Four dimensional intravenous cone-beam computed tomographic subtraction angiography. In vitro study of feasibility

We demonstrate the feasibility of 4D intravenous computed tomographic (CT) subtraction cerebral angiography using in vitro, anthropomorphic techniques.

High-resolution 3D cone-beam CT datasets (0.45 mm isotropic voxel size, 120 kVp, 90 mA) of a cadaver-derived cerebrovascular phantom, containing a saccular aneurysm, were acquired at a rate of 1 Hz for 20 seconds. A computer-controlled pump provided physiologically realistic blood-flow waveforms using a water-glycerol blood-mimicking fluid (10 mL/s mean flow). Contrast agent injected at 0.94 mL/s for 5 seconds provided a clinically realistic intravenous vascular enhancement of approximately 300 Hounsfield units. The first 4 to 5 volumes (precontrast) provided a mask dataset for volumetric subtraction. Vascular enhancement was measured in the dynamic, time-resolved, subtracted 3D angiograms. Contrast-to-noise ratio was measured in 3D source data and maximum intensity projections (MIPs). Dose measurements were made using an ionization chamber.

MIP images of the time-resolved volumetric data were of diagnostic quality, clearly showing the aneurysm dome and neck, and cerebral vessels. Dynamic flow information (contrast wash-in/wash-out) was observed, including differential opacification and draining of the anterior and posterior vasculature and the aneurysm. Contrast-to-noise ratio was measured to be in the range of 3 to 4.5 in averaged volumes, and 10.5 to 17 in the corresponding MIPs, at an effective patient dose of 2.8 mSv, with 4 cm of axial coverage.

We have demonstrated the feasibility of 4D volumetric, intravenous CT subtraction angiography, in vitro, providing time-resolved, diagnostic quality 3D datasets. We were able to show time-resolved blood-flow information and high-resolution local and global anatomic renderings, from a single 20-second scan, at acceptable x-ray dose.