Validation of compositional MRI from a histological standpoint: Advantages of three-dimensional T1ρ mapping for quantitative evaluation of articular cartilage

PURPOSE

We aimed to investigate the relationship between quantitative evaluation by compositional MRI, including T1ρ, and histological and macroscopic assessments, to verify the validity of compositional MRI, and examine the relationship between compositional MRI evaluation reconstructed in three dimensions (3D) and histological and visual assessments.

METHOD

Twenty-seven patients with knee osteoarthritis underwent T1ρ and T2 magnetic resonance imaging (MRI). Histological and gross tissue evaluations were performed on the excised bone sections of total knee arthroplasty. Semi-quantitative histological evaluation of tissue changes were assessed by measuring the optical density of digitally captured safranin O-stained and Collagen type II antibody-stained paraffin sections. Macroscopic cartilage severity was determined on a 5-grade scale (G0-G5). T1ρ and T2 values (3D and 2D), and their correlation with each of these parameters were investigated.

RESULTS

3D T1 ρ is negatively correlated with histological evaluations and positively correlated with visual assessments. Only 3D T1ρ values correlated with histological quantitative evaluation (Safranin-O staining; r = -0.53, P = 0.014, Collagen type II antibody staining; r = -0.60, P = 0.019). 2D T1ρ and 3D, 2D T2 values did not correlate with histological evaluation results. Macroscopic cartilage severity grade correlated with all T1ρ and T2 values (3D T1ρ; r = 0.61, P < 0.001, 2D T1ρ; r = 0.52, P < 0.001, 3D T2; r = 0.33, P = 0.045, 2D T2; r = 0.41, P = 0.01).

CONCLUSIONS

3D T1ρ mapping reflects the changes in the molecular structure of the cartilage matrix that occur in arthropathic changes and may be an effective tool for detecting cartilage degeneration.

Portable NMR for quantification of breast density in vivo: Proof-of-concept measurements and comparison with quantitative MRI

Mammographic Density (MD) is the degree of radio-opacity of the breast in an X-ray mammogram. It is determined by the Fibroglandular: Adipose tissue ratio. MD has major implications in breast cancer risk and breast cancer chemoprevention. This study aimed to investigate the feasibility of accurate, low-cost quantification of MD in vivo without ionising radiation. We used single-sided portable nuclear magnetic resonance ("Portable NMR") due to its low cost and the absence of radiation-related safety concerns. Fifteen (N = 15) healthy female volunteers were selected for the study and underwent an imaging routine consisting of 2D X-ray mammography, quantitative breast 3T MRI (Dixon and T₁-based 3D compositional breast imaging), and 1D compositional depth profiling of the right breast using Portable NMR. For each participant, all the measurements were made within 3-4 h of each other. MRI-determined tissue water content was used as the MD-equivalent quantity. Portable NMR depth profiles of tissue water were compared with the equivalent depth profiles reconstructed from Dixon and T₁-based MR images, which were used as the MD-equivalent reference standard. The agreement between the depth profiles acquired using Portable NMR and the reconstructed reference-standard profiles was variable but overall encouraging. The agreement was somewhat inferior to that seen in breast tissue explant measurements conducted in vitro, where quantitative micro-CT was used as the reference standard. The lower agreement in vivo can be attributed to an uncertainty in the positioning of the Portable NMR sensor on the breast surface and breast compression in Portable NMR measurements. The degree of agreement between Portable NMR and quantitative MRI is encouraging. While the results call for further development of quantitative Portable NMR, they demonstrate the in-principle feasibility of Portable NMR-based quantitative compositional imaging in vivo and show promise for the development of safe and low-cost protocols for quantification of MD suitable for clinical applications.

Knee Cartilage Imaging

Articular cartilage injury and degeneration represent common causes of knee pain, which can be evaluated accurately and noninvasively using MRI. This review describes the structure of cartilage focusing on its histologic appearance to emphasize that structure will dictate patterns of tissue failure as well as MR appearance. In addition to identifying cartilage loss, MRI can demonstrate signal changes that correspond to intrinsic structural abnormalities which place the cartilage at risk for subsequent more serious injury or premature degeneration, allowing for earlier intervention and treatment of important causes of pain and morbidity.

Proteoglycan loss in the articular cartilage is associated with severity of joint inflammation in psoriatic arthritis-a compositional magnetic resonance imaging study

Background

Even though cartilage loss is a known feature of psoriatic arthritis (PsA), little is known about its role in the pathogenesis of PsA. Using delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC) as a non-invasive marker of the tissue’s proteoglycan content, such early (i.e., pre-morphological) changes have been associated with inflammation in rheumatoid arthritis (RA). Yet, this association has not been studied before in PsA.

Methods

The metacarpophalangeal (MCP), proximal interphalangeal (PIP), and distal interphalangeal (DIP) joints of 17 patients with active PsA were evaluated by high-resolution clinical standard morphological and dGEMRIC sequences using a 3T MRI scanner (Magnetom Skyra, Siemens) and a dedicated 16-channel hand coil. Images were analyzed by two independent raters for dGEMRIC indices, PsA MRI scores (PsAMRIS), and total cartilage thickness (TCT). Kendall tau correlation coefficients (τ) were calculated.

Results

We found significant negative correlations between dGEMRIC indices and total PsAMRIS (τ = − 0.5, p = 0.012), synovitis (τ = − 0.56, p = 0.006), flexor tenosynovitis (τ = − 0.4, p = 0.049), and periarticular inflammation (τ = − 0.72, p < 0.001). Significant positive correlations were found between TCT and dGEMRIC indices at all joint levels (τ = 0.43, p < 0.001). No significant correlations were determined between dGEMRIC indices and bone erosion, bone edema, or bone proliferation.

Conclusion

In PsA, proteoglycan loss as assessed by dGEMRIC is associated with periarticular inflammation, synovitis, and flexor tenosynovitis, but not with bone erosion or proliferation. Thereby, these findings contribute to in vivo concepts of the disease’s pathophysiology. Beyond morphology, advanced MRI techniques may be used to assess cartilage composition in PsA and to identify early changes in the cartilage as an imaging biomarker with potential application in detection, monitoring, and prediction of outcomes of PsA.

Trial registration

2014123117, December 2014.

Compositional MRI techniques for evaluation of cartilage degeneration in osteoarthritis

Osteoarthritis (OA), a leading cause of disability, affects 27 million people in the United States and its prevalence is rising along with the rise in obesity. So far, biomechanical or behavioral interventions as well as attempts to develop disease-modifying OA drugs have been unsuccessful. This may be partly due to antiquated imaging outcome measures such as radiography, which are still endorsed by regulatory agencies such as the United States Food and Drug Administration (FDA) for use in clinical trials. Morphological magnetic resonance imaging (MRI) allows unparalleled multi-feature assessment of the OA joint. Furthermore, advanced MRI techniques also enable evaluation of the biochemical or ultrastructural composition of articular cartilage relevant to OA research. These compositional MRI techniques have the potential to supplement clinical MRI sequences in identifying cartilage degeneration at an earlier stage than is possible today using morphologic sequences only. The purpose of this narrative review is to describe compositional MRI techniques for cartilage evaluation, which include T2 mapping, T2* Mapping, T1 rho, dGEMRIC, gagCEST, sodium imaging and diffusion weighted imaging (DWI). We also reviewed relevant clinical studies that have utilized these techniques for the study of OA. The different techniques are complementary. Some focus on isotropy or the collagen network (e.g., T2 mapping) and others are more specific in regard to tissue composition, e.g., gagCEST or dGEMRIC that convey information on the GAG concentration. The application and feasibility of these techniques is also discussed, as they will play an important role in implementation in larger clinical trials and eventually clinical practice.