Page 12 of 14
RD1.1,RD2.1-2 | Imaging Modality Foundations — Graded Quiz
Click any question card to reveal the correct answer.
A clinician must justify why ultrasound, rather than radiography, is preferred for first-look assessment of a solid-organ abdominal problem in a young patient. Which physical property of ultrasound underlies this preference?
Correct. Diagnostic ultrasound uses piezoelectric transducers to emit and receive high-frequency sound — it carries no ionising-radiation risk, which is why it is favoured for first-look soft-tissue assessment, especially in the young.
Ultrasound = high-frequency sound, non-ionising; this drives its first-line use in soft-tissue and paediatric/obstetric imaging.
Ultrasound is sound-based and non-ionising. Option B describes radiography, C describes nuclear medicine, and D describes MRI.
Click to reveal answer
Among the ionising modalities, which delivers a radiation dose to the patient by administering a radiopharmaceutical that emits radiation from within the body?
Correct. Nuclear medicine introduces a radiopharmaceutical that emits radiation from inside the patient, which the gamma camera/PET detector records. Radiography, fluoroscopy and CT use an external X-ray source.
Nuclear medicine = internal radiation source (radiotracer); X-ray/fluoroscopy/CT = external X-ray source.
Only nuclear medicine uses an internal radiation source (a radiopharmaceutical). Radiography, fluoroscopy and CT all use an external X-ray tube.
Click to reveal answer
Applying the ALARA principle to a fluoroscopy-guided procedure, which combination of measures most directly reduces operator and patient radiation exposure?
Correct. ALARA is operationalised through the three classic levers — reduce time, increase distance, and interpose shielding. These directly lower dose to patient and staff.
ALARA levers: time (less), distance (more), shielding — the core of radiation protection.
ALARA = As Low As Reasonably Achievable, achieved by minimising time, maximising distance, and using shielding — the opposite of option A. Gadolinium does not reduce radiation dose.
Click to reveal answer
A patient about to undergo contrast-enhanced CT reports that they are 'allergic to iodine' and to shellfish. How should this information be interpreted during contrast screening?
Correct. 'Iodine allergy' and shellfish allergy do NOT predict iodinated-contrast reactions; the screening item that matters is a documented prior reaction to iodinated contrast media itself.
Pearl: iodine/shellfish 'allergy' does not predict contrast reactions — ask about prior iodinated-contrast reaction.
Shellfish/'iodine' allergy is a common but incorrect reason to cancel a needed contrast study. The real risk factor is a prior reaction to iodinated contrast media; gadolinium is not a CT agent.
Click to reveal answer
Competency RD2.1 specifies a structured four-domain pre-imaging history. Which set best represents these four screening domains?
Correct. The structured pre-imaging screen covers allergies (contrast reactions), renal function (contrast safety), pregnancy (radiation), and implanted devices (magnetic-field safety) — exactly the domains named in RD2.1.
Four-domain pre-imaging screen: allergies, renal function, pregnancy, implanted devices.
RD2.1's four screening domains are allergies, renal function, pregnancy, and implanted devices — each mapping to a specific hazard (contrast, radiation, or magnetic field).
Click to reveal answer
A 25-year-old presents with chronic medically refractory focal seizures; the team needs detailed structural imaging of the brain to look for a subtle cortical or hippocampal lesion. Which modality is most appropriate?
Correct. MRI is the modality of choice for soft tissue and CNS, giving superior contrast resolution to detect subtle cortical dysplasia or mesial temporal sclerosis that CT would miss.
MRI excels for CNS and soft-tissue detail; CT is for acute/bony/emergent assessment.
Detailed CNS/soft-tissue characterisation is an MRI strength. CT and plain films lack the soft-tissue contrast to show subtle epileptogenic lesions.
Click to reveal answer
A 5-year-old child needs cross-sectional imaging that, if performed by CT, would deliver a significant radiation dose. Applying the patient-axis override in modality selection, which principle should guide the decision?
Correct. RD2.2 requires mindfulness of paediatric radiosensitivity (and sedation needs); where a non-ionising modality answers the clinical question, it is preferred to protect the child from avoidable radiation.
Paediatric patients: shift toward non-ionising modalities where adequate; weigh radiosensitivity and sedation.
Children are more radiosensitive, so the patient axis shifts modality choice toward USG/MRI when they can answer the question — sedation needs are weighed too. CT is not chosen merely for speed in a child.
Click to reveal answer
A 68-year-old presents within 2 hours of sudden-onset dense left hemiparesis; the team must rapidly exclude intracranial haemorrhage before considering thrombolysis. Which is the most appropriate first imaging study?
Correct. In hyperacute stroke, a non-contrast CT head is first-line to rapidly exclude haemorrhage before thrombolysis — it is fast and highly sensitive to acute blood. MRI is slower and not the immediate gatekeeper for thrombolysis decisions.
CT first in acute stroke and trauma — speed plus sensitivity to acute haemorrhage.
Acute stroke is a CT scenario: a non-contrast CT head quickly rules out haemorrhage so that thrombolysis can be considered. MRI is too slow for this time-critical decision, and the other options do not assess the brain.
Click to reveal answer