Diffusion tensor imaging and fiber tractography of the median nerve at 1.5T: optimization of b value
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The objective of this study was to systematically assess the optimal b value for diffusion tensor imaging and fiber tractography of the median nerve at 1.5 T.
Materials and methods
This is a prospective study which was carried out with institutional review board approval and written informed consent from the study subjects. Fifteen healthy volunteers (seven men, eight women; mean age, 31.2 years) underwent diffusion tensor imaging of the wrist. A single-shot spin-echo-based echo-planar imaging sequence (TR/TE, 7000/103 ms) was performed in each subject at eight different b values ranging from 325 to 1,550 s/mm2. Number and length of reconstructed fiber tracts, fiber density index (FDi), fractional anisotropy (FA), and apparent diffusion coefficient (ADC) were calculated for the median nerve. Signal-to-noise ratio (SNR) was also calculated for each acquisition. The overall image quality was assessed by two readers in consensus by ranking representative fiber tract images for each subject using a scale range from 1 to 8 (1 = best to 8 = worst image quality).
Longest fibers were observed for b values between 675 and 1,025 s/mm2. Maximum FDi was found at b values of 1,025 s/mm2. FA was between 0.5 and 0.6 for all b values. ADC gradually decreased from 1.44 × 10−3 to 0.92 × 10−3 mm2/s with increasing b values. Maximum SNR ± standard deviation (175.4 ± 72.6) was observed at the lowest b value and decreased with increasing b values. SNR at b values of 1,025 s/mm2 was 48.5% of the maximum SNR. Optimal fiber tract image quality was found for b values of 1,025 s/mm2.
The optimal b value for diffusion tensor imaging and fiber tractography of the median nerve at 1.5 T was 1,025 s/mm2.
KeywordsMRI Diffusion tensor imaging Fiber tractography Median nerve
Dr. Gustav Andreisek is supported by a grant from the Holcim Foundation for the Advancement of Scientific Research, Switzerland.
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