Diagnostic interventions in nuclear medicine

Abstract

Diagnostic interventions in nuclear medicine may be defined as the coadministration of a nonradioactive drug or application of a physical stimulus or physiologic maneuver to enhance the diagnostic utility of a nuclear medicine test. The rationale for each interventional maneuver follows from the physiology or metabolism of the particular organ or organ system under evaluation. Diagnostic inference is drawn from the pattern of change in the biodistribution of the tracer in response to the intervention-induced change in metabolism or function.In current practice, the most commonly performed interventional maneuvers are aimed at studies of the heart, genitourinary system, hepatobiliary system, and gastrointestinal tract. The single most commonly performed interventional study in the United States is the stress Thallium-201 myocardial perfusion scan aimed at the diagnosis of coronary artery disease. The stress portion of the study is accomplished with dynamic leg exercise on a treadmill and is aimed at increasing myocardial oxygen demands. Areas of myocardium distal to hemodynamically significant lesions in the coronary arteries become ischemic at peak stress due to the inability of the stenotic vessel to respond to the oxygen demand/blood flow needs of the myocardium. Ischemic areas are readily recognized as photopenic defects on scans obtained immediately after exercise, with "normalization" upon delayed imaging.Diuresis renography is aimed at the differential diagnosis of hydroureteronephrosis. By challenging the urinary tract collecting structures with an augmented urine flow, dilated, unobstructed systems can be differentialed from systems with significant mechanical obstruction. Obstructed systems have a low ability to respond even after effective diuresis, resulting in a characteristic prolonged retention of the radiotracer.Hepatobiliary interventions are most commonly employed in the clinical setting of suspected acute cholecystitis. Administering a cholecystogogue before a hepatobiliary tracer promotes visualization of the gallbladder by causing it to go through a contraction/filling cycle in gallbladder by causing it to go through a contraction/filling cycle in which the filling phase occurs during maximum exposure to the radionuclide. This maneuver can convert a false positive study that suggests the presence of acute cholecystitis to a true negative study. Other gastrointestinal interventions are aimed at enhancing the detection of gastroesophageal reflux and gastrointestinal bleeding.Many new interventions have been developed that are currently aimed at research problems rather than clinical problems. Elegant studies eliciting cortical activation in response to visual, auditory, and cognitive stimulae have been described for the brain and show clinical promise for the future. New interventions are also under investigation for the heart and kidney. The development of new tracers and instrumentation will continue to be paralleled by the development of new interventional maneuvers.