Physiological and Real-Time Gating of Data for Positron Emission Computed Tomography

Data for emission computed tomography (ECT) studies is obtained from detector arrays positioned around a subject. In ECT studies dynamic data is taken representing such functions as blood flow, blood pool, cell perfusion and cell metabolism. These may vary with time due to physiological reasons or cyclicly due to bio-mechanical (e.g. cardiac) reasons. Since the time to acquire statistically significant data is typically much longer than the period of these physiological cycles, data must be taken for discrete divisions of many cycles, in synchronism with the physiological process. Physiological gating may be applied, for instance, to ECT studies of the heart. In these studies, the time period of the cardiac cycle is subdivided. Data from each division of the cycle is compiled into a separate image. A single cardiac cycle does not provide enough data at reasonable subject dose rates to compile an image for each division; therefore, data is taken for several cardiac cycles with separate storage for each division. The resulting image for each division will show increased resolution due to minimization of distortion. This technique may also be applied to respiratory and other dynamic processes. An alternate form of gating creates a cycle based on clock time rather than a physiological process. This method allows the use of high speed buffering to increase the rate of data images acquired. This paper presents a method of providing gating based on either physiological processes or clock time.