Motion suppression in MR imaging of the liver: comparison of respiratory-triggered and nontriggered fast spin-echo sequences.

Abstract

Our purpose was to compare the effectiveness of a respiratory-triggered fast spin-echo (RTFSE) pulse sequence and a nontriggered fast spin-echo pulse sequence for imaging liver masses. Forty-one patients with suspected liver masses were imaged at 1.5 T with a fast spin-echo sequence and an RTFSE sequence designed to trigger data acquisition at end expiration. All other imaging parameters were identical. MR images were compared qualitatively for lesion detection and conspicuity, anatomic sharpness, vascular definition, phase artifacts, and overall image quality. Quantitative analysis was performed to obtain lesion-liver contrast and contrast-to-noise ratio (CNR) measurements of all liver masses. Thirty-three patients had liver masses. The RTFSE images showed superior anatomic sharpness in 83% of examinations and superior overall image quality in 85% of examinations. Lesion detection and conspicuity were superior for the RTFSE images in 53% of examinations and were similar for the two techniques in 38%. In 10 patients we detected more lesions on RTFSE images, and in one patient we detected more lesions on fast spin-echo images. In the remaining patients the number of lesions detected on RTFSE images was identical to the number detected on fast spin-echo images. Respiratory artifacts were less noticeable on the RTFSE images in 66% of examinations and on the fast spin-echo images in 14%. Quantitative analysis showed a 29% increase in mean relative lesion-liver contrast and a 34% increase in mean relative CNR for the RTFSE images. Mean lesion-liver contrast and CNR for the RTFSE images (152.6 +/- 100.9, 14.2 +/- 9.3) were superior to corresponding values for the fast spin-echo images (123.4 +/- 88.0, 10.9 +/- 7.4) (p < .0001). Compared with nontriggered fast spin-echo MR images, the RTFSE MR images were superior for our evaluation of liver masses. By acquiring data during a period of reduced respiratory motion, the RTFSE sequence produced images with sharper anatomic detail, equal or less phase ghosting, and measurable improvement in the lesion-liver contrast and CNR.