Assessment of Tumor Angiogenesis: Dynamic Contrast-enhanced MR Imaging and Beyond

Dynamic contrast-enhanced (DCE) MR imaging is used increasingly often to evaluate tumor angiogenesis and the efficacy of antiangiogenic drugs. In clinical practice DCE-MR imaging applications are largely centered on lesion detection, characterization, and localization. In research, DCE-MR imaging helps inform decision making in early-phase clinical trials by showing efficacy and by selecting dose and schedule. However, the role of these techniques in patient selection is uncertain. Future research is required to optimize existing DCE-MR imaging methods and to fully validate these biomarkers for wider use in patient care and in drug development.

Technical aspects of MR perfusion

The most common methods for measuring perfusion with MRI are arterial spin labelling (ASL), dynamic susceptibility contrast (DSC-MRI), and T(1)-weighted dynamic contrast enhancement (DCE-MRI). This review focuses on the latter approach, which is by far the most common in the body and produces measures of capillary permeability as well. The aim is to present a concise but complete overview of the technical issues involved in DCE-MRI data acquisition and analysis. For details the reader is referred to the references. The presentation of the topic is essentially generic and focuses on technical aspects that are common to all DCE-MRI measurements. For organ-specific problems and illustrations, we refer to the other papers in this issue. In Section 1 "Theory" the basic quantities are defined, and the physical mechanisms are presented that provide a relation between the hemodynamic parameters and the DCE-MRI signal. Section 2 "Data acquisition" discusses the issues involved in the design of an optimal measurement protocol. Section 3 "Data analysis" summarizes the steps that need to be taken to determine the hemodynamic parameters from the measured data.

Quantitative imaging biomarkers in the clinical development of targeted therapeutics: current and future perspectives

Targeted therapeutics have challenged how imaging techniques assess tumour response to treatment because many new agents are thought to cause cytostasis rather than cytotoxicity. Advanced tracer development, image acquisition, and image analysis have been used to produce quantitative biomarkers of pathophysiology, with particular focus on measurement of tumour vascular characteristics. Here, we critically appraise strategies available to generate imaging biomarkers for use in development of targeted therapeutics. We consider important practical and technical features of data acquisition and analysis because these factors determine the precise physiological meaning of every biomarker. We discuss the merits of volume-based and other size-based metrics for assessment of targeted therapeutics, and we examine the strengths and weaknesses of CT, MRI, and PET biomarkers derived from conventional clinical data. We review imaging biomarkers of tumour microvasculature and discuss imaging strategies that probe other physiological processes including cell proliferation, apoptosis, and tumour invasion. We conclude on the need to develop comprehensive compound-specific imaging biomarkers that are appropriate for every class of targeted therapeutics, and to investigate the complementary information given in multimodality imaging studies of targeted therapeutics.