Arterial contour detectability in head CT angiography.

Abstract

Arterial contour extraction is essential for visualization and analysis of vasculature in CT angiography (CTA). A means for evaluating the detectability of artery contours CTA images is required. We developed and tested a new method for this purpose based on phase information from two-dimensional Fourier transforms of CTA images. The relationship between arterial contour detectability and a patient's ocular lens dose was evaluated in CTA images obtained with various tube voltages and currents. A head phantom was designed for use as a target object containing a simulated vascular tree, filled with dilute contrast medium (10 mg iodine/ml). The head phantom was scanned using a 64-multidetector CT scanner with tube voltages of 80-140 kV and tube currents corresponding to volume CT dose index [Formula: see text] ranging from 24.4 to 72.8 mGy. Lens doses were measured using the planar silicon PIN-photodiode system. The quality of artery contours in the CTA source images was assessed using a computed detectability index. Lens dose increased proportionally with tube voltage and current. The use of 80 kV provided the highest contour detectability. However, for each tube voltage, the detectability of artery contours was almost constant across the CTDI(vol) values. These results were mostly consistent with the subjective recognition of artery contours on CTA images. A CTA protocol using 80 kV and 420 mA can reduce the radiation exposure to ocular lens by approximately 40 %, and improve the artery contour detectability compared with a routine protocol.