Nuclear Medicine

Advances in monoclonal antibody research, radio-pharmaceuticals, and computer technology have allowed nuclear medicine practitioners to probe deeper into the workings of the human body. Tumor-specific antibodies have been labeled or mixed with radiopharmaceuticals and administered to patients for both localizing and treating various types of tumors.

Conventional planar studies do not give detailed information about the depth of an abnormality seen on an image. The tomographic (tomos is the Greek word for slice) principle has been applied to nuclear medicine procedures enabling the physician to see regions of an organ in slices or layers. Two tomographic methods in nuclear medicine are single proton emission computerized tomography (SPECT) and positron emission tomography (PET). Like conventional images, tomographic images show how a radiopharmaceutical is distributed within an organ. Areas of normal, increased, or decreased distribution can be seen, thus revealing areas of altered biochemical and physiological function. When a tomographic study is obtained, the gamma camera detector circles the body and obtains multiple two dimensional images at various angles. The images are reconstructed by a special computer program and an organ can be visualized, in slices or layers, from top to bottom, front to back, and left to right. Viewing organs in slices eliminates interference from areas overlying a possible abnormality.

Single photon emission computed tomography (SPECT) studies are most often used for cardiac imaging and brain imaging, although the tomographic technology can be helpful for viewing other organs as well. SPECT studies use conventional radionuclides such as ^99mtechnetium and ¹²³Iodine. PET studies use only positron emitting radionculides such as ¹¹Carbon, and ¹⁸Fluorine. The radionuclides used for PET are very short lived and therefore a cyclotron must be on site. Cyclotrons and PET equipment is very expensive, so there are few institutions that perform these tests. Their clinical use is consequently very limited. The focus of PET is biochemical rather than structural and is used most often for exploring neurochemical phenomena in the brain. PET can help distinguish one form of dementia from another, test for psychiatric drug effectiveness, and demonstrate regional metabolic differences between certain psychiatric disorders. PET and SPECT imaging procedures are used to study the areas of the brain affected by strokes, epilepsy, and Parkinson's disease. Newer SPECT radiopharmaceuticals, because of their ability to cross the blood-brain barrier, have made it possible to study brain function and metabolism. Since assessing brain function is important to both physical medicine and behavioral medicine, SPECT may very well move these studies into the clinical setting.