Your FREE CT Flashcards 2026 – 100+ Cards

Estimated glomerular filtration rate — a measure of kidney function used to screen before iodinated IV contrast. A low eGFR raises the risk of contrast-associated kidney injury, so protocols are adjusted.

Low-osmolality iodinated contrast that does not dissociate into ions. It is far better tolerated than ionic (high-osmolality) agents and is the standard for intravascular CT injection.

Metformin is renally cleared; if contrast impairs kidney function, metformin can accumulate and (rarely) cause lactic acidosis. Follow ACR/FDA guidance — assess renal function and hold metformin per protocol in at-risk patients.

Leakage of injected contrast into the soft tissue around the IV instead of the vein. Stop the injection, elevate and apply cold/warm compresses per policy, assess for compartment syndrome, and document.

A patient with a prior iodinated-contrast reaction who still needs contrast may receive a corticosteroid + antihistamine premedication protocol (per ACR) to reduce the risk of a repeat reaction.

The patient must be told the procedure's risks, benefits, and alternatives — including potential contrast reactions — and consent before contrast administration; the technologist verifies it is documented.

A pre-procedure pause to verify correct patient, correct procedure/site, and correct protocol/orders before scanning — a patient-safety standard against wrong-patient/wrong-exam errors.

Confirm identity with two identifiers (e.g., full name and date of birth) — never the room/table location — before any CT exam or contrast injection.

BP ≈ 120/80 mmHg, heart rate 60–100 bpm, respiratory rate 12–20/min, SpO₂ 95–100%, temperature ≈ 37 °C (98.6 °F). Recognize deviations during monitored CT.

Mild (limited hives, nausea, flushing) → observe; moderate (diffuse urticaria, mild bronchospasm, vomiting) → treat; severe (laryngeal edema, anaphylaxis, cardiovascular collapse) → emergency response, epinephrine, call a code.

Stop the contrast injection immediately, maintain IV access, assess the patient (airway, breathing, circulation), call for help/physician, and follow the emergency reaction protocol.

A single-head injector delivers contrast only; a dual-head injector delivers contrast plus a saline flush (pushing the contrast bolus and clearing the line). Set flow rate and volume per protocol.

Saline injected after the contrast bolus to push residual contrast from the tubing/arm veins into central circulation — tightening the bolus and reducing streak artifact at the injection site.

Higher flow rates (e.g., CTA) require a larger-bore, well-placed IV (e.g., 18–20 g in the antecubital). Matching flow rate to catheter/vein reduces extravasation risk.

Check renal function (eGFR/creatinine) and relevant labs (e.g., per protocol). Screen for prior reactions, diabetes/metformin, asthma/allergy, and pregnancy before iodinated IV contrast.

Hand hygiene, gloves/PPE for body-fluid contact, aseptic technique for IV access, and cleaning the table, gantry bore, and accessories between patients (clean, disinfect, sterilize as appropriate).

The minimum infection-control practices used for every patient regardless of diagnosis: hand hygiene, PPE as needed, respiratory hygiene, safe injection practices, and equipment cleaning.

Volume CT Dose Index (mGy) — the average radiation dose within the scanned volume, normalized for pitch. The primary dose metric displayed on the console for a single scan series.

CTDIvol × scan length, in mGy·cm. It estimates the total radiation delivered over the whole scan and is used to estimate effective dose (DLP × a region-specific k factor).

As Low As Reasonably Achievable — keep every CT radiation dose to the patient and staff as low as possible while still producing a diagnostic image.

Automatic adjustment of mA based on patient size/attenuation along the scan (angular and z-axis). It delivers uniform image quality at the lowest dose; brand names include SmartmA, CARE Dose4D, SURE Exposure.

Radiation intensity is inversely proportional to the square of the distance from the source; doubling distance reduces intensity to one quarter — the basis for maximizing distance for staff protection.

Time, distance, and shielding — minimize time near the source, maximize distance (most effective), and use shielding (lead) to keep occupational and patient dose ALARA.

The SI unit of absorbed dose — energy deposited per unit mass of tissue. CT dose metrics (CTDIvol, DLP) are expressed in milligray (mGy).

The SI unit of equivalent/effective dose — absorbed dose weighted for biological harm. Effective dose from CT is estimated in millisieverts (mSv).

An x-ray interaction in which a photon is totally absorbed by an inner-shell electron — it builds image contrast, depends strongly on atomic number and lower energy, and contributes to patient dose.

An x-ray photon ejects an outer-shell electron and continues deflected. Scatter degrades contrast and is the principal source of occupational dose to staff in the CT room.

Extra rotations beyond the planned scan range in helical CT needed for reconstruction interpolation, adding dose. Reduced by adaptive (dynamic) z-collimation.

A campaign to child-size CT technique: lower kVp/mAs, weight/size-based protocols, scan only the indicated area, and avoid unnecessary multiphase scans, because children are more radiosensitive.

Verify pregnancy status before scanning; weigh benefit vs. fetal dose, shield/limit the field where feasible, and consider alternatives. Document justification — the embryo/fetus is highly radiosensitive.

Restricting the x-ray beam to the detector array width reduces patient dose and scatter. Total beam width = number of detector rows × slice width.

Console thresholds (CTDIvol/DLP) set per protocol that warn the operator when a planned scan would exceed a facility limit — a dose-management safety check before scanning.

Documenting and reporting scanning errors, dose events, and contrast reactions per facility policy and regulation — part of the CT quality and safety program.

The standardized CT number for tissue attenuation: water = 0 HU, air = −1000 HU, dense cortical bone ≈ +1000 HU or more. Fat is about −100 to −50; soft tissue +30 to +60.

Table travel per gantry rotation ÷ total nominal beam width. Pitch > 1 spreads the beam (faster scan, less overlap, lower dose); pitch < 1 overlaps the beam (more dose, less noise).

The range of Hounsfield units displayed as shades of gray. A wide window (e.g., lung/bone) shows many HU values with low contrast; a narrow window shows few HU values with high contrast.

The center Hounsfield value of the displayed window — it sets the midpoint of the gray scale (brightness). Choose WL near the HU of the tissue of interest (e.g., ~40 for brain).

As the polychromatic x-ray beam passes through dense tissue, low-energy photons are absorbed first, raising the mean beam energy. This produces dark streaks/cupping, classically between dense bone (posterior fossa) or metal.

A shaped filter at the tube that equalizes x-ray intensity across the fan beam — more attenuation at the periphery (thin body) and less centrally — reducing peripheral patient dose and beam-hardening artifact.

A scanner with multiple rows of detectors along the z-axis, acquiring several slices per rotation. More detector rows mean faster coverage, thinner slices, and isotropic volumetric data.

A voxel with equal dimensions in all three axes (x, y, z). Isotropic data allow high-quality multiplanar (MPR) and 3D reformations in any plane without loss of resolution.

Reconstructing axial volumetric data into coronal, sagittal, or oblique planes. Requires thin, overlapping slices (ideally isotropic) for the best results.

A post-processing display that projects the highest-attenuation voxels along a ray — used to show contrast-filled vessels in CT angiography.

Continuous tube rotation while the table moves through the gantry, acquiring a volume of data in one breath-hold. Enables thin slices, fast coverage, and overlapping reconstructions.

A reconstruction method that repeatedly refines the image by comparing it to the raw projection data, reducing image noise and allowing lower-dose scanning compared with filtered back projection.

The classic CT reconstruction algorithm that back-projects filtered projection data into the image. Fast and simple, but noisier at low dose than iterative methods.

The mathematical filter applied during reconstruction. A 'sharp/bone' kernel boosts spatial resolution but increases noise; a 'smooth/soft-tissue' kernel lowers noise but blurs fine detail.

The preliminary low-dose projection image acquired first to plan the scan range, centering, and AEC reference — not for diagnosis.

Acquiring data at two x-ray energies to differentiate materials by their energy-dependent attenuation — e.g., separating uric acid from calcium in gout, or iodine maps and virtual non-contrast images.

Rotating electrical contacts that transmit power and data to the continuously spinning gantry, enabling helical (continuous-rotation) scanning.

The electronics that receive the detector signals, convert them from analog to digital, and pass the projection data to the array processor for reconstruction.

How efficiently detectors convert incident x-ray photons into usable signal. Higher DQE means lower noise for a given dose — better dose efficiency.

An artifact where a voxel spans more than one tissue type, so its HU is an average of them — causing blurred or inaccurate values. Reduced by thinner slices.

Streaks and dark/bright bands from high-density implants caused by beam hardening, photon starvation, and scatter. Reduced with higher kVp, metal artifact reduction (MAR) algorithms, and gantry angulation.

Concentric circular artifact from a miscalibrated or faulty detector element in a third-generation rotate-rotate scanner; corrected by detector calibration.

The ability to distinguish small, closely spaced high-contrast objects (line pairs/cm). Improved by smaller FOV, thinner slices, sharp kernels, and a smaller focal spot.

The ability to distinguish tissues with similar attenuation (low contrast). CT excels here; improved by higher mAs (less noise), smooth kernels, and lower kVp (more iodine contrast).

Lower kVp brings the beam energy nearer iodine's k-edge (33 keV), increasing iodine attenuation/contrast and often allowing lower contrast dose — but it increases image noise unless mAs is raised.

Display/scan FOV sets how the matrix maps to anatomy. A smaller FOV spreads the same matrix over less area, giving smaller pixels and higher spatial resolution.

Grainy variation in CT numbers, dominated by quantum mottle (too few photons). Reduced by raising mAs, lowering kVp's effect via thicker slices, smoother kernels, or iterative reconstruction — at a dose trade-off.

SFOV sets the calibration/bowtie and data collected; DFOV (≤ SFOV) selects the reconstructed area. A targeted small DFOV improves displayed spatial resolution.

The spacing between reconstructed slices. Overlapping (interval < slice thickness) improves MPR/3D quality and lesion detection without re-scanning the patient.

A 3D post-processing technique that assigns color/opacity to ranges of HU to display surfaces and depth — useful for vascular and skeletal anatomy.

A 3D rendering showing only the surface of structures above a chosen threshold — fast but discards internal data, largely replaced by volume rendering.

The reconstruction matrix (e.g., 512 × 512) and the FOV together set pixel size: pixel size = FOV ÷ matrix. Smaller pixels (smaller FOV or larger matrix) raise spatial resolution.

PACS stores, retrieves, and distributes images; DICOM is the standard format/protocol for medical image data and metadata, enabling cross-system communication and teleradiology.

The cathode emits electrons by thermionic emission; they strike the rotating anode (target), producing x-rays. The tube must dissipate large heat loads during continuous CT scanning.

The table is stationary during each rotation, then steps to the next position. Used where helical motion is undesirable (e.g., some perfusion or high-resolution protocols).

Iodine's k-shell binding energy is ~33 keV. X-ray energies just above it are strongly absorbed by iodine, which is why lower kVp boosts iodine (vascular) contrast.

Routine CT QC includes CT number accuracy/calibration (water = 0 HU), noise/uniformity, slice thickness, spatial/contrast resolution, and laser/alignment checks to keep the scanner within tolerance.

Water must measure 0 ± a few HU; air must be near −1000 HU. Routine water-phantom calibration keeps Hounsfield values accurate for diagnosis.

Blurring, doubling, or streaks from patient or physiologic motion (breathing, cardiac, peristalsis). Reduced by breath-hold, faster scans, gating, and patient immobilization/communication.

Streak artifact in highly attenuating regions (e.g., shoulders, hips) where too few photons reach the detector. Reduced by tube-current modulation, higher mA, or adaptive filtering.

A scanning technique that places an ROI in a target vessel and automatically triggers the scan when contrast enhancement reaches a set HU threshold — timing the scan to peak vascular opacification.

A small test injection of contrast scanned repeatedly at one level to measure time-to-peak enhancement, then used to set the optimal scan delay for the diagnostic acquisition.

Synchronizing acquisition (prospective) or reconstruction (retrospective) to the cardiac cycle (usually diastole) to freeze heart motion. Prospective gating gives lower dose; retrospective allows functional/phase data.

Given to lower and stabilize the heart rate (target ~ <60 bpm), reducing cardiac motion and improving coronary artery image quality on gated cardiac CT.

The first study in suspected stroke — it is performed to exclude intracranial hemorrhage before any thrombolytic therapy or contrast study.

Cerebral blood flow, a key parameter measured in brain CT perfusion to distinguish salvageable ischemic penumbra from infarcted core in acute stroke.

Contrast-enhanced chest CT timed to the pulmonary arterial phase (~ peak pulmonary artery enhancement) to detect pulmonary embolism.

Suspected renal/ureteral calculi are imaged without contrast, because contrast in the collecting system would obscure (or mimic) the high-attenuation stones.

Imaging the liver in arterial, portal-venous, and sometimes delayed phases to characterize lesions by their enhancement pattern (e.g., arterial hypervascularity of hepatocellular carcinoma).

A multiphase study (non-contrast, nephrographic, and excretory phases) that opacifies the collecting systems, ureters, and bladder to evaluate the urinary tract.

Abdominal CT using a large volume of neutral (low-density) oral contrast to distend the small bowel, improving detection of bowel wall and mucosal disease (e.g., Crohn's).

Scanning the same anatomy at multiple time points after contrast (arterial, venous, delayed) to characterize lesion enhancement and washout (e.g., adrenal, renal, liver lesions).

Positive (iodinated/barium) oral contrast opacifies the GI tract to distinguish bowel from masses/abscess; neutral (water/low-HU) oral contrast distends bowel for wall assessment (enterography).

Image acquisition during peak arterial enhancement (commonly ~ 20–35 s after injection start, varies by protocol/patient) to show hypervascular lesions and arteries (CTA).

Abdominal imaging ~ 60–70 s after injection, when the liver parenchyma and portal/hepatic veins are maximally enhanced — the workhorse phase for most abdominal CT.

A non-contrast, ECG-gated cardiac CT that quantifies calcified coronary plaque (Agatston score) to assess cardiovascular risk.

Low-dose CT of the insufflated, cleansed colon with 2D and 3D 'fly-through' review to screen for colorectal polyps and cancer.

The Couinaud system divides the liver into 8 functionally independent segments based on portal/hepatic venous supply — essential for localizing lesions on CT.

The arterial anastomotic ring at the base of the brain (anterior/posterior cerebral, communicating, internal carotid arteries) — a key target of head/neck CT angiography.

Thin slices (≈ 1–2.5 mm) improve detection of small intracranial lesions and reduce posterior fossa beam-hardening; the posterior fossa is often imaged thinner than the supratentorial brain.

High-resolution CT uses thin slices and a sharp (high-spatial-frequency) kernel to evaluate the lung parenchyma and interstitial disease (e.g., interstitial lung disease, nodules).

A non-contrast, low-dose chest CT used to screen high-risk patients for lung cancer, minimizing dose while detecting pulmonary nodules.

The central thoracic compartment between the lungs containing the heart, great vessels, trachea, esophagus, thymus, and lymph nodes — a key region on chest CT.

Multiphase adrenal imaging (non-contrast, portal-venous, and 15-min delayed) calculating absolute/relative washout to distinguish benign adenomas from other lesions.

Contrast-enhanced CT timed to peak arterial enhancement with thin slices, used with MIP/3D reformations to evaluate arteries (e.g., aorta, coronaries, pulmonary, runoff).

Abdomen/pelvis CT extended through the pelvis to fully include the appendix; findings include a dilated, non-filling appendix with wall thickening and periappendiceal fat stranding.

A dedicated thin-slice, high-resolution, bone-kernel study of the petrous temporal bones / internal auditory canal for the ossicles, cochlea, and middle/inner ear structures.

Aligning the acquisition or reformations parallel to the intervertebral disc spaces optimizes visualization of disc spaces and spinal alignment.

Rapid contrast-enhanced CT of head, c-spine, chest, abdomen, and pelvis to survey major injuries in the unstable/multitrauma patient.

Interventional procedures using CT to guide needle placement for tissue sampling (biopsy) or to drain fluid collections/abscesses, with strict aseptic technique.

On non-contrast CT, calculi appear as high-attenuation foci; secondary signs include hydronephrosis, ureteral dilation, and perinephric stranding.

The liver and adrenal glands are common metastatic sites for lung cancer, so the staging chest CT extends to include the upper abdomen.

Imaging ~ several minutes after injection when contrast is excreted into the collecting systems and ureters — assessing patency and filling of the urinary tract.

HCC classically shows arterial-phase hyperenhancement with portal-venous/delayed washout — the reason multiphase liver CT is performed.

A gated CT of the aortic root and a CTA of the vascular access route to size the valve annulus and plan transcatheter aortic valve replacement.

CT of the esophagus, often with oral contrast, to evaluate the esophageal wall, masses, or leaks.

Contrast is instilled into the bladder via catheter, then CT is performed to evaluate bladder integrity (e.g., suspected rupture).