Magnetization transfer imaging of normal and abnormal liver at 0.1 T

Magnetization transfer (MT) contrast is a new technique that may improve contrast in magnetic resonance imaging. High-protein tissues have a greater MT effect, resulting in a decrease in signal intensity. This study evaluates the MT technique on normal and abnormal liver tissue on a low-field system. The magnitude of the magnetization transfer was studied to determine its effect on image visualization and tissue characterization.

Ten volunteers and 25 patients with benign and malignant liver pathology, including left lateral segment hepatectomy, were imaged on a 0.1 T system. Gradient-recalled-echo T2-weighted sequence pairs were obtained with and without MT pulse saturation. Signal intensity measurements were made using region-of-interest tracings in liver, spleen, skeletal muscle, fat, and selected liver pathology. Liver-to-lesion contrast ratios and conspicuity changes were analyzed.

The average signal intensity decrease for normal liver was .27. Skeletal muscle demonstrated the greatest MT effect (.48), while fat showed minimal (.01) MT change. Two hemangiomas and two liver cysts showed a small MT effect (.13 and .02, respectively). Of the malignant lesions imaged, melanoma metastases showed a mean MT effect of .34, while hepatomas showed mean effect of .15. Edematous liver tissue had an intermediate mean effect of .18.

While T2 sequences are more versatile for standard liver imaging, an MT sequence may be helpful for tissue characterization in specific imaging situations. Melanoma metastases and hepatomas demonstrated significant MT effect and increased conspicuity of the malignant lesions.