Advanced Magnetic Resonance Imaging (MRI) of diffuse liver disease

Abstract

With the continued increased prevalence of diffuse liver diseases (mostly due to nonalcoholic fatty liver disease and HCV infection), MRI plays an increasingly important role in the evaluation of patients with chronic liver disease because of the lack of ionizing radiation and the possibility of performing multi parametric imaging combining conventional and functional sequences. However, more clinical evidence is needed to determine which method or combination of methods achieves the best accuracy for assessment of fibrosis, fat, and iron deposition. In phase and opposed phase MR imaging allows reliable detection of focal steatosishepatis owing to the chemical shift cancellation artifact. Areas of steatosis demonstrate signal loss on opposed phase images. In addition, T2* effects allow reliable detection of iron storage diseases related susceptibility artifacts. Areas of iron storage demonstrate pronounced signal loss on the image with the longer echo time. MR spectroscopy has potential tool utility for assessment of metabolic function, particularly with respect to liver fat quantification. It also may provide useful information about other aspects of diffuse liver disease (e.g., inflammation and fibrosis). However, in vivo application of MR spectroscopy in the abdomen and pelvis is limited by spectral resolution, SNR, and motion. Diffusion weighted imaging and ADC maps of the liver offer functional and even quantitative information about hepatic tissue that can be used in conjunction with other MRI sequences to help with diagnosis of disease, treatment planning, and assessing treatment success. A major advantage of DWI over the use of intravenous contrast enhanced liver imaging is that it can be used in patients with compromised kidney function and not put them at risk for nephrogenic systemic fibrosis. There is also less risk and fewer complications compared with biopsy and other invasive methods of assessing the liver. As MRI software and hardware continues to evolve, the quality of DWI will continue to improve and it is likely to become even more useful in the clinical setting. MR elastography promises to play a larger role in the early detection of hepatic fibrosis.