What is contrast to noise ratio?

Contrast to noise ratio (CNR) is a measure used in medical imaging to assess the quality of an image. CNR is defined as the ratio of the difference in signal intensity between two regions of interest (ROI) divided by the noise level in the image. In other words, CNR measures the ability of an imaging system to produce clear and distinguishable images by comparing the strength of the signal that represents the desired information to the noise present in the image. A higher CNR indicates a better image quality whereas a lower CNR indicates low image quality or noise. CNR is commonly used in the fields of radiology, cardiology, and oncology to evaluate the effectiveness of imaging techniques and to optimize image quality for diagnostic purposes.