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.

There is a clinical need for alternatives to gadolinium contrast-enhanced magnetic resonance imaging (MRI) to facilitate early detection and assessment of femoral head ischemia in pediatric patients with Legg-Calv & eacute;-Perthes disease (LCPD), a juvenile form of idiopathic osteonecrosis of the femoral head. The purpose of this study was to determine if intravoxel incoherent motion (IVIM), a noncontrastenhanced MRI method to simultaneously measure tissue perfusion and diffusion, can detect femoral head ischemia using a piglet model of LCPD. Twelve 6-week-old piglets underwent unilateral hip surgery to induce complete femoral head ischemia. The unoperated, contralateral femoral head served as a perfused control. The bilateral hips of the piglets were imaged in vivo at 3T MRI using IVIM and contrast enhanced MRI 1 week after surgery. Median apparent diffusion coefficient (ADC) and IVIM parameters (diffusion coefficient: Ds; perfusion coefficient: Df; perfusion fraction: f; and perfusion flux: f*Df) were compared between regions of interest comprising the epiphyseal bone marrow of the ischemic and control femoral heads. Contrast-enhanced MRI confirmed complete femoral head ischemia in 11/12 piglets. IVIM perfusion fraction (f) and flux (f*Df) were significantly decreased in the ischemic versus control femoral heads: on average, f decreased 47 +/- 27% (Delta f = -0.055 +/- 0.034; p = 0.0003) and f*Df decreased 50 +/- 27% (Delta f*Df = -0.59 +/- 0.49 x 10(-3) mm(2)/s; p = 0.0026). In contrast, IVIM diffusion coefficient (Ds) and ADC were significantly increased in the ischemic versus control femoral heads: on average, Ds increased 78 +/- 21% (Delta Ds = 0.60 +/- 0.14 x 10(-3) mm(2)/s; p < 0.0001) and ADC increased 60 +/- 36% (Delta ADC = 0.50 +/- 0.23 x 10(-3) mm(2)/s; p < 0.0001). In conclusion, IVIM is sensitive in detecting bone marrow ischemia in a piglet model of LCPD.

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.

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.

The concept of transform processing domain with locally low rank denoising is proposed as T-NORDIC and demonstrated for MSK and brain applications. The improvements on quantitative maps may be leveraged for faster acquisitions by relaxing the number of averages needed to obtain sufficient SNR for high resolution acquisitions and for application of low rank denoising to common clinical acquisitions.

Intravoxel incoherent motion (IVIM) is a promising method to measure both tissue diffusion and perfusion using a single multi b-value diffusion-weighted imaging (DWI) acquisition. In this work, we investigated whether IVIM is sensitive in detecting surgically-induced femoral head ischemia in a piglet model of avascular necrosis. We found that the IVIM perfusion coefficient ( D f ) and fraction ( f ) decreased in the ischemic vs. contralateral-control femoral heads. Conversely, the IVIM diffusion coefficient ( D s ) increased as a result of subsequent injury to the operated femoral head. These findings suggest that IVIM may provide a non-contrast-enhanced means to assess bone ischemia and perfusion.

Purpose To develop an extension to locally low rank (LLR) denoising techniques based on transform domain processing that reduces the number of images required in the MR image series for high-quality denoising. Theory and Methods LLR methods with random matrix theory-based thresholds are successfully used in the denoising of MR image series in a number of applications. The performance of these methods depend on how well the LLR assumption is satisfied, which deteriorates with few numbers of images, as is commonly encountered in quantitative MRI applications. We propose a transform-domain approach for denoising of MR image series to represent the underlying signal with higher fidelity when using a locally low rank approximation. The efficacy of the method is demonstrated for fully-sampled k-space, undersampled k-space, DICOM images, and complex-valued SENSE-1 images in quantitative MRI applications with as few as 4 images. Results For both MSK and brain applications, the transform domain denoising preserves local subtle variability, whereas the quantitative maps based on image domain LLR methods tend to be locally more homogeneous. Conclusion A transform domain extension to LLR denoising produces high quality images and is compatible with both raw k-space data and vendor reconstructed data. This allows for improved imaging and more accurate quantitative analyses and parameters obtained therefrom.

The intervertebral disc (IVD) aids in motion and acts to absorb energy transmitted to the spine. With little inherent regenerative capacity, degeneration of the intervertebral disc results in intervertebral disc disease, which contributes to low back pain and significant disability in many individuals. Increasing evidence suggests that IVD degeneration is a disease of the whole joint that is associated with significant inflammation. Moreover, studies show elevated macrophage accumulation within the IVD with increasing levels of disease severity; however, we still need to understand the roles, be they causative or consequential, of macrophages during the degenerative process. In this narrative review, we discuss hallmarks of IVD degeneration, showcase evidence of macrophage involvement during disc degeneration, and explore burgeoning research aimed at understanding the molecular pathways regulating macrophage functions during intervertebral disc degeneration.

Purpose To develop a dual-echo phase-contrast (DEPC) MRI approach with which each echo is acquired by using a different velocity sensitivity within one repetition time (TR) and demonstrate the feasibility of this approach to measure transmitral blood flow (E) and myocardial tissue (E m) velocities. Materials and Methods The flow across tubes of known diameter was measured by using the proposed DEPC method and compared with flowmeter measurements and theoretic predictions. Then, with both the DEPC MRI sequence and the conventional single-echo phase-contrast (SEPC) MRI sequence, E, E m, and E/E m were measured in six healthy volunteers (mean age, 49 years ± 13 [standard deviation]) and eight patients (mean age, 54 years ± 15) being evaluated for cardiac disease. Differences between the DEPC and conventional SEPC MRI methods were assessed by percent error, Pearson correlation, and Bland-Altman analyses. Results Velocities measured in vitro and in vivo by using the SEPC and DEPC MRI approaches were well correlated (r 2 > 0.97), with negligible bias (<0.5 cm/sec) and comparable velocity-to-noise ratios. Imaging times were approximately 19% shorter with the DEPC method (TR, 5.7 msec) than with the SEPC method (TR, 2.8 msec ± 4.2) (P < .05). Conclusion The proposed DEPC method was sensitive to two velocity regimes within a single TR, resulting in a shorter imaging time compared with the imaging time in conventional SEPC MRI. Preliminary human study results suggest the feasibility of using this approach to estimate E/E m.Supplemental material is available for this article.© RSNA, 2020.

Motivation: Denoising algorithms may significantly improve the SNR of relaxation time maps of the bone and cartilage. Goal(s): To compare the performance of T-NORDIC and MPPCA denoising techniques for 3D T2 mapping of the femoral head. Approach: 3D T2 maps of the femoral heads from 12 piglets imaged at 3T MRI were denoised using MPPCA and T-NORDIC with parametric dimensions of 4 and 12. The results of qualitatively and quantitatively compared for image quality and quantitative accuracy. Results: T-NORDIC provided superior performance with limited parametric dimension (4 weighted images), demonstrating its promise for magnetization-prepared mapping sequences of the hip joint. Impact: T2 relaxation time mapping is critically investigated for addressing several MSK related diagnosis, but possibly due to thin and sensitive structures in the femoral head even slightest of the perturbations can lead to ineffective computation of quantitative mapping.

Legg-Calvé-Perthes disease (LCPD) is a pediatric hip disorder caused by femoral head ischemia and osteonecrosis. In this work, we investigated whether 3D T2 and T1ρ relaxation time mapping are sensitive to ischemic injury to the bone and marrow of the femoral epiphysis and metaphysis following surgical induction of femoral head ischemia in a piglet model of LCPD. We found that T2 and T1ρ increased in the ischemic femoral epiphysis and decreased in the perfused metaphyseal spongiosa. Our findings support the potential clinical use of T2 and T1ρ mapping to assess the severity of femoral head injury in patients with LCPD.

We demonstrate the feasibility of obtaining high b-value (b > 2400 s/mm2) DWI images of the prostate obtained with short echo times (TE ~ 50 ms) on a prototype high-performance whole-body gradient system (Gmax = 200 mT/m, and SRmax = 200 T/m/s). Preliminary results from volunteers suggest that the apparent differences in the perfusion fraction metric of the IVIM model between the transition and peripheral zones of the prostate partly can be substantially diminished by choosing a shorter TE using high-performance gradients.

Motivation: Intravoxel incoherent motion (IVIM) is a promising noninvasive technique to measure tissue diffusion and perfusion using a single multi-b-value diffusion-weighted imaging (DWI) acquisition. Goal(s): To determine whether IVIM is sensitive to acute femoral head ischemia in the piglet model using RESOLVE and single-shot EPI. Approach: 24 piglets underwent bilateral hip imaging using a 3T MRI before and after surgical induction of unilateral femoral head ischemia. IVIM and apparent diffusion coefficient (ADC) values were compared between the pre- and post-operative scans. Results: IVIM is sensitive in detecting ischemia and subsequent injury to the femoral head. RESOLVE outperforms ssEPI in detecting changes in perfusion. Impact: IVIM may be a clinically useful non-contrast-enhanced alternative to CE-MRI to measure femoral head ischemia and perfusion changes for detecting, staging, and monitoring LCPD and other forms of osteonecrosis of the femoral head.

Quantitative mapping of T2, T1ρ, adiabatic T1ρ, and adiabatic T2ρ relaxation times may be useful to assess ischemic injury to the femoral head. In this work, we investigated whether these relaxation times are sensitive in detecting compositional changes to the primary spongiosa (the region of the metaphysis adjacent to the growth plate) following ischemic injury to the femoral head in a piglet model. We found that T1ρ and adiabatic T2ρ decreased in the primary spongiosa following ischemic injury to the femoral epiphysis, which suggests these methods may be useful to assess femoral head growth disturbances following ischemic injury.

Motivation: Relaxation time mapping may be clinically useful to inform the severity of ischemic injury to bone marrow in osteonecrosis of the femoral head. Goal(s): To compare the temporal response of T2, adiabatic T1ρ, and adiabatic T2ρ mapping to acute ischemic injury to the femoral head. Approach: 24 piglets were imaged using 3D relaxation time mapping at 3T MRI before and after surgical induction of unilateral femoral head ischemia. Corresponding cellular changes were evaluated histologically. Results: T2 and adiabatic T2ρ were the most sensitive in detecting acute injury to the femoral head, as early as 24 hours after onset of ischemia. Impact: T2 and/or adiabatic T2ρ relaxation time mapping can potentially address a clinical need for a non-contrast-enhanced imaging technique to establish the severity and extent of bone marrow necrosis in the earliest stages of osteonecrosis of the femoral head.

Motivation: Despite the IVIM model’s ability to noninvasively provide insight into tissue microstructure and perfusion, estimation of IVIM parameters in low-perfused tissues such as bone marrow remains a challenge. Goal(s): In this work, we propose an optimized analytical segmented (opAS) approach for extracting IVIM diffusion (Ds) and perfusion (Df and f). Approach: We compare the performance of this new approach against the analytical segmented (AS) method previously proposed for low-perfused tissues using numerical simulations and a piglet model. Results: Our findings indicate that opAS outperforms AS in the estimation of all IVIM parameters (Ds, Df, and f), particularly in the low perfusion regime. Impact: The proposed opAS method outperforms the prior AS method in estimating IVIM diffusion (Ds) and perfusion (Df and f) parameters, bringing IVIM a step closer to being a clinically useful non-contrast-enhanced technique to assess bone marrow perfusion.