Alexandra R. Armstrong

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.

Background: Intervertebral disc (IVD) degeneration contributes significantly to chronic low back pain and represents a major clinical challenge. Quantitative MRI (qMRI) techniques offer the potential to assess biochemical and structural disc changes noninvasively, but its use has been slow to be incorporated into studies utilizing spontaneous large animal models. This study characterizes qMRI‐derived biomarkers of IVD degeneration across the lifespan in a clinically relevant ovine model. Methods: Ex vivo thoracolumbar spine segments from 10 sheep (13–130 months old) were assessed using 3T MRI, including T2, T2*, T1ρ, adiabatic T1ρ, adiabatic T2ρ, and ADC mapping. Relaxation times were compared with Pfirrmann grade, disc height index, biomechanical testing, GAG/water content, and histological scores. Results: T2 and T2* values in the nucleus pulposus (NP) were negatively correlated with age, Pfirrmann grade, and histological degeneration, and positively correlated with GAG and water content. T2 relaxation times in the annulus fibrosus (AF) were inversely related to biomechanical stiffness, whereas T2* relaxation times in the NP were positively associated. Strong inter‐metric correlations were observed between most qMRI measures, but aT1ρ and ADC showed more distinct profiles. Conclusion: These findings support the sensitivity of qMRI in detecting regional and age‐related IVD changes and reinforce its utility for noninvasive disc assessment in translational models of degeneration.

Osteochondrosis/osteochondritis dissecans (OC/OCD) is a developmental orthopedic disease primarily affecting the knee, ankle, and elbow joints of children and multiple animal species. Subclinical lesions of OC/OCD have been described, but most can be visualized only histologically in cadaveric specimens. To monitor the evolution of these lesions and to allow early separation of lesions that will undergo spontaneous healing versus requiring surgical intervention, Magnetic resonance imaging (MRI) techniques that are precise and can be used in vivo are needed. The purpose of this study was to demonstrate the utility of noninvasive 3 T MRI in the identification of naturally occurring OC lesions in the articular epiphyseal cartilage complex (AECC) and growth plate of the distal humerus in domestic piglets. N = 4 asymptomatic piglets underwent four consecutive, in vivo, bilateral elbow joint MRI exams under anesthesia at 4, 6, 8, and 11 weeks of age. 3D Double echo steady state (DESS) morphological images and cartilage T2 relaxation time maps were acquired using a clinical 3 T MRI scanner. After the last MRI, piglets were euthanized, and distal humeri were harvested for histologic evaluation. Multiple preclinical OC lesions were detected in the AECC and the growth plate of the examined humeri and their temporal progression or resolution was successfully monitored using MRI. Although most lesions resolved by 11 weeks of age, those remaining on MRI were confirmed histologically at necropsy.Clinical Significance: In vivo 3 T MRI may allow for longitudinal monitoring of early OC lesions and determination of whether a lesion is resolving or progressing to clinical OCD that may necessitate surgical intervention.

Clinical management of children with Legg-Calvé-Perthes Disease (LCPD) is hampered by incomplete understanding of how the extent of ischemic injury and the duration and quality of subsequent repair determine patient outcome. The traditional piglet model of LCPD is limited to capturing global femoral head ischemia; thus, a new model is needed in which the extent of ischemia can be varied to replicate the spectrum of disease seen in children. In this exploratory study, we used an iterative approach to test and refine methods to bilaterally occlude vessels supplying the femoral heads in n = 8 young piglets under angiographic control. The deep and/or acetabular medial femoral circumflex arteries (DMFCA and AMFCA) were identified and embolized using either embolic particles or liquid embolic agents. The extent of ischemia was assessed immediately post-embolization (4 piglets) and/or 7 days following embolization (7 piglets) using contrast-enhanced magnetic resonance imaging (CE-MRI). After the final CE-MRI, piglets were euthanized, and their femora were harvested for histologic evaluation. Embolization of the DMFCA alone caused transient ischemia that largely resolved by 7 days with small regions of fibrovascular repair of ischemic injury remaining on histology. Embolization of both the DMFCA and AMFCA resulted in a greater degree of pathologic changes at 7 days post-operatively, but also with nearly complete restoration of femoral head perfusion. We found that combining injection of embolic particles with subsequent placement of an embolic micro-coil was the most effective approach to induce ischemic injury, which may be aided in larger piglets. While our findings should be interpreted cautiously due to the wide range in the age and size of animals investigated, they demonstrate that transarterial embolization of the vascular supply of the femoral head results in transient ischemia and histological changes consistent with partial ischemic injury. These results will inform further development of a minimally invasive piglet model of LCPD that offers a unique representation of the spectrum of pathophysiology of LCPD compared to the traditional model.

EGFR-targeted therapies are efficacious, but toxicity is common and can be severe. Urokinase type plasminogen activator receptor (uPAR)-targeted drugs are only emerging, so neither their efficacy nor toxicity is fully established. Recombinant eBAT was created by combining cytokines EGF and uPA on the same single-chain molecule with truncated Pseudomonas toxin. Its purpose was to simultaneously target tumors and their vasculature in the tumor microenvironment. In prior studies on mice and dogs, the drug proved efficacious. Here, we report the safety of eBAT in normal wildtype, uPAR knockout, and immunoreplete and immunodeficient tumor-bearing mice, as well as in dogs with spontaneous sarcoma that more closely mirror human cancer onset. In immunocompetent mice, tumor-bearing mice, uPAR knockout mice, and mice receiving species-optimized eBAT, toxicities were mild and self-limiting. Likewise, in dogs with life-threatening sarcoma given dosages found to be biologically active, eBAT was well tolerated. In mice receiving higher doses, eBAT was associated with dose-dependent evidence of liver injury, including portal biliary hyperplasia, oval cell proliferation, lymphoplasmacytic inflammation, periportal hepatocellular microvesicular change, hemorrhage, necrosis, and apoptosis. The results support continuing the clinical development of eBAT as a therapeutic agent for individuals with sarcoma and other cancers.

Legg‐Calvé‐Perthes disease (LCPD) is a childhood hip disorder characterized by ischemic injury to the epiphysis of the femoral head, but changes to the metaphysis have also been implicated in its pathogenesis. Quantitative magnetic resonance imaging (MRI) relaxation time mapping techniques are potentially useful to detect injury in LCPD, but studies to date have focused on the epiphysis. The purpose of this study was to assess whether T2, T1ρ, adiabatic T1ρ, and adiabatic T2ρ relaxation times can detect early metaphyseal changes in an LCPD piglet model. Complete epiphyseal ischemia of one femoral head was surgically induced and confirmed using contrast‐enhanced MRI in n = 10 6‐week‐old piglets; the contralateral side was unoperated. The bilateral hips were imaged 1 week after surgery in vivo at 3T MRI using relaxation time mapping and contrast‐enhanced MRI. Relaxation times and thicknesses of the metaphyseal primary and secondary spongiosa were measured and compared between the ischemic and contralateral‐control femoral heads using paired t‐tests. In the ischemic femoral heads, T2 relaxation times were significantly increased in the primary spongiosa (6.7 ± 9.8 ms, p = 0.029), and T2, T1ρ, adiabatic T1ρ, and adiabatic T2ρ relaxation times were significantly decreased in the secondary spongiosa (respectively: −13.3 ± 9.3 ms, p = 0.013; −32 ± 23 ms, p < 0.001; −43 ± 41 ms, p = 0.009; and −39 ± 13 ms, p < 0.001). The secondary spongiosa thickness was also significantly decreased in the ischemic femoral heads (p < 0.001). In conclusion, T2, T1ρ, adiabatic T1ρ, and adiabatic T2ρ relaxation time mapping techniques can detect early changes in the metaphysis following ischemic injury to the epiphysis of the femoral head in a piglet model of LCPD.

Failure of endochondral ossification due to interruption of the vascular supply to the epiphyseal cartilage is a critical step in the development of osteochondritis dissecans (OCD). Herein we describe the vascular architecture of the distal humeral epiphyseal cartilage in pigs and identify characteristic features that have been associated with sites predisposed to OCD development across species. Distal humeral specimens were harvested from pigs (n = 5, ages = 1, 10, 18, 30, and, 42 days old) and imaged at 9.4T magnetic resonance imaging (MRI) using a 3D gradient recalled echo sequence. The MRI data were processed using a quantitative susceptibility mapping (QSM) pipeline to visualize the vascular architecture. Specimens were also evaluated histologically to identify the presence of ischemic epiphyseal cartilage necrosis (osteochondrosis [OC]‐latens) and associated failure of endochondral ossification (OC‐manifesta). The QSM data enabled visualization of two distinct vascular beds arising from the perichondrium at the lateral and medial aspects of the distal humeral epiphysis. Elongated vessels originating from these beds coursed axially to supply the lateral and medial thirds of epiphyseal cartilage. At 18 days of age and older, a shift from perichondrial to transosseous blood supply was noted axially, which appeared more pronounced on the lateral side. This shift coincided with histologic identification of OC‐latens (30‐ and 42‐day‐old specimens) and OC‐manifesta (18‐ and 42‐day‐old specimens) lesions in the corresponding regions. The vascular anatomy and its evolution at the distal humeral epiphysis closely resembles that previously reported at predilection sites of knee OCD, suggesting a shared pathophysiology between the knee and elbow joints.

Juvenile osteochondritis dissecans (JOCD) is a pediatric orthopedic disorder that involves the articular–epiphyseal cartilage complex and underlying bone. Clinical disease is often characterized by the presence of radiographically apparent osteochondral flaps and fragments. The existence of early JOCD lesions (osteochondrosis latens [OCL] and osteochondrosis manifesta [OCM]) that precede the development of osteochondral flaps and fragments is also well recognized. However, identification of naturally occurring OCL lesions (confined to cartilage) using noninvasive imaging techniques has not yet been accomplished. We hypothesized that 10.5 T magnetic resonance imaging (MRI) can identify naturally occurring OCL lesions at predilection sites in intact joints of juvenile pigs. Unilateral elbows and knees (stifles) were harvested from three pigs aged 4, 8, and 12 weeks, and scanned in a 10.5 T MRI to obtain morphological 3D DESS images, and quantitative T2 and T1ρ relaxation time maps. Areas with increased T2 and T1ρ relaxation times in the articular–epiphyseal cartilage complex were identified in 1/3 distal femora and 3/3 distal humeri and were considered suspicious for OCL or OCM lesions. Histological assessment confirmed the presence of OCL or OCM lesions at each of these sites and failed to identify additional lesions. Histological findings included necrotic vascular profiles associated with areas of chondronecrosis either confined to the epiphyseal cartilage (OCL, 4‐ and 8‐week‐old specimens) or resulting in a delay in endochondral ossification (OCM, 12‐week‐old specimen). Future studies with clinical MR systems (≤7 T) are needed to determine whether these MRI methods are suitable for the in vivo diagnosis of early JOCD lesions in humans.