NMTCB(CT) key terms

As Low As Reasonably Achievable: the principle that radiation dose to patients and staff should be kept to the minimum needed for diagnostic information, while weighing economic, technical, and practical factors.

Volume computed tomography dose index: a standardized measure of radiation dose delivered per unit volume by a given protocol, reported on the scanner console and used to compare protocols and scanners.

Dose-length product: the product of CTDIvol and the scanned length in centimeters. It estimates total radiation output for a complete scan and is used to derive effective dose.

An estimate of whole-body radiation risk in millisieverts, calculated from DLP using body-region conversion factors. It compares examination types but does not predict individual risk.

Size-specific dose estimate: a dose index that adjusts CTDIvol for patient body size using anteroposterior and lateral dimensions, giving more accurate estimates in children and small adults.

Automatic adjustment of tube current along the scan and around the patient based on measured attenuation. It preserves image quality while lowering dose to less dense or thinner regions.

In helical scanning, table travel per gantry rotation divided by beam collimation. Higher pitch scans faster and lowers dose, but increases noise and can add artifacts.

A reconstruction method that repeatedly refines the image to suppress noise, allowing lower tube current or kVp while maintaining diagnostic quality compared with traditional filtered back projection.

A shield placed over superficial radiosensitive tissues such as breast or thyroid. It lowers surface dose but can increase internal scatter and artifacts, so routine use is now limited.

Extra tube rotations at the beginning and end of a helical scan required for data interpolation. The added dose grows with wider collimation and with lower pitch values.

A normalized CT attenuation value on a scale where water is 0 and air is about -1000. It helps identify tissue composition and varies with beam energy and reconstruction.

Display settings mapping a range of CT numbers to gray shades. Width controls contrast and level controls brightness, letting one dataset be viewed as lung, bone, or soft tissue.

The ability to distinguish small, closely spaced objects of high contrast. It depends on detector size, focal spot, slice thickness, field of view, and reconstruction kernel.

The ability to distinguish structures of similar attenuation from background noise. It improves with higher dose, thinner slices, optimized kVp, and noise-reducing reconstruction.

Random variation in pixel values producing a grainy appearance. Noise increases with lower mA, lower kVp, and thinner slices, and decreases with lower pitch and iterative reconstruction.

Streaks, bands, or cupping caused by preferential absorption of low-energy photons as the beam crosses dense material such as bone or metal. Filtration, higher kVp, and correction algorithms reduce it.

Marked noise and streaking that occurs when too few photons reach the detectors, typically through thick regions such as the shoulders or in large patients. Increased mA or kVp helps.

Blurring or streaks from patient motion, breathing, or cardiac movement during acquisition. Faster rotation, shorter scan time, clear breath-hold instructions, and gating reduce it.

Continuous tube rotation with simultaneous table movement that produces a volumetric dataset. It enables overlapping slices, multiplanar reformatting, and short breath-hold scan times.

A scanner with multiple detector rows that acquires several slices per rotation. It enables thinner slices, wider anatomic coverage, and rapid scanning of large body regions.

The nominal thickness of a reconstructed image, set by detector configuration and reconstruction parameters. Thinner slices improve z-axis resolution but increase noise and dose.

A mathematical filter applied during reconstruction that emphasizes either spatial resolution (sharp or bone kernels) or low noise (soft or smooth kernels), altering image texture and noise.

The reconstructed area of the patient displayed in the image matrix. A smaller field of view yields smaller pixels and better displayed detail; a larger one includes more anatomy.

Reformatting volumetric CT data into coronal, sagittal, oblique, or curved planes. Image quality depends on thin slices and near-isotropic voxels from the original acquisition.

A rendering technique displaying the brightest voxels along each viewing ray. It highlights vessels, airways, and high-attenuation structures within a volume on a single image.

Contrast-enhanced CT timed to peak arterial enhancement, using thin slices and rapid acquisition. Reconstructions such as maximum intensity projection or volume rendering display the vessels.

A technique that monitors contrast arrival in a selected vessel and starts scanning when a preset attenuation threshold is reached, optimizing arterial enhancement and timing consistency.

A post-contrast acquisition timed roughly 25 to 35 seconds after injection, when arteries and hypervascular lesions enhance strongly before venous structures fill.

A post-contrast acquisition timed about 60 to 80 seconds after injection, when the liver parenchyma and portal veins are maximally enhanced. It is standard for abdominal tumor detection.

The ability of a scanner to freeze motion, determined mainly by gantry rotation time and reconstruction method. It is critical in cardiac, vascular, and pediatric imaging.

Synchronizing acquisition or reconstruction with the cardiac cycle to reduce cardiac motion. It is used for coronary CT angiography and coronary calcium scoring.

Real-time CT imaging used to guide biopsies, drainages, and other interventions. Staff dose is controlled with lead shielding, short exposures, distance, and intermittent technique.

Iodine-based solutions that enhance blood vessels and tissues. Their iodine concentration, osmolality, and viscosity influence enhancement, patient comfort, and adverse-effect risk.

Leakage of contrast from the vein into surrounding soft tissue, causing swelling, pain, and occasionally compartment injury. Management includes stopping the injection, elevating the limb, and cold compresses.

Acute kidney injury developing within days of iodinated contrast administration. Risk rises with pre-existing renal impairment, diabetes, dehydration, and large contrast volumes, so renal screening matters.

Estimated glomerular filtration rate, calculated from serum creatinine. It screens kidney function before iodinated contrast and guides hydration, premedication, or alternative imaging decisions.

An oral diabetes medication that may be withheld after iodinated contrast in patients with impaired renal function because of a theoretical risk of lactic acidosis.

A non-IgE-mediated adverse reaction to contrast ranging from urticaria and flushing to bronchospasm and hypotension. Treatment includes antihistamines, oxygen, fluids, and epinephrine when severe.

A corticosteroid and antihistamine regimen given before contrast to patients with prior allergic-like reactions, reducing the likelihood and severity of a repeat reaction.