Academe Learn
CBME Curriculum Preview

Page 8 of 8

RD6.1 | Patient Preparation for Imaging — PBL Case

CLINICAL SETTING

You are the intern attached to a busy radiology department for the morning list. Three patients in the waiting area have all been referred for different imaging studies, and the radiographer asks you to help confirm that each is correctly prepared before they are called in. The list comprises: Mr A (38), referred for an MRI lumbar spine for chronic back pain; Mrs B (34), referred for a transabdominal pelvic ultrasound; and Mr C (59, diabetic on metformin), referred for a contrast-enhanced CT abdomen. As you start checking, several preparation problems and one near-miss begin to surface. Work through the triggers in order and decide, at each step, what should happen before any patient is scanned.

Trigger 1: The MRI near-miss

Mr A is already gowned and waiting outside the MRI room. On reviewing his screening form you notice it was left half-completed — the 'implants/devices' section is blank. When you ask him directly, he mentions casually that he had 'a heart operation years ago' and thinks 'something was put in.' His wife adds that he sometimes sets off shop security alarms. The radiographer is keen not to delay the list.

DISCUSSION POINTS

  • Why is an incompletely filled MRI safety screening form a serious problem rather than a paperwork formality?
  • What specific implanted devices and ferromagnetic hazards must MRI screening actively exclude, and which of Mr A's clues raise concern?
  • What is the correct action now — should the list pressure change your decision? What confirmatory steps are needed before Mr A could ever enter the scanner?
  • How does this near-miss illustrate that MRI contraindications genuinely exist and that verbal re-screening complements the written form?
Click to reveal Trigger 2: The ultrasound that can't be seen (discuss previous trigger first!)

Trigger 2: The ultrasound that can't be seen

Mrs B is called for her transabdominal pelvic ultrasound, but the sonographer reports that the pelvic organs are poorly visualised. On questioning, Mrs B says she went to the toilet just before coming in because she 'didn't want to be uncomfortable during the scan,' and that nobody had clearly told her otherwise. She also volunteers that her period is two weeks late and she 'might be pregnant.'

DISCUSSION POINTS

  • Why was Mrs B's transabdominal pelvic ultrasound suboptimal, and what bladder preparation should she have received and why?
  • How would the bladder instruction differ if she were instead booked for a transvaginal scan?
  • Given the possibility of pregnancy, why is ultrasound an appropriate modality here, and how would the preparation and counselling change if an ionising study had been requested instead?
  • What does this case reveal about the failure of instruction delivery — what should the written-and-verbal preparation have contained?
Click to reveal Trigger 3: The diabetic on metformin (discuss previous trigger first!)

Trigger 3: The diabetic on metformin

Mr C is next for his contrast-enhanced CT abdomen with iodinated contrast. His chart shows type 2 diabetes on metformin and an eGFR of 50 mL/min/1.73m². The referral letter contains no instruction about his metformin, and he tells you he took his usual morning dose with breakfast two hours ago. He is also worried because a friend told him 'the dye can damage your kidneys.'

DISCUSSION POINTS

  • What is the correct metformin instruction for Mr C given his eGFR, and what is the danger if it is ignored?
  • Distinguish the metformin-withholding threshold from the contrast-associated AKI caution threshold — which applies to Mr C?
  • He has already eaten and taken his metformin; what should happen now, and what should have been on the referral and patient instruction sheet?
  • How would you counsel Mr C, in plain language, about the real risks and the steps taken to protect his kidneys?

Group Task Assignments

  • Design a single-page pre-imaging preparation checklist that a clinician could use at the point of referral, with a procedure-specific column for MRI, ultrasound (transabdominal vs transvaginal), iodinated-contrast CT, and barium studies.
  • Draft the key points of a patient-facing instruction sheet for ONE of the three procedures above, then role-play delivering it verbally with teach-back to confirm understanding.
  • List the door-step safety checks the radiology team should perform to verify that preparation actually succeeded for each of the three patients before scanning.

Learning Issues

Research these questions and bring your findings to the discussion.

  1. [RD6.1] What must MRI safety screening exclude (pacemakers/non-conditional devices, cochlear implants, aneurysm clips, intra-ocular metallic foreign bodies), and how do written and verbal screening complement each other?
  2. [RD6.1] Why does transabdominal pelvic/obstetric ultrasound require a full bladder while transvaginal scanning requires an empty bladder?
  3. [RD6.1] What are the rules for metformin and iodinated contrast (withhold for 48 h if eGFR <60, resume after renal review) and how does this differ from the CA-AKI caution threshold of eGFR <30?
  4. [RD6.1] How should pregnancy be excluded before ionising-radiation studies, and how does modality choice change the preparation and counselling for a woman who may be pregnant?
  5. [RD6.1] How should procedure-specific preparation instructions be delivered in both written and verbal form so that each channel covers the other's weakness?