The incidence of pulmonary embolism (PE) is greatly increased in pregnant patients (1 in 1600 pregnancies) and early post partum. PE is the leading cause of maternal death.
The clinical diagnosis of PE is complicated by normal physiological changes during pregnancy. Ventilation perfusion lung scanning (VQ) was the most commonly performed for diagnosis
of PE until the newer technology of Computer Tomography Pulmonary Angiography (CTPA) was introduced in 1990’s. CTPA offers direct imaging of pulmonary arteries and is often favoured
due to its greater availability for PE. Tc-99 labelled MAA is used in VQ scan to assess lung tissue. Patient is imaged on a gamma camera with Single Photon Emission Computer Tomography (SPECT) or planar imaging. Doctors compare perfusion and ventilation images for diagnosis of either normal or positive PE. Positive PE will show mismatch between perfusion and ventilation images. Cold defect with no activity on a perfusion image indicates occlusion of a branch of an artery when no defect on ventilation image of the corresponding perfusion part of the image is detected.
South Western Sydney Local Health District