Imaging techniques hold promise for the noninvasive assessment of liver fibrosis. However, at the current time most of the available modalities have limitations. For example, ultrasound with microbubble contrast examines the transit time of blood through the liver and has been touted mainly for the diagnosis of cirrhosis.1 This test and phosphorus spectroscopy (i.e., phosphomonoester to phosphodiester ratios) appear to be capable of tracking the progression of fibrosis but are no more sensitive or specific than serum tests, particularly for intermediate levels of fibrosis.2 Also, phosphorus spectroscopy requires hardware that is available only in research centers. Proton spectroscopy identifies various metabolites (choline and aliphatic hydrocarbons, among others), which may be altered in both steatosis and fibrosis. Thus, its specificity for fibrosis remains to be demonstrated. It can be performed on a standard 1.5 Tesla clinical imager (with dedicated technical assistance), but informative spectra may require higher field strength magnets (3 or 7 T), which at present are research tools only. Diffusion-weighted magnetic resonance (MR) imaging can distinguish cirrhosis and chronic hepatitis from normal liver but with substantial overlap between the groups.3
We look forward to further refinements in each of these various modalities. The combination of proton spectroscopy and diffusion-weighted MR has proven informative for a variety of brain injuries4 and may be worthy of study also for noninvasive assessment of liver fibrosis.