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1956. Non-Invasive Diagnosis and Grading of Cartilage Defects in the Knee: Initial Experience with Ultra High Field 7T MRI
Authors * Denotes Presenting Author
  1. Shayan Vadie *; Houston Methodist Hospital
  2. Nakul Gupta; Houston Methodist Hospital
  3. John Labis; Houston Methodist Hospital
  4. Michael Trakhtenbroit; Houston Methodist Hospital
  5. David Dong; Houston Methodist Hospital
  6. Haley Goble; Houston Methodist Hospital
  7. Patrick McCulloch; Houston Methodist Hospital
Objective:
To estimate of the accuracy of 7T MRI in the detection and grading of cartilage defects in the knee with an arthroscopic gold standard.

Materials and Methods:
Twenty of 100 planned patients scheduled for knee arthroscopy have been prospectively recruited for pre-operative 7T MRI (Magnetom Terra, Siemens) in addition to standard of care (SOC) 1.5 or 3T MRI. Arthroscopic data are available for n=17. 7T and SOC scans were reviewed by 2 radiologists who graded all 6 articular surfaces using the modified Outerbridge classification. The surgeon was blinded to 7T MRI and graded each surface using the Outerbridge classification. Image quality (IQ) metrics of sharpness, contrast and noise were assessed on 7T and SOC on a 5 point scale (1=worst, 5=best). IQ ratings were averaged for each scan to obtain a composite IQ score. Signal to noise ratio (SNR) for cartilage (SNRc) and muscle (SNRm) was assessed as the mean of a circular region of interest (ROI) divided by the respective standard deviation (SD). SNR was normalized to voxel volume. SNR and composite IQ scores were compared with a paired t-test. Agreement between readers and between MRI and arthroscopy for lesion grades was assessed with weighted kappa statistics. Receiver operating characteristic (ROC) analysis for SOC and 7T MRI was performed per articular surface (n=102).

Results:
SNRc and SNRm were higher at 7T than SOC; 40.0 vs. 19.7 (p<0.001) and 68.6 vs. 35.2 (p<0.001). Composite IQ for 7T vs. SOC was 4.17 vs. 3.47 (Reader 1; p=0.001) and 4.18 vs. 3.15 (Reader 2; p<0.001). Sharpness (p<0.001) and contrast (p=0.002) were higher at 7T than SOC. Good inter-reader agreement was seen for MRI cartilage grades (k=0.748), and for 7T and SOC with arthroscopic grades (Reader 1 k=0.719 and 0.644; Reader 2 k=0.731 and 0.686, respectively). Sensitivity and specificity were (7T vs. SOC) 69.4 and 93.9% vs. 63.9 and 92.4% (Reader 1), and 75.0 and 83.3% vs. 86.1 and 87.9% (Reader 2). Area under curve (AUC) for 7T and SOC was 0.831 and 0.792 (p=0.395; Reader 1) and 0.844 vs. 0.877 (p=0.249; Reader 2).

Conclusion:
Initial data from the first 20 out of a planned 100 patients demonstrates better SNR and subjective IQ measures of sharpness and contrast with 7T as compared to SOC 1.5 or 3T MRI. Inter-reader agreement for cartilage grade was good, and diagnostic accuracy is similar between 7T and SOC. Knee MRI at 7T demonstrates improved image quality, sharpness and SNR as compared to 1.5 or 3T, although our initial results do not indicate a significant improvement in diagnostic accuracy.