Diffusion-Weighted and Perfusion-Weighted MRI to Evaluate Therapeutic Response in Lymphoma: A Comparison with FDG-PET/CT

The treatment of both Hodgkin’s lymphoma (HL) and non-Hodgkin’s lymphoma (NHL) frequently results in residual masses [1] . A high-prognostic-value imaging modality is needed to assess the response to treatment and identify patients with active disease within the residual mass. Positron emission tomography/computed tomography (PET/CT) allows for a complete assessment of the whole body and is now considered an essential tool to evaluate the posttreatment response in fluorodeoxyglucose (FDG)-avid lymphoma [2] , although its accuracy is challenging. In long-term follow-up, often in young patients, an important issue to consider is the exposure to ionizing radiation. The mean effective dose of PET/CT examinations is 19.6 ± 6.1 mSv [3] , corresponding with the radiation of about 1,000 chest X-rays and 10 head CTs [4] . Few studies have investigated the role of advanced magnetic resonance (MR) techniques by the 2 quantitative parameters, diffusion-weighted imaging (DwI) and perfusion-weighted imaging (PwI). DwI is able to provide an assessment of tumor cellular cramming, while PwI can quantitatively evaluate the combined effects of plasma blood flow, permeability, and capillary surface area.