USING FAST SEQUENTIAL ASYMMETRIC FANBEAM TRANSMISSION CT FOR ATTENUATION CORRECTION OF CARDIAC SPECT IMAGING

The objective of this study was to determine the feasibility of using a fast (short-duration) transmission computed tomogram (TCT), acquired immediately before or after the emission CT, to correct for photon at tenuation in cardiac SPECT. Methods: The asymmetric fanbeam geometry w ith a (99)mTc line source was used to acquire TCTs after conventional cardiac emission CT imaging on a triple-head SPECT system. The TCTs we re reconstructed to generate patient-specific attenuation maps, which were used with an iterative maximum likelihood algorithm to reconstruc t attenuation-corrected cardiac SPECT studies. The results of attenuat ion correction based on TCTs as short as 1 min were compared with long -duration transmission imaging for a phantom and several human studies . Results: Attenuation correction based on asymmetric fanbeam TCT sign ificantly improves the uniformity of images of a uniform tracer distri bution in a cardiac-thorax phantom configured to simulate a large pati ent. By using a high-activity line source and a rapid camera rotation, a suitable attenuation map for this phantom can be obtained from a 4- min TCT, A similar result is obtained for patients with thorax widths of <40 cm. Conclusion: A sequential imaging protocol for acquiring a f ast TCT can be used for attenuation correction of cardiac SPECT imagin g. The sequential TCT can be acquired without significantly extending the duration of the imaging study. This method provides a way to perfo rm attenuation correction on existing triple-head SPECT systems withou t extensively modifying the system.