Lung V/Q Scintigraphy

What it does

Lung V/Q Scintigraphy reads the ventilation/perfusion study, the preferred test for pulmonary embolism when CT pulmonary angiography is a poor choice: in pregnancy, in renal failure and in patients with contrast allergy. It is also the screening test for chronic thromboembolic disease before a CTEPH work-up. Upload the ventilation and perfusion images, planar or tomographic, with the CT of a SPECT/CT when there is one.

The run compares the two acquisitions segment by segment. A perfusion defect in a region that is normally ventilated is a mismatch, the scintigraphic sign of embolism; matched defects point to parenchymal or airway disease instead. The result lists the mismatched defects by lung segment and gives the overall call that the EANM guideline asks for: PE present, PE absent or non-diagnostic.

Intended use

Decision support for a study that emergency physicians often need out of hours, when an experienced reader may not be on site: a segment-level map of mismatched defects and a guideline-structured conclusion. In suspected chronic thromboembolic disease, the defect map documents the extent of residual perfusion loss.

Who it is for

Nuclear-medicine physicians and radiologists who report V/Q studies, emergency physicians, obstetric teams and pulmonologists who act on the result, and pulmonary hypertension services screening for CTEPH.

Accepted input

• V/Q SPECT or SPECT/CT: DICOM NM tomographic ventilation and perfusion series, with the low-dose CT when acquired.
• Planar V/Q: DICOM NM static images of the ventilation and perfusion studies in the standard projections.
• Both acquisitions belong to one examination; a perfusion-only study cannot show a mismatch.

Requirements

Requirement	Why
Ventilation and perfusion acquisitions of the same examination	Mismatch is defined by comparing the two
Matching projections or a tomographic acquisition for both	Defects are compared region by region
Original DICOM NM images, not screenshots	Count distribution and segmental mapping need the source data
CT of a SPECT/CT (optional)	Anatomical context for matched defects, such as consolidation or effusion

Tomographic V/Q, the acquisition the EANM 2019 guideline recommends, allows segmental mapping in three dimensions; planar studies are read by projection.

Optional context

Pregnancy, the question asked (acute embolism or chronic thromboembolic disease), recent chest radiograph or CT findings and known lung disease can be passed in clinical_context; they shape the guidance.

The result

Section	Content
Pulmonary embolism	Mismatched perfusion defects by lung segment, matched defects, and an overall call: PE present, PE absent or non-diagnostic
Draft report	Opt-in (options.report): an English narrative that interprets the result for the reader (findings, impression, limitations); every number is checked against the findings

The defects are shown on the ventilation and perfusion images side by side, so each mismatch can be checked against the regions it was drawn from.

Standards

• Guideline: EANM guideline for ventilation/perfusion single-photon emission computed tomography (SPECT) for diagnosis of pulmonary embolism and beyond (2019).
• Reporting: the conclusion categories of that guideline: PE present, PE absent, or non-diagnostic for studies that cannot answer the question.
• Terminology: SNOMED CT and RadLex for findings and lung segments.
• DICOM: Key Object Selection of the images with flagged defects; Encapsulated PDF.

Why segmental mismatch

Embolism blocks blood flow while the airways stay open, so perfusion falls in a region whose ventilation is normal. Counting mismatched defects at the level of lung segments and subsegments is how the EANM criteria separate embolism from the matched defects of pneumonia, emphysema or airway disease.