Table 1.
Lexicon of terms relevant to radionuclide studies of brain perfusion
| Term | Explanation |
|---|---|
| Absorbed dose | The amount of energy deposited by ionizing radiation in materials through which they pass, measured in units of rad (radiation-absorbed dose) or gray. |
| Activity | When used in the context of radionuclides, a measure of amount of a radioactive substance based on its rate of decay, as in millicurie or megabecquerel. |
| Anger camera | A specific design of gamma camera, eponymously named for the inventor Hal Anger. |
| Angiographic | A series of dynamic images designed to portray flow within vessels. |
| Blood pool | Distribution of activity within the vascular system following initial mixing and dilution of RP within the intravascular volume. |
| Blush | Nonspecific visualization of activity within a tissue on flow or blood pool imaging. |
| Bolus | As in "RP bolus." A concentration of material that when administered will introduce a relatively brief perturbation of the system. |
| Cine-loop | A method of displaying dynamic images as a short repeating image loop ("movie"). |
| Diffusible | See lipophilic. |
| Dosage | An amount of a medicine or RP. Radioactive substances administered to patients are measured in units of millicurie or megabecquerel. |
| Dose | Short for “absorbed dose.” See “absorbed dose.” |
| Dynamic | As in "dynamic imaging." Acquisition of a number of images at fixed time intervals to portray the change in distribution of an RP over time. |
| Flow phase | In brain imaging, referring to a dynamic series of images with a 1- or 2-second time base portraying the intravascular flow of blood. |
| Gamma (emission) | Referring to the emission of gamma particles, photons of energy that originate in the nuclei of radioactive atoms upon their radioactive decay. |
| Gamma-camera | A generic term for imaging devices used to spatially map the distribution of gamma-emitting radionuclides. |
| Lipophilic | Category of RPs that can freely diffuse across cell membranes such as the blood brain barrier. |
| Lipophobic | Category of RPs that cannot freely diffuse across cell membranes in the blood brain barrier, also known as "nonlipophilic." |
| Megabecquerel (MBq) | Système International measurement of radioactive material related to the number of disintegrations per second. One becquerel (Bq) represents a rate of radioactive decay equal to 1 disintegration per second. |
| Millicurie (mCi) | A common measurement of radioactive material which predates adoption of the becquerel. One curie is equal to 37 billion (3.7 × 1010) disintegrations per second. |
| Nondiffusible | See lipophobic. |
| Nonlipophilic | See lipophobic. |
| Nuclear medicine | The discipline of medicine involved in use of unsealed sources of radioactivity to diagnose and treat disease. |
| Parenchymal phase | Referring to the delayed phase of brain imaging with lipophilic RPs following diffusion of the RP into cells and trapping within the cytoplasm. |
| Particulate emission | Emission of alpha, beta, or neutron particles in the course of radioactive decay. |
| Perfuse | To force blood or other fluid (1) to flow from the artery through the vascular bed of a tissue or (2) to flow through the lumen of a hollow structure. |
| Planar | As in "planar imaging." Referring to a 2-dimensional projection of activity from the subject being imaged onto an external detector. |
| Projection (as in "anterior projection") | Angular positioning of the radiation detector with respect to the subject being imaged. |
| Radioactivity | The release of energy by unstable nuclei. |
| Radionuclide | A radioactive nuclide. |
| Radionuclide angiography | Series of dynamic scintigraphic images designed to portray flow within vessels. |
| Radiopharmaceutical (RP) | A radioactive compound administered for diagnostic or therapeutic purposes. |
| Radiotracer | Colloquial term for RP. See RP. |
| Scalp tourniquet | Application of a tight band around the supraorbital skull to minimize scalp flow. |
| Scintigraphy | The method of producing images based on the spatial distribution of radioactive materials. |
| SPECT | Acronym for “Single Photon Emission Computer Tomography,” a method of tomography used in radionuclide imaging. |
| Tomography | A method of generating 3-dimensional images from 2-dimensional planar images. |
| Tracer | Short form of “radiotracer.” See “radiotracer.” |
RP = radiopharmaceutical