Hanzhang Lu
It is known that angiogenesis plays a major role in tumor progression and is an important indicator of tumor grade. Tumor angiogenesis has two important features that can be exploited for noninvasive imaging. One is that cerebral blood volume (CBV) in the angiogenic region is often elevated, as more blood vessels tend to occupy more space in the brain parenchyma. A second feature is that the newly formed blood vessels in the tumor region are usually immature vessels, in that they do not have a blood-brain barrier (BBB) that a regular vessel has. Previous imaging methods have usually focused on either CBV or BBB leakage for brain tumor grading. For example, dynamic susceptibility contrast (DSC) MRI has been used to assess CBV, whereas dynamic contrast-enhanced (DCE) MRI has been used to study BBB leakage. While these methods have demonstrated sensitivity for tumor grading, a technique that incorporates both effects is expected to provide a superior delineation accuracy.
Vascular-space occupancy (VASO) MRI is a method that is sensitive to both CBV and BBB leakage in the brain. Importantly, both effects add constructively in VASO. That is, VASO signal increases with both greater CBV and higher BBB leakage in cerebral vessels. In this paper, we studied patients with brain tumor with a range of grades and found that VASO signal can provide an estimation of tumor grade with a high sensitivity and specificity, with a receiver operating characteristic (ROC) area of 0.985. Therefore, VASO MRI may provide a practical approach for noninvasive tumor grading with a better accuracy than conventional DSC or DCE techniques.
Another important aspect of angiogenesis in brain tumor that is not well explored is the fact that newly formed blood vessels are not equipped with smooth muscles, unlike mature vessels. Therefore, these vessels, when faced with a vasoactive stimulus, are not capable of dilating or constricting. This may be another important opportunity to detect angiogenesis in