Fast Field Echo Magnetic Resonance Imaging For Quantifying Acetabular Wall Coverage: A Validation Study With Computed Tomography

Background: Acetabular morphology in hip dysplasia is typically assessed using computed tomography (CT) for bone coverage and magnetic resonance imaging (MRI) for soft tissues. However, agreement between CT and 3.0-T fast field echo (FFE) MRI for anterior and posterior acetabular sector angles (AASA, PASA) remains insufficiently defined. Hypothesis: FFE T1-weighted MRI measurements would strongly correlate with CT-based acetabular sector angles (ASAs). Study Design: Cohort study (diagnosis); Level of evidence, 2. Methods: A total of 65 symptomatic dysplastic hips were evaluated. Two independent observers measured on CT and 3.0-T MRI scans the lateral center-edge angle (LCEA), anterior and posterior acetabular wall indices (AWI, PWI), Tönnis angle, and pelvic signs. Equatorial, intermediate, and proximal AASA and PASA were obtained on each modality. CT-MRI agreement was assessed using Spearman rho (ρ). Results: Intermediate AASA demonstrated strong CT-MRI correlation (ρ = 0.807), whereas equatorial and proximal AASA correlations were moderate (ρ = 0.408 and 0.398, respectively). All PASA measurements showed good MRI-CT agreement (equatorial ρ = 0.766; intermediate ρ = 0.747; proximal ρ = 0.739). AWI correlated well with CT-AASAs but weakly with MRI-derived AASAs (equatorial ρ = 0.345; intermediate ρ = 0.325; proximal ρ = 0.255). Conclusion: T1-weighted FFE MRI cannot currently replace CT for measuring acetabular coverage of the femoral head. Although MRI and CT seemed to correlate better at the posterior level, they did not correlate accurately anteriorly; thus, the estimation of AWI by MRI with the current echo sequence alone may lead to misinterpretation. Given that the most common type of dysplasia in the setting of normal LCEA is that with an anterior wall defect only, the authors strongly recommend using CT (or other MRI sequences) to assess patients who are potential candidates for hip joint preservation surgery.