[1] It is a preferred choice of imaging in the diagnosis of PE due to its minimally invasive nature for the patient, whose only requirement for the scan is an intravenous line.

Modern MDCT (multi-detector CT) scanners are able to deliver images of sufficient resolution within a short time period, such that CTPA has now supplanted previous methods of testing, such as direct pulmonary angiography, as the gold standard for diagnosis of pulmonary embolism.

[2] The patient receives an intravenous injection of an iodine-containing contrast agent at a high rate using an injector pump.

A normal CTPA scan will show the contrast filling the pulmonary vessels, appearing as bright white.

Any mass filling defects, such as an embolus, will appear dark in place of the contrast, filling/blocking the space where blood should be flowing into the lungs.

[10] Many hospitals use bolus tracking, where the scan commences when the contrast is detected at the level of the proximal pulmonary arteries.

[3] High contrast flow rate of 4ml/sec through 18G branula at antecubital fossa is recommended to achieve optimal quality images.

However, for those with peripheral arterial disease and those with central venous catheter with low flow rate, 2.0 to 2.5 ml/sec are still manage to produce acceptable images.

This is particularly the case, as patients undergoing CTPA are frequently seriously unwell requiring oxygen treatment and/or close monitoring.