the average radiation exposure is 9.4 msv, which when compared with a typical 2 view chest x-ray (.1 msv) is equivalent to 94 chest x-rays. several radiopharmaceuticals and radionuclides may be used for this, each giving different information. in the myocardial perfusion scans using 99mtc, the radiopharmaceuticals 99mtc-tetrofosmin (myoview, ge healthcare) or 99mtc-sestamibi (cardiolite, bristol-myers squibb) are used. following this, myocardial stress is induced, either by exercise or pharmacologically with adenosine, dobutamine or dipyridamole(persantine), which increase the heart rate or by regadenoson(lexiscan), a vasodilator. (aminophylline can be used to reverse the effects of dipyridamole and regadenoson). scanning may then be performed with a conventional gamma camera, or with spect/ct. cardiac ventriculography in cardiac ventriculography, a radionuclide, usually 99mtc, is injected, and the heart is imaged to evaluate the flow through it, to evaluate coronary artery disease, valvular heart disease, congenital heart diseases, cardiomyopathy, and other cardiac disorders. as a nuclear stress test, the average radiation exposure is 9.4 msv, which when compared with a typical 2 view chest x-ray (.1 msv) is equivalent to 94 chest x-rays. it exposes patients to less radiation than comparable chest x-ray studies. functional brain imaging usually the gamma-emitting tracer used in functional brain imaging is 99mtc-hmpao (hexamethylpropylene amine oxime, exametazime). the similar 99mtc-ec tracer may also be used. these molecules are preferentially distributed to regions of high brain blood flow, and act to assess brain metabolism regionally, in an attempt to diagnose and differentiate the different causal pathologies of dementia. when used with the 3-d spect technique, they compete with brain fdg-pet scans and fmri brain scans as techniques to map the regional metabolic rate of brain tissue. sentinel-node identification the radioactive properties of 99mtc can be used to identify the predominant lymph nodes draining a cancer, such as breast cancer or malignant melanoma. this is usually performed at the time of biopsy or resection.99mtc-labelled filtered sulfur colloid or technetium (99mtc) tilmanocept are injected intradermally around the intended biopsy site. the general location of the sentinel node is determined with the use of a handheld scanner with a gamma-sensor probe that detects the technetium-99m–labeled tracer that was previously injected around the biopsy site. an injection of methylene blue or isosulfan blue is done at the same time to dye any draining nodes visibly blue. an incision is then made over the area of highest radionuclide accumulation, and the sentinel node is identified within the incision by inspection; the isosulfan blue dye will usually stain any lymph nodes blue that are draining from the area around the tumor. immunoscintigraphy immunoscintigraphy incorporates 99mtc into a monoclonal antibody, an immune system protein, capable of binding to cancer cells. a few hours after injection, medical equipment is used to detect the gamma rays emitted by the 99mtc; higher concentrations indicate where the tumor is. this technique is particularly useful for detecting hard-to-find cancers, such as those affecting the intestines. these modified antibodies are sold by the german company hoechst (now part of sanofi-aventis) under the name scintimun. blood pool labeling when 99mtc is combined with a tin compound, it binds to red blood cells and can therefore be used to map circulatory system disorders. it is commonly used to detect gastrointestinal bleeding sites as well as ejection fraction, heart wall motion abnormalities, abnormal shunting, and to perform ventriculography. pyrophosphate for heart damage a pyrophosphate ion with 99mtc adheres to calcium deposits in damaged heart muscle, making it useful to gauge damage after a heart attack. sulfur colloid for spleen scan the sulfur colloid of 99mtc is scavenged by the spleen, making it possible to image the structure of the spleen. meckel's diverticulum pertechnetate is actively accumulated and secreted by the mucoid cells of the gastric mucosa, and therefore, technetate(vii) radiolabeled with tc99m is injected into the body when looking for ectopic gastric tissue as is found in a meckel's diverticulum with meckel's scans.