Acetabular cartilage assessment in patients with femoroacetabular impingement by using T2* mapping with arthroscopic verification

Purpose: To evaluate the ability of T2* mapping to help differentiate damaged from normal acetabular cartilage in patients with femoroacetabular impingement (FAI). Materials and Methods: The institutional review board approved this retrospective study, and the requirement to obtain informed consent was waived. The study complied with HIPAA guidelines. The authors reviewed T2* relaxation time maps of 28 hips from 26 consecutive patients (mean patient age, 28.2 years; range, 12.53 years; eight male patients (nine hips) with a mean age of 26.7 years [range, 16.53 years]; 18 female patients (19 hips) with a mean age of 28.9 years [range, 12.46 years]). Conventional diagnostic 3.0-T magnetic resonance (MR) arthrography was augmented by including a multiecho gradient-recalled echo sequence for T2* mapping. After imaging, acetabular and femoral data were separated and acetabular regions of interest were identified. Arthroscopic cartilage assessment with use of a modified Beck scale for acetabular cartilage damage was performed by an orthopedic surgeon who was blinded to the results of T2* mapping. A patient-specific acetabular projection with a T2* overlay was developed to anatomically correlate imaging data with those from surgery (the standard of reference). Results were analyzed by using receiver operating characteristic (ROC) curves. Results: The patient-specific acetabular projection enabled colocalization between the MR imaging and arthroscopic findings. T2* relaxation times for normal cartilage (Beck score 1, 35.3 msec ± 7.0) were significantly higher than those for cartilage with early changes (Beck score 2, 20.7 msec ± 6.0) and cartilage with more advanced degeneration (Beck scores 3.6, ≤19.8 msec ± 5.6) (P , .001). At ROC curve analysis, a T2* value of 28 msec was identified as the threshold for damaged cartilage, with a 91% truepositive and 13% false-positive rate for differentiating Beck score 1 cartilage (normal) from all other cartilages. Conclusion: The patient-specific acetabular projection with a T2* mapping overlay enabled good anatomic localization of cartilage damage defined with a T2* threshold of 28 msec and less.