Abstract
The A.Rose (1974) model of signal-to-noise ratios in images has been applied to diagnostic imaging instrumentation, extending it by taking into account effects due to finite spatial resolution, background effects and texture. The model leads to an understanding of the impact of the physics of the total system (object and instrument) on output contrast and signal-to-noise ratios. Principally, it leads to an understanding of the fact that nuclear images ar not (by and large) statistics limited. The model can also be used to compare different imaging techniques. To the extent that the signal-to-noise ratio is a necessary but not sufficient estimator of the detectability of a lesion, the model does not provide a complete description of the imaging characteristics of an instrument.