ARRT CT common mistakes
ARRT CT · Understand the traps and how to avoid them.
Clearing a patient for IV iodinated contrast after asking only about allergies, without checking eGFR/creatinine or metformin and AKI history.
Candidates memorise 'iodinated contrast is safe' and the allergy question as the whole screening ritual, so the renal-function and medication portion of the checklist drops out under time pressure.
What to do instead
Before every contrast exam, run a fixed five-item verbal checklist in the same order every time: allergy type and reaction, renal function/eGFR value and date, metformin/other nephrotoxic meds, pregnancy/breastfeeding status, and prior contrast reaction. Rehearse the checklist aloud on practice scenarios until it is automatic.
Treating a vasovagal reaction (bradycardia, hypotension, diaphoresis, pallor) as an allergic reaction, or vice versa, and starting the wrong intervention.
Both present within minutes of injection and both involve a distressed patient, so candidates pattern-match on 'reaction after contrast' instead of checking pulse and blood pressure first.
What to do instead
Memorise the discriminating vitals: vasovagal = bradycardia plus hypotension; anaphylactoid = tachycardia plus hypotension with urticaria/bronchospasm. On any post-injection event, take a pulse and BP before deciding, and drill 5–10 contrasting vignettes until the vital-sign pattern drives the answer.
Detecting an extravasation but continuing the injection or pulling the cannula immediately without assessing volume, then failing to describe the correct post-care (elevation, cold/warm compress, documentation, physician notification).
Extravasation appears as a single 'stop the injection' fact in review material, so the sequence and follow-up care are under-learned relative to the recognition step.
What to do instead
Write out and rehearse the full ordered sequence: stop injection, leave cannula in place to aspirate if protocol allows, remove, elevate extremity, apply compress per departmental policy, notify radiologist, document volume/site/symptoms, and arrange follow-up. Recall it as a numbered list, not a single keyword.
Choosing the wrong acquisition delay for multiphase studies - e.g. using a fixed 70-second delay for all abdominal phases, or scanning a CTA too late to catch arterial enhancement.
Candidates learn that 'liver is portal venous' and 'CTA is arterial' as labels but never attach the timing, bolus-triggering method, or contrast volume/rate to each phase, so numbers get guessed.
What to do instead
Build a one-page timing table pairing each protocol with its delay or trigger threshold (arterial, portal venous, delayed/excretory, CT urography, CTA, PE). Practice by naming the phase first, then reciting the delay and trigger before checking the answer.
Setting the wrong scan extent or landmark - cutting off the lung apices on a PE study, missing the skull base on a sinus protocol, or scanning far beyond the region of interest and inflating dose.
Attention goes to mA/kV/contrast and the topogram is treated as a formality, so the reconstructed volume is never checked against the ordered anatomy.
What to do instead
Adopt a routine: after the topogram, mark the superior and inferior boundaries on the scout and verify them against a memorised landmark list for each protocol. For high-yield exams (PE, sinus, cervical spine, renal colic) memorise the required start and end anatomy and recite it before each practice scan.
Confusing patient preparation requirements - giving oral contrast where it is contraindicated or unnecessary, allowing food when fasting is required, or omitting bowel prep for CT colonography.
Prep details are taught as departmental habit rather than as exam-specific rules, so candidates assume 'CT prep' is uniform across protocols.
What to do instead
Make a protocol-by-protocol prep matrix (fasting, oral contrast, IV access, bowel prep/tagging, medication holds) and self-quiz by exam name only. Flag the exceptions explicitly - e.g. exams where positive oral contrast obscures the finding you are looking for.
Computing pitch incorrectly or assuming that raising pitch increases patient dose.
Pitch is defined as table feed per gantry rotation divided by total beam collimation, and candidates invert it, use the single-slice collimation instead of the total, or apply an intuitive 'more pitch = more dose' rule.
What to do instead
Write the formula on a card, then work 10 numerical problems where detector configuration varies (e.g. 64 × 0.625 mm). Pair each answer with the dose relationship: with mA held constant, higher pitch generally lowers dose and can increase noise/artefact.
Mixing up what automatic exposure control (mA modulation) changes versus what tube-voltage selection changes, and expecting AEC to alter kV.
Both are 'automatic technique' features and both affect dose, so their inputs and outputs blur together; candidates also forget that AEC modulates along the z-axis and angularly.
What to do instead
Memorise two clean statements: AEC adjusts mA (and thus tube current) rotation-by-rotation and along z based on the attenuation measured on the topogram; kV is chosen by the technologist based on patient size, contrast enhancement, and artefact considerations. Then practise predicting which parameter moves in a given scenario.
Attributing spatial resolution to the wrong factor - believing window width, contrast concentration, or kV controls spatial resolution, or thinking a thinner slice improves low-contrast detectability.
Spatial resolution, contrast resolution, and noise are taught as a cluster of 'image quality' terms, so candidates assign effects to the wrong variable under exam pressure.
What to do instead
Build a cause-effect table: slice thickness, matrix size, FOV/pixel size, focal spot, and reconstruction kernel drive spatial resolution; mAs, slice thickness, and iterative reconstruction drive noise and low-contrast detectability; window settings only change display. Drill by predicting the change from one variable at a time.
Confusing dose descriptors and their units - reporting CTDIvol in mGy·cm, treating DLP as the displayed scanner value, or skipping the conversion to effective dose.
CTDIvol, DLP, and effective dose appear together in dose discussions and the units look similar, so candidates attach the wrong unit or formula to the right concept.
What to do instead
Anchor three facts: CTDIvol is weighted/averaged dose for a single rotation in mGy; DLP = CTDIvol × scan length in mGy·cm; effective dose = DLP × a region-specific conversion coefficient in mSv. Practise by converting a given CTDIvol and scan length through to DLP and effective dose.