T1ρ and T2 mapping detect acute ischemic injury in a piglet model of Legg–Calvé–Perthes disease

Abstract

This study investigated the sensitivity of T1ρ 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–Calvé–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 T1ρ 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 T1ρ 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, T1ρ spin‐lock frequency, and fat saturation were also investigated. Five piglets with histologically confirmed ischemic injury were quantitatively analyzed. T1ρ 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 T1ρ and T2 mapping in detecting ischemic injury were maintained after a freeze/thaw cycle, and T1ρ sensitivity was maintained after varying spin‐lock frequency and applying fat saturation. In conclusion, T1ρ 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.

Intravoxel incoherent motion (IVIM) detects femoral head ischemia in a piglet model of Legg‐Calvé‐Perthes disease

“…1,9 Quantitative MRI techniques, including apparent diffusion coefficient (ADC) mapping using diffusion-weighted imaging (DWI) and T2 and T1ρ relaxation time mapping, have been proposed as alternative or complementary approaches to CE-MRI to assess earlystage LCPD. [10][11][12][13][14][15][16][17][18] For example, ADC has been shown to increase in the SOC in response to ischemic injury to the bone marrow of the femoral head. [10][11][12] While these methods may be useful to assess the severity and extent of the injury and/or repair to the femoral head, they do not provide information on whether or not the bone marrow is perfused.…”

“…A noncontrast‐enhanced method would also allow MRI to be used more frequently, facilitating serial exams, which may not only inform treatment decisions but also lead to better understanding of the complex pathogenesis of LCPD 1,9 . Quantitative MRI techniques, including apparent diffusion coefficient (ADC) mapping using diffusion‐weighted imaging (DWI) and T2 and T1ρ relaxation time mapping, have been proposed as alternative or complementary approaches to CE‐MRI to assess early‐stage LCPD 10–18 . For example, ADC has been shown to increase in the SOC in response to ischemic injury to the bone marrow of the femoral head 10–12 .…”

Naturally occurring osteochondrosis latens lesions identified by quantitative and morphological 10.5 T MRI in pigs

“…Due to limited access to cadaveric specimens of children for histological evaluation, further understanding of the pathophysiology of JOCD requires the development of a noninvasive approach that can identify and monitor the progression and/or resolution of OCL and OCM lesions in vivo. Implementation of quantitative and morphologic MRI techniques in animal models of orthopedic disorders that are characterized by ischemic necrosis of the epiphyseal cartilage (OC and Legg‐Calvé‐Perthes Disease) demonstrated the sensitivity of T2 and T1ρ relaxation time maps to acute ischemic injury, suggesting that these are suitable methods to further examine the pathophysiology of JOCD 12–14 . These quantitative cartilage mapping methods have been used to identify surgically induced OCL and OCM lesions in a goat model of OC by focusing on specific areas that were rendered ischemic after transection of cartilage canal vessels 12,15 .…”

“…Implementation of quantitative and morphologic MRI techniques in animal models of orthopedic disorders that are characterized by ischemic necrosis of the epiphyseal cartilage (OC and Legg-Calvé-Perthes Disease) demonstrated the sensitivity of T2 and T1ρ relaxation time maps to acute ischemic injury, suggesting that these are suitable methods to further examine the pathophysiology of JOCD. [12][13][14] These quantitative cartilage mapping methods have been used to identify surgically induced OCL and OCM lesions in a goat model of OC by focusing on specific areas that were rendered ischemic after transection of cartilage canal vessels. 12,15 The use of these imaging methods to identify naturally occurring OCL and OCM lesions at predilection sites has not previously been accomplished.…”