Line-Spread Function
An improved method of estimating spatial resolution of a gamma camera
is based on the use of a line-spread function (LSF). A long plastic tubing
filled with a radioactive solution is placed in the field of view of the detec-
tor. The gamma camera interfaced with a computer collects and stores
counts from the line source in a single view, and then the computer gener-
ates the LSF. The counts (response) obtained at incremental distances are
plotted against the distance from the center axis of the collimator to give a
bell-shaped LSF (Fig. 10.5). The FWHM of the LSF curve gives the spatial
resolution of the imaging device.
Spatial resolution by the LSF method varies with the design of the colli-
mator and is, therefore, different for parallel-hole, converging, and diverg-
ing collimators. Also, the FWHM values of the LSF may not represent the
true spatial resolution, because the scatter and septal penetration compo-
nents fall in the tail part of the LSF (i.e., below 50%) and therefore are not
accounted for.
124 10. Performance Parameters of Gamma Cameras
Fig. 10.5. Line spread function of a gamma camera equipped with a low-energy all-
purpose parallel hole collimator obtained in (a) air and (b) water at different dis-
tances using a 99mTc-line source. Note that the resolution deteriorates in water due
to attenuation.