Precise size evaluation of extraocular muscles using fat-suppressed fast T1-weighted gradient-recalled echo imaging and multiple gaze fixation targets

Abstract

We studied the feasibility of the precise size measurement of extraocular muscles using fast magnetic resonance imaging sequences and gaze fixation targets. We recruited 20 healthy volunteers and optimized fat-suppressed fast T1-weighted gradient-recalled echo (FS T1-GRE) and single-shot fast spin-echo (SSFSE) imaging for evaluating extraocular muscles. With each eye at 40° abduction and adduction, we scanned the short-axis plane at the maximum diameter of the bilateral lateral and medial rectus muscles and measured the maximal cross-sectional area of the muscles during extension and contraction. We evaluated interobserver reproducibility and variability between the size measurements using the two MR sequences and the measurement reproducibility using FS T1-GRE imaging. The interobserver reproducibility in the muscle size measurements using FS T1-GRE and SSFSE imaging was excellent (r=0.93-0.94) and moderate to good (r=0.54-0.75), respectively. The interobserver variability was less with FS T1-GRE than SSFSE imaging (p<0.01). The reproducibility of the size measurement using FS T1-GRE was good to excellent (r=0.78-0.92). FS T1-GRE imaging with the subject staring at each of multiple targets is useful for evaluating precisely the size of extraocular muscles.