We tested the hypothesis that quantitative 3D analysis of myocardial perfusion from MDCT images obtained during regadenoson stress would more accurately detect the presence of significant coronary artery disease (CAD) than the same analysis when performed on resting MDCT images. Fifty consecutive patients referred for CT coronary angiography (CTCA) underwent additional imaging with regadenoson (0.4mg, Astellas) using prospective gating (256-channel, Philips). Custom software was used to calculate for each myocardial segment an index of severity and extent of perfusion abnormality, Qh, which was compared to perfusion defects predicted by the presence and severity of coronary stenosis on CTCA. In segments supplied by arteries with luminal narrowing >50%, myocardial attenuation was slightly reduced compared to normally perfused segments at rest (91±21 vs. 93±26 HU, NS), and to a larger extent at stress (102±21 vs. 112±20 HU, p<0.05). In contrast, index Qh was significantly increased in these segments at rest (0.40±0.48 vs. 0.26±0.41, p<0.05) and reached a nearly 3-fold difference at stress (0.66±0.74 vs. 0.28±0.51, p<0.05). The addition of regadenoson improved the diagnosis of CAD, as reflected by an increase in sensitivity (from 0.57 to 0.91) and improvement in accuracy (0.65 to 0.77). In conclusion, quantitative 3D analysis of MDCT images allows objective detection of CAD, the accuracy of which is improved by regadenoson stress.