Physiological gating of the MARS spectral micro CT scanner

Two methods of physiological gating, prospective and retrospective, have been investigated for the Medipix All-Resolution Systems (MARS) spectral CT scanner in order to reduce image blurring due to cardiovascular motion. The scanner is currently designed for scanning small animals, however there are plans to extend it to clinical applications in future. Prospective gating has been implemented such that projection data is collected at specific times, dependent on the state of the heart and lungs. The alternative approach of retrospective gating allows the scanner to collect projections as fast as possible, but records the state of the heart and lungs at each acquisition. In order to validate the effectiveness of the gating, a heart and lungs phantom operated by means of a pneumatic system was built. The phantom was created by laying liquid latex over a 3D printed former and proved successful at simulating rhythmical motion. A marker attached to the “heart” outer surface was used to assess how consistently projection acquisitions could be obtained. Preliminary results for prospective gating with the phantom show some success. The standard deviation of marker Euclidean distance ranged between 45.0 μm and 116.0 μm for cardiac rates of 60, 200 and 320 bpm. Investigation indicated that there was significant variation in the time between the trigger signal from the gating detection system and the data acquisition. Further development will be required to reduce this variation.