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Imaging in urology: ultrasound, CT, MRI and scintigraphy
Each clinical question has its test: ultrasound for first evaluation, in pregnancy and in children; low-dose non-contrast CT for stones; CT urography for haematuria; MAG3 with furosemide for obstruction; DMSA for scars and split function; VCUG for reflux and urethral valves.
Why it matters in the exam
Imaging questions recur in almost every exam: which is the test of choice for a stone, haematuria, scarring or obstruction. Low-dose non-contrast CT detects almost every stone, including uric acid stones, except indinavir stones. CT urography includes an unenhanced phase, a nephrographic phase and an excretory phase (or a split-bolus technique), and shows both the parenchyma and the urothelium. When there is a contraindication to iodinated contrast — MR urography or retrograde pyelography.
In renal scintigraphy: DMSA is a static scan that binds to the cortex, so it is the best test for scars and split function; MAG3 is a dynamic scan that measures drainage, and with furosemide it separates dilatation without obstruction from true obstruction — a clearance half-time over 20 minutes fits obstruction and under 10 minutes normal drainage. VCUG is the test of choice for diagnosing and grading reflux and for posterior urethral valves. Retrograde urethrography shows stricture and injury of the anterior urethra.
Multiparametric prostate MRI is scored by PI-RADS and done before biopsy, and PSMA PET is used for staging and recurrence of prostate cancer. As for iodinated contrast: the risk of kidney injury rises mainly when eGFR is below 30, and then an alternative or hydration is considered; in patients on metformin with eGFR below 30 or with acute kidney injury it is stopped temporarily. In pregnancy — ultrasound first, then MRI without gadolinium, and low-dose CT only when there is no choice.
Key points
- Stone — low-dose non-contrast CT.
- Haematuria — CT urography.
- Obstruction — MAG3 with furosemide.
- Scars — DMSA.
- Reflux — VCUG.
Summary table
| Clinical question | Test of choice | Note |
|---|---|---|
| Suspected stone | Low-dose non-contrast CT | In pregnancy and children — ultrasound |
| Haematuria | CT urography | Without contrast — MR urography |
| Obstruction versus dilatation | MAG3 with furosemide | Clearance half-time over 20 minutes — obstruction |
| Scars and split function | DMSA | Static cortical scan |
| Reflux and urethral valves | VCUG | In boys shows the posterior urethra |
| Prostate cancer | Multiparametric MRI, PSMA PET | PI-RADS before biopsy |
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Sources
- EAU Guidelines on Urolithiasis, 2025 edition — Diagnostic imaging
- ACR Appropriateness Criteria: Hematuria, 2019 — Imaging recommendations
- ESUR Guidelines on Contrast Agents, version 10 (2018) — Post-contrast acute kidney injury
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.
See also: Urinary tract imaging: haematuria, stones, infection, trauma and the transplanted kidney