Free ARRT CT Exam Flashcards

Iodinated contrast can transiently worsen renal function; in a patient taking metformin with reduced renal function, impaired metformin clearance raises the risk of lactic acidosis. Protocol is to check renal function (eGFR/creatinine) first and involve the ordering physician about holding metformin — not to withhold contrast from every metformin patient automatically.

An eGFR below roughly 30 mL/min/1.73m² (severe renal impairment) is the key threshold prompting physician consultation before iodinated contrast. Between 30-45 the decision is more individualized based on risk/benefit; above 45, contrast is generally given without extra renal precautions.

Mild (hives, itching, mild nausea) is monitored and treated symptomatically. Moderate (bronchospasm, facial/laryngeal edema, hypotension) needs medication and close observation. Severe (anaphylactoid shock, cardiopulmonary arrest) requires an emergency response with epinephrine and the code team. The severity level — not just the presence of a reaction — determines the treatment pathway.

A common regimen gives an oral corticosteroid (e.g., prednisone) at roughly 13, 7, and 1 hour before contrast, plus an antihistamine about 1 hour before. Premedication reduces recurrence risk but does not eliminate it, so the patient still requires full monitoring during and after the injection.

Stop the injection immediately, elevate the affected limb, apply a warm or cold compress per department protocol, and document the estimated extravasated volume. Most cases are managed conservatively; a surgical consult is reserved for large volumes, skin blistering, or signs of vascular/nerve compromise.

Many departments have moved away from strict fasting orders for contrast-enhanced CT, since nausea/vomiting risk with modern low- and iso-osmolar iodinated contrast is low — clear liquids are often permitted until shortly before the scan. Actual practice still varies by department, so confirm local protocol rather than assuming a blanket NPO rule.

As Low As Reasonably Achievable — minimize radiation dose to patients and staff while still obtaining diagnostic image quality. It means optimizing technique for the clinical question, not simply lowering technique factors until an image becomes non-diagnostic.

CTDIvol (in mGy) reflects the dose intensity at a given scan location, based on a standard phantom. DLP (in mGy·cm) reflects total exam dose — essentially CTDIvol multiplied by scan length. A short scan with a high CTDIvol can still produce a lower DLP than a long scan with a lower CTDIvol.

SSDE adjusts CTDIvol using the patient's actual effective diameter, giving a more accurate individual dose estimate than CTDIvol alone, which is based on a fixed 32 cm or 16 cm reference phantom regardless of the patient's true body size.

Adjusts mA in real time along the z-axis and/or angularly around the patient based on attenuation, lowering dose through thinner regions (e.g., chest) while raising current through thicker or denser regions (e.g., shoulders, pelvis) to keep noise consistent across the scan.

Iterative reconstruction reduces image noise at a given dose — or allows a lower dose at equivalent noise — compared with traditional filtered back projection, at the cost of greater computational processing time per image.

CT technologists wear a personal dosimeter (commonly at the collar) to track cumulative occupational exposure against regulatory annual limits. This monitors staff dose over time — it has no bearing on an individual patient's exam dose, which is tracked separately through CTDIvol/DLP.

Extra dose delivered just beyond the prescribed scan range, needed because helical reconstruction requires raw data from slightly before and after the requested anatomy to complete the first and last image slices. Overranging dose grows with wider collimation and lower pitch, making it a larger factor on wide-detector scanners.

Pitch = table feed per gantry rotation ÷ total beam collimation width. Pitch of 1 gives contiguous coverage; pitch below 1 overlaps data per rotation (higher dose, better resolution); pitch above 1 leaves wider spacing between helical sweeps per rotation (generally lower dose, faster coverage).

kVp controls the energy and penetration of the x-ray beam, affecting contrast and beam hardening; mAs controls the quantity of photons, primarily affecting image noise. Raising kVp helps penetrate a large patient, while raising mAs mainly reduces noise rather than improving penetration.

Thinner slices improve z-axis spatial resolution and reduce partial-volume averaging, which helps detect small lesions or fine fractures, but they increase image noise per slice. Thicker slices lower noise but blur small structures through greater partial-volume averaging.

Voxels with equal dimensions along x, y, and z axes, which enable high-quality coronal and sagittal reformats without loss of detail compared with the original axial images. Non-isotropic (elongated) voxels degrade reformatted image quality even if the original axial images look sharp.

Reconstruction interval is the spacing between reconstructed image planes and can be set smaller than the acquired slice thickness to create overlapping images — improving 3D reformats and small-lesion detection — without any additional patient dose, since the raw helical data was already acquired.

Bolus tracking monitors attenuation in a region of interest (e.g., the aorta) during the actual diagnostic injection and auto-triggers the scan at a set HU threshold. Test bolus instead uses a small preliminary injection to measure time-to-peak enhancement before the full diagnostic bolus is given — both time image acquisition to peak enhancement, but by different methods.

Window width sets the range of Hounsfield Units displayed across the full gray scale (controls image contrast); window level sets the center HU value of that range (controls overall brightness). A wide lung window reveals subtle density differences in aerated lung; a narrower soft-tissue window boosts contrast between similar-density abdominal structures.

Acquires data at two different x-ray energy spectra, enabling material decomposition — such as distinguishing iodine from calcium or hemorrhage — and generation of virtual monochromatic and virtual non-contrast images, a capability standard single-energy CT cannot provide.

Appears as dark streaks or cupping between two dense structures (e.g., between the petrous bones, or across a thick pelvis) because lower-energy photons are preferentially absorbed passing through dense tissue, shifting the remaining beam to a higher mean energy. Partly corrected with beam-hardening correction algorithms or, in some cases, higher kVp.

Bright and dark streaking radiating from high-density metal (implants, dental hardware) caused by photon starvation and beam hardening. Metal artifact reduction (MAR) algorithms and dual-energy virtual monochromatic reconstructions reduce, but do not fully eliminate, this artifact.

Causes blurring or streaking from patient movement — voluntary or involuntary (cardiac/respiratory) — during acquisition. Mitigated by shorter scan times and patient instruction, and for cardiac motion, by ECG gating — not by adjusting kVp or mA, which affect noise, not motion.

A complete circular artifact centered on the axis of rotation, caused by a miscalibrated or malfunctioning detector element. Fixed through detector recalibration and routine QC, not by adjusting an individual patient's scan parameters.

Occurs when a voxel contains a mixture of tissue types with different attenuation, producing an averaged CT number that doesn't represent any single tissue accurately. Most problematic with thick slices and small structures oriented obliquely to the scan plane.

Water is fixed at 0 HU and air at -1000 HU on the Hounsfield scale, with dense cortical bone near +1000 HU or higher and fat in the negative range (roughly -50 to -100 HU). These fixed reference points anchor daily CT number accuracy quality control.

A water phantom is scanned each day to confirm the CT number for water reads within an accepted tolerance and that noise/uniformity meet specification. This catches scanner calibration drift before it affects patient studies, distinct from periodic dosimetry or accreditation testing.

The first imaging study for suspected acute stroke, used to rapidly rule out hemorrhage before thrombolytic therapy is considered. It does not reliably show early ischemic infarct — excluding bleeding is the deciding factor for tPA eligibility, not detecting the infarct itself.

Requires very thin (submillimeter) slices and a high-spatial-frequency bone reconstruction kernel to resolve fine structures like the ossicles and semicircular canals. A standard soft-tissue kernel and routine slice thickness will not adequately depict these small structures.

Uses thin-slice acquisition with sagittal and coronal reformats to assess alignment and fracture, typically without contrast — unless vascular injury such as vertebral artery dissection is suspected, which adds a CT angiogram component to the study.

Typically timed to peak venous/parenchymal enhancement — a later phase than arterial timing — to best evaluate lymph nodes and soft-tissue masses. A neck CT angiogram instead uses earlier arterial-phase timing, so the clinical question determines which delay is used.

Used to evaluate the spinal canal and nerve roots when MRI is contraindicated, such as with certain implanted hardware. Contrast is injected intrathecally via lumbar puncture before scanning — not given intravenously as with most other CT studies.

Typically thin-slice, noncontrast images reformatted in coronal and axial planes to evaluate the osteomeatal complex before functional endoscopic sinus surgery. Contrast is reserved for suspected infection complications or tumor — not part of the routine anatomic protocol.

Requires precise bolus timing — usually bolus tracking on the main pulmonary artery — so peak contrast enhancement coincides with acquisition. Mistimed injection is a leading cause of a nondiagnostic PE study, unlike routine chest CT where timing is less critical.

Uses thin slices with a sharp reconstruction kernel and often adds prone imaging to distinguish fixed fibrosis from dependent atelectasis. Prone positioning is the key added step that separates an HRCT protocol from a standard chest CT.

A noncontrast, reduced-dose technique for eligible high-risk smokers, with findings classified using the Lung-RADS system. This differs from a standard diagnostic chest CT, which uses full-dose technique to work up an already-identified abnormality.

Acquires unenhanced, arterial (~25-35 seconds post-injection), and portal venous (~60-70 seconds) phases to characterize hypervascular liver lesions such as hepatocellular carcinoma, which enhance in the arterial phase and washout on later imaging. A single-phase study would miss that washout pattern entirely.

Performed as a noncontrast, low-dose CT because contrast can obscure small calcifications and mimic or hide stones. Giving contrast for this indication is a protocol error, not a dose-optimization choice.

IV contrast is standard for adult appendicitis CT to evaluate bowel wall enhancement and detect complications like abscess or perforation. Oral contrast use varies by institution and patient body habitus rather than being universally required with modern scanners.

Requires colonic insufflation (room air or CO2) plus both supine and prone (or decubitus) positioning to fully distend the colon and distinguish fixed polyps from mobile stool. Inadequate distension, not scan technique, is the most common cause of a nondiagnostic exam.

Divides the contrast dose into two separate injections — for example, an earlier portal-venous-timed dose and a later excretory-timed dose — to combine two enhancement phases into a single acquisition, reducing total dose compared with running two separate full scans.

Gives a spatial, surgeon-friendly overview of fracture fragment displacement, but it is a post-processing display technique. Diagnosis and detailed fracture characterization still rely on the underlying thin-slice axial and multiplanar reformatted images, not the 3D rendering alone.

Dedicated MAR algorithms, together with adjusted kVp/mAs technique, reduce streak artifact around joint prostheses and fixation hardware, improving visualization of adjacent bone and soft tissue. Standard reconstruction alone often leaves the region near the hardware non-diagnostic.

CT provides precise real-time needle localization for bone and soft-tissue lesions, particularly valuable for deep or complex targets such as the pelvis or spine, where ultrasound cannot adequately visualize the lesion.

CT is reserved for complex intra-articular fractures, surgical planning, or equivocal radiographs — it is not a routine first-line study for simple extremity trauma, where plain radiography remains the initial modality.

Requires arterial-phase timing and full coverage from the aortic root through the femoral arteries to identify the intimal flap and distinguish the true lumen from the false lumen. Incomplete coverage can miss distal extension of the dissection.

Images the arterial tree from the abdominal aorta to the feet in a single contrast bolus, with table speed matched to the bolus's travel down the legs to evaluate peripheral arterial disease. Timing is calibrated to bolus transit rather than a single fixed delay used in most other CTA studies.

Uses CT to plan and confirm a safe percutaneous needle or catheter trajectory to a fluid collection while avoiding bowel, vessels, and other critical structures — the image guidance during needle advancement is what distinguishes this from a purely diagnostic scan.

Provides near real-time image updates during needle advancement for biopsy or drainage, improving procedural speed and accuracy compared with conventional step-and-shoot CT guidance. It delivers continuous dose to both patient and operator, which requires careful ALARA management, including using pulsed technique and keeping hands out of the beam.