Relaxation Time Mapping of Early-Stage Osteonecrosis of the Femoral Head: An In Vivo Piglet Model Study

Quantitative magnetic resonance imaging (MRI) relaxation time mapping techniques may be useful to evaluate early-stage osteonecrosis of the femoral head, particularly in children with Legg-Calvé-Perthes disease (LCPD). The purpose of this study was to assess the sensitivities of T2, T1ρ, adiabatic T1ρ (aT1ρ), and adiabatic T2ρ (aT2ρ) relaxation time mapping to detect early-stage ischemic injury to the secondary ossification center (SOC) of the femoral head in vivo in a piglet model of LCPD. We hypothesized that relaxation times would be increased in the SOCs of ischemic versus contralateral-control femoral heads 1 week following onset of ischemia. Bilateral hips of n = 13 piglets with confirmed, surgically-induced complete ischemia of the SOC were imaged 1 week post-operatively using a clinical 3 T MRI scanner. Median T2 (n = 13), T1ρ (n = 13), aT1ρ (n = 10), and aT2ρ (n = 10) relaxation times were measured for the total SOC, as well as its central and peripheral subregions, and were compared between the ischemic versus control femoral heads using paired t-tests (p < 0.05). All four relaxation times were significantly increased in the ischemic versus control femoral heads, with a more pronounced increase in the peripheral versus central subregion of the SOC. T2 and aT2ρ had the greatest percent increases and effect sizes of the four relaxation times. In conclusion, T2, T1ρ, aT1ρ, and aT2ρ relaxation time mapping techniques are sensitive in detecting ischemic injury to bone marrow of the femoral head in vivo in a piglet model of LCPD at clinical 3 T MRI field strength.