Imaging distribution of radioactivity within the human body II. Collimator point response function effects in optimum data processing

In the present study we investigate the effects of collimator response function on optimum fidelity, where we again employ the mean-square fit measure of fidelity. At a fixed count rate we find (as expected) that delta-function collimation is optimal. The importance of this result is that the theoretic performance of the delta-function collimator gives an ideal standard by which we can measure the performance of more practical collimators. In studying collimators of finite width we find that the form of the collimator response function can have a significant effect on the accuracy of imaging the radioisotope distribution. For example, one of the hypothetical clinical situations discussed suggests that choice of collimator shape can save a factor of ten or more in needed count total. With all collimator shapes considered, we find that for fidelity one feature of a good collimator is that its resolution-width should be about one-half the width of the essential structure of the isotope distribution (when the expected count total is proportional to the square of the collimator resolution-width).