View source for Medicine:Nuclear medicine

{{short description|Medical specialty}}
{{Infobox interventions
|  Name        = Nuclear medicine
|  Image       = Viewer medecine nucleaire keosys.JPG
|  Caption     = A nuclear medicine PET scan
|  ICD10       = {{ICD10PCS|C|C}}
|  ICD9unlinked = {{ICD9proc|92}}
|  MeshID      = D009683
|  OPS301      = {{OPS301|3-70}}-{{OPS301|3-72}}, {{OPS301|8-53}}
|  OtherCodes  =
}}

'''Nuclear medicine''' or '''nucleology'''<ref>[https://www.answers.com/Q/What_is_nucleology What is nucleology?]</ref> is a medical specialty involving the application of radioactive substances in the [[Medicine:Diagnosis|diagnosis]] and treatment of [[Disease|disease]]. Nuclear imaging, in a sense, is "[[Medicine:Radiology|radiology]] done inside out" because it records [[Physics:Radiation|radiation]] [[Physics:Radiant exitance|emit]]ted from within the body rather than [[Physics:Radiation|radiation]] that is [[Physics:Transmittance|transmit]]ted through the body from external sources like [[Physics:X-ray generator|X-ray generator]]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 [[Medicine:Functional imaging|physiological imaging modality]]. Single photon emission computed tomography (SPECT) and [[Physics:Positron emission tomography|positron emission tomography]] (PET) scans are the two most common imaging modalities in nuclear medicine.<ref>{{cite web|url=http://www.saintpetershcs.com/Nuclear-Medicine|title=Nuclear Medicine|access-date=20 August 2015|archive-url=https://web.archive.org/web/20150227082414/http://www.saintpetershcs.com/Nuclear-Medicine/|archive-date=27 February 2015|url-status=dead}}</ref>

== Diagnostic medical imaging ==

=== Diagnostic ===
In nuclear medicine imaging, radiopharmaceuticals are taken internally, for example, through inhalation, intravenously, or orally. Then, external detectors ([[Physics:Gamma camera|gamma camera]]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.{{cn|date=April 2022}}

There are several techniques of diagnostic nuclear medicine.
* 2D: ''Scintigraphy'' ("scint") is the use of internal radionuclides to create two-dimensional images.<ref>[http://medical-dictionary.thefreedictionary.com/scintigraphy scintigraphy] Citing: Dorland's Medical Dictionary for Health Consumers, 2007 by Saunders; Saunders Comprehensive Veterinary Dictionary, 3 ed. 2007; McGraw-Hill Concise Dictionary of Modern Medicine, 2002 by The McGraw-Hill Companies</ref>
<gallery class="center">
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 for the rest images (bottom rows) and Tc-Sestamibi 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. 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 adjacent to the left inferior pole of the thyroid gland. The above study was performed with Technetium-Sestamibi (1st column) and iodine-123 (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.
File:Thyroid scan.jpg|Thyroid scan with iodine-123 for evaluation of hyperthyroidism.
</gallery>
* 3D: ''SPECT'' is a 3D tomographic technique that uses gamma camera data from many projections and can be reconstructed in different planes. ''[[Physics:Positron emission tomography|Positron emission tomography]]'' (PET) uses coincidence detection to image functional processes.

<gallery class="center">
  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.
  File:PET-MIPS-anim.gif|Maximum intensity projection (MIP) of a whole-body positron emission tomography (PET) acquisition of a 79&nbsp;kg female after intravenous injection of 371&nbsp;MBq of 18F-FDG (one hour prior measurement).
</gallery>

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 scans or [[Biology:PET-CT|PET/CT]] scans, [[Chemistry:Gallium scan|gallium scan]]s, indium white blood cell scans, MIBG and [[Medicine:Octreotide scan|octreotide scan]]s.

[[File:Iodine wb scan.jpg|thumb|Iodine-123 whole body scan for thyroid cancer evaluation. The study above was performed after the total thyroidectomy and TSH stimulation with thyroid hormone medication withdrawal. The study shows a small residual thyroid tissue in the neck and a mediastinum lesion, consistent with the thyroid cancer metastatic disease. The observable uptakes in the stomach and bladder are normal physiologic findings.]]
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 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 [[Biology:Radioactive tracer|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 ([[Chemistry:Medronic acid|MDP]]) can be preferentially taken up by bone. By chemically attaching [[Physics:Technetium-99m|technetium-99m]] 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.
<gallery class="center">
  File:nl petct.jpg|Normal whole body PET/CT scan with [[Chemistry:Fludeoxyglucose (18F)|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.
</gallery>

=== 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, "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 as low as reasonably practicable. 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 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 [[Physics:Background radiation|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) 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 [[3D computer graphics|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.{{citation needed|date=October 2013}}

Time sequences can be further analysed using kinetic models such as [[Multi-compartment model|multi-compartment model]]s or a [[Patlak plot]].

== Interventional nuclear medicine ==
{{Main|Medicine:Unsealed source radiotherapy|Medicine:Brachytherapy}}
Radionuclide therapy can be used to treat conditions such as [[Medicine:Hyperthyroidism|hyperthyroidism]], [[Medicine:Thyroid cancer|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 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.

'''Common nuclear medicine [[Medicine:Unsealed source radiotherapy|(unsealed source) therapies]]'''
{| class="wikitable"
|-
! Substance
! Condition
|-
| [[Physics:Iodine-131|Iodine-131]]-sodium iodide
| [[Medicine:Hyperthyroidism|hyperthyroidism]] and [[Medicine:Thyroid cancer|thyroid cancer]]
|-
| Yttrium-90-[[Chemistry:Ibritumomab tiuxetan|ibritumomab tiuxetan]] (Zevalin) and Iodine-131-[[Chemistry:Tositumomab|tositumomab]] (Bexxar)
| refractory [[Medicine:Lymphoma|lymphoma]]
|-
| <sup>131</sup>I-MIBG (metaiodobenzylguanidine)
| neuroendocrine tumors
|-
| [[Physics:Samarium-153|Samarium-153]] or [[Physics:Strontium-89|Strontium-89]]
| palliative [[Biology:Bone pain|bone pain]] treatment
|-
|[[Chemistry:Rhenium|Rhenium]]-188
|[[Medicine:Squamous cell carcinoma|squamous cell carcinoma]] or [[Medicine:Basal-cell carcinoma|basal cell carcinoma]] of the skin
|}

In some centers the nuclear medicine department may also use implanted capsules of isotopes ([[Medicine:Brachytherapy|brachytherapy]]) to treat cancer.

'''Commonly used radiation sources (radionuclides) for brachytherapy'''<ref>{{cite web|url=http://www.nndc.bnl.gov/wallet/wc7.html|title=Nuclear Wallet Cards|access-date=20 August 2015}}</ref>

{| class="wikitable"
|-
! Radionuclide
! Type
! Half-life
! Energy
|-
| [[Physics:Caesium-137|Caesium-137]] (<sup>137</sup>Cs)
| γ-ray
| 30.17 years
| 0.662 MeV
|-
| [[Physics:Cobalt-60|Cobalt-60]] (<sup>60</sup>Co)
| γ-ray
| 5.26 years
| 1.17, 1.33 MeV
|-
| [[Physics:Iridium-192|Iridium-192]] (<sup>192</sup>Ir)
| β<sup>−</sup>-particles
| 73.8 days
| 0.38 MeV (mean)
|-
| [[Physics:Iodine-125|Iodine-125]] (<sup>125</sup>I)
| γ-rays
| 59.6 days
| 27.4, 31.4 and 35.5 keV
|-
| [[Physics:Palladium-103|Palladium-103]] (<sup>103</sup>Pd)
| γ-ray
| 17.0 days
| 21 keV (mean)
|-
| [[Physics:Ruthenium-106|Ruthenium-106]] (<sup>106</sup>Ru)
| β<sup>−</sup>-particles
| 1.02 years
| 3.54 MeV
|}

== 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 [[Organization:Oak Ridge National Laboratory|Oak Ridge National Laboratory]] for medicine-related use, in 1946.<ref name="Edwards">{{cite journal|pmid=388628|year=1979|last1=Edwards|first1=C. L.|title=Tumor-localizing radionuclides in retrospect and prospect|journal=Seminars in Nuclear Medicine|volume=9|issue=3|pages=186–9|doi=10.1016/s0001-2998(79)80030-6}}</ref>

The origins of this medical idea date back as far as the mid-1920s in Freiburg, Germany, when [[Biography:George de Hevesy|George de Hevesy]] made experiments with radionuclides administered to rats, thus displaying metabolic pathways of these substances and establishing the [[Biology:Radioactive tracer|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 [[Biography:Ernest Lawrence|Ernest Lawrence]] at his new radiation laboratory (now known as the [[Organization:Lawrence Berkeley National Laboratory|Lawrence Berkeley National Laboratory]]) in Berkeley, {{wipe|California}}. Later on, John Lawrence made the first application in patients of an artificial radionuclide when he used [[Physics:Phosphorus-32|phosphorus-32]] to treat [[Medicine:Leukemia|leukemia]].<ref>[http://jnm.snmjournals.org/content/40/1/16N.full.pdf Donner Laboratory: The Birthplace of. Nuclear Medicine]</ref><ref>{{Cite web |url=http://interactive.snm.org/index.cfm?PageID=1107 |title=Important Moments in the History of Nuclear Medicine |access-date=2012-01-03 |archive-date=2013-12-14 |archive-url=https://web.archive.org/web/20131214202136/http://interactive.snm.org/index.cfm?PageID=1107 |url-status=dead }}</ref>

Many historians consider the discovery of artificially produced radionuclides by [[Biography:Frédéric Joliot-Curie|Frédéric Joliot-Curie]] and [[Biography:Irène Joliot-Curie|Irène Joliot-Curie]] in 1934 as the most significant milestone in nuclear medicine.<ref name="Edwards" /> 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 for X-ray, [[Biography:Henri Becquerel|Henri Becquerel]] for radioactive uranium salts, and [[Biography:Marie Curie|Marie Curie]] (mother of Irène Curie) for radioactive thorium, polonium and coining the term "radioactivity." Taro Takemi studied the application of [[Physics:Nuclear physics|nuclear physics]] 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.<ref name="pmid21025609">{{cite journal | vauthors = Hertz S, Roberts A | title = Radioactive iodine in the study of thyroid physiology; the use of radioactive iodine therapy in hyperthyroidism | journal = Journal of the American Medical Association | volume = 131 | pages = 81–6 | date = May 1946 | pmid = 21025609 | doi = 10.1001/jama.1946.02870190005002}}</ref> Additionally, Sam Seidlin.<ref name="pmid20274882">{{cite journal | vauthors = Seidlin SM, Marinelli LD, Oshry E | title = Radioactive iodine therapy; effect on functioning metastases of adenocarcinoma of the thyroid | journal = Journal of the American Medical Association | volume = 132 | issue = 14 | pages = 838–47 | date = December 1946 | pmid = 20274882 | doi = 10.1001/jama.1946.02870490016004}}</ref> 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.<ref name="nmtext">{{cite book | vauthors = Henkin R, etal | title = Nuclear Medicine | edition = First | date = 1996 | isbn = 978-0-8016-7701-4}}</ref> 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 [[Physics:Technetium-99m|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 [[Medicine:Radionuclide generator|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 in developing the first [[Medicine:Rectilinear scanner|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 [[Place:Scandinavia|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 [[Physics:Xenon-133|xenon-133]] inhalation;<ref>{{cite journal| vauthors = Lassen NA, Ingvar DH  |author-link2=:sv:David H. Ingvar|title=Quantitative determination of regional cerebral blood-flow in man|journal=The Lancet|year=1961|volume=278|issue=7206|pages=806–807 |doi=10.1016/s0140-6736(61)91092-3}}</ref> an intra-arterial equivalent was developed soon after, enabling measurement of the local distribution of cerebral activity for patients with [[Biology:Neuropsychiatry|neuropsychiatric]] disorders such as schizophrenia.<ref>{{cite journal | vauthors = Ingvar DH, Franzén G | title = Distribution of cerebral activity in chronic schizophrenia | journal = Lancet | volume = 2 | issue = 7895 | pages = 1484–6 | date = December 1974 | pmid = 4140398 | doi = 10.1016/s0140-6736(74)90221-9 | url = http://www.thelancet.com/journals/lancet/article/PIIS0140-6736%2874%2990221-9/abstract | author1-link = :sv:David H. Ingvar }}</ref> Later versions would have 254 [[Physics:Scintillator|scintillator]]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.<ref>{{cite journal|last1=Lassen|first1=Niels A.|author-link1=Niels A. Lassen|last2=Ingvar|first2=David H.|author-link2=:sv:David H. Ingvar|last3=Skinhøj|first3=Erik|author-link3=:da:Erik Skinhøj | name-list-style = vanc |title=Brain Function and Blood Flow| journal=Scientific American|volume=239|issue=4|pages=62–71|date=October 1978|doi=10.1038/scientificamerican1078-62|pmid=705327|bibcode=1978SciAm.239d..62L}}</ref> The technique was also used to investigate, e.g., imagined sequential movements, mental calculation and mental spatial navigation.<ref>{{cite journal | vauthors = Roland PE, Larsen B, Lassen NA, Skinhøj E | title = Supplementary motor area and other cortical areas in organization of voluntary movements in man | journal = Journal of Neurophysiology | volume = 43 | issue = 1 | pages = 118–36 | date = January 1980 | pmid = 7351547 | doi = 10.1152/jn.1980.43.1.118 | author-link4 = :da:Erik Skinhøj | author-link3 = Niels A. Lassen | author-link1 = :sv:Per E. Roland }}</ref><ref>{{Cite news | last1=Roland|first1=Per E.| author-link1=:sv:Per E. Roland|last2=Friberg|first2=Lars|author-link2=:sv:Lars Friberg  | name-list-style = vanc | title = Localization of cortical areas activated by thinking | journal = Journal of Neurophysiology | volume = 53 | issue = 5 | pages = 1219–1243 | year = 1985 | url = http://jn.physiology.org/content/53/5/1219 }}</ref>

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.<ref name="snm">{{cite web|url=http://interactive.snm.org/docs/whatisnucmed.pdf|title=What is nuclear medicine|website=Society of Nuclear Medicine|access-date=2009-01-17|archive-date=2016-01-17|archive-url=https://web.archive.org/web/20160117015555/http://interactive.snm.org/docs/whatisnucmed.pdf|url-status=dead}}</ref> In 1972, the [[Organization:American Board of Nuclear Medicine|American Board of Nuclear Medicine]] was established, and in 1974, the [[Organization:American Osteopathic Board of Nuclear Medicine|American Osteopathic Board of Nuclear Medicine]] 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 ([[Physics:Positron emission tomography|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.{{Citation needed|date=March 2010}} 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 [[Organization:Washington University School of Medicine|Washington University School of Medicine]]. These innovations led to fusion imaging with SPECT and CT by Bruce Hasegawa from [[Organization:University of California, San Francisco|University of California, San Francisco]] (UCSF), and the first PET/CT prototype by D. W. Townsend from University of Pittsburgh in 1998.{{Citation needed|date=March 2010}}

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.{{citation needed|date=October 2013}}

== Sources of radionuclides ==
<sup>99m</sup>Tc is normally supplied to hospitals through a [[Medicine:Radionuclide generator|radionuclide generator]] containing the parent radionuclide [[Physics:Molybdenum-99|molybdenum-99]]. <sup>99</sup>Mo is [[Physics:Technetium-99m#Production|typically obtained]] as a fission product of [[Physics:Uranium-235|<sup>235</sup>U]] in nuclear reactors, however global supply shortages have led to the exploration of [[Physics:Technetium-99m#Production|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 [[Physics:Petten nuclear reactor|Petten nuclear reactor]] in the Netherlands. Another third of the world's supply, and most of North America's supply, was produced at the [[Organization:Chalk River Laboratories|Chalk River Laboratories]] in Chalk River, Ontario, Canada until its permanent shutdown in 2018.<ref>{{cite web |title=Canada permanently closes NRU research reactor |url=https://www.neimagazine.com/news/newscanada-permanently-closes-nru-research-reactor-6107149/ |website=Nuclear Engineering International |date=6 April 2018}}</ref>

The most commonly used radioisotope in PET, [[Physics:Fluorine-18|<sup>18</sup>F]], is not produced in a nuclear reactor, but rather in a circular accelerator called a [[Physics:Cyclotron|cyclotron]]. The cyclotron is used to accelerate [[Physics:Proton|proton]]s to bombard the stable heavy isotope of oxygen [[Physics:Oxygen-18|<sup>18</sup>O]]. The <sup>18</sup>O constitutes about 0.20% of ordinary [[Chemistry:Oxygen|oxygen]] (mostly [[Physics:Oxygen-16|oxygen-16]]), from which it is extracted. The <sup>18</sup>F is then typically used to make [[Chemistry:Fludeoxyglucose (18F)|FDG]].

{| class="wikitable"  style="float:right; text-align:center;"
<!-- atomic number order -->
|+Common isotopes used in nuclear medicine
<ref>Eckerman KF, Endo A: MIRD: Radionuclide Data and Decay Schemes. Society for Nuclear Medicine, 2008. {{ISBN|978-0-932004-80-2}}</ref><ref>[http://ie.lbl.gov/toi/ Table of Radioactive Isotopes] {{webarchive|url=https://web.archive.org/web/20041204122154/http://ie.lbl.gov/toi/ |date=2004-12-04 }}</ref><ref>{{cite journal | vauthors = Dash A, Pillai MR, Knapp FF | title = Production of (177)Lu for Targeted Radionuclide Therapy: Available Options | journal = Nuclear Medicine and Molecular Imaging | volume = 49 | issue = 2 | pages = 85–107 | date = June 2015 | pmid = 26085854 | pmc = 4463871 | doi = 10.1007/s13139-014-0315-z }}</ref>
! isotope !! symbol !! Z !! T<sub>1/2</sub> !! decay !! gamma (keV) !! Maximum β
energy (keV) / 

Abundance<ref>{{cite web |title=Données atomiques et nucléaires |url=http://www.lnhb.fr/donnees-nucleaires/donnees-nucleaires-tableau/ |access-date=24 October 2022 |website=Laboratoire National Henri Becquerel}}</ref>
|-
| style="text-align:left;" colspan="7"| Imaging:
|-
| [[Physics:Fluorine-18|fluorine-18]] || <sup>18</sup>F || 9 || 109.77 m || β<sup>+</sup> || 511 (193%) || 634 (97%)
|-
| [[Physics:Gallium-67|gallium-67]] || <sup>67</sup>Ga || 31 || 3.26 d || ec || 93 (39%),<br />185 (21%),<br />300 (17%) || -
|-
| [[Physics:Krypton-81m|krypton-81m]] || <sup>81m</sup>Kr || 36 || 13.1 s || IT || 190 (68%) || -
|-
| [[Physics:Rubidium-82|rubidium-82]]|| <sup>82</sup>Rb || 37 || 1.27 m || β<sup>+</sup> || 511 (191%)|| 3381 (81.8%)
2605 (13.1%)

1906 (0.14%)

1209 (0.32%)
|-
| [[Physics:Nitrogen-13|nitrogen-13]]|| <sup>13</sup>N || 7 || 9.97 m || β<sup>+</sup> || 511 (200%)|| 1198 (99.8%)
|-
| [[Physics:Technetium-99m|technetium-99m]] || <sup>99m</sup>Tc || 43 || 6.01 h || IT || 140 (89%) || -
|-
| [[Physics:Indium-111|indium-111]] || <sup>111</sup>In || 49 || 2.80 d || ec || 171 (90%),<br />245 (94%) || -
|-
| [[Chemistry:Iodine-123|iodine-123]] || <sup>123</sup>I || 53 || 13.3 h || ec || 159 (83%) || -
|-
| [[Physics:Xenon-133|xenon-133]] || <sup>133</sup>Xe || 54 || 5.24 d || β<sup>−</sup> || 81 (31%) || 346 (99.1%)
267 (0.9%)
|-
| [[Physics:Thallium-201|thallium-201]] || <sup>201</sup>Tl || 81 || 3.04 d || ec || 69–83<sup>*</sup> (94%),<br />167 (10%) || -
|-
| style="text-align:left;" colspan="7"| Therapy:
|-
| [[Physics:Yttrium-90|yttrium-90]] || <sup>90</sup>Y || 39 || 2.67 d || β<sup>−</sup> || - || 2279 (99.98%)
|-
| [[Physics:Iodine-131|iodine-131]] || <sup>131</sup>I || 53 || 8.02 d || β<sup>−</sup> || 364 (81%)<!--, 0.636 (7%), 0.284 (6%) --> || 807 (0.4%)
606 (89.4%)

334 (7.2%)

248 (2.1%)
|-
|[[Physics:Isotopes of lutetium|lutetium-177]]
|<sup>177</sup>Lu
|71
|6.65 d
|β<sup>−</sup>
|113 (6.6%),
208 (11%)
|498 (79.3%)
385 (9.1%)

177 (11.6%)
|-
| style="text-align:left;" colspan="7"|
<small>Z = atomic number, the number of protons; T<sub>1/2</sub> = half-life; decay = mode of decay</small><br />
<small>photons = principle photon energies in kilo-electron volts, keV, (abundance/decay)</small><br />
<small>β = beta maximum energy in kilo-electron volts, keV, (abundance/decay)</small><br />
<small>β<sup>+</sup> = [[Physics:Beta decay#β+ decay|β<sup>+</sup> decay]]; β<sup>−</sup> = [[Physics:Beta decay#β− decay|β<sup>−</sup> decay]]; IT = isomeric transition; ec = [[Physics:Electron capture|electron capture]]</small><br />
<small>* X-rays from progeny, [[Chemistry:Mercury (element)|mercury]], Hg</small>
|}

A typical nuclear medicine study involves administration of a [[Physics:Radionuclide|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 [[Chemistry:Micro-encapsulation|micro-encapsulation]]. Some studies require the labeling of a patient's own blood cells with a radionuclide (leukocyte scintigraphy and [[Biology:Red blood cell|red blood cell]] scintigraphy). Most diagnostic radionuclides emit [[Physics:Gamma ray|gamma ray]]s either directly from their decay or indirectly through [[Physics:Electron–positron annihilation|electron–positron annihilation]], while the cell-damaging properties of beta particles are used in therapeutic applications. Refined radionuclides for use in nuclear medicine are derived from [[Physics:Nuclear fission|fission]] or fusion processes in [[Physics:Nuclear reactor|nuclear reactor]]s, which produce radionuclides with longer half-lives, or [[Physics:Cyclotron|cyclotron]]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, and indium-111 labeled leukocytes.{{citation needed|date=January 2020}} The most commonly used gaseous/aerosol radionuclides are xenon-133, krypton-81m, (aerosolised) technetium-99m.<ref>[https://web.archive.org/web/20110718042409/http://jcsmr.anu.edu.au/technegas/home.html Technegas] a radioaerosol invented in Australia by Dr Bill Burch and Dr Richard Fawdry</ref>

== Policies and procedures ==

===Radiation dose===
A patient undergoing 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 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 [[Physics:Sievert|sievert]]s (usually given in millisieverts, mSv). The effective dose resulting from an investigation is influenced by the amount of radioactivity administered in mega[[Becquerel|becquerel]]s (MBq), the [[Physics:Half-life|physical properties]] of the [[Medicine:Radiopharmaceutical|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 [[Chemistry:Chromium|chromium]]-51 EDTA measurement of [[Medicine:Glomerular filtration rate|glomerular filtration rate]] to 11.2 mSv (11,200 μSv) for a 80 MBq [[Chemistry:Thallium|thallium]]-201 [[Chemistry:Myocardial perfusion imaging|myocardial imaging]] procedure. The common bone scan with 600 MBq of technetium-99m [[Chemistry:Technetium (99mTc) medronic acid|MDP]] has an effective dose of approximately 2.9 mSv (2,900 μSv).<ref>{{cite web |last1=Administration of Radioactive Substances Advisory Committee |title=ARSAC notes for guidance |url=https://www.gov.uk/government/publications/arsac-notes-for-guidance |website=GOV.UK |publisher=[[Organization:Public Health England|Public Health England]] |language=en |format=pdf |date=19 February 2021}}</ref>

Formerly, units of measurement were the [[Physics:Curie (unit)|curie]] (Ci), being 3.7E10 Bq, and also 1.0 [[Gram|gram]]s of [[Chemistry:Radium|Radium]] (Ra-226); the [[Rad (unit)|rad]] (radiation absorbed dose), now replaced by the [[Physics:Gray (unit)|gray]]; and the rem (Röntgen equivalent man), now replaced with the [[Physics:Sievert|sievert]].<ref>{{Cite web|last=Chandler|first=David|date=2011-03-28|title=Explained: rad, rem, sieverts, becquerels|url=https://news.mit.edu/2011/explained-radioactivity-0328|access-date=2021-04-25|website=MIT News {{!}} Massachusetts Institute of Technology|language=en}}</ref> The rad and rem are essentially equivalent for almost all nuclear medicine procedures, and only alpha radiation will produce 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 is a key focus of Medical Physics.

=== 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 (NRC) and the [[Organization:Food and Drug Administration|Food and Drug Administration]] (FDA) have guidelines in place for hospitals to follow.<ref>{{Citation|last=Le|first=Dao|title=An Overview of the Regulations of Radiopharmaceuticals|date=2021|url=https://doi.org/10.1007/978-3-030-56267-0_10|work=Locoregional Radionuclide Cancer Therapy: Clinical and Scientific Aspects|pages=225–247|editor-last=Wong|editor-first=Franklin C.L.|place=Cham|publisher=Springer International Publishing|language=en|doi=10.1007/978-3-030-56267-0_10|isbn=978-3-030-56267-0|s2cid=230547683|access-date=2021-04-25}}</ref> 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.<ref>{{Cite web|date=2020-06-08|title=Nuclear Medicine: What It Is – and Isn't|url=https://www.nrc.gov/about-nrc/radiation/protects-you/nuclear-medicine.html|access-date=2021-04-25|website=NRC Web}}</ref> International organizations, such as the [[Organization:International Atomic Energy Agency|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.<ref>{{Cite web|date=2017-10-30|title=IAEA Safety Standards and medical exposure|url=https://www.iaea.org/resources/rpop/resources/international-safety-standards/iaea-safety-standards-and-medical-exposure|access-date=2021-04-25|website=www.iaea.org|language=en}}</ref><ref>{{Cite web|title=Human Health Campus – Nuclear Medicine|url=https://humanhealth.iaea.org/HHW/NuclearMedicine/index.html|access-date=2021-04-25|website=humanhealth.iaea.org|date=21 February 2020 }}</ref> Other factors that are considered in nuclear medicine include a patient's medical history as well as post-treatment management. Groups like [[Organization:International Commission on Radiological Protection|International Commission on Radiological Protection]] have published information on how to manage the release of patients from a hospital with unsealed radionuclides.<ref>{{Cite journal|date=June 2004|title=Release of patients after therapy with unsealed radionuclides|url=http://journals.sagepub.com/doi/10.1016/j.icrp.2004.08.001|journal=Annals of the ICRP|language=en|volume=34|issue=2|pages=v–vi|doi=10.1016/j.icrp.2004.08.001|pmid=15571759|issn=0146-6453|author1=International Commission on Radiological Protection|s2cid=43014655}}</ref>

== See also ==
<!-- New links in alphabetical order please -->
* [[Medicine:Human subject research|Human subject research]]
* [[Organization:List of Nuclear Medicine Societies|List of Nuclear Medicine Societies]]
* [[Medicine:Nuclear medicine physician|Nuclear medicine physician]]
* [[Medicine:Nuclear pharmacy|Nuclear pharmacy]]
* [[Engineering:Nuclear technology|Nuclear technology]]
* Radiographer

== References ==
{{Reflist}}

== Further reading ==
{{refbegin}}
* {{cite book | vauthors = Mas JC | title = A Patient's Guide to Nuclear Medicine Procedures: English-Spanish. | publisher = Society of Nuclear Medicine | date = 2008 | isbn = 978-0-9726478-9-2 }}
* {{cite book | vauthors = Taylor A, Schuster DM, Naomi Alazraki N | title = A Clinicians' Guide to Nuclear Medicine | edition = 2nd | publisher = Society of Nuclear Medicine | date = 2000 | isbn = 978-0-932004-72-7 }}
* {{cite book | vauthors = Shumate MJ, Kooby DA, Alazraki NP | title = A Clinician's Guide to Nuclear Oncology: Practical Molecular Imaging and Radionuclide Therapies| publisher = Society of Nuclear Medicine | year= 2007 | isbn = 978-0-9726478-8-5 }}
* {{cite book | vauthors = Ell P, Gambhir S | title = Nuclear Medicine in Clinical Diagnosis and Treatment | publisher = Churchill Livingstone | date = 2004 | pages = 1950 | isbn = 978-0-443-07312-0}}
* {{cite book | vauthors = Jones DW, Hogg P, Seeram E | title = Practical SPECT/CT In Nuclear Medicine | year= 2013 | publisher = Springer | isbn = 978-1447147022 }}
{{refend}}

== External links ==
* {{Curlie|Health/Medicine/Medical_Specialties/Nuclear_Medicine/}}
* [https://purl.fdlp.gov/GPO/gpo28578 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

{{Library resources box
|by=no
|onlinebooks=no
|others=no
|about=yes
|label=Nuclear medicine}}

{{Medicine}}
{{Nuclear technology}}

[[Category:Nuclear medicine| ]]
[[Category:Radiology]]
[[Category:Medicinal radiochemistry]]

{{Sourceattribution|Nuclear medicine}}