Nuclear medicine exploit the way that the body handles substances differently when there is disease or pathology present. And The radionuclide introduced into the body
is often chemically bound to a complex that acts characteristically within the body; this is commonly known as a tracer. In the presence of disease, a tracer will often be distributed around the body and/or processed differently. For example, the ligand methylene-diphosphonate (MDP) can be preferentially taken up by bone. By chemically attaching technetium-99m to MDP, radioactivity can be transported and attached to bone via the hydroxyapatite for imaging. And Any increased physiological function, such as due to a fracture in the bone, will usually mean increased concentration of the tracer. This often results in the appearance of a 'hot-spot' which is a focal increase in radio-accumulation, or a general increase in radio-accumulation throughout the physiological system. and Some disease processes result in the exclusion of a tracer, resulting in the appearance of a 'cold-spot'. And Many tracer complexes have been developed in order to image or treat many different organs, glands, and physiological processes. And The types of tests can be split into two broad groups: in-vivo and in-vitro:
Types of studies
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 radionuclide (leukocyte scintigraphy and red blood cell scintigraphy). And Most diagnostic radionuclides emit gamma rays, while the cell-damaging properties of beta particles are used in therapeutic applications. And Refined radionuclides 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-99m (technetium-99m)
* Iodine-123 and 131
* Thallium-201
* Gallium-67
* Fluorine-18 Fluorodeoxyglucose
* Indium-111 Labeled Leukocytes
The most commonly used gaseous/aerosol radionuclides are:
* Xenon-133
* Krypton-81m
* Technetium-99m Technegas
* Technetium-99m DTPA
Analysis
The end result of the nuclear medicine imaging process is a "dataset" comprising one or more images. And In multi-image datasets the array of images may represent a time sequence (ie. cine or movie) often called a "dynamic" dataset, a cardiac gated time sequence, or a spatial sequence where the gamma-camera is moved relative to the patient. SPECT (single photon emission computed tomography) is the process by which images acquired from a rotating gamma-camera are reconstructed to produce an image of a "slice" through the patient at a particular position. And A collection of parallel slices form a slice-stack, a three-dimensional representation of the distribution of radionuclide is in the patient.
And The nuclear medicine computer may require millions of lines of source code to provide quantitative analysis packages for each of the specific imaging techniques available in nuclear medicine.
In Time sequences can be further analysed using kinetic models such as multi-compartment models or a Patlak plot.
Radiation dose
A patient undergoing a nuclear medicine procedure will receive a radiation dose. And Under present international guidelines it is assumed that any radiation dose, however small, presents a risk.and The radiation doses delivered to a patient in a nuclear medicine investigation present a very small risk of inducing cancer. And In this respect it is similar to the risk from X-ray investigations except that the dose is delivered internally rather than from an external source such as an X-ray machine.
The radiation dose from a nuclear medicine investigation is expressed as an effective dose with units of sieverts (usually given in millisieverts, mSv). And The effective dose resulting from an investigation is influenced by the amount of radioactivity administered in megabecquerels (MBq), and the physical properties of the radiopharmaceutical used, its distribution in the body and its rate of clearance from the body.
Effective doses can range from 6 µSv (0.006 mSv) for a 3 MBq chromium-51 EDTA measurement of glomerular filtration rate to 37 mSv for a 150 MBq thallium-201 non-specific tumour imaging procedure. The common bone scan with 600 MBq of technetium-99m-MDP has an effective dose of 3 mSv .
Formerly, units of measurement were the Curie (Ci), being 3.7E10 Bq, and also 1.0 grams of Radium (Ra-226); the Rad (radiation absorbed dose), now replaced by the Gray; and the rem (Röntgen equivalent man), now replaced with the Sievert. and The Rad and Rem are essentially equivalent for almost all nuclear medicine procedures, and only alpha radiation will produce a higher Rem or Sv value, and due to its much higher Relative Biological Effectiveness (RBE). And Alpha emitters are nowadays rarely used in nuclear medicine, but were used extensively before the advent of nuclear reactor and accelerator produced radioisotopes. and The concepts involved in radiation exposure to humans is covered by the field of Health Physics.
Types of studies
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 radionuclide (leukocyte scintigraphy and red blood cell scintigraphy). And Most diagnostic radionuclides emit gamma rays, while the cell-damaging properties of beta particles are used in therapeutic applications. And Refined radionuclides 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-99m (technetium-99m)
* Iodine-123 and 131
* Thallium-201
* Gallium-67
* Fluorine-18 Fluorodeoxyglucose
* Indium-111 Labeled Leukocytes
The most commonly used gaseous/aerosol radionuclides are:
* Xenon-133
* Krypton-81m
* Technetium-99m Technegas
* Technetium-99m DTPA
Analysis
The end result of the nuclear medicine imaging process is a "dataset" comprising one or more images. And In multi-image datasets the array of images may represent a time sequence (ie. cine or movie) often called a "dynamic" dataset, a cardiac gated time sequence, or a spatial sequence where the gamma-camera is moved relative to the patient. SPECT (single photon emission computed tomography) is the process by which images acquired from a rotating gamma-camera are reconstructed to produce an image of a "slice" through the patient at a particular position. And A collection of parallel slices form a slice-stack, a three-dimensional representation of the distribution of radionuclide is in the patient.
And The nuclear medicine computer may require millions of lines of source code to provide quantitative analysis packages for each of the specific imaging techniques available in nuclear medicine.
In Time sequences can be further analysed using kinetic models such as multi-compartment models or a Patlak plot.
Radiation dose
A patient undergoing a nuclear medicine procedure will receive a radiation dose. And Under present international guidelines it is assumed that any radiation dose, however small, presents a risk.and The radiation doses delivered to a patient in a nuclear medicine investigation present a very small risk of inducing cancer. And In this respect it is similar to the risk from X-ray investigations except that the dose is delivered internally rather than from an external source such as an X-ray machine.
The radiation dose from a nuclear medicine investigation is expressed as an effective dose with units of sieverts (usually given in millisieverts, mSv). And The effective dose resulting from an investigation is influenced by the amount of radioactivity administered in megabecquerels (MBq), and the physical properties of the radiopharmaceutical used, its distribution in the body and its rate of clearance from the body.
Effective doses can range from 6 µSv (0.006 mSv) for a 3 MBq chromium-51 EDTA measurement of glomerular filtration rate to 37 mSv for a 150 MBq thallium-201 non-specific tumour imaging procedure. The common bone scan with 600 MBq of technetium-99m-MDP has an effective dose of 3 mSv .
Formerly, units of measurement were the Curie (Ci), being 3.7E10 Bq, and also 1.0 grams of Radium (Ra-226); the Rad (radiation absorbed dose), now replaced by the Gray; and the rem (Röntgen equivalent man), now replaced with the Sievert. and The Rad and Rem are essentially equivalent for almost all nuclear medicine procedures, and only alpha radiation will produce a higher Rem or Sv value, and due to its much higher Relative Biological Effectiveness (RBE). And Alpha emitters are nowadays rarely used in nuclear medicine, but were used extensively before the advent of nuclear reactor and accelerator produced radioisotopes. and The concepts involved in radiation exposure to humans is covered by the field of Health Physics.
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