| Scintigraphy | |
|---|---|
 Scintigraphy | |
| ICD-9-CM | 92.0-92.1 |
| MeSH | D011877 |
| OPS-301 code | 3-70 |
Scintigraphy (from Latinscintilla, "spark"), also known as agamma scan, is a diagnostic test innuclear medicine, whereradioisotopes attached to drugs that travel to a specific organ or tissue (radiopharmaceuticals) are taken internally and the emittedgamma radiation is captured bygamma cameras, which are external detectors that form two-dimensional images[1] in a process similar to the capture ofX-ray images. In contrast,SPECT andpositron emission tomography (PET) form 3-dimensional images and are therefore classified as separate techniques from scintigraphy, although they also usegamma cameras to detect internal radiation. Scintigraphy is unlike a diagnostic X-ray where external radiation is passed through the body to form an image.
Scintillography is animaging method ofnuclear events provoked bycollisions orcharged current interactions among nuclear particles orionizing radiation andatoms which result in a brief, localised pulse ofelectromagnetic radiation, usually in thevisible light range (Cherenkov radiation). This pulse (scintillation) is usually detected and amplified by aphotomultiplier orcharge-coupled device elements, and its resulting electrical waveform is processed bycomputers to provide two- and three-dimensional images of a subject orregion of interest.
Scintillography is mainly used inscintillation cameras inexperimental physics. For example, hugeneutrino detection underground tanks filled withtetrachloroethylene are surrounded by arrays of photo detectors in order to capture the extremely rare event of a collision between the fluid's atoms and aneutrino.
Another extensive use of scintillography is inmedical imaging techniques which usegamma ray detectors calledgamma cameras. Detectors coated with materials which scintillate when subjected to gamma rays are scanned with optical photon detectors andscintillation counters. The subjects are injected with specialradionuclides which irradiate in the gamma range inside the region of interest, such as theheart or thebrain. A special type of gamma camera is theSPECT (Single Photon Emission Computed Tomography). Another medical scintillography technique, thePositron-emission tomography (PET), which uses the scintillations provoked byelectron-positron annihilation phenomena.
Scintigraphy of thebiliary system is calledcholescintigraphy and is done to diagnose obstruction of thebile ducts by a gallstone (cholelithiasis), a tumor, or another cause.[2] It can also diagnosegallbladder diseases, e.g. bile leaks ofbiliary 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]
The most common indication for lung scintigraphy is to diagnosepulmonary embolism, e.g. with aventilation/perfusion scan and may be appropriate for excluding PE in pregnancy.[3] Many centres now routinely useSPECT (single-photon emission computed tomography) rather than just planar imaging for V/Q scans; in a survey of Australia, Canada, France, Germany, and the United States, over80 % of centres used SPECT for acute pulmonary embolism diagnosis, and in >70 % of those combined it with CT imaging. Less common indications include evaluation oflung transplantation, preoperative evaluation, evaluation ofright-to-left shunts.[4]
In the ventilation phase of a ventilation/perfusion scan, a gaseous radionuclidexenon ortechnetiumDTPA in an aerosol form (or ideally using Technegas, a radioaerosol invented in Australia by Dr Bill Burch and Dr Richard Fawdry) 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 technetiummacro aggregated albumin (Tc99m-MAA). A gamma camera acquires the images for both phases of the study.
For example, the ligandmethylene-diphosphonate (MDP) can be preferentially taken up by bone. By chemically attachingtechnetium-99m to MDP, radioactivity can be transported and attached to bone via thehydroxyapatite for imaging. Any increased physiological function, such as a fracture in the bone, will usually mean increased concentration of the tracer.
Athallium stress test is a form of scintigraphy, where the amount ofthallium-201 detected in cardiac tissues correlates with tissue blood supply. Viable cardiac cells have normalNa+/K+ ion exchange pumps. Thallium binds the K+ pumps and is transported into the cells. Exercise ordipyridamole induces widening (vasodilation) of normal coronary arteries. This produces coronary steal from areas of ischemia where arteries are already maximally dilated. Areas of infarct orischemic tissue will remain "cold". Pre- and post-stress thallium may indicate areas that will benefit from myocardialrevascularization. Redistribution indicates the existence ofcoronary steal and the presence of ischemiccoronary artery disease.[5]
Tc99m-sestamibi is used to detectparathyroid adenomas.[6]
To detect metastases/function of thyroid, the isotopestechnetium-99m oriodine-123 are generally used,[7][8] and for this purpose the iodide isotope does not need to be attached to another protein or molecule, because thyroid tissue takes up free iodide actively.
Examples aregallium scans,indium white blood cell scans,iobenguane scan (MIBG) andoctreotide scans. The MIBG scan detects adrenergic tissue and thus can be used to identify the location oftumors[9] such aspheochromocytomas andneuroblastomas.
Certain tests, such as theSchilling test andurea breath test, use radioisotopes but are not used to produce a specific image.
Scintigraphic scanning was invented and proven by Neurologist and Radiologist professor Bernard George Ziedses des Plantes.[10] He presented the results in 1950 under the name 'indirectAutoradiograph'. In 1970, the Physikalisch-Medizinische Gesellschaft für Neuroradiologie (The Physics and Medical Society for Neuroradiology) instituted the 'Ziedses des Plantes Medal'. It was first awarded to W. Oldendorf en G. Hounsfield in 1974 forComputer Tomography (CT). Later, in 1985, the medal was awarded to Ziedses des Plantes himself. In 1977 he received The Roentgen Medal.[11]
