Implementation of physiological gating on the high resolution research tomograph

The HRRT scanner accepts, with a minor adjustment of the connectors, positive TTL signals. The connectors are sampled reliably with a frequency of 1000 Hz. The presence as well as the duration of TTL signals can be derived from the gating tag words inserted in the listmode file. Emission data can be sorted into bins with less than 1% data loss due to rounding errors resulting from the bin definitions. A first example of cardiac gating is presented for the HRRT scanner. At present, use of TTL signals during transmission scans is limited due to the fixed trajectory of the transmission source. Future work will therefore focus on assessment of optimal attenuation and scatter correction methods for gated emission measurements. Yet, a substantial improvement of image quality was seen and the usefullness of physiological gating for HRRT small animal studies has been demonstrated. The gain in image quality observed by physical gating in combination with PSF reconstructions [2] may enable use of image derived input functions [9], which will be explored in the near future.