The Emerging Technique of Using Diffusion Tensor Imaging to Perform Muscle Fibre Tracking - Essay Example

Q Discuss the emerging technique of using diffusion tensor imaging (DTI) to perform muscle fibre tracking (approx. 1000 words) I want paraphrasethis Diffusion Diffusion refers to the random movement of particles due to the kinetic energy they possess. For instance, a molecule of water will always slide and bump against other water molecules within a fluid. By incorporating diffusion gradients to SE-EPI sequence, an MRI sequence can be modified to measure the random movements of molecules. I want paraphrase this DWI Diffusion weighted imaging (DWI) is an MRI sequence designed to measure the random movements of water particles to further assess different tissue characteristics such as membrane permeability. By virtue of the kinetic energy that each molecule possesses, these molecules collide and slide against each other. These collisions eventually cause the molecules to follow different trajectories, described as random walk. (m852, module1) I want paraphrase this DTI Diffusion tensor imaging (DTI), on the other hand, is another MRI sequence which is indicated for tissues with internal stuctures demonstrating anisotropy similar to that of some crystals, such as white matter axons in the brain or heart muscle fibers. With this anisotropic structure, the water molecules will diffuse faster along the internal structure and slower as it moves perpicularly. Hence, the direction of movement of the molecules, whether parallel or perpendicular to the internal structure will cause a change in the rate of diffusion. The infrastructure of muscle fibre is complicated. This infrastructure determines the functionality of the muscle itself. Diffusion tensor imaging (‘DTI’) is a technique that can be used to better the muscle fibre/functionality relationship (Damon et al, 2002, pp.97-104). In addition to investigation of skeletal muscles, DTI is used for viewing the muscles of the heart, kidney, spinal cord, and brain. DTI is a non-invasive technique that is particularly used for in vivo analysis (Frank et al, 2010, p. 1510). For example, researchers are increasingly interested in the direction information concerning fibrous structures in muscle that DTI can reveal (Villanova et al, 2005, pp 1-38). Direction information concerning fibrous structures in white matter can also be obtained. The following figure, Figure 1, shows Images of the white matters comparing children and adolescents using DTI technology (Barnea Goraly et al 2005, p. 1849). Figure 1: Images of the white matters comparing children and adolescents using DTI technology (Barnea Goraly et al 2005, p. 1849). Thus, DTI is increasingly used for the investigation of conditions affecting the white matter in the body as well (Damon et al, 2002, pp.97-104). Theory DTI measuring water diffusion in vivo is a pioneering modality (Villanova et al, 2005, pp 1-38). The theory behind DTI is based of cell physiology. Within the cell, the cell membranes and proteins influence the flow of water. These cell membranes and proteins tend to limit the diffusion rate of water molecules (Damon et al., 2002, pp.97-104). They also encourage the water molecules to move uniformly in a particular direction (Damon et al., 2002, pp.97-104). Generally, compared to the rate of water diffusion along the transverse axis, the water diffusion rate is much faster along the longitudinal axis. DTI uses these fundamentals and calculations of the water diffusion rate to determine the cell infrastructure. The principal eigenvalue of long axis of muscle fibre is used in calculations. The free diffusion of water molecules, which corresponds to the principal eigenvalue of long axis muscle fibre, is measured by tensors. Discussion and benefits of DTI method DTI can provide information concerning the characteristics of water diffusion, the orientation of diffusion, and the extension of diffusion (Mori, 2005, pp.468-480). The method of DTI is derived from the assumption that the eigenvector is parallel to the cell’s longitudinal axis. DTI therefore is underpinned by the fact that the eigenvalue has been adequately verified in vivo qualitatively and quantitatively (Damon et al., 2002, pp.97-104). In simple terms, orientation dependence of diffusion is the phenomenon that DTI focuses. The role of a diffusion tensor is therefore, assuming free diffusion in a uniform anisotropic medium, also known as Gaussian diffusion, to describe the orientation dependence of diffusion (Villanova et al., 2005, pp 1-38). An overview of the muscle fibre is provided using a combination of the data based on voxel results and the data of local water molecule direction along with a fibre-tracking algorithm. Limitations There are a number of limitations concerning DTI to date. Developing techniques for enhancing image acquisition through DTI is the focus of a number of research papers (Villanova et al., 2005, pp.1-38). Research in this area tends to focus on techniques for improving resolution and techniques for reducing noise, distortion of images, and time required for imaging (Villanova et al., 2005, pp.1-38). Firstly, DTI is a technique that places high demands on the practitioner. This means that human error can affect the effectiveness of DTI application. Thus one limitation of DTI is that without specialist training, it can be challenging modality to use. During the processing of DTI, the production of noise is one of the dominant limitations of DTI (Villanova et al., 2005, pp 1-38). Despite the fact that methods of fibre tracking use major coherent fibre structures to relate values spatially, many errors can arise (Villanova et al., 2005, pp 1-38). Numerical integration inaccuracies, partial volume effects, and noise cause errors in results of DTI. Dimensionality can be an issue. As methods of fibre tracking tend to reduce tensor dimensionality from 6D to 3D, noise can be produced (Villanova et al., 2005, pp 1-38). This is because DTI provided 3D vector field is known for containing noise and this can cause deviation away from the real fibre orientation. This category of limitation can caused significant error (Mori, 2005, pp.468-480). To date, the most common approach to minimizing or mitigating this effect is through the manipulation of tensor fields (Mori, 2005, pp.468-480). I want paraphrase this Figure 1 shows white matter structures and the corresponding information derived from the DTI-based images. The image in (A) demonstrates anisotropic map with good white and gray matter resolution. By adding DTI sequence, the white matter can be visualized into coloured tracts (B) or a vector map(C). With DTI- based images, it is possible to differentiate large white matter tracts, consisting of parallel-oriented neuroglia and axons. Meanwhile, the image in (D) shows a pixel, consisting of axons and neuroglial cells. (Mori, 2005, pp.468-480). Figure 1. Fibre tracking of the brain. Source: Mori, 2005, pp.468-480 Due to multivalued tensors, visualisation can be difficult using the DTI technique. Nonetheless, the nature of the DTI modality is that minor errors, to a certain limit, are acceptable. Q-2 Discuss current and emerging MRI techniques used in the imaging of cartilage. Suggest a grading system that could be used to describe cartilage damage (approx. 1000 words) Conventional x-ray fails to provide accurate information for the diagnosis of cartilage diseases. The reason for this is the slow and peculiar injury response that cartilage exhibits in relation to stress induced damages. Magnetic Resonance Imaging (‘MRI’) is used as a method to visualise cartilage structures that can complex. Field strength must be modified and resolution modified using maximum sequences for best viewing using MRI. Abrasion, clefts, fissures, and damage to surrounding structures can be visualised using MRI. The modality is also believed to provide better information concerning cartilage stress areas and recovery areas as well. Accuracy There is limited scope to repair cartilage. Diseases of cartilage have an in depth and complicated pathology. For the best prognosis for patients, early diagnosis is essential. Recently, MR spectroscopy has been heralded as a complimentary technique, complimenting conventional MRI. This technique, MR spectroscopy, provides in depth information about the metabolic outcomes, cell markers, and overall structure of cartilage. MR spectroscopy focuses on the amount of fat that is present in cartilage tissue. As cartilage is prone to stress injury and pressure exerted by surrounding anatomical structures, MRI is a useful technique for imaging for the purposes of early intervention Benefits One of the advantages of MRI is that it can be used to visualise and identify early degeneration signs in cartilage tissue. It achieves this using its capacity to adjust contrast. MRI is commonly applied as it can provide information concerning the response of cartilage post surgical or pharmaceutical intervention (Link, pp.49-66). A high spatial resolution is necessary to visualize cartilage on MRI. Common techniques to identify defects in cartilage include standard spin echo, 3D SE, gradient –recalled echo sequences, fast SE sequences, and GRE, among others. MRI is a technique that provide quantitative and semi quantitative data. This data can be used to help research and development groups better under the effects of pharmaceutical (Crema et al, 2011, pp.37-62). I want paraphrase this Meanwhile, assessment of the composition of cartilage with MRI requires the use of T2 mapping, delayed gadolinium-enhanced MR imaging of cartilage (dGEMRIC), T1p mapping, sodium technique, and diffusion weighted imaging (‘DWI’) (Crema et al., 2011, pp.37-62). Another one of the strengths of MRI is that the power of the magnetic forces can be adjusted for the purposes of obtaining the best information about the proteoglycan content of cartilage and the relevant networks of collagen (Crema et al., 2011, pp.37-62). Present and emerging techniques Current and emerging MRI techniques concerning cartilage have shifted the focus from morphological detail towards treatment response. These techniques focus on gathering data concerning the cartilage segmentation and margins and the composition of the cartilage. Current and emerging MRI techniques tend to involve high- field, ultra high- field imaging MRI. Composition assessments detect biochemical changes in tissue while morphological assessments detect surface irregularity (Chu et al, 2010, pp.91-98). MRI for visualization of cartilaginous structures 1. 2D fast SE 2D fast SE is a typical technique used for diagnostic imaging procedures and clinical research. Techniques using T1, T2, and proton density sequences allow the clinicians and researchers to clearly delineate cartilage from the surrounding fluid. 2D fast SE is an effective technique for contrast variations in the target tissue. 2D fast SE provides desirable descriptions in the imaging plain. The disadvantage of 2D fast SE, however, is that oblique or small tissue structures tend to be not captured clearly and this leads to proton density images being blurred in some instances (Link, pp.49-66). Anisotropic voxel and partial volume effects are also problems of 2D fast SE (Crema et al., 2011, pp.37-62). Having said this, 2D fast SE generally is a suitable technique for investigating menisci, bone marrow, and ligaments. I want paraphrase this Figure 2 shows sagittal 2D fast SE images of the knee using various techniques. (a) T1-weighted image does not clearly demarcate the cartilage surface from the synovial fluid, which interferes with accurate assessment of cartilaginous problems (black arrows). Meanwhile, (b, c) T2- weighted (b) and proton density–weighted (c) images show improved contrast between the synovial fluid and the surface of the cartilage, which allows better evaluation of the extent of the damage (arrowheads). In addition, a tear in the posterior horn of the medial meniscus is appreciable in Figures 2.a–c. Figure 3. Sagittal 2D Fast SE images of the knee. Source: Crema, M.D., Roemer, F.W. & Marra, M.D. (2011). 2. 3D fast SE 3D fast SE is a technique in which the sections used are very thin. Cartilage exhibits low to moderate signal intensity while degenerative cartilage tissue exhibits high intensity signals. Fluid from joint spaces also exhibits high intensity signals. Using 3D fast SE a classic contrast can be seen between cartilage and fluid. A disadvantage of the technique is however, that it tends to be unsuitable concerning low contrast lesion (Chu et al, 2010, pp.91-98; Link, pp.49-66). . I want paraphrase this Figure 4 shows 3D fast SE images of the elbow. (a) Coronal 3D intermediate-weighted fast SE image using isotropic spatial resolution does not illustrate any cartilage defects. Meanwhile, (b, c) axial (b) and sagittal (c) images which were acquired using a reformatted coronal image dataset reveal a defect (arrow) at the trochlear groove. Figure 4: 3D Fast SE images of the elbow. Source: Crema, M.D., Roemer, F.W. & Marra, M.D. (2011). 3. 3D Spoiled Gradient-Recalled Echo or SPGR 3D SPGR (spoiled gradient-recalled echo) has superior sensitivity over techniques such as the than 2D fast SE method. 3D SPGR (spoiled gradient-recalled echo) is therefore a technique that occurs with fewer volume artefacts and by using isotropic voxel multiple plains can be adjusted for greater sensitivity (Crema et al., 2011, pp.37-62). . I want paraphrase this The figure below shows a Coronal 3D SPGR image illustrating an intact high signal- intensity cartilaginous surface along the lateral and medial tibiofemoral aspects of the knee. This technique made use of lipid suppression, which imparts a good contrast between the subchondral bone and cartilage. Figure 5 . A 3D SPGR image of the knee on coronal cut. Source: Crema, M.D., Roemer, F.W. & Marra, M.D. (2011). . 4. 3D DESS (dual-echo steady state) 3D DESS (dual-echo steady state) is a technique that operates through using multiple gradient echoes and pulse sequence. 3D DESS (dual-echo steady state) resets the multiple gradient echoes and pulse sequence thereby offering a combined reconstruction of the image. The advantages of 3D DESS (dual-echo steady state) are its ability to provide distinct cartilage and fluid contrast and give high SNR. 3D DESS (dual-echo steady state) shares many characteristics with 3D SE (Crema et al., 2011, pp.37-62). One disadvantage of the modality is that greater flip angles are often required. I want paraphrase this The upper panel shows Figure (6a), demonstrating a sagittal T2-weighted fat-suppressed fast SE image on the patella. (6a) shows a defect on the patella as indicated by the white arrow. On the other hand, (6b) shows a sagittal water excitation DESS image of the same patella. However, the defect seen in (6a) cannot be clearly seen in (6b) (arrow). Meanwhile, the lower panel shows Figure 7, demonstrating a sagittal T2-weighted fat-suppressed fast SE image (a) and water excitation DESS image using a 90flip angle (b) of a patella from a different patient. Both images clearly illustrate the defect (white arrowheads). Figures 6,7. 3D Dual-Echo Steady State (DESS) images of a patella on a sagittal section. Source: Crema, M.D., Roemer, F.W. & Marra, M.D. (2011). . I want paraphrase this Figure 8 shows a segmentation of 3D DESS images of a knee taken in two different planes. This technique enables the identification of cartilaginous structures in the weight-bearing areas of the patella (shown in pink), femoral condyles (in red and yellow), trochle (light blue), and tibial plateaus (dark blue and green). Figure 8. Segmentation of 3D DESS images of a knee, demonstrating the cartilaginous components as coloured structures. Source: Crema, M.D., Roemer, F.W. & Marra, M.D. (2011). 5. 3D bSSFP (balanced steady state free precession) 3D bSSFP (balanced steady state free precession) is a technique which is very similar to 3D DESS. One of the only notable differences is however that 3D bSSFP (balanced steady state free precession) has a higher incidence of banding artefact due to longer TR leads (Crema et al., 2011, pp.37-62). I want paraphrase this Figure 9 exhibits 3D bSSFP sequence of the knee. The image in (a) exhibits a 3D water excitation bSSFP of a medial femoral condyle in sagittal section, demonstrating a partial- thickness defect. On coronal view (b), the extent of the damage is more apparent as pointed by the white arrows. Also shown in the image are femoral osteophyte and medial meniscal extrusion. Figure 9. Sagittal section of femoral condyle obtained using 3D bSSFP technique. Source: Crema, M.D., Roemer, F.W. & Marra, M.D. (2011). 6. 3D DEFT (driven equilibrium Fourier transform) 3D DEFT (driven equilibrium Fourier transform) is a technique that focused on the signal intensity of fluid as opposed to the signal intensity cartilage. 3D DEFT (driven equilibrium Fourier transform) achieves this by enhancing the signal intensity of fluid. 3D DEFT (driven equilibrium Fourier transform) offers information which is comparable 2D fast SE and SPGR techniques. A disadvantage of 3D DEFT (driven equilibrium Fourier transform), however is that it is a time consuming technique when investigating deficient fat saturation at times (Crema et al., 2011, pp.37-62). I want paraphrase this Shown in Figure 10 is a 3D DEFT image of a knee in sagittal cut, which depicts a fissure (arrow) located at the medial tibial plateau, bordered by the high intensity signal of the synovial fluid. Figure 10. Sagittal 3D DEFT image of a knee showing a fissure at the medial tibial plateau. Source: Crema, M.D., Roemer, F.W. & Marra, M.D. (2011). 7. 3D fast SE SPACE 3D fast SE SPACE is a technique that provides excellent SNR. 3D fast SE SPACE uses isotropic voxel for the purposes of restructuring multiple planes. 3D fast SE SPACE maintains a steady state by using turbo factors in conjunction with the flip angle. A drawback of 3D fast SE SPACE is prolonged processing time (Crema et al., 2011, pp.37-62). I want paraphrase this Figure 11 shows a sagittal view of the knee using a 3D SPACE water image, illustrating the thinning of carilage at the medial femoral condyle (arrowheads). A tear in the posterior horn of the medial meniscus, as pointed by the white arrow, is also appreciable. Figure 11. Sagittal section of a 3D SPACE water image of the knee. Source: Crema, M.D., Roemer, F.W. & Marra, M.D. (2011). MR imaging techniques for composition of cartilage: 1. T2 mapping T2 mapping is a technique that is useful in visualizing networks of collagen. It is also used to approximate the fluid content of cartilaginous areas within different structures. (Crema et al., 2011, pp.37-62). I want paraphrase this Figure 12 demonstrates sagittal 3D T2- weighted images of the different structures of the knee in a 51-year-old man after anterior cruciate ligament repair. Specifically, the images below show higher T2 values (yellow) in the medial (a) and lateral (b) tibiofemoral compartment, indicating collagen network deterioration Figure 12. 3D T2- weighted sagittal sections of the different structures within the knee. Source:Crema, M.D., Roemer, F.W. & Marra, M.D. (2011). 2. dGEMRIC- What is the delay in dGEMRIC?  can you answer this question in this part dGEMRIC is used to measure the content of Glycosaminoglycans in cartilage. It is a procedure that involves intravenous contrast being applied during the procedure Increasingly, dGEMRIC is used in clinical research. (Crema et al., 2011, pp.37-62). I want paraphrase this Figure 13 compares the dGEMRIC index of a patient with knee osteoarthritis (b) to that of a patient without knee osteoarthritis (a). The image in (b) has a corresponding lower index values, which is indicative of glycosaminoglycan depletion (arrowheads). Figure 13. dGEMRIC index of patients with and without knee osteoarthritis. Source: Crema, M.D., Roemer, F.W. & Marra, M.D. (2011). 3. T1p imaging T1p imaging is another one of the techniques that is used to measure the content of Glycosaminoglycans in cartilage and to access collagen network infrastructure. T1p imaging is a technique that does not require contrast agent and provides a excellent accuracy when detecting early degeneration signs (Crema et al., 2011, pp.37-62). Figure 14 compares T1p images of a patient with healthy knee certilage (a) to that of a patient with knee osteoarthritis (Kellgren and Lawrence grade 3). Image (b) has a higher T1p values compared to (a). Figure 14. A comparison of T1p images of a diseased and healthy knee cartilage. Source: Crema, M.D., Roemer, F.W. & Marra, M.D. (2011). 4. Sodium imaging- What special equipment do you need for sodium imaging? can you answer this question in this part Sodium imaging is another one of the techniques that is used to measure the content of Glycosaminoglycans. Sodium imaging measurements directly correlate with glycosaminoglycans content without the need for contrast agent. Despite these benefits, Sodium imaging is seldom used in some settings due to its low signal: noise ratio and less powerful spatial resolution (Crema et al., 2011, pp.37-62). I want paraphrase this Figure 15 shows a whole-knee sodium MR image of a 20 year-old patient taken using a proton density–weighted SPGR sequence. The image depicts a high signal intensity at the medial compartment of the knee. Specifically, these images were obtained at a spatial resolution of 1.25 × 1.25 × 4 mm at 20 min acquisition time. Figure 15. Proton-density weighted SPGR sequence of a whole-knee sodium MRI. Source: Crema, M.D., Roemer, F.W. & Marra, M.D. (2011). . 5. Diffusion weighted imaging (‘DWI’) Diffusion weighted imaging is another one of the techniques that is used to measure the content of Glycosaminoglycans in cartilage and to access collagen network infrastructure (Crema et al., 2011, pp.37-62). I want paraphrase this Figure 16 shows a sagittal section of ADC through a diffusion- weighted MRI of the knee. The image reveals a higher signal intensity at the posterior aspect of the medial femoral condyle, which indicates increased mobility of water proton secondary to a disrupted cartilage. Figure 1. Diffusion- weighted MRI of the knee in sagittal view. Source: Crema, M.D., Roemer, F.W. & Marra, M.D. (2011). Grading of Cartilaginous Lesions The grading of cartilaginous lesions using MRI occurs using the ‘Modified Noyes scale’. The ‘Modified Noyes scale’ uses arthroscopic grading, which is a type of grading based on the cartilage lesion’s shape and structure (Gold et al, 2009, pp.91-98). The following table, Table 1, provides the typical findings on MRI that correlate with Modified Noyes scores of 0, 1, 2, 3, and 4. Modified Noyes score Interpretations 0 Unremarkable 1 Change in signal ( Increase T2) 2 Incomplete thickness defect < 50% 3 Incompele thickness defect >50% 4 Compelete thickness defect The following images show cartilage damage. Figure 17-19 show axial fast spin-echo (FSE) images of fat saturation concerning cartilage damage (Gold et al, 2009, pp.91-98). The grade of Modified Noyes score is shown. Figure 17. An intermediate-weighted FSE image in axial cut exhibiting increased signal, which is classified as grade 1 cartilage damage in the lateral facet (Gold et al, 2009, pp.91-98). Figure 18: An intermediate-weighted FSE axial section revealing a cartilage loss of Read More