TABLE 2-1 Half-Lives of Common Radionuclides. Positron emission tomography (PET) imaging with 2-[(18)F]fluoro-2-deoxy-D-glucose (FDG) forms the basis of molecular imaging. in the case of FDG (fluorodeoxyglucose) … Compton scatter often occurs when the path of a photon crosses two materials of differing density, such as soft tissue and bone, or bone and air. Cameras designed for scans involving positron emitters have all an annular (ring-like) structure. Scans with cameras of this kind are generally faster and offer much higher-resolution images than those with ETCD cameras. The light output varies depending on the crystal composition. In the process of radioactive decay, energy is released, usually in the form of a particle (positron and beta decay) or a photon (gamma decay). These are, as their name suggests, random in occurrence and are difficult to correct. The photons thus released have energies of 511 keV (0.511 MeV) and are detected by coincidence imaging as they strike scintillation crystals made of bismuth germinate (BGO), lutetium oxyorthosilicate (LSO), or gadolinium silicate (GSO). The majority of positron emitting isotopes are produced in a cyclotron. This concept will be explained later. Random events are the result of two positron decays occurring simultaneously, resulting in an errant LOR. Hence, PET provides molecular imaging of biological function instead of anatomy. Figure 2-1 Typical commercially available cyclotron. The advantages and disadvantages of the two methods are beyond the scope of this book, but the various scanner manufacturers utilize different protocols in the hope of acquiring the optimal image. The detection and localization of positron decay within the body is the means by which positron emission tomography (PET) images are created. Figure 2-5 Normal physiologic uptake of FDG. PET allows for the three-dimensional mapping of administered … Concept of 2D vs. 3D image acquisition and retractable septa. This is of no clinical significance, however, since the inherent resolution of a typical PET camera is approximately 5 mm due to design. Recently, commercial availability of FDG has increased such that more imaging facilities have ready access to FDG on a routine basis. These planar projections can then be used to three-dimensional image of where the radioactive tracers are located in the patient. Both gamma reach simultaneously a pair of opposing detectors placed on either side of the annihilation location. PET images are essentially a map of positron decay occurring within the body from the distribution of radiotracer in the body after administration, whether injected, administered orally, or inhaled. Coincidence events are photons detected 180 degrees apart within a certain time span, typically on the order of nanoseconds, to ensure true events are recorded rather than random events or scattered events. Previously, the short half-life of F-18 (110 minutes) obviated the need for a cyclotron in-house or in very close proximity to the imaging center. A normal PET scan (Figure 2-5) and a scan depicting treated neoplasm (Figure 2-6) are shown for comparison. This technique is known as Emission Tomography with Coincidence Detection (ETCD). Beta decay consists of an electron emission and does not produce medically useful images. However, in recent years, cyclotrons have been purchased by commercial companies to produce medically useful isotopes, specifically, positron emitting isotopes. In routine practice, both systems lead toaccurate attenuation correction. A PET image is color coded — different colors show various levels of cell activity. Combination PET-CT scanners provide the anatomical detail of CT scanning with the functionality of PET imaging in one machine (Figure 2-2). A typical CT scan is acquired in a 512 × 512 matrix, consisting of 262,144 pi-xels image, leading to significantly higher spatial resolution from a CT image when compared to a PET image, assuming an identical FOV for each scanner. These organs provide part of the background activity on PET scans. A typical CT scan is acquired in a 512 × 512 matrix, consisting of 262,144 pi-xels image, leading to significantly higher spatial resolution from a CT image when compared to a PET image, assuming an identical FOV for each scanner. Situations in which there is more falsely elevated density than expected (e.g., intravenous contrast or metallic prostheses) can lead to additional artifacts; however, these artifacts are relatively easy to identify. Previously, cyclotrons were located only in research institutions and academic centers, due to the high cost and resources needed to operate and maintain a cyclotron. Now titled Principles and Practice of PET and PET/CT, this Second Edition includes many PET/CT images and new chapters dealing with CT scanning and PET/CT image fusion. Normal tissue undergoing physiologic metabolism also accounts for the remaining background activity on PET scans. Beta decay consists of an electron emission and does not produce medically useful images. A positron emission tomography (PET) scan is an imaging test that helps reveal how your tissues and organs are functioning. Abstract. Economic Considerations of PET Scanning in Diagnosis, Staging, and Radiation Therapy Treatment Planning, PET-CT in Radiotherapy Treatment Planning. Once synthesized, sterility and purity tests are performed prior to patient administration to ensure patient safety. Advantages of iterative methods are better attenuation correction (which will be explained later) and better scatter correction, leading to significantly better image quality. However, in recent years, cyclotrons have been purchased by commercial companies to produce medically useful isotopes, specifically, positron emitting isotopes. A CT scan shows the exact locations of the body’s organs and also can show abnormal growths. Positron emitting radionuclides will be discussed here. Advantages of iterative methods are better attenuation correction (which will be explained later) and better scatter correction, leading to significantly better image quality.6,7 Images are typically reconstructed in axial, sagittal, and coronal projections and are displayed with and without attenuation correction. 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