Computations of the Signal-to-Noise Ratio for Medical X-Ray Imagers

If the signal in a medical X-ray imaging detector is formed by integrating the scintillation (or electrical) pulses, rather than by counting them, the signal-to-noise ratio is reduced by a factor which depends on the pulse height distribution. Formulas are expanded from Swank's publication to derive the signal-to-noise ratio for any given optical or electrical pulse-size distribution. A new quantity called noise-equivalent absorption is defined which bears a simple relationship to the signal-to-noise ratio of integrated X-ray imaging as the quantum absorption to the signal-to-noise ratio of photon-counting X-ray imaging.