Purpose: To investigate the feasibility of a vessel size imaging (VSI) technique with separate contrast agent injections for evaluation of the vessel caliber in normal tissues and in brain tumors.
Materials and methods: Computer simulation was first performed to assess the potential errors in the estimation of vessel caliber that could result from time shifts between the dual contrast agent injections. Eight patients (four female, four male, 37-77 years old) with brain tumors (three high-grade gliomas, two low-grade gliomas, and three meningiomas) were recruited for clinical study. Dynamic susceptibility contrast magnetic resonance imaging (MRI) using gradient echo (GE) and spin echo (SE) echo-planar imaging sequences were performed separately with a 10-minute interval on a 3.0T scanner. Vessel caliber maps were calculated and analyzed in regions of interest at cortical gray matter (GM), thalamus, white matter (WM), and tumors.
Results: From the computer simulation, the error of vessel caliber measurement was less than 8% when the difference between the time-to-peak of the GE and the SE studies was 1.5 seconds, and reduced to within 5% when the difference was 1 second. From the patient datasets of a 64 x 64 matrix, the estimated vessel calibers were 37.4 +/- 12.9 microm for cortical gray matter, 20.7 +/- 8.8 microm for thalamus, and 15.0 +/- 5.1 microm for white matter, comparable to results in the literature. Two patients had a VSI with 128 x 128 matrix and showed similar results in vessel calibers of normal tissues. All the tumors had larger mean vessel diameter than normal-appearing tissues. The difference in vascular size between normal tissue and tumor was demonstrated clearly in both the VSIs of regular and high spatial resolution.
Conclusion: This study suggests that VSI with a dual injection method is a feasible technique for estimating microvascular calibers of normal tissues and brain tumors in clinical scanners.