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Using Fast Sequential Asymmetric Fanbeam Transmission CT for Attenuation Correction of Cardiac SPECT Imaging

Department of Diagnostic Radiology and Nuclear Medicine and Section of Medical Physics, Rush-Presbyterian-St. Luke's Medical Center, Chicago, Illinois

Correspondence: For correspondence or reprints contact: Edward F. Hollinger, MS, Section of Medical Physics, Rush-Presbyterian-St.Luke's Medical Center, 1653 West Congress Pkwy., Chicago, IL 60612.

ABSTRACT

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 attenuation in cardiac SPECT. Methods: The asymmetric fanbeam geometry with a ^99mTc line source was used to acquire TCTs after conventional cardiac emission CT imaging on a triple-head SPECT system. The TCTs were reconstructed to generate patient-specific attenuation maps, which were used with an iterative maximum likelihood algorithm to reconstruct attenuation-corrected cardiac SPECT studies. The results of attenuation correction based on TCTs as short as 1 min were compared with long-duration transmission imaging for a phantom and several human studies. Results: Attenuationcorrectionbased on asymmetric fanbeam TCT significantly improves the uniformity of images of a uniform tracer distribution in a cardiac-thorax phantom configured to simulate a large patient. 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 fast TCT can be used for attenuation correction of cardiac SPECT imaging. The sequential TCT can be acquired without significantly extending the duration of the imaging study. This method provides a way to perform attenuation correction on existing triple-head SPECT systems without extensively modifying the system.

Key Words: attenuation correction • transmission CT • SPECT