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Cardiac positron emission tomography (PET) myocardial perfusion imaging is an outstanding tool for diagnosis and risk stratification of patients with known or suspected coronary artery disease with many important differences compared to SPECT imaging. Its clinical use in assessing patients for CAD as well as other nonperfusion indications is expanding rapidly. Cardiac PET offers excellent diagnostic accuracy and image quality, low radiation exposure as well as a noninvasive means of measuring myocardial blood flow reserve. Cardiovascular PET is becoming an important tool for nuclear cardiologists to consider not only for perfusion imaging, but also for a growing number of other cardiovascular conditions such as myocardial viability, infection, and inflammation. Its role in nuclear cardiology has expanded with the increased and continuous availability of PET radiopharmaceuticals and PET camera systems (see Chapters 3 and 4 on radiopharmaceuticals and instrumentation). This chapter will review the principles of cardiovascular PET, data on diagnostic accuracy, image quality, radiation exposure, indications, and addition of myocardial blood flow (MBF) for myocardial perfusion imaging (MPI), as well as exciting new nonperfusion applications.
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PRINCIPLES OF CARDIAC PET
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PET imaging provides superior temporal and spatial resolution of radioactive atoms as they decay. A PET radioactive tracer, which has been engineered to be taken up in to the organ of interest, is injected into the patient. After it reaches the target organ, the radioactive agent begins to decay and emits a positron (Fig. 10-1). This positron then collides with a nearby electron. The resulting collision causes annihilation of both an electron and a positron, creating a high-energy discharge of 1.02 MeV. This energy is split into two gamma rays of 511-keV energy, which are emitted 180 degrees from each other. For image collection, multiple detectors encircle the patient; absorption from both emissions simultaneously occurs, and events that are not 180% are eliminated. The distance to the annihilation event impacts ultimate image quality. The processing of these simultaneous events forms the basis of PET imaging.1
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CARDIAC PET INSTRUMENTATION
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Cardiac PET instrumentation is discussed in detail in Chapter 4. A PET camera appearance is similar to a computed axial tomography (CT) system. However, in the gantry of the PET camera are multiple detectors placed circularly around the patient (Fig. 10-2). These detectors are grouped into cassettes filled with a specified number of crystals (4,000–24,000). Data from the crystals are then transmitted to photomultiplier tubes similar to Single Photon Emission Computed Tomography (SPECT) imaging. In contrast to SPECT acquisition which requires multiple acquisitions from the same crystals rotating spatially around the patient, PET data acquisition occurs simultaneously surrounding the patient. Most scanners are full-ring design but some have partial-ring detectors with a rapidly rotating gantry.2 An attenuation correction scan with either ...