Diffusion-weighted magnetic resonance imaging: biomarker for treatment response in oncology*

The assessment of cancer and its metastases by means of functional imaging techniques may lead to a more reliable diagnosis and early knowledge of the treatment efficacy. Diffusion-weighted magnetic resonance imaging (MRI) represents a promising imaging tool for tissue characterization, prediction and evaluation of therapeutic response in oncology. In cases of liver disease, diffusion-weighted imaging presents higher sensitivity in the detection of lesions as compared with T2weighted sequences. Diffusion-weighted MRI is a noninvasive imaging technique which measures the water mobility within the tissues. The quantitative diffusion analysis is performed by means of the apparent diffusion coefficient (ADC), which is inversely proportional to the cellularity. High ADC values correspond to greater freedom of motion of water molecules, for example, when some intact cell structures, such as membranes, are present. Processes such as cell apoptosis and proliferation influence the cell density and therefore the ADC value. Diffusion is a cell marker. Malignant lesions, such as liver metastases, frequently demonstrate low ADC values, except in cases of treated lesions or necrosis. Low INTRODUCTION