Reliability of fast T1 VIBE Dixon MRI for femoral version measurement in FAI patients: A comparative study with CT.

Purpose Patients with femoroacetabular impingement (FAI) can present with abnormal femoral version(FV). Discrepancies were reported for FV Measurement comparing MRI and CT. We assessed difference of FV measurement on MRI and on matched CT. Methods A retrospective IRB-approved comparative study involving 100 hips of symptomatic FAI patients was performed. All patients(100 hips) had hip pain(mean age 28 ± 10 years) and underwent pelvic CT scan and MRI of the same hip. Routine unilateral, multiplanar MRI of the hip was acquired for chondrolabral lesions. Of them, 52 hips(46 patients) underwent hip MRI with standard T1 images, while 48 hips underwent hip MRI with an additional fast MRI with Dixon based images(bilateral T1 Vibe Dixon based images of pelvis and knee) to measure FV. Two readers independently measured FV(Murphy method) on CT and MRI. Results Difference of FV decreased significantly(p < 0.001) between CT and MRI with standard images from 4.9 ± 4.5° for Reader 1(7.3 ± 6.7° for Reader 2) to -0.05 ± 1.5°(r = 0.993, p < 0.001)for Reader 1 (0.73 ± 2.95°, r = 0.975, p < 0.001, for Reader 2) with fast Dixon based images.Difference of FV of CT between two readers was 1.9 ± 3.2°(r = 0.969, p < 0.001) and was not significantly different compared to fast MRI with Dixon based images (1.1 ± 4.4°,r = 0.943, p < 0.001).Number of hips with Difference of FV> 5° between CT and MRI were significantly(p < 0.001) reduced from 35 hips (67%,with standard images) to 2 hips (4%, Dixon based images) for reader 1. Conclusion We changed our clinical practice and use fast MRI with T1 Dixon-based images for FV measurement. This decreased measurement errors in FV and misdiagnosis of FV and could potentially reduce CT scans.