Abstract: The patient's ECG signal is employed in a traverse-and-rotate type CT scanner as a time base for triggering the beginning of a traverse such that the traveling beam reaches the heart at a desired phase of the cardiac cycle. For a purely-rotational-type CT scanner, continuously generated scan data is only stored for corresponding phases of successive cardiac cycles. Alternatively, gating of the beams themselves can be controlled by the ECG signal. The use of a pacemaker to stabilize the cardiac period is described along with a system for recognizing unacceptable variations in the cardiac period. In a traverse-and-rotate-type fan-beam CT scanner, the effective beam width is narrowed to hasten the traverse of the heart.

Abstract: In a radiographic digital subtraction system utilizing a contrast agent for enhancing a difficult-to-image anatomic region of interest, a method of selecting a superior difference image. The difference image selected represents the differential between a pair of digitized radiographic images selected from a series of such images acquired before and after the contrast appears in the region of interest during a dynamic imaging study.