The Relationship Between NMR and Other Functional Measurement Techniques

Abstract

Although nowadays radioisotope tests are synonymous with imaging, the original application of radioisotope studies was in the sphere of functional measurement. One of the earliest techniques for measuring in vivo metabolism was the use of radioiodine to study the function of the thyroid gland in health and disease (Rall 1956). The development of improved Geiger counting systems and scintillation detectors gave clinicians the opportunity to measure and image various aspects of body physiology including cerebral perfusion and cardiac function. The scintillation counter is a highly sensitive device but requires suitable collimation to define an area of interest within the body. The development of collimators and dual crystal counting systems produced an isosensitive technique which could measure radioactivity in any part of the body without the problem of errors due to attenuation. However the difficulty of ensuring that all of the uptake came from the organ alone, without the complications of including radiation from surrounding tissues, continued until the advent of rectilinear scanning and the use of the Anger camera. The current combination of gamma camera and a digital computer is a powerful one, enabling accurate estimation of radiation emanating from a defined area within the body. Emission tomography has further improved measurement techniques so that radioactivity distributions in three dimensions can be defined and measured (Webb et al. 1985).