Magnetic Resonance Neurography of the Brachial Plexus Using 3D SHINKEI: Comparative Evaluation with Conventional Magnetic Resonance Sequences for the Visualization of Anatomy and Detection of Nerve Injury at 1.5T

Abstract

Background and purpose: This work aims at optimizing and studying the feasibility of imaging the brachial plexus at 1.5T using 3D nerve-SHeath signal increased with INKed rest-tissue RARE imaging (3D SHINKEI) neurography sequence by comparing with routine sequences.

Materials and methods: The study was performed on a 1.5T Achieva scanner. It was designed in two parts: (a) Optimization of SHINKEI sequence at 1.5T; and (b) Feasibility study of the optimized SHINKEI sequence for generating clinical quality magnetic resonance neurography images at 1.5T. Simulations and volunteer experiments were conducted to optimize the T2 preparation duration for optimum nerve-muscle contrast at 1.5T. Images from the sequence under study and other routine sequences from 24 patients clinically referred for brachial plexus imaging were scored by a panel of radiologists for diagnostic quality. Injury detection efficacy of these sequences were evaluated against the surgical information available from seven patients.

Results: T2 preparation duration of 50 ms gives the best contrast to noise between nerve and muscle. The images of 3D SHINKEI and short-term inversion recovery turbo spin-echo sequences are of similar diagnostic quality but significantly better than diffusion weighted imaging with background signal suppression. In comparison with the surgical findings, 3D SHINKEI has the lowest specificity; however, it had the highest sensitivity and predictive efficacy compared to other routine sequences.

Conclusion: 3D SHINKEI sequence provides a good nerve-muscle contrast and has high predictive efficacy of nerve injury, indicating that it is a potential screening sequence candidate for brachial plexus scans at 1.5T also.

Keywords: Diffusion-weighted imaging with background signal suppression; MSDE; SHINKEI; T2prep; short-term inversion recovery.

Figure 1

iMSDE preparation module. Gradients shown are applied in the direction in which the motion sensitization is desired. T2_prep is the MSDE duration that also contributes to an additional T2 contrast. In the SHeath signal increased with INKed rest-tissue RARE imaging sequence, this is followed by a fat suppressing spectral adiabatic inversion recovery pulse

Figure 2

(a) The exponential decay of the nerve and muscle signal. Simulation values and experimental relative signal values from nerve and muscle after normalization are depicted. (b) The cost function Nerve- Muscle contrast; Experimental validation of iMSDE optimization in comparison to the theoretical values. The nerve-muscle contrast peaks at T2_prep time of 50 ms. iMSDE T2_prep time is hence chosen as 50 ms. (c) Visualization of the anatomy of the brachial plexus in a 24-year-old volunteer with maximum intensity projection images. The oval and square ROIs indicate how the nerve and background SNR is measured

Figure 3

A comparison between SHeath signal increased with INKed rest-tissue RARE imaging, short-term inversion recovery turbo spin-echo and diffusion-weighted imaging with background signal suppression image quality based on grading at various anatomical regions of the brachial plexus. The bars indicate the number of cases where a particular anatomical region has obtained a high score of 3 on 4 (“good” to “excellent” visualization)

Figure 4

A 29-year-old male following road traffic accident shows root avulsions at left C5, C6, C7 and C8 levels. (a) SHINKEI shows root avulsion at C5 to C8 (arrows) and distorted distal plexus (small arrows) compared to the normal right side (b). Short-term inversion recovery turbo spin echo (c) and diffusion-weighted imaging with background signal suppression (d) for comparison

Figure 5

A 22 year old male with RTA: SHeath signal increased with INKed rest tissue RARE imaging (a and d), short term inversion recovery (b and e) and diffusion weighted imaging with background signal suppression (c and f) show lower root avulsion with pseudomeningioceles (arrows); SHeath signal increased with INKed rest tissue RARE imaging and short term inversion recovery show hyperintensity in the suprascapular nerve (arrowhead, a and b), which was not appreciated in the diffusion weighted imaging with background signal suppression (c). Distal nerve injury is better depicted in SHINKEI and short term inversion recovery sequence

Figure 6

A 30-year-old female with transection of the right roots and trunks of brachial plexus with neuroma formation, better appreciated in the SHeath signal increased with INKed rest-tissue RARE imaging (a) and short-term inversion recovery (b) images compared to the diffusion weighted imaging with background signal suppression (c). Nerve conduction study findings were correlating with the imaging findings

Figure 7

A 35 year old male patient with injury to right distal brachial plexus. The grade 1 sub acute injury is discernible on the SHeath signal increased with INKed rest tissue RARE imaging (a) and the short term inversion recovery as hyperintensities (white arrows) (b) and is not well appreciated in diffusion weighted imaging with background signal suppression image (c)