The Physics of Medical X-ray Imaging

In this section, we will discuss a model of human visual perception called the Rose model, named after its formulator Albert Rose. Dr. Rose was a scientist at the Radio Corporation of America (RCA) investigating the basic operating parameters of television in the 1940's and 1950's. In particular, he was trying to relate levels of contrast, resolution, and noise. Isaac Newton once said, "To see over the horizon, you must stand on the shoulders of giants". This has occurred over and over in science, for example when Johannes Kepler built his model of the heliocentric universe based on the painstaking data of planetary motion collected by Tycho Brahe. In much the same way, Rose built his model of human visual perception on the painstaking data of Richard Blackwell. We therefore will digress and talk about Blackwell's studies, before continuing with the discussion of the Rose model and its application in diagnostic radiology. Richard Blackwell was a scientist who worked on visual perception studies for the United States Navy during World War II. The Navy was interested in what level of light and how large of an object was required by a sailor to spot an enemy vessel at night. It is obvious that a large light is easier to see than a smaller light, and that a bright light is easier to see than a dim light. But is a large dim light easier to see than a small bright light? The Navy (or someone in the Navy) wanted to know the answer to this question, and provided Blackwell with funds to conduct this research. The bygone days of governmental largess for research are apparent in the study that Blackwell performed. For his work, he hired 20 young women and kept them housed and fed in a dormitory built close to his laboratory. For two years he had the women observe simple images of gray circles on plain backgrounds. During each observation, each woman reported whether or not she saw the circle, and in which quadrant of the projection screen it was located. Blackwell and his young female subjects performed thousands of observation studies, and slowly out of this painstaking work emerged a pattern which related the size of the target and the contrast level between the target and background, to the level of illumination (or noise level) of the scene. The results published in graphical form by Blackwell formed …