A. Martinez-Möller, N. Navab, M. Schwaiger, S. Nekolla Photon Attenuation Correction in Misaligned PET/CT Cardiac Perfusion Images ICMP - International Conference on Medical Physics, held in Nuremberg, Germany, September 2005. (bib)
	Purpose To understand, quantify and minimize the impact of emission-transmission misalignment in cardiac PET/CT. We propose a fully automatic algorithm which realigns the mu-map contour of the left ventricle to the measured PET reducing significantly the artefacts caused by this common mismatch. Methods and Materials: PET/CT NH3 rest/stress scans were obtained for 16 patients and the PET/CT mismatch was visually evaluated for all scans. Using correctly aligned emission-transmission scans, misalignment was simulated by shifting the mu-map and its effects on regional tracer uptake after reconstruction were quantified. The correction algorithm was applied to these scans and its performance evaluated. The algorithm was then applied to all scans with motion. Results: 9 out of 32 scans were classified as having major misalignment, and only 7 appeared correctly aligned. The simulated motion showed a decrease of uptake in the anterior and lateral walls up to 42% and, in less extent, in the apex. This decrease resulted in false-positive findings. The correction algorithm was able to importantly reduce this decrease. In the scans with major PET/CT misalignment, the algorithm increased the uptake by 25±11% in average in the anterior wall and 16±6% in the lateral wall. Discussion and Conclusion: Despite the use of combined imaging devices, patient respiration and motion result in significant emission-transmission misalignment which biases the photon attenuation correction. This results in decreased uptake and false-positive findings in the anterior and lateral walls. The proposed correction algorithm reduced significantly the impact of this misalignment improving the attenuation corrected images.
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