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Assessment of the influence of PET and CT data misalignment errors in cardiac PET/CT Examination: Patient and phantom studies

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Author(s): Pardis Ghafarian | Seyed Mahmoud Reza Aghamiri | Mohammad Reza Ay | Armaghan Fard Esfahani | Habib Zaidi

Journal: Iranian Journal of Nuclear Medicine
ISSN 1681-2824

Volume: 18;
Issue: Suppl 1;
Start page: 81;
Date: 2010;
Original page

Keywords: Cardiac PET/CT | Misalignment | Attenuation correction

ABSTRACT
Introduction: Nowadays with the advent of 64-slice CT modules associated with PET scanners, full clinical cardiac assessment is possible. But, the use of CT for AC of PET image can introduce misalignment artifacts due to time discrepancy between CT and PET data acquisition and produce the artifactual distribution uptake values in all segments of the myocardial wall. The aim of this study is to evaluate the misalignment effect induced by spurious patient motion in-between the two modalities on regional uptake value in the myocardial wall. Methods: The study was performed using 3 patients including one NH3 perfusion and two 18F-fluorodeoxyglucose viability examinations acquired on the Biograph TP 64 PET/CT scanners using routine cardiac PET/CT protocol. For accurate quantitative analysis, attenuation and emission data were also obtained using RSD thorax phantom . Manual shifts between the CT and PET images ranging from 0 to 20 mm in six different directions were applied. Thereafter, attenuation correction was applied to the emission data using the manually shifted CT images .The reconstructed PET images using shifted CT images for attenuation correction were compared with the reference PET image (PET image corrected with misalignment free original CT image). VOI-based analysis , regression and Box and Whisker plots were determined using 500 VOIs located within the myocardial wall in each PET dataset. For accurate assessment of the activity distribution in myocardium wall, 17-segment bull's eye view analysis was evaluated for PET images. Results: The absolute percentage relative difference in uptake value increased in all simulated movements with increasing misalignments for both phantom and clinical studies. In patient studies, in reference to the bull's eye view models, VOI-based analysis and visual analysis of PET images in standard axes as evaluated by expert clinicians, the significant variation in uptake value in comparion with the reference PET images were observed in the anteroseptal (23.55±9.92) and lateroinferior (32.96±9.74)segments in backward and forward directions respectively. Conclusion: although misalignment can introduce artifactual nonuniformities in myocardial wall but the anterior,lateral and septal regions were more vulnerable by misalignment. The variation were more significant for right,backward and forward directions.so that were caused erroneous clinical interpretation even in little misalignment(5 mm).but the significant errors can observe in medium(10mm) mismatch for PET image corrected using shifted CT in the left ,down and up directions.
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