MRI of tumor angiogenesis

Abstract

Angiogenesis has long been established as a key element in the pathophysiology of tumor growth and metastasis. Increasingly, new molecularly targeted antiangiogenic drugs are being developed in the fight against cancer. These drugs bring with them a need for an accurate means of diagnosing tumor angiogenesis and monitoring response to treatment. Imaging techniques can offer this in a noninvasive way, while also providing functional information about the tumor. Among the many clinical imaging techniques available, MRI alone can provide relatively good spatial resolution and specificity, without ionizing radiation and with limited side effects. Arterial spin labeling (ASL) and blood oxygenation level-dependent (BOLD) imaging techniques can be employed to confer indirect measures of angiogenesis, such as blood flow and blood volume, without the need for external contrast agents. Dynamic contrast-enhanced (DCE)-MRI is rapidly emerging as a standard method for directly measuring angiogenesis during angiogenesis-inhibitor drug trials. As macromolecular MR contrast agents become available, they will inevitably be utilized in the assessment of tumor perfusion and vessel permeability. Meanwhile, technological advances have made imaging at a molecular level a possibility. They have brought the potential to directly target MR contrast agents to markers of angiogenesis, such as the ␣ v ␤ 3 integrin. Before this is used clinically, however, substantial gains in sensitivity brought about by improved coils, pulse sequences, and contrast agents will be needed. Herein we discuss the techniques currently available for MRI of angiogenesis, along with their respective advantages and disadvantages, and what the future holds for this evolving field of imaging.

Feasibility of FAIR imaging for evaluating tumor perfusion

“…Therefore, we suggest that the comparison would be more accurate between FAIR and DCE-MR than between FAIR and microvascular density. Second, perfusion-related parameters on DCE-MR, such as K ep and the amount of contrast enhancement, have been shown to strongly correlate with angiogenesis activity (13,14). Third, microvascular density may be variable according to observer and identifying blood vessels in histological sections do not discern whether the vessels provide routes of blood flow (15,16).…”

Angiogenesis in pre-malignant conditions

“…These two interventions targeting different cell types may act synergistically, resulting in a more effective prophylaxis than can be achieved with either individually. Advances in non-invasive imaging, facilitating the assessment of angiogenesis in tissues, may allow clinicians to monitor angiopreventive strategies (Barrett et al, 2007). Recent research has demonstrated that statins promote endothelial cell death and inhibit experimental angiogenesis induced by growth factors, providing 'proof of principle' for developing statin-based angiopreventive strategies (Boodhwani et al, 2006).…”

Dynamic contrast‐enhanced MRI of primary rectal cancer: Quantitative correlation with positron emission tomography/computed tomography

“…In human tumors, angiogenesis can be assessed by the expression levels of microvessel density and vascular endothelial growth factor (VEGF) using histopathological methods (4,(7)(8)(9)(10)(11). However, these techniques require tumor tissues and need to be performed on either preoperative biopsy samples or postoperative surgical specimens.…”