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Basic Science Investigations |
1 Division of Cardiology, Department of Medicine, University of Texas Medical School, Memorial Hermann Hospital, Houston, Texas
2 Weatherhead PET Center for Preventing and Reversing Atherosclerosis, University of Texas Medical School, Memorial Hermann Hospital, Houston, Texas
3 Department of Medicine, Division of Cardiology, University of Texas Medical School, Memorial Hermann Hospital, Houston, Texas
Misregistration between attenuation and emission images causes artifactual abnormalities on cardiac PET images that result in false-positive defects. This study determines the frequency and mechanisms of misregistration artifacts, identifies their predictors, and validates a method for their routine clinical identification, prevention, or correction. Methods: We performed 1,177 consecutive diagnostic myocardial perfusion PET studies using 1 of 3 protocols: (a) 3 initial consecutive measured attenuation correction (MAC) scans, followed by resting and dipyridamole emission scans; (b) an initial MAC scan (early MAC), followed by emission scans; and (c) a MAC attenuation scan obtained after emission scans (late MAC). Emission images were manually shifted to obtain coregistration with attenuation and reconstructed again using shifted emission data that eliminated artifactual defects. Measurements on PET images included heart size, heart and diaphragm displacement after dipyridamole, objective quantitative misregistration of attenuation and emission images, and size or severity of image defects before and after shifting emission images. Results: Of 1,177 rest-dipyridamole PET perfusion studies, 252 (21.4%) had artifactual defects due to attenuation–emission misregistration. By shifting emission images, quantitative severity and size of misregistration and artifactual defects significantly decreased (P < 0.001) with visual normalization. Artifactual defects were predicted by horizontal plane misregistration (odds ratio [OR] = 1.545, confidence intervals [CI] = 1.113–2.145, P = 0.009), body mass index (OR = 2.659, CI = 1.032–6.855, P = 0.043), and whole heart area in the horizontal plane at rest (OR = 1.096, CI = 1.018–1.179, P = 0.015). Quantitative misregistration was predicted by diaphragm displacement between rest and dipyridamole (P = 0.001, CI = 0.158–0.630), body mass index (P = 0.005, CI = 0.202–1.124), and whole heart area in the horizontal plane at rest (P = 0.004, CI = –0.144 to –0.028). Diaphragm displacement was significantly larger for obese compared with lean patients (P = 0.027) during the initial 10 min of the imaging protocol. Conclusion: Misregistration of attenuation and emission images is common in cardiac PET imaging and causes artifactual defects predicted by diaphragmatic displacement, body mass index, and heart size. Multiattenuation imaging sequences and manual, visually optimized coregistration of attenuation and emission images substantially eliminate artifacts for reliably identifying mild perfusion defects of early nonobstructive coronary atherosclerosis as the basis for intense lifestyle and pharmacologic treatment.
Key Words: PET • image registration • heart • attenuation • artifact
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