V/Q or perfusion-only scintigraphy
Both lungs, multiple projections or SPECT per local protocol
Typical, not policy
Timings, volumes and delays here are representative values drawn from published guidance. Scanner generation, injector, cardiac output and local preference all move them. Confirm against your department's own protocol before you rely on a number.
When to use it
- Suspected pulmonary embolism where CT pulmonary angiography is undesirable — pregnancy, severe contrast allergy, significant renal impairment.
- Requires a normal or near-normal chest radiograph to be interpretable.
Technique
- Perfusion-only imaging is commonly used in pregnancy to reduce dose; local pathways differ on whether ventilation is added.
Where it goes wrong
- Non-diagnostic in the presence of significant parenchymal lung disease — check the chest radiograph before choosing this over CTPA.
Clinical questions that reach this study
Contrast
None
Acquisition
Safety checks this protocol carries
Derived from the contrast agent and phases above, not authored here — which is why they cannot drift apart from what the protocol actually does.
- Intravenous access adequate for the planned injection· radiographer at scan
- Pregnancy status before an ionising exposure· radiographer at scan