A new method to analyze dGEMRIC measurements in femoroacetabular impingement: preliminary validation against arthroscopic findings

Objective: To validate a new method to analyze delayed Gadolinium-Enhanced Magnetic Resonance Imaging of Cartilage (dGEMRIC) measurements in the hip for early assessment of cartilage defects in femoroacetabular impingement (FAI). Methods: We performed a retrospective review of 10 hips in 10 FAI patients, who underwent hip arthroscopy. T-1-weighted images and dGEMRIC T-1 maps were acquired at 1.5 T on coronal planes, including the anterior superior, superior, posterior superior hip cartilage. For all slices, a region of interest (ROI) was defined over the central portion of the femoral cartilage, assumed to be healthy, and T-1 values (x) were transformed to standard scores (z) using z = (x - mu)/sigma, where mu and sigma are the average and standard deviation of T-1 in the femoral ROI. Diagnostic performance of the resulting standardized dGEMRIC maps was evaluated against intraoperative findings and compared with that of a previously proposed dGEMRIC analysis as well as morphologic assessment. Results: Assuming z = 2 or z = -3 as the threshold between normal and degenerated cartilage, sensitivity, specificity and accuracy were 88%, 51% and 62%, and 71%, 63% and 65%, respectively. By using T-1 = 500 ms as single threshold for all dGEMRIC T-1 maps, these values became 47%, 58% and 55%, whereas they were 47%, 79% and 70% for morphologic evaluation. Conclusions: Standardized dGEMRIC can increase the sensitivity in detecting abnormal cartilage in FAI and has the potential to improve the clinical interpretation of dGEMRIC measurements in FAI, by removing the effect of inter- and intra-patient T-1 variability. (C) 2012 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.