Physical specification of a gamma camera.

Anger (1 ) , a number of papers describing both the physical characteristics of the instrument and its ap plications have been published (2—12) . However, the performance of the gamma camera has usually been discussed in terms of the parameters fundamental to a conventional scanner, and insufficient emphasis has been placed on characteristics that are unique to the camera. It is, of course, necessary to compare the camera with the scanner to assess its value, and consequently there has been much investigation into the sensitivity and limits of resolution of the camera. However, the uniformity of response over the crystal area is an equally limiting factor in the cam era's ability to represent accurately the differences in distribution of an isotope within a volume. Fur thermore, linearity, which is a measure of the image distortion of the spatial distribution of an isotope, is also a factor in camera performance. Except for line stagger or scalloping, linearity presents no prob lem in mechanically moving scanners. In practice, resolution, uniformity, linearity and sensitivity are interdependent, and because optimum operating conditions for one may not be optimum for the other parameters, some compromise based on the relative importance of each parameter must be arrived at. It is also important to keep in mind the fact that these parameters will vary over the sen sitive area of the crystal and that these variations should be included in the specification of camera performance. All of these factors have practical sig nificance because it is important for the performance of such an instrument to be readily measurable and for optimum operating conditions to be checked with the minimum time spent in routine adjustments. We will discuss the performance of a Nuclear Chicago gamma camera using a 28-cm-diameter, 1.27-cm-thick sodium iodide crystal in terms of the basic parameters mentioned above. We hope that the definitions described below for these parameters will simplify the assessment of the performance of gamma cameras. DEFINITIONS