Nuclear Medicine
Nuclear Medicine

Nuclear medicine is a way to gather medical information that would otherwise be unavailable, requires surgery, or necessitates more expensive diagnostic tests.

Nuclear medicine is a branch of medicine and medical imaging that uses the nuclear properties of matter in diagnosis and therapy. More specifically, nuclear medicine is a part of molecular imaging because it produces images that reflect biological processes that take place at the cellular and sub cellular level.

Nuclear medicine imaging is an excellent diagnostic tool because it shows not only the anatomy (structure) of an organ or body part, but the function of the organ as well. This additional "functional information" allows nuclear medicine to diagnose certain diseases and various medical conditions much sooner than other medical imaging examinations, which provide mainly anatomic (structural) information about an organ or body part. Nuclear medicine can be valuable in the early diagnosis, treatment and prevention of numerous medical conditions and continues to grow as a powerful medical tool.

This is possible because the radio nuclides (low-level radioactive chemicals used in nuclear medicine studies) are absorbed by or taken up at varying rates (or in different concentrations) by different tissue types. For instance, the thyroid gland takes up more radioactive iodine than other parts of the body. The amount of radiation that is taken up and then emitted by a specific body part is linked to the metabolic activity (cellular function) of the organ or tissue. For example, cells which are dividing rapidly (like cancer tissue cells) may be seen as "hot spots" of metabolic activity on a nuclear medicine image, since they absorb more of the radio nuclide.

While nuclear medicine images may show less detail (spatial resolution) than other types of imaging, the functional information they provide can be valuable (and in some cases, may not available from other types of imaging). A diseased or poorly functioning tissue will emit a different signal than healthy tissue, thus giving the physician an indication of how the tissue or organ is functioning. For example, infection of bone results in increased cellular activity of bone tissue, causing radionuclides to be taken up in greater amounts by diseased bone. Thus the functional image of the bone may show the disease sooner than the anatomic image provided by an x-ray or CT scan.

During most nuclear medicine examinations, you will lie down on a scanning table. Consequently, the only piece of equipment you may notice is the specialized nuclear imaging camera used during the procedure. It is enclosed in metallic housing designed to facilitate imaging of specific parts of the body. It can look like a large round metallic apparatus suspended from a tall, moveable post or a sleek one-piece metal arm that hangs over the examination table. The camera can also be located within a large, doughnut-shaped structure. Sometimes, the camera is beneath the table out of view.

A nearby computer console, possibly in another room, processes the data from the procedure.

Nuclear Medicine History

During 1930,Nuclear Medicine came under prominence. Artificially produced radioisotopes were immediately used for therapeutic and laboratory procedures. Radiation monitoring equipment were developed which allowed the distribution of the radioisotope to be determined, either in-vivo or in-vitro. These devices output the results as a count-rate over the organ or sample. With the improvement in technology these devices became more sophisticated.

Rectilinear Scanner’s output was usually recorded on white paper with a series of black marks being printed by a mechanical printer - similar to the conventional dot matrix printer. An alternative was the use of a colour ribbon or light sensitive film. In all cases, the intensity of exposure or depth of colour corresponded to the concentration of radioisotope in the incident area. The first gamma camera was produced in 1950 and which did not rely on continuous motion. This became the predecessor of the present day gamma cameras where the input is stored on the hard disk of a computer and the output can be manipulated and recorded on a variety of media. Single and multi-headed cameras are now commonplace in most Nuclear Medicine Departments.

How Nuclear Medicine Works

You’ve seen patients undergoing radiation therapy for cancer, and doctors ordering PET scans to diagnose patients. These are part of the medical specialty called nuclear medicine. Nuclear medicine uses radioactive substances to image the body and treat disease. It looks at the physiology and the anatomy of the body in establishing diagnosis and treatment.

Here are some of the techniques and terms used in nuclear medicine. You'll learn how radiation helps doctors see deeper inside the human body than they ever could.

Imaging in Nuclear Medicine

Human body is opaque, and looking inside is painful. In the past, exploratory surgery was one common way to look inside the body, but today doctors can use a huge array of non-invasive techniques. Some of these techniques include things like X-rays, MRI scanners, CAT scans, ultrasound and so on. These techniques have many advantages and disadvantages that make them useful.

Nuclear medicine imaging techniques

These techniques give doctors another way to look inside the human body. The techniques combine the use of computers, detectors, and radioactive substances. These techniques include:

  • Bone scanning

  • Positron emission tomography (PET)

  • Single photon emission computed tomography (SPECT)

  • Cardiovascular imaging

All of these techniques use different properties of radioactive elements to create an image.

Nuclear medicine imaging is useful for detecting:

  • Irregular or inadequate blood flow to various tissues

  • Tumors

  • Aneurysms (weak spots in blood vessel walls)

  • Blood cell disorders and inadequate functioning of organs, such as thyroid and pulmonary function deficiencies.

The use of any specific test, or combination of tests, depends upon the patient's symptoms and the disease being diagnosed.

Common Uses of Nuclear Medicine

Nuclear medicine images can assist the physician in diagnosing diseases. Tumors, infection and other disorders can be detected by evaluating organ function. Specifically, nuclear medicine can be used to:

  • Analyze kidney function

  • Image blood flow and function of the heart

  • Scan lungs for respiratory and blood-flow problems

  • Identify blockage of the gallbladder

  • Evaluate bones for fracture, infection, arthritis or tumor

  • Determine the presence or spread of cancer

  • Identify bleeding into the bowel

  • Locate the presence of infection

  • Measure thyroid function to detect an overactive or under active thyroid

Therapeutic Uses of Nuclear Medicine

Although nuclear medicine is commonly used for diagnostic purposes, it is also used to provide valuable therapeutic applications. Among these therapeutic uses are: treatment of hyperthyroidism treatment of thyroid cancer, treatment of blood imbalances pain relief from certain types of bone cancers.

Studies into Nuclear Medicine

A typical nuclear medicine study involves administration of a radionuclide into the body by intravenous injection in liquid or aggregate form, ingestion while combined with food, inhalation as a gas or aerosol, or rarely, injection of a radionuclide that has undergone micro-encapsulation. Some studies require the labeling of a patient's own blood cells with a radio nuclide (leukocyte scintigraphy and red blood cell scintigraphy). Most diagnostic radionuclides emit gamma rays, while the cell-damaging properties of beta particles are used in therapeutic applications. Refined radio nuclides for use in nuclear medicine are derived from fission or fusion processes in nuclear reactors, which produce radioisotopes with longer half-lives, or cyclotrons, which produce radioisotopes with shorter half-lives, or take advantage of natural decay processes in dedicated generators, i.e. Molybdenum/Technetium or Strontium/Rubidium.

The most commonly used intravenous radionuclides are:

Technetium

The lightest chemical element with no stable isotope. It has atomic number 43 and is given the symbol Tc. The chemical properties of this silvery grey, crystalline transition metal are intermediate between rhenium and manganese. Its short-lived gamma-emitting nuclear isomer 99mTc (technetium-99m) is used in nuclear medicine for a wide variety of diagnostic tests. 99Tc is used as a gamma ray-free source of beta particles.

Iodine-123 and 131

Chemically, iodine is the least reactive of the halogens, and the most electropositive halogen after astatine. Iodine is primarily used in medicine, photography and dyes. It is required in trace amounts by most living organisms.

Iodine is an essential trace element; its only known roles in biology are as constituents of the thyroid hormones, thyroxine (T4) and triiodothyronine (T3). These are made from addition condensation products of the amino acid tyrosine, and are stored prior to release in a protein-like molecule called thryroglobulin. T4 and T3 contain four and three atoms of iodine per molecule, respectively. The thyroid gland actively absorbs iodide from the blood to make and release these hormones into the blood, actions that are regulated by a second hormone TSH from the pituitary. Thyroid hormones are phylogenetically very old molecules which are synthesized by most multicellular organisms, and which even have some effect on unicellular organisms.

Thyroid hormones play a very basic role in biology, acting on gene transcription to regulate the basal metabolic rate. The total deficiency of thyroid hormones can reduce basal metabolic rate up to 50%, while in excessive production of thyroid hormones the basal metabolic rate can be increased by 100%. T4 acts largely as a precursor to T3, which is (with some minor exceptions) the biologically active hormone.

Thallium-201

This soft gray malleable poor metal resembles tin but discolors when exposed to air. Thallium is highly toxic and is used in rat poisons and insecticides but since it might also cause cancer, this use has been cut back or eliminated in many countries. It has even been used in some murders, earning the nicknames "The Poisoner's Poison" and "Inheritance powder" (alongside arsenic).

In nuclear medicine, it is used for diagnostic purposes in nuclear medicine, particularly in stress tests used for risk stratification in patients with coronary artery disease. This isotope of thallium can be generated using a transportable generator, which is similar to the technetium cow. The generator contains lead-201 (half life 9.33 hours), which decays by electron capture to the thallium-201. The lead-201 can be produced in a cyclotron by the bombardment of thallium with protons or deuterons by the (p, 3n) and (d, 4n) reactions.

Gallium-67

A soft silvery metallic poor metal, gallium is a brittle solid at low temperatures but liquefies slightly above room temperature and will melt in the hand. Elemental gallium is not found in nature, but it is easily obtained by smelting. Very pure gallium metal has a brilliant silvery color and its solid metal fractures conchoidally like glass.

The semiconductor applications are the main reason for the low-cost commercial availability of the extremely high-purity (99.9999+%) metal. However, it is also widely used in medical applications such as:

A low temperature liquid eutectic alloy of gallium, indium, and tin, is widely available in medical thermometers (fever thermometers), replacing problematic mercury. This alloy, with the trade name Galinstan (with the "-stan" referring to the tin), has a freezing point of −20°C.

  • Gallium salts such as gallium citrate and gallium nitrate are used as radiopharmaceutical agents in nuclear medicine imaging. (The form or salt is not important, since it is the free dissolved gallium ion Ga3+ that is active). For these applications, a radioactive isotope such as 67Ga is used. The body handles Ga3+ in many ways as though it were iron, and thus it is bound (and concentrates) in areas of inflammation, such as infection, and also areas of rapid cell division. This allows such sites to be imaged by nuclear scan techniques. This use has largely been replaced by fluorodeoxyglucose (FDG) for positron emission tomography, "PET" scans.

  • Gallium nitrate, both oral and topical, is finding use in treating arthritis.

  • Much research is being devoted to gallium alloys as substitutes for mercury dental amalgams, but these compounds have yet to see wide acceptance.

  • Research is being conducted to determine whether gallium can be used to fight bacterial infections in people with cystic fibrosis. Gallium is similar in size to iron, an essential nutrient for respiration. When bacteria such as Pseudomonas mistakenly pick up gallium, the bacteria's ability to respire is interfered with and the bacteria die. The mechanism behind this is that iron is redox active, which allows for the transfer of electrons during respiration, but gallium is redox inactive.

Fluorine-18 Fluorodeoxyglucose

Atomic fluorine is univalent and is the most chemically reactive and electronegative of all the elements. In its elementally isolated (pure) form, fluorine is a poisonous, pale, yellowish brown gas, with chemical formula F2. Like other halogens, molecular fluorine is highly dangerous; it causes severe chemical burns on contact with skin.

Flouring -18 is a radioactive isotope that emits positrons, is often used in positron emission tomography, because its half-life of 110 minutes is long by the standards of positron-emitters.

Indium-111 Labeled Leukocytes

This rare, soft, malleable and easily fusible poor metal is chemically similar to aluminum or gallium but more closely resembles zinc. Its current primary application is to form transparent electrodes from indium tin oxide in liquid crystal displays.

Indium-111 is used in medical imaging to monitor the activity of white blood cells. A blood test is taken from the patient, white cells removed and labelled with the radioactive Indium-111, then re-injected back into the patient. Gamma imaging will reveal any areas of high white cell activity such as an abscess.

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