Liver metastasis on Diffusion-weighted MRI

Magnetic resonance (MR) imaging plays an important role in the evaluation of liver disease. The new techniques are developed and utilized to improve lesion characterization. Diffusion weighted (DW) MR imaging is one which is increasingly used to improve image quality and better quantitative measurement of water molecule within tissue without use of contrast agent. This technique has been widely used in routine liver MR protocol.
MRI yields diagnostic information with varying signal intensity based on restricted, free water diffusion, vascularity, fibrosis, necrosis and hemorrhage in metastasis. There has been increasing usage of DW imaging in detection of liver lesions superior to T2 weighted and superparamagnetic iron oxide (SPIO)-enhanced MR imaging. Furthermore, DW imaging has improved the detection rate of number of focal lesions in the liver especially smaller ones eg. hemangioma, hepatocellular carcinoma and metastasis. Metastasis are the most common malignant liver lesions. Most metastasis are hypo- to isointense on T1 and iso- to hyperintense on T2-weighted images. Hypovascular liver metastasis (from breast, stomach, colorectal, lung carcinoma) usually show perilesional enhancement. While hypervascular metastasis (from renal cell carcinoma, breast (rare), melanoma, carcinoids) shows arterial dominant enhancement to early wash out. Diffusion in water molecule is often restricted (high signal intensity) in liver metastasis due to increased intratumoral matrices and cellularity. DW imaging can be used in patients with renal dysfunction keeping in view the risk of nephrogenic systemic fibrosis and contrast nephropathy. In today’s scenario, parallel imaging techniques and multichannel coils have allowed high quality acquisition of DW images in body imaging without compromising ADC measurement. DW MR imaging has high lesion-to-liver contrast-to-noise ratio for metastasis. Thus addition of DW imaging has certainly opened up a new chapter in diagnostic imaging in improving detection of liver lesions.