10
Performance Parameters of
Gamma Cameras
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The quality and detail of an image obtained by gamma cameras are affected
by several parameters associated with these imaging systems. These para-
meters include spatial resolution, sensitivity, uniformity, and contrast, and
they are described here in detail. A brief description of the quality control
tests for gamma cameras is also included.
Spatial Resolution
The spatial resolution of a gamma camera is a measure of the ability of the
device to faithfully reproduce the image of an object, thus clearly depicting
the variations in the distribution of radioactivity in the object (Erickson,
1984). The spatial resolution of a gamma camera is empirically defined as
the minimum distance between two points in an image that can be detected
by the system. The overall spatial resolution (Ro) of a gamma camera com-
prises three components, namely, intrinsic resolution (Ri) of the detection
system, collimator resolution (Rg), and scatter resolution (Rs), and is given
by
(10.1)The smaller numerical values of Ro indicate better resolution and vice
versa.
Intrinsic Resolution
Intrinsic resolution,Ri, is the component of spatial resolution contributed
by the detector and associated electronics, and is a measure of how well an
imaging device can localize an event on the image. Intrinsic resolution arises
primarily from the statistical fluctuations in pulse formation that have been
discussed in the section entitled Gamma Ray Spectrometry in Chapter 8.
The statistical variations in the production of light photons after g-ray inter-
action in the detector and variations in the number of electrons emitted
R RRRoigs=++^222