Scintigraphy
Scintigraphy ("scint," Latin scintilla, spark) is a form of diagnostic test used in nuclear medicine, wherein radioisotopes (here called radiopharmaceuticals) are taken internally, and the emitted radiation is captured by external detectors (gamma cameras) to form two-dimensional[1] images. In contrast, SPECT and positron emission tomography (PET) form 3-dimensional images, and are therefore classified as separate techniques to scintigraphy, although they also use gamma cameras to detect internal radiation. Scintigraphy is unlike a diagnostic X-ray where external radiation is passed through the body to form an image.
By organ or organ system
Biliary system (Cholescintigraphy)
Scintigraphy of the biliary system is called cholescintigraphy and is done to diagnose obstruction of the bile ducts by a gallstone (cholelithiasis), a tumor, or another cause.[2] It can also diagnose gallbladder diseases, e.g. bile leaks of biliary fistulas.[2] In cholescintigraphy, the injected radioactive chemical is taken up by the liver and secreted into the bile. The radiopharmaceutical then goes into the bile ducts, the gallbladder, and the intestines. The gamma camera is placed on the abdomen to picture these perfused organs.[2] Other scintigraphic tests are done similarly.[2]
Lung scintigraphy
The most common indication for lung scintigraphy is to diagnose pulmonary embolism, e.g. with a ventilation/perfusion scan. Less common indications include evaluation of lung transplantation, preoperative evaluation, evaluation of right-to-left shunts.[3]
In the ventilation phase of a ventilation/perfusion scan, a gaseous radionuclide xenon or technetium DTPA in an aerosol form is inhaled by the patient through a mouthpiece or mask that covers the nose and mouth. The perfusion phase of the test involves the intravenous injection of radioactive technetium macro aggregated albumin (Tc99m-MAA). A gamma camera acquires the images for both phases of the study.
Bone
For example, the ligand methylene-diphosphonate (MDP) can be preferentially taken up by bone. By chemically attaching technetium-99m to MDP, radioactivity can be transported and attached to bone via the hydroxyapatite for imaging. Any increased physiological function, such as due to a fracture in the bone, will usually mean increased concentration of the tracer.
Heart
A thallium stress test is a form of scintigraphy, where the amount of thallium-201 detected in cardiac tissues correlates with tissue blood supply. Viable cardiac cells have normal Na+/K+ ion exchange pumps. Thallium binds the K+ pumps and is transported into the cells. Exercise or dipyridamole induces widening (vasodilation) of normal coronary arteries. This produces coronary steal from areas where arteries are maximally dilated. Areas of infarct or ischemic tissue will remain "cold". Pre- and post-stress thallium may indicate areas that will benefit from myocardial revascularization. Redistribution indicates the existence of coronary steal and the presence of ischemic coronary artery disease.[4]
Full body
Examples are gallium scans, indium white blood cell scans, Iobenguane scan (MIBG) and octreotide scans.
See also
References
- ^ thefreedictionary.com > scintigraphy Citing: Dorland's Medical Dictionary for Health Consumers, 2007 by Saunders; Saunders Comprehensive Veterinary Dictionary, 3 ed. 2007; McGraw-Hill Concise Dictionary of Modern Medicine, 2002 by The McGraw-Hill Companies
- ^ a b c d MedicineNet.com > Definition of Scintigraphy Last Editorial Review: 12/6/2003
- ^ Society of Nuclear Medicine Procedure - Guideline for Lung Scintigraphy. Version 3.0, approved February 7, 2004 [1]
- ^ George J. Taylor (2004). Primary Care Cardiology. Wiley-Blackwell. p. 100. ISBN 1405103868.
