Abstract
Objectives:
Osteoarthritis (OA) is a joint disease characterized by degradation of articular cartilage and subchondral bone. Cartilage injury plays an important role in the pathogenesis of osteoarthritis, and disease modifying treatments aiming to preserve and possibly regenerate cartilage are an area of active interest. Early diagnosis is crucial, as the disease may be more responsive to treatment at an early stage, and there is a critical unmet need for improved non-invasive morphologic cartilage imaging techniques. Standard clinical MRI is performed on a 1.5T or 3T machine. Ultra-high field (UHF) 7-Tesla (7T) magnetic resonance imaging (MRI) is a new technology that offers 2.3x improved signal-to noise ratio (SNR) compared to 3T MRI and 2.8x SNR compared to 1.5T MRI.
The purpose of this study was to estimate the accuracy of 7T MRI for the detection and grading of cartilage lesions in the knee. The hypothesis was that 7T images would offer better detection and more accurate grading of chondral lesions than standard clinical grade MRI scans.
Methods:
In this prospective, paired, blinded study, patients who had undergone a 1.5 or 3T standard of care (SOC) MRI and were scheduled for knee arthroscopy were enrolled (10/2019 to 08/2021) and a study intervention 7T MRI was performed prior to surgery. The study was approved by our institutional review board, and it was funded by the Methodist-Siemens Collaboration. Exclusion criteria included contraindication to MRI (e.g., pacemaker), weight less than 30 kg, and pregnancy. Scans were reviewed by three independent fellowship-trained radiologists who were blinded to clinical and arthroscopic data. Scans were reviewed over 5 days, with a 4 week “washout” period between review of SOC and 7T scans to limit recall bias. Readers were blinded to clinical and arthroscopic data and graded all six articular surfaces of the knee (patella, trochlea, lateral condyle, medial condyle, lateral tibia, medial tibia) using a modified Outerbridge classification system. At the time of arthroscopy, each articular surface was graded by the operating surgeon according to a modified Outerbridge system similar to above, with the exception that Grade 1 = softening of the articular cartilage. The surgeon was blinded to 7T images at the time of arthroscopy, although they had access to the SOC MRI, which was necessary for patient care. Using arthroscopy as the gold standard, we calculated sensitivity and specificity of SOC MRI and 7T MRI. An Outerbridge grade of 0 was classified as negative, while a grade of 1-4 was classified as positive. A secondary analysis of sensitivity and specificity was performed on a per articular surface basis, with 6 articular surfaces per patient after correction for within subject clustered data. A Mann-Whitney U test was used to compare diagnostic scores and ratings between instruments (SOC vs. 7T). Coefficients of variation between observers within each instrument were compared for each variable using a paired sample t-test. Type-I error was set at alpha=0.05
Results:
A total of 100 patients (age: 43 ± 14, 54 female, 46 male) were enrolled. 7T MRI resulted in improved sharpness (defined by visibility of nerve fascicles) and shading (based on artifacts) compared to SOC MRI (Figure 1, p < 0.001 for both). There was improved contrast between fluid and cartilage with 7T MRI (using confidence rating at axial mid-patella, p = 0.003). 7T MRI had a higher sensitivity in detecting cartilage lesions for five of the six articular surfaces when using the arthroscopic gold standard, but with lower specificity for all surfaces (Figure 2). Finally, there was improved inter-observer reliability in detecting and grading cartilage defects with 7T compared to SOC MRI (p < 0.05).
Conclusion:
Based on our findings thus far, 7T MRI appears to result in improved measurement ratings, sensitivity, and inter-observer reliability compared to SOC in detecting cartilage lesions in the knee. Further work is needed to evaluate cost effectiveness of 7T MRI.
