Ventilation-perfusion scanning is a radiological procedure which is often used to confirm or exclude the diagnosis of pulmonary embolism. It may also be used to monitor treatment.
Ventilation (V) – Achieved by the inhalation of Technetium DTPA. DTPA is an elongated version of EDTA and is a heavy metal chelator. Ventilation is assessed under a gamma camera.
Perfusion (Q) – Achieved by injecting the patient with Technetium 99m, which is coupled with macro aggregated albumin (MAA). An embolus shows up as a cold area when the patient is placed under a gamma camera.
V/Q Scan Results Likelihood of pulmonary embolism according to scan category and clinical probability in PIOPED study 2 6 0 Normal or near normal Clinical probability of emboli 4 15 40 Low 15 28 66 Intermediate 56 86 95 High Low Intermediate High Scan Category
In older CT scanners, the X-ray source would move in a circular fashion to acquire a single slice. Once the slice had been completed, the scanner table would move to position the patient for the next slice.
In helical CT the X-ray source and detectors are attached to a freely rotating gantry. During a scan, the table moves the patient smoothly through the scanner. The name derives from the helical or spiral path traced out by the X-ray beam.