Usefulness of simultaneous acquisition of spatial harmonics technique for MRI of the knee

Abstract

Objective: Simultaneous acquisition of spatial harmonics (SMASH) is a parallel-imaging technique that uses fewer echoes than conventional techniques to obtain the desired resolution. Images are produced in a shorter time period using the SMASH technique than conventional techniques. This study assesses the usefulness of the SMASH technique in the MRI evaluation of the knee. SUBJECTS AND METHODS. Three experienced musculoskeletal radiologists prospectively interpreted MR images of the knee in 50 consecutive patients. All patients underwent a complete MRI examination of the knee on a 1.5-T MRI scanner. Sagittal proton density fat-saturated and coronal T1-weighted images were obtained. In addition, fat-saturated T2-weighted images were obtained in the coronal, sagittal, and axial planes. SMASH T2-weighted imaging in the coronal, axial and sagittal planes took 6 min 38 sec, whereas fast spin-echo conventional T2-weighted imaging took 11 min 45 sec to obtain images in the same planes. Each radiologist interpreted the knee MR examinations prospectively and was unaware whether the images had been obtained using the SMASH T2-weighted or fat-saturated T2-weighted technique. The radiologists provided a report. The three radiologists independently performed a retrospective review of both the fat-saturated T2-weighted and SMASH T2-weighted images. The radiologists were blinded as to which sequence was fat-saturated T2-weighted and which was SMASH T2-weighted. They were asked to reinterpret the images and determine whether either of the T2-weighted sequences altered the original interpretation.

Results: There was no intraobserver variability in MRI interpretations with the use of SMASH imaging as compared with fat-saturated T2-weighted images. Thirty-four patients underwent arthroscopy after imaging. Findings at arthroscopy in those patients were as follows: 28 meniscal tears, 12 anterior cruciate ligament tears, and nine chondral defects. In some patients, multiple abnormalities were detected on MRI. All arthroscopy findings correlated with prospective MRI interpretations.

Conclusion: The use of SMASH T2-weighted imaging as opposed to fat-saturated T2-weighted imaging results in a significant decrease in imaging time (> 5-min decrease for each knee examination) without affecting the MRI interpretation or patient clinical outcome.