Magnetization Transfer Ratio in Peripheral Nerve Tissue: Does It Depend on Age or Location?

Background and Purpose Magnetization transfer contrast imaging provides indirect information on the concentration of "bound" water protons and their interactions with "free" water molecules. The purpose of this study is to analyze location- and age-dependent changes in the magnetization transfer ratio (MTR) of lower extremity nerves. Materials and Methods Ten younger (20–32 years) and 5 older (50–63 years) healthy volunteers underwent magnetization transfer contrast imaging at 3 Tesla Two 3-dimensional gradient echo sequences with and without an off-resonance saturation pulse (repetition time: 58 milliseconds; echo time: 2.46 milliseconds; band width: 530 Hz/Px; flip angle: α = 7°) were acquired at 3 different locations covering the proximal thigh to the distal lower leg in the group of younger volunteers and at 2 different locations covering the proximal to distal thigh in the group of older volunteers. Sciatic and tibial nerve regions of interest (ROIs) were manually drawn and additional ROIs were placed in predetermined muscles. Magnetization transfer ratios were extracted from respective ROIs and calculated for each individual and location. Results In young volunteers, mean values of nerve and muscle MTR were not different between the proximal thigh (nerve: 20.34 ± 0.91; muscle: 31.71 ± 0.29), distal thigh (nerve: 19.90 ± 0.98; P = 0.76; muscle: 31.53 ± 0.69; P = 0.87), and lower leg (nerve: 20.82 ± 1.07; P = 0.73; muscle: 32.44 ± 1.11; P = 0.51). An age-dependent decrease of sciatic nerve MTR was observed in the group of older volunteers (16.95 ± 1.2) compared with the group of younger volunteers (20.12 ± 0.65; P = 0.019). Differences in muscle MTR were not significant between older (31.01 ± 0.49) and younger (31.62 ± 0.37; P = 0.20) volunteers. Conclusion The MTR of lower extremity nerves shows no proximal-to-distal gradient in young healthy volunteers but decreases with age. For future studies using MTR in peripheral nerve disorders, these findings suggest that referencing magnetization transfer contrast values in terms of age, but not anatomical nerve location is required. Received for publication December 4, 2017; and accepted for publication, after revision, January 18, 2018. Conflicts of interest and source of funding: Dr Kollmer was supported by a research grant from Alnylam Pharmaceuticals. Prof Heiland and Prof Bendszus were supported by the German Research Foundation (SFB 1118). For the remaining authors, none were declared. Correspondence to: Jennifer Kollmer, MD, Department of Neuroradiology, Heidelberg University Hospital, Im Neuenheimer Feld 400, D-69120 Heidelberg, Germany. E-mail: jennifer.kollmer@med.uni-heidelberg.de. Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.

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