During what phase does the CT scanner capture images when using prospective gating?

The correct phase for capturing images using prospective gating in a CT scanner is diastole. During this phase, the heart muscle relaxes and the chambers of the heart fill with blood. The relatively quiescent state of the heart during diastole allows for clearer and more stable images to be acquired, as there is less cardiac motion compared to other phases of the cardiac cycle.

In prospective gating, the timing of image acquisition is synchronized with the cardiac cycle to minimize motion artifacts. By choosing to capture images during diastole, the scanner can take advantage of the heart's slower motion, which enhances the quality of the images obtained for assessment of cardiac structures and function.

This technique is particularly beneficial in patients where motion artifacts caused by the heartbeat could compromise the diagnostic quality of the CT scans. Other phases, such as systole or end diastole, are less optimal due to increased heart activity or rapid changes in blood volume that could lead to blurring in the images.