A gallium scan is a type of

nuclear medicine Nuclear medicine or nucleology is a medical specialty involving the application of radioactive substances in the diagnosis and treatment of disease. Nuclear imaging, in a sense, is "radiology done inside out" because it records radiation emit ...

test that uses either a

gallium-67 Natural gallium (31Ga) consists of a mixture of two stable isotopes: gallium-69 and gallium-71. The most commercially important radioisotopes are gallium-67 and gallium-68. Gallium-67 (half-life 3.3 days) is a gamma-emitting isotope (the gamma ...

(⁶⁷Ga) or gallium-68 (⁶⁸Ga)

radiopharmaceutical Radiopharmaceuticals, or medicinal radiocompounds, are a group of pharmaceutical drugs containing radioactive isotopes. Radiopharmaceuticals can be used as diagnostic and therapeutic agents. Radiopharmaceuticals emit radiation themselves, which is ...

to obtain images of a specific type of tissue, or disease state of tissue.

Gallium Gallium is a chemical element with the symbol Ga and atomic number 31. Discovered by French chemist Paul-Émile Lecoq de Boisbaudran in 1875, Gallium is in group 13 of the periodic table and is similar to the other metals of the group ( alum ...

salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quanti ...

s like gallium

citrate Citric acid is an organic compound with the chemical formula HOC(CO2H)(CH2CO2H)2. It is a colorless weak organic acid. It occurs naturally in citrus fruits. In biochemistry, it is an intermediate in the citric acid cycle, which occurs in t ...

and gallium

nitrate Nitrate is a polyatomic ion with the chemical formula . Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are soluble in water. An example of an insoluble ...

may be used. The form of salt is not important, since it is the freely dissolved gallium ion Ga³⁺ which is active. Both ⁶⁷Ga and ⁶⁸Ga salts have similar uptake mechanisms. Gallium can also be used in other forms, for example ⁶⁸Ga-PSMA is used for

cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal bl ...

imaging. The

gamma emission A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically s ...

of gallium-67 is imaged by a

gamma camera A gamma camera (γ-camera), also called a scintillation camera or Anger camera, is a device used to image gamma radiation emitting radioisotopes, a technique known as scintigraphy. The applications of scintigraphy include early drug development ...

, while the

positron emission Positron emission, beta plus decay, or β+ decay is a subtype of radioactive decay called beta decay, in which a proton inside a radionuclide nucleus is converted into a neutron while releasing a positron and an electron neutrino (). Positron e ...

of gallium-68 is imaged by

positron emission tomography Positron emission tomography (PET) is a functional imaging technique that uses radioactive substances known as radiotracers to visualize and measure changes in metabolic processes, and in other physiological activities including blood flow, ...

(PET). Gallium salts are taken up by tumors, inflammation, and both acute and chronic infection, allowing these pathological processes to be imaged. Gallium is particularly useful in imaging

osteomyelitis Osteomyelitis (OM) is an infection of bone. Symptoms may include pain in a specific bone with overlying redness, fever, and weakness. The long bones of the arms and legs are most commonly involved in children e.g. the femur and humerus, while the ...

that involves the spine, and in imaging older and chronic infections that may be the cause of a

fever of unknown origin Fever of unknown origin (FUO) refers to a condition in which the patient has an elevated temperature (fever) but, despite investigations by a physician, no explanation has been found.

. Gallium-68 DOTA scans are increasingly replacing octreotide scans (a type of

indium-111 Indium-111 (111In) is a radioactive isotope of indium (In). It decays by electron capture to stable cadmium-111 with a half-life of 2.8 days. Indium-111 chloride (111InCl) solution is produced by proton irradiation of a cadmium target (112Cd( ...

scan using octreotide as a somatostatin receptor ligand). The gallium-68 is bound to an octreotide derivative chemical such as DOTATOC and the positrons it emits are imaged by

PET-CT Positron emission tomography–computed tomography (better known as PET-CT or PET/CT) is a nuclear medicine technique which combines, in a single gantry, a positron emission tomography (PET) scanner and an x-ray computed tomography (CT) scann ...

scan. Such scans are useful in locating

neuroendocrine tumors Neuroendocrine tumors (NETs) are neoplasms that arise from cells of the endocrine ( hormonal) and nervous systems. They most commonly occur in the intestine, where they are often called carcinoid tumors, but they are also found in the pancreas, lun ...

and

pancreatic cancer Pancreatic cancer arises when cells in the pancreas, a glandular organ behind the stomach, begin to multiply out of control and form a mass. These cancerous cells have the ability to invade other parts of the body. A number of types of panc ...

Gallium citrate scan

Gallium 67 Scan (Diagnosis of Sarcoidosis)

In the past, the gallium scan was the

gold standard A gold standard is a Backed currency, monetary system in which the standard economics, economic unit of account is based on a fixed quantity of gold. The gold standard was the basis for the international monetary system from the 1870s to the ...

for

lymphoma Lymphoma is a group of blood and lymph tumors that develop from lymphocytes (a type of white blood cell). In current usage the name usually refers to just the cancerous versions rather than all such tumours. Signs and symptoms may include enl ...

staging, until it was replaced by

(PET) using fludeoxyglucose (FDG). Gallium imaging is still used to image inflammation and chronic infections, and it still sometimes locates unsuspected tumors as it is taken up by many kinds of cancer cells in amounts that exceed those of normal tissues. Thus, an increased uptake of gallium-67 may indicate a new or old infection, an inflammatory focus from any cause, or a cancerous tumor. It has been suggested that gallium imaging may become an obsolete technique, with indium leukocyte imaging and technetium antigranulocyte antibodies replacing it as a detection mechanism for infections. For detection of

tumor A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...

s, especially lymphomas, gallium imaging is still in use, but may be replaced by fludeoxyglucose PET imaging in the future. In infections, the gallium scan has an advantage over indium leukocyte imaging in imaging

(bone infection) of the spine, lung infections and inflammation, and for chronic infections. In part this is because gallium binds to

neutrophil Neutrophils (also known as neutrocytes or heterophils) are the most abundant type of granulocytes and make up 40% to 70% of all white blood cells in humans. They form an essential part of the innate immune system, with their functions varying in ...

membranes, even after neutrophil death. Indium leukocyte imaging is better for acute infections (where neutrophils are still rapidly and actively localizing to the infection), and also for osteomyelitis that does not involve the spine, and for

abdominal The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the torso ...

and

pelvic The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton). The ...

infections. Both the gallium scan and indium leukocyte imaging may be used to image

(elevated temperature without an explanation). However, the indium leukocyte scan will image only the 25% of such cases which are caused by acute infections, while gallium will also localize to other sources of fever, such as chronic infections and tumors.

Mechanism

The body generally handles Ga³⁺ as though it were

ferric In chemistry, iron(III) refers to the element iron in its +3 oxidation state. In ionic compounds (salts), such an atom may occur as a separate cation (positive ion) denoted by Fe3+. The adjective ferric or the prefix ferri- is often used to s ...

iron (Fe-III), and thus the free isotope ion is bound (and concentrates) in areas of inflammation, such as an infection site, and also areas of rapid cell division. Gallium (III) (Ga³⁺) binds to

transferrin Transferrins are glycoproteins found in vertebrates which bind to and consequently mediate the transport of iron (Fe) through blood plasma. They are produced in the liver and contain binding sites for two Fe3+ ions. Human transferrin is encoded ...

leukocyte White blood cells, also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and derived from mul ...

lactoferrin Lactoferrin (LF), also known as lactotransferrin (LTF), is a multifunctional protein of the transferrin family. Lactoferrin is a globular glycoprotein with a molecular mass of about 80 kDa that is widely represented in various secretory fluids, ...

bacterial Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

siderophore Siderophores (Greek: "iron carrier") are small, high-affinity iron- chelating compounds that are secreted by microorganisms such as bacteria and fungi. They help the organism accumulate iron. Although a widening range of siderophore functions is n ...

inflammatory protein Inflammatory may refer to: * Inflammation, a biological response to harmful stimuli * The word ''inflammatory'' is also used to refer literally to fire and flammability, and figuratively in relation to comments that are provocative and arouse pa ...

s, and cell-membranes in neutrophils, both living and dead. Lactoferrin is contained within leukocytes. Gallium may bind to lactoferrin and be transported to sites of inflammation, or binds to lactoferrin released during bacterial

phagocytosis Phagocytosis () is the process by which a cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs phagocytosis i ...

at infection sites (and remains due to binding with macrophage receptors). Gallium-67 also attaches to the siderophore molecules of bacteria themselves, and for this reason can be used in

leukopenic Leukopenia () is a decrease in the number of leukocytes (WBC). Found in the blood, they are the white blood cells, and are the body's primary defense against an infection. Thus the condition of leukopenia places individuals at increased risk of ...

patients with bacterial infection (here it attaches directly to bacterial proteins, and leukocytes are not needed). Uptake is thought to be associated with a range of tumour properties including transferring receptors, a