In 1970, Eckelman and Richards presented the first "kit" containing all the ingredients required to release the<unk> , "milked" from the generator, in the chemical form to be administered to the patient.<unk>  is used in 20 million diagnostic nuclear medical procedures every year. Approximately 85% of diagnostic imaging procedures in nuclear medicine use this isotope as radioactive tracer. Klaus Schwochau's book Technetium lists 31 radiopharmaceuticals based on<unk>  for imaging and functional studies of the brain, myocardium, thyroid, lungs, liver, gallbladder, kidneys, skeleton, blood, and tumors. A more recent review is also available. Depending on the procedure, the<unk>  is tagged (or bound to) a pharmaceutical that transports it to its required location. For example, when<unk>  is chemically bound to exametazime (HMPAO), the drug is able to cross the blood–brain barrier and flow through the vessels in the brain for cerebral blood-flow imaging. This combination is also used for labeling white blood cells<unk>  labeled WBC) to visualize sites of infection.<unk>  sestamibi is used for myocardial perfusion imaging, which shows how well the blood flows through the heart. Imaging to measure renal function is done by attaching<unk>  to mercaptoacetyl triglycine (MAG3); this procedure is known as a MAG3 scan.<unk>  <unk>  can be readily detected in the body by medical equipment because it emits 140.5 keV gamma rays (these are about the same wavelength as emitted by conventional X-ray diagnostic equipment), and its half-life for gamma emission is six hours (meaning 94% of it decays to<unk>  in 24 hours). Besides, it emits no particle radiation, thus keeping radiation dosage low. Its decay product, Tc-99 is stable and emits little radiation. The short physical half-life of<unk>  and its biological half-life of 1 day with its other favourable properties allows scanning procedures to collect data rapidly and keep total patient radiation exposure low. Chemically, technetium selectively concentrated in thyroid, salivary glands, and stomach and excluded from cerebrospinal fluid. Combination with perchlorate abolishes its selectiveness. Radiation side-effects Diagnostic treatment involving<unk>  will result in radiation exposure to technicians, patients, and passers-by. Typical quantities of technetium administered for immunoscintigraphy tests, such as SPECT tests, range from (millicurie or mCi; and Mega-Becquerel or MBq) for adults. These doses result in radiation exposures to the patient around 10 mSv (1000 mrem), the equivalent of about 500 chest X-ray exposures. This level of radiation exposure carries a 1 in 1000 lifetime risk of developing a solid cancer or leukemia in the patient. The risk is higher in younger patients, and lower in older ones. Unlike a chest x-ray, the radiation source is inside the patient and will be carried around for a few days, exposing others to second-hand radiation. A spouse who stays constantly by the side of the patient through this time might receive one thousandth of patient's radiation dose this way. The short half-life of the isotope allows for scanning procedures that collect data rapidly. The isotope is also of a very low energy level for a gamma emitter. Its ~140 keV of energy make it safer for use because of the substantially reduced ionization compared with other gamma emitters. The energy of gammas from<unk>  is about the same as the radiation from a commercial diagnostic X-ray machine, although the number of gammas emitted results in radiation doses more comparable to X-ray studies like computed tomography.<unk>  has several features that make it safer than other possible isotopes. Its gamma decay mode can be easily detected by a camera, allowing the use of smaller quantities. And because<unk>  has a short half-life, its quick decay into the far less radioactive<unk> results in relatively low total radiation dose to the patient per unit of initial activity after administration, as compared with other radioisotopes. In the form administered in these medical tests (usually pertechnetate),<unk>  and<unk> are eliminated from the body within a few days. 3-D scanning technique: SPECT Single-photon emission computed tomography (SPECT) is a nuclear medicine imaging technique using gamma rays. It may be used with any gamma-emitting isotope, including<unk> . In the use of<unk> , the radioisotope is administered to the patient and the escaping gamma rays are incident upon a moving gamma camera which computes and processes the image. To acquire SPECT images, the gamma camera is rotated around the patient. Projections are acquired at defined points during the rotation, typically every three to six degrees. In most cases, a full 360° rotation is used to obtain an optimal reconstruction. The time taken to obtain each projection is also variable, but 15–20 seconds are typical. This gives a total scan time of 15–20 minutes. The<unk>  radioisotope is used predominantly in bone and brain scans. For bone scans, the pertechnetate ion is used directly, as it is taken up by osteoblasts attempting to heal a skeletal injury, or (in some cases) as a reaction of these cells to a tumor (either primary or metastatic) in the bone. In brain scanning,<unk>  is attached to the chelating agent HMPAO to create technetium<unk>  exametazime, an agent which localizes in the brain according to region blood flow, making it useful for the detection of stroke and dementing illnesses that decrease regional brain flow and metabolism. Most recently,<unk>  scintigraphy has been combined with CT coregistration technology to produce SPECT/CT scans. These employ the same radioligands and have the same uses as SPECT scanning, but are able to provide even finer 3-D localization of high-uptake tissues, in cases where finer resolution is needed. An example is the sestamibi parathyroid scan which is performed using the<unk>  radioligand sestamibi, and can be done in either SPECT or SPECT/CT machines. Bone scan The nuclear medicine technique commonly called the bone scan usually uses<unk> . It is not to be confused with the "bone density scan", DEXA, which is a low-exposure X-ray test measuring bone density to look for osteoporosis and other diseases where bones lose mass without rebuilding activity. The nuclear medicine technique is sensitive to areas of unusual bone rebuilding activity, since the radiopharmaceutical is taken up by osteoblast cells which build bone. The technique therefore is sensitive to fractures and bone reaction to bone tumors, including metastases. For a bone scan, the patient is injected with a small amount of radioactive material, such as of<unk> -medronic acid and then scanned with a gamma camera. Medronic acid is a phosphate derivative which can exchange places with bone phosphate in regions of active bone growth, so anchoring the radioisotope to that specific region. To view small lesions (less than ) especially in the spine, the SPECT imaging technique may be required, but currently in the United States, most insurance companies require separate authorization for SPECT imaging. Myocardial perfusion imaging Myocardial perfusion imaging (MPI) is a form of functional cardiac imaging, used for the diagnosis of ischemic heart disease. The underlying principle is, under conditions of stress, diseased myocardium receives less blood flow than normal myocardium. MPI is one of several types of cardiac stress test. 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. Several radiopharmaceuticals and radionuclides may be used for this, each giving different information. In the myocardial perfusion scans using<unk> , the radiopharmaceuticals<unk> -tetrofosmin (Myoview, GE Healthcare) or<unk> -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<unk> , 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<unk> -HMPAO (hexamethylpropylene amine oxime, exametazime). The similar<unk> -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<unk>  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<unk>  tilmanocept are injected intradermally around the intended biopsy site. The general location
Technetium-99m
Technetium 
Strontium-90
Radium-223
Dotinurad
Rubidium-82 chloride
Methylene blue
Fenpentadiol