Baseline subtraction in quantitative cardiovascular computed tomography

Beam-hardening (BH) effect was evaluated to determine its potential significance in quantitative blood flow measurements using computed tomography (CT). CT scans of a water bath containing a range of concentrations of iodine (0-15 mg/ml) placed outside and within the chest of a dead dog were obtained at different kVp levels (100, 120, and 130 kVp). The mean CT number and standard deviation were measured over a small region of interest for each concentration. The CT numbers measured outside the chest were significantly higher (p less than 0.01) than those measured inside, suggesting a BH effect. However, this BH error was almost eliminated (p greater than 0.01) when water values (CTw) were subtracted from the CT numbers of the iodine solutions (delta CT = CT1 - CTW). Water subtraction was used to simulate baseline tissue CT numbers prior to contrast enhancement so that the delta CT values were analogous to those generally used to analyze blood flow. The BH effect was therefore not found to be significant for blood flow measurement accuracy in cardiovascular CT.