Externally triggered gating of nuclear medicine acquisitions: a useful method for partitioning data.

Physiological gating in nuclear medicine image acquisition was introduced over 30 years ago to subdivide data from the beating heart into short time frames to minimize motion blurring and permit evaluation of contractile parameters. It has since been widely applied in planar gamma camera imaging, SPECT, positron tomography (PET) and anatomical modalities such as x-ray CT and MRI, mostly for cardiac or respiratory investigations. However, the gating capability of gamma cameras and PET scanners can be employed to produce multiply partitioned, statistically independent projection data that can be used in various ways such as to study the effect of varying total acquired counts or time, or administered radioactivity, on image quality and multiple observations for statistical image analyses. Externally triggered gating essentially provides 'something for nothing' as no data are lost and a 'non-gated' data set is easily synthesized post hoc, and there are few reasons for not acquiring the data in this manner (e.g., slightly longer processing time, extra disk space, etc). We present a number of examples where externally triggered gating and partitioning of image data has been useful.