Radionuclide Test
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Nuclear medicine (nuclear radiology, nucleology), is a
medical specialty A medical specialty is a branch of medical practice that is focused on a defined group of patients, diseases, skills, or philosophy. Examples include those branches of medicine that deal exclusively with children (pediatrics), cancer (oncology), ...
involving the application of
radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is conside ...
substances in the
diagnosis Diagnosis (: diagnoses) is the identification of the nature and cause of a certain phenomenon. Diagnosis is used in a lot of different academic discipline, disciplines, with variations in the use of logic, analytics, and experience, to determine " ...
and treatment of
disease A disease is a particular abnormal condition that adversely affects the structure or function (biology), function of all or part of an organism and is not immediately due to any external injury. Diseases are often known to be medical condi ...
. Nuclear imaging is, in a sense, ''
radiology Radiology ( ) is the medical specialty that uses medical imaging to diagnose diseases and guide treatment within the bodies of humans and other animals. It began with radiography (which is why its name has a root referring to radiation), but tod ...
done inside out'', because it records
radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or a material medium. This includes: * ''electromagnetic radiation'' consisting of photons, such as radio waves, microwaves, infr ...
emitted from within the body rather than
radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or a material medium. This includes: * ''electromagnetic radiation'' consisting of photons, such as radio waves, microwaves, infr ...
that is transmitted through the body from external sources like
X-ray generator An X-ray machine is a device that uses X-rays for a variety of applications including medicine, X-ray fluorescence, electronic assembly inspection, and measurement of material thickness in manufacturing operations. In medical applications, X-ra ...
s. In addition, nuclear medicine scans differ from radiology, as the emphasis is not on imaging anatomy, but on the function. For such reason, it is called a physiological imaging modality.
Single photon emission computed tomography Single-photon emission computed tomography (SPECT, or less commonly, SPET) is a nuclear medicine tomographic imaging technique using gamma rays. It is very similar to conventional nuclear medicine planar imaging using a gamma camera (that is, ...
(SPECT) and
positron emission tomography Positron emission tomography (PET) is a functional imaging technique that uses radioactive substances known as radiotracers to visualize and measure changes in metabolic processes, and in other physiological activities including blood flow, r ...
(PET) scans are the two most common imaging modalities in nuclear medicine.


Diagnostic medical imaging


Diagnostic

In nuclear medicine imaging,
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 ...
are taken internally, for example, through inhalation, intravenously, or orally. Then, external detectors (
gamma camera A gamma camera (γ-camera), also called a scintillation camera or Anger camera, is a device used to image gamma radiation emitting radioisotopes, a technique known as scintigraphy. The applications of scintigraphy include early drug development ...
s) 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. * 2D: ''
Scintigraphy Scintigraphy (from Latin ''scintilla'', "spark"), also known as a gamma scan, is a diagnostic test in nuclear medicine, where radioisotopes attached to drugs that travel to a specific organ or tissue (radiopharmaceuticals) are taken internally a ...
'' ("scint") is the use of internal radionuclides to create two-dimensional images. File:Nl bone scan2.jpg, A nuclear medicine whole body bone scan. The nuclear medicine whole body bone scan is generally used in evaluations of various bone-related pathology, such as for bone pain, stress fracture, nonmalignant bone lesions, bone infections, or the spread of cancer to the bone. File:Nl mpi2.jpg, Nuclear medicine myocardial perfusion scan with
thallium-201 Thallium (81Tl) has 42 isotopes with atomic masses that range from 176 to 217. 203Tl and 205Tl are the only stable isotopes and 204Tl is the most stable radioisotope with a half-life of 3.78 years. 207Tl, with a half-life of 4.77 minutes, has the ...
for the rest images (bottom rows) and
Tc-Sestamibi Technetium (99mTc) sestamibi (INN; commonly sestamibi; USP: technetium Tc 99m sestamibi; trade name Cardiolite) is a pharmaceutical agent used in nuclear medicine imaging. The drug is a coordination complex consisting of the radioisotope techn ...
for the stress images (top rows). The nuclear medicine myocardial perfusion scan plays a pivotal role in the non-invasive evaluation of
coronary artery disease Coronary artery disease (CAD), also called coronary heart disease (CHD), or ischemic heart disease (IHD), is a type of cardiovascular disease, heart disease involving Ischemia, the reduction of blood flow to the cardiac muscle due to a build-up ...
. The study not only identifies patients with coronary artery disease; it also provides overall prognostic information or overall risk of adverse cardiac events for the patient. File:Parathyroid subtraction.jpg, A nuclear medicine parathyroid scan demonstrates a
parathyroid adenoma A parathyroid adenoma is a benign tumor of the parathyroid gland. It generally causes hyperparathyroidism; there are very few reports of parathyroid adenomas that were not associated with hyperparathyroidism. A human being usually has four parath ...
adjacent to the left inferior pole of the thyroid gland. The above study was performed with Technetium-Sestamibi (1st column) and
iodine-123 Iodine-123 (123I) is a radioactive isotope of iodine used in nuclear medicine imaging, including single-photon emission computed tomography (SPECT) or SPECT/CT exams. The isotope's half-life is 13.2232 hours; the decay by electron capture to t ...
(2nd column) simultaneous imaging and the subtraction technique (3rd column). File:HIDA.jpg, Normal hepatobiliary scan ( HIDA scan). The nuclear medicine hepatobiliary scan is clinically useful in the detection of the gallbladder disease. File:Ventperf.jpg, Normal pulmonary ventilation and perfusion (V/Q) scan. The nuclear medicine V/Q scan is useful in the evaluation of
pulmonary embolism Pulmonary embolism (PE) is a blockage of an pulmonary artery, artery in the lungs by a substance that has moved from elsewhere in the body through the bloodstream (embolism). Symptoms of a PE may include dyspnea, shortness of breath, chest pain ...
. File:Thyroid scan.jpg, Thyroid scan with iodine-123 for evaluation of hyperthyroidism.
* 3D: ''
SPECT Single-photon emission computed tomography (SPECT, or less commonly, SPET) is a nuclear medicine tomographic imaging technique using gamma rays. It is very similar to conventional nuclear medicine planar imaging using a gamma camera (that is, ...
'' is a 3D tomographic technique that uses gamma camera data from many projections and can be reconstructed in different planes. ''
Positron emission tomography Positron emission tomography (PET) is a functional imaging technique that uses radioactive substances known as radiotracers to visualize and measure changes in metabolic processes, and in other physiological activities including blood flow, r ...
'' (PET) uses coincidence detection to image functional processes. File:hemangioma scan.jpg, A nuclear medicine SPECT liver scan with technetium-99m labeled autologous red blood cells. A focus of high uptake (arrow) in the liver is consistent with a
hemangioma A hemangioma or haemangioma is a usually benign vascular tumor derived from blood vessel cell types. The most common form, seen in infants, is an infantile hemangioma, known colloquially as a "strawberry mark", most commonly presenting on the sk ...
. File:PET-MIPS-anim.gif, Maximum intensity projection (MIP) of a whole-body positron emission tomography (PET) acquisition of a 79 kg female after intravenous injection of 371 MBq of 18F-FDG (one hour prior measurement).
Nuclear medicine tests differ from most other imaging modalities in that nuclear medicine scans primarily show 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 the whole body based on certain cellular receptors or functions. Examples are whole body
PET scan Positron emission tomography (PET) is a functional imaging technique that uses radioactive substances known as radiotracers to visualize and measure changes in Metabolism, metabolic processes, and in other physiological activities including bloo ...
s or PET/CT scans,
gallium scan A gallium scan is a type of nuclear medicine diagnostic investigation that uses either a gallium-67 (67Ga) or gallium-68 (68Ga) radiopharmaceutical to obtain images of a specific type of tissue, or disease state of tissue. The gamma emission o ...
s,
indium white blood cell scan The indium white blood cell scan is a nuclear medicine procedure in which white blood cells (mostly neutrophils) are removed from the patient, tagged with the radioisotope Indium-111, and then injected intravenously into the patient. The tagged le ...
s,
MIBG Iobenguane, or MIBG, is an aralkylguanidine analog of the adrenergic neurotransmitter norepinephrine (noradrenaline), typically used as a radiopharmaceutical. It acts as a blocking agent for adrenergic neurons. When radiolabeled, it can be use ...
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 Functional magnetic resonance imaging or functional MRI (fMRI) measures brain activity by detecting changes associated with blood flow. This technique relies on the fact that cerebral blood flow and neuronal activation are coupled. When an area o ...
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 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 Technetium-99m (99mTc) is a metastable nuclear isomer of technetium-99 (itself an isotope of technetium), symbolized as 99mTc, that is used in tens of millions of medical diagnostic procedures annually, making it the most commonly used Radiophar ...
to MDP, radioactivity can be transported and attached to bone via 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 the appearance of a "cold spot". Many tracer complexes have been developed to image or treat many different organs, glands, and physiological processes.


Hybrid scanning techniques

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 the anatomy and function, which would otherwise be unavailable or would require a more invasive procedure or surgery. File:nl petct.jpg, Normal whole body PET/CT scan with FDG-18. The whole body PET/CT scan is commonly used in the detection, staging and follow-up of various cancers. File:abnl petct.jpg, Abnormal whole body PET/CT scan with multiple metastases from a cancer. The whole body PET/CT scan has become an important tool in the evaluation of cancer.


Practical concerns in nuclear imaging

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 As low as reasonably practicable (ALARP), or as low as reasonably achievable (ALARA), is a principle in the regulation and management of safety-critical and safety-involved systems. The principle is that the residual risk shall be reduced as far a ...
, "ALARP". (Originally, this was known as "As Low As Reasonably Achievable" (ALARA), but this has changed in modern draftings of 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 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 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 Ionizing (ionising) radiation, including nuclear radiation, consists of subatomic particles or electromagnetic waves that have enough energy per individual photon or particle to ionize atoms or molecules by detaching electrons from them. Some pa ...
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 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.


Analysis

The result of 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 (SPECT, or less commonly, SPET) is a nuclear medicine tomographic imaging technique using gamma rays. It is very similar to conventional nuclear medicine planar imaging using a gamma camera (that is, ...
(single photon emission computed tomography) is the process by which images acquired from 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 In geometry, a three-dimensional space (3D space, 3-space or, rarely, tri-dimensional space) is a mathematical space in which three values (''coordinates'') are required to determine the position (geometry), position of a point (geometry), poi ...
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 model A multi-compartment model is a type of mathematical model used for describing the way materials or energies are transmitted among the ''compartments'' of a system. Sometimes, the physical system that we try to model in equations is too complex, so ...
s or a Patlak plot.


Interventional nuclear medicine

Radionuclide therapy can be used to treat conditions such as
hyperthyroidism Hyperthyroidism is a endocrine disease in which the thyroid gland produces excessive amounts of thyroid hormones. Thyrotoxicosis is a condition that occurs due to elevated levels of thyroid hormones of any cause and therefore includes hyperth ...
,
thyroid cancer Thyroid cancer is cancer that develops from the tissues of the thyroid gland. It is a disease in which cells grow abnormally and have the potential to spread to other parts of the body. Symptoms can include swelling or a lump in the neck, ...
, 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 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 Brachytherapy is a form of radiation therapy where a sealed radiation, radiation source is placed inside or next to the area requiring treatment. The word "brachytherapy" comes from the Ancient Greek, Greek word , meaning "short-distance" or "s ...
) to treat cancer.


History

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 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 Oak Ridge National Laboratory (ORNL) is a federally funded research and development centers, federally funded research and development center in Oak Ridge, Tennessee, United States. Founded in 1943, the laboratory is sponsored by the United Sta ...
for medicine-related use, in 1946. The origins of this medical idea date back as far as the mid-1920s in
Freiburg Freiburg im Breisgau or simply Freiburg is the List of cities in Baden-Württemberg by population, fourth-largest city of the German state of Baden-Württemberg after Stuttgart, Mannheim and Karlsruhe. Its built-up area has a population of abou ...
, Germany, when
George de Hevesy George Charles de Hevesy (born György Bischitz; ; ; 1 August 1885 – 5 July 1966) was a Hungarian radiochemist and Nobel Prize in Chemistry laureate, recognized in 1943 for his key role in the development of radioactive tracers to study ch ...
made experiments with radionuclides administered to rats, thus displaying metabolic pathways of these substances and establishing 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 The Yale School of Medicine is the medical school of Yale University, a private research university in New Haven, Connecticut. It was founded in 1810 as the Medical Institution of Yale College and formally opened in 1813. It is the sixth-oldest m ...
, to visit his brother
Ernest Lawrence Ernest Orlando Lawrence (August 8, 1901 – August 27, 1958) was an American accelerator physicist who received the Nobel Prize in Physics in 1939 for his invention of the cyclotron. He is known for his work on uranium-isotope separation for ...
at his new radiation laboratory (now known as the
Lawrence Berkeley National Laboratory Lawrence Berkeley National Laboratory (LBNL, Berkeley Lab) is a Federally funded research and development centers, federally funded research and development center in the Berkeley Hills, hills of Berkeley, California, United States. Established i ...
) in
Berkeley Berkeley most often refers to: *Berkeley, California, a city in the United States **University of California, Berkeley, a public university in Berkeley, California *George Berkeley (1685–1753), Anglo-Irish philosopher Berkeley may also refer to ...
,
California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...
. Later on, John Lawrence made the first application in patients of an artificial radionuclide when he used
phosphorus-32 Phosphorus-32 (32P) is a radioactive isotope of phosphorus. The nucleus of phosphorus-32 contains 15 protons and 17 neutrons, one more neutron than the most common isotope of phosphorus, phosphorus-31. Phosphorus-32 only exists in small quantiti ...
to treat
leukemia Leukemia ( also spelled leukaemia; pronounced ) is a group of blood cancers that usually begin in the bone marrow and produce high numbers of abnormal blood cells. These blood cells are not fully developed and are called ''blasts'' or '' ...
. Many historians consider the discovery of artificially produced radionuclides by
Frédéric Joliot-Curie Jean Frédéric Joliot-Curie (; ; 19 March 1900 – 14 August 1958) was a French chemist and physicist who received the 1935 Nobel Prize in Chemistry with his wife, Irène Joliot-Curie, for their discovery of induced radioactivity. They were t ...
and
Irène Joliot-Curie Irène Joliot-Curie (; ; 12 September 1897 – 17 March 1956) was a French chemist and physicist who received the 1935 Nobel Prize in Chemistry with her husband, Frédéric Joliot-Curie, for their discovery of induced radioactivity. They were ...
in 1934 as the most significant milestone in nuclear medicine. In February 1934, they reported the first artificial production of radioactive material in 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 Wilhelm may refer to: People and fictional characters * William Charles John Pitcher, costume designer known professionally as "Wilhelm" * Wilhelm (name), a list of people and fictional characters with the given name or surname Other uses * Wilhe ...
for X-ray,
Henri Becquerel Antoine Henri Becquerel ( ; ; 15 December 1852 – 25 August 1908) was a French nuclear physicist who shared the 1903 Nobel Prize in Physics with Marie and Pierre Curie for his discovery of radioactivity. Biography Family and education Becq ...
for radioactive uranium salts, and
Marie Curie Maria Salomea Skłodowska-Curie (; ; 7 November 1867 – 4 July 1934), known simply as Marie Curie ( ; ), was a Polish and naturalised-French physicist and chemist who conducted pioneering research on radioactivity. She was List of female ...
(mother of Irène Curie) for radioactive thorium, polonium and coining the term "radioactivity." Taro Takemi studied the application of
nuclear physics Nuclear physics is the field of physics that studies atomic nuclei and their constituents and interactions, in addition to the study of other forms of nuclear matter. Nuclear physics should not be confused with atomic physics, which studies th ...
to medicine in 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) 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 Iodine-131 (131I, I-131) is an important radioisotope of iodine discovered by Glenn Seaborg and John Livingood in 1938 at the University of California, Berkeley. It has a radioactive decay half-life of about eight days. It is associated with nu ...
). 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 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 Technetium-99m (99mTc) is a metastable nuclear isomer of technetium-99 (itself an isotope of technetium), symbolized as 99mTc, that is used in tens of millions of medical diagnostic procedures annually, making it the most commonly used Radiophar ...
. 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 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 Benedict may refer to: People Names *Benedict (given name), including a list of people with the given name *Benedict (surname), including a list of people with the surname Religious figures * Pope Benedict I (died 579) *Pope Benedict II (635– ...
in developing 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 Scandinavia is a subregion#Europe, subregion of northern Europe, with strong historical, cultural, and linguistic ties between its constituent peoples. ''Scandinavia'' most commonly refers to Denmark, Norway, and Sweden. It can sometimes also ...
, 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 was developed soon after, enabling measurement of the local distribution of cerebral activity for patients with
neuropsychiatric Neuropsychiatry is a branch of medicine that deals with psychiatry as it relates to neurology, in an effort to understand and attribute behavior to the interaction of neurobiology and social psychology factors. Within neuropsychiatry, the mind i ...
disorders such as schizophrenia. Later versions would have 254
scintillator A scintillator ( ) is a material that exhibits scintillation, the property of luminescence, when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate (i.e. re-emit the ab ...
s 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 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 The American Medical Association (AMA) is an American professional association and lobbying group of physicians and medical students. This medical association was founded in 1847 and is headquartered in Chicago, Illinois. Membership was 271,660 ...
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 The American Osteopathic Board of Nuclear Medicine (AOBNM) is an organization that provides board certification to qualified Doctors of Osteopathic Medicine (D.O.) who specialize in the use of radioactive substances in the diagnosis and treatment ...
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 the invention of the first positron emission tomography scanner (
PET A pet, or companion animal, is an animal kept primarily for a person's company or entertainment rather than as a working animal, livestock, or a laboratory animal. Popular pets are often considered to have attractive/ cute appearances, inte ...
). 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 the
Washington University School of Medicine Washington University School of Medicine (WashU Medicine) is the medical school of Washington University in St. Louis, located in the Central West End neighborhood of St. Louis, Missouri. Founded in 1891, the School of Medicine shares a ca ...
. These innovations led to fusion imaging with SPECT and CT by Bruce Hasegawa from
University of California, San Francisco The University of California, San Francisco (UCSF) is a Public university, public Land-grant university, land-grant research university in San Francisco, California, United States. It is part of the University of California system and is dedic ...
(UCSF), and the first PET/CT prototype by D. W. Townsend from
University of Pittsburgh The University of Pittsburgh (Pitt) is a Commonwealth System of Higher Education, state-related research university in Pittsburgh, Pennsylvania, United States. The university is composed of seventeen undergraduate and graduate schools and colle ...
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 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.


Sources of radionuclides

99mTc is normally supplied to hospitals through a
radionuclide generator A radionuclide generator is a device which provides a local supply of a short-lived radioactive substance from the decay of a longer-lived parent radionuclide. They are commonly used in nuclear medicine to supply a radiopharmacy. The generator prov ...
containing the parent radionuclide
molybdenum-99 Molybdenum (42Mo) has 39 known isotopes, ranging in atomic mass from 81 to 119, as well as four metastable nuclear isomers. Seven isotopes occur naturally, with atomic masses of 92, 94, 95, 96, 97, 98, and 100. All unstable isotopes of molybdenum ...
. 99Mo is typically obtained as a fission product of 235U 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 , Terminology of the Low Countries, informally Holland, is a country in Northwestern Europe, with Caribbean Netherlands, overseas territories in the Caribbean. It is the largest of the four constituent countries of the Kingdom of the Nether ...
. Another third of the world's supply, and most of North America's supply, was produced at the
Chalk River Laboratories Chalk River Laboratories (; also known as CRL, Chalk River Labs and formerly Chalk River Nuclear Laboratories, CRNL) is a Canadian nuclear research facility in Deep River, about north-west of Ottawa. CRL is a site of significant research and ...
in
Chalk River Chalk River (2016 population: 1029) is a community located within the town of Laurentian Hills in Renfrew County, Ontario, Canada. It is located in the Upper Ottawa Valley along Highway 17 (Ontario), Highway 17 (Trans-Canada Highway), inland ...
,
Ontario Ontario is the southernmost Provinces and territories of Canada, province of Canada. Located in Central Canada, Ontario is the Population of Canada by province and territory, country's most populous province. As of the 2021 Canadian census, it ...
, Canada until its permanent shutdown in 2018. The most commonly used radioisotope in PET, 18F, is not produced in a nuclear reactor, but rather in a circular accelerator called a
cyclotron A cyclotron is a type of particle accelerator invented by Ernest Lawrence in 1929–1930 at the University of California, Berkeley, and patented in 1932. Lawrence, Ernest O. ''Method and apparatus for the acceleration of ions'', filed: Januar ...
. The cyclotron is used to accelerate
proton A proton is a stable subatomic particle, symbol , Hydron (chemistry), H+, or 1H+ with a positive electric charge of +1 ''e'' (elementary charge). Its mass is slightly less than the mass of a neutron and approximately times the mass of an e ...
s to bombard the stable heavy isotope of oxygen 18O. The 18O constitutes about 0.20% of ordinary
oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...
(mostly
oxygen-16 Oxygen-16 (symbol: 16O or ) is a nuclide. It is a stable isotope of oxygen, with 8 neutrons and 8 protons in its nucleus, and when not ionized, 8 electrons orbiting the nucleus. Oxygen-16 has a mass of . It is the most abundant isotope of oxyg ...
), from which it is extracted. The 18F is then typically used to make FDG. A typical nuclear medicine study involves administration of a
radionuclide A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess numbers of either neutrons or protons, giving it excess nuclear energy, and making it unstable. This excess energy can be used in one of three ...
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 Microencapsulation is a process in which tiny particles or droplets are surrounded by a coating to give small capsules, with useful properties. In general, it is used to incorporate food ingredients, enzymes, cells or other materials on a micr ...
. Some studies require the labeling of a patient's own blood cells with a radionuclide ( leukocyte scintigraphy and
red blood cell Red blood cells (RBCs), referred to as erythrocytes (, with -''cyte'' translated as 'cell' in modern usage) in academia and medical publishing, also known as red cells, erythroid cells, and rarely haematids, are the most common type of blood cel ...
scintigraphy). Most diagnostic radionuclides emit
gamma ray A gamma ray, also known as gamma radiation (symbol ), is a penetrating form of electromagnetic radiation arising from high energy interactions like the radioactive decay of atomic nuclei or astronomical events like solar flares. It consists o ...
s either directly from their decay or indirectly through
electron–positron annihilation Electron–positron annihilation occurs when an electron () and a positron (, the electron's antiparticle) collide. At low energies, the result of the collision is the annihilation of the electron and positron, and the creation of energetic ph ...
, while the cell-damaging properties of
beta particles A beta particle, also called beta ray or beta radiation (symbol β), is a high-energy, high-speed electron or positron emitted by the radioactive decay of an atomic nucleus, known as beta decay. There are two forms of beta decay, β− decay and Π...
are used in therapeutic applications. Refined radionuclides for use in nuclear medicine are derived from fission or fusion processes in
nuclear reactor A nuclear reactor is a device used to initiate and control a Nuclear fission, fission nuclear chain reaction. They are used for Nuclear power, commercial electricity, nuclear marine propulsion, marine propulsion, Weapons-grade plutonium, weapons ...
s, which produce radionuclides with longer half-lives, or
cyclotron A cyclotron is a type of particle accelerator invented by Ernest Lawrence in 1929–1930 at the University of California, Berkeley, and patented in 1932. Lawrence, Ernest O. ''Method and apparatus for the acceleration of ions'', filed: Januar ...
s, 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 []Fluorodeoxyglucose (International Nonproprietary Name, INN), or fluorodeoxyglucose F 18 (United States Adopted Name, USAN and United States Pharmacopeia, USP), also commonly called fluorodeoxyglucose and abbreviated []FDG, 2-[]FDG o ...
, and indium-111 labeled leukocytes. The most commonly used gaseous/aerosol radionuclides are xenon-133, krypton-81m, (aerosolised) technetium-99m.


Policies and procedures


Radiation dose

A patient undergoing a nuclear medicine procedure will receive a
radiation dose Ionizing (ionising) radiation, including nuclear radiation, consists of subatomic particles or electromagnetic waves that have enough energy per individual photon or particle to ionize atoms or molecules by detaching electrons from them. Some pa ...
. 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 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
sievert The sievert (symbol: SvPlease note there are two non-SI units that use the same Sv abbreviation: the sverdrup and svedberg.) is a derived unit in the International System of Units (SI) intended to represent the stochastic health risk of ionizin ...
s (usually given in millisieverts, mSv). The effective dose resulting from an investigation is influenced by the amount of radioactivity administered in mega
becquerel The becquerel (; symbol: Bq) is the unit of radioactivity in the International System of Units (SI). One becquerel is defined as an activity of one per second, on average, for aperiodic activity events referred to a radionuclide. For applicatio ...
s (MBq), the
physical properties A physical property is any property of a physical system that is measurable. The changes in the physical properties of a system can be used to describe its changes between momentary states. A quantifiable physical property is called ''physical ...
of the
radiopharmaceutical 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 ...
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 Chromium is a chemical element; it has Symbol (chemistry), symbol Cr and atomic number 24. It is the first element in Group 6 element, group 6. It is a steely-grey, Luster (mineralogy), lustrous, hard, and brittle transition metal. Chromium ...
-51 EDTA measurement of
glomerular filtration rate Renal functions include maintaining an acid–base balance; regulating fluid balance; regulating sodium, potassium, and other electrolytes; clearance (medicine), clearing toxins; absorption of glucose, amino acids, and other small molecules; reg ...
to 11.2 mSv (11,200 μSv) for an 80 MBq
thallium Thallium is a chemical element; it has Symbol (chemistry), symbol Tl and atomic number 81. It is a silvery-white post-transition metal that is not found free in nature. When isolated, thallium resembles tin, but discolors when exposed to air. Che ...
-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
curie Curie may refer to: *Curie family, a family of distinguished scientists: :* Jacques Curie (1856–1941), French physicist, Pierre's brother :* Pierre Curie (1859–1906), French physicist and Nobel Prize winner, Marie's husband :* Marie Curi ...
(Ci), equal to 3.7 × 1010 Bq, and also equal to 1.0 grams of
radium Radium is a chemical element; it has chemical symbol, symbol Ra and atomic number 88. It is the sixth element in alkaline earth metal, group 2 of the periodic table, also known as the alkaline earth metals. Pure radium is silvery-white, ...
( Ra-226); *the rad (radiation absorbed dose), now replaced by the
gray Grey (more frequent in British English) or gray (more frequent in American English) is an intermediate color between black and white. It is a neutral or achromatic color, meaning that it has no chroma. It is the color of a cloud-covered s ...
; and * the rem ( Röntgen equivalent man), now replaced by the
sievert The sievert (symbol: SvPlease note there are two non-SI units that use the same Sv abbreviation: the sverdrup and svedberg.) is a derived unit in the International System of Units (SI) intended to represent the stochastic health risk of ionizin ...
. The rad and rem are essentially equivalent for almost all nuclear medicine procedures, and only
alpha radiation Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus). The parent nucleus transforms or "decays" into a daughter product, with a mass number that is reduced by four and an atom ...
will produce a higher Rem or Sv value, due to its much higher
Relative Biological Effectiveness In radiobiology, the relative biological effectiveness (often abbreviated as RBE) is the ratio of biological effectiveness of one type of ionizing radiation relative to another, given the same amount of absorbed energy. The RBE is an empirical ...
(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 Health physics, also referred to as the science of radiation protection, is the profession devoted to protecting people and their environment from potential radiation hazards, while making it possible to enjoy the beneficial uses of radiation. H ...
; the development and practice of safe and effective nuclear medicinal techniques is a key focus of
Medical Physics Medical physics deals with the application of the concepts and methods of physics to the prevention, diagnosis and treatment of human diseases with a specific goal of improving human health and well-being. Since 2008, medical physics has been incl ...
.


Regulatory frameworks and guidelines

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 The United States Nuclear Regulatory Commission (NRC) is an independent agency of the United States government tasked with protecting public health and safety related to nuclear energy. Established by the Energy Reorganization Act of 1974, the ...
(NRC) and the
Food and Drug Administration The United States Food and Drug Administration (FDA or US FDA) is a List of United States federal agencies, federal agency of the United States Department of Health and Human Services, Department of Health and Human Services. The FDA is respo ...
(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 the agency and instead are regulated by the individual states. International organizations, such as the
International Atomic Energy Agency The International Atomic Energy Agency (IAEA) is an intergovernmental organization that seeks to promote the peaceful use of nuclear technology, nuclear energy and to inhibit its use for any military purpose, including nuclear weapons. It was ...
(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 The International Commission on Radiological Protection (ICRP) is an independent, international, non-governmental organization, with the mission to protect people, animals, and the environment from the harmful effects of ionising radiation. Its ...
have published information on how to manage the release of patients from a hospital with unsealed radionuclides.


See also

*
Human subject research Human subject research is systematic, scientific investigation that can be either interventional (a "trial") or observational (no "test article") and involves human beings as research subjects, commonly known as test subjects. Human subject r ...
* List of Nuclear Medicine Societies * Nuclear medicine physician * Nuclear pharmacy *
Nuclear technology Nuclear technology is technology that involves the nuclear reactions of atomic nucleus, atomic nuclei. Among the notable nuclear technologies are nuclear reactors, nuclear medicine and nuclear weapons. It is also used, among other things, in s ...
*
Radiographer Radiographers, also known as radiology technologists, radiologic technologists, diagnostic radiographers and medical radiation technologists, are healthcare professionals who specialise in the imaging of human anatomy for the diagnosis and tr ...


References


Further reading

* * * * *


External links


Solving the Medical Isotope Crisis
Hearing before the Subcommittee on Energy and Environment of the Committee on Energy and Commerce, House of Representatives, One Hundred Eleventh Congress, First Session, September 9, 2009 {{Authority control Radiology Medicinal radiochemistry