Medical Physics

Unit Overview

This elective is concerned with the basic physics principles underlying human vision and hearing to make sense of the environment. It begins by considering the structures of the eye and its optical system for adjusting to different object distances. Defects of vision and the study of their corrections are introduced. Resolution is introduced to explain the fineness of detail discernible by the eye. The question of how colour vision is generated leads to the study of the rods and cones in the retina. Rods are responsible for vision in dim light while cones are responsible for the more acute vision experienced in ordinary daylight conditions. A brief look at the structure of the ear serves to introduce students to concepts of transferring energy using a transducer and how different frequencies of sound waves are discriminated in the inner ear. Attention is then given to the applications of sound waves and visible light for seeing inside the body. A brief look at the work of ultrasound scanners and endoscopes serves to introduce students to pulse-echo and the total internal reflection of waves. Ionizing radiation, such as X-rays and gamma rays, is introduced to students as an alternative means of examining the anatomical structures and functions of a body for medical diagnosis. In hospitals and clinics around the world, literally hundreds of thousands of patients daily receive medical imaging tests in which X-rays, radionuclides, ultrasound and computed tomography (CT) are used. In virtually all these devices, physics has developed from our understanding of the electromagnetic spectrum, the radioactivity of specific nuclides and the wave properties of ultrasound beams. Such devices have enabled radiologists to see through the body without surgery. The medical uses of radioactive substances are introduced to students and the ways in which gamma radiation can be detected by gamma cameras to produce images for medical diagnosis are considered. It should be emphasised that the development of new imaging modalities is an evolutionary process. It may start with the discovery of a new physical phenomenon or a variation of an existing one. At all stages, expertise in physics is essential. There is considerable interest in medical physics in the field of radiation oncology, nuclear medicine and radiology, and some students will want to know more about such developments.