Positron-emission tomography (PET) is a nuclear medicine functional
imaging technique that is used to observe metabolic processes in the
body as an aid to the diagnosis of disease. The system detects pairs
of gamma rays emitted indirectly by a positron-emitting radionuclide
(tracer), which is introduced into the body on a biologically active
molecule. Three-dimensional images of tracer concentration within the
body are then constructed by computer analysis. In modern PET-CT
scanners, three-dimensional imaging is often accomplished with the aid
of a CT
X-ray scan performed on the patient during the same session,
in the same machine.
If the biologically active molecule chosen for PET is fludeoxyglucose
(FDG), an analogue of glucose, the concentrations of tracer imaged
will indicate tissue metabolic activity as it corresponds to the
regional glucose uptake. Use of this tracer to explore the possibility
of cancer metastasis (i.e., spreading to other sites) is the most
common type of PET scan in standard medical care (90% of current
scans). Less often, other radioactive tracers are used to image the
tissue concentration of other types of molecules of interest. One of
the disadvantages of PET scanners is their operating cost.
1.4 Infectious diseases
1.6 Small animal imaging
1.7 Musculo-skeletal imaging
3.1 Radionuclides and radiotracers
3.3 Localization of the positron annihilation event
3.4 Image reconstruction
3.5 Combination of PET with CT or MRI
6 Quality Control
7 See also
9 External links
PET/CT-System with 16-slice CT; the ceiling mounted device is an
injection pump for CT contrast agent
Whole-body PET scan using 18F-FDG
PET is both a medical and research tool. It is used heavily in
clinical oncology (medical imaging of tumours and the search for
metastases), and for clinical diagnosis of certain diffuse brain
diseases such as those causing various types of dementias. PET is also
an important research tool to map normal human brain and heart
function, and support drug development.
PET is also used in pre-clinical studies using animals, where it
allows repeated investigations into the same subjects. This is
particularly valuable in cancer research, as it results in an increase
in the statistical quality of the data (subjects can act as their own
control) and substantially reduces the numbers of animals required for
a given study.
Alternative methods of scanning include x-ray computed tomography
(CT), magnetic resonance imaging (MRI) and functional magnetic
resonance imaging (fMRI), ultrasound and single-photon emission
computed tomography (SPECT).
While some imaging scans such as CT and MRI isolate organic anatomic
changes in the body, PET and SPECT are capable of detecting areas of
molecular biology detail (even prior to anatomic change). PET scanning
does this using radiolabelled molecular probes that have different
rates of uptake depending on the type and function of tissue involved.
Changing of regional blood flow in various anatomic structures (as a
measure of the injected positron emitter) can be visualized and
relatively quantified with a PET scan.
PET imaging is best performed using a dedicated PET scanner. It is
also possible to acquire PET images using a conventional dual-head
gamma camera fitted with a coincidence detector. Although the quality
of gamma-camera PET is considerably lower and acquisition is slower,
this method allows institutions with low demand for PET to provide
on-site imaging, instead of referring patients to another centre or
relying on a visit by a mobile scanner.
PET scanning with the tracer fluorine-18 (F-18) fluorodeoxyglucose
(FDG), called FDG-PET, is widely used in clinical oncology. This
tracer is a glucose analog that is taken up by glucose-using cells and
phosphorylated by hexokinase (whose mitochondrial form is greatly
elevated in rapidly growing malignant tumors). A typical dose of FDG
used in an oncological scan has an effective radiation dose of
14 mSv. Because the oxygen atom that is replaced by F-18 to
generate FDG is required for the next step in glucose metabolism in
all cells, no further reactions occur in FDG. Furthermore, most
tissues (with the notable exception of liver and kidneys) cannot
remove the phosphate added by hexokinase. This means that FDG is
trapped in any cell that takes it up until it decays, since
phosphorylated sugars, due to their ionic charge, cannot exit from the
cell. This results in intense radiolabeling of tissues with high
glucose uptake, such as the brain, the liver, and most cancers. As a
result, FDG-PET can be used for diagnosis, staging, and monitoring
treatment of cancers, particularly in Hodgkin's lymphoma, non-Hodgkin
lymphoma, and lung cancer.
A few other isotopes and radiotracers are slowly being introduced into
oncology for specific purposes. For example, 11C-labelled metomidate
(11C-metomidate), has been used to detect tumors of adrenocortical
FDOPA PET-CT, in centers which offer it, has
proven to be a more sensitive alternative to finding, and also
localizing, pheochromocytoma than the MIBG scan.
Main article: Brain positron emission tomography
PET scan of the human brain
Neurology: PET neuroimaging is based on an assumption that areas of
high radioactivity are associated with brain activity. What is
actually measured indirectly is the flow of blood to different parts
of the brain, which is, in general, believed to be correlated, and has
been measured using the tracer oxygen-15. Because of its 2-minute
half-life, O-15 must be piped directly from a medical cyclotron for
such uses, which is difficult. In practice, since the brain is
normally a rapid user of glucose, and since brain pathologies such as
Alzheimer's disease greatly decrease brain metabolism of both glucose
and oxygen in tandem, standard FDG-PET of the brain, which measures
regional glucose use, may also be successfully used to differentiate
Alzheimer's disease from other dementing processes, and also to make
early diagnoses of Alzheimer's disease. The advantage of FDG-PET for
these uses is its much wider availability. PET imaging with FDG can
also be used for localization of seizure focus: A seizure focus will
appear as hypometabolic during an interictal scan. Several
radiotracers (i.e. radioligands) have been developed for PET that are
ligands for specific neuroreceptor subtypes such as [11C] raclopride,
[18F] fallypride and [18F] desmethoxyfallypride for dopamine D2/D3
receptors, [11C] McN 5652 and [11C]
DASB for serotonin transporters,
Mefway for serotonin 5HT1A receptors, [18F]
Nifene for nicotinic
acetylcholine receptors or enzyme substrates (e.g. 6-
FDOPA for the
AADC enzyme). These agents permit the visualization of neuroreceptor
pools in the context of a plurality of neuropsychiatric and neurologic
The development of a number of novel probes for noninvasive, in vivo
PET imaging of neuroaggregate in human brain has brought amyloid
imaging to the doorstep of clinical use. The earliest amyloid imaging
probes included 2-(1- 6-[(2-[18F]fluoroethyl)(methyl)amino]-2-naphthyl
ethylidene)malononitrile ([18F]FDDNP) developed at the University
of California, Los Angeles and
(termed Pittsburgh compound B) developed at the University of
Pittsburgh. These amyloid imaging probes permit the visualization of
amyloid plaques in the brains of Alzheimer's patients and could assist
clinicians in making a positive clinical diagnosis of AD pre-mortem
and aid in the development of novel anti-amyloid therapies. [11C]PMP
(N-[11C]methylpiperidin-4-yl propionate) is a novel
radiopharmaceutical used in PET imaging to determine the activity of
the acetylcholinergic neurotransmitter system by acting as a substrate
for acetylcholinesterase. Post-mortem examination of AD patients have
shown decreased levels of acetylcholinesterase. [11C]PMP is used to
map the acetylcholinesterase activity in the brain, which could allow
for pre-mortem diagnoses of AD and help to monitor AD treatments.
Avid Radiopharmaceuticals of
Philadelphia has developed a compound
called 18F-AV-45 that uses the longer-lasting radionuclide fluorine-18
to detect amyloid plaques using PET scans.
Neuropsychology / Cognitive neuroscience: To examine links between
specific psychological processes or disorders and brain activity.
Psychiatry: Numerous compounds that bind selectively to neuroreceptors
of interest in biological psychiatry have been radiolabeled with C-11
or F-18. Radioligands that bind to dopamine receptors (D1, D2
receptor, reuptake transporter), serotonin receptors (5HT1A,
5HT2A, reuptake transporter) opioid receptors (mu) and other sites
have been used successfully in studies with human subjects. Studies
have been performed examining the state of these receptors in patients
compared to healthy controls in schizophrenia, substance abuse, mood
disorders and other psychiatric conditions.
Stereotactic surgery and radiosurgery: PET-image guided surgery
facilitates treatment of intracranial tumors, arteriovenous
malformations and other surgically treatable conditions.
Main article: Cardiac PET
Cardiology, atherosclerosis and vascular disease study: In clinical
cardiology, FDG-PET can identify so-called "hibernating myocardium",
but its cost-effectiveness in this role versus SPECT is unclear.
FDG-PET imaging of atherosclerosis to detect patients at risk of
stroke is also feasible and can help test the efficacy of novel
Imaging infections with molecular imaging technologies can improve
diagnosis and treatment follow-up. PET has been widely used to image
bacterial infections clinically by using fluorodeoxyglucose (FDG) to
identify the infection-associated inflammatory response.
Three different PET contrast agents have been developed to image
bacterial infections in vivo: [18F]maltose, [18F]maltohexaose and
[18F]2-fluorodeoxysorbitol (FDS). FDS has also the added benefit
of being able to target only Enterobacteriaceae.
Pharmacokinetics: In pre-clinical trials, it is possible to radiolabel
a new drug and inject it into animals. Such scans are referred to as
biodistribution studies. The uptake of the drug, the tissues in which
it concentrates, and its eventual elimination, can be monitored far
more quickly and cost effectively than the older technique of killing
and dissecting the animals to discover the same information. Much more
commonly, drug occupancy at a purported site of action can be inferred
indirectly by competition studies between unlabeled drug and
radiolabeled compounds known apriori to bind with specificity to the
site. A single radioligand can be used this way to test many potential
drug candidates for the same target. A related technique involves
scanning with radioligands that compete with an endogenous (naturally
occurring) substance at a given receptor to demonstrate that a drug
causes the release of the natural substance.
Small animal imaging
PET technology for small animal imaging: A miniature PE tomograph has
been constructed that is small enough for a fully conscious and mobile
rat to wear on its head while walking around. This RatCAP (Rat
Conscious Animal PET) allows animals to be scanned without the
confounding effects of anesthesia. PET scanners designed specifically
for imaging rodents, often referred to as microPET, as well as
scanners for small primates, are marketed for academic and
pharmaceutical research. The scanners are apparently based on
microminiature scintillators and amplified avalanche photodiodes
(APDs) through a new system recently invented uses single chip silicon
Musculoskeletal imaging: PET has been shown to be a feasible technique
for studying skeletal muscles during exercises like walking. One
of the main advantages of using PET is that it can also provide muscle
activation data about deeper lying muscles such as the vastus
intermedialis and the gluteus minimus, as compared to other muscle
studying techniques like electromyography, which can be used only on
superficial muscles (i.e., directly under the skin). A clear
disadvantage is that PET provides no timing information about muscle
activation because it has to be measured after the exercise is
completed. This is due to the time it takes for FDG to accumulate in
the activated muscles.
PET scanning is non-invasive, but it does involve exposure to ionizing
18F-FDG, which is now the standard radiotracer used for PET
neuroimaging and cancer patient management, has an effective
radiation dose of 14 mSv.
The amount of radiation in
18F-FDG is similar to the effective dose of
spending one year in the American city of
Denver, Colorado (12.4
mSv/year). For comparison, radiation dosage for other medical
procedures range from 0.02 mSv for a chest x-ray and 6.5–8 mSv for a
CT scan of the chest. Average civil aircrews are exposed to 3
mSv/year, and the whole body occupational dose limit for nuclear
energy workers in the USA is 50mSv/year. For scale, see Orders of
PET-CT scanning, the radiation exposure may be
substantial—around 23–26 mSv (for a 70 kg person—dose is
likely to be higher for higher body weights).
Schematic view of a detector block and ring of a PET scanner
Radionuclides and radiotracers
List of PET radiotracers and Fludeoxyglucose
Radionuclides used in PET scanning are typically isotopes with short
half-lives  such as carbon-11 (~20 min), nitrogen-13 (~10 min),
oxygen-15 (~2 min), fluorine-18 (~110 min), gallium-68 (~67 min),
zirconium-89 (~78.41 hours), or rubidium-82(~1.27 min). These
radionuclides are incorporated either into compounds normally used by
the body such as glucose (or glucose analogues), water, or ammonia, or
into molecules that bind to receptors or other sites of drug action.
Such labelled compounds are known as radiotracers. PET technology can
be used to trace the biologic pathway of any compound in living humans
(and many other species as well), provided it can be radiolabeled with
a PET isotope. Thus, the specific processes that can be probed with
PET are virtually limitless, and radiotracers for new target molecules
and processes are continuing to be synthesized; as of this writing
there are already dozens in clinical use and hundreds applied in
research. At present,[when?] by far the most commonly used radiotracer
in clinical PET scanning is fluorodeoxyglucose (also called FDG or
fludeoxyglucose), an analogue of glucose that is labeled with
fluorine-18. This radiotracer is used in essentially all scans for
oncology and most scans in neurology, and thus makes up the large
majority of all of the radiotracer (> 95%) used in PET and PET-CT
Due to the short half-lives of most positron-emitting radioisotopes,
the radiotracers have traditionally been produced using a cyclotron in
close proximity to the PET imaging facility. The half-life of
fluorine-18 is long enough that radiotracers labeled with fluorine-18
can be manufactured commercially at offsite locations and shipped to
imaging centers. Recently rubidium-82 generators have become
commercially available. These contain strontium-82, which decays
by electron capture to produce positron-emitting rubidium-82.
To conduct the scan, a short-lived radioactive tracer isotope is
injected into the living subject (usually into blood circulation).
Each tracer atom has been chemically incorporated into a biologically
active molecule. There is a waiting period while the active molecule
becomes concentrated in tissues of interest; then the subject is
placed in the imaging scanner. The molecule most commonly used for
this purpose is F-18 labeled fluorodeoxyglucose (FDG), a sugar, for
which the waiting period is typically an hour. During the scan, a
record of tissue concentration is made as the tracer decays.
Schema of a PET acquisition process
As the radioisotope undergoes positron emission decay (also known as
positive beta decay), it emits a positron, an antiparticle of the
electron with opposite charge. The emitted positron travels in tissue
for a short distance (typically less than 1 mm, but dependent on
the isotope), during which time it loses kinetic energy, until it
decelerates to a point where it can interact with an electron. The
encounter annihilates both electron and positron, producing a pair of
annihilation (gamma) photons moving in approximately opposite
directions. These are detected when they reach a scintillator in the
scanning device, creating a burst of light which is detected by
photomultiplier tubes or silicon avalanche photodiodes (Si APD). The
technique depends on simultaneous or coincident detection of the pair
of photons moving in approximately opposite directions (they would be
exactly opposite in their center of mass frame, but the scanner has no
way to know this, and so has a built-in slight direction-error
tolerance). Photons that do not arrive in temporal "pairs" (i.e.
within a timing-window of a few nanoseconds) are ignored.
Localization of the positron annihilation event
The most significant fraction of electron–positron annihilations
results in two 511 keV gamma photons being emitted at almost 180
degrees to each other; hence, it is possible to localize their source
along a straight line of coincidence (also called the line of
response, or LOR). In practice, the LOR has a non-zero width as the
emitted photons are not exactly 180 degrees apart. If the resolving
time of the detectors is less than 500 picoseconds rather than about
10 nanoseconds, it is possible to localize the event to a segment of a
chord, whose length is determined by the detector timing resolution.
As the timing resolution improves, the signal-to-noise ratio (SNR) of
the image will improve, requiring fewer events to achieve the same
image quality. This technology is not yet common, but it is available
on some new systems.
The raw data collected by a PET scanner are a list of 'coincidence
events' representing near-simultaneous detection (typically, within a
window of 6 to 12 nanoseconds of each other) of annihilation photons
by a pair of detectors. Each coincidence event represents a line in
space connecting the two detectors along which the positron emission
occurred (i.e., the line of response (LOR)).
Analytical techniques, much like the reconstruction of computed
tomography (CT) and single-photon emission computed tomography (SPECT)
data, are commonly used, although the data set collected in PET is
much poorer than CT, so reconstruction techniques are more difficult.
Coincidence events can be grouped into projection images, called
sinograms. The sinograms are sorted by the angle of each view and tilt
(for 3D images). The sinogram images are analogous to the projections
captured by computed tomography (CT) scanners, and can be
reconstructed in a similar way. The statistics of data thereby
obtained are much worse than those obtained through transmission
tomography. A normal PET data set has millions of counts for the whole
acquisition, while the CT can reach a few billion counts. This
contributes to PET images appearing "noisier" than CT. Two major
sources of noise in PET are scatter (a detected pair of photons, at
least one of which was deflected from its original path by interaction
with matter in the field of view, leading to the pair being assigned
to an incorrect LOR) and random events (photons originating from two
different annihilation events but incorrectly recorded as a
coincidence pair because their arrival at their respective detectors
occurred within a coincidence timing window).
In practice, considerable pre-processing of the data is
required—correction for random coincidences, estimation and
subtraction of scattered photons, detector dead-time correction (after
the detection of a photon, the detector must "cool down" again) and
detector-sensitivity correction (for both inherent detector
sensitivity and changes in sensitivity due to angle of incidence).
Filtered back projection
Filtered back projection (FBP) has been frequently used to reconstruct
images from the projections. This algorithm has the advantage of being
simple while having a low requirement for computing resources.
Disadvantages are that shot noise in the raw data is prominent in the
reconstructed images, and areas of high tracer uptake tend to form
streaks across the image. Also, FBP treats the data
deterministically—it does not account for the inherent randomness
associated with PET data, thus requiring all the pre-reconstruction
corrections described above.
Statistical, likelihood-based approaches: Statistical,
likelihood-based   iterative expectation-maximization
algorithms such as the Shepp-Vardi algorithm are now the preferred
method of reconstruction. These algorithms compute an estimate of the
likely distribution of annihilation events that led to the measured
data, based on statistical principles. The advantage is a better noise
profile and resistance to the streak artifacts common with FBP, but
the disadvantage is higher computer resource requirements. A further
advantage of statistical image reconstruction techniques is that the
physical effects that would need to be pre-corrected for when using an
analytical reconstruction algorithm, such as scattered photons, random
coincidences, attenuation and detector dead-time, can be incorporated
into the likelihood model being used in the reconstruction, allowing
for additional noise reduction. Iterative reconstruction has also been
shown to result in improvements in the resolution of the reconstructed
images, since more sophisticated models of the scanner Physics can be
incorporated into the likelihood model than those used by analytical
reconstruction methods, allowing for improved quantification of the
Research has shown that Bayesian methods that involve a Poisson
likelihood function and an appropriate prior probability (e.g., a
smoothing prior leading to total variation regularization or a
Laplacian distribution leading to
displaystyle ell _ 1
-based regularization in a wavelet or other domain), such as via Ulf
Grenander's Sieve estimator  or via Bayes penalty methods 
 or via I.J. Good's roughness method  , may yield superior
performance to expectation-maximization-based methods which involve a
Poisson likelihood function but do not involve such a
Attenuation correction: Quantitative PET Imaging requires attenuation
correction. In these systems attenuation correction is based on a
transmission scan using 68Ge rotating rod source.
transmission scans directly measure attenuation values at 511keV.
Attenuation occurs when photons emitted by the radiotracer inside the
body are absorbed by intervening tissue between the detector and the
emission of the photon. As different LORs must traverse different
thicknesses of tissue, the photons are attenuated differentially. The
result is that structures deep in the body are reconstructed as having
falsely low tracer uptake. Contemporary scanners can estimate
attenuation using integrated x-ray CT equipment, in place of earlier
equipment that offered a crude form of CT using a gamma ray (positron
emitting) source and the PET detectors.
While attenuation-corrected images are generally more faithful
representations, the correction process is itself susceptible to
significant artifacts. As a result, both corrected and uncorrected
images are always reconstructed and read together.
2D/3D reconstruction: Early PET scanners had only a single ring of
detectors, hence the acquisition of data and subsequent reconstruction
was restricted to a single transverse plane. More modern scanners now
include multiple rings, essentially forming a cylinder of detectors.
There are two approaches to reconstructing data from such a scanner:
1) treat each ring as a separate entity, so that only coincidences
within a ring are detected, the image from each ring can then be
reconstructed individually (2D reconstruction), or 2) allow
coincidences to be detected between rings as well as within rings,
then reconstruct the entire volume together (3D).
3D techniques have better sensitivity (because more coincidences are
detected and used) and therefore less noise, but are more sensitive to
the effects of scatter and random coincidences, as well as requiring
correspondingly greater computer resources. The advent of
sub-nanosecond timing resolution detectors affords better random
coincidence rejection, thus favoring 3D image reconstruction.
Time-of-flight (TOF) PET: For modern systems with a higher time
resolution (roughly 3 nanoseconds) a technique called "Time-of-flight"
is used to improve the overall performance. Time-of-flight PET makes
use of very fast gamma-ray detectors and data processing system which
can more precisely decide the difference in time between the detection
of the two photons. Although it is technically impossible to localize
the point of origin of the annihilation event exactly (currently
within 10 cm) thus image reconstruction is still needed, TOF
technique gives a remarkable improvement in image quality, especially
PET-CT fusion image
PET-MRI fusion image
Combination of PET with CT or MRI
PET-CT and PET-MRI
PET scans are increasingly read alongside CT or magnetic resonance
imaging (MRI) scans, with the combination (called "co-registration")
giving both anatomic and metabolic information (i.e., what the
structure is, and what it is doing biochemically). Because PET imaging
is most useful in combination with anatomical imaging, such as CT,
modern PET scanners are now available with integrated high-end
multi-detector-row CT scanners (so-called "PET-CT"). Because the two
scans can be performed in immediate sequence during the same session,
with the patient not changing position between the two types of scans,
the two sets of images are more precisely registered, so that areas of
abnormality on the PET imaging can be more perfectly correlated with
anatomy on the CT images. This is very useful in showing detailed
views of moving organs or structures with higher anatomical variation,
which is more common outside the brain.
At the Jülich Institute of Neurosciences and Biophysics, the world's
PET-MRI device began operation in April 2009: a 9.4-tesla
magnetic resonance tomograph (MRT) combined with a positron emission
tomograph (PET). Presently, only the head and brain can be imaged at
these high magnetic field strengths.
For brain imaging, registration of CT, MRI and PET scans may be
accomplished without the need for an integrated
PET-CT or PET-MRI
scanner by using a device known as the N-localizer.
The minimization of radiation dose to the subject is an attractive
feature of the use of short-lived radionuclides. Besides its
established role as a diagnostic technique, PET has an expanding role
as a method to assess the response to therapy, in particular, cancer
therapy, where the risk to the patient from lack of knowledge
about disease progress is much greater than the risk from the test
Limitations to the widespread use of PET arise from the high costs of
cyclotrons needed to produce the short-lived radionuclides for PET
scanning and the need for specially adapted on-site chemical synthesis
apparatus to produce the radiopharmaceuticals after radioisotope
preparation. Organic radiotracer molecules that will contain a
positron-emitting radioisotope cannot be synthesized first and then
the radioisotope prepared within them, because bombardment with a
cyclotron to prepare the radioisotope destroys any organic carrier for
it. Instead, the isotope must be prepared first, then afterward, the
chemistry to prepare any organic radiotracer (such as FDG)
accomplished very quickly, in the short time before the isotope
decays. Few hospitals and universities are capable of maintaining such
systems, and most clinical PET is supported by third-party suppliers
of radiotracers that can supply many sites simultaneously. This
limitation restricts clinical PET primarily to the use of tracers
labelled with fluorine-18, which has a half-life of 110 minutes and
can be transported a reasonable distance before use, or to rubidium-82
(used as rubidium-82 chloride) with a half-life of 1.27 minutes, which
is created in a portable generator and is used for myocardial
perfusion studies. Nevertheless, in recent years a few on-site
cyclotrons with integrated shielding and "hot labs" (automated
chemistry labs that are able to work with radioisotopes) have begun to
accompany PET units to remote hospitals. The presence of the small
on-site cyclotron promises to expand in the future as the cyclotrons
shrink in response to the high cost of isotope transportation to
remote PET machines. In recent years the shortage of PET scans has
been alleviated in the US, as rollout of radiopharmacies to supply
radioisotopes has grown 30%/year.
Because the half-life of fluorine-18 is about two hours, the prepared
dose of a radiopharmaceutical bearing this radionuclide will undergo
multiple half-lives of decay during the working day. This necessitates
frequent recalibration of the remaining dose (determination of
activity per unit volume) and careful planning with respect to patient
The concept of emission and transmission tomography was introduced by
David E. Kuhl, Luke Chapman and Roy Edwards in the late 1950s. Their
work later led to the design and construction of several tomographic
instruments at the University of Pennsylvania. In 1975 tomographic
imaging techniques were further developed by Michel Ter-Pogossian,
Michael E. Phelps,
Edward J. Hoffman and others at Washington
University School of Medicine.
Work by Gordon Brownell, Charles Burnham and their associates at the
Massachusetts General Hospital
Massachusetts General Hospital beginning in the 1950s contributed
significantly to the development of PET technology and included the
first demonstration of annihilation radiation for medical imaging.
Their innovations, including the use of light pipes and volumetric
analysis, have been important in the deployment of PET imaging. In
1961, James Robertson and his associates at Brookhaven National
Laboratory built the first single-plane PET scan, nicknamed the
One of the factors most responsible for the acceptance of positron
imaging was the development of radiopharmaceuticals. In particular,
the development of labeled 2-fluorodeoxy-D-glucose (2FDG) by the
Brookhaven group under the direction of Al Wolf and Joanna Fowler was
a major factor in expanding the scope of PET imaging. The compound
was first administered to two normal human volunteers by Abass Alavi
in August 1976 at the University of Pennsylvania. Brain images
obtained with an ordinary (non-PET) nuclear scanner demonstrated the
concentration of FDG in that organ. Later, the substance was used in
dedicated positron tomographic scanners, to yield the modern
The logical extension of positron instrumentation was a design using
two 2-dimensional arrays. PC-I was the first instrument using this
concept and was designed in 1968, completed in 1969 and reported in
1972. The first applications of PC-I in tomographic mode as
distinguished from the computed tomographic mode were reported in
1970. It soon became clear to many of those involved in PET
development that a circular or cylindrical array of detectors was the
logical next step in PET instrumentation. Although many investigators
took this approach, James Robertson and Zang-Hee Cho were the
first to propose a ring system that has become the prototype of the
current shape of PET.
PET-CT scanner, attributed to Dr. David Townsend and Dr. Ronald
Nutt, was named by TIME Magazine as the medical invention of the year
This section needs to be updated. Please update this article to
reflect recent events or newly available information. (February 2018)
As of August 2008,
Cancer Care Ontario reports that the current
average incremental cost to perform a PET scan in the province is
Can$1,000–1,200 per scan. This includes the cost of the
radiopharmaceutical and a stipend for the physician reading the
In England, the
NHS reference cost (2015-2016) for an adult outpatient
PET scan is £798, and £242 for direct access services.
The overall performance of PET systems can be evaluated by quality
control tools such as the Jaszczak phantom.
Diffuse optical imaging
Hot cell (Equipment used to produce the radiopharmaceuticals used in
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^ a b c Carlson, Neil (January 22, 2012). Physiology of Behavior.
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^ a b Exposure fact sheet Health Physics Society
^ Khan TS; Sundin A; Juhlin C; Långström B; et al. (2003).
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^ Minn H; Salonen A; Friberg J; Roivainen A; et al. (June 2004).
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^ full text of early article on
FDOPA PET for pheochromocytoma
^ imaging overview
^ Luster M; Karges W; Zeich K; Pauls S; et al. (2010). "Clinical value
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