Accelerating Knee MRI: 3D Modulated Flip-Angle Technique in Refocused Imaging with an Extended Echo Train and Compressed Sensing

He Sui,1,* Jin Li,2,3,* Lin Liu,1 Zhongwen Lv,1 Yunfei Zhang,4 Yongming Dai,4 Zhanhao Mo1 1China-Japan Union Hospital of Jilin University, Changchun, People’s Republic of China; 2Jilin Province People’s Hospital, Changchun, People’s Republic of China; 3The Department of Trauma Surgery, Shanghai Oriental Hospital, Shanghai, People’s Republic of China; 4Central Research Institute, United Imaging Healthcare, Shanghai, 201800, People’s Republic of China*These authors contributed equally to this workCorrespondence: Zhanhao Mo, China-Japan Union Hospital of Jilin University, No. 126 Xiantai Street, Erdao District, Changchun, People’s Republic of China, Email mozhanhao@jlu.edu.cnPurpose: The three-dimensional (3D) sequence of magnetic resonance imaging (MRI) plays a critical role in the imaging of musculoskeletal joints; however, its long acquisition time limits its clinical application. In such conditions, compressed sensing (CS) is introduced to accelerate MRI in clinical practice. We aimed to investigate the feasibility of an isotropic 3D variable-flip-angle fast spin echo (FSE) sequence with CS technique (CS-MATRIX) compared to conventional 2D sequences in knee imaging.Methods: Images from different sequences of both the accelerated CS-MATRIX and the corresponding conventional acquisitions were prospectively analyzed and compared. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of the structures within the knees were measured for quantitative analysis. The subjective image quality and diagnostic agreement were compared between CS-MATRIX and conventional 2D sequences. Quantitative and subjective image quality scores were statistically analyzed with the paired t-test and Wilcoxon signed-rank test, respectively. Diagnostic agreements of knee substructure were assessed using Cohen’s weighted kappa statistic.Results: For quantitative analysis, images from the CS-MATRIX sequence showed a significantly higher SNR than T2-fs 2D sequences for visualizing cartilage, menisci, and ligaments, as well as a higher SNR than proton density (pd) 2D sequences for visualizing menisci and ligaments. There was no significant difference between CS-MATRIX and 2D T2-fs sequences in subjective image quality assessment. The diagnostic agreement was rated as moderate to very good between CS-MATRIX and 2D sequences.Conclusion: This study demonstrates the feasibility and clinical potential of the CS-MATRIX sequence technique for detecting knee lesions The CS-MATRIX sequence allows for faster knee imaging than conventional 2D sequences, yielding similar image quality to 2D sequences.Keywords: knee MRI, compressed sensing, 3D variable-flip-angle fast spin echo