T1 rho and T2 mapping detect acute ischemic injury in a piglet model of Legg-Calve-Perthes disease

This study investigated the sensitivity of T1 rho and T2 relaxation time mapping to detect acute ischemic injury to the secondary ossification center (SOC) and epiphyseal cartilage of the femoral head in a piglet model of Legg-Calve-Perthes disease. Six piglets underwent surgery to induce global right femoral head ischemia and were euthanized 48 h later. Fresh operated and contralateral-control femoral heads were imaged ex vivo with T1, T2, and T1 rho mapping using a 9.4T magnetic resonance imaging scanner. The specimens were imaged a second time after a freeze/thaw cycle and then processed for histology. T1, T2, and T1 rho measurements in the SOC, epiphyseal cartilage, articular cartilage, and metaphysis were compared between operated and control femoral heads using paired t tests. The effects of freeze/thaw, T1 rho spin-lock frequency, and fat saturation were also investigated. Five piglets with histologically confirmed ischemic injury were quantitatively analyzed. T1 rho was increased in the SOC (101 +/- 15 vs. 73 +/- 16 ms; p = 0.0026) and epiphyseal cartilage (84.9 +/- 9.2 vs. 74.3 +/- 3.6 ms; p = 0.031) of the operated versus control femoral heads. T2 was also increased in the SOC (28.7 +/- 2.0 vs. 22.7 +/- 1.7; p = 0.0037) and epiphyseal cartilage (57.4 +/- 4.7 vs. 49.0 +/- 2.7; p = 0.0041). No changes in T1 were detected. The sensitivities of T1 rho and T2 mapping in detecting ischemic injury were maintained after a freeze/thaw cycle, and T1 rho sensitivity was maintained after varying spin-lock frequency and applying fat saturation. In conclusion, T1 rho and T2 mapping are sensitive in detecting ischemic injury to the SOC and epiphyseal cartilage of the femoral head as early as 48 h after ischemia induction.