CONTRAST-MEDIA IN LIVER SONOGRAPHY - CORRELATION WITH ENHANCED DYNAMIC MAGNETIC-RESONANCE-IMAGING

Both color Doppler sonography and magnetic resonance are imaging techn iques which do not use ionizing radiations, but despite this common fe ature there remain many differences between them. Thus, color Doppler sonography is a cost-effective technique using mechanical waves and pr oviding real-time images while magnetic resonance imaging is much more expensive, uses magnetic fields and radiofrequency energy and provide s static images. The former method is very sensitive in detecting foca l liver lesions >1 cm, but its specificity in characterization is not as good, not even with the color Doppler technique. The main differenc es between color Doppler sonography, with and/or without echocontrast agents, and contrast-enhanced (Gadolinium chelates) dynamic magnetic r esonance imaging in focal liver lesions can be summarized as follows: (1) magnetic resonance imaging depicts tumor vascularization only afte r paramagnetic contrast media injection. Enhanced images completely de pend upon the contrast agent and cannot be achieved without it. In con trast, color Doppler signal is not modified by the contrast agent, it just becomes stronger. (2) Contrast-enhanced magnetic resonance signal (as well as contrast-enhanced computed tomography signal) provides mo re pieces of information than color Doppler signal about the flow char acteristics of liver nodules-i.e. it shows not only blood flow (hyper- /hypovascular nodule), but also the interstitial spread of the agent a nd its wash-out. For example, hepatocellular carcinoma and focal nodul ar hyperplasia have similar perfusion while agent spread and wash-out decrease very quickly in the former and more slowly in the latter, exc ept for the low decrease of the central scar. (3) Color Doppler techno logy improvements, higher sensitivity to slow flows and better signal/ noise ratio reduce the applications of contrast-enhanced sonography in focal liver lesions because the agents modify only sensitivity and no t the imaging in slow flow studies. (4) The higher cost of contrast st udies is justified only in selected cases, namely treatment follow-up in the lesions with rich pretreatment vascularization. Finally, the hi gher cost of contrast magnetic resonance studies is justified to incre ase sensitivity and especially to allow lesion characterization. (C) 1 998 Elsevier Science Ireland Ltd. All rights reserved.