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Evaluates cardiac lesion detectability with triple-head 360° versus dual-head 180° myocardial perfusion SPECT scans with equal acquisition time. The channelized Hotelling observer (CHO) and human observers were used. A male and a female voxelized cardiac-torso phantoms were used to generate the 360° and the 180° projection data. A cold lesion was placed in eight different locations of myocardium and had a lesion contrast of 25%. Sixteen time frames of the cardiac cycle were averaged to create the cardiac motion blurring to simulate the clinical ungated scan. Sufficient Poisson noise was added to set the area under the receiver operating characteristic (ROC) curve (Az) to be between 0.75 and 0.85 in a pilot study and to simulate the clinical case where dual-head 180° and triple-head 360° scans both have the same total acquisition time. For each lesion location, multiple realizations of lesion-present and of lesion-absent data were generated. Five-iteration ordered subsets expectation maximization with eight subsets was used to reconstruct the data. There was no attenuation correction (AC) in reconstruction with images used in the human study, while CHO was applied on images both reconstructed with and without AC. A three-dimensional Hann filter with 0.7 times the Nyquist frequency was used to smooth the reconstructed images. For images reconstructed without AC, both the CHO and the human observer study showed better detection performance for the 180° scan, especially for the female phantom. For images reconstructed with AC, the CHO study showed better detection performance for the 360° scan, especially for the female phantom. The CHO results demonstrated the detection performance with 360° scan was improved more than with 180° scan after AC.