AJR:189, October 2007 923 AJR 2007; 189:923–927 0361–803X/07/1894–923 © American Roentgen Ray Society Kabakci et al. Tractography of Median Nerve Musculoskeletal Imaging • Original Research Diffusion Tensor Imaging and Tractography of Median Nerve: Normative Diffusion Values Neslihan Kabakci 1 Bengi Gürses 1 Zeynep Firat 1 Ali Bayram 1 Aziz Müfit Uluğ 2,3 Arzu Kovanlıkaya 1 İlhami Kovanlıkaya 1 Kabakci N, Gürses B, Firat Z, et al. Keywords: diffusion tensor imaging, median nerve, MRI DOI:10.2214/AJR.07.2423 Received January 29, 2007; accepted after revision May 13, 2007. Preliminary data presented at the 2006 Annual Scientific Meeting of the European Society for Magnetic Resonance in Medicine and Biology, Warsaw, Poland. 1 Department of Radiology, Yeditepe University Hospital, Devlet Yolu Ankara Cad. 102-104, 34752 Kozyataği, Istanbul, Turkey. Address correspondence to N. Kabakci (nkabakci@yeditepe.edu.tr). 2 Department of Biomedical Engineering, Yeditepe University School of Engineering, Istanbul, Turkey. 3 Department of Radiology, Weill Medical College of Cornell University, New York, NY. OBJECTIVE. The purposes of this study were to visualize the human median nerve on dif- fusion tensor imaging and to determine the normal fractional anisotropy (FA) value and appar- ent diffusion coefficient (ADC) of the normal median nerve. SUBJECTS AND METHODS. The wrists of 20 healthy volunteers and of two patients with carpel tunnel syndrome were examined with a 3-T MRI system with a standard eight-chan- nel sensitivity-encoding head coil. Diffusion tensor imaging was performed with a spin-echo echo-planar sequence. A T1-weighted sequence was performed for anatomic reference. After tractography, the FA value and ADC of the whole nerve were calculated automatically. Manual focal measurements also were obtained at the levels of the flexor retinaculum, wrist, and forearm. RESULTS. We visualized the median nerve with MR diffusion tensor tractography and fol- lowed the nerve for approximately 77.5 mm. We found the normative diffusion values of the me- dian nerve were an FA of 0.709 ± 0.046 (SD) and an ADC of 1.016 ± 0.129 × 10 −3 mm 2 /s. There was a statistically significant difference between the FA values obtained at the level of the flexor retinaculum and the values obtained from the other parts of the median nerve (p < 0.0001). We found a decrease in FA value (p < 0.01) and an increase in ADC (p < 0.05) with advancing age. CONCLUSION. The normative diffusion values of the human median nerve can be used as a reference in evaluation, diagnosis, and follow-up of entrapment, trauma, and regeneration of the median nerve. he median nerve is one of three main nerves of the forearm. It arises from the lateral and medial cords of the brachial plexus (C6–T1). At the wrist level, it passes under the flexor retinaculum deep in relation to the flexor digitorum superficialis tendons through the car- pal tunnel and divides into digital and muscular branches distal in relation to the flexor retinac- ulum. Several entrapment and compression syndromes affect these nerves of the forearm. Carpal tunnel syndrome (CTS) is the most common peripheral neuropathy of the upper extremity resulting from dysfunction of the me- dian nerve. CTS is characterized by numbness in the first three digits and the radial aspect of the fourth digit and by thenar atrophy. There are several diagnostic methods for CTS, such as the Phalen maneuver, Flick test, and electromy- ography [1, 2]. Although the sensitivity and specificity of MRI in the diagnosis of CTS are low (sensitivity, 23–96%; specificity, 39–87%), a few signs, such as nerve enlargement, nerve flattening, and increased nerve signal intensity, do occur [1]. With application of the appropriate magnetic field gradients, MRI can be sensitized to the ther- mally driven random motion (diffusion) of water molecules in the direction of the field gradient. This technique is called diffusion-weighted im- aging (DWI) [3]. Many materials have intrinsic structural properties that hinder diffusion so that diffusivity is greater in some directions than in others. This property is known as anisotropy. If there is no directional variation in diffusion rate, diffusion is said to be isotropic. Biologic tissues often are anisotropic because structures such as cell membranes and large protein molecules re- strict the motion of water molecules. This prop- erty is called restricted diffusion. DWI usually shows diffusion information in one direction. In an anisotropic sample, diffusion tensor imaging (DTI) is required to fully characterize diffusion. In theory, to determine all elements of the diffu- sion tensor, at least six independent measure- ments with diffusion gradients applied sequen- tially along six noncollinear directions are required [4–7]. The direction of maximum diffu- sivity has been shown to coincide with the fiber tract orientation [6, 7]. In white matter fiber bun- T Downloaded from www.ajronline.org by 52.73.204.196 on 05/16/22 from IP address 52.73.204.196. Copyright ARRS. For personal use only; all rights reserved