A review of micro- and macrovascular analyses in the assessment of tumor-associated vasculature as visualized by MR

Abstract

There is currently no noninvasive, reliable method of assessing brain tumor malignancy or of monitoring tumor treatment response. Monitoring changes to tumor vasculature might provide an effective means of assessing both tumor aggressiveness and treatment efficacy. To date, most such research has concentrated upon tumor "microvascular" imaging, with permeability and/or perfusion imaging used to assess vessel changes at the subvoxel level. An alternative approach assesses tumor vasculature at the "macroscopic" level, calculating the numbers and shapes of the larger vessels discriminable by magnetic resonance angiography. This paper provides an overview of magnetic resonance (MR) vascular imaging at both the microscopic (dynamic MR perfusion and permeability) and macroscopic (MR angiographic) levels. The two approaches provide different, complementary information and together could provide important insights into cancer growth as well as new methods of assessing malignancy and tumor treatment response.

Figures

Figure 1

Healthy (left) and cancer-associated (right) posterior cerebral artery segmented from time-of-flight, unenhanced brain MRA (MOTSA technique, 5 slabs, TR/TE 35msec/3msec, 0.5 × 0.5 × 0.8 mm3, 352 × 448 × 192 voxels). Note the “many smaller bends upon each larger bend” that characterize cancer-associated vessel morphology. The closest lesion detectable on gadolinium-enhanced MR was over a centimeter away.

Figure 2

Blood flow increase in high grade glioma. A: The patient has a mass in the left parietal lobe which shows enhancement (arrows) on post contrast T1 weighted image (axial, gadolinium-enhanced, TR/TE 1700/4.38, voxel size 1 × 1 × 1.5 mm3, voxels 256 × 256 × 130). B: The corresponding cerebral blood flow map (T2*-weighted EPI sequence, TR/TE 54/2000) shows a corresponding area of high blood flow (arrows). Red indicates higher blood flow, blue lower. Interpretation may be complicated by normally high blood flow in grey matter and surface vessels.

Figure 3

Improvement of vessel tortuosity abnormalities during successful treatment. A: Axial slice of a T1-GAD baseline scan showing a large tumor (arrow). Acquisition parameters are the same as outlined in Figure 2. B: Lateral view of the vessels segmented from the baseline MRA, with MRA acquisition parameters the same as described in Figure 1. Rectangle outlines the region magnified in C. C: Tortuosity abnormalities involve both smaller branches and the large frontopolar arteries (arrows). D: The tumor has regressed at month 2 of treatment (arrow). E: At month 2 the small, abnormal vessel branches have largely disappeared and there is normalization of the larger vessels’ shapes. The tumor continued to regress during the following 8 months.