Post-treatment changes in tumor microenvironment: Dynamic contrast-enhanced and diffusion-weighted magnetic resonance imaging

One method for noninvasively assessing tumor physiology and metabolism is magnetic resonance imaging (MRI). This chapter presents the potential of dynamic contrast-enhanced MRI (DCE-MRI) and diffusion-weighted MRI (DW-MRI) to monitor post-treatment changes in the tumor microenvironment in both the preclinical and clinical settings. DCE-MRI is widely used in the diagnosis and staging of cancer and is emerging as a promising method for monitoring tumor response to treatment. It is used experimentally to monitor the effectiveness of a variety of treatments, including chemotherapy, radiotherapy, hormonal manipulation, and novel therapeutic approaches, such as anti-angiogenic drugs. Diffusion-weighted MRI can detect tumor response to chemotherapy quantitatively, sensitively, and early in the treatment regimen. While DCE-MRI provides information regarding tumor vasculature, ADCw is sensitive to cellular volume fractions (cellularity). Because they image different markers of response, DCE- and DW-MRI may show differences in amplitude and timing of response. Hence, these techniques are complementary and could be combined in experimental studies. As DCE-MRI is noninvasive, the tumor can be monitored longitudinally over a period of time to study the changes in tumor vascularity occurring during growth and alterations induced by various kinds of therapy. Initial results in the clinic using the low-molecular-weight contrast agent Gd-DTPA indicate that DCE-MRI is useful for both diagnosis and prognosis.