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Positron emission tomography (PET) is a noninvasive modality that produces tomographic images of the distribution of a radionuclide-labeled tracer injected in the body. As the name suggests, PET imaging is based on radionuclides that decay by positron emission (Figure 1.1A. For example, fluorine-18 (F)decays to oxygen-18 (O), emitting a positron (β) and a neutrino (v): (The neutrino does not affect PET imaging and may be ignored in this discussion.) A positron is an elementary particle classified as antimatter and is analogous to an electron, having identical mass but opposite electrical charge. The positron is ejected from the nucleus and rapidly loses its kinetic energy through collisions with numerous nearby electrons. Since antimatter and matter are mutually unstable, the positron and an electron then undergo a process known as and are converted into a pair of gamma-ray photons. Because total energy is conserved, each gamma ray has energy of 511 keV, which is equivalent to the mass of the positron and of the electron according to the well-known relationship . Because total momentum is conserved, the two gamma rays travel in opposite directions with a relative angle very close to 180 degrees.

The words (CT) refer to a method of tomographic imaging in which a “tomographic,” or cross-sectional, slice is imaged with the aid of computer processing to obtain an exact representation of the slice. Tomographic imaging is important since in conventional projection imaging, such as plane-film x-ray imaging, a small feature may be difficult to visualize because of the confusing superposition of many overlying layers of different structures. X-ray tomographic imaging was developed more than 50 years ago as an approach to cross-section slice imaging. One of the most successful commercial devices was the axial tomograph developed by Takahashi, which in some ways is the precursor to modern CT scanners. The x-ray tube and a plane film positioned at a nearly perpendicular angle rotated around the body, exposing a single cross-section slice. The x-ray projections at each angle were recorded as crossing the film, and were accumulated. Today we call this a simple backprojection image. Although these images were useful, they were somewhat blurred because simple backprojection is only a first-order solution to the problem of reconstructing a cross-section image from rotational projections. This is where the computer part of the name becomes critical: to provide digital processing to remove the tomographic blur. The projection data are gathered and backprojected using digital data rather than film. The resulting backprojection image is then “deblurred,” or reconstructed, by applying a simple sharpening filter, which is sometimes referred to as a . You can think of this process as a kind of edge-enhancement process, and it is sometimes referred to as filtered backprojection. In the end, the marriage of computer filtering and axial tomography resulted in the new field of computed tomography.

The recent development of combined positron emission tomography/computed tomography (PET/CT) instrumentation is an important evolution in imaging technology. Since the introduction of the first prototype CT scanner in the early 1970s, tomographic imaging has made significant contributions to the diagnosis and staging of disease. Rapid commercial development followed the introduction of the first CT scanner in 1972, and within 3 years of its appearance more than 12 companies were marketing, or intending to market, CT scanners; about half that number actually market CT scanners today. With the introduction of magnetic resonance imaging (MRI) in the early 1980s, CT was, at that time, predicted to last another 5 years at most before being replaced by MRI for anatomical imaging. Obviously, this did not happen, and today, with multislice detectors, spiral acquisition, and subsecond rotation times, CT continues to develop and to play a major role in clinical imaging, in particular for the assessment of cardiovascular disease. Indeed, one of the main driving forces for the current development in CT is for applications in cardiology.

This chapter focuses on several applications of tracer-kinetic methods to PET imaging of the heart. It will be useful, first, to review some general, basic principles of compartment analysis that have been well described by several other authors. This review emphasizes the most important underlying assumptions and requirements for obtaining accurate quantitative measurements of myocardial perfusion or metabolism from dynamic PET image data. The review is followed by descriptions of several different tracer-kinetic techniques that have been used for imaging tissue perfusion, viability, and oxygen consumption, using a variety of radiolabeled tracers.

The clinical value of cardiac positron emission tomography (PET) imaging was demonstrated more than 20 years ago, but its clinical utilization has been low until recently. This was due to the limitation of PET imaging to research centers with a PET camera and a cyclotron, its great expense, and the lack of reimbursement for clinical PET studies. Another disincentive was lack of standardized software for cardiac PET image processing, display, or regional quantification on most PET imaging systems.

Cardiac computed tomography (CT) is a noninvasive imaging test that requires the use of intravenously administered contrast material and high-resolution, high-speed CT machinery to obtain detailed volumetric images of cardiac anatomy, coronary circulation, and great vessels. Most contrast-enhanced CT examinations in the West are performed with nonionic iodinated contrast media. However, adverse events still exist and consist of allergylike contrast reactions, chemo- or osmotoxic contrast reaction, contrast media-induced nephropathy, injection-related adverse events, and complications due to various coexisting conditions. Identification of patients at risk for developing contrast media reactions is likely to prevent serious adverse events and to enhance safety. Likewise, appropriate management strategies can be adopted to reduce morbidity and mortality associated with adverse reactions of iodinated contrast media used in cardiac CT scanning.

The development of magnetic resonance imaging and computed tomography (CT) of the heart has provided significant advances in the diagnosis and management of patients with acquired and congenital heart disease. Certainly, the dramatic improvement in temporal resolution obtained using electrocardiogram (ECG)-gated multidetector CT scanning has set the stage for the implementation of this mature technology into the daily practice of cardiac medicine. A particular characteristic of cardiac CT scanning is acquisition of image data in the axial body plane. That is, conventional cardiac imaging has been in radiographic projection (plain films, cineangiography) and, subsequently, in tomographic section (echocardiography and nuclear imaging). However, image data was never presented to the cardiac imager in axial body section. Although the heart lies obliquely in the chest, and the axial body section therefore displays cardiac structure oblique to the intrinsic cardiac axes, image data obtained in this format provides a wealth of anatomic information. Since most cardiologists are not familiar with image data displayed in this view, the cardiac imager utilizing this exciting modality should become familiar with the appearance of the heart in axial section. Furthermore, acquisition of isotropic image voxels on higher resolution (namely, 64-detector) CT scanners provides a robust data set for the reconstruction of the heart in arbitrary or traditional cardiac-based sections. To construct these axes, one must first be able to recognize standard cardiac landmarks on the original axial data acquisition sets.

With the introduction of dual-modality positron emission and transmission computed tomography (PET/CT) systems, concurrent acquisition and subsequent generation of coregistered functional (PET) and anatomic (CT) images have become the preferred diagnostic method. This capability has caused concern about increased patient radiation doses and occupational exposures to healthcare personnel. To address this concern, we need to determine the patient’s optimum administered radiopharmaceutical dosage and the appropriate CT scanning parameters as well as to instruct personnel in radiation-exposure-reduction techniques. The CT component can be used to correct for tissue attenuation, which is otherwise accomplished with an external radionuclide source, or to generate diagnostically suitable CT images. In either case, there should be an attempt to minimize the radiation dose while maintaining the diagnostic efficacy of the scan.

In the operation of a stress test laboratory, the foremost concerns are patient safety, study quality, and efficiency. In addition to quality of care, customer service also plays a significant role in ensuring that patients have a satisfying experience and that the referring physicians continue to utilize services. Myocardial positron emission tomography (PET) and PET/computed tomography (CT) perfusion imaging are noteworthy for high efficiency, rapid throughput, and, in a high-volume setting, low operational costs. This chapter reviews the requirements regarding equipment, personnel, patient screening and preparation, and stress protocols used in a cardiac PET and integrated PET/CT imaging laboratory.

The primary clinical applications of positron emission tomography (PET) myocardial perfusion imaging are to diagnose, localize, and quantify the severity of coronary artery stenoses. As a result, most clinical applications of myocardial perfusion imaging are performed in conjunction with stress testing. Exercise stress testing with single photon emission computed tomography (SPECT) is widely used in the evaluation of patients with known or suspected coronary artery disease. Although exercise stress testing offers several advantages, the short physical half-life of most PET radiotracers makes it logistically impractical for use in conjunction with PET imaging. In addition, a significant proportion of patients referred for stress imaging are unable to exercise adequately due to difficulties with ambulation related to prior stroke, peripheral vascular disease, orthopedic problems or deconditioning. Submaximal exercise can reduce test sensitivity for detection of ischemic heart disease and should be avoided. Pharmacologic stress testing with dipyridamole, adenosine or dobutamine infusions are useful to evaluate patients that are unable to exercise or have suboptimal exercise capicity. Chapter 9 provides a detailed discussion of stress protocols. The aim of this chapter is to provide a review of clinically useful imaging protocols for evaluation of CAD, along with guidelines for quality control of PET and PET/CT images. For a better understanding of protocols for PET myocardial perfusion imaging, the reader should be familiar with basic principles of PET and PET/CT (discussed in Chapters 1 and ) and PET radiopharmaceuticals (discussed in Chapter 5).