- From the IAEA: Diagnostic Nuclear Medicine - Image Quality and Quality Control
- From Harvard: Physical Characteristics of Nuclear Medicine Images (more detail than IAEA, but still not too technical)
- A short course in image quality with applications to Nuclear Medicine (state of the art, but very technical)
- Wikipedia pages on MTF, PSF, Poisson statistics, shot noise, signal to noise ratio
Many of the terms that we use to describe image quality are quite general and can be used to describe the quality of any two-dimensional image, not just those from a gamma camera. The online book The Joy of Visual Perception discusses many of these functions. See especially the chapter on Point and Line spread functions and Modulation Transfer Functions and click through the links.