Tumor Vasculature

A multitude of imaging techniques are available for assessment of tissue vasculature on a structural, functional, and molecular level. All these methods have been successfully used preclinically and may aid in antiangiogenic drug development in animal studies. Up to now, only imaging of functional hemodynamic parameters like Ktrans, blood flow, and blood volume is currently used in the clinical arena for evaluation of antiangiogenic and cytotoxic chemotherapies. However, results are often hard to interpret in their physiological meaning. Macromolecular MRI and CT contrast agents will become clinically available and may facilitate the interpretation of these hemodynamic parameters. Concerning imaging of molecular angiogenesis parameters, only few radiotracers have been used in humans up to now. Their role in assessment of antiangiogenic therapies is still unsettled. Although v3 is by far the most extensively studied angiogenic factor for imaging, future trials have to show which target structure is optimal for angiogenic activity assessment. Concerning the optimum imaging technique, the radiotracer approach may be the first used on a wider scale in patients in the intermediate term, due to its high sensitivity and low amounts of required tracer. Therefore, toxicity issues are of less importance compared to MRI or ultrasound probes. In the long term, MRI might be a formidable alternative, due to its lack of ionizing radiation and high spatial resolution. However, it is likely that not one single parameter, target structure, or imaging technique will be used for assessment of angiogenesis in the future, but rather a combination of parameters allowing evaluation of the angiogenic cascade in its full complexity.