Medical displays

Abstract

Medical imaging is an integral part of any healthcare practice today and cuts across multiple disciplines and clinical special specialties to provide information to clinicians that will help them render diagnostic decisions and make treatment recommendations. The technologies available have expanded rapidly in recent years, and the number and range of image types clinicians have available to them is vast. Radiologic images are the most commonly acquired and used, but other specialties such as pathology, ophthalmology, and dermatology and the telemedicine implementation of nearly every other clinical specialty are acquiring, archiving, transmitting, and viewing images on a daily basis. Although the acquisition technologies differ, all of these images do have one thing in common - they must be displayed in a fashion that the healthcare professional can view them and render an accurate and efficient diagnostic decision. In order for that to happen, the display itself must be considered as well as the environ-ment in which the display is located. This chapter will review some of the basic factors to consider for the optimal display of medical images. Before discussing the display options, it is important to realize that a key goal when choosing a display device for a given medical imaging application is to match the output of the imaging system to the display and then optimize the display to the observer’s visual system for a given reading environment. Thus there are a few properties of the human eye-brain system that are useful to understand before talking about the displays themselves. The human visual system operates on (and limited by) its anatomic and physiological properties. Photoreception is the mechanism by which light from the environment (in this case the display) produces changes in the photoreceptors or nerve cells in the retina. Rods (about 115 million rods) sense contrast, brightness, and motion and are located mostly in the periphery of the retina; and cones (6.5 million cones) are for fine spatial resolution and color vision, and they are located in the foveal and parafoveal regions. When light hits these receptors, pigments undergo chemical transformations that convert light energy into electrical energy, which then acts on nerve cells that connect the eye to the optic nerve and subsequent visual pathways that extend to the visual cortices in the brain. Two key visual properties that relate to displays are spatial and contrast resolution. Spatial resolution is the ability to see fine details and is highest at the fovea and declines sharply toward the retinal periphery. Contrast resolution is the ability to distinguish differences in intensity in an image. It permits one to distinguish between objects and background in an image. Contrast resolution depends on both the quality of the image and the visual capabilities of the human observer. Therefore, whenever a new type of image, display, or presentation state is developed, it is necessary to characterize its contrast resolution.