RD1.1,RD2.1-2 | Imaging Modality Foundations — Assignment

CLINICAL SCENARIO

You are the resident in a busy general medical unit. Over a single morning you receive four imaging requests, each of which requires you to decide on the most appropriate modality and to complete the pre-imaging suitability screen before the request leaves your hands.

1. A 32-year-old woman, 26 weeks pregnant, with right-upper-quadrant pain and suspected gallstones.
2. A 58-year-old diabetic man (eGFR 22 mL/min/1.73m², on metformin) for whom your consultant has written 'CT abdomen with contrast to characterise a renal mass'.
3. A 27-year-old man with chronic refractory focal epilepsy needing detailed structural brain imaging — he mentions he has 'a metal plate in my forearm from an old fracture' and an 'old pacemaker'.
4. A 4-year-old child after a fall, with a clinically suspected forearm fracture.

Case 1 — Pregnant patient with suspected gallstones

State your first-line modality and justify it on physical principles (non-ionising vs ionising) and on biliary suitability. Explain which screening domain dominates here and how pregnancy changes the decision.

Guidance: Recall that USG is first-line for biliary disease and the preferred modality in pregnancy because it is non-ionising and needs no contrast.

Case 2 — Diabetic patient with low eGFR for contrast CT

Critically appraise the consultant's request. Identify the contrast-safety concern and explain what you would do about the iodinated contrast and the metformin. State whether and how the study should be modified, and what alternative could answer the clinical question.

Guidance: Iodinated contrast caution applies at eGFR <30; review/withhold metformin around contrast. Consider whether a non-contrast study or ultrasound can answer the question, and never assume contrast is simply 'safe'.

Case 3 — Epilepsy patient requiring brain MRI with implants

Justify MRI as the modality for detailed CNS/soft-tissue assessment, then run the magnetic-field safety screen. Explain how you would handle the forearm metal plate versus the 'old pacemaker', and what determines whether MRI can proceed.

Guidance: MRI excels for CNS and soft tissue. The magnetic-field screen targets implanted devices; an older non-MRI-conditional pacemaker is a critical concern. MRI contraindications EXIST — never record 'none'. Verify device MRI-conditionality before proceeding.

Case 4 — Child with suspected forearm fracture

Select the modality and justify it. Explain how paediatric radiosensitivity and ALARA shape your approach even for a simple study, and name the regulator responsible for radiation safety in India.

Guidance: Plain X-ray is first-line for bone/fracture. Apply ALARA (time, distance, shielding) and be mindful of paediatric radiosensitivity; the AERB is India's radiation regulator.

Synthesis — A reusable decision framework

In a short closing paragraph, distil a two-question framework you would apply to every imaging request (the clinical problem, then the patient), and explain how it would have prevented any inappropriate request in the four cases above.

Guidance: First fix the pathology type and body region; then let the patient group (adult/child/pregnant) and the suitability screen shift the choice toward the safest modality that still answers the question.