Bush__The_Essential_Physics_for_Medical_Imaging - Biomedical ...

FIGURE 21-1. Modern rectangular head, large field-of-view scintillation camera.(Courtesy of Siemens Medical Systems, Nuclear Medicine Group.)with higher resolution collimators, thus producing images of better spatial resolution.The scintillation camera is also more flexible in its positioning, permittingimages to be obtained from almost any angle. Although it can produce satisfactoryimages using x- or gamma rays ranging in energy from about 70 keY (TI-201) to364 keY (I-131) or even 511 keY (F-18), the scintillation camera is best suited forimaging photons with energies in the range of 100 to 200 keY. Figure 21-1 showsa modern scintillation camera.Scintillation cameras of other designs have been devised, and one, the multicrystalscintillation camera, achieved limited commercial success. However, thesuperior performance of the Anger camera for most applications has caused it todominate nuclear imaging. The term scintillation camera will refer exclusively to theAnger scintillation camera throughout this chapter.Design and Principles of OperationDetector and Electronic CircuitsA scintillation camera (Fig. 21-2), contains a disk-shaped or rectangular thalliumactivatedsodium iodide NaI(TI) crystal, typically 0.95 cm ('/s inch) thick, opticallycoupled to a large number (typically 37 to 91) of 5.1- to 7.6-cm (2- to 3-inch)diameter photomultiplier tubes (PMTs). PMTs were described in Chapter 20. Somecamera designs incorporate a Lucite light-pipe between the glass cover of the crystaland PMTs; in others, the PMTs are directly coupled to the glass cover. In mostcameras, a preamplifier is connected to the output of each PMT. Between thepatient and the crystal is a collimator, usually made of lead, that only allows x- orgamma rays approaching from certain directions to reach the crystal. The collima-