Complex confounder-corrected R2* mapping for liver iron quantification with MRI.

OBJECTIVES: MRI-based R2* mapping may enable reliable and rapid quantification of liver iron concentration (LIC). However, the performance and reproducibility of R2* across acquisition protocols remain unknown. Therefore, the objective of this work was to evaluate the performance and reproducibility of complex confounder-corrected R2* across acquisition protocols, at both 1.5 T and 3.0 T. METHODS: In this prospective study, 40 patients with suspected iron overload and 10 healthy controls were recruited with IRB approval and informed written consent and imaged at both 1.5 T and 3.0 T. For each subject, acquisitions included four different R2* mapping protocols at each field strength, and an FDA-approved R2-based method performed at 1.5 T as a reference for LIC. R2* maps were reconstructed from the complex data acquisitions including correction for noise effects and fat signal. For each subject, field strength, and R2* acquisition, R2* measurements were performed in each of the nine liver Couinaud segments and the spleen. R2* measurements were compared across protocols and field strength (1.5 T and 3.0 T), and R2* was calibrated to LIC for each acquisition and field strength. RESULTS: R2* demonstrated high reproducibility across acquisition protocols (p > 0.05 for 96/108 pairwise comparisons across 2 field strengths and 9 liver segments, ICC > 0.91 for each field strength/segment combination) and high predictive ability (AUC > 0.95 for four clinically relevant LIC thresholds). Calibration of R2* to LIC was LIC = - 0.04 + 2.62 × 10-2 R2* at 1.5 T and LIC = 0.00 + 1.41 × 10-2 R2* at 3.0 T. CONCLUSIONS: Complex confounder-corrected R2* mapping enables LIC quantification with high reproducibility across acquisition protocols, at both 1.5 T and 3.0 T. KEY POINTS: • Confounder-corrected R2* of the liver provides reproducible R2* across acquisition protocols, including different spatial resolutions, echo times, and slice orientations, at both 1.5 T and 3.0 T. • For all acquisition protocols, high correlation with R2-based liver iron concentration (LIC) quantification was observed. • The calibration between confounder-corrected R2* and LIC, at both 1.5 T and 3.0 T, is determined in this study.

Indirect soft-tissue and osseous signs on knee MRI of surgically proven meniscal tears.

OBJECTIVE: The purpose of this study was to determine the frequency of abnormal MR signal intensity in soft tissues and osseous structures in association with surgically proven meniscal tears. MATERIALS AND METHODS: Seventy patients underwent 1.5-T MRI of the knee and arthroscopy within 3 months. MR images were reviewed by two radiologists for parameniscal cysts, bowing and edema around the collateral ligament, meniscal extrusion, cartilage loss, and nonlinear and linear subchondral marrow edema. The findings were correlated with the arthroscopic findings. The positive predictive value (PPV), sensitivity, and specificity of indirect signs were calculated. RESULTS: Fifty-three medial and 28 lateral meniscal tears were found at arthroscopy. The PPV of indirect signs of meniscal tear was 0.17-1.00 for reader 1 and 0.37-1.00 for reader 2. The PPV of parameniscal cysts was 1.00 for medial and lateral meniscal tears for both readers. The specificity and PPV of periligamentous edema and cruciate ligament bowing for medial meniscal tear were 0.94 and 0.98 for both readers, 0.88 and 0.94 for reader 1, and 0.94 and 0.97 for reader 2. The specificity and PPV of subchondral marrow edema for medial meniscal tear were 0.88 and 0.96 for reader 1 and 0.94 and 0.97 for reader 2 and for lateral meniscal tear were 0.98 and 0.92 for reader 1 and 1.00 and 1.00 for reader 2. The specificity and PPV of linear subchondral marrow edema for medial meniscal tear were 0.94 and 0.97 for reader 1 and 1.00 and 1.00 for reader 2. For lateral meniscal tear, the values were 0.98 and 0.89 for reader 1 and 1.00 and 1.00 for reader 2. The specificity and PPV of nonlinear subchondral marrow edema for medial meniscal tear were 0.94 and 0.89 for reader 1 and 1.00 and 1.00 for reader 2. For lateral meniscal tear, the values were 0.89 and 0.97 for reader 1 and 1.00 and 1.00 for reader 2. The specificity and PPV of cartilage loss for medial meniscal tear were 0.88 and 0.94 for reader 1 and 0.88 and 0.93 for reader 2. For lateral meniscal tear, the values were 0.85 and 0.56 for reader 1 and 0.97 and 0.80 for reader 2. CONCLUSION: Indirect MRI signs occur in association with meniscal tears and can aid diagnostic confidence when the MRI meniscal appearance is equivocal.