Glossary of Molecular Imaging Terms

 

Alzheimer's disease (AD)
An irreversible, progressive brain neurodegenerative disorder that slowly destroys memory and thinking function. AD, the most common form of dementia, begins deep in the brain where healthy neurons begin to work less efficiently and eventually die. This process gradually spreads to the brain's learning and memory center—the hippocampus—and other areas of the brain, which begin to shrink. At the same time, two abnormal structures, beta-amyloid plaques and neurofibrillary tangles, begin to multiply throughout the brain

amino acid
An organic compound containing nitrogen, carbon, hydrogen and oxygen; one of the 20 building blocks of protein.

annihilation
The process of a particle and its corresponding anti-particle (a particle with the same mass but opposite electric charge) combining to produce energy in the form of photons.

antibody
A protein produced by the body's immune system in response to the presence of a foreign substance, called an antigen. The body fights off infection by producing antibodies, which destroy or neutralize bacteria, viruses, or other harmful toxins.

antigen
Any foreign substance, such as a protein, toxin or other particle that stimulates the body's immune system to produce antibodies. Antigens can be substances like bacteria, viruses, or even pollen that invade the body.

axillary lymph node dissection
The surgical removal of up to 30 lymph nodes from the armpit area so they may be examined under a microscope for evidence of cancer.

axillary lymph nodes
Lymph nodes that are located in the axillary, or armpit, area.

axon
A long, slender projection from a nerve cell, or neuron, that conducts electrical impulses away from the cell.

benign
A process or a growth in the body, or in an organ, that is not cancerous.  Also called non-malignant.

beta-amyloid plaques
Thick deposits of proteins in the brain considered one of the hallmarks of Alzheimer's disease (AD).

biological pathway
The molecular interaction involved in biological processes; often a cascade of actions among molecules in a cell that leads to a product or outcome.

bioluminescent imaging
One of two major types of optical imaging, in which light-producing molecules designed to attach to specific cells such as cancer cells or brain chemicals are injected into the patient's bloodstream. Imaging is then performed using devices that are able to detect these molecules inside the body. Bioluminescent imaging uses natural chemicals such as luciferase, the substance that enables fireflies to glow, to trace the movement of certain cells or to identify the location of specific chemical reactions within the body.

biomarker (molecular marker and signature molecule)
A molecule or substance in the body that is used as an indicator of a specific biological process occurring in the body. The most common use is to find indications of disease. For example, the presence of prostate specific antigen (PSA) in the body is a marker for prostate disease.

biopsy
The process of removing a small amount of tissue from the body for examination under a microscope.

blood-brain barrier
A separation between the circulating blood and cerebrospinal fluid that selectively prevents substances from passing out of the blood stream into brain tissue and cerebrospinal fluid.

bone marrow
The soft, spongy tissue, found in the hollow interior of bones, that produces white blood cells, red blood cells and platelets.

bone scan
A diagnostic imaging test in which radioactive material called a radiotracer when injected into the patient's bloodstream accumulates predominantly in the bones and can be detected by an imaging device. The resulting two-dimensional or three-dimensional images can reveal various processes such as bony fractures, infection, inflammation and changes secondary to presence of cancer cells.

Breast-specific gamma imaging
A diagnostic procedure performed as a follow-up study to a mammogram to detect additional lesions missed by mammography and physical exam and cancers that are difficult to detect using mammography. The procedure involves the use of a radiotracer that is injected into the patient's bloodstream and accumulates in malignant tissue where it can be detected by a special gamma camera modified for breast imaging.

carcinoembryonic antigen (CEA)
A protein normally found in small amounts in the blood and in fetal tissue. It is also produced by some types of tumors, including some breast and gastrointestinal cancers, making it a tumor marker, or an indication that disease may be present on molecular images. Colorectal cancer is the most common cancer that raises the level of this tumor marker in the blood.

cartilage
Dense connective tissue found in many parts of the body, primarily in association with bony joints and interfaces.

chemotherapy
The use of chemicals to kill cancer cells and/or prevent them from growing.

colorectal cancer
Cancer that occurs in the colon (part of the large intestine) or the rectum.

colorectal
Pertaining to the colon, the longest part of the large intestine or the rectum, the terminal continuation of the colon.

computed tomography (CT) (CT imaging, CT scan)
A medical imaging technique that uses a computer to acquire a volume of x-ray based images, generally reconstructed as two-dimensional (2D) or three-dimensional (3D) pictures of inside the body. These images can be rotated and viewed from any angle. Each CTimages is effectively a single ‘slice' of anatomy.

contrast agent (contrast media or contrast material)
A compound or other substance introduced into the body in order to create a difference in the apparent density of various organs and tissues, making it easier to see the delineate adjacent body tissues and organs.

co-registration (fusion imaging or hybrid imaging)
The combining of the two different imaging techniques allowing a information from two different studies to be viewed as a single set of superimposed images. e.g. PET and CT. .

coronary artery disease
A condition involving the narrowing of the coronary arteries that carry blood and oxygen to the heart muscle.

cryosurgery
A procedure that uses liquid nitrogen to freeze and destroy cells; it may be used to treat melanoma.

dementia
A general term for memory loss and decline in intellectual functioning that is severe enough to interfere with an individual's ability to perform routine tasks.

diagnostic imaging (diagnostic scan)
Diagnostic imaging uses technologies such as x-ray, CT, MRI, ultrasound, PET and SPECT to provide physicians with a way to look inside the body without surgery. Diagnostic imaging is considered a non-invasive diagnostic technique, as opposed to a biopsy or exploratory surgery. PET, SPECT and some types of MRimaging also provide information about how certain tissues and organs are functioning.

differentiated thyroid cancer
A type of cancer of the thyroid gland. Differentiated thyroid cancers include papillary, follicular and Hürthle cell thyroid cancers. The cells of these cancers appear similar to normal thyroid tissue when looked at under a microscope.

diffuse
Spread out.

ductal carcinoma in situ (DCIS)
A breast cancer that has not spread beyond the lining of the milk ducts into the surrounding breast tissue.

ducts
Tubes that carry a substance from one region of the body to another.  e.g.  tubes that carry milk from glandular tissue to the nipples of the breast.

electrodessication and curettage
A type of surgical procedure used to treat melanoma that involves alternately scraping and burning the tumor.

electromagnetic radiation
A spectrum of energy, demonstrating the phenomenon of self-propagating waves, and both electric and magnetic fields. Visible light, radio waves, gamma rays, and x-rays, are all within the spectrum of electromagnetic radiation. The subdivisions are a function of differences in frequency and wavelength. Photons, an often used unit of energy within the molecular imaging realm, is part of this spectrum.

electron
A subatomic particle that carries a negative charge. An electron orbits and is bound to the nucleus of an atom by electromagnetic forces.

FDDNP
An imaging agent used in positron emission tomography scanning of the brain. FDDNP binds to abnormal beta-amyloid plaques and neurofibrillary tangles associated with Alzheimer's disease which allows them to be visualized on a PET scan.

FDG (18F-fluorodeoxyglucose)
A frequently used radiotracer in PET scanning. FDG is a compound in which a radioactive fluoride atom is attached to a molecular of glucose, or sugar. Once in the body, the FDG molecule is absorbed by various tissues. Radiation from the fluorine is used to create pictures of how the radiotracer is distributed within the body.

fluorescence imaging (fluorescent molecular tomography [FMT])
One of two major types of optical imaging in which light-producing molecules designed to attach to specific cells such as cancer cells or brain chemicals are injected into the patient's bloodstream. Imaging is then performed using devices that are able to detect these molecules inside the body. Fluorescence imaging uses proteins that produce light when activated by an external light source, such as a laser, to trace the movement of cells or identify the location of chemical reactions in the body.

fluorine
The chemical element represented by the symbol F and the atomic number 9. A radioactive fluorine atom is attached to a molecule of glucose or sugar to create the radiotracer FDG, used in positron emission tomography.

follicular thyroid cancer
One of several types of thyroid cancer; it may be identified and staged with low-dose I-123, and potentially treated with I-131 radiotherapy.

frontotemporal dementia
A group of rare brain disorders that involves the shrinking (atrophy) of tissues in the frontal and temporal lobes of the brain. Pick's disease is an example of this type of dementia.

fusion imaging (co-registration or hybrid imaging)
The combination of the two imaging techniques that allows information from two different studies to be viewed in a single set of images.

gamma camera
A specialized camera that is capable of detecting gamma rays- the byproduct of a radiotracer, which is a combination of a radioactive atom, called an isotope, and another substance. The gamma camera creates two-dimensional pictures of the inside of the body from different angles.

gastric
Relating to or involving the stomach.

gastrointestinal (GI) tract
A long twisting tube within the human body along which food passes for digestion. The GI tract includes the esophagus, stomach, small intestine, large intestine, rectum and anus.

hippocampus
A part of the brain that plays a central role in many functions, including the processing of memories.

Hodgkin's disease (HD) (Hodgkin's lymphoma)
One of two types of lymphoma or cancer of the lymphatic system, which includes the lymph nodes, spleen, thymus and bone marrow.

Hurthle cell thyroid cancer
One of several types of thyroid cancer; it may be treated with high-dose I-131 radiotherapy.

hybrid imaging (co-registration or fusion imaging)
The combination of the two imaging techniques that allows information from two different studies to be viewed in a single set of images.

I-131 radiotherapy
The use of  radioactive iodine I-131 directly to thyroid cancer cells to destroy them. 

imaging agent (imaging probe, radiotracer)
A substance introduced into the body as part of a diagnostic procedure. In nuclear medicine, imaging agents are typically a compound consisting of a drug or a natural substance, such as glucose, and a small amount of radioactive material, which can be detected by an imaging device to produce pictures of the inside of the body.

imaging biomarker (see biomarker)
Imaging biomarkers are measurable characteristics obtained by imaging that indicate a specific biological process is occurring in the body. They help speed drug development because the biomarkers show effectiveness earlier than anatomic changes. They have been historically difficult to use in drug trials and clinical practice due to a lack of standardized methods and regulatory approval.

imaging device
A technological apparatus used to produce detailed images of the inside of the body for diagnostic or therapeutic purposes. In molecular imaging, examples of these devices include the gamma camera, PET scanner, MRI unit, optical imaging detector, and ultrasound machine.

imaging probe (imaging agent)
A molecule that can bind both to a radiotracer and to a molecule of interest, such as cancer cells, within the body so that they may be imaged with molecular imaging technologies.

immunotherapy
A treatment that modulates cellular activity in the body's immune system in which white cells recognize invading organisms and respond by secreting a protein substance called an antibody that hones in on an antigen on foreign cells, allowing other white cells to destroy it. In immunotherapy, scientists create monoclonal antibodies in a laboratory that are designed to recognize and bind to the antigen of a specific cancer cell. When the antibodies are combined with a radioactive material (called radioimmunotherapy) and injected in a patient's bloodstream, the antibody travels to and binds to cancer cells allowing a high dose of radiation to be delivered directly to the tumor.

incidental cancers
Unexpected cancerous lesions identified by diagnostic imaging tests in addition to different primary disease being investigated.

indium-111-octreotide
A radiopharmaceutical being evaluated in clinical trials as an alternative to radioiodine for patients whose thyroid cancer is not responsive to I-131 radiotherapy with iodine.

intravenous (IV)
Within or by means of a vein.

ionizing radiation
Subatomic particles or electromagnetic waves that are energetic enough to detach electrons from atoms or molecules, a process called ionization. Radiation on the short-wavelength end of the electromagnetic spectrum, such as x-rays and gamma rays are ionizing. Ionizing radiation is produced by radioactive decay, nuclear fission and nuclear fusion and by particle accelerators.

isotope
Atoms of a single element that have differing masses. Isotopes are either stable or unstable (radioisotope). Radioisotopes are radioactive: they emit particulate (alpha, beta) or electromagnetic (gamma) radiation as they transform or decay into stable isotopes.

larynx
Also called the voicebox. An organ in the respiratory system, primarily composed of cartilage, and located just below the pharynx in the neck.  It contains the vocal cords.

ligand
In medical imaging, ligands are molecules that can bind both to a tracer (radioactive or light emitting) and to a molecule of interest within a living system. For example, in radioimmunotherapy a radioisotope is attached to a monoclonal antibody. The antibody is the ligand; it is designed to bind with specific molecules on the surface of cancer cells, so it carries the radioisotope to the tumor. The radiation kills the cancer cell while sparing nearby tissue. In optical imaging, the ligand might carry a bioluminescent protein. The antibody binds to a receptor on the surface of the cell being studied, delivering the bioluminescent protein directly where the researcher wants it.

lobules
Glands within the breast that make milk.

localize
To identify the location of or to accumulate in a specific location.

lumpectomy
A surgical procedure to remove a tumor and surrounding tissue from the breast.

lymph node biopsy
The removal of all or part of a lymph node to be examined under a microscope for evidence of cancer cells.

lymph nodes
Small, bean-shaped organs located clustered in various areas of the body along system of lymph vessels. Lymph nodes produce immune cells to fight infection, store white blood cells and filter bacteria and other foreign material from lymph.

lymph vessels
Thin tubes that carry lymph through the lymphatic system. They branch, like blood vessels, into all parts of the body.

lymph
A clear, watery fluid that contains white blood cells, plasma and other substances and is transported throughout the body in tubes known as lymph vessels. Lymph is collected from tissues throughout the body, flows through vessels and lymph nodes, and is eventually added to the bloodstream.

lymphatic system
A network of organs, lymph nodes and vessels that removes lymph fluid from the tissues of the body and return it to the blood stream. A major component of the body's immune system that makes and stores cells needed to fight infection and diseases such as cancer.

lymphocyte
A type of white blood cell formed in lymph nodes, the spleen, and bone marrow. The main types of lymphocytes are T and B-lymphocytes.

lymphoma
Cancer of the lymphatic system, which includes the lymph nodes, spleen, thymus and bone marrow. There are two types of lymphoma: Hodgkin's disease (HD) and non-Hodgkin lymphoma (HGL).

lymphoscintigraphy
A procedure that uses a radiotracer and gamma camera to produce images of the lymphatic system to help identify the first, or sentinel, lymph nodes into which a melanoma site drains.

magnetic resonance imaging (MRI)
Magnetic resonance imaging is a diagnostic scan that uses high-strength magnetic fields rather than radiation. MRI techniques are used primarily to study anatomy, but a special type of MR scan, functional MRI (fMRI) can be used to map blood flow for functional studies.

magnetic resonance spectroscopy (MRS)
A diagnostic imaging exam in which magnetic resonance (MR) imaging is used to measure metabolites, which are substances produced by chemical reactions in the brain and other areas of the body. MR spectroscopy provides information on both the location and biochemical activity of cells.

malignant
Cancerous cells able to grow into surrounding tissue, spread to other parts of the body and destroy normal cells.

masectomy
Surgical removal of the breast, usually to remove cancerous tissue.

mediastinoscopy
A surgical procedure performed to determine whether non-small cell cancer has spread to the lymph nodes in the chest cavity. PET-CT guidance may be used to identify the lymph nodes most likely to contain cancer cells.

melanin
Pigment produced by skin or melanocyte cells that give the skin a darker hue.

melanocytes
Cells throughout the skin that produce pigment called melanin that makes the skin tan.

melanoma
The third most common form of skin cancer that begins in melanocytes, the cells throughout the skin that produce pigment called melanin that makes the skin tan.

metabolism
The set of chemical reactions that occur in living organisms to convert fuel into energy.

metabolites
Any substance produced by or involved in a chemical reaction that is part of metabolism.

metastasize
The spread from one part of the body to another, as in cancer cells.

micro- (PET, MR, CT, SPECT)
Medical imaginginstruments or techniques specifically designed for medical research using small animals. Micro-imagingstudies are useful in preclinical investigations of new imaging agents or with existing imaging agents to evaluate new therapies using exiting agents in animal models.

microbubbles
Extremely small hollow structures either containing or attached to therapeutic or imaging molecules. They are used clinically with ultrasound as a contrast agent.

mild cognitive impairment (MCI)
A condition in which memory or other cognitive functions are below normal but do not interfere with daily functioning. MCI is considered a transitional state between normal forgetfulness and dementia.

molecular imaging (MI)
Molecular imaging is an array of non-invasive, diagnostic imaging technologies that can create images of both physical and functional aspects of the living body. It can provide information that would otherwise require surgery or other invasive procedures to obtain. Molecular imaging differs from microscopy, which can also produce images at the molecular level, in that microscopy is used on samples of tissue that have been removed from the body, not on tissues still within a living organism. It differs from X-rays and other radiological techniques in that molecular imaging primarily provides information about biological processes (function) while CT, X-rays, MRI and ultrasound, image physical structure (anatomy).

Molecular imaging technologies include traditional nuclear medicine, optical imaging, magnetic resonance spectroscopy, PET and SPECT. Ultrasound, traditionally an anatomical imaging technique, uses microbubbles to create molecular images.

molecular markers
An imaging biomarker that is molecule based, as opposed to being a single atom or an ion.  e.g. fragments of DNA, or an antibody

molecular ultrasound
The use of targeted microbubbles, extremely small, hollow structures that serve as a contrast agent during an ultrasound exam.

monoclonal antibodies (genetically engineered antibodies)
A substance created in a laboratory that is designed to recognize and bind to the antigen of a specific cancer cell when introduced into the body. When these antibodies are combined with a radioactive material and injected in a patient's bloodstream, (a treatment called radioimmunotherapy) the antibody travels to and binds to cancer cells allowing a high dose of radiation to be delivered directly to the tumor.

monoclonal antibody imaging (radioimmunoscintigraphy [RIS])
The use of a laboratory-developed molecule called a monoclonal antibody that is designed to attach to specific cancer cells in order to produce pictures of a tumor inside the body. Once the monoclonal antibody is combined, or labeled, with a radioactive atom and injected into the patient, single-photon emission computed tomography (SPECT) imaging is performed, creating three-dimensional images of the tumor.

monoclonal antibody imaging
Also called radioimmunoscintigraphy (RIS)
A diagnostic imaging test that allows physicians to locate and determine the extent of cancer cells in the body. It involves the use of a laboratory-developed molecule called a monoclonal antibody that is designed to attach to specific cancer cells. Monoclonal antibodies are attached to, or labeled with, a radioactive atom or isotope that can be detected by a gamma camera. Once the radioactive compound is injected into the patient's bloodstream, imaging is performed producing three-dimensional images of cancer cells in the body.

monoclonal antibody
A molecule developed in a laboratory that mimics one of the proteins called antibodies produced by the body's immune system. Monoclonal antibodies, which are designed to attach to specific cancer cells, are used in molecular imaging to produce pictures of a tumor inside the body.

myelin
A white, fatty material that surrounds the axons of nerve cells.

myocardial perfusion scan
A common cardiac nuclear medicine procedure that produces images of blood-flow patterns within the heart. Additonal information such as thickness of the myocardium as well as ventricular systolic function may also be assessed using this technique.

nanometer
A metric unit of length equal to one billionth of a meter.

nanoparticle
Any microscopic particle less than about 100 nanometers (nm) in diameter. Nanoparticles are unique structures that are designed for specific purpose. Their extremely small size makes them very useful in medical applications where specifically designed particles scan deliver drugs directly into targeted cells and even across the blood-brain barrier.

nanotechnology
The use of extremely small physical structures (100 nanometers or smaller) for a directed outcome. At that size, many physical interactions do not follow the same rules as larger structures. Nanoscale structures that can be extremely useful in the medical field.

National Oncologic PET Registry (NOPR)
In order to determine how best to expand coverage of positron emission tomography (PET) scanning for Medicare cancer patients, the Centers for Medicare and Medicaid Services (CMS) is collecting information on PET scans with this registry.

nerve
A bundle of nerve fibers or axons.

nervous system
The collection of approximately 10 billion nerve cells called neurons that conduct, receive and transfer electrical impulses. It includes the central nervous system (brain, spinal cord and optic nerves) and peripheral nervous system including nerve roots, nerve plexuses, and nerves throughout the body.

neurodegenerative diseases
Conditions in which nerve cells, called neurons, of the brain and spinal cord cease to function and eventually die, including Parkinson's disease, amyotrophic lateral sclerosis (ALS), multiple sclerosis, Huntington's disease, Alzheimer's disease and other forms of dementia.

neurofibrillary tangles
An abnormal structure that forms inside nerve cells in the brain, causing dysfunction and the eventual death of the cell. Neurofibrillary tangles are considered one of the hallmarks of Alzheimer's disease (AD).

neuroimaging probes
Imaging agents such as FDDNP developed especially for diagnostic imaging of specific areas or functions of the central nervous system.

neuroimaging
A branch of medical imaging dedicated to imaging the brain.

neuron
Nerve cells that make up the central nervous system. Neurons consist of a nucleus, a single axon that conveys electrical signals to other neurons and a host of dendrites that deliver incoming signals.

non-Hodgkin lymphoma (HGL)
A type of lymphoma, a cancer in the lymphatic system, in which the cells abnormally reproduce, eventually causing tumors to grow.

nuclear cardiology
The use of a radiotracer and an imaging device to study physiological processes of the cardiovascular system, primarily the heart. Nuclear cardiology exams can assess how well the heart is pumping, reveal vessel blockages that have resulted in or may cause a heart attack, and identify which areas of the heart muscle were damaged by a heart attack. New radiotracers are being developed that bind to and can demonstrate the build-up of plaque in the arteries.

nuclear medicine/nuclear imaging
The use of very small amounts of radioactive materials (called radiopharmaceuticals or radiotracer) to evaluate molecular, metabolic, physiologic and pathologic conditions of the body for the purposes of diagnosis, therapy and research. Nuclear medicine procedures can often identify abnormalities very early in the progress of a disease — long before many medical problems are apparent with other diagnostic tests.

nucleus
The core of an atom that contains particles known as protons and neutrons. Electrons orbit around the atomic nucleus. Depending on the arrangement of particles within the atom, it may be extremely stable, or it may be unstable, in which case the atom can gain or lose particles, generating radioactivity.

opacity
The degree to which light or electromagnetic radiation is permitted to pass through a material.

optical imaging
A molecular imaging procedure in which light-producing molecules designed to attach to specific cells, such as cancer cells or brain chemicals, are injected into the patient's bloodstream. Imaging is then performed using devices that are able to detect these molecules inside the body. The two major types of optical imaging are bioluminescent imaging, which uses a natural chemical, such as luciferase, the substance that enables fireflies to glow, to trace the movement of certain cells or to identify the location of specific chemical reactions within the body and fluorescence imaging, which uses proteins that produce light when activated by an external light source such as a laser.

papillary thyroid cancer
One of several types of differentiated thyroid cancer; it may be treated with I-131 radiotherapy.

Parkinson's disease
A neurodegenerative diseasein which the cells of the brain and spinal cord cease to function and eventually die.

PET-CT
A combination of positron emission tomography (PET) and computed tomography (CT) that produces special views of the body. A combined PET-CT study is able to provide detail on both the anatomy and function of organs and tissues. This is accomplished by superimposing the precise localization of abnormal metabolic activity (from PET) against the detailed anatomic image (from CT).

pharmacodynamics
The study of the way drugs effect a living organism including the relationship between size of dose and the effect of the drug.

pharmacogenetics
The study of how a body reacts to a drug based on the individual's genetic make-up.

pharmacokinetics
The study of how living tissues process drugs, i.e. alter their chemical make-up as a drug is absorbed, distributed, metabolized and excreted. By tagging a drug with a probe or tracer before it is introduced into the body, molecular imagingallows researcher to follow a drug as it progresses through a living system.

pharynx
A hollow tube about five inches long that begins behind the nose and leads to the esophagus (the tube leading to the stomach) and the trachea (the tube that leads to the lungs). The pharynx has three parts: the upper part behind the nose called the nasopharynx; the middle called the oropharynx including the soft palate, base of the tongue, and tonsils; and the hypopharynx at the lower end.  Part of the respiratory system.

photodynamic therapy
A treatment for melanoma in which a chemical is applied to the skin and exposed to a light source.

photon
The smallest unit of light, or electromagnetic radiation.

PiB
An imaging agent or probe used in brain imaging to bind to the abnormal plaques and tangles associated with Alzheimer's disease and so they can be visualized on a PET scan.

Pick's disease
A type of frontotemporal dementia, which is a group of rare brain disorders that involves the shrinking or atrophy of tissues in the frontal and temporal lobes of the brain.

plaque
A buildup of fat, cholesterol and other substances that accumulates in the walls of the arteries.

positron emission mammography (PEM)
A high-resolution PET scanner designed specifically for breast cancer detection. PEM works much like PET scanning: the patient is injected with a very small amount of a radiotracer such as 18F-fluorodeoxyglucose (FDG), which travels through the body and is absorbed by breast tissue. The breast is then imaged with detectors mounted on compression paddles similar to those used in traditional mammography. Working with a computer, the scanner creates three-dimensional images showing the distribution of the radiotracer in the breast. Because highly active cancer cells absorb more glucose than normal cells, these cells appear brighter on PET scans.

positron emission tomography (PET)
Positron emission tomography (PET) is a medical imaging technique that uses radiopharmaceuticals that emit positrons (positively charged electrons). A radiopharmaceutical such as FDG is injected into the patient. The fluorine emits positrons which react with the first electron they come in contact with, annihilating both and producing energy according to Einstein's famous E=MC2 formula. This energy takes the form of two photons (particles of light) with a very specific energy level that shoot off in opposite directions. When these photon pairs are detected by the PET scanner, the location of the original fluorine atom can be extrapolated. Although positron/electron annihilation is one of the most powerful reactions known to science, the amount of mass involved is so small that the actual energy produced is not harmful to the patient, and the fluorine decays rapidly into harmless oxygen.

A PET scanner consists of a circular array of detectors tuned to detect photons at the specific energy level created by the positron/electron annihilation. Tomographic reconstruction software assembles these signals into images that show the location and concentration of the radiopharmaceutical inside the patient. When scanning with FDG, the rapidly dividing cancer cells use a lot of glucose to fuel their growth; therefore, they show up as "hot spots" on the PET image. PET is useful in diagnosing certain cardiovascular and neurological diseases as well because it highlights areas of increased, diminished, or absent metabolic activity.

PET is used predominately in determining the presence and severity of cancers, neurological conditions, and cardiovascular disease. It is also used to identify and stage cancers in the initial diagnosis and to check for recurrences. An example of how PET can be uniquely useful is in following patients after radiation therapy. The radiation may create scar tissue at the cancer site. Other medical imaging techniques can only identify the scar tissue as a "mass," i.e. it looks the same before and after therapy, while PET can indicate whether or not the mass is still malignant.

positron
A particle with the same mass as an electron but the opposite charge. Positrons are emitted in the natural decay of 18F-fluorodeoxyglucose (FDG), an imaging agent used in PET scanning.

ProstaScint scan (prostate-specific membrane antigen (PSMA) study)
A molecular imaging tool used to detect prostate cancer cells in the body.

ProstaScint® scan
Also called a  prostate-specific membrane antigen (PSMA) study
A diagnostic imaging test that allows physicians to locate and determine the extent of prostate cancer in patients who are newly diagnosed prostate cancer, who have had their prostate gland removed or who have an increase in prostate-specific antigen (PSA). The study involves a special molecule called a fragmented monoclonal antibody developed in a laboratory and designed to bind to the prostate-specific membrane antigen on cancer cells. This antibody is paired with a radioactive material called Indium-111 that can be detected by a gamma camera. When injected into the patient's bloodstream, the radioactive antibody attaches to cancer cells and the gamma camera produces three-dimensional images of the tumor and its location inside the body.

prostate gland
A gland near a man's bladder and urethra that secretes a thin fluid that is part of semen.

prostatectomy
The surgical removal of part or all of the prostate gland.

prostate-specific antigen (PSA)
A protein produced by the cells of the prostate gland that is present in small quantities in the blood of normal men but often elevated in the presence of prostate cancer or other prostate disorders.

prostate-specific membrane antigen (PSMA) study (ProstaScint scan)
A molecular imaging tool used to detect prostate cancer cells in the body.

radiation therapy
The use of high-energy waves or particles of radiation to kill cancer cells and shrink tumors.

radioactivity
The spontaneous decay or disintegration of an unstable atomic nucleus accompanied by the emission of radiation.

radioimmunoscintigraphy (RIS) (monoclonal antibody imaging)
The use of a laboratory-developed molecule called a monoclonal antibody that is designed to attach to specific cancer cells. Once the monoclonal antibody is combined, or labeled, with a radioactive atom and injected into the patient, single-photon emission computed tomography (SPECT) imaging is performed, creating three-dimensional images of the tumor.

radioimmunotherapy (RIT)
The use of specially designed antibodies to deliver radioisotopes to targeted cells (usually cancer cells). The radiation then destroys those cells. Because the antibodies are designed to attach only to very specific types of cells, radioimmunotherapy maximizes the radiation that can be delivered to the diseased tissue and minimizes the amount of radiation to which healthy tissue is exposed.

radioiodine
Also called radioactive iodine. The radioisotope of iodine, a naturally occurring non-metallic element that is used in molecular imaging and treatment. Two forms have medical purposes: I-123 is used as a radiotracer for imaging the thyroid and I-131 is used both as a radiotracer and as a therapeutic agent for thyroid cancer.

radioisotope
A radioisotope is a radioactive version of an element. Radioactive elements differ from the stable versions of the same element in that they have either more or fewer neutrons. For example all forms of carbon have the same number on protons (six), but the most common form has six neutrons as well. Forms with five (11C), seven (13C) and eight (the famous 14C) neutrons are radioactive. Some radioisotopes have very long half-lives. For example, the half-life of 14C is 5700 years, making it useful for dating organic materials. And some have very short half-lives: the half-live of 11C is only 20 minutes. There is no chemical difference between the way the radioactive and non-radioactive versions of an element react. The fact that there is no difference allows the radioactive versions of the element to be substituted for the non-radioactive versions to produce a tracer. This principal can also be applied to therapy. Iodine, which was the first element used in nuclear medicine, is used exclusively by the thyroid gland. If a radioactive isotope of iodine is introduced into the body, it will be taken up by the thyroid gland in exactly the same way as non-radioactive iodine. A gamma camera can then be used to determine how well the thyroid is working. Similarly, a large dose of radioactive iodine can be used to treat thyroid cancer by delivering a tumor-killing radiation dose directly to the cancerous tissue.

radiopharmaceutical
A type of imaging agent used in nuclear medicine, a branch of molecular imaging. It is a compound consisting of a drug and a small amount of radioactive material that localizes in specific organs or areas of the body and can be detected by an imaging device.

Radiotracer (tracer)
A compound that includes a radioactive atom or isotope that is used as an imaging agent in a branch of molecular imaging called nuclear medicine. Radioactive imaging agents are introduced into the body where they accumulate in a target organ or attach to specific cells and are detected by an imaging device,which creates pictures of how the agent is distributed in the body. Non-radioactive tracers used in molecular imaging include bioluminescent and fluorescent molecules and microbubbles.

rectum
The lower section of the large intestine or colon that ends in the anus and acts as storage area for fecal waste.

reporter-gene systems
The use of engineered genes that are designed to adhere to specific cells in body that may be detected by molecular imaging technologies.

re-staging
A re-evaluation of the extent of disease, after a round of treatment, that provides the basis for ongoing management.

sarcoma
A malignant or cancerous tumor that occurs in the connective tissues of the body including the bones, cartilage, tendons and soft tissues.

sentinel lymph node(s)
The first few lymph nodes into which a tumor drains and those most likely to contain cancer cells if the tumor has metastasized or spread.

sentinel node biopsy
A surgical procedure used to determine if cancer has spread beyond a primary tumor into the lymphatic system. It is most commonly used to evaluate melanoma and breast cancer, as a alternative to an axillary lymph node dissection. The procedure involves using molecular imaging is used to identify the sentinel, or first few, lymph nodes into which a tumor drains and those most likely to contain cancer cells if the disease has metastasized, or spread. Only the sentinel nodes are surgically removed, which results in fewer complications and side effects for the patient, including lymphedema.

Since molecular imaging works at the cellular and molecular level, it can provide accurate information about disease processes at a very early stage. Molecular imaging provides personalized information about an individual's specific disease and how that disease may react or has reacted to specific treatments.

single-photon emission-computed tomography (SPECT)
SPECTuses a gamma camera to detectradioisotopes that emit high-energy radiation. The gamma camera, which rotates around the patient, works with a computer to create three-dimensional images of the distribution of the tracer in the body.

SPECT scan
SPECT stands for "single-photon emission-computed tomography." A SPECT scan uses a gamma camera to detect radioisotopes that emit high-energy radiation. The gamma camera works with a computer to create three-dimensional images of the distribution of the tracer in the body. SPECT is most often used in cardiology to provide information about blood flow through the heart muscle that can be used to diagnose heart disease. It is also used for brain and bone scans and to detect infection and certain types of tumors.

spleen
An organ located on the left side of the abdomen near the stomach that is part of the lymphatic system. It produces lymphocytes, filters the blood, stores blood cells and destroys old blood cells.

stage
A measure of the extent of disease present in the body.

stroke
A loss of brain function due to an interruption in the flow of blood to the brain due to a clot blocking a blood vessel or the rupture of an artery in the brain.

Technetium Tc99m Sestamibi
A radiotracer used in breast-specific gamma imaging to detect additional lesions missed by mammography and physical exam and cancers that are difficult to detect using mammography. The radiotracer is injected into the patient's bloodstream and accumulates in malignant tissue where it can be detected by a special gamma camera.

Technetium-99m sulfur-colloid
A radiotracer used in lymphoscintigraphy that can be detected by a gamma camera to help identify the first, or sentinel, lymph nodes into which a melanoma site drains.

thymus
An organ located in the upper portion of the chest cavity just behind the sternum that produces T lymphocytes, white blood cells that fight infection and destroy abnormal cells as part of the body's immune defense system.

thyroid
An organ located at the base of the throat that makes hormones that help control heart rate, blood pressure, body temperature and weight.

tomography, tomographic reconstruction
Tomographic reconstruction is a technique that uses a series of two-dimensional images to create a three-dimensional image. For example, a computed tomography (CT) scanner acquires a series of cross-sectional x-rays, which are combined (using tomographic reconstructionalgorithm software) into a three-dimensional image of the body that can be viewed from any direction.

transient ischemic attack (TIA)
A temporary loss of blood supply to tissues in the brain, also called a ‘mini-stroke.' It can cause brief symptoms such as dizziness, slurred speech, weakness or numbness but no permanent damage.

translational medicine
Translational medicine is the process of moving basic laboratory research into mainstream medical practice. Translational medicinefocuses on the necessary steps—including patient testing and clinical trials—that will ensure safety before a technique can be used on patients in clinical practice.

tumor marker
The presence of a substance either released by cancer cells into the blood or urine or that is created by the body in response to cancer cells. Elevated levels of these substances may indicate that disease is present. Tumor markers are also used by molecular imaging technologies to detect disease, evaluate how well a patient has responded to treatment or to check for a tumor recurrence.

tumor
An abnormal growth of tissue that results from excessive cell division that can be benign or malignant (cancerous).

ultrasound (US)
Essentially an anatomical imaging technology that uses sound waves to create images of tissue within the body. It can be a molecular imaging technique when used in conjunction with targeted microbubbles.

urethra
The duct or tube from the bladder through which urine passes as it leaves the body.

x-rays
A noninvasive medical test that helps physicians diagnose and treat medical conditions. Imaging with x-rays involves exposing a part of the body to a small dose of ionizing radiation to produce pictures of the inside of the body.

yttrium-90 labeled octreotide
A radiopharmaceutical being evaluated in clinical trials as an alternative to radioiodine for patients whose thyroid cancer is not responsive to I-131 radiotherapy with iodine.

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