Determination of optimum pixel size and slice thickness for tractography and ulnar nerve diffusion tensor imaging at the cubital tunnel using 3T MRI

Abstract

Background Small peripheral nerve tractography is challenging because of the trade-off among resolution, image acquisition time, and signal-to-noise ratio. Purpose To optimize pixel size and slice thickness parameters for fiber tractography and diffusion tensor imaging (DTI) of the ulnar nerve at the cubital tunnel using 3T magnetic resonance imaging (MRI). Material and Methods Fifteen healthy volunteers (mean age 30 ± 6.8 years) were recruited prospectively. Axial T2-weighted and DTI scans were acquired, covering the cubital tunnel, using different pixel sizes and slice thicknesses. Three-dimensional (3D) nerve tractography was evaluated for the median number and length of the reconstructed fiber tracts and visual score from 0 to 5. Two-dimensional (2D) cross-sectional DTI was evaluated for fractional anisotropy (FA) values throughout the length of the ulnar nerve. Results A pixel size of 1.3 mm2 revealed the highest number of reconstructed nerve fibers compared to that of 1.1 mm2 ( P = 0.048), with a good visual score. A slice thickness of 4 mm had the highest number of reconstructed nerve fibers and visual score compared with other thicknesses (all P < 0.05). In 2D cross-sectional images, the median FA values were in the range of 0.40–0.63 at the proximal, central, and distal portions of the cubital tunnel. Inter-observer agreement for all parameters was good to excellent. Conclusion For fiber tractography and DTI of the ulnar nerve at the cubital tunnel, optimal image quality was obtained using a 1.3-mm2 pixel size and 4-mm slice thickness under MR parameters of this study at 3T.

Meta-analysis of the normal diffusion tensor imaging values of the peripheral nerves in the upper limb

“…In the region of the elbow, the ulnar nerve appeared to have a 12% lower FA than the median and radial nerves (CI − 0.25, 0.00; p < 0.001, I 2 96%). The normal MD of the median 51 , 52 , radial 51 and ulnar 39 , 41 , 44 , 46 , 49 , 51 , 52 , 54 , 54 nerves in the elbow region was 1.01 × 10 –3 mm 2 /s (CI 0.68, 1.34), 0.71 × 10 –3 mm 2 /s (CI 0.64, 0.78) and 1.11 × 10 –3 mm 2 /s (CI 1.01, 1.20), respectively (eFigure S12 ). The radial nerve had lower MD than the ulnar nerve (− 0.40 × 10 –3 mm 2 /s CI − 0.76, − 0.04]; p < 0.001, I 2 93%) but was similar to the median nerve.…”

“…Around the elbow, the normal FA of the median 51 , 52 , radial 51 and ulnar 38 , 39 , 41 , 44 , 46 , 49 , 51 , 52 , 54 nerves are shown in Fig. 2 .…”

“…Studies were performed most commonly on Siemens (9 studies 31,[38][39][40][41][42][43] , 43%) or Philips (9 studies 29,44,[44][45][46][47][48][49][50][51] , 43%) scanners with the remainder using GE (3 studies 28,52,53 , 14%). Nineteen studies were performed at 3T 28,29,[38][39][40][41][42][43][44][46][47][48][49][50][51][52][53][54] , with one at 1.5T 45 and another at 7T 31 .…”

“…Studies were performed most commonly on Siemens (9 studies 31,[38][39][40][41][42][43] , 43%) or Philips (9 studies 29,44,[44][45][46][47][48][49][50][51] , 43%) scanners with the remainder using GE (3 studies 28,52,53 , 14%). Nineteen studies were performed at 3T 28,29,[38][39][40][41][42][43][44][46][47][48][49][50][51][52][53][54] , with one at 1.5T 45 and another at 7T 31 . The majority of studies used single-shot echo planar imaging (ssEPI; 17 studies, 85%), one compared ssEPI to readout-segmented echo planar imaging (rsEPI) 39 and 3 studies 28,31,40 did not specify the type of sequence.…”

“…The majority of studies used single-shot echo planar imaging (ssEPI; 17 studies, 85%), one compared ssEPI to readout-segmented echo planar imaging (rsEPI) 39 and 3 studies 28,31,40 did not specify the type of sequence. Subjects were most commonly in the "superman" position (i.e., prone with the shoulder and elbow extended, with the elbow positioned in the isocentre of the magnet; 17 studies 28,29,31,38,38,39,[41][42][43]45,46,[48][49][50][51][52]54 , 85%) whilst the others positioned individuals supine with their arm extended overhead 40 , supine in the anatomical position 44,47 or did not report the position 53 . The receiver coils used were most commonly flexible extremity coils (11 studies 29,31,39,[41][42][43][44]47,51,54 , 55%) with the remainder using head 48 , knee 38,46,50,52 , wrist 28,45 or unspecified 53 coils.…”