[The chemical shift imaging of liver]

Tissue characterization of different pathologies of the liver can be achieved by differences of relaxation time on changing of pulse sequences in magnetic resonance imaging (MRI). The usefulness of MRI for detection of liver disease is limited when the pathological change is subtle. Chemical shift is a fundamental characteristics in nuclear magnetic resonance (NMR). Chemical shift imaging (CSI) in MRI is based on the different Larmor frequency of proton in water and fat; and therefore it was able to enhance the effectiveness of pathology. For this study, Dixon's method was used to detect liver pathologies and compare its detectability with conventional pulse sequences. Forty cases were enrolled for study; they included 5 health volunteers, 15 hepatomas, 1 cholangiocarcinoma, 5 metastatic hepatic tumors and 14 fatty livers. In hepatic tumors, the lesion number, tumor margination and lesion-to-liver contrast in images were read and analyzed. Signal intensities, signal-to-noise ratio and contrast-to-noise ratio were compared, after measurement, from stored data. In fatty livers, the relative change of signal intensities in different areas of the liver in in-phase and out-phase images were compared with the back muscle and spleen to find where the fatty metamorphosis happened. CSI in spin echo or gradient echo pulse sequences was found to be adequate and valuable for detecting fatty liver, when compared with conventional MRI. CSI not only identified the extension of disease itself but also characterized the fatty change in liver parenchyma. Though CSI affords no further advantages than conventional pulse sequences for detection of hepatic tumors, occasionally, when the image quality of the conventional pulse sequences is not satisfactory or equivocal in lesion detection, the use of CSI might be attempted.