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An Index to Compare the Performance of Scintigraphic Imaging Systems

University of California Medical Center, San Francisco, California

Correspondence: For reprints contact: F. David Rollo, Div. of Nuclear Medicine, University of California Medical Center, San Francisco, Calif. 94143.

ABSTRACT

The contrast-efficiency function is a suitable means of describing the spatial-resolution characteristics of a system but cannot be used to describe total-system performance since it does not include the factor of plane sensitivity. The concept of performance index is presented as a measure of total-system performance. This function includes the system's spatial resolution in terms of the contrast-efficiency function and plane sensitivity as measured by statistical fluctuation. The index has special merit in that it measures how well a given system will reproduce a specific input problem in the image plane. Therefore, when used to compare the performance of various systems or to study the effect of varying a parameter within a given system, all comparisons are made on the basis of how well the systems in question are able to reproduce an object having specific geometry in the image plane for equal times of observation. The results of experimental studies show that for small lesion sizes, systems having high spatial resolution give the best performance whereas for large lesions, the system having the highest plane sensitivity gives the best results. For intermediate lesion sizes, the concept shows, as should be expected, that the system having the optimum trade-off between spatial resolution and plane sensitivity for the lesion size evaluated gives the best performance.

One problem, which is of minor importance, is that the index does not as yet include the effect of a change in MTF with distance off the focal plane. This effect will only be important when evaluating the performance of lesion detection when the size of the lesion is such that the MTF varies significantly over the source distance. Application of the performance index concept in future investigations includes the following: (A) pulse-amplitude discrimination level studies on radioisotopes in clinical use; (B) total-system performance studies of collimators available for scintigraphic imaging systems; and (C) comparison of the systems performance of the various stationary scintigraphic imaging devices currently available.