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RD1.1,RD2.1-2 | Imaging Modality Foundations — Practice Quiz
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A 6-week-old infant presents with a palpable abdominal mass thought to be of renal origin. The paediatrician wants first-line cross-sectional assessment of the kidneys. Which imaging modality is most appropriate as the initial investigation?
Correct. Ultrasound is the first-line modality for renal assessment in infants — it is non-ionising, requires no sedation or contrast, and resolves renal anatomy well, which is especially important given paediatric radiosensitivity.
USG is first-line for renal, biliary, obstetric and paediatric imaging because it avoids ionising radiation and contrast.
Ultrasound is preferred as the first-line renal investigation in an infant because it is non-ionising and needs no contrast or sedation, sparing a radiosensitive child unnecessary radiation.
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A clinician is reasoning about which modality best demonstrates a small amount of free air under the diaphragm in suspected perforation. On physical principles, which statement correctly explains the appropriate choice?
Correct. Air-containing structures are imaged better on X-ray than on ultrasound; ultrasound beams are scattered/reflected at air interfaces, obscuring deeper structures, whereas free air is clearly seen as lucency on an erect radiograph.
Ultrasound performs poorly across air interfaces; air-containing structures are better demonstrated on X-ray.
Gas scatters the ultrasound beam, so USG is poor for free air. By contrast, air is well seen on X-ray — air-containing structures are imaged better on X-ray than on ultrasound (the worked example in competency RD1.1).
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Which one of the following imaging modalities does NOT deposit ionising radiation in the patient?
Correct. MRI uses a static magnetic field and radiofrequency pulses — no ionising radiation. CT, fluoroscopy and nuclear medicine (bone scan) all deliver ionising radiation.
Ionising = X-ray, fluoroscopy, CT, nuclear medicine; non-ionising = ultrasound and MRI.
MRI is non-ionising (magnetic field + radiofrequency). CT, fluoroscopy and Tc-99m bone scan all involve ionising radiation.
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In India, which statutory body is the radiation regulator responsible for radiation safety standards in diagnostic imaging?
Correct. The AERB (Atomic Energy Regulatory Board), constituted under the Atomic Energy Act 1962, is India's radiation regulator. The NRC is the US body and the ICRP issues international recommendations but is not a national regulator.
AERB regulates radiation safety in India; ICRP/NRC are international/US bodies, not the Indian regulator.
For India the regulator is the AERB (Atomic Energy Regulatory Board). The NRC is American; the ICRP only makes international recommendations.
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A 58-year-old man with type 2 diabetes is scheduled for a contrast-enhanced CT. His eGFR is 24 mL/min/1.73m². Regarding iodinated contrast and his metformin, which action is most appropriate?
Correct. An eGFR <30 is a recognised caution for iodinated contrast (contrast-associated AKI risk), and metformin should be reviewed/withheld around contrast administration in significant renal impairment. Gadolinium is an MRI agent, not used for CT.
Iodinated contrast caution: eGFR <30 and metformin; assess renal function before ordering.
eGFR <30 is a key caution for iodinated contrast, and metformin needs review around the study. Gadolinium is not a CT agent, and imaging is not absolutely banned — it is modified after risk assessment.
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A patient is referred for MRI. Which item from the pre-imaging screen is the most important absolute safety concern specific to the MRI environment?
Correct. The MRI safety checklist exists because the strong static magnetic field is hazardous to ferromagnetic and electronic implants; a non-MRI-conditional pacemaker is a critical contraindication. Iodinated-contrast/shellfish history is irrelevant to magnetic-field safety.
MRI screening targets implanted devices/ferromagnetic material; MRI contraindications exist — never say 'none'.
MRI screening is about magnetic-field hazards — implanted devices (e.g., a non-conditional pacemaker) are the key concern. Iodinated contrast and shellfish allergy do not bear on magnetic-field safety.
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A 30-year-old woman at 28 weeks' gestation presents with right-upper-quadrant pain and suspected gallstones. Which is the most appropriate first-line imaging modality?
Correct. Ultrasound is first-line for biliary pathology and is the modality of choice in pregnancy because it is non-ionising and needs no contrast — it answers the gallstone question directly while protecting the fetus.
USG is first-line for biliary disease and the preferred modality in pregnancy (non-ionising, no contrast).
Biliary disease is assessed first with ultrasound, and in pregnancy the non-ionising nature of USG makes it the clear first choice over CT, plain film or scintigraphy.
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A 40-year-old man is brought in after a high-speed road traffic accident with reduced consciousness and possible multi-system injury. Which modality is most appropriate for rapid assessment of acute trauma including the head?
Correct. CT is the modality of choice in acute major trauma — it is fast, widely available, and excellent for acute haemorrhage, fractures and visceral injury. MRI is too slow for an unstable trauma patient, and ultrasound of the adult skull is not useful for brain injury.
CT is first-line for acute trauma and acute stroke; MRI excels for soft tissue/CNS in stable patients.
Acute trauma (and acute stroke) is a CT scenario: speed, availability and sensitivity to acute blood and fractures. MRI is too slow for the unstable patient and head ultrasound does not assess the adult brain.
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