Gallium scan
Encyclopedia
A gallium scan or gallium 67 scan (also called "gallium imaging") is a type of nuclear medicine
study that uses a radioactive tracer
to obtain images of a specific type of tissue, or disease state of tissue. Gallium
salt
s like gallium citrate
and gallium nitrate
are used. The form of salt is not important, since it is the freely dissolved gallium ion Ga+3 which is active. For these applications, the radioactive isotope
gallium-67 (67Ga), which has a decay half-life of 3.26 days, is used.
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) (Ga+3) binds to transferrin
, leukocyte lactoferrin
, bacterial siderophore
s, inflammatory proteins, and cell-membranes in neutrophils both living and dead.
This binding allows sites with tumor, inflammation, and both acute and chronic infection to be imaged by nuclear scan techniques.
for cancer
diagnosis and staging, until it was replaced by positron emission tomography
using fludeoxyglucose. 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
s, especially lymphoma
, gallium imaging is still in use, but may be replaced by PET imaging in the future.
In infections, the gallium scan has an advantage over indium leukocyte imaging (also called indium-111 white blood cell scan) in imaging osteomyelitis
(bone infection) of the spine, lung infections and inflammation, and for chronic infections. In part this is because gallium binds to neutrophil 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 and pelvic infections. Both the gallium scan and indium leukocyte imaging may be used to image fever of unknown origin
(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.
to produce two-dimensional images. After the tracer has been injected, images are taken by a gamma camera
at 24, 48, and in some cases, 72, and 96 hours later. Each set of images takes 30–60 minutes, depending on the size of the area being imaged. The resulting image will have bright areas that collected large amounts of tracer, because inflammation is present or rapid cell division is occurring. Single photon emission computed tomography
(SPECT) images may also be acquired. In some imaging centers, SPECT images may be combined with computed tomography
scan using either fusion software or SPECT/CT hybrid cameras to superimpose both physiological image-information from the gallium scan, and anatomical information from the CT scan.
Nuclear medicine
In nuclear medicine procedures, elemental radionuclides are combined with other elements to form chemical compounds, or else combined with existing pharmaceutical compounds, to form radiopharmaceuticals. These radiopharmaceuticals, once administered to the patient, can localize to specific organs...
study that uses a radioactive tracer
Radiopharmacology
Radiopharmacology is the study and preparation of radiopharmaceuticals, which are radioactive pharmaceuticals. Radiopharmaceuticals are used in the field of nuclear medicine as tracers in the diagnosis and treatment of many diseases. Many radiopharmaceuticals use technetium-99m which has many...
to obtain images of a specific type of tissue, or disease state of tissue. Gallium
Gallium
Gallium is a chemical element that has the symbol Ga and atomic number 31. Elemental gallium does not occur in nature, but as the gallium salt in trace amounts in bauxite and zinc ores. A soft silvery metallic poor metal, elemental gallium is a brittle solid at low temperatures. As it liquefies...
salt
Salt
In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...
s like gallium citrate
Citrate
A citrate can refer either to the conjugate base of citric acid, , or to the esters of citric acid. An example of the former, a salt is trisodium citrate; an ester is triethyl citrate.-Other citric acid ions:...
and gallium nitrate
Nitrate
The nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a...
are used. The form of salt is not important, since it is the freely dissolved gallium ion Ga+3 which is active. For these applications, the radioactive isotope
Radionuclide
A radionuclide is an atom with an unstable nucleus, which is a nucleus characterized by excess energy available to be imparted either to a newly created radiation particle within the nucleus or to an atomic electron. The radionuclide, in this process, undergoes radioactive decay, and emits gamma...
gallium-67 (67Ga), which has a decay half-life of 3.26 days, is used.
Mechanism
The body generally handles Ga3+ as though it were ferricFerric
Ferric refers to iron-containing materials or compounds. In chemistry the term is reserved for iron with an oxidation number of +3, also denoted iron or Fe3+. On the other hand, ferrous refers to iron with oxidation number of +2, denoted iron or Fe2+...
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) (Ga+3) binds to transferrin
Transferrin
Transferrins are iron-binding blood plasma glycoproteins that control the level of free iron in biological fluids. In humans, it is encoded by the TF gene.Transferrin is a glycoprotein that binds iron very tightly but reversibly...
, leukocyte lactoferrin
Lactoferrin
Lactoferrin , also known as lactotransferrin , 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, such as milk, saliva, tears, and nasal secretions...
, bacterial siderophore
Siderophore
Siderophores are small, high-affinity iron chelating compounds secreted by grasses and microorganisms such as bacteria and fungi...
s, inflammatory proteins, and cell-membranes in neutrophils both living and dead.
This binding allows sites with tumor, inflammation, and both acute and chronic infection to be imaged by nuclear scan techniques.
Uses in medicine
In the past, the gallium scan was the gold standardGold standard (test)
In medicine and statistics, gold standard test refers to a diagnostic test or benchmark that is the best available under reasonable conditions. It does not have to be necessarily the best possible test for the condition in absolute terms...
for cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
diagnosis and staging, until it was replaced by positron emission tomography
Positron emission tomography
Positron emission tomography is nuclear medicine imaging technique that produces a three-dimensional image or picture of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide , which is introduced into the body on a...
using fludeoxyglucose. 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
Tumor
A tumor or tumour is commonly used as a synonym for a neoplasm that appears enlarged in size. Tumor is not synonymous with cancer...
s, especially lymphoma
Lymphoma
Lymphoma is a cancer in the lymphatic cells of the immune system. Typically, lymphomas present as a solid tumor of lymphoid cells. Treatment might involve chemotherapy and in some cases radiotherapy and/or bone marrow transplantation, and can be curable depending on the histology, type, and stage...
, gallium imaging is still in use, but may be replaced by PET imaging in the future.
In infections, the gallium scan has an advantage over indium leukocyte imaging (also called indium-111 white blood cell scan) in imaging osteomyelitis
Osteomyelitis
Osteomyelitis simply means an infection of the bone or bone marrow...
(bone infection) of the spine, lung infections and inflammation, and for chronic infections. In part this is because gallium binds to neutrophil 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 and pelvic infections. Both the gallium scan and indium leukocyte imaging may be used to image fever of unknown origin
Fever of unknown origin
Fever of unknown origin , pyrexia of unknown origin or febris e causa ignota refers to a condition in which the patient has an elevated temperature but despite investigations by a physician no explanation has been found....
(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.
Technique
The main technique uses scintigraphyScintigraphy
Scintigraphy is a form of diagnostic test used in nuclear medicine, wherein radioisotopes are taken internally, and the emitted radiation is captured by external detectors to form two-dimensional images...
to produce two-dimensional images. After the tracer has been injected, images are taken by a gamma camera
Gamma camera
A gamma camera, also called a scintillation camera or Anger camera, is a device used to image gamma radiation emitting radioisotopes, a technique known as scintigraphy...
at 24, 48, and in some cases, 72, and 96 hours later. Each set of images takes 30–60 minutes, depending on the size of the area being imaged. The resulting image will have bright areas that collected large amounts of tracer, because inflammation is present or rapid cell division is occurring. Single photon emission computed tomography
Single photon emission computed tomography
Single-photon emission computed tomography is a nuclear medicine tomographic imaging technique using gamma rays. It is very similar to conventional nuclear medicine planar imaging using a gamma camera. However, it is able to provide true 3D information...
(SPECT) images may also be acquired. In some imaging centers, SPECT images may be combined with computed tomography
Computed tomography
X-ray computed tomography or Computer tomography , is a medical imaging method employing tomography created by computer processing...
scan using either fusion software or SPECT/CT hybrid cameras to superimpose both physiological image-information from the gallium scan, and anatomical information from the CT scan.