Multiparametric MRI of Epiphyseal Cartilage Necrosis (Osteochondrosis) with Histological Validation in a Goat Model

Generalized inhomogeneity-resilient relaxation along a fictitious field (girRAFF) for improved robustness in rotating frame relaxometry at 3T

PURPOSE

To optimize Relaxation along a Fictitious Field (RAFF) pulses for rotating frame relaxometry with improved robustness in the presence ofB 0 $$ {\mathrm{B}}_0 $$ andB 1 + $$ {\mathrm{B}}_1^{+} $$ field inhomogeneities.

METHODS

The resilience of RAFF pulses againstB 0 $$ {\mathrm{B}}_0 $$ andB 1 + $$ {\mathrm{B}}_1^{+} $$ inhomogeneities was studied using Bloch simulations. A parameterized extension of the RAFF formulation was introduced and used to derive a generalized inhomogeneity-resilient RAFF (girRAFF) pulse. RAFF and girRAFF preparation efficiency, defined as the ratio of the longitudinal magnetization before and after the preparation (M z ( T p ) / M 0 $$ {M}_z\left({T}_p\right)/{M}_0 $$ ), were simulated and validated in phantom experiments.T RAFF $$ {T}_{\mathrm{RAFF}} $$ andT girRAFF $$ {T}_{\mathrm{girRAFF}} $$ parametric maps were acquired at 3T in phantom, the calf muscle, and the knee cartilage of healthy subjects. The relaxation time maps were analyzed for resilience against artificially induced field inhomogeneities and assessed in terms of in vivo reproducibility.

RESULTS

Optimized girRAFF preparations yielded improved preparation efficiency (0.95/0.91 simulations/phantom) with respect to RAFF (0.36/0.67 simulations/phantom).T girRAFF $$ {T}_{\mathrm{girRAFF}} $$ preparations showed in phantom/calf 6.0/4.8 times higher resilience toB 0 $$ {\mathrm{B}}_0 $$ inhomogeneities than RAFF, and a 4.7/5.3 improved resilience toB 1 + $$ {\mathrm{B}}_1^{+} $$ inhomogeneities. In the knee cartilage,T girRAFF $$ {T}_{\mathrm{girRAFF}} $$ (53± $$ \pm $$ 14 ms) was higher thanT RAFF $$ {T}_{\mathrm{RAFF}} $$ (42± $$ \pm $$ 11 ms). Moreover, girRAFF preparations yielded 7.6/4.9 times improved reproducibility acrossB 0 $$ {\mathrm{B}}_0 $$ /B 1 + $$ {\mathrm{B}}_1^{+} $$ inhomogeneity conditions, 1.9 times better reproducibility across subjects and 1.2 times across slices compared with RAFF. Dixon-based fat suppression led to a further 15-fold improvement in the robustness of girRAFF to inhomogeneities.

CONCLUSIONS

RAFF pulses display residual sensitivity to off-resonance and pronounced sensitivity toB 1 + $$ {\mathrm{B}}_1^{+} $$ inhomogeneities. Optimized girRAFF pulses provide increased robustness and may be an appealing alternative for applications where resilience against field inhomogeneities is required.

Relationship between the extent of vascular injury and the evolution of surgically induced osteochondrosis lesions in a piglet model

Ostechondritis dissecans (OCD) is an orthopaedic disease characterized by formation of osteochondral defects in developing joints. Epiphyseal cartilage necrosis (osteochondrosis [OC]) caused by focal failure of vascular supply is the known precursor lesion of OCD, but it remains to be established how the severity of vascular failure drives lesion healing or progression. In the current study we have implemented a novel piglet model of induced osteochondrosis of the lateral trochlear ridge of the femur to determine the role that the extent of ischemia plays in the development and progression of OC/OCD lesions. Ten 4-week-old Yorkshire piglets underwent surgical interruption of the vascular supply to the entirety (n = 4 pigs) or the distal half (n = 6 pigs) of the lateral trochlear ridge of the femur. At 2, 6, and 12 weeks postoperatively, distal femora were evaluated by magnetic resonance imaging (MRI) to determine the fate of induced OC lesions. At 12 weeks, piglets were euthanized, and the surgical sites were examined histologically. After complete devascularization, lesion size increased between the 6- and 12-week MRI by an average of 24.8 mm2 (95% CI: [-2.2, 51.7]; p = 0.071). During the same period, lesion size decreased by an average of 7.6 mm2 (95% CI: [-24.5, 19.4]; p = 0.83) in piglets receiving partial devascularization. At 12 weeks, average ± SD lesion size was larger (p<0.001) in piglets undergoing complete (73.5 ± 17.6 mm2) vs. partial (16.5 ± 9.8 mm2) devascularization. Our study demonstrates how the degree of vascular interruption determines lesion size and likelihood of healing in a large animal model of trochlear OC.

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

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.

Longitudinal 3T MRI T2 * mapping of Juvenile osteochondritis dissecans (JOCD) lesions differentiates operative from non-operative patients-Pilot study

Juvenile osteochondritis dissecans (JOCD) is an orthopedic joint disorder of children and adolescents that can lead to premature osteoarthritis. Thirteen patients (mean age: 12.3 years, 4 females), 15 JOCD-affected and five contralateral healthy knees, that had a baseline and a follow-up magnetic resonance imaging (MRI) (mean interval of 8.9 months) and were treated nonoperatively during this interval were included. Retrospectively, patients were assigned to operative or nonoperative groups based on their electronic medical records. Volumetric mean T2 * values were calculated within regions of interest (progeny lesion, interface, parent bone) and region matched control bone in healthy contralateral knees and condyles. The normalized percentage difference of T2 * between baseline and follow up MRI in nonoperative patients significantly increased in progeny lesion (-47.8%, p < 0.001), parent bone (-13.9%, p < 0.001), and interface (-32.3%, p = 0.011), whereas the differences in operative patients were nonsignificant and below 11%. In nonoperative patients, the progeny lesion (p < 0.001) and interface T2 * values (p = 0.012) were significantly higher than control bone T2 * at baseline, but not at follow-up (p = 0.219, p = 1.000, respectively). In operative patients, the progeny lesion and interface T2 * values remained significantly elevated compared to the control bone both at baseline (p < 0.001, p < 0.001) and follow-up (p < 0.001, p < 0.001), respectively. Clinical Significance: Longitudinal T2 * mapping differentiated nonhealing from healing JOCD lesions following initial nonoperative treatment, which may assist in prognosis and improve the ability of surgeons to make recommendations regarding operative versus nonoperative treatment.

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

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.

Identification of Areas of Epiphyseal Cartilage Necrosis at Predilection Sites of Juvenile Osteochondritis Dissecans in Pediatric Cadavers

BACKGROUND

The pathogenesis of human juvenile osteochondritis dissecans (JOCD) remains poorly understood, with multiple factors implicated, including ischemia, repetitive trauma, and genetic predisposition. Similarities in the predilection site and the diagnostic and clinical features of JOCD to the well-characterized veterinary counterpart, osteochondrosis dissecans, suggest that, similar to the animal disease, the pathogenesis JOCD may also be initiated in the first few years of life, when disruption of blood supply to the epiphyseal growth cartilage leads to failure of endochondral ossification. To gather data in support of the hypothesis that JOCD and osteochondrosis dissecans have a shared pathogenesis, biopsy specimens obtained from predilection sites of JOCD in juvenile human cadavers were histologically examined to determine whether they contained lesions similar to those found in animals diagnosed with subclinical osteochondrosis dissecans.

METHODS

In this descriptive laboratory study, 59 biopsy specimens (6 mm in diameter) were harvested from the central aspect (i.e., the notch side) of the femoral condyles of 26 human cadavers (1 month to 11 years old). Specimens were histologically evaluated for the presence of areas of cartilage necrosis and the morphology of cartilage canal blood vessels.

RESULTS

Locally extensive areas of necrotic epiphyseal cartilage were identified in 4 specimens obtained from 3 donors (ages 2 to 4 years). Areas of cartilage necrosis accompanied by focal failure of endochondral ossification or surrounded by subchondral bone were identified in biopsy specimens from 4 donors (ages 4 to 9 years).

CONCLUSIONS

The identification of epiphyseal cartilage necrosis identical to that described in animals with subclinical osteochondrosis, found in biopsy specimens obtained from femoral predilection sites of JOCD in pediatric cadavers, suggests a shared pathogenesis of JOCD in humans and osteochondrosis dissecans in animals.

CLINICAL RELEVANCE

These findings imply that the pathogenesis of human JOCD likely starts 5 to 10 years prior to the development of clinical symptoms. Enhanced understanding of the temporal features of JOCD pathogenesis provides an opportunity for earlier diagnosis and treatment, likely resulting in improved outcomes for this condition in the future.

Quantitative MRI Helps to Detect Hip Ischemia: Preclinical Model of Legg-Calvé-Perthes Disease

Purpose To determine whether quantitative MRI relaxation time mapping techniques can help to detect ischemic injury to the developing femoral head. Materials and Methods For this prospective animal study conducted from November 2015 to February 2018, 10 male 6-week-old piglets underwent an operation to induce complete right femoral head ischemia. Animals were humanely killed at 48 hours (n = 2) or 4 weeks (n = 8) after the operation, and the operated and contralateral-control femoral heads were harvested and frozen. Thawed specimens were imaged at 9.4-T MRI by using T1, T2, T1 in the rotating frame (T1ρ), adiabatic T1ρ, relaxation along a fictitious field (RAFF), and T2* mapping and evaluated with histologic analysis. Paired relaxation time differences between the operated and control femoral heads were measured in the secondary ossification center (SOC), epiphyseal cartilage, articular cartilage, and metaphysis and were analyzed by using a paired t test. Results In the SOC, T1ρ and RAFF had the greatest percent increases in the operated versus control femoral heads at both 48 hours (112% and 72%, respectively) and 4 weeks (74% and 70%, respectively). In the epiphyseal and articular cartilage, T2, T1ρ, and RAFF were similarly increased at both points (range, 24%-49%). At 4 weeks, T2, T1ρ, adiabatic T1ρ, and RAFF were increased in the SOC (P = .004, .018, < .001, and .001, respectively), epiphyseal cartilage (P = .009, .008, .011, and .007, respectively), and articular cartilage (P = .005, .016, .033, and .018, respectively). Histologic assessment identified necrosis in SOC and deep layer of the epiphyseal cartilage at both points. Conclusion T2, T1 in the rotating frame, adiabatic T1 in the rotating frame, and relaxation along a fictitious field maps are sensitive in helping to detect ischemic injury to the developing femoral head. © RSNA, 2018 Online supplemental material is available for this article.

Predicting early symptomatic osteoarthritis in the human knee using machine learning classification of magnetic resonance images from the osteoarthritis initiative

The purpose of this study is to evaluate the ability of a machine learning algorithm to classify in vivo magnetic resonance images (MRI) of human articular cartilage for development of osteoarthritis (OA). Sixty-eight subjects were selected from the osteoarthritis initiative (OAI) control and incidence cohorts. Progression to clinical OA was defined by the development of symptoms as quantified by the Western Ontario and McMaster Universities Arthritis (WOMAC) questionnaire 3 years after baseline evaluation. Multi-slice T2 -weighted knee images, obtained through the OAI, of these subjects were registered using a nonlinear image registration algorithm. T2 maps of cartilage from the central weight bearing slices of the medial femoral condyle were derived from the registered images using the multiple available echo times and were classified for "progression to symptomatic OA" using the machine learning tool, weighted neighbor distance using compound hierarchy of algorithms representing morphology (WND-CHRM). WND-CHRM classified the isolated T2 maps for the progression to symptomatic OA with 75% accuracy.

CLINICAL SIGNIFICANCE

Machine learning algorithms applied to T2 maps have the potential to provide important prognostic information for the development of OA. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2243-2250, 2017.

In vivo visualization using MRI T2 mapping of induced osteochondrosis and osteochondritis dissecans lesions in goats undergoing controlled exercise

In vivo visualization of subclinical osteochondrosis (OC) lesions, characterized by necrosis of epiphyseal growth cartilage, is necessary to clarify the pathogenesis of this disease. Hence, our objectives were to demonstrate induced necrosis of the epiphyseal cartilage in vivo using MRI and to monitor progression or resolution of resulting lesions. We also aimed to improve the goat model of OC by introducing controlled exercise. Vascular supply to the epiphyseal cartilage was surgically interrupted in four 5-day-old goats to induce ischemic cartilage necrosis in a medial femoral condyle. Starting 3 weeks postoperatively, goats underwent daily controlled exercise until euthanasia at 6, 10, 11 (n = 2) weeks postoperatively. T2 maps of operated and control femora were obtained in vivo at 3 (n = 4), 6 (n = 4), 9 (n = 3), and 11 (n = 2) weeks postoperatively using a 3 T MR scanner. In vivo MRI findings were validated against MRI results obtained ex vivo at 9.4 T in three goats and compared to histological results in all goats. Surgical interruption of the vascular supply caused ischemic cartilage necrosis in three out of four goats. T2 maps obtained in vivo at 3 T identified regions of increased relaxation time consistent with discrete areas of cartilage necrosis 3-11 weeks postoperatively and demonstrated delayed progression of the ossification front at 9 (n = 1) and 11 (n = 2) weeks postoperatively. In vivo MRI findings were confirmed by ex vivo MRI at 9.4 T and by histology. Identification of cartilage necrosis in clinical patients in the early stages of OC using T2 maps may provide valuable insight into the pathogenesis of this condition. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:868-875, 2017.

Insights into the Epiphyseal Cartilage Origin and Subsequent Osseous Manifestation of Juvenile Osteochondritis Dissecans with a Modified Clinical MR Imaging Protocol: A Pilot Study

Purpose To retrospectively determine if a modified clinical magnetic resonance (MR) imaging protocol provides information on the origin of juvenile osteochondritis dissecans (JOCD) lesions and allows for staging on the basis of the proposed natural history of JOCD to better guide clinical management of the disease. Materials and Methods This institutional review board-approved, HIPAA-compliant, retrospective study was performed in 13 consecutive patients (mean age, 14.9 years; age range, 10-22 years; nine male and four female patients) and one additional comparative patient (a 44-year-old man), in which 19 knees with 20 JOCD lesions were imaged. Seventeen lesions occurred in the medial femoral condyle, two occurred in the lateral femoral condyle, and one occurred in the medial trochlea. The clinical 3-T MR imaging protocol was supplemented with a routinely available multiecho gradient-recalled-echo sequence with the shortest attainable echo time of approximately 4 msec (T2* mapping). Results At the earliest manifestation, the lesion was entirely cartilaginous (n = 1). Subsequently, primary cartilaginous lesions within the epiphyseal cartilage developed a rim calcification that originated from normal subjacent bone, which defined a clear cleft between the lesion progeny and the parent bone (n = 9). Secondarily, progeny lesions became ossified (n = 7) while at the same time forming varying degrees of osseous bridging and/or clefting with the parent bone. Two healed lesions with a linear bony scar and one detached lesion were identified. Conclusion The modified MR imaging protocol allowed for identification of the epiphyseal cartilage origin and subsequent stages of ossification in JOCD. The approach allows further elucidation of the natural history of the disease and may better guide clinical management. ^© RSNA, 2016.

Quantitative susceptibility mapping detects abnormalities in cartilage canals in a goat model of preclinical osteochondritis dissecans

PURPOSE

To use quantitative susceptibility mapping (QSM) to investigate changes in cartilage canals in the distal femur of juvenile goats after their surgical transection.

METHODS

Chondronecrosis was surgically induced in the right medial femoral condyles of four 4-day-old goats. Both the operated and control knees were harvested at 2, 3, 5, and 10 weeks after the surgeries. Ex vivo MRI scans were conducted at 9.4 Tesla using T_RAFF (relaxation time along a fictitious field)-weighted fast spin echo imaging and QSM to detect areas of chondronecrosis and investigate cartilage canal abnormalities. Histological sections from these same areas stained with hematoxylin and eosin and safranin O were evaluated to assess the affected tissues.

RESULTS

Both the histological sections and the T_RAFF -weighted images of the femoral condyles demonstrated focal areas of chondronecrosis, evidenced by pyknotic chondrocyte nuclei, loss of matrix staining, and altered MR image contrast. At increasing time points after surgery, progressive changes and eventual disappearance of abnormal cartilage canals were observed in areas of chondronecrosis by using QSM.

CONCLUSION

Abnormal cartilage canals were directly visualized in areas of surgically induced chondronecrosis. Quantitative susceptibility mapping enabled investigation of the vascular changes accompanying chondronecrosis in juvenile goats. Magn Reson Med 77:1276-1283, 2017. © 2016 International Society for Magnetic Resonance in Medicine.