Technetium-99m, ^99mTc

The firsttechnetium-99m generator, 1958. A99mTc pertechnetate solution is being eluted from99Mo molybdate bound to a chromatographic substrate
General
Symbol	99mTc
Names	technetium-99m, 99mTc, Tc-99m
Protons(Z)	43
Neutrons(N)	56
Nuclide data
Half-life(t1/2)	6.0067 h[1]
Isotope mass	98.9063Da
Spin	1/2−
Excess energy	−87327.195keV
Binding energy	8613.603 keV
Parent isotopes	99Mo (65.976 h)
Decay products	99Tc
Decay modes
Decay mode	Decay energy (MeV)
Isomeric transition γ emission 87.87%	98.6%: 0.1405 MeV 1.4%: 0.1426 MeV
Isotopes of technetium Complete table of nuclides

Technetium-99m (^99mTc) is ametastablenuclear isomer oftechnetium-99 (itself an isotope oftechnetium), symbolized as^99mTc, that is used in tens of millions of medical diagnostic procedures annually, making it the most commonly usedmedical radioisotope in the world.

Technetium-99m is used as aradioactive tracer and can be detected in the body by medical equipment (gamma cameras). It is well suited to the role, because it emits readily detectablegamma rays with aphoton energy of 140 keV (these 8.8 pmphotons are about the same wavelength as emitted by conventional X-ray diagnostic equipment) and itshalf-life for gamma emission is 6.0058 hours (meaning 93.7% of it decays to⁹⁹Tc in 24 hours). The relatively "short" physicalhalf-life of the isotope and itsbiological half-life of 1 day (in terms of human activity and metabolism) allows for scanning procedures which collect data rapidly but keep total patient radiation exposure low. The same characteristics make the isotope unsuitable for therapeutic use.

Technetium-99m was discovered as a product ofcyclotron bombardment ofmolybdenum. This procedure producedmolybdenum-99, a radionuclide with a longer half-life (2.75 days), which decays to^99mTc. This longer decay time allows for⁹⁹Mo to be shipped to medical facilities, where^99mTc is extracted from the sample as it is produced. In turn,⁹⁹Mo is usually created commercially by fission ofhighly enriched uranium in a small number of research and material testing nuclear reactors in several countries.

In 1938,Emilio Segrè andGlenn T. Seaborg isolated for the first time themetastable isotope technetium-99m, after bombarding natural molybdenum with 8 MeVdeuterons in the 37-inch (940 mm)cyclotron ofErnest Orlando Lawrence'sRadiation laboratory.^[2] In 1970 Seaborg explained that:^[3]

we discovered an isotope of great scientific interest, because it decayed by means of an isomeric transition with emission of a line spectrum of electrons coming from an almost completely internally converted gamma ray transition. [actually, only 12% of the decays are by internal conversion] (...) This was a form of radioactive decay which had never been observed before this time. Segrè and I were able to show that this radioactive isotope of the element with the atomic number 43 decayed with a half-life of 6.6 h [later updated to 6.0 h] and that it was the daughter of a 67-h [later updated to 66 h] molybdenum parent radioactivity. This chain of decay was later shown to have the mass number 99, and (...) the 6.6-h activity acquired the designation ‘technetium-99m.

Later in 1940, Emilio Segrè andChien-Shiung Wu published experimental results of an analysis of fission products of uranium-235, including molybdenum-99, and detected the presence of an isomer of element 43 with a 6-hour half life, later labelled as technetium-99m.^[4][5]

^99mTc remained a scientific curiosity until the 1950s whenPowell Richards realized the potential of technetium-99m as a medical radiotracer and promoted its use among the medical community. While Richards was in charge of the radioisotope production at the Hot Lab Division of theBrookhaven National Laboratory, Walter Tucker andMargaret Greene were working on how to improve the separation process purity of the short-livedeluteddaughter productiodine-132 from its parent,tellurium-132 (with a half life of 3.2 days), produced in the Brookhaven Graphite Research Reactor.^[6] They detected a trace contaminant which proved to be^99mTc, which was coming from⁹⁹Mo and was following tellurium in the chemistry of the separation process for other fission products. Based on the similarities between the chemistry of the tellurium-iodine parent-daughter pair, Tucker and Greene developed the firsttechnetium-99m generator in 1958.^[7][8] It was not until 1960 that Richards became the first to suggest the idea of using technetium as a medical tracer.^{[9][10][11][12]}

The first US publication to report on medical scanning of^99mTc appeared in August 1963.^[13][14] Sorensen and Archambault demonstrated that intravenously injected carrier-free⁹⁹Mo selectively and efficiently concentrated in the liver, becoming an internal generator of^99mTc. After build-up of^99mTc, they could visualize the liver using the 140 keV gamma ray emission.

The production and medical use of^99mTc rapidly expanded across the world in the 1960s, benefiting from the development and continuous improvements of thegamma cameras.

Between 1963 and 1966, numerous scientific studies demonstrated the use of^99mTc asradiotracer or diagnostic tool.^{[15][16][17][18]} As a consequence the demand for^99mTc grew exponentially and by 1966,Brookhaven National Laboratory was unable to cope with the demand. Production and distribution of^99mTc generators were transferred to private companies."TechneKow-CS generator", the first commercial^99mTc generator, was produced by Nuclear Consultants, Inc. (St. Louis, Missouri) andUnion Carbide Nuclear Corporation (Tuxedo, New York).^[19][20] From 1967 to 1984,⁹⁹Mo was produced forMallinckrodt Nuclear Company at theMissouri University Research Reactor (MURR).

Union Carbide actively developed a process to produce and separate useful isotopes like⁹⁹Mo from mixedfission products that resulted from the irradiation ofhighly enriched uranium (HEU) targets in nuclear reactors developed from 1968 to 1972 at the Cintichem facility (formerly the Union Carbide Research Center built in the Sterling forest in Tuxedo, New York (41°14′6.88″N74°12′50.78″W / 41.2352444°N 74.2141056°W /41.2352444; -74.2141056)).^[21] The Cintichem process originally used 93% highly enriched U-235 deposited as UO₂ on the inside of a cylindrical target.^[22][23]

At the end of the 1970s, 200,000 Ci (7.4×10¹⁵ Bq) of total fission product radiation were extracted weekly from 20 to 30 reactor bombarded HEU capsules, using the so-called "Cintichem [chemical isolation] process."^[24] The research facility with its 1961 5-MW pool-type research reactor was later sold to Hoffman-LaRoche and became Cintichem Inc.^[25] In 1980, Cintichem, Inc. began the production/isolation of⁹⁹Mo in its reactor, and became the single U.S. producer of⁹⁹Mo during the 1980s. However, in 1989, Cintichem detected an underground leak of radioactive products that led to the reactor shutdown and decommissioning, putting an end to the commercial production of⁹⁹Mo in the USA.^[26]

The production of⁹⁹Mo started in Canada in the early 1970s and was shifted to the NRU reactor in the mid-1970s.^[27] By 1978 the reactor provided technetium-99m in large enough quantities that were processed by AECL's radiochemical division, which was privatized in 1988 as Nordion, nowMDS Nordion.^[28] In the 1990s a substitution for the aging NRU reactor for production of radioisotopes was planned. TheMultipurpose Applied Physics Lattice Experiment (MAPLE) was designed as a dedicated isotope-production facility. Initially, two identical MAPLE reactors were to be built atChalk River Laboratories, each capable of supplying 100% of the world's medical isotope demand. However, problems with the MAPLE 1 reactor, most notably a positivepower co-efficient of reactivity, led to the cancellation of the project in 2008.

The first commercial^99mTc generators were produced inArgentina in 1967, with⁹⁹Mo produced in theCNEA'sRA-1 Enrico Fermi reactor.^[29][30] Besides its domestic market CNEA supplies⁹⁹Mo to some South American countries.^[31]

In 1967, the first^99mTc procedures were carried out inAuckland,New Zealand.^[32]99Mo was initially supplied by Amersham, UK, then by the Australian Nuclear Science and Technology Organisation (ANSTO) in Lucas Heights, Australia.^[33]

In May 1963, Scheer and Maier-Borst were the first to introduce the use of^99mTc for medical applications.^[13][34]In 1968,Philips-Duphar (later Mallinckrodt, todayCovidien) marketed the first technetium-99m generator produced in Europe and distributed from Petten, the Netherlands.

Global shortages of technetium-99m emerged in the late 2000s because two aging nuclear reactors (NRU andHFR) that provided about two-thirds of the world's supply of molybdenum-99, which itself has a half-life of only 66 hours, were shut down repeatedly for extended maintenance periods.^[35][36][37] In May 2009, theAtomic Energy of Canada Limited announced the detection of a small leak ofheavy water in the NRU reactor that remained out of service until completion of the repairs in August 2010.

After the observation of gas bubble jets released from one of the deformations of primary cooling water circuits in August 2008, the HFR reactor was stopped for a thorough safety investigation.NRG received in February 2009 a temporary license to operate HFR only when necessary for medical radioisotope production. HFR stopped for repairs at the beginning of 2010 and was restarted in September 2010.^[38]

Two replacement Canadian reactors (seeMAPLE Reactor) constructed in the 1990s were closed before beginning operation, for safety reasons.^[35][39] A construction permit for a new production facility to be built inColumbia, MO was issued in May 2018.^[40]

Technetium-99m is a metastablenuclear isomer, as indicated by the "m" after itsmass number 99. This means it is a nuclide in an excited (metastable) state that lasts much longer than is typical. The nucleus will eventually relax (i.e., de-excite) to itsground state through the emission ofgamma rays orinternal conversion electrons. Both of these decay modes rearrange thenucleons withouttransmuting the technetium into another element.

^99mTc decays mainly by gamma emission, slightly less than 88% of the time. (^99mTc →⁹⁹Tc + γ) About 98.6% of these gamma decays result in 140.5 keV gamma rays and the remaining 1.4% are to gammas of a slightly higher energy at 142.6 keV. These are the radiations that are picked up by a gamma camera when^99mTc is used as aradioactive tracer formedical imaging. The remaining approximately 12% of^99mTc decays are by means ofinternal conversion, resulting in ejection of high speed internal conversion electrons in several sharp peaks (as is typical of electrons from this type of decay) also at about 140 keV (^99mTc →⁹⁹Tc⁺ + e⁻). These conversion electrons willionize the surrounding matter likebeta radiation electrons would do, contributing along with the 140.5 keV and 142.6 keV gammas to the total depositeddose.

Pure gamma emission is the desirabledecay mode for medical imaging because other particles deposit more energy in the patient body (radiation dose) than in the camera. Metastable isomeric transition is the only nuclear decay mode that approaches pure gamma emission.

^99mTc'shalf-life of 6.0058 hours is considerably longer (by 14 orders of magnitude, at least) than most nuclear isomers, though not unique. This is still a short half-life relative to many other known modes ofradioactive decay and it is in the middle of the range of half lives forradiopharmaceuticals used formedical imaging.

After gamma emission or internal conversion, the resulting ground-state technetium-99 then decays with a half-life of 211,000 years tostableruthenium-99. This process emits soft beta radiation without a gamma. Such low radioactivity from the daughter product(s) is a desirable feature for radiopharmaceuticals.

${\displaystyle {}_{43}{}^{99\text{m}}\text{Tc}\underset{6\text{h}}{\overset{\gamma 141\text{keV}}{\to }}{}_{43}{}^{99}\text{Tc}\underset{211,000\text{y}}{\overset{\beta {}^{-}249\text{keV}}{\to }}\stackrel{\text{ruthenium}-99}{\overbrace{\underset{(\text{stable})}{{}_{44}{}^{99}\text{Ru}}}}}$

Theparent nuclide of^99mTc,⁹⁹Mo, is mainly extracted for medical purposes from thefission products created in neutron-irradiateduranium-235 targets, the majority of which is produced in five nuclearresearch reactors around the world usinghighly enriched uranium (HEU) targets.^[41][42] Smaller amounts of⁹⁹Mo are produced fromlow-enriched uranium in at least three reactors.

Production of⁹⁹Mo byneutron activation of natural molybdenum, or molybdenum enriched in⁹⁸Mo,^[46] is another, currently smaller, route of production.^[47]

The feasibility of^99mTc production with the 22-MeV-proton bombardment of a¹⁰⁰Mo target in medical cyclotrons was demonstrated in 1971.^[48] The recent shortages of^99mTc reignited the interest in the production of "instant" 99mTc by proton bombardment of isotopically enriched¹⁰⁰Mo targets (>99.5%) following the reaction¹⁰⁰Mo(p,2n)^99mTc.^[49] Canada is commissioning such cyclotrons, designed byAdvanced Cyclotron Systems, for^99mTc production at theUniversity of Alberta and theUniversité de Sherbrooke, and is planning others at theUniversity of British Columbia,TRIUMF,University of Saskatchewan andLakehead University.^[50][51][52]

A particular drawback of cyclotron production via (p,2n) on¹⁰⁰Mo is the significant co-production of^99gTc. The preferential in-growth of this nuclide occurs due to the larger reaction cross-section pathway leading to the ground state, which is almost five times higher at the cross-section maximum in comparison with the metastable one at the same energy. Depending on the time required to process the target material and recovery of^99mTc, the amount of^99mTc relative to^99gTc will continue to decrease, in turn reducing the specific activity of^99mTc available. It has been reported that ingrowth of^99gTc as well as the presence of other Tc isotopes can negatively affect subsequent labelling and/or imaging;^[53] however, the use of high purity¹⁰⁰Mo targets, specified proton beam energies, and appropriate time of use have shown to be sufficient for yielding^99mTc from a cyclotron comparable to that from a commercial generator.^[54][55] Liquid metal molybdenum-containing targets have been proposed that would aid in streamlined processing, ensuring better production yields.^[56] A particular problem associated with the continued reuse of recycled, enriched¹⁰⁰Mo targets is unavoidable transmutation of the target as other Mo isotopes are generated during irradiation and cannot be easily removed post-processing.

Other particle accelerator-based isotope production techniques have been investigated. The supply disruptions of⁹⁹Mo in the late 2000s and the ageing of the producing nuclear reactors forced the industry to look into alternative methods of production.^[57] The use of cyclotrons or electron accelerators to produce⁹⁹Mo from¹⁰⁰Mo via (p,pn)^[58][59][60] or (γ,n)^[61] reactions, respectively, has been further investigated. The (n,2n) reaction on¹⁰⁰Mo yields a higher reaction cross-section for high energy neutrons than of (n,γ) on⁹⁸Mo with thermal neutrons.^[62] In particular, this method requires accelerators that generate fast neutron spectrums, such as ones using D-T^[63] or other fusion-based reactions,^[64] or high energy spallation or knock out reactions.^[65] A disadvantage of these techniques is the necessity for enriched¹⁰⁰Mo targets, which are significantly more expensive than natural isotopic targets and typically require recycling of the material, which can be costly, time-consuming, and arduous.^[66][67]

Technetium-99m's short half-life of 6 hours makes storage impossible and would make transport very expensive. Instead, its parent nuclide⁹⁹Mo is supplied to hospitals after its extraction from the neutron-irradiated uranium targets and its purification in dedicated processing facilities.^{[notes 1][69]} It is shipped by specialised radiopharmaceutical companies in the form oftechnetium-99m generators worldwide or directly distributed to the local market. The generators, colloquially known as moly cows, are devices designed to provide radiation shielding for transport and to minimize the extraction work done at the medical facility. A typical dose rate at 1 metre from the^99mTc generator is 20-50 μSv/h during transport.^[70] These generators' output declines with time and must be replaced weekly, since the half-life of⁹⁹Mo is still only 66 hours.

Molybdenum-99 spontaneously decays to excited states of⁹⁹Tc throughbeta decay. Over 87% of the decays lead to the142 keV excited state of^99mTc. A
β⁻
electron and a
ν
_eelectron antineutrino are emitted in the process (⁹⁹Mo →^99mTc +
β⁻
+
ν
_e). The
β⁻
electrons are easilyshielded for transport, and^99mTc generators are only minor radiation hazards, mostly due to secondary X-rays produced by the electrons (also known asBremsstrahlung).

At the hospital, the^99mTc that forms through⁹⁹Mo decay is chemically extracted from the technetium-99m generator. Most commercial⁹⁹Mo/^99mTc generators usecolumn chromatography, in which⁹⁹Mo in the form of water-soluble molybdate, MoO₄²⁻ isadsorbed onto acid alumina (Al₂O₃). When the⁹⁹Mo decays, it formspertechnetate TcO₄⁻, which, because of its single charge, is less tightly bound to the alumina. Pulling normal saline solution through the column of immobilized⁹⁹MoO₄²⁻elutes the soluble^99mTcO₄⁻, resulting in a saline solution containing the^99mTc as the dissolvedsodium salt of the pertechnetate. One technetium-99m generator, holding only a few micrograms of⁹⁹Mo, can potentially diagnose 10,000 patients^{[citation needed]} because it will be producing^99mTc strongly for over a week.

Technetium exits the generator in the form of the pertechnetate ion, TcO₄⁻. Theoxidation state of Tc in this compound is +7. This is directly suitable for medical applications only inbone scans (it is taken up by osteoblasts) and some thyroid scans (it is taken up in place of iodine by normal thyroid tissues). In other types of scans relying on^99mTc, areducing agent is added to the pertechnetate solution to bring the oxidation state of the technecium down to +3 or +4. Secondly, aligand is added to form acoordination complex. The ligand is chosen to have an affinity for the specific organ to be targeted. For example, theexametazime complex of Tc in oxidation state +3 is able to cross the blood–brain barrier and flow through the vessels in the brain for cerebral blood flow imaging. Other ligands includesestamibi for myocardial perfusion imaging and mercapto acetyl triglycine forMAG3 scan to measure renal function.^[71]

In 1970, Eckelman and Richards presented the first "kit" containing all the ingredients required to release the^99mTc, "milked" from the generator, in the chemical form to be administered to the patient.^{[71][72][73][74]}

Technetium-99m is used in 20 million diagnosticnuclear medical procedures every year. Approximately 85% of diagnostic imaging procedures in nuclear medicine use this isotope asradioactive tracer. Klaus Schwochau's bookTechnetium lists 31radiopharmaceuticals based on^99mTc for imaging and functional studies of thebrain,myocardium,thyroid,lungs,liver,gallbladder,kidneys,skeleton,blood, andtumors.^[75] A more recent review is also available.^[76]

Depending on the procedure, the^99mTc is tagged (or bound to) a pharmaceutical that transports it to its required location. For example, when^99mTc is chemically bound toexametazime (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 (^99mTc labeled WBC) to visualize sites of infection.^99mTc sestamibi is used for myocardial perfusion imaging, which shows how well the blood flows through the heart. Imaging to measurerenal function is done by attaching^99mTc to mercaptoacetyl triglycine (MAG3); this procedure is known as aMAG3 scan.

Technetium-99m (Tc-99m) can be readily detected in the body by medical equipment because it emits 140.5keVgamma rays (these are about the same wavelength as emitted by conventional X-ray diagnostic equipment), and itshalf-life for gamma emission is six hours (meaning 94% of it decays to⁹⁹Tc in 24 hours). Besides, it emits virtually no beta radiation, thus keeping radiation dosage low. Its decay product,⁹⁹Tc, has a relatively long half-life (211,000 years) and emits little radiation. The short physicalhalf-life of^99mTc and itsbiological 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-99m is selectively concentrated in the stomach, thyroid, and salivary glands, and excluded fromcerebrospinal fluid; combining it with perchlorate abolishes its selectiveness.^[77]

Diagnostic treatment involving technetium-99m will result in radiation exposure to technicians, patients, and passers-by. Typical quantities of technetium administered for immunoscintigraphy tests, such asSPECT tests, range from 400 to 1,100 MBq (11 to 30 mCi) (millicurie or mCi; and Mega-Becquerel or MBq) for adults.^[78][79] These doses result in radiation exposures to the patient around 10 mSv (1000 mrem), the equivalent of about 500chest X-ray exposures.^[80] This level of radiation exposure is estimated by thelinear no-threshold model to carry a 1 in 1000 lifetime risk of developing a solid cancer or leukemia in the patient.^[81] The risk is higher in younger patients, and lower in older ones.^[82] 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 reducedionization compared with other gamma emitters. The energy of gammas from^99mTc 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 likecomputed tomography.

Technetium-99m 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 technetium-99m has a short half-life, its quick decay into the far less radioactive technetium-99 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), technetium-99m and technetium-99 are eliminated from the body within a few days.^{[citation needed]}

Single-photon emission computed tomography (SPECT) is anuclear medicine imaging technique using gamma rays. It may be used with any gamma-emitting isotope, including^99mTc. In the use of technetium-99m, the radioisotope is administered to the patient and the escaping gamma rays are incident upon a movinggamma 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 technetium-99m radioisotope is used predominantly in bone and brain scans. Forbone 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,^99mTc is attached to the chelating agent HMPAO to createtechnetium (^99mTc) 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, technetium-99m scintigraphy has been combined with CT coregistration technology to produceSPECT/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 thesestamibi parathyroid scan which is performed using the^99mTc radioligandsestamibi, and can be done in either SPECT or SPECT/CT machines.

Thenuclear medicine technique commonly called thebone scan usually uses^99mTc. 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 byosteoblast 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 700–1,100 MBq (19–30 mCi) of^99mTc-medronic acid and then scanned with agamma camera. Medronic acid is aphosphate 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 1 centimetre (0.39 in)) especially in the spine, theSPECT imaging technique may be required, but currently in the United States, most insurance companies require separate authorization for SPECT imaging.

Myocardial perfusion imaging (MPI) is a form of functional cardiac imaging, used for the diagnosis ofischemic heart disease. The underlying principle is, under conditions of stress, diseasedmyocardium receives less blood flow than normal myocardium. MPI is one of several types ofcardiac stress test. As anuclear 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.^[83]

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 withadenosine,dobutamine ordipyridamole(Persantine), which increase the heart rate or byregadenoson(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.

Incardiac ventriculography, a radionuclide, usually^99mTc, is injected, and the heart is imaged to evaluate the flow through it, to evaluatecoronary artery disease,valvular heart disease,congenital heart diseases,cardiomyopathy, and othercardiac disorders. As anuclear 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.^[83][84] It exposes patients to less radiation than comparablechest X-ray studies.^[84]

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 ofdementia. When used with the 3-DSPECT technique, they compete with brainFDG-PET scans andfMRI brain scans as techniques to map the regional metabolic rate of brain tissue.

The radioactive properties of^99mTc can be used to identify the predominantlymph nodes draining a cancer, such asbreast cancer ormalignant melanoma. This is usually performed at the time ofbiopsy orresection.^99mTc-labelled filtered sulfur colloid orTechnetium (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 ofMethylene blue orisosulfan 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.^[85]

Immunoscintigraphy incorporates^99mTc into amonoclonal antibody, animmune systemprotein, capable of binding tocancer 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 theintestines. These modified antibodies are sold by the German companyHoechst (now part ofSanofi-Aventis) under the nameScintimun.^[86]

When^99mTc is combined with atin compound, it binds tored blood cells and can therefore be used to mapcirculatory system disorders. It is commonly used to detect gastrointestinal bleeding sites as well asejection fraction, heart wall motion abnormalities, abnormal shunting, and to performventriculography.

Apyrophosphate ion with^99mTc adheres tocalcium deposits in damagedheart muscle, making it useful to gauge damage after aheart attack.^{[citation needed]}

Thesulfur colloid of^99mTc is scavenged by thespleen, making it possible to image the structure of the spleen.^[87]

Pertechnetate is actively accumulated and secreted by the mucoid cells of the gastric mucosa,^[88] and therefore, technetate(VII) radiolabeled with Tc99m is injected into the body when looking for ectopic gastric tissue as is found in aMeckel's diverticulum with Meckel's Scans.^[89]

Carbon inhalation aerosol labeled with technetium-99m (Technegas) isindicated for the visualization of pulmonary ventilation and the evaluation of pulmonary embolism.^[90][91][92]

• Cholescintigraphy
• Isotopes of technetium
• Transient equilibrium

Citations

Bibliography

Wikimedia Commons has media related toTechnetium-99m.

• P. Saraswathy, A.C. Dey, S.K. Sarkar, C. Koth, alkar, P. Naskar, G. Arjun, S.S. Arora, A.K.Kohli, V. Meera, V.Venugopal and N.Ramamoorthy (2007)."99mTc generators for clinical use based on zirconium molybdate gel and (n, gamma) produced 99 Mo: Indian experience in the development and deployment of indigenous technology and processing facilities"(PDF).Proceedings of the 2007 International RERTR Meeting.{{cite journal}}: CS1 maint: multiple names: authors list (link)
• Iturralde MP (1 December 1996). "Molybdenum-99 production in South Africa".European Journal of Nuclear Medicine.23 (12):1681–1687.doi:10.1007/BF01249633.S2CID 28154691.
• Hansell C (1 July 2008)."Nuclear Medicine's Double Hazard: Imperiled Treatment and the Risk of Terrorism"(PDF).The Nonproliferation Review.15 (2):185–208.doi:10.1080/10736700802117270.S2CID 8559456. Archived fromthe original(PDF) on 18 July 2013. Retrieved24 May 2012.

• ^99mTc production simulator – IAEA

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