Image quality

Image quality has a commonsense meaning that most people understand but it is difficult to find agreement about a precise technical definition. Most people rate image sharpness as the most desirable features of a high-quality image, but in medical imaging there is a general consensus that the final arbiter of image quality is diagnostic performance. A high-quality image is one that enables accurate diagnosis by an intelligent observer. There is also general agreement that it is important to be able to evaluate imaging systems objectively in order to set performance standards, optimize system parameters for maximum effectiveness, and determine which of two or more competing systems is best. The concept of task-dependent image quality is very important. The task provides a common ground for the comparison of imaging systems. For example, the performance of two systems that produce images with very different physical properties, such as magnetic resonance imaging and computed tomography, can be compared as long as the diagnostic task is the same.

The two components of an imaging system

It is convenient to think of imaging systems as having two major components: the first converts a radiant signal received from the patient under study into a detected image, and the second consists of image processing devices that convert the detected image into a displayed image with an appearance that is matched to the intelligent decision maker, which for the most part is a human observer.