It is the functional, as opposed to the morphological, capability of nuclear medicine investigations that is their great strength. Initially, the technique involved the injection of suitable gamma-emitting radionuclides into the blood or CSF to produce an image of regional function in the brain (cerebral scintigraphy) or of CSF flow (radionuclide cisternography). Disease was then detected by assessing the degree to which the so-called blood brain barrier could be breached or to what extent the normal channels of CSF flow were altered.

If a solitary gamma-ray detection device, such as a gamma camera, is used to map the radionuclide distribution in one plane at a time, the resulting images are referred to as planar images. Alternatively, if the detector is designed to accumulate images at intervals over 360° around the brain, computer techniques similar to those described in Chapter 1(a) can be used to reconstruct cross-sectional representations of function.

Planar cerebral imaging

Routine cerebral scintigraphy became universally available when appropriate detectors and radionuclides could be combined. The basis of all detection systems is the scintillation unit (Fig. 1.38), containing the all-important sodium iodide crystal and photomultiplier tubes. These constituted the old rectilinear scanners, which preceded the gamma camera, invented by Hal Anger in 1961 (Fig. 1.39). Gamma cameras make use of one large scintillator crystal and a number of photomultiplier tubes arranged so that the spatial relationships of radioactive tracers in the brain can be precisely recorded, stored and displayed in many ways on a screen or as hard copy (Fig. 1.40).