methods from other fields for the generation of MRI tensor data and 2) the usable introduction of a three dimensional selective neural tract "vector graphic" concept operating at a macroscopic level above the scale of the image voxel, in a field where two dimensional pixel imaging (bit mapped graphics) had been the only method used since MRI was originated.
Applications
The principal application is in the imaging of white matter where the location, orientation, and anisotropy of the tracts can be measured. The architecture of the axons in parallel bundles, and their myelin sheaths, facilitate the diffusion of the water molecules preferentially along their main direction. Such preferentially oriented diffusion is called anisotropic diffusion.
Tractographic reconstruction of neural connections via DTI
The imaging of this property is an extension of diffusion MRI. If a series of diffusion gradients (i.e. magnetic field variations in the MRI magnet) are applied that can determine at least 3 directional vectors (use of 6 different gradients is the minimum and additional gradients improve the accuracy for "off-diagonal" information), it is possible to calculate, for each voxel, a tensor (i.e. a symmetric positive definite 3 ×3 matrix) that describes the 3-dimensional shape of diffusion. The fiber direction is indicated by the tensor’s main eigenvector. This vector can be color-coded, yielding a cartography of the tracts' position and direction (red for left-right, blue for superior-inferior, and green for anterior-posterior). The brightness is weighted by the fractional anisotropy which is a scalar measure of the degree of anisotropy in a given voxel. Mean Diffusivity (MD) or Trace is a scalar measure of the total diffusion within a voxel. These measures are commonly used clinically to localize white matter lesions that do not show up on other forms of clinical MRI.
Diffusion tensor imaging data can be used to perform tractography within white matter. Fiber tracking algorithms can be used to track a fiber along its whole length (e.g. the corticospinal tract, through which the motor information transit from the motor cortex to the spinal cord and the peripheral nerves). Tractography is a useful tool for measuring deficits in white matter, such as in aging. Its estimation of fiber orientation and strength is increasingly accurate, and it has widespread potential implications in the fields of cognitive neuroscience and neurobiology.
Some clinical applications of DTI are in the tract-specific localization of white matter lesions such as trauma and in defining the severity of diffuse traumatic brain injury. The localization of tumors in relation to the white matter tracts (infiltration, deflection), has been one the most important initial applications. In surgical planning for some types of brain tumors, surgery is aided by knowing the proximity and relative position of the corticospinal tract and a tumor.
The use of DTI for the assessment of white matter in development, pathology and degeneration has been the focus of over 2,500 research publications since 2005. It promises to be very helpful in distinguishing Alzheimer's disease from other types of dementia. Applications in brain research cover e.g. connectionistic investigation of neural networks in vivo.[14]
DTI also has applications in the characterization of skeletal and cardiac muscle. The sensitivity to fiber orientation also appears to be helpful in the arena of sports medicine where it greatly aids imaging of structure and injury in muscles and tendons.
A recent study at Barnes-Jewish Hospital and Washington University School of Medicine of healthy persons and both newly affected and chronically-afflicted individuals with optic neuritis caused by multiple sclerosis (MS) showed that DTI can be used to assess the course of the condition's effects on the eye's optic nerve and the vision because it can assess axial diffusivity of water flow in the area.
VIDEO
NEXT UP
Magnetic Resonance Imaging
Diffusion MRI
Diffusion MRI is a magnetic resonance imaging (MRI) method that produces in vivo images of biological tissues weighted with the local microstructural characteristics of water diffusion. The field of diffusion MRI can best be understood in terms of two distinct classes of application - Diffusion Weighted MRI and Diffusion Tensor MRI.
In Diffusion Weighted Imaging (DWI), each image voxel (three dimensional pixel) has an image intensity that reflects a single best measurement of the rate of water diffusion at that location. This measurement is far more sensitive to early changes after a stroke than more traditional MRI measurements such as T1 or T2 relaxation rates. DWI is most applicable when the tissue of interest is dominated by isotropic water movement - the diffusion rate appears to be the same when measured along any axis.
Diffusion Tensor Imaging (DTI) is important when a tissue - such as the neural axons of white matter in the brain or muscle fibers in the heart - has an internal fibrous structure analogous to the anisotropy of some crystals. The result is that water will diffuse more rapidly in the direction aligned with the internal structure and more slowly as it moves perpendicular to the preferred direction. This also means that the measured rate of diffusion will differ depending on the direction from which an observer is looking. In DTI, each voxel therefore has one or more pairs of parameters: a rate of diffusion and a preferred direction of diffusion - described in terms of three dimensional space - for which that parameter is valid. The properties of each voxel of a single DTI image is usually calculated by vector or tensor math from six or more different diffusion weighted acquisitions, each obtained with a different orientation of the diffusion sensitizing gradients. In some methods, hundreds of measurements - each making up a complete image - are made to generate a single resulting calculated image data set. The higher information content of a DTI voxel makes it extremely sensitive to subtle pathology in the brain. In addition the directional information can be exploited at a higher level of structure to select and follow neural tracts through the brain - a process called tractography. [1][2]
A more precise statement of the image acquisition process is that, the image-intensities at each position are attenuated, depending on the strength (b-value) and direction of the so-called magnetic diffusion gradient, as well as on the local microstructure in which the water molecules diffuse. The more attenuated the image is at a given position, the more diffusion there is in the direction of the diffusion gradient. In order to measure the tissue's complete diffusion profile, one needs to repeat the MR scans, applying different directions (and possibly strengths) of the diffusion gradient for each scan.
Traditionally, in diffusion-weighted imaging (DWI), three gradient-directions are applied, sufficient to estimate the trace of the diffusion tensor or 'average diffusivity', a putative measure of edema. Clinically, trace-weighted images have proven to be very useful to diagnose vascular strokes in the brain, by early detection (within a couple of minutes) of the hypoxic edema.
More extended diffusion tensor imaging (DTI) scans derive neural tract directional information from the data using 3D or multidimensional vector algorithms based on three, six, or more gradient directions, sufficient to compute the diffusion tensor. The diffusion model is a rather simple model of the diffusion process, assuming homogeneity and linearity of the diffusion within each image-voxel. From the diffusion tensor, diffusion anisotropy measures such as the Fractional Anisotropy (FA), can be computed. Moreover, the principal direction of the diffusion tensor can be used to infer the white-matter connectivity of the brain (i.e. tractography; trying to see which part of the brain is connected to which other part).
Recently, more advanced models of the diffusion process have been proposed that aim to overcome the weaknesses of the diffusion tensor model. Amongst others, these include q-space imaging and generalized diffusion tensor imaging.
Bloch-Torrey Equation
In 1956, H.C. Torrey mathematically showed how the Bloch equation for magnetization would change with the addition of diffusion.[3] Torrey modified Bloch's original description of transverse magnetization to include diffusion terms and the application of a spatially varying gradient. The Bloch-Torrey equation neglecting relaxation is:
\frac{dM_+}{dt}=-j \gamma \vec r \cdot \vec G M_+ + \vec \nabla^T \cdot \vec {\vec D} \cdot \vec \nabla M_+
For the simplest case where the diffusion is isotropic the diffusion tensor is
\vec {\vec D} = D \cdot \vec I = D \cdot \begin{bmatrix} 1 & 0 & 0 \\ 0 & 1 & 0 \\ 0 & 0 & 1 \end{bmatrix},
which means that the Bloch-Torrey equation will have the solution
M_+(\vec r,t)=M_0e^{-\frac{1}{3}D\gamma ^2G^2t^3}e^{-j\gamma \vec r \cdot \int_0^tdt' \vec G(t')}.
This demonstrates a cubic dependence of transverse magnetization on time. Anisotropic diffusion will have a similar solution method, but with a more complex diffusion tensor.
Diffusion-weighted imaging
Diffusion-weighted imaging is an MRI method that produces in vivo magnetic resonance images of biological tissues weighted with the local characteristics of water diffusion.
DWI is a modification of regular MRI techniques, and is an approach which utilizes the measurement of Brownian motion of molecules. Regular MRI acquisition utilizes the behaviour of protons in water to generate contrast between clinically relevant features of a particular subject. The versatile nature of MRI is due to this capability of producing contrast, called weighting. In a typical T1-weighted image, water molecules in a sample are excited with the imposition of a strong magnetic field. This causes many of the protons in water molecules to precess simultaneously, producing signals in MRI. In T2-weighted images, contrast is produced by measuring the loss of coherence or synchrony between the water protons. When water is in an environment where it can freely tumble, relaxation tends to take longer. In certain clinical situations, this can generate contrast between an area of pathology and the surrounding healthy tissue.
In diffusion-weighted images, instead of a homogeneous magnetic field, the homogeneity is varied linearly by a pulsed field gradient. Since precession is proportional to the magnet strength, the protons begin to precess at different rates, resulting in dispersion of the phase and signal loss. Another gradient pulse is applied in the same direction but with opposite magnitude to refocus or rephase the spins. The refocusing will not be perfect for protons that have moved during the time interval between the pulses, and the signal measured by the MRI machine is reduced. This reduction in signal due to the application of the pulse gradient can be related to the amount of diffusion that is occurring through the following equation:
\frac{S}{S_0} = e^{-\gamma^2 G^2 \delta^2 \left( \Delta - \delta /3 \right) D} = e^{-b D}\,
where S0 is the signal intensity without the diffusion weighting, S is the signal with the gradient, γ is the gyromagnetic ratio, G is the strength of the gradient pulse, δ is the duration of the pulse, Δ is the time between the two pulses, and finally, D is the diffusion constant.
By rearranging the formula to isolate the diffusion-coefficient, it is possible to obtain an idea of the properties of diffusion occurring within a particular voxel (volume picture element). These values, called apparent diffusion coefficient (ADC) can then be mapped as an image, using diffusion as the contrast.
The first successful clinical application of DWI was in imaging the brain following stroke in adults. Areas which were injured during a stroke showed up "darker" on an ADC map compared to healthy tissue. At about the same time as it became evident to researchers that DWI could be used to assess the severity of injury in adult stroke patients, they also noticed that ADC values varied depending on which way the pulse gradient was applied. This orientation-dependent contrast is generated by diffusion anisotropy, meaning that the diffusion in parts of the brain has directionality. This may be useful for determining structures in the brain which could restrict the flow of water in one direction, such as the myelinated axons of nerve cells (which is affected by multiple sclerosis). However, in imaging the brain following a stroke, it may actually prevent the injury from being seen. To compensate for this, it is necessary to apply a mathematical operator, called a tensor, to fully characterize the motion of water in all directions. This tensor is called a diffusion tensor: \bar{D} = \begin{vmatrix} D_{xx} & D_{xy} & D_{xz} \\ D_{xy} & D_{yy} & D_{yz} \\ D_{xz} & D_{yz} & D_{zz} \end{vmatrix}
Diffusion-weighted images are very useful to diagnose vascular strokes in the brain. Diffusion tensor imaging is being developed for studying the diseases of the white matter of the brain as well as for studies of other body tissues (see below).
Diffusion Anisotropy indices
There are various coefficients used for estimating the anisotropy from the diffusion matrix. Here is a list of a few of them:
Fractional Anisotropy (FA)
\sqrt{3[(\lambda_1-\langle\lambda\rangle)^2+(\lambda_2-\langle\lambda\rangle)^2+(\lambda_3-\langle\lambda\rangle)^2] \over 2(\lambda_1^2+\lambda_2^2+\lambda_3^2)}
Diffusion tensor imaging
Diffusion tensor imaging (DTI) is a magnetic resonance imaging (MRI) technique that enables the measurement of the restricted diffusion of water in tissue in order to produce neural tract images instead of using this data solely for the purpose of assigning contrast or colors to pixels in a cross sectional image. It also provides useful structural information about muscle - including heart muscle, as well as other tissues such as the prostate. [4]
History
In 1990, Michael Moseley reported that water diffusion in white matter was anisotropic - the effect of diffusion on proton relaxation varied depending on the orientation of tracts relative to the orientation of the diffusion gradient applied by the imaging scanner. He also pointed out that this should best be described by a tensor.[5] Aaron Filler and colleagues reported in 1991 on the use of MRI for tract tracing in the brain using a contrast agent method but pointed out that Moseley's report on polarized water diffusion along nerves would affect the development of tract tracing.[6] A few months after submitting that report, in 1991, the first successful use of diffusion anisotropy data to carry out the tracing of neural tracts curving through the brain without contrast agents was accomplished.[7][1][8] Filler and colleagues identified both vector and tensor based methods in the patents, but the data for these initial images was obtained using the following sets of vector formulas:
(\text{vector length})^2 = BX^2 + BY^2 + BZ^2 \,
\text{diffusion vector angle between }BX\text{ and }BY = \arctan \frac{BY}{BX}
\text{diffusion vector angle between }BX\text{ and }BZ = \arctan \frac{BZ}{BX}
\text{diffusion vector angle between }BY\text{ and }BZ = \arctan \frac{BY}{BZ}
The first DTI image showing neural tracts curving through the brain in Macaca fascicularis (Filler et al. 1992)[8]
The use of mixed contributions from gradients in the three primary orthogonal axes in order to generate an infinite number of differently oriented gradients for tensor analysis was also identified in 1992 as the basis for accomplishing tensor descriptions of water diffusion in MRI voxels.[9][10][11] Both vector and tensor methods provide a "rotationally invariant" measurement - the magnitude will be the same no matter how the tract is oriented relative to the gradient axes - and both provide a three dimensional direction in space, however the tensor method is more efficient and accurate for carrying out tractography.[1]
The use of electromagnetic data acquisitions from six or more directions to construct a tensor ellipsoid was known from other fields at the time,[12] as was the use of the tensor ellipsoid to describe diffusion. [13] The invention of DTI therefore involved two aspects - 1) the application of known methods from other fields for the generation of MRI tensor data and 2) the usable introduction of a three dimensional selective neural tract "vector graphic" concept operating at a macroscopic level above the scale of the image voxel, in a field where two dimensional pixel imaging (bit mapped graphics) had been the only method used since MRI was originated.
Applications
The principal application is in the imaging of white matter where the location, orientation, and anisotropy of the tracts can be measured. The architecture of the axons in parallel bundles, and their myelin sheaths, facilitate the diffusion of the water molecules preferentially along their main direction. Such preferentially oriented diffusion is called anisotropic diffusion.
Tractographic reconstruction of neural connections via DTI
The imaging of this property is an extension of diffusion MRI. If a series of diffusion gradients (i.e. magnetic field variations in the MRI magnet) are applied that can determine at least 3 directional vectors (use of 6 different gradients is the minimum and additional gradients improve the accuracy for "off-diagonal" information), it is possible to calculate, for each voxel, a tensor (i.e. a symmetric positive definite 3 ×3 matrix) that describes the 3-dimensional shape of diffusion. The fiber direction is indicated by the tensor’s main eigenvector. This vector can be color-coded, yielding a cartography of the tracts' position and direction (red for left-right, blue for superior-inferior, and green for anterior-posterior). The brightness is weighted by the fractional anisotropy which is a scalar measure of the degree of anisotropy in a given voxel. Mean Diffusivity (MD) or Trace is a scalar measure of the total diffusion within a voxel. These measures are commonly used clinically to localize white matter lesions that do not show up on other forms of clinical MRI.
Diffusion tensor imaging data can be used to perform tractography within white matter. Fiber tracking algorithms can be used to track a fiber along its whole length (e.g. the corticospinal tract, through which the motor information transit from the motor cortex to the spinal cord and the peripheral nerves). Tractography is a useful tool for measuring deficits in white matter, such as in aging. Its estimation of fiber orientation and strength is increasingly accurate, and it has widespread potential implications in the fields of cognitive neuroscience and neurobiology.
Some clinical applications of DTI are in the tract-specific localization of white matter lesions such as trauma and in defining the severity of diffuse traumatic brain injury. The localization of tumors in relation to the white matter tracts (infiltration, deflection), has been one the most important initial applications. In surgical planning for some types of brain tumors, surgery is aided by knowing the proximity and relative position of the corticospinal tract and a tumor.
The use of DTI for the assessment of white matter in development, pathology and degeneration has been the focus of over 2,500 research publications since 2005. It promises to be very helpful in distinguishing Alzheimer's disease from other types of dementia. Applications in brain research cover e.g. connectionistic investigation of neural networks in vivo.[14]
DTI also has applications in the characterization of skeletal and cardiac muscle. The sensitivity to fiber orientation also appears to be helpful in the arena of sports medicine where it greatly aids imaging of structure and injury in muscles and tendons.
A recent study at Barnes-Jewish Hospital and Washington University School of Medicine of healthy persons and both newly affected and chronically-afflicted individuals with optic neuritis caused by multiple sclerosis (MS) showed that DTI can be used to assess the course of the condition's effects on the eye's optic nerve and the vision because it can assess axial diffusivity of water flow in the area.
VIDEO
NEXT UP
Magnetic Resonance Imaging
Sunday, June 21, 2009
Phage therapy
PROCEDURE OF THE DAY
Phage therapy
Phage therapy is the therapeutic use of bacteriophages to treat pathogenic bacterial infections. Although extensively used and developed mainly in former Soviet Union countries for about 90 years, this method of therapy is still being tested elsewhere for treatment of a variety of bacterial and poly-microbial biofilm infections, and has not yet been approved in countries other than Georgia. Phage therapy has many potential applications in human medicine as well as dentistry, veterinary science, and agriculture.[1] If the target host of a phage therapy treatment is not an animal, however, then the term "biocontrol" (as in phage-mediated biocontrol of bacteria) is sometimes employed rather than "phage therapy".
A hypothetical benefit of phage therapy is that bacteriophages can be much more specific than more common drugs, so they can be chosen to be indirectly harmless not only to the host organism (human, animal, or plant), but also to other beneficial bacteria, such as gut flora, reducing the chances of opportunistic infections. They also have a high therapeutic index, that is, phage therapy gives rise to few if any side effects, as opposed to drugs, and does not stress the liver. Because phages replicate in vivo, a smaller effective dose can be used. On the other hand, this specificity is also a disadvantage: A phage will only kill a bacterium if it is a match to the specific strain. Thus, phage mixtures are often applied to improve the chances of success, or samples can be taken and an appropriate phage identified and grown.
Phages are currently being used therapeutically to treat bacterial infections that do not respond to conventional antibiotics, particularly in the country of Georgia.[2][3][4] They tend to be more successful than antibiotics where there is a biofilm covered by a polysaccharide layer, which antibiotics typically cannot penetrate. [5] In the West, no therapies are currently authorized for use on humans, although phages for killing food poisoning bacteria (Listeria) are now in use.[6]
History
Following the discovery of bacteriophages by Frederick Twort and Felix d'Hérelle[7] in 1915 and 1917, phage therapy was immediately recognized by many to be a key way forward for the eradication of bacterial infections. A Georgian, George Eliava, was making similar discoveries. He travelled to the Pasteur Institute in Paris where he met d'Hérelle, and in 1926 he founded the Eliava Institute in Tbilisi, Georgia, devoted to the development of phage therapy.
In neighbouring countries including Russia, extensive research and development soon began in this field. In the USA during the 1940s, commercialization of phage therapy was undertaken by the large pharmaceutical company, Eli Lilly.
Whilst knowledge was being accumulated regarding the biology of phages and how to use phage cocktails correctly, early uses of phage therapy were often unreliable. When antibiotics were discovered in 1941 and marketed widely in the USA and Europe, Western scientists mostly lost interest in further use and study of phage therapy for some time.[8]
Isolated from Western advances in antibiotic production in the 1940s, Russian scientists continued to develop already successful phage therapy to treat the wounds of soldiers in field hospitals. During World War II, the Soviet Union used bacteriophages to treat many soldiers infected with various bacterial diseases e.g. dysentery and gangrene. The success rate was as good as, if not better than any antibiotic.[citation needed] Russian researchers continued to develop and to refine their treatments and to publish their research and results. However, due to the scientific barriers of the Cold War, this knowledge was not translated and did not proliferate across the world.[9][10]
There is an extensive library and research center at the Eliava Institute in Tbilisi, Georgia. Phage therapy is today a widespread form of treatment in that region. For 80 years Georgian doctors have been treating local people, including babies and newborns, with phages.
As a result of the development of antibiotic resistance since the 1950s and an advancement of scientific knowledge, there has been renewed interest worldwide in the ability of phage therapy to eradicate bacterial infections and chronic polymicrobial biofilm, along with other strategies.
Phages have been investigated as a potential means to eliminate pathogens like Campylobacter in raw food[11] and Listeria in fresh food or to reduce food spoilage bacteria.[12] In agricultural practice phages were used to fight pathogens like Campylobacter, Escherichia and Salmonella in farm animals, Lactococcus and Vibrio pathogens in fish from aquaculture and Erwinia and Xanthomonas in plants of agricultural importance. The oldest use was, however, in human medicine. Phages have been used against diarrheal diseases caused by E. coli, Shigella or Vibrio and against wound infections caused by facultative pathogens of the skin like staphylococci and streptococci. Recently the phage therapy approach has been applied to systemic and even intracellular infections and the addition of non-replicating phage and isolated phage enzymes like lysins to the antimicrobial arsenal. However, actual proof for the efficiency of these phage approaches in the field or the hospital is not available.[12]
Some of the interest in the West can be traced back to 1994, when Soothill demonstrated (in an animal model) that the use of phages could improve the success of skin grafts by reducing the underlying Pseudomonas aeruginosa infection.[13] Recent studies have provided additional support for these findings in the model system.[14]
Although not phage therapy in the original sense, the use of phages as delivery mechanisms for traditional antibiotics has been proposed.[15][16] The use of phages to deliver antitumor agents has also been described, in preliminary in vitro experiments for cells in tissue culture.[17].
Potential benefits
A hypothetical benefit of phage therapy is freedom from the adverse effects of antibiotics. Additionally, it is conceivable that, although bacteria rapidly develop resistance to phage, the resistance might be easier to overcome than resistance to antibiotics.
Bacteriophages are very specific, targeting only one or a few strains of bacteria.[18] Traditional antibiotics have more wide-ranging effect, killing both harmful bacteria and useful bacteria such as those facilitating food digestion. The specificity of bacteriophages might reduce the chance that useful bacteria are killed when fighting an infection.
Increasing evidence shows the ability of phages to travel to a required site — including the brain, where the blood brain barrier can be crossed — and multiply in the presence of an appropriate bacterial host, to combat infections such as meningitis. However the patient's immune system can, in some cases mount an immune response to the phage (2 out of 44 patients in a Polish trial[19]).
Development and production is faster than antibiotics, on condition that the required recognition molecules are known.[citation needed]
Research groups in the West are engineering a broader spectrum phage and also target MRSA treatments in a variety of forms - including impregnated wound dressings, preventative treatment for burn victims, phage-impregnated sutures.[20] Enzobiotics are a new development at Rockefeller University that create enzymes from phage. These show potential for preventing secondary bacterial infections e.g. pneumonia developing with patients suffering from flu, otitis etc..[citation needed]
Some bacteria such as multiply resistant Klebsiella pneumoniae have no non toxic antibiotics available, and yet killing of the bacteria via intraperitoneal, intravenous or intranasal of phages in vivo has been shown to work in laboratory tests.[21]
Risks of Phage Therapy
Phase therapy also has disadvantages:
Unlike antibiotics, phages must be refrigerated until used,[22] and a physician wishing to prescribe them needs special training in order to correctly prescribe and use phages.
Phages come in a great variety. That diversity becomes a disadvantage when the exact species of an infecting bacteria is unknown or if there is a multiple infection. For best results, the phages should be tested prior to application in the lab. For this reason, phages are less suitable for acute cases. Mixtures consisting of several phages can fight mixed infections.
Another con is that like viruses, bacteria can become resistant to treatments, and in this case they can mutate to survive the phage onslaught. Mutant bacteria can be destroyed by other types of phages, however. And phages are found throughout nature. This means that it is easy to find new phages when bacteria become resistant to them. Evolution drives the rapid emergence of new phages that can destroy bacteria that have become resistant. This means that there should be an ‘inexhaustible’ supply.
Phages that are injected into the bloodstream are recognized by the human immune system. Some of them are quickly excreted and, after a certain period, antibodies against the phages are produced by the body. For this reason, it appears that one type of phage can only be used once for intravenous treatment.[23]
Application
Collection
In its simplest form, phage treatment works by collecting local samples of water likely to contain high quantities of bacteria and bacteriophages, for example effluent outlets, sewage and other sources.[2] They can also be extracted from corpses. The samples are taken and applied to the bacteria that are to be destroyed which have been cultured on growth medium.
The bacteria usually die, and the mixture is centrifuged. The phages collect on the top of the mixture and can be drawn off.
The phage solutions are then tested to see which ones show growth suppression effects (lysogeny) and/or destruction (lysis) of the target bacteria. The phage showing lysis are then amplified on cultures of the target bacteria, passed through a filter to remove all but the phages, then distributed.
Treatment
Phages are "bacterium specific" and it is therefore necessary in many cases to take a swab from the patient and culture it prior to treatment. Occasionally, isolation of therapeutic phages can typically require a few months to complete, but clinics generally keep supplies of phage cocktails for the most common bacterial strains in a geographical area.
Phages in practice are applied orally, topically on infected wounds or spread onto surfaces, or used during surgical procedures. Injection is rarely used, avoiding any risks of trace chemical contaminants that may be present from the bacteria amplification stage,and recognizing that the immune system naturally fights against viruses introduced into the bloodstream or lymphatic system.
The direct human use of phage might possibly be safe; suggestively, in August 2006, the United States Food and Drug Administration approved spraying meat with phages. Although this initially raised concerns since without mandatory labeling consumers won't be aware that meat and poultry products have been treated with the spray,[24] it confirms to the public that, for example, phages against Listeria are generally recognized as safe (GRAS status) within the worldwide scientific community and opens the way for other phages to also be recognized as having GRAS status.
Phage therapy has been attempted for the treatment of a variety of bacterial infections including: laryngitis, skin infections, dysentery, conjunctivitis, periodontitis, gingivitis, sinusitis, urinary tract infections and intestinal infections, burns, boils, etc.[2] - also poly-microbial biofilms on chronic wounds, ulcers and infected surgical sites.[citation needed]
In 2007, Phase 2a clinical trials have been reported at the Royal National Throat, Nose and Ear Hospital, London for Pseudomonas aeruginosa infections (otitis).[25].[26][27] Documentation of the Phase-1 and Phase-2a study is not available as of 2009[update].
Phase 1 clinical trials are underway in the South West Regional Wound Care Center, Lubbock, Texas for an approved cocktail of phages against bacteria, including P. aeruginosa, Staphylococcus aureus and Escherichia coli (better known as E. coli).[citation needed]
Reviews of phage therapy indicate that more clinical and microbiological research is needed to meet current standards.[28]
Distribution
Phages can usually be freeze-dried and turned into pills without materially impacting efficiency.[2] In pill form temperature stability up to 55 C, and shelf lives of 14 months have been shown.[citation needed]
Application in liquid form is possible, stored preferably in refrigerated vials.[citation needed]
Oral administration works better when an antacid is included, as this increases the number of phages surviving passage through the stomach.[citation needed]
Topical administration often involves application to gauzes that are laid on the area to be treated.[citation needed]
Obstacles
General
The high bacterial strain specificity of phage therapy may make it necessary for clinics to make different cocktails for treatment of the same infection or disease because the bacterial components of such diseases may differ from region to region or even person to person.
In addition, due to the specificity of individual phages, for a high chance of success, a mixture of phages is often applied. This means that 'banks' containing many different phages are needed to be kept and regularly updated with new phages.
Further, bacteria can evolve different receptors either before or during treatment; this can prevent the phages from completely eradicating the bacteria.
The need for banks of phages makes regulatory testing for safety harder and more expensive. Such a process would make it difficult for large scale production of phage therapy. Additionally, patent issues (specifically on living organisms) may complicate distribution for pharmaceutical companies wishing to have exclusive rights over their "invention"; making it unlikely that a for-profit corporation will invest capital in the widespread application of this technology.
As it has been known for at least thirty years or more, mycobacterias such as Mycobacterium tuberculosis have specific bacteriophages.[29]. As for Clostridium difficile, which is responsible of many nosocomial diseases, no lytic phage has yet been discovered but some temperate phages (integrated in the genome) are nevertheless known for this species which opens encouraging avenues.
To work, the virus has to reach the site of the bacteria, and viruses do not necessarily reach the same places that antibiotics can reach.
Funding for phage therapy research and clinical trials is generally insufficient and difficult to obtain, since it is a lengthy and complex process to patent bacteriophage products. Scientists comment that 'the biggest hurdle is regulatory', whereas an official view is that individual phages would need proof individually because it would be too complicated to do as a combination, with many variables. Due to the specificity of phages, phage therapy would be most effective with a cocktail injection, which are generally rejected by the FDA. Researchers and observers predict that for phage therapy to be successful the FDA must change its regulatory stance on combination drug cocktails.[30] Public awareness and education about phage therapy are generally limited to scientific or independent research rather than mainstream media.[31]
The negative public perception of viruses may also play a role in the reluctance to embrace phage therapy.[32]
Safety
Phage therapy is generally considered safe. As with antibiotic therapy and other methods of countering bacterial infections, endotoxins are released by the bacteria as they are destroyed within the patient (Herxheimer reaction). This can cause symptoms of fever, or in extreme cases toxic shock (a problem also seen with antibiotics) is possible.[33] Janakiraman Ramachandran, a former president of AstraZeneca India who 2 years ago launched GangaGen Inc., a phage-therapy start-up in Bangalore,[34] argues that this complication can be avoided in those types of infection where this reaction is likely to occur by using genetically engineered bacteriophages; which have had their gene responsible for producing endolysin removed. Without this gene the host bacterium still dies but remains intact because the lysis is disabled. On the other hand this modification stops the exponential growth of phages, so one administered phage means one dead bacterial cell.[4] Eventually these dead cells are consumed by the normal house cleaning duties of the phagocytes, which utilise enzymes to break the whole bacterium and its contents down into its harmless sub-units of proteins, polysaccharides and lipids.[35]
Care has to be taken in manufacture that the phage medium is free of bacterial fragments and endotoxins from the production process.
Lysogenic bacteriophages are not generally used therapeutically. This group can act as a way for bacteria to exchange DNA, and this can help spread antibiotic resistance or even, theoretically, can make the bacteria pathogenic (see Cholera).
The lytic bacteriophages available for phage therapy are best kept refrigerated but discarded if the pale yellow clear liquid goes cloudy.
Effectiveness
In Russia, phage therapies produced by manufacturers have been shown to have approximately a 50% success rate at eradicating target bacteria.
VIDEO
NEXT UP
Diffusion MRI
Phage therapy
Phage therapy is the therapeutic use of bacteriophages to treat pathogenic bacterial infections. Although extensively used and developed mainly in former Soviet Union countries for about 90 years, this method of therapy is still being tested elsewhere for treatment of a variety of bacterial and poly-microbial biofilm infections, and has not yet been approved in countries other than Georgia. Phage therapy has many potential applications in human medicine as well as dentistry, veterinary science, and agriculture.[1] If the target host of a phage therapy treatment is not an animal, however, then the term "biocontrol" (as in phage-mediated biocontrol of bacteria) is sometimes employed rather than "phage therapy".
A hypothetical benefit of phage therapy is that bacteriophages can be much more specific than more common drugs, so they can be chosen to be indirectly harmless not only to the host organism (human, animal, or plant), but also to other beneficial bacteria, such as gut flora, reducing the chances of opportunistic infections. They also have a high therapeutic index, that is, phage therapy gives rise to few if any side effects, as opposed to drugs, and does not stress the liver. Because phages replicate in vivo, a smaller effective dose can be used. On the other hand, this specificity is also a disadvantage: A phage will only kill a bacterium if it is a match to the specific strain. Thus, phage mixtures are often applied to improve the chances of success, or samples can be taken and an appropriate phage identified and grown.
Phages are currently being used therapeutically to treat bacterial infections that do not respond to conventional antibiotics, particularly in the country of Georgia.[2][3][4] They tend to be more successful than antibiotics where there is a biofilm covered by a polysaccharide layer, which antibiotics typically cannot penetrate. [5] In the West, no therapies are currently authorized for use on humans, although phages for killing food poisoning bacteria (Listeria) are now in use.[6]
History
Following the discovery of bacteriophages by Frederick Twort and Felix d'Hérelle[7] in 1915 and 1917, phage therapy was immediately recognized by many to be a key way forward for the eradication of bacterial infections. A Georgian, George Eliava, was making similar discoveries. He travelled to the Pasteur Institute in Paris where he met d'Hérelle, and in 1926 he founded the Eliava Institute in Tbilisi, Georgia, devoted to the development of phage therapy.
In neighbouring countries including Russia, extensive research and development soon began in this field. In the USA during the 1940s, commercialization of phage therapy was undertaken by the large pharmaceutical company, Eli Lilly.
Whilst knowledge was being accumulated regarding the biology of phages and how to use phage cocktails correctly, early uses of phage therapy were often unreliable. When antibiotics were discovered in 1941 and marketed widely in the USA and Europe, Western scientists mostly lost interest in further use and study of phage therapy for some time.[8]
Isolated from Western advances in antibiotic production in the 1940s, Russian scientists continued to develop already successful phage therapy to treat the wounds of soldiers in field hospitals. During World War II, the Soviet Union used bacteriophages to treat many soldiers infected with various bacterial diseases e.g. dysentery and gangrene. The success rate was as good as, if not better than any antibiotic.[citation needed] Russian researchers continued to develop and to refine their treatments and to publish their research and results. However, due to the scientific barriers of the Cold War, this knowledge was not translated and did not proliferate across the world.[9][10]
There is an extensive library and research center at the Eliava Institute in Tbilisi, Georgia. Phage therapy is today a widespread form of treatment in that region. For 80 years Georgian doctors have been treating local people, including babies and newborns, with phages.
As a result of the development of antibiotic resistance since the 1950s and an advancement of scientific knowledge, there has been renewed interest worldwide in the ability of phage therapy to eradicate bacterial infections and chronic polymicrobial biofilm, along with other strategies.
Phages have been investigated as a potential means to eliminate pathogens like Campylobacter in raw food[11] and Listeria in fresh food or to reduce food spoilage bacteria.[12] In agricultural practice phages were used to fight pathogens like Campylobacter, Escherichia and Salmonella in farm animals, Lactococcus and Vibrio pathogens in fish from aquaculture and Erwinia and Xanthomonas in plants of agricultural importance. The oldest use was, however, in human medicine. Phages have been used against diarrheal diseases caused by E. coli, Shigella or Vibrio and against wound infections caused by facultative pathogens of the skin like staphylococci and streptococci. Recently the phage therapy approach has been applied to systemic and even intracellular infections and the addition of non-replicating phage and isolated phage enzymes like lysins to the antimicrobial arsenal. However, actual proof for the efficiency of these phage approaches in the field or the hospital is not available.[12]
Some of the interest in the West can be traced back to 1994, when Soothill demonstrated (in an animal model) that the use of phages could improve the success of skin grafts by reducing the underlying Pseudomonas aeruginosa infection.[13] Recent studies have provided additional support for these findings in the model system.[14]
Although not phage therapy in the original sense, the use of phages as delivery mechanisms for traditional antibiotics has been proposed.[15][16] The use of phages to deliver antitumor agents has also been described, in preliminary in vitro experiments for cells in tissue culture.[17].
Potential benefits
A hypothetical benefit of phage therapy is freedom from the adverse effects of antibiotics. Additionally, it is conceivable that, although bacteria rapidly develop resistance to phage, the resistance might be easier to overcome than resistance to antibiotics.
Bacteriophages are very specific, targeting only one or a few strains of bacteria.[18] Traditional antibiotics have more wide-ranging effect, killing both harmful bacteria and useful bacteria such as those facilitating food digestion. The specificity of bacteriophages might reduce the chance that useful bacteria are killed when fighting an infection.
Increasing evidence shows the ability of phages to travel to a required site — including the brain, where the blood brain barrier can be crossed — and multiply in the presence of an appropriate bacterial host, to combat infections such as meningitis. However the patient's immune system can, in some cases mount an immune response to the phage (2 out of 44 patients in a Polish trial[19]).
Development and production is faster than antibiotics, on condition that the required recognition molecules are known.[citation needed]
Research groups in the West are engineering a broader spectrum phage and also target MRSA treatments in a variety of forms - including impregnated wound dressings, preventative treatment for burn victims, phage-impregnated sutures.[20] Enzobiotics are a new development at Rockefeller University that create enzymes from phage. These show potential for preventing secondary bacterial infections e.g. pneumonia developing with patients suffering from flu, otitis etc..[citation needed]
Some bacteria such as multiply resistant Klebsiella pneumoniae have no non toxic antibiotics available, and yet killing of the bacteria via intraperitoneal, intravenous or intranasal of phages in vivo has been shown to work in laboratory tests.[21]
Risks of Phage Therapy
Phase therapy also has disadvantages:
Unlike antibiotics, phages must be refrigerated until used,[22] and a physician wishing to prescribe them needs special training in order to correctly prescribe and use phages.
Phages come in a great variety. That diversity becomes a disadvantage when the exact species of an infecting bacteria is unknown or if there is a multiple infection. For best results, the phages should be tested prior to application in the lab. For this reason, phages are less suitable for acute cases. Mixtures consisting of several phages can fight mixed infections.
Another con is that like viruses, bacteria can become resistant to treatments, and in this case they can mutate to survive the phage onslaught. Mutant bacteria can be destroyed by other types of phages, however. And phages are found throughout nature. This means that it is easy to find new phages when bacteria become resistant to them. Evolution drives the rapid emergence of new phages that can destroy bacteria that have become resistant. This means that there should be an ‘inexhaustible’ supply.
Phages that are injected into the bloodstream are recognized by the human immune system. Some of them are quickly excreted and, after a certain period, antibodies against the phages are produced by the body. For this reason, it appears that one type of phage can only be used once for intravenous treatment.[23]
Application
Collection
In its simplest form, phage treatment works by collecting local samples of water likely to contain high quantities of bacteria and bacteriophages, for example effluent outlets, sewage and other sources.[2] They can also be extracted from corpses. The samples are taken and applied to the bacteria that are to be destroyed which have been cultured on growth medium.
The bacteria usually die, and the mixture is centrifuged. The phages collect on the top of the mixture and can be drawn off.
The phage solutions are then tested to see which ones show growth suppression effects (lysogeny) and/or destruction (lysis) of the target bacteria. The phage showing lysis are then amplified on cultures of the target bacteria, passed through a filter to remove all but the phages, then distributed.
Treatment
Phages are "bacterium specific" and it is therefore necessary in many cases to take a swab from the patient and culture it prior to treatment. Occasionally, isolation of therapeutic phages can typically require a few months to complete, but clinics generally keep supplies of phage cocktails for the most common bacterial strains in a geographical area.
Phages in practice are applied orally, topically on infected wounds or spread onto surfaces, or used during surgical procedures. Injection is rarely used, avoiding any risks of trace chemical contaminants that may be present from the bacteria amplification stage,and recognizing that the immune system naturally fights against viruses introduced into the bloodstream or lymphatic system.
The direct human use of phage might possibly be safe; suggestively, in August 2006, the United States Food and Drug Administration approved spraying meat with phages. Although this initially raised concerns since without mandatory labeling consumers won't be aware that meat and poultry products have been treated with the spray,[24] it confirms to the public that, for example, phages against Listeria are generally recognized as safe (GRAS status) within the worldwide scientific community and opens the way for other phages to also be recognized as having GRAS status.
Phage therapy has been attempted for the treatment of a variety of bacterial infections including: laryngitis, skin infections, dysentery, conjunctivitis, periodontitis, gingivitis, sinusitis, urinary tract infections and intestinal infections, burns, boils, etc.[2] - also poly-microbial biofilms on chronic wounds, ulcers and infected surgical sites.[citation needed]
In 2007, Phase 2a clinical trials have been reported at the Royal National Throat, Nose and Ear Hospital, London for Pseudomonas aeruginosa infections (otitis).[25].[26][27] Documentation of the Phase-1 and Phase-2a study is not available as of 2009[update].
Phase 1 clinical trials are underway in the South West Regional Wound Care Center, Lubbock, Texas for an approved cocktail of phages against bacteria, including P. aeruginosa, Staphylococcus aureus and Escherichia coli (better known as E. coli).[citation needed]
Reviews of phage therapy indicate that more clinical and microbiological research is needed to meet current standards.[28]
Distribution
Phages can usually be freeze-dried and turned into pills without materially impacting efficiency.[2] In pill form temperature stability up to 55 C, and shelf lives of 14 months have been shown.[citation needed]
Application in liquid form is possible, stored preferably in refrigerated vials.[citation needed]
Oral administration works better when an antacid is included, as this increases the number of phages surviving passage through the stomach.[citation needed]
Topical administration often involves application to gauzes that are laid on the area to be treated.[citation needed]
Obstacles
General
The high bacterial strain specificity of phage therapy may make it necessary for clinics to make different cocktails for treatment of the same infection or disease because the bacterial components of such diseases may differ from region to region or even person to person.
In addition, due to the specificity of individual phages, for a high chance of success, a mixture of phages is often applied. This means that 'banks' containing many different phages are needed to be kept and regularly updated with new phages.
Further, bacteria can evolve different receptors either before or during treatment; this can prevent the phages from completely eradicating the bacteria.
The need for banks of phages makes regulatory testing for safety harder and more expensive. Such a process would make it difficult for large scale production of phage therapy. Additionally, patent issues (specifically on living organisms) may complicate distribution for pharmaceutical companies wishing to have exclusive rights over their "invention"; making it unlikely that a for-profit corporation will invest capital in the widespread application of this technology.
As it has been known for at least thirty years or more, mycobacterias such as Mycobacterium tuberculosis have specific bacteriophages.[29]. As for Clostridium difficile, which is responsible of many nosocomial diseases, no lytic phage has yet been discovered but some temperate phages (integrated in the genome) are nevertheless known for this species which opens encouraging avenues.
To work, the virus has to reach the site of the bacteria, and viruses do not necessarily reach the same places that antibiotics can reach.
Funding for phage therapy research and clinical trials is generally insufficient and difficult to obtain, since it is a lengthy and complex process to patent bacteriophage products. Scientists comment that 'the biggest hurdle is regulatory', whereas an official view is that individual phages would need proof individually because it would be too complicated to do as a combination, with many variables. Due to the specificity of phages, phage therapy would be most effective with a cocktail injection, which are generally rejected by the FDA. Researchers and observers predict that for phage therapy to be successful the FDA must change its regulatory stance on combination drug cocktails.[30] Public awareness and education about phage therapy are generally limited to scientific or independent research rather than mainstream media.[31]
The negative public perception of viruses may also play a role in the reluctance to embrace phage therapy.[32]
Safety
Phage therapy is generally considered safe. As with antibiotic therapy and other methods of countering bacterial infections, endotoxins are released by the bacteria as they are destroyed within the patient (Herxheimer reaction). This can cause symptoms of fever, or in extreme cases toxic shock (a problem also seen with antibiotics) is possible.[33] Janakiraman Ramachandran, a former president of AstraZeneca India who 2 years ago launched GangaGen Inc., a phage-therapy start-up in Bangalore,[34] argues that this complication can be avoided in those types of infection where this reaction is likely to occur by using genetically engineered bacteriophages; which have had their gene responsible for producing endolysin removed. Without this gene the host bacterium still dies but remains intact because the lysis is disabled. On the other hand this modification stops the exponential growth of phages, so one administered phage means one dead bacterial cell.[4] Eventually these dead cells are consumed by the normal house cleaning duties of the phagocytes, which utilise enzymes to break the whole bacterium and its contents down into its harmless sub-units of proteins, polysaccharides and lipids.[35]
Care has to be taken in manufacture that the phage medium is free of bacterial fragments and endotoxins from the production process.
Lysogenic bacteriophages are not generally used therapeutically. This group can act as a way for bacteria to exchange DNA, and this can help spread antibiotic resistance or even, theoretically, can make the bacteria pathogenic (see Cholera).
The lytic bacteriophages available for phage therapy are best kept refrigerated but discarded if the pale yellow clear liquid goes cloudy.
Effectiveness
In Russia, phage therapies produced by manufacturers have been shown to have approximately a 50% success rate at eradicating target bacteria.
VIDEO
NEXT UP
Diffusion MRI
Saturday, June 20, 2009
Electrotherapy
PROCEDURE OF THE DAY
Electrotherapy
Electrotherapy is the use of electrical energy as a medical treatment[1] In medicine, the term electrotherapy can apply to a variety of treatments, including the use of electrical devices such as deep brain stimulators for neurological disease. The term has also been applied specifically to the use of electrical current to speed wound healing. Additionally, the term "electrotherapy" or "electromagnetic therapy" has also been applied to a range of alternative medical devices and treatments.
History
In 1855 Guillaume Duchenne, the father of electrotherapy, announced that alternating was superior to direct current for electrotherapeutic triggering of muscle contractions.[2] What he called the 'warming affect' of direct currents irritated the skin, since, at voltage strengths needed for muscle contractions, they cause the skin to blister (at the anode) and pit (at the cathode). Furthermore, with DC each contraction requiring the current to be stopped and restarted. Moreover alternating current could produce strong muscle contractions regardless of the condition of the muscle, whereas DC-induced contractions were strong if the muscle was strong, and weak if the muscle was weak.
Since that time almost all rehabilitation involving muscle contraction has been done with a symmetrical rectangular biphasic waveform. In the 1940s, however, the US War Department, investigating the application of electrical stimulation not just to retard and prevent atrophy but to restore muscle mass and strength, employed what was termed galvanic exercise on the atrophied hands of patients who had an ulnar nerve lesion from surgery upon a wound.[3] These Galvanic exercises employed a monophasic wave form, direct current - electrochemistry.
Current use
Although a 1999 meta-analysis found that electrotherapy could speed the healing of wounds,[4] in 2000 the Dutch Medical Council found that although it was widely used, there was insufficient evidence for its benefits.[5] Since that time, a few publications have emerged that seem to support its efficacy, but data is still scarce. [6]
The use of electrotherapy has been widely researched and the advantages have been well accepted in the field of rehabilitation[7] (electrical muscle stimulation). The American Physical Therapy Association acknowledges the use of Electrotherapy for: [8] 1. Pain management Improve range of joint movement 2. Treatment of neuromuscular dysfunction Improvement of strength Improvement of motor control Retard muscle atrophy Improve local blood flow 3. Improve range of joint mobility Induce repeated stretching of contracted, shortened soft tissues 4. Tissue repair Enhance microcirculation and protein synthesis to heal wounds Restore integrity of connective and dermal tissues 5. Acute and chronic edema Accelerate absorption rate Affect blood vessel permeability Increase mobility of proteins, blood cells and lymphatic flow 6. Peripheral blood flow Induce arterial, venous and lymphatic flow 7. Iontophoresis Delivery of pharmacological agents 8. Urine and fecal incontinence Affect pelvic floor musculature to reduce pelvic pain and strengthen musculature Treatment may lead to complete continence
Electrotherapy is used for relaxation of muscle spasms, prevention and retardation of disuse atrophy, increase of local blood circulation, muscle rehabilitation and re-education electrical muscle stimulation, maintaining and increasing range of motion, management of chronic and intractable pain, post-traumatic acute pain, post surgical acute pain, immediate post-surgical stimulation of muscles to prevent venous thrombosis, wound healing and drug delivery.
Reputable medical and therapy Journals have published peer-reviewed research articles that attest to the medical properties of the various electro therapies. Yet some of the treatment effectiveness mechanisms are little understood. Therefore effectiveness and best practices for their use in some instances are still anecdotal.
Electrotherapy devices have been studied in the treatment of chronic wounds and pressure ulcers. A 1999 meta-analysis of published trials found some evidence that electrotherapy could speed the healing of such wounds, though it was unclear which devices were most effective and which types of wounds were most likely to benefit.[4] However, a more detailed review by the Cochrane Library found no evidence that electromagnetic therapy, a subset of electrotherapy, was effective in healing pressure ulcers[9] or venous stasis ulcers.
VIDEO
*None*
NEXT UP
Phage therapy
Electrotherapy
Electrotherapy is the use of electrical energy as a medical treatment[1] In medicine, the term electrotherapy can apply to a variety of treatments, including the use of electrical devices such as deep brain stimulators for neurological disease. The term has also been applied specifically to the use of electrical current to speed wound healing. Additionally, the term "electrotherapy" or "electromagnetic therapy" has also been applied to a range of alternative medical devices and treatments.
History
In 1855 Guillaume Duchenne, the father of electrotherapy, announced that alternating was superior to direct current for electrotherapeutic triggering of muscle contractions.[2] What he called the 'warming affect' of direct currents irritated the skin, since, at voltage strengths needed for muscle contractions, they cause the skin to blister (at the anode) and pit (at the cathode). Furthermore, with DC each contraction requiring the current to be stopped and restarted. Moreover alternating current could produce strong muscle contractions regardless of the condition of the muscle, whereas DC-induced contractions were strong if the muscle was strong, and weak if the muscle was weak.
Since that time almost all rehabilitation involving muscle contraction has been done with a symmetrical rectangular biphasic waveform. In the 1940s, however, the US War Department, investigating the application of electrical stimulation not just to retard and prevent atrophy but to restore muscle mass and strength, employed what was termed galvanic exercise on the atrophied hands of patients who had an ulnar nerve lesion from surgery upon a wound.[3] These Galvanic exercises employed a monophasic wave form, direct current - electrochemistry.
Current use
Although a 1999 meta-analysis found that electrotherapy could speed the healing of wounds,[4] in 2000 the Dutch Medical Council found that although it was widely used, there was insufficient evidence for its benefits.[5] Since that time, a few publications have emerged that seem to support its efficacy, but data is still scarce. [6]
The use of electrotherapy has been widely researched and the advantages have been well accepted in the field of rehabilitation[7] (electrical muscle stimulation). The American Physical Therapy Association acknowledges the use of Electrotherapy for: [8] 1. Pain management Improve range of joint movement 2. Treatment of neuromuscular dysfunction Improvement of strength Improvement of motor control Retard muscle atrophy Improve local blood flow 3. Improve range of joint mobility Induce repeated stretching of contracted, shortened soft tissues 4. Tissue repair Enhance microcirculation and protein synthesis to heal wounds Restore integrity of connective and dermal tissues 5. Acute and chronic edema Accelerate absorption rate Affect blood vessel permeability Increase mobility of proteins, blood cells and lymphatic flow 6. Peripheral blood flow Induce arterial, venous and lymphatic flow 7. Iontophoresis Delivery of pharmacological agents 8. Urine and fecal incontinence Affect pelvic floor musculature to reduce pelvic pain and strengthen musculature Treatment may lead to complete continence
Electrotherapy is used for relaxation of muscle spasms, prevention and retardation of disuse atrophy, increase of local blood circulation, muscle rehabilitation and re-education electrical muscle stimulation, maintaining and increasing range of motion, management of chronic and intractable pain, post-traumatic acute pain, post surgical acute pain, immediate post-surgical stimulation of muscles to prevent venous thrombosis, wound healing and drug delivery.
Reputable medical and therapy Journals have published peer-reviewed research articles that attest to the medical properties of the various electro therapies. Yet some of the treatment effectiveness mechanisms are little understood. Therefore effectiveness and best practices for their use in some instances are still anecdotal.
Electrotherapy devices have been studied in the treatment of chronic wounds and pressure ulcers. A 1999 meta-analysis of published trials found some evidence that electrotherapy could speed the healing of such wounds, though it was unclear which devices were most effective and which types of wounds were most likely to benefit.[4] However, a more detailed review by the Cochrane Library found no evidence that electromagnetic therapy, a subset of electrotherapy, was effective in healing pressure ulcers[9] or venous stasis ulcers.
VIDEO
*None*
NEXT UP
Phage therapy
Friday, June 19, 2009
Immunization
PROCEDURE OF THE DAY
Immunization
Immunization, or immunisation, is the process by which an individual's immune system becomes fortified against an agent (known as the immunogen).
When an immune system is exposed to molecules that are foreign to the body (non-self), it will orchestrate an immune response, but it can also develop the ability to quickly respond to a subsequent encounter (through immunological memory). This is a function of the adaptive immune system. Therefore, by exposing an animal to an immunogen in a controlled way, their body can learn to protect itself: this is called active immunization.
The most important elements of the immune system that are improved by immunization are the B cells (and the antibodies they produce) and T cells. Memory B cell and memory T cells are responsible for a swift response to a second encounter with a foreign molecule. Passive immunization is when these elements are introduced directly into the body, instead of when the body itself has to make these elements.
Immunization can be done through various techniques, most commonly vaccination. Vaccines against microorganisms that cause diseases can prepare the body's immune system, thus helping to fight or prevent an infection. The fact that mutations can cause cancer cells to produce proteins or other molecules that are unknown to the body forms the theoretical basis for therapeutic cancer vaccines. Other molecules can be used for immunization as well, for example in experimental vaccines against nicotine (NicVAX) or the hormone ghrelin (in experiments to create an obesity vaccine).
Passive and active immunization
Immunization can be achieved in an active or passive fashion: vaccination is an active form of immunization.
Active immunization
Active immunization entails the introduction of a foreign molecule into the body, which causes the body itself to generate immunity against the target. This immunity comes from the T cells and the B cells with their antibodies.
Active immunization can occur naturally when a person comes in contact with, for example, a microbe. If the person has not yet come into contact with the microbe and has no pre-made antibodies for defense (like in passive immunization), the person becomes immunized. The immune system will eventually create antibodies and other defenses against the microbe. The next time, the immune response against this microbe can be very efficient; this is the case in many of the childhood infections that a person only contracts once, but then is immune.
Artificial active immunization is where the microbe, or parts of it, are injected into the person before they are able to take it in naturally. If whole microbes are used, they are pre-treated. Depending on the type of disease, this technique also works with dead microbes, parts of the microbe, or treated toxins from the microbe.
Passive immunization
Passive immunization is where pre-synthesized elements of the immune system are transferred to a person so that the body does not need to produce these elements itself. Currently, antibodies can be used for passive immunization. This method of immunization begins to work very quickly, but it is short lasting, because the antibodies are naturally broken down, and if there are no B cells to produce more antibodies, they will disappear.
Passive immunization occurs physiologically, when antibodies are transferred from mother to fetus during pregnancy, to protect the fetus before and shortly after birth.
Artificial passive immunization is normally administered by injection and is used if there has been a recent outbreak of a particular disease or as an emergency treatment for toxicity (for example, for tetanus). The antibodies can be produced in animals ("serum therapy") although there is a high chance of anaphylactic shock because of immunity against animal serum itself. Thus, humanized antibodies produced in vitro by cell culture are used instead if available.
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Immunization
Immunization, or immunisation, is the process by which an individual's immune system becomes fortified against an agent (known as the immunogen).
When an immune system is exposed to molecules that are foreign to the body (non-self), it will orchestrate an immune response, but it can also develop the ability to quickly respond to a subsequent encounter (through immunological memory). This is a function of the adaptive immune system. Therefore, by exposing an animal to an immunogen in a controlled way, their body can learn to protect itself: this is called active immunization.
The most important elements of the immune system that are improved by immunization are the B cells (and the antibodies they produce) and T cells. Memory B cell and memory T cells are responsible for a swift response to a second encounter with a foreign molecule. Passive immunization is when these elements are introduced directly into the body, instead of when the body itself has to make these elements.
Immunization can be done through various techniques, most commonly vaccination. Vaccines against microorganisms that cause diseases can prepare the body's immune system, thus helping to fight or prevent an infection. The fact that mutations can cause cancer cells to produce proteins or other molecules that are unknown to the body forms the theoretical basis for therapeutic cancer vaccines. Other molecules can be used for immunization as well, for example in experimental vaccines against nicotine (NicVAX) or the hormone ghrelin (in experiments to create an obesity vaccine).
Passive and active immunization
Immunization can be achieved in an active or passive fashion: vaccination is an active form of immunization.
Active immunization
Active immunization entails the introduction of a foreign molecule into the body, which causes the body itself to generate immunity against the target. This immunity comes from the T cells and the B cells with their antibodies.
Active immunization can occur naturally when a person comes in contact with, for example, a microbe. If the person has not yet come into contact with the microbe and has no pre-made antibodies for defense (like in passive immunization), the person becomes immunized. The immune system will eventually create antibodies and other defenses against the microbe. The next time, the immune response against this microbe can be very efficient; this is the case in many of the childhood infections that a person only contracts once, but then is immune.
Artificial active immunization is where the microbe, or parts of it, are injected into the person before they are able to take it in naturally. If whole microbes are used, they are pre-treated. Depending on the type of disease, this technique also works with dead microbes, parts of the microbe, or treated toxins from the microbe.
Passive immunization
Passive immunization is where pre-synthesized elements of the immune system are transferred to a person so that the body does not need to produce these elements itself. Currently, antibodies can be used for passive immunization. This method of immunization begins to work very quickly, but it is short lasting, because the antibodies are naturally broken down, and if there are no B cells to produce more antibodies, they will disappear.
Passive immunization occurs physiologically, when antibodies are transferred from mother to fetus during pregnancy, to protect the fetus before and shortly after birth.
Artificial passive immunization is normally administered by injection and is used if there has been a recent outbreak of a particular disease or as an emergency treatment for toxicity (for example, for tetanus). The antibodies can be produced in animals ("serum therapy") although there is a high chance of anaphylactic shock because of immunity against animal serum itself. Thus, humanized antibodies produced in vitro by cell culture are used instead if available.
VIDEO
NEXT UP
Electrotherapy
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