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94-544: In nuclear medicine imaging, radiopharmaceuticals are taken internally, for example, through inhalation, intravenously, or orally. Then, external detectors ( gamma cameras ) capture and form images from the radiation emitted by the radiopharmaceuticals. This process is unlike a diagnostic X-ray, where external radiation is passed through the body to form an image. There are several techniques of diagnostic nuclear medicine. Nuclear medicine tests differ from most other imaging modalities in that nuclear medicine scans primarily show

188-470: A Patlak plot . Radionuclide therapy can be used to treat conditions such as hyperthyroidism , thyroid cancer , skin cancer and blood disorders. In nuclear medicine therapy, the radiation treatment dose is administered internally (e.g. intravenous or oral routes) or externally direct above the area to treat in form of a compound (e.g. in case of skin cancer). The radiopharmaceuticals used in nuclear medicine therapy emit ionizing radiation that travels only

282-523: A radionuclide into the body by intravenous injection in liquid or aggregate form, ingestion while combined with food, inhalation as a gas or aerosol, or rarely, injection of a radionuclide that has undergone micro-encapsulation . Some studies require the labeling of a patient's own blood cells with a radionuclide ( leukocyte scintigraphy and red blood cell scintigraphy). Most diagnostic radionuclides emit gamma rays either directly from their decay or indirectly through electron–positron annihilation , while

376-481: A 68-minute half-life , produced by elution from germanium-68 in a gallium-68 generator or by proton irradiation of zinc-68. H or tritium is a beta emitter. In is a gamma emitter. Iodine-123 (I-123) is a gamma emitter. It is used only diagnostically, as its radiation is penetrating and short-lived. Thyroid metastases imaging I is a gamma emitter with a long half-life of 59.4 days (the longest of all radioiodines used in medicine). Iodine-123

470-430: A Helium ion with a +2 charge (missing its two electrons). If the ion gains electrons from its environment, the alpha particle can be written as a normal (electrically neutral) helium atom 2 He . Beta particles are high-energy, high-speed electrons or positrons emitted by certain types of radioactive nuclei , such as potassium-40 . The production of beta particles is termed beta decay . They are designated by

564-448: A close second. Other stochastic effects of ionizing radiation are teratogenesis , cognitive decline , and heart disease . Although DNA is always susceptible to damage by ionizing radiation, the DNA molecule may also be damaged by radiation with enough energy to excite certain molecular bonds to form pyrimidine dimers . This energy may be less than ionizing, but near to it. A good example

658-503: A compromise that has shifted over time. For example, at one time, assistants in shoe shops in the US used X-rays to check a child's shoe size , but this practice was halted when the risks of ionizing radiation were better understood. Neutron radiation is essential to the working of nuclear reactors and nuclear weapons . The penetrating power of x-ray, gamma, beta, and positron radiation is used for medical imaging , nondestructive testing , and

752-635: A fast recoil proton that ionizes in turn. At the end of its path, the neutron is captured by a nucleus in an (n,γ)-reaction that leads to the emission of a neutron capture photon. Such photons always have enough energy to qualify as ionizing radiation. Neutron radiation, alpha radiation, and extremely energetic gamma (> ~20 MeV) can cause nuclear transmutation and induced radioactivity . The relevant mechanisms are neutron activation , alpha absorption , and photodisintegration . A large enough number of transmutations can change macroscopic properties and cause targets to become radioactive themselves, even after

846-495: A gas per ion pair formed , which combines ionization energy plus the energy lost to other processes such as excitation . At 38 nanometers wavelength for electromagnetic radiation , 33 eV is close to the energy at the conventional 10 nm wavelength transition between extreme ultraviolet and X-ray radiation, which occurs at about 125 eV. Thus, X-ray radiation is always ionizing, but only extreme-ultraviolet radiation can be considered ionizing under all definitions. Neutrons have

940-435: A higher Rem or Sv value, due to its much higher Relative Biological Effectiveness (RBE). Alpha emitters are nowadays rarely used in nuclear medicine, but were used extensively before the advent of nuclear reactor and accelerator produced radionuclides. The concepts involved in radiation exposure to humans are covered by the field of Health Physics ; the development and practice of safe and effective nuclear medicinal techniques

1034-403: A larger amount of ionization from the daughter products of fission. Outside the nucleus, free neutrons are unstable and have a mean lifetime of 14 minutes, 42 seconds. Free neutrons decay by emission of an electron and an electron antineutrino to become a proton, a process known as beta decay : In the adjacent diagram, a neutron collides with a proton of the target material, and then becomes

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1128-403: A low-energy electron, annihilation occurs, resulting in their conversion into the energy of two or more gamma ray photons (see electron–positron annihilation ). As positrons are positively charged particles they can directly ionize an atom through Coulomb interactions. Positrons can be generated by positron emission nuclear decay (through weak interactions ), or by pair production from

1222-449: A lower energy than gamma rays, and an older convention was to define the boundary as a wavelength of 10 m (or a photon energy of 100 keV). That threshold was driven by historic limitations of older X-ray tubes and low awareness of isomeric transitions . Modern technologies and discoveries have shown an overlap between X-ray and gamma energies. In many fields they are functionally identical, differing for terrestrial studies only in origin of

1316-436: A neutral electrical charge often misunderstood as zero electrical charge and thus often do not directly cause ionization in a single step or interaction with matter. However, fast neutrons will interact with the protons in hydrogen via linear energy transfer , energy that a particle transfers to the material it is moving through. This mechanism scatters the nuclei of the materials in the target area, causing direct ionization of

1410-418: A nuclear medicine procedure will receive a radiation dose . Under present international guidelines it is assumed that any radiation dose, however small, presents a risk. The radiation dose delivered to a patient in a nuclear medicine investigation, though unproven, is generally accepted to present a very small risk of inducing cancer. In this respect it is similar to the risk from X-ray investigations except that

1504-453: A pharmaceutical; these are also included. There is a section for each radioisotope with a table of radiopharmaceuticals using that radioisotope. The sections are ordered alphabetically by the English name of the radioisotope. Sections for the same element are then ordered by atomic mass number . Ca is a beta and gamma emitter. C is a positron emitter. Parathyroid imaging C

1598-416: A proton emission forming nitrogen-16 , which decays to oxygen-16. The short-lived nitrogen-16 decay emits a powerful beta ray. This process can be written as: O (n,p) N (fast neutron capture possible with >11 MeV neutron) N → O + β (Decay t 1/2 = 7.13 s) This high-energy β further interacts rapidly with other nuclei, emitting high-energy γ via Bremsstrahlung While not a favorable reaction,

1692-671: A protracted time can cause cancer . The International Commission on Radiological Protection (ICRP) issues guidance on ionizing radiation protection, and the effects of dose uptake on human health. Ionizing radiation may be grouped as directly or indirectly ionizing. Any charged particle with mass can ionize atoms directly by fundamental interaction through the Coulomb force if it carries sufficient kinetic energy. Such particles include atomic nuclei , electrons , muons , charged pions , protons , and energetic charged nuclei stripped of their electrons. When moving at relativistic speeds (near

1786-557: A rotating gamma-camera are reconstructed to produce an image of a "slice" through the patient at a particular position. A collection of parallel slices form a slice-stack, a three-dimensional representation of the distribution of radionuclide in the patient. The nuclear medicine computer may require millions of lines of source code to provide quantitative analysis packages for each of the specific imaging techniques available in nuclear medicine. Time sequences can be further analysed using kinetic models such as multi-compartment models or

1880-706: A short distance, thereby minimizing unwanted side effects and damage to noninvolved organs or nearby structures. Most nuclear medicine therapies can be performed as outpatient procedures since there are few side effects from the treatment and the radiation exposure to the general public can be kept within a safe limit. In some centers the nuclear medicine department may also use implanted capsules of isotopes ( brachytherapy ) to treat cancer. The history of nuclear medicine contains contributions from scientists across different disciplines in physics, chemistry, engineering, and medicine. The multidisciplinary nature of nuclear medicine makes it difficult for medical historians to determine

1974-472: A sufficient amount of the procedure to achieve a diagnosis, then it would be inappropriate to proceed with injecting the patient with the radioactive tracer. When the benefit does justify the procedure, then the radiation exposure (the amount of radiation given to the patient) should also be kept "ALARP". This means that the images produced in nuclear medicine should never be better than required for confident diagnosis. Giving larger radiation exposures can reduce

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2068-496: A sufficiently energetic photon . Positrons are common artificial sources of ionizing radiation used in medical positron emission tomography (PET) scans. Charged nuclei are characteristic of galactic cosmic rays and solar particle events and except for alpha particles (charged helium nuclei) have no natural sources on earth. In space, however, very high energy protons, helium nuclei, and HZE ions can be initially stopped by relatively thin layers of shielding, clothes, or skin. However,

2162-419: A variety of industrial gauges. Radioactive tracers are used in medical and industrial applications, as well as biological and radiation chemistry . Alpha radiation is used in static eliminators and smoke detectors . The sterilizing effects of ionizing radiation are useful for cleaning medical instruments, food irradiation , and the sterile insect technique . Measurements of carbon-14 , can be used to date

2256-416: Is a beta emitter. Cr is a gamma emitter. Co is a gamma emitter. Co is a gamma emitter. Er is a beta emitter. F is a positron emitter with a half-life of 109 minutes. It is produced in medical cyclotrons, usually from oxygen-18, and then chemically attached to a pharmaceutical formulation. Myocardial imaging Ga is a gamma emitter. Ga is a positron emitter, with

2350-776: Is a beta emitter. Technetium-99m is a gamma emitter. It is obtained on-site at the imaging center as the soluble pertechnetate which is eluted from a technetium-99m generator , and then either used directly as this soluble salt, or else used to synthesize a number of technetium-99m-based radiopharmaceuticals. Stomach and salivary gland imaging Meckel's diverticulum imaging Brain imaging Micturating cystogram First pass blood flow imaging First pass peripheral vascular imaging GI Bleeding Gastric emptying imaging Spleen imaging Cardiac blood pool imaging Peripheral vascular imaging First pass blood flow imaging Non-specific tumor imaging Thyroid tumor imaging Breast imaging Myocardial imaging Myocardial imaging Tl

2444-414: Is a gamma emitter. Lu is a beta emitter. N is a positron emitter. O is a positron emitter. Myocardial blood flow imaging P is a beta emitter. Ra is an alpha emitter. Rb is a positron and gamma emitter. Sm is a beta and gamma emitter. Se is a gamma emitter. Na is a positron and gamma emitter. Na is a beta and gamma emitter. Sr

2538-509: Is a gamma emitter. Thyroid tumor imaging Myocardial imaging Parathyroid imaging Xe is a gamma emitter. Y is a beta emitter. Radiation dose Ionizing radiation (US, ionising radiation in the UK), including nuclear radiation , consists of subatomic particles or electromagnetic waves that have sufficient energy to ionize atoms or molecules by detaching electrons from them. Some particles can travel up to 99% of

2632-633: Is a key focus of Medical Physics . Different countries around the world maintain regulatory frameworks that are responsible for the management and use of radionuclides in different medical settings. For example, in the US, the Nuclear Regulatory Commission (NRC) and the Food and Drug Administration (FDA) have guidelines in place for hospitals to follow. With the NRC, if radioactive materials aren't involved, like X-rays for example, they are not regulated by

2726-615: Is a particular hazard in semiconductor microelectronics employed in electronic equipment, with subsequent currents introducing operation errors or even permanently damaging the devices. Devices intended for high radiation environments such as the nuclear industry and extra-atmospheric (space) applications may be made radiation hard to resist such effects through design, material selection, and fabrication methods. Proton radiation found in space can also cause single-event upsets in digital circuits. The electrical effects of ionizing radiation are exploited in gas-filled radiation detectors, e.g.

2820-616: Is closest to visible energies, have been proven to result in formation of reactive oxygen species in skin, which cause indirect damage since these are electronically excited molecules which can inflict reactive damage, although they do not cause sunburn (erythema). Like ionization-damage, all these effects in skin are beyond those produced by simple thermal effects. The table below shows radiation and dose quantities in SI and non-SI units. Ionizing radiation has many industrial, military, and medical uses. Its usefulness must be balanced with its hazards,

2914-541: Is dependent on the speed of the neutron, whether fast or thermal or somewhere in between. It is also dependent on the nuclei it strikes and its neutron cross section . In inelastic scattering, neutrons are readily absorbed in a type of nuclear reaction called neutron capture and attributes to the neutron activation of the nucleus. Neutron interactions with most types of matter in this manner usually produce radioactive nuclei. The abundant oxygen-16 nucleus, for example, undergoes neutron activation, rapidly decays by

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3008-510: Is extracted. The F is then typically used to make FDG . Z = atomic number, the number of protons T 1/2 = half-life decay = mode of decay photons = principal photon energies in kilo-electron volts, keV , (abundance/decay) β = beta maximum energy in kilo-electron volts, keV , (abundance/decay) β = β decay ; β = β decay ; IT = isomeric transition ; ec = electron capture * X-rays from progeny, mercury , Hg A typical nuclear medicine study involves administration of

3102-415: Is of concern when shielding beta emitters, as the interaction of beta particles with some shielding materials produces Bremsstrahlung. The effect is greater with material having high atomic numbers, so material with low atomic numbers is used for beta source shielding. The positron or antielectron is the antiparticle or the antimatter counterpart of the electron . When a low-energy positron collides with

3196-425: Is preferred for imaging, so I-125 is used diagnostically only when the test requires a longer period to prepare the radiopharmaceutical and trace it, such as a fibrinogen scan to diagnose clotting. I-125's gamma radiation is of medium penetration, making it more useful as a therapeutic isotope for brachytherapy implant of radioisotope capsules for local treatment of cancers. I is a beta and gamma emitter. It

3290-570: Is significantly absorbed by the Earth's atmosphere, which is a radiation shield equivalent to about 10 meters of water. The alpha particle was named by Ernest Rutherford after the first letter in the Greek alphabet , α , when he ranked the known radioactive emissions in descending order of ionising effect in 1899. The symbol is α or α . Because they are identical to helium nuclei, they are also sometimes written as He or 2 He indicating

3384-872: Is the branch of pharmacology that specializes in these agents. The main group of these compounds are the radiotracers used to diagnose dysfunction in body tissues . While not all medical isotopes are radioactive, radiopharmaceuticals are the oldest and remain the most common of such drugs. As with other pharmaceutical drugs, there is standardization of the drug nomenclature for radiopharmaceuticals, although various standards coexist. The International Nonproprietary Names (INNs), United States Pharmacopeia (USP) names, and IUPAC names for these agents are usually similar other than trivial style differences. The details are explained at Radiopharmacology § Drug nomenclature for radiopharmaceuticals . A list of nuclear medicine radiopharmaceuticals follows. Some radioisotopes are used in ionic or inert form without attachment to

3478-466: Is the dominant mechanism in organic materials for photon energies below 100 keV, typical of classical X-ray tube originated X-rays . At energies beyond 100 keV, photons ionize matter increasingly through the Compton effect , and then indirectly through pair production at energies beyond 5 MeV. The accompanying interaction diagram shows two Compton scatterings happening sequentially. In every scattering event,

3572-610: Is ultraviolet spectrum energy which begins at about 3.1 eV (400 nm) at close to the same energy level which can cause sunburn to unprotected skin, as a result of photoreactions in collagen and (in the UV-B range) also damage in DNA (for example, pyrimidine dimers). Thus, the mid and lower ultraviolet electromagnetic spectrum is damaging to biological tissues as a result of electronic excitation in molecules which falls short of ionization, but produces similar non-thermal effects. To some extent, visible light and also ultraviolet A (UVA) which

3666-470: Is used both to destroy thyroid and thyroid cancer tissues (via beta radiation, which is short-range), and also other neuroendocrine tissues when used in MIBG. It can also be seen by a gamma camera , and can serve as a diagnostic imaging tracer, when treatment is also being attempted at the same time. However iodine-123 is usually preferred when only imaging is desired. Fe is a beta and gamma emitter. Kr

3760-401: Is used in a wide variety of fields such as medicine , nuclear power , research, and industrial manufacturing, but presents a health hazard if proper measures against excessive exposure are not taken. Exposure to ionizing radiation causes cell damage to living tissue and organ damage . In high acute doses, it will result in radiation burns and radiation sickness , and lower level doses over

3854-519: Is well understood, but quantitative models predicting the level of risk remain controversial. The most widely accepted model, the Linear no-threshold model (LNT), holds that the incidence of cancers due to ionizing radiation increases linearly with effective radiation dose at a rate of 5.5% per sievert . If this is correct, then natural background radiation is the most hazardous source of radiation to general public health, followed by medical imaging as

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3948-530: The Chernobyl disaster . Monatomic fluids, e.g. molten sodium , have no chemical bonds to break and no crystal lattice to disturb, so they are immune to the chemical effects of ionizing radiation. Simple diatomic compounds with very negative enthalpy of formation , such as hydrogen fluoride will reform rapidly and spontaneously after ionization. The ionization of materials temporarily increases their conductivity, potentially permitting damaging current levels. This

4042-514: The Geiger-Muller counter or the ion chamber . Most adverse health effects of exposure to ionizing radiation may be grouped in two general categories: The most common impact is stochastic induction of cancer with a latent period of years or decades after exposure. For example, ionizing radiation is one cause of chronic myelogenous leukemia , although most people with CML have not been exposed to radiation. The mechanism by which this occurs

4136-478: The Greek letter beta (β). There are two forms of beta decay, β and β , which respectively give rise to the electron and the positron. Beta particles are much less penetrating than gamma radiation, but more penetrating than alpha particles. High-energy beta particles may produce X-rays known as bremsstrahlung ("braking radiation") or secondary electrons ( delta ray ) as they pass through matter. Both of these can cause an indirect ionization effect. Bremsstrahlung

4230-413: The O (n,p) N reaction is a major source of X-rays emitted from the cooling water of a pressurized water reactor and contributes enormously to the radiation generated by a water-cooled nuclear reactor while operating. For the best shielding of neutrons, hydrocarbons that have an abundance of hydrogen are used. In fissile materials, secondary neutrons may produce nuclear chain reactions , causing

4324-678: The Washington University School of Medicine . These innovations led to fusion imaging with SPECT and CT by Bruce Hasegawa from University of California, San Francisco (UCSF), and the first PET/CT prototype by D. W. Townsend from University of Pittsburgh in 1998. PET and PET/CT imaging experienced slower growth in its early years owing to the cost of the modality and the requirement for an on-site or nearby cyclotron. However, an administrative decision to approve medical reimbursement of limited PET and PET/CT applications in oncology has led to phenomenal growth and widespread acceptance over

4418-628: The physical properties of the radiopharmaceutical used, its distribution in the body and its rate of clearance from the body. Effective doses can range from 6 μSv (0.006 mSv) for a 3 MBq chromium -51 EDTA measurement of glomerular filtration rate to 11.2 mSv (11,200 μSv) for an 80 MBq thallium -201 myocardial imaging procedure. The common bone scan with 600 MBq of technetium-99m MDP has an effective dose of approximately 2.9 mSv (2,900 μSv). Formerly, units of measurement were: The rad and rem are essentially equivalent for almost all nuclear medicine procedures, and only alpha radiation will produce

4512-466: The speed of light , and the electromagnetic waves are on the high-energy portion of the electromagnetic spectrum . Gamma rays , X-rays , and the higher energy ultraviolet part of the electromagnetic spectrum are ionizing radiation, whereas the lower energy ultraviolet , visible light , nearly all types of laser light, infrared , microwaves , and radio waves are non-ionizing radiation . The boundary between ionizing and non-ionizing radiation in

4606-651: The speed of light , c) these particles have enough kinetic energy to be ionizing, but there is considerable speed variation. For example, a typical alpha particle moves at about 5% of c, but an electron with 33 eV (just enough to ionize) moves at about 1% of c. Two of the first types of directly ionizing radiation to be discovered are alpha particles which are helium nuclei ejected from the nucleus of an atom during radioactive decay, and energetic electrons, which are called beta particles . Natural cosmic rays are made up primarily of relativistic protons but also include heavier atomic nuclei like helium ions and HZE ions . In

4700-545: The tracer principle. Possibly, the genesis of this medical field took place in 1936, when John Lawrence , known as "the father of nuclear medicine", took a leave of absence from his faculty position at Yale Medical School , to visit his brother Ernest Lawrence at his new radiation laboratory (now known as the Lawrence Berkeley National Laboratory ) in Berkeley , California . Later on, John Lawrence made

4794-590: The 1930s. The history of nuclear medicine will not be complete without mentioning these early pioneers. Nuclear medicine gained public recognition as a potential specialty when on May 11, 1946, an article in the Journal of the American Medical Association (JAMA) by Massachusetts General Hospital's Dr. Saul Hertz and Massachusetts Institute of Technology's Dr. Arthur Roberts, described the successful use of treating Graves' Disease with radioactive iodine (RAI)

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4888-453: The 1960s became a practical method for medical use. Today, Technetium-99m is the most utilized element in nuclear medicine and is employed in a wide variety of nuclear medicine imaging studies. Widespread clinical use of nuclear medicine began in the early 1950s, as knowledge expanded about radionuclides, detection of radioactivity, and using certain radionuclides to trace biochemical processes. Pioneering works by Benedict Cassen in developing

4982-416: The activation energy required for the reaction. Optical materials deteriorate under the effect of ionizing radiation. High-intensity ionizing radiation in air can produce a visible ionized air glow of telltale bluish-purple color. The glow can be observed, e.g., during criticality accidents , around mushroom clouds shortly after a nuclear explosion , or the inside of a damaged nuclear reactor like during

5076-627: The agency and instead are regulated by the individual states. International organizations, such as the International Atomic Energy Agency (IAEA), have regularly published different articles and guidelines for best practices in nuclear medicine as well as reporting on emerging technologies in nuclear medicine. Other factors that are considered in nuclear medicine include a patient's medical history as well as post-treatment management. Groups like International Commission on Radiological Protection have published information on how to manage

5170-458: The anatomy and function, which would otherwise be unavailable or would require a more invasive procedure or surgery. Although the risks of low-level radiation exposures are not well understood, a cautious approach has been universally adopted that all human radiation exposures should be kept As Low As Reasonably Practicable , "ALARP". (Originally, this was known as "As Low As Reasonably Achievable" (ALARA), but this has changed in modern draftings of

5264-561: The appearance of a "cold spot". Many tracer complexes have been developed to image or treat many different organs, glands, and physiological processes. In some centers, the nuclear medicine scans can be superimposed, using software or hybrid cameras, on images from modalities such as CT or MRI to highlight the part of the body in which the radiopharmaceutical is concentrated. This practice is often referred to as image fusion or co-registration, for example SPECT/CT and PET/CT. The fusion imaging technique in nuclear medicine provides information about

5358-466: The atmosphere such particles are often stopped by air molecules, and this produces short-lived charged pions, which soon decay to muons, a primary type of cosmic ray radiation that reaches the surface of the earth. Pions can also be produced in large amounts in particle accelerators . Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus . Alpha particle emissions are generally produced in

5452-528: The birthdate of nuclear medicine. This can probably be best placed between the discovery of artificial radioactivity in 1934 and the production of radionuclides by Oak Ridge National Laboratory for medicine-related use, in 1946. The origins of this medical idea date back as far as the mid-1920s in Freiburg , Germany, when George de Hevesy made experiments with radionuclides administered to rats, thus displaying metabolic pathways of these substances and establishing

5546-429: The bulk of the ionization effects are due to secondary ionization. Even though photons are electrically neutral, they can ionize atoms indirectly through the photoelectric effect and the Compton effect . Either of those interactions will cause the ejection of an electron from an atom at relativistic speeds, turning that electron into a beta particle (secondary beta particle) that will ionize other atoms. Since most of

5640-776: The cell-damaging properties of beta particles are used in therapeutic applications. Refined radionuclides for use in nuclear medicine are derived from fission or fusion processes in nuclear reactors , which produce radionuclides with longer half-lives, or cyclotrons , which produce radionuclides with shorter half-lives, or take advantage of natural decay processes in dedicated generators, i.e. molybdenum/technetium or strontium/rubidium. The most commonly used intravenous radionuclides are technetium-99m, iodine-123, iodine-131, thallium-201, gallium-67, fluorine-18 fluorodeoxyglucose , and indium-111 labeled leukocytes . The most commonly used gaseous/aerosol radionuclides are xenon-133, krypton-81m, ( aerosolised ) technetium-99m. A patient undergoing

5734-667: The decay of radioactive isotopes are the primary sources of natural ionizing radiation on Earth, contributing to background radiation . Ionizing radiation is also generated artificially by X-ray tubes , particle accelerators , and nuclear fission . Ionizing radiation is not immediately detectable by human senses, so instruments such as Geiger counters are used to detect and measure it. However, very high energy particles can produce visible effects on both organic and inorganic matter (e.g. water lighting in Cherenkov radiation ) or humans (e.g. acute radiation syndrome ). Ionizing radiation

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5828-465: The dose is delivered internally rather than from an external source such as an X-ray machine, and dosage amounts are typically significantly higher than those of X-rays. The radiation dose from a nuclear medicine investigation is expressed as an effective dose with units of sieverts (usually given in millisieverts, mSv). The effective dose resulting from an investigation is influenced by the amount of radioactivity administered in mega becquerels (MBq),

5922-428: The energy of the first ball divided between the two unequally. When a charged nucleus strikes a relatively slow-moving nucleus of an object in space, LET occurs and neutrons, alpha particles, low-energy protons, and other nuclei will be released by the collisions and contribute to the total absorbed dose of tissue. Indirectly ionizing radiation is electrically neutral and does not interact strongly with matter, therefore

6016-451: The first ionization energy of oxygen, and the ionization energy of hydrogen, both about 14 eV. In some Environmental Protection Agency references, the ionization of a typical water molecule at an energy of 33 eV is referenced as the appropriate biological threshold for ionizing radiation: this value represents the so-called W-value , the colloquial name for the ICRU 's mean energy expended in

6110-447: The first rectilinear scanner and Hal O. Anger 's scintillation camera ( Anger camera ) broadened the young discipline of nuclear medicine into a full-fledged medical imaging specialty. By the early 1960s, in southern Scandinavia , Niels A. Lassen , David H. Ingvar , and Erik Skinhøj developed techniques that provided the first blood flow maps of the brain, which initially involved xenon-133 inhalation; an intra-arterial equivalent

6204-399: The first application in patients of an artificial radionuclide when he used phosphorus-32 to treat leukemia . Many historians consider the discovery of artificially produced radionuclides by Frédéric Joliot-Curie and Irène Joliot-Curie in 1934 as the most significant milestone in nuclear medicine. In February 1934, they reported the first artificial production of radioactive material in

6298-433: The gamma ray transfers energy to an electron, and it continues on its path in a different direction and with reduced energy. The lowest ionization energy of any element is 3.89 eV, for caesium . However, US Federal Communications Commission material defines ionizing radiation as that with a photon energy greater than 10 eV (equivalent to a far ultraviolet wavelength of 124 nanometers ). Roughly, this corresponds to both

6392-484: The hydrogen atoms. When neutrons strike the hydrogen nuclei, proton radiation (fast protons) results. These protons are themselves ionizing because they are of high energy, are charged, and interact with the electrons in matter. Neutrons that strike other nuclei besides hydrogen will transfer less energy to the other particle if linear energy transfer does occur. But, for many nuclei struck by neutrons, inelastic scattering occurs. Whether elastic or inelastic scatter occurs

6486-421: 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. This often results in the appearance of a "hot spot", which is a focal increase in radio accumulation or a general increase in radio accumulation throughout the physiological system. Some disease processes result in the exclusion of a tracer, resulting in

6580-493: The invention of the first positron emission tomography scanner ( PET ). The concept of emission and transmission tomography, later developed into single photon emission computed tomography (SPECT), was introduced by David E. Kuhl and Roy Edwards in the late 1950s. Their work led to the design and construction of several tomographic instruments at the University of Pennsylvania. Tomographic imaging techniques were further developed at

6674-400: The ionized atoms are due to the secondary beta particles, photons are indirectly ionizing radiation. Radiated photons are called gamma rays if they are produced by a nuclear reaction , subatomic particle decay, or radioactive decay within the nucleus. They are called x-rays if produced outside the nucleus. The generic term "photon" is used to describe both. X-rays normally have

6768-440: The journal Nature , after discovering radioactivity in aluminum foil that was irradiated with a polonium preparation. Their work built upon earlier discoveries by Wilhelm Konrad Roentgen for X-ray, Henri Becquerel for radioactive uranium salts, and Marie Curie (mother of Irène Curie) for radioactive thorium, polonium and coining the term "radioactivity." Taro Takemi studied the application of nuclear physics to medicine in

6862-409: The last few years, which also was facilitated by establishing 18F-labelled tracers for standard procedures, allowing work at non-cyclotron-equipped sites. PET/CT imaging is now an integral part of oncology for diagnosis, staging and treatment monitoring. A fully integrated MRI/PET scanner is on the market from early 2011. Tc is normally supplied to hospitals through a radionuclide generator containing

6956-456: The legislation to add more emphasis on the "Reasonably" and less on the "Achievable".) Working with the ALARP principle, before a patient is exposed for a nuclear medicine examination, the benefit of the examination must be identified. This needs to take into account the particular circumstances of the patient in question, where appropriate. For instance, if a patient is unlikely to be able to tolerate

7050-476: The noise in an image and make it more photographically appealing, but if the clinical question can be answered without this level of detail, then this is inappropriate. As a result, the radiation dose from nuclear medicine imaging varies greatly depending on the type of study. The effective radiation dose can be lower than or comparable to or can far exceed the general day-to-day environmental annual background radiation dose. Likewise, it can also be less than, in

7144-417: The nuclear medicine imaging process is a dataset comprising one or more images. In multi-image datasets the array of images may represent a time sequence (i.e. cine or movie) often called a "dynamic" dataset, a cardiac gated time sequence, or a spatial sequence where the gamma-camera is moved relative to the patient. SPECT (single photon emission computed tomography) is the process by which images acquired from

7238-479: The original source is removed. Ionization of molecules can lead to radiolysis (breaking chemical bonds), and formation of highly reactive free radicals . These free radicals may then react chemically with neighbouring materials even after the original radiation has stopped. (e.g., ozone cracking of polymers by ozone formed by ionization of air). Ionizing radiation can also accelerate existing chemical reactions such as polymerization and corrosion, by contributing to

7332-536: The parent radionuclide molybdenum-99 . Mo is typically obtained as a fission product of U in nuclear reactors, however global supply shortages have led to the exploration of other methods of production . About a third of the world's supply, and most of Europe's supply, of medical isotopes is produced at the Petten nuclear reactor in the Netherlands . Another third of the world's supply, and most of North America's supply,

7426-528: The physiological function of the system being investigated as opposed to traditional anatomical imaging such as CT or MRI. Nuclear medicine imaging studies are generally more organ-, tissue- or disease-specific (e.g.: lungs scan, heart scan, bone scan, brain scan, tumor, infection, Parkinson etc.) than those in conventional radiology imaging, which focus on a particular section of the body (e.g.: chest X-ray, abdomen/pelvis CT scan, head CT scan, etc.). In addition, there are nuclear medicine studies that allow imaging of

7520-576: The process of alpha decay . Alpha particles are a strongly ionizing form of radiation, but when emitted by radioactive decay they have low penetration power and can be absorbed by a few centimeters of air, or by the top layer of human skin. More powerful alpha particles from ternary fission are three times as energetic, and penetrate proportionately farther in air. The helium nuclei that form 10–12% of cosmic rays, are also usually of much higher energy than those produced by radioactive decay and pose shielding problems in space. However, this type of radiation

7614-545: The radiation. In astronomy, however, where radiation origin often cannot be reliably determined, the old energy division has been preserved, with X-rays defined as being between about 120 eV and 120 keV, and gamma rays as being of any energy above 100 to 120 keV, regardless of source. Most astronomical " gamma-ray astronomy " are known not to originate in nuclear radioactive processes but, rather, result from processes like those that produce astronomical X-rays, except driven by much more energetic electrons. Photoelectric absorption

7708-408: The range of, or higher than the radiation dose from an abdomen/pelvis CT scan. Some nuclear medicine procedures require special patient preparation before the study to obtain the most accurate result. Pre-imaging preparations may include dietary preparation or the withholding of certain medications. Patients are encouraged to consult with the nuclear medicine department prior to a scan. The result of

7802-475: The release of patients from a hospital with unsealed radionuclides. Radiopharmaceuticals Radiopharmaceuticals , or medicinal radiocompounds , are a group of pharmaceutical drugs containing radioactive isotopes . Radiopharmaceuticals can be used as diagnostic and therapeutic agents. Radiopharmaceuticals emit radiation themselves, which is different from contrast media which absorb or alter external electromagnetism or ultrasound. Radiopharmacology

7896-453: The remains of long-dead organisms (such as wood that is thousands of years old). Ionizing radiation is generated through nuclear reactions, nuclear decay, by very high temperature, or via acceleration of charged particles in electromagnetic fields. Natural sources include the sun, lightning and supernova explosions. Artificial sources include nuclear reactors, particle accelerators, and x-ray tubes . The United Nations Scientific Committee on

7990-452: The resulting interaction will generate secondary radiation and cause cascading biological effects. If just one atom of tissue is displaced by an energetic proton, for example, the collision will cause further interactions in the body. This is called " linear energy transfer " (LET), which utilizes elastic scattering . LET can be visualized as a billiard ball hitting another in the manner of the conservation of momentum , sending both away with

8084-492: The thyroid gland, quantification of the thyroid function, and therapy for hyperthyroidism. Among the many radionuclides that were discovered for medical-use, none were as important as the discovery and development of Technetium-99m . It was first discovered in 1937 by C. Perrier and E. Segre as an artificial element to fill space number 43 in the Periodic Table. The development of a generator system to produce Technetium-99m in

8178-701: The ultraviolet area cannot be sharply defined, as different molecules and atoms ionize at different energies . The energy of ionizing radiation starts between 10  electronvolts (eV) and 33 eV. Ionizing subatomic particles include alpha particles , beta particles , and neutrons . These particles are created by radioactive decay , and almost all are energetic enough to ionize. There are also secondary cosmic particles produced after cosmic rays interact with Earth's atmosphere, including muons , mesons , and positrons . Cosmic rays may also produce radioisotopes on Earth (for example, carbon-14 ), which in turn decay and emit ionizing radiation. Cosmic rays and

8272-573: The way that the body handles substances differently when there is disease or pathology present. The radionuclide introduced into the body is often chemically bound to a complex that acts characteristically within the body; this is commonly known as a tracer . In the presence of disease, a tracer will often be distributed around the body and/or processed differently. 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

8366-660: The whole body based on certain cellular receptors or functions. Examples are whole body PET scans or PET/CT scans, gallium scans , indium white blood cell scans , MIBG and octreotide scans . While the ability of nuclear metabolism to image disease processes from differences in metabolism is unsurpassed, it is not unique. Certain techniques such as fMRI image tissues (particularly cerebral tissues) by blood flow and thus show metabolism. Also, contrast-enhancement techniques in both CT and MRI show regions of tissue that are handling pharmaceuticals differently, due to an inflammatory process. Diagnostic tests in nuclear medicine exploit

8460-569: Was also used to investigate, e.g., imagined sequential movements, mental calculation and mental spatial navigation. By the 1970s most organs of the body could be visualized using nuclear medicine procedures. In 1971, American Medical Association officially recognized nuclear medicine as a medical specialty. In 1972, the American Board of Nuclear Medicine was established, and in 1974, the American Osteopathic Board of Nuclear Medicine

8554-430: Was developed soon after, enabling measurement of the local distribution of cerebral activity for patients with neuropsychiatric disorders such as schizophrenia. Later versions would have 254 scintillators so a two-dimensional image could be produced on a color monitor. It allowed them to construct images reflecting brain activation from speaking, reading, visual or auditory perception and voluntary movement. The technique

8648-424: Was established, cementing nuclear medicine as a stand-alone medical specialty. In the 1980s, radiopharmaceuticals were designed for use in diagnosis of heart disease. The development of single photon emission computed tomography (SPECT), around the same time, led to three-dimensional reconstruction of the heart and establishment of the field of nuclear cardiology. More recent developments in nuclear medicine include

8742-617: Was produced at the Chalk River Laboratories in Chalk River , Ontario , Canada until its permanent shutdown in 2018. The most commonly used radioisotope in PET, F , is not produced in a nuclear reactor, but rather in a circular accelerator called a cyclotron . The cyclotron is used to accelerate protons to bombard the stable heavy isotope of oxygen O . The O constitutes about 0.20% of ordinary oxygen (mostly oxygen-16 ), from which it

8836-433: Was published. Additionally, Sam Seidlin . brought further development in the field describing a successful treatment of a patient with thyroid cancer metastases using radioiodine ( I-131 ). These articles are considered by many historians as the most important articles ever published in nuclear medicine. Although the earliest use of I-131 was devoted to therapy of thyroid cancer, its use was later expanded to include imaging of

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