REAL-TIME SYSTEM FOR RESPIRATORY-CARDIAC GATING IN POSITRON TOMOGRAPHY

A Macintosh-based signal processing system has been developed to suppo rt simultaneous respiratory and cardiac gating on the ECAT EXACT HR PE T scanner. Using the Lab-View real-time software environment, the syst em reads analog inputs from a pneumatic respiratory bellows and an ECG monitor to compute an appropriate histogram memory location for the P ET data. Respiratory state is determined by the bellows signal amplitu de; cardiac state is based on the time since the last R-wave. These tw o states are used in a 2D lookup table to determine a combined respira tory-cardiac state. A 4-bit address encoding the selected histogram is directed from the system to the ECAT scanner, which dynamically switc hes the destination of tomograph events as respiratory-cardiac state c hanges. To test the switching efficiency of the combined Macintosh/ECA T system, a rotating emission phantom was built, Acquisitions with 25 msec states while the phantom was rotating at 240 rpm demonstrate the system could effectively stop motion at this rate, with approximately 5 msec switching time between states.