Gadolinium is a chemical element with symbol Gd and atomic number 64. Gadolinium is a silvery-white, malleable, and ductile rare earth metal. It is found in nature only in oxidized form, and even when separated, it usually has impurities of the other rare earths. Gadolinium was discovered in 1880 by Jean Charles de Marignac, who detected its oxide by using spectroscopy. It is named after the mineral gadolinite, one of the minerals in which gadolinium is found, itself named for the chemist Johan Gadolin. Pure gadolinium was first isolated by the chemist Paul Emile Lecoq de Boisbaudran around 1886.
Gadolinium possesses unusual metallurgical properties, to the extent that as little as 1% of gadolinium can significantly improve the workability and resistance to oxidation at high temperatures of iron, chromium, and related metals. Gadolinium as a metal or a salt absorbs neutrons and is, therefore, used sometimes for shielding in neutron radiography and in nuclear reactors.
Like most of the rare earths, gadolinium forms trivalent ions with fluorescent properties, and salts of gadolinium(III) are used as phosphors in various applications.
The kinds of gadolinium(III) ions occurring in water-soluble salts are toxic to mammals. However, chelated gadolinium(III) compounds are far less toxic because they carry gadolinium(III) through the kidneys and out of the body before the free ion can be released into the tissues. Because of its paramagnetic properties, solutions of chelated organic gadolinium complexes are used as intravenously administered gadolinium-based MRI contrast agents in medical magnetic resonance imaging.
|Standard atomic weight Ar, std(Gd)||157.25(3)|
|Gadolinium in the periodic table|
|Atomic number (Z)||64|
|Electron configuration||[Xe] 4f7 5d1 6s2|
Electrons per shell
|2, 8, 18, 25, 9, 2|
|Phase at STP||solid|
|Melting point||1585 K (1312 °C, 2394 °F)|
|Boiling point||3273 K (3000 °C, 5432 °F)|
|Density (near r.t.)||7.90 g/cm3|
|when liquid (at m.p.)||7.4 g/cm3|
|Heat of fusion||10.05 kJ/mol|
|Heat of vaporization||301.3 kJ/mol|
|Molar heat capacity||37.03 J/(mol·K)|
|Vapor pressure (calculated)|
|Oxidation states||+1, +2, +3 (a mildly basic oxide)|
|Electronegativity||Pauling scale: 1.20|
|Atomic radius||empirical: 180 pm|
|Covalent radius||196±6 pm|
Spectral lines of gadolinium
|Crystal structure|| hexagonal close-packed (hcp)|
|Speed of sound thin rod||2680 m/s (at 20 °C)|
|Thermal expansion||α poly: 9.4 µm/(m·K) (at 100 °C)|
|Thermal conductivity||10.6 W/(m·K)|
|Electrical resistivity||α, poly: 1.310 µΩ·m|
|Magnetic ordering||ferromagnetic-paramagnetic transition at 293.4 K|
|Magnetic susceptibility||+755,000.0·10−6 cm3/mol (300.6 K)|
|Young's modulus||α form: 54.8 GPa|
|Shear modulus||α form: 21.8 GPa|
|Bulk modulus||α form: 37.9 GPa|
|Poisson ratio||α form: 0.259|
|Vickers hardness||510–950 MPa|
|Naming||after the mineral Gadolinite (itself named after Johan Gadolin)|
|Discovery||Jean Charles Galissard de Marignac (1880)|
|First isolation||Lecoq de Boisbaudran (1886)|
|Main isotopes of gadolinium|
Gadolinium is a silvery-white malleable and ductile rare earth metal. It crystallizes in the hexagonal close-packed α-form at room temperature, but, when heated to temperatures above 1235 °C, it transforms into its β-form, which has a body-centered cubic structure.
The isotope gadolinium-157 has the highest thermal-neutron capture cross-section among any stable nuclide: about 259,000 barns. Only xenon-135 has a higher capture cross-section, about 2.0 million barns, but this isotope is radioactive.
Gadolinium is believed to be ferromagnetic at temperatures below 20 °C (68 °F) and is strongly paramagnetic above this temperature. There is evidence that gadolinium is a helical antiferromagnetic, rather than a ferromagnetic, below 20 °C (68 °F). Gadolinium demonstrates a magnetocaloric effect whereby its temperature increases when it enters a magnetic field and decreases when it leaves the magnetic field. The temperature is lowered to 5 °C (41 °F) for the gadolinium alloy Gd85Er15, and this effect is considerably stronger for the alloy Gd5(Si2Ge2), but at a much lower temperature (<85 K (−188.2 °C; −306.7 °F)). A significant magnetocaloric effect is observed at higher temperatures, up to about 300 kelvins, in the compounds Gd5(SixGe1−x)4.
Individual gadolinium atoms can be isolated by encapsulating them into fullerene molecules, where they can be visualized with transmission electron microscope. Individual Gd atoms and small Gd clusters can be incorporated into carbon nanotubes.
Gadolinium combines with most elements to form Gd(III) derivatives. It also combines with nitrogen, carbon, sulfur, phosphorus, boron, selenium, silicon, and arsenic at elevated temperatures, forming binary compounds.
which spalls off, exposing more surface to oxidation.
Gadolinium is a strong reducing agent, which reduces oxides of several metals into their elements. Gadolinium is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form gadolinium hydroxide:
Gadolinium metal reacts with the halogens (X2) at temperature about 200 °C:
In the great majority of its compounds, gadolinium adopts the oxidation state +3. All four trihalides are known. All are white, except for the iodide, which is yellow. Most commonly encountered of the halides is gadolinium(III) chloride (GdCl3). The oxide dissolves in acids to give the salts, such as gadolinium(III) nitrate.
Gadolinium(III), like most lanthanide ions, forms complexes with high coordination numbers. This tendency is illustrated by the use of the chelating agent DOTA, an octadentate ligand. Salts of [Gd(DOTA)]− are useful in magnetic resonance imaging. A variety of related chelate complexes have been developed, including gadodiamide.
Reduced gadolinium compounds are known, especially in the solid state. Gadolinium(II) halides are obtained by heating Gd(III) halides in presence of metallic Gd in tantalum containers. Gadolinium also form sesquichloride Gd2Cl3, which can be further reduced to GdCl by annealing at 800 °C. This gadolinium(I) chloride forms platelets with layered graphite-like structure.
Naturally occurring gadolinium is composed of six stable isotopes, 154Gd, 155Gd, 156Gd, 157Gd, 158Gd and 160Gd, and one radioisotope, 152Gd, with the isotope 158Gd being the most abundant (24.84% natural abundance). The predicted double beta decay of 160Gd has never been observed (the only lower limit on its half-life of more than 1.3×1021 years has been set experimentally).
29 radioisotopes of gadolinium have been observed, with the most stable being 152Gd (naturally occurring), with a half-life of about 1.08×1014 years, and 150Gd, with a half-life of 1.79×106 years. All of the remaining radioactive isotopes have half-lives of less than 75 years. The majority of these have half-lives of less than 25 seconds. Gadolinium isotopes have four metastable isomers, with the most stable being 143mGd (t1/2 = 110 seconds), 145mGd (t1/2 = 85 seconds) and 141mGd (t1/2 = 24.5 seconds).
The isotopes with atomic masses lower than the most abundant stable isotope, 158Gd, primarily decay by electron capture to isotopes of europium. At higher atomic masses, the primary decay mode is beta decay, and the primary products are isotopes of terbium.
Gadolinium is named after the mineral gadolinite, in turn named after Finnish chemist and geologist Johan Gadolin. In 1880, the Swiss chemist Jean Charles Galissard de Marignac observed the spectroscopic lines from gadolinium in samples of gadolinite (which actually contains relatively little gadolinium, but enough to show a spectrum) and in the separate mineral cerite. The latter mineral proved to contain far more of the element with the new spectral line. De Marignac eventually separated a mineral oxide from cerite, which he realized was the oxide of this new element. He named the oxide "gadolinia". Because he realized that "gadolinia" was the oxide of a new element, he is credited with discovery of gadolinium. The French chemist Paul Émile Lecoq de Boisbaudran carried out the separation of gadolinium metal from gadolinia in 1886.
Gadolinium is a constituent in many minerals such as monazite and bastnäsite, which are oxides. The metal is too reactive to exist naturally. Paradoxically, as noted above, the mineral gadolinite actually contains only traces of this element. The abundance in the Earth's crust is about 6.2 mg/kg. The main mining areas are in China, the US, Brazil, Sri Lanka, India, and Australia with reserves expected to exceed one million tonnes. World production of pure gadolinium is about 400 tonnes per year. The only known mineral with essential gadolinium, lepersonnite-(Gd), is very rare.
Gadolinium is produced both from monazite and bastnäsite.
Gadolinium metal is obtained from its oxide or salts by heating it with calcium at 1450 °C in an argon atmosphere. Sponge gadolinium can be produced by reducing molten GdCl3 with an appropriate metal at temperatures below 1312 °C (the melting point of Gd) at a reduced pressure.
Gadolinium has no large-scale applications, but it has a variety of specialized uses.
Because 157Gd has a high neutron cross-section, it is used to target tumors in neutron therapy. This element is effective for use with neutron radiography and in shielding of nuclear reactors. It is used as a secondary, emergency shut-down measure in some nuclear reactors, particularly of the CANDU reactor type. Gadolinium is also used in nuclear marine propulsion systems as a burnable poison.
Gadolinium possesses unusual metallurgic properties, with as little as 1% of gadolinium improving the workability and resistance of iron, chromium, and related alloys to high temperatures and oxidation.
Gadolinium is paramagnetic at room temperature, with a ferromagnetic Curie point of 20 °C. Paramagnetic ions, such as gadolinium, enhance nuclear relaxation rates, making gadolinium useful for magnetic resonance imaging (MRI). Solutions of organic gadolinium complexes and gadolinium compounds are used as intravenous MRI contrast agent to enhance images in medical magnetic resonance imaging and magnetic resonance angiography (MRA) procedures. Magnevist is the most widespread example. Nanotubes packed with gadolinium, called "gadonanotubes", are 40 times more effective than the usual gadolinium contrast agent. Once injected, gadolinium-based contrast agents accumulate in abnormal tissues of the brain and body, which provides a greater image contrast between normal and abnormal tissues, facilitating location of abnormal cell growths and tumors.
Gadolinium as a phosphor is also used in other imaging. In X-ray systems gadolinium is contained in the phosphor layer, suspended in a polymer matrix at the detector. Terbium-doped gadolinium oxysulfide (Gd2O2S:Tb) at the phosphor layer converts the X-rays released from the source into light. This material emits green light at 540 nm due to the presence of Tb3+, which is very useful for enhancing the imaging quality. The energy conversion of Gd is up to 20%, which means that 1/5 of the X-ray energy striking the phosphor layer can be converted into visible photons. Gadolinium oxyorthosilicate (Gd2SiO5, GSO; usually doped by 0.1–1% of Ce) is a single crystal that is used as a scintillator in medical imaging such as positron emission tomography or for detecting neutrons.
Gadolinium-153 is produced in a nuclear reactor from elemental europium or enriched gadolinium targets. It has a half-life of 240±10 days and emits gamma radiation with strong peaks at 41 keV and 102 keV. It is used in many quality-assurance applications, such as line sources and calibration phantoms, to ensure that nuclear-medicine imaging systems operate correctly and produce useful images of radioisotope distribution inside the patient. It is also used as a gamma-ray source in X-ray absorption measurements or in bone density gauges for osteoporosis screening, as well as in the Lixiscope portable X-ray imaging system.
Gadolinium is used for making gadolinium yttrium garnet (Gd:Y3Al5O12); it has microwave applications and is used in fabrication of various optical components and as substrate material for magneto-optical films.
Gadolinium can also serve as an electrolyte in solid oxide fuel cells (SOFCs). Using gadolinium as a dopant for materials like cerium oxide (in the form of gadolinium-doped ceria) creates an electrolyte with both high ionic conductivity and low operating temperatures, which are optimal for cost-effective production of fuel cells.
Research is being conducted on magnetic refrigeration near room temperature, which could provide significant efficiency and environmental advantages over conventional refrigeration methods. Gadolinium-based materials, such as Gd5(SixGe1−x)4, are currently the most promising materials, owing to their high Curie temperature and giant magnetocaloric effect. Pure Gd itself exhibits a large magnetocaloric effect near its Curie temperature of 20 °C, and this has sparked great interest into producing Gd alloys with a larger effect and tunable Curie temperature. In Gd5(SixGe1−x)4, Si and Ge compositions can be varied to adjust the Curie temperature. This technology is still very early in development, and significant material improvements still need to be made before it is commercially viable.
Gadolinium has no known native biological role, but its compounds are used as research tools in biomedicine. Gd3+ compounds are components of MRI contrast agents. It is used in various ion channel electrophysiology experiments to block sodium leak channels and stretch activated ion channels. Gadolinium has recently been used to measure the distance between two points in a protein via electron paramagnetic resonance, something that gadolinium is especially amenable to thanks to EPR sensitivity at w-band (95 GHz) frequencies. 
|GHS signal word||Danger|
As a free ion, gadolinium is reported often to be highly toxic, but MRI contrast agents are chelated compounds and are considered safe enough to be used in most persons. The toxicity of free gadolinium ions in animals is due to interference with a number of calcium-ion channel dependent processes. The 50% lethal dose is about 100–200 mg/kg. Toxicities have not been reported following low dose exposure to gadolinium ions. Toxicity studies in rodents, however show that chelation of gadolinium (which also improves its solubility) decreases its toxicity with regard to the free ion by at least a factor of 100 (i.e., the lethal dose for the Gd-chelate increases by 100 times). It is believed therefore that clinical toxicity of gadolinium-based contrast agents (GBCAs) in humans will depend on the strength of the chelating agent; however this research is still not complete. About a dozen different Gd-chelated agents have been approved as MRI contrast agents around the world.
Although gadolinium agents are useful for patients with renal impairment, in patients with severe renal failure requiring dialysis, there is a risk of a rare but serious illness called nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy, that is linked to the use of MRI contrast agents containing gadolinium. The disease resembles scleromyxedema and to some extent scleroderma. It may occur months after a contrast agent has been injected. Its association with gadolinium and not the carrier molecule is confirmed by its occurrence with various contrast materials in which gadolinium is carried by very different carrier molecules. Due to this, it is not recommended to use these agents for any individual with end-stage renal failure as they will require emergent dialysis. Similar but not identical symptoms to NSF may occur in subjects with normal or near normal renal function within hours to 2 months following the administration of GBCAs; the name "gadolinium deposition disease" (GDD) has been proposed for this condition, which occurs in the absence of pre-existent disease or subsequently developed disease of an alternate known process. A 2016 study reported numerous anecdotal cases of GDD. However, in that study, participants were recruited from online support groups for subjects self-identified as having gadolinium toxicity, and no relevant medical history or data were collected. There have yet to be definitive scientific studies proving the existence of the condition. In addition, gadolinium deposition in neural tissues has solely been demonstrated in patients with inflammatory, infective, or malignant disease, and no healthy volunteer studies have assessed the potential of gadolinium deposition within the brain, skin, or bones.
Included in the current guidelines from the Canadian Association of Radiologists are that dialysis patients should only receive gadolinium agents where essential and that they should receive dialysis after the exam. If a contrast-enhanced MRI must be performed on a dialysis patient, it is recommended that certain high-risk contrast agents be avoided but not that a lower dose be considered. The American College of Radiology recommends that contrast-enhanced MRI examinations be performed as closely before dialysis as possible as a precautionary measure, although this has not been proven to reduce the likelihood of developing NSF. The FDA recommends that potential for gadolinium retention be considered when choosing the type of GBCA used in patients requiring multiple lifetime doses, pregnant women, children, and patients with inflammatory conditions.
An arthrogram is a series of images of a joint after injection of a contrast medium, usually done by fluoroscopy or MRI. The injection is normally done under a local anesthetic.The radiologist or radiographer performs the study using fluoroscopy or ultrasound to guide the placement of the needle into the joint and then injects an appropriate amount of contrast.Gadobenic acid
Gadobenic acid (INN, trade name MultiHance) is a complex of gadolinium with the ligand BOPTA. In the form of the methylglucamine salt meglumine gadobenate (INNm) or gadobenate dimeglumine (USAN), it is used as a gadolinium-based MRI contrast medium.BOPTA is a derivative of DTPA in which one terminal carboxyl group, –C(O)OH is replaced by -C–O–CH2C6H5. Thus gadobenic acid is closely related to gadopentetic acid. BOPTA itself was first synthesized in 1995.
In the "gadobenate" ion gadolinium ion is 9-coordinate with BOPTA acting as an 8-coordinating ligand. The ninth position is occupied by a water molecule, which exchanges rapidly with water molecules in the immediate vicinity of the strongly paramagnetic complex, providing a mechanism for MRI contrast enhancement. 139La NMR studies on the diamagnetic La-BOPTA2− complex suggest that the Gd complex maintains in solution the same kind of coordination as found, by X-ray crystallography, in the solid state for Gd-BOPTA disodium salt.Gadodiamide
Gadodiamide is a gadolinium-based MRI contrast agent, used in MR imaging procedures to assist in the visualization of blood vessels. It is commonly marketed under the trade name Omniscan.Gadofosveset
Gadofosveset (trade names Vasovist, Ablavar) is a gadolinium-based MRI contrast agent. It was used as the trisodium salt monohydrate form. It acts as a blood pool agent by binding to human serum albumin. The manufacturer (Lantheus Medical) discontinued production in 2017 due to poor sales.Gadolinium(III) bromide
Gadolinium(III) bromide is a crystalline compound of gadolinium atoms and three bromine atoms. Gadolinium bromide is hygroscopic.Gadolinium(III) chloride
Gadolinium(III) chloride, also known as gadolinium trichloride, is GdCl3. It is a colorless, hygroscopic, water-soluble solid. The hexahydrate GdCl3∙6H2O is commonly encountered and is sometimes also called gadolinium trichloride. Gd3+ species are of special interest because the ion has the maximum number of unpaired spins possible, at least for known elements. With seven valence electrons and seven available f-orbitals, all seven electrons are unpaired and symmetrically arranged around the metal. The high magnetism and high symmetry combine to make Gd3+ a useful component in NMR spectroscopy and MRI.Gadolinium(III) nitrate
Gadolinium(III) nitrate is an inorganic compound of gadolinium. It is used as a water-soluble neutron poison in nuclear reactors. Gadolinium nitrate, like all nitrates, is an oxidizing agent.Gadolinium(III) oxide
Gadolinium(III) oxide (archaically gadolinia) is an inorganic compound with the formula Gd2O3. It is one of the most commonly available forms of the rare-earth element gadolinium, derivatives of which are potential contrast agents for magnetic resonance imaging.Gadolinium gallium garnet
Gadolinium Gallium Garnet (GGG, Gd3Ga5O12) is a synthetic crystalline material of the garnet group, with good mechanical, thermal, and optical properties. It is typically colorless. It has a cubic lattice, a density of 7.08 g/cm3 and its Mohs hardness is variously noted as 6.5 and 7.5. Its crystals are produced with the Czochralski method. During production, various dopants can be added for colour modification. The material is also used in fabrication of various optical components and as a substrate material for magneto–optical films (magnetic bubble memory). It also finds use in jewelry as a diamond simulant. GGG can also be used as a seed substrate for the growth of other garnets such as YIG.Gadopentetic acid
Gadopentetic acid is one of the trade names for a gadolinium-based MRI contrast agent, usually administered as a salt of a complex of gadolinium with DTPA (diethylenetriaminepentacetate) with the chemical formula A2[Gd(DTPA)(H2O)]; when cation A is the protonated form of the amino sugar meglumine the salt goes under the name "gadopentetate dimeglumine". It was described in 1981 by Hanns-Joachim Weinmann and colleagues and introduced as the first MRI contrast agent in 1987 by the Schering AG. It is used to assist imaging of blood vessels and of inflamed or diseased tissue where the blood vessels become "leaky". It is often used when viewing intracranial lesions with abnormal vascularity or abnormalities in the blood–brain barrier. It is usually injected intravenously. Gd-DTPA is classed as an acyclic, ionic gadolinium contrast medium. Its paramagnetic property reduces the T1 relaxation time (and to some extent the T2 and T2* relaxation times) in NMR, which is the source of its clinical utility.
Marketed as Magnevist by Bayer AG, it was the first intravenous contrast agent to become available for clinical use, and is in widespread use around the world. Similar contrast agents are Magnetol manufactured by Isorad, Dotarem (gadoterate) manufactured by Guerbet, MultiHance (gadobenate dimeglumine) and ProHance (gadoteridol) manufactured by Bracco, Omniscan (gadodiamide) manufactured by GE Healthcare, and OptiMARK (gadoversetamide) manufactured by Mallinckrodt.
Gadolinium based agents may cause a toxic reaction known as nephrogenic systemic fibrosis (NSF) in patients with severe kidney problems.Compared to other gadolinium-based MRI contrast agents, Gadopentetate dimeglumine (Gd-DTPA2-) chelates allow delayed Gadolinium-enhanced Magnetic Resonance of Cartilage (dGEMRIC). The unique charge characteristic of this complex allows researchers to inversely measure spin-lattice relaxation times as they are related to the concentration of proteoglycan aggregates and charged glycosaminoglycan side chains in articular cartilage.Gadoteric acid
Gadoteric acid (gadoterate meglumine, trade names Artirem, Dotarem and Clariscan) is a macrocycle-structured gadolinium-based MRI contrast agent (GBCA). It consists of the organic acid DOTA as a chelating agent, and gadolinium (Gd3+), and is used in form of the meglumine salt (Gadoterate meglumine). The paramagnetic property of gadoteric acid reduces the T1 relaxation time (and to some extent the T2 and T2* relaxation times) in MRI, which is the source of its clinical utility. Because it has magnetic properties, gadoteric acid develops a magnetic moment when put under a magnetic field, which increases the signal intensity (brightness) of tissues during MRI imaging.Gadoteridol
Gadoteridol (INN) is a gadolinium-based MRI contrast agent, used particularly in the imaging of the central nervous system. It is sold under the brand name ProHance.Gadoversetamide
Gadoversetamide is a gadolinium-based MRI contrast agent, particularly for imaging of the brain, spine and liver. It is marketed under the trade name OptiMARK.Gadoxetic acid
Gadoxetic acid is a gadolinium-based MRI contrast agent. Its salt, gadoxetate disodium, is marketed as Primovist in Europe and Eovist in the United States by Bayer HealthCare Pharmaceuticals.Isotopes of gadolinium
Naturally occurring gadolinium (64Gd) is composed of 6 stable isotopes, 154Gd, 155Gd, 156Gd, 157Gd, 158Gd and 160Gd, and 1 radioisotope, 152Gd, with 158Gd being the most abundant (24.84% natural abundance). The predicted double beta decay of 160Gd has never been observed; only lower limit on its half-life of more than 1.3×1021 years has been set experimentally.Thirty radioisotopes have been characterized, with the most stable being alpha-decaying 152Gd (naturally occurring) with a half-life of 1.08×1014 years, and 150Gd with a half-life of 1.79×106 years. All of the remaining radioactive isotopes have half-lives less than 74.7 years. The majority of these have half-lives less than 24.6 seconds. Gadolinium isotopes have 10 metastable isomers, with the most stable being 143mGd (t1/2=110 seconds), 145mGd (t1/2=85 seconds) and 141mGd (t1/2=24.5 seconds).
The primary decay mode at atomic weights lower than the most abundant stable isotope, 158Gd, is electron capture, and the primary mode at higher atomic weights is beta decay. The primary decay products for isotopes of weights lower than 158Gd are the element Eu (europium) isotopes and the primary products at higher weights are the element Tb (terbium) isotopes.
Gadolinium-153 has a half-life of 240.4±10 days and emits gamma radiation with strong peaks at 41 keV and 102 keV. It is used as a gamma ray source for X-ray absorptiometry and fluorescence, for bone density gauges for osteoporosis screening, and for radiometric profiling in the Lixiscope portable x-ray imaging system, also known as the Lixi Profiler. In nuclear medicine, it serves to calibrate the equipment needed like single-photon emission computed tomography systems (SPECT) to make x-rays. It ensures that the machines work correctly to produce images of radioisotope distribution inside the patient. This isotope is produced in a nuclear reactor from europium or enriched gadolinium. It can also detect the loss of calcium in the hip and back bones, allowing the ability to diagnose osteoporosis.Gadolinium-148 would be ideal for radioisotope thermoelectric generators due to its 74-year half life, high density, and dominant alpha decay mode. However, Gadolinium-148 cannot be economically synthesized in sufficient quantities to power a RTG.MRI contrast agent
MRI contrast agents are contrast agents used to improve the visibility of internal body structures in magnetic resonance imaging (MRI). The most commonly used compounds for contrast enhancement are gadolinium-based. Such MRI contrast agents shorten the relaxation times of nuclei within body tissues following oral or intravenous administration. In MRI scanners, sections of the body are exposed to a very strong magnetic field causing primarily the hydrogen nuclei ("spins") of water in tissues to be polarized in the direction of the magnetic field. An intense radiofrequency pulse is applied that tips the magnetization generated by the hydrogen nuclei in the direction of the receiver coil where the spin polarization can be detected. Random molecular rotational oscillations matching the resonance frequency of the nuclear spins provide the "relaxation" mechanisms that bring the net magnetization back to its equilibrium position in alignment with the applied magnetic field. The magnitude of the spin polarization detected by the receiver is used to form the MR image but decays with a characteristic time constant known as the T1 relaxation time. Water protons in different tissues have different T1 values, which is one of the main sources of contrast in MR images. A contrast agent usually shortens, but in some instances increases, the value of T1 of nearby water protons thereby altering the contrast in the image.Neutron capture therapy of cancer
Neutron capture therapy (NCT) is a noninvasive therapeutic modality for treating locally invasive malignant tumors such as primary brain tumors and recurrent head and neck cancer. Briefly summarized, it is a two-step procedure: first, the patient is injected with a tumor-localizing drug containing the non-radioactive isotope boron-10 (10B) that has a high propensity or cross section (σ) to capture slow neutrons. The cross section of the 10B is many times greater than that of the other elements present in tissues such as hydrogen, oxygen, and nitrogen. In the second step, the patient is radiated with epithermal neutrons, the source of which is either a nuclear reactor or, more recently, an accelerator. After losing energy as they penetrate tissue, the neutrons are absorbed by the capture agent, which subsequently emits high-energy charged particles that can selectively kill tumor cells that have taken up sufficient quantities of 10B.
All of the clinical experience to date with NCT is with the non-radioactive isotope boron-10, and this is known as boron neutron capture therapy (BNCT). At this time, the use of other non-radioactive isotopes, such as gadolinium, has been limited, and to date, it has not been used clinically. BNCT has been evaluated clinically as an alternative to conventional radiation therapy for the treatment of malignant brain tumors (gliomas), and recurrent, locally advanced head and neck cancer and cutaneous and extracutaneous melanomas.Perfusion MRI
Perfusion MRI or perfusion-weighted imaging (PWI) is perfusion scanning by the use of a particular MRI sequence. The acquired data are then postprocessed to obtain perfusion maps with different parameters, such as BV (blood volume), BF (blood flow), MTT (mean transit time) and TTP (time to peak).Ribonucleotide reductase inhibitor
Ribonucleotide reductase inhibitors are a family of anti-cancer drugs that interfere with the growth of tumor cells by blocking the formation of deoxyribonucleotides (building blocks of DNA).
fludarabine, cladribine, gemcitabine, tezacitabine, and triapine
gallium maltolate, gallium nitrate