Diffusion Tensor Imaging - Essay Example

?Diffusion Tensor Imaging (DTI) Diffusion tensor imaging is an emerging MRI (magnetic resonance imaging) technique that supports the measurement of the limited water diffusion in tissue for the purpose of creating neural tract images instead of using this measurement to allocate contrast or colours to pixels in a cross sectional image. The most fascinating feature of DTI is that it is not a contrast-based MRI technique and, therefore, it eliminates the risks of using gadolinium-based contrast agents and “measurement of the restrictions on the Brownian motion of water molecules” is the underlying principle of DTI (Borrero et al., 2011). In a pure liquid, water molecules can move freely in all three dimensions whereas it is not possible in case of tissues. Conventionally, T2-weighted MRI images were used to identify muscle strains. These MRI images were capable of optimising contrast between injured muscles and normal uninjured muscles. Recently, the DTI was invented as a more accurate method for identifying muscle damage as compared to the T2 weighted MRI. The DTI variables exhibit a strong and quick response to damage whereas the T2 signal may take a prolonged period to respond to the change. According to a recent research conducted in the United States, “diffusion tensor imaging based muscle fibre tracking enables the measurement of muscle architectural parameters, such as pennation angle (theta) and fibre tract length (L(ft), throughout the entire muscle” (Acton, 2011, p. 949). Experts opine that the DTI technique can be effectively deployed to examine the three dimensional architecture of the skeletal muscle and get exact information regarding muscle damage. The DTI based muscle fibre tracking method has the potential to reconstruct muscle architecture and, hence, it can be considered as one of the most potential inventions of medical science. As Sinha and Sinha (2011) point out, one of the most significant advantages of this technique is that the diffusion tensor images have the potential to support larger volume imaging without centring and repositioning the magnet value. In case of elongated structures like muscle fibres, the diffusion coefficient of water is higher along the fibre. By taking diffusion measurements in at least six directions, it is possible to calculate a diffusion tensor and which in turn would be beneficial to extract the main direction of the diffusion. Subsequently, this directional information can be integrated into neighbouring pixels to facilitate fibre trajectory reconstruction. In the view of Heemskerk, (2009), this process is helpful to estimate muscle architectural parameters including fibre length, pennation angle, and psychological cross sectional area. In addition, the DT-MRI muscle fibre tracking is a potential method to take pennation angle measurements of human muscle. The DTI based muscle fibre tracking technique is still at its developmental stages and this process offers greater future scope. MRI techniques for cartilage imaging Recently, a number of advanced MRI techniques have been developed with intent to facilitate more accurate imaging of cartilage. Major MRI techniques for cartilage imaging include hip imaging, parallel imaging, delayed gadolinium-enhanced MRI of cartilage (DGEMRIC), high resolution MRI, sodium MRI, T1p relaxation, and T2 relaxation. Most of these methods are very effective in applying cartilage imaging. Hip imaging is specifically demanding due to the joint’s spherical nature, thin articular cartilage, and deep anatomical position (Kim & Mamisch, 2008). As Hitt and Meel (2009) point out, this technique is mainly used for the examination of the acetabulum and acetabular labrum. Hip imaging is generally acquired in the specified ‘axial, coronal, and sagittal planes’ (ibid). The hip imaging technique will provide ‘true parallel slices of the acetabulum, acetabular labrum, femoral head and neck, and trochanter anatomies’ (ibid). This method is of great importance in cartilage imaging when it comes to the fact that imaging the entire acetabular labrum using other imaging techniques is a tough task. Here, the hip imaging provides a complete view of the entire acetabular circumference. The method of parallel imaging has a range of benefits including high resolution morphological imaging and newer biochemical imaging (Kim & Mamisch, 2008). Nowadays, the parallel imaging method is widely applied in the imaging of knee cartilage. High resolution imaging is one of the most notable features of parallel imaging technique. The multi-element based new coil technology enhances the scope of parallel imaging, which is very useful to decrease the scan time significantly regardless of the high resolutions parameters. Here, each element is related to a radiofrequency channel. Since these radiofrequency signals can be easily processed and jointed together, the parallel imaging technique is extremely potential to get accurate results. In addition, reduced acquisition time and elimination of some artefacts are other notable benefits of parallel imaging. Many orthopaedic surgeons are of the opinion that the DGEMRIC is the most effective method available for cartilage imaging. This technique is used to measure glycosaminoglycan content and hence maintain an effective correlation with mechanical stiffness (Center for Diagnostic Imaging., 2009). Patients also prefer to choose this technique for assessing articular damage since it has been proved safe and effective. Experts opine that DGEMRIC can be used to detect glycosaminoglycan variations in the cartilage of an arthritis patient (ibid). If the cartilage is biochemically abnormal, methods like x-rays and standard MR images may fail to identify the abnormality. In this situation, the method of DGEMRIC can be effectively used. Similarly, radiographs and MRI scans may give normal results for patients with obvious symptoms of femoroacetabular impingement; here also newly developed techniques like DGEMRIC would be useful (ibid). The IDEAL-SPGR is also an innovative technique for creating high resolution 3D cartilage imaging (Siepmann, et al., 2007). While comparing to the conventional fat-saturated SPGR, the IDEAL-SPGR imaging facilitates effective separation of fat water and promotes cartilage SNR (ibid). In addition, the use of IDEAL-SPGR significantly improved cartilage fluid contrast to noise ratio. Orthopaedic practitioners reflect that this high resolution 3D cartilage imaging technique will contribute to the reliability of cartilage volume measurements and identification of cartilage surface defects (ibid). Experts also point that morphological features of the knee cartilage can be excellently evaluated in five minutes using the IDEAL-SPGR based high resolution 3D imaging(ibid). Sodium MRI is also a potential method mainly because of its low 23Na concentrations in biological tissues as well quick bi-exponential signal decay. It has been identified that proteoglycan depletion in the cartilage matrix is a sign of osteoarthritis. The sodium MRI can correlate with proteoglycan concentration and hence this method is potential track early proteoglycan depletion. In addition, it is possible to obtain high resolution sodium images (voxels of 1?1?2 mm3) within less than 22 minutes. Medical practitioners opine that the scope of sodium MRI is beyond the anatomic imaging; it has also the potential to provide valuable information on physiology and cellular metabolism. According to Ouwerkerk (2007), the transverse relaxation time (T2) of sodium is very smaller and it is bi-exponential in majority of the tissues and cells. Experts point out that sodium MRI has the ability to diagnose osteoarthritis before it is got deteriorated. According to an opinion, “sodium images generated of an in vitro bovine patella clearly distinguish the region of proteoglycan depletion from the region of healthy cartilage” (Reddy et al, 1998). Likewise, T1p relaxation weighted imaging is a potential alternative to many other proteoglycan sensitive methods. The T1p imaging closely observes the slow pace and even the slightest interaction between motion restricted water molecules and their local environment. The T1p is capable of identifying the spin lattice relaxation process taking place in the rotating frame. While taking the measurements of Tp1, changes to the extracellular matrix including proteoglycan loss are considered. Decrease in the T1p relaxation rate is directly proportional to the decrease in proteoglycan content. From a number of studies, an increased cartilage T1p has been identified for patients with osteoarthritis. It has been proven that the T1p mapping has the potential to early detect biochemical changes occurring in articular cartilage and intervertebral discs. In both these cases, the T1p highly relates to the tissue’s proteoglycan content. In addition, this technique has further scope in asymptomatic and symptomatic human models. Finally, T2 relaxation also provides detailed cartilage information within a reasonable scan time. This method is based on the capability of free water proton molecules travel and to share energy inside the cartilaginous matrix. Researchers indicate that the T2 relaxation time may be increased with collagen proteoglycan matrix damage and water content rise in the degenerating cartilage. Evidences suggest that T2 values may be high in patients with OA. To describe cartilage damage, the arthroscopic grading system developed by the International Cartilage Repair Society would be effective. This system ranks cartilage defects as: grade 0: normal cartilage grade 1: cartilage with soft spot grade2: cartilage with visible minor tears grade3: cartilage damages with deep crevices grade4: cartilage damage exposes the underlying bone References Acton, Q A., 2011. Issues in Biomedical Engineering Research and Application: 2011 Edition. Scholarly Editions. Borrero, C G, Mountz, J M & Mountz, J D., 2011. Emerging MRI methods in rheumatoid arthritis, Nature Reviews: Rheumatology, 7, pp. 85-95. Center for Diagnostic Imaging, 2009. AAOS: New MRI techniques benefit cartilage damage diagnosis, [Online] Available at: [Accessed 24 May 2012]. Heemsherk, A M, Sinha, T K L, Wilson, K J, Ding, Z & Damon, B M.., 2009. Quantitative assessment of DTI-based muscle fiber tracking and optimal tracking parameters, Magnetic Resonance in Medicine, 61(2), pp. 467-472. Hitt, D., & Meel, M. V. 2009. Ace tabular radial hip imaging. FieldStrength. 38. 42-45. [online] Available at: http://incenter.medical.philips.com/doclib/enc/fetch/2000/4504/3634249/3634100/4987812/5025553/5771083/6065169/FS38_P_Aptip_radial_hip.pdf%3fnodeid%3d6066053%26vernum%3d3 [Accessed 24 May 2012]. Kim, Y, Mamisch, T C., 2008. Clinical application of delayed gadolinium enhanced MRI of cartilage (DGEMRIC), Siemens, pp. 96-99, [Online] Available at: Ouwerkerk. R. 2007. American College of Radiology. Sodium Magnetic Resonance Imaging: From Research to Clinical Use. 739-741. [online] Available at: http://www.mri.jhmi.edu/~rouwerke/rouwerke_data/JACR4p741.pdf [Accessed 24 May 2012]. Reddy, R. et al. 1998. National Center for Biotechnology Information, U.S. National Library of Medicine, 39 (5):697-701. [Online] Available at: http://www.ncbi.nlm.nih.gov/pubmed/9581599 [Accessed 24 May 2012]. Siepmann, D B, McGovern, J Brittain, J H & Reeder, S B., 2007. High-resolution 3D cartilage imaging with IDEAL-SPGR at 3T, American Journal of Roentgenology, 189, pp. 1510-1515, [online] Available at: [Accessed 24 May 2012]. Sinha, S, & Sinha, U., 2011. Reproducibility analysis of diffusion tensor indices and fiber architecture of human calf muscles. In vivo at 1.5 Tesla in neutral and plantar?exed ankle positions at rest, Journal of Magnetic Resonance Imaging, 34, pp. 107-119. Read More