MR imaging of tumor microcirculation: Promise for the new millenium

Abstract

Dynamic contrast-enhanced magnetic resonance imaging (DCE MRI) is a method of imaging the physiology of the microcirculation. A series of recent clinical studies have shown that DCE MRI can measure and predict tumor response to therapy. Recent advances in MR technology provide the enhanced spatial and temporal resolution that allow the application of this methodology in the management of cancer patients. The September issue of this journal provided a microcirculation section to update readers on this exciting and challenging topic. Evidence is mounting that DCE MRI-based measures correlate well with tumor angiogenesis. DCE MRI has already been shown in several types of tumors to correlate well with traditional outcome measures, such as histopathologic studies, and with survival. These new measures are sensitive to tumor physiology and to the pharmacokinetics of the contrast agent in individual tumors. Moreover, they can present anatomical images of tumor microcirculation at excellent spatial resolution. Several issues have emerged from recent international workshops that must be addressed to move this methodology into routine clinical practice. First, is complex modeling of DCE MRI really necessary to answer clinical questions reliably? Clinical research has shown that, for tumors such as bone sarcomas, reliable outcome measures of tumor response to chemotherapy can be extracted from DCE MRI by methods ranging from simple measures of enhancement to pharmacokinetic models. However, the use of similar methods to answer a different question - the differentiation of malignant from benign breast tumors has yielded contradictory results. Thus, no simple, one-size-fits-all- tumors solution has yet been identified. Second, what is the most rational and reliable data collection procedure for the DCE MRI evaluation? Several groups have addressed population variations in some key variables, such as tumor T1O (T1 prior to contrast administration) and the arterial input function C(a)(t) for contrast agent, and how they influence the precision and accuracy of DCE MRI outcomes. However, despite these potential complications, clinical studies in this section show that some tumor types can be assessed by relatively simple dynamic measures and analyses. The clinical scenario and tumor type may well determine the required complexity of the DCE MRI exam procedure and its analysis. Finally, we suggest that a consensus on naming conventions (nomenclature) is needed to facilitate comparison and analysis of the results of studies conducted at different centers.