ARRT CT key terms

The process of explaining a procedure's purpose, risks, benefits, and alternatives to a patient, confirming understanding, and obtaining voluntary permission before the examination begins. It is documented before contrast is given or an invasive step is performed.

Leakage of iodinated contrast out of a vein into surrounding soft tissue during a power injection. It causes pain and swelling and requires stopping the injection, removing the cannula, and documenting and monitoring the site.

A rise in serum creatinine occurring within a few days after iodinated contrast administration, reflecting a temporary decline in kidney function. Risk is higher in patients with existing renal impairment, diabetes, or dehydration.

A calculated estimate of how well the kidneys filter blood, derived from serum creatinine plus age and sex. It is used to screen patients before iodinated contrast and to guide hydration or alternative-imaging decisions.

A corticosteroid regimen, sometimes combined with an antihistamine, given hours before contrast to reduce the severity of allergic-type reactions in patients with a prior reaction. It lowers but does not eliminate risk.

A sudden immune-like reaction to contrast that can include hives, bronchospasm, hypotension, and airway swelling. It is managed promptly with epinephrine, oxygen, intravenous fluids, and antihistamines following department protocol.

As Low As Reasonably Achievable: the practice of keeping radiation dose to patients and staff as low as practical while still producing diagnostic images, using technique selection, shielding, and protocol optimization.

A required inquiry about pregnancy or the possibility of pregnancy before scanning the abdomen or pelvis. If pregnancy is possible, the radiologist is consulted to confirm the examination is justified or to adjust the protocol.

Rules for selecting a vein and cannula able to withstand rapid contrast injection, typically a large forearm vein with an adequately sized catheter, checked for patency and blood return before connection.

Methods such as swaddling, positioning aids, or parental presence used to keep a child still during CT, reducing motion artifact and the need for repeat scanning or sedation.

A technique in which repeated low-dose images monitor contrast arrival in a target vessel; the scan starts automatically once a preset enhancement threshold is reached, timing the acquisition to peak contrast.

A small contrast injection followed by rapid low-dose imaging at a fixed level to measure how long contrast takes to reach the vessel of interest, so the main scan can be timed accordingly.

An examination that images the same anatomy at several time points after contrast injection, such as unenhanced, arterial, portal venous, and delayed phases, to characterize vessels and lesions.

A contrast-enhanced study timed to opacify arteries, using thin slices and fast helical acquisition, then post-processed with reformats or projections to display vessels clearly.

A multiphase study of the urinary tract combining unenhanced, nephrographic, and excretory phases, often with thin-slice reformats, to evaluate stones, masses, and collecting-system anatomy.

A lung protocol using thin collimation, a high-spatial-frequency reconstruction kernel, and often reduced dose to show fine parenchymal detail such as interlobular septa and honeycombing.

Two-dimensional images reconstructed from a volumetric dataset in planes other than the original acquisition plane, such as coronal, sagittal, or oblique, without additional patient dose.

A post-processing method that displays only the brightest voxel along each viewing ray, making contrast-filled vessels and bone stand out across a slab or volume.

A three-dimensional display technique that assigns color and opacity to voxel values, producing a rotatable image that shows surface and internal anatomy together.

Using CT images to plan and confirm needle placement for tissue sampling, often with limited or intermittent CT fluoroscopic exposure to keep staff and patient dose low.

A low-dose study of the cleansed, gas-distended colon, with images reviewed in two and three dimensions to detect polyps and masses; preparation and insufflation quality strongly affect accuracy.

Cardiac imaging in which the ECG signal is used to acquire or reconstruct data during a consistent phase of the cardiac cycle, reducing motion blur caused by heartbeats.

A non-contrast, low-dose CT of the heart that quantifies calcified plaque in the coronary arteries; the score is calculated from calcification area and density to estimate cardiovascular risk.

A voxel with equal dimensions along all three axes, so reformats in any plane keep the same spatial resolution; thin-slice helical acquisition is used to create them.

A scaled CT number expressing tissue attenuation relative to water, where water is 0 and air is about -1000. It lets observers compare tissue density across scanners and examinations.

A measure of how much a beam's intensity is reduced per unit thickness of material. In CT it depends on photon energy and tissue composition and underlies the reconstructed CT number.

A photon is completely absorbed by an inner-shell electron, which is ejected. It dominates at lower energies and in higher-atomic-number materials such as bone and iodine, producing strong contrast.

A photon interacts with an outer-shell electron, transfers part of its energy, and is deflected. It dominates at higher energies and in soft tissue, adding scatter and noise rather than contrast.

For helical scanning, table travel per gantry rotation divided by the total collimated beam width. Higher pitch shortens scan time and dose but can raise noise and artifacts if set too high.

The scanner adjusts tube current along the scan or around the patient based on measured attenuation, maintaining image quality while lowering dose in thinner or less dense regions.

An image reconstruction approach that repeatedly compares calculated projections with measured data to reduce noise, allowing lower dose while preserving diagnostic image quality.

Volume computed tomography dose index: the average absorbed dose to a standard phantom from one rotation divided by pitch, reported in milligray and used to compare protocol dose.

The product of CTDIvol and scan length in centimeters, expressed in mGy·cm; it estimates the total radiation output for a scan series and is used to derive effective dose.

A CTDIvol-based value corrected for patient or body-part thickness, giving a closer approximation of dose for an individual than the fixed phantom index alone.

Dark streaks or bands caused when lower-energy photons are absorbed preferentially as the beam passes through dense material, so the beam hardens and reconstruction assumes nonuniform attenuation.

A voxel containing a mixture of tissues receives a CT number reflecting the average, so small objects or edges may appear falsely low or high in density.

A shaped pre-patient filter that is thin at the center and thick at the edges, reducing dose to peripheral tissue and shaping the beam to the patient's cross-section.

Extra rotations at the start and end of a helical scan needed to reconstruct the first and last images, adding dose beyond the imaged volume; it grows with wider collimation and higher pitch.