Leo J. Rigler lecture. MR imaging of the liver

Abstract

Recent technical and clinical advances in MR of the liver are reviewed with special reference to the role of MR as a primary screening technique for detection of space-occupying lesions, especially metastases. The major current problem in upper abdominal MR imaging is physiologic motions, and this appears to have been effectively solved by newly introduced pulse-sequence and timing-parameter strategies. Short-TR/TE spin-echo sequences with extensive signal averaging and heavy T1-weighting produce images with exceptional anatomic detail and liver-cancer contrast differences. With this sequence superior sensitivity for liver-cancer detection has been shown in quantitative signal-difference to noise comparisons with other pulse sequences and in clinical comparisons with CT. MR discovered 14% more individual metastases and 3% more patients with liver cancer than CT in a blinded comparative study of 142 patients undergoing both exams. MR also showed greater specificity (98%) than CT (91%) in distinguishing patients without liver metastases. Differentiation of hemangioma from metastases was possible with greater than 90% specificity by using heavily T2-weighted sequences. Use of a fast-scan, gradient-recalled echo technique can also produce good-quality, multislice, T1-weighted studies of the liver in 20 sec--a breath-hold. MR contrast agents (such as gadolinium-DTPA and reticuloendothelial-system-specific, superparamagnetic ferrite-iron-oxide particles) offer further promise for enhanced sensitivity for liver-cancer detection. When optimal pulse sequences are employed, MR can now be appropriate as a primary screening method for detecting liver neoplasms.