Introduction

The use of radioactive isotopes for medical purposes has been investigated since 1920, and since 1940 attempts have been undertaken at imaging radionuclide concentration in the human body.

In the early 1950s, Ben Cassen introduced the rectilinear scanner, a “zero-dimensional” scanner, which (very) slowly scanned in two dimensions to produce a two-dimensional image of the radionuclide concentration in the body. In the late 1950s, Hal Anger developed the first “true” gamma camera, introducing an approach that is still being used in the design of virtually all modern camera’s: the Anger scintillation camera, a 2D planar detector to produce a 2D projection image without scanning.

The Anger camera can also be used for tomography. The projection images can then be used to compute the original spatial distribution of the radionuclide within a slice or a volume. Already in 1917, Radon published the mathematical method for reconstruction from projections, but only in the 1970s, the method was introduced in medical applications, first in CT and next in nuclear medicine imaging. At the same time, iterative reconstruction methods were being investigated, but the application of those methods had to wait for sufficient computer power till the 1980s.

The Anger camera is often called gamma camera, because it detects gamma rays. When it is designed for tomography, it is also called a SPECT camera. SPECT stands for Single Photon Emission Computed Tomography and contrasts with PET, i.e. Positron Emission Tomography, which detects photon pairs. Anger showed that two scintillation camera’s could be combined to detect photon pairs originating after positron emission. Ter-Pogossian et al. built the first dedicated PET-system in the 1970s, which was used for phantom studies. Soon afterwards, Phelps, Hoffman et al built the first PET-scanner (also called PET-camera) for human studies. Since its development, the PET-camera has been regarded nearly exclusively as a research system. Only in about 1995, it became a true clinical instrument.

Below, PET and SPECT will be discussed together since they have a lot in common. However, there are also important differences. One is the cost price: PET systems are about 4 times as expensive as gamma cameras. In addition, many PET-tracers have a very short half life (i.e. the time after which the radioactivity decreases to 50%), so it is mandatory to have a small cyclotron, a laboratory and a radiopharmacy expert in the close neighborhood of the PET-center.

An excellent book on this subject is “Physics in Nuclear Medicine”, by Cherry, Sorenson and Phelps SR Cherry et al. (2012). Two useful books have been published in the Netherlands, one to provide insight HY Oei et al. (n.d.), the other describing procedures JAJ Camps et al. (n.d.). An excellent book for researchers in the field is the one of H. Barrett and K. Meyers Harrison H. Barrett & Kyle J. Myers (2003). The International Atomic Energy Agency (IAEA) publishes books with free online access, e.g. IAEA (2015).