The Establishment of an Intravoxel Incoherent Motion Based MRI-Protocol for Differentiation of Focal Lesions in the Pancreas

Abstract

The mortality related to pancreatic cancer is high. It spreads rapidly and as the situation is today it is often not diagnosed until a quite late stage. However, recent studies have shown that the intravoxel incoherent motion model in diffusion-weighted MRI, which includes the effects of perfusion as well as diffusion, shows promising results in earlier detection of pathological tissue.

Today one of the standard protocols in the diagnosis of pancreatic cancer at St. Olavs Hospital is the conventional diffusion-weighted sequence. There is now a desire to develop this further, so that an examination also includes an intravoxel incoherent motion based sequence. The aim is to improve the grounds for diagnosis, as well as the evaluation of the treatment response.

In this project some of the preliminary work in the process of establishing a new protocol based on the intravoxel incoherent motion model were done. Based on a review of current literature, the existing diffusion-weighted imaging sequence and a preliminary study, several protocols were developed and tested on healthy volunteers. This was done on a 1.5 Tesla clinical scanner. Fitting and analysis were performed according to the intravoxel incoherent motion theory and was carried out on data extracted from a region of interest drawn on part of the pancreas.

By introducing different breathing techniques during measurements the effects of motion, both respiratory and due to the activity in the colon, were examined. Motion proved to have a large effect on the resulting signal, rendering it too unstable to later perform a reliable analysis following the intravoxel incoherent motion model. Motion induced signal loss was observed in the images, and estimated parameters were highly inconsistent with large uncertainties.

It was concluded, due to the extent of motion induced errors, that the protocols as they are today are not applicable for clinical use. Additional studies should be conducted, introducing sedatives to the colon to further reduce the degree of motion.