RESUMO
Objective To optimize the parameters for the diffusion tensor imaging (DTI)of the ulnar nerve in elbow.Methods 5 groups of DTI sequences with different b values and numbers of diffusion gradient directions (NDGDs)were used to collect ulnar nerve images from 13 volunteers,and then the diffusion tensor tractography (DTT)was established.The fractional anisotropy (FA),apparent diffusion coefficient (ADC),length of ulnar nerve fiber and DTI image quality were compared under different imaging parameters. Results DTI results for 18 normal ulnar nerves were included in the study.Under different imaging conditions,FAs showed no significant differences.With constant NDGDs,increasing b value decreased both image quality and ADCs of the ulnar nerve.NDGDs had no significant effects on ADCs or image quality.When b=1 000 s/mm2 and NDGDs=20,the length of the ulnar nerve fiber was the longest and DTT had the best subjective scoring in image quality.Conclusion b=1 000 s/mm2 and NDGDs=20 is recommended for DTI of elbow ulnar nerve,so as to obtain high image quality and stable observing targets.
RESUMO
OBJECTIVE: To assess the effects of varying the number of diffusion gradient directions (NDGDs) on diffusion tensor fiber tracking (FT) in human brain white matter using tract characteristics. MATERIALS AND METHODS: Twelve normal volunteers underwent diffusion tensor imaging (DTI) scanning with NDGDs of 6, 11, 15, 21, and 31 orientations. Three fiber tract groups, including the splenium of the corpus callosum (CC), the entire CC, and the full brain tract, were reconstructed by deterministic DTI-FT. Tract architecture was first qualitatively evaluated by visual observation. Six quantitative tract characteristics, including the number of fibers (NF), average length (AL), fractional anisotropy (FA), relative anisotropy (RA), mean diffusivity (MD), and volume ratio (VR) were measured for the splenium of the CC at the tract branch level, for the entire CC at tract level, and for the full brain tract at the whole brain level. Visual results and those of NF, AL, FA, RA, MD, and VR were compared among the five different NDGDs. RESULTS: The DTI-FT with NDGD of 11, 15, 21, and 31 orientations gave better tracking results compared with NDGD of 6 after the visual evaluation. NF, FA, RA, MD, and VR values with NDGD of six were significantly greater (smallest p = 0.001 to largest p = 0.042) than those with four other NDGDs (11, 15, 21, or 31 orientations), whereas AL measured with NDGD of six was significantly smaller (smallest p = 0.001 to largest p = 0.041) than with four other NDGDs (11, 15, 21, or 31 orientations). No significant differences were observed in the results among the four NDGD groups of 11, 15, 21, and 31 directions (smallest p = 0.059 to largest p = 1.000). CONCLUSION: The main fiber tracts were detected with NDGD of six orientations; however, the use of larger NDGD (> or = 11 orientations) could provide improved tract characteristics at the expense of longer scanning time.