14 - Functional imaging: from tumour biology to the clinic

Summary

Introduction

The increasing demand for in vivo imaging to provide early biomarkers of disease response as well as to report on predictive and prognostic features of tumours is driving the need for a combined structural and functional approach. Morphological imaging is usually only useful in assessing response late after therapy and, while volumetric measures, for example in cervical cancer, are crucial prognostic indicators, their use in small, early-stage disease is less useful in this regard. With the advent of techniques such as dynamic contrast-enhanced (DCE) computed tomography (CT) or magnetic resonance imaging (MRI), diffusion-weighted (DW) imaging, lymph node-specific contrast agents and positron emission tomography (PET) with F-FDG or other targeted radiotracers, there is a burgeoning field of ‘functional’ techniques that can be exploited for use in the clinic. This chapter describes the range of techniques available, their relationship to tumour biology and their utility in the context of patient management pathways.

Available techniques

Dynamic contrast-enhanced CT or MRI

The microvascular properties of tissue can be interrogated with DCE-CT or DCE-MRI, where rapid image acquisition before, during and after a bolus of intravenously injected contrast agent enables pharmacokinetic modelling of its passage through the circulation and into the tissue compartment. The presence of the contrast agent (iodinated in the case of CT, weakly paramagnetic in the case of MRI) increases X-ray attenuation or signal intensity, respectively; the degree of enhancement is determined by blood flow, vascular density, capillary permeability and capillary surface area in the early vascular phase and by extravascular space volume in the interstitial phase.