“Annual” means a period of 12 consecutive months, not to exceed a period of 14 months.
“Computed tomography (CT)” means the production of a tomogram by the acquisition and computer processing of X-ray transmission data. Computed tomography includes the capability of producing axial tomograms.
“Computed Tomography Dose Index” means the integral from -7T to +7T of the dose profile along a line perpendicular to the tomographic plane divided by the product of the nominal tomographic section thickness and the number of tomograms produced in a single scan. This definition assumes that the dose profile is centered around z = 0 and that, for a multiple tomogram system, the scan increment between adjacent scans is nT.
“Contrast scale” or “CS” means the change in the linear attenuation coefficient per CTN relative to water.
“CT conditions of operation” means all selectable parameters governing the operation of a CT X-ray system including, but not limited to, nominal tomographic section thickness, filtration, and the technique factors as defined in OAR 333-106-0005 (Definitions).
“CT gantry” means the tube housing assemblies, beam-limiting devices, detectors, and the supporting structures and frames which hold these components.
“CT number” means the number used to represent the X-ray attenuation associated with each elemental area of the CT image.
“CT scanner” means a CT machine capable of performing CT scans of the head, other body parts, or full body patient procedures including PET/CT and SPECT/CT hybrid scanners if used for diagnostic CT procedures.
“CTDIvol” (see computed tomography dose index).
CTN (see CT number).
“Dose-length product (DLP)” is the CTDIvol multiplied by the scan length (image thickness multiplied by the number of adjacent, non-overlapped images in the acquisition in centimeters.
“Dose profile” means the dose as a function of position along a line.
“Elemental area” means the smallest area within a tomogram for which the X-ray attenuation properties of a body are depicted (see also picture element.)
“Multiple tomogram system” means a computed tomography X-ray system which obtains X-ray transmission data simultaneously during a single scan to produce more than one tomogram.
“Noise” means the standard deviation of the fluctuations in CTN expressed as a percentage of the attenuation coefficient of water.
“Nominal tomographic section thickness” means the full width at half-maximum of the sensitivity profile taken at the center of the cross-sectional volume over which X-ray transmission data are collected.
“Picture element” means an elemental area of a tomogram.
“Positron emission tomography (PET)” means an imaging technique that uses positron-emitting radionuclides to produce 3-dimensional images of functional processes in the body.
“Reference plane” means a plane which is displaced from and parallel to the tomographic plane.
“Scan” means the complete process of collecting X-ray transmission data for the production of a tomogram. Data can be collected simultaneously during a single scan for the production of one or more tomograms.
“Scan increment” means the amount of relative displacement of the patient with respect to the CT X-ray system between successive scans measured along the direction of such displacement.
“Scan sequence” means a preselected set of two or more scans performed consecutively under preselected CT conditions of operation.
“Scan time” means the period of time between the beginning and end of X-ray transmission data accumulation for a single scan.
“Single photon emission computed tomography (SPECT)” means an imaging technique that uses radionuclides to produce 3-dimensional images of functional processes in the body.
“Single Tomogram System” means a CT X-ray system which obtains X-ray transmission data during a scan to produce a single tomogram.
“Tomogram” means the depiction of the attenuation properties of a section through a body.
“Tomographic plane” means that geometric plane which is identified as corresponding to the output tomogram.
“Tomographic section” means the volume of an object whose X-ray attenuation properties are imaged in a tomogram.
“Traceable to a national standard” means an instrument is calibrated at either the National Institute of Standards and Technology (NIST) or at a calibration laboratory that participates in a proficiency program with the NIST at least once every two years and the results of the proficiency test conducted within 24 months of calibration show agreement within plus or minus three percent of the national standard in the appropriate energy range.