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Optimal pulmonary artery opacification for detecting pulmonary embolism-how good was the CT you ordered?
The PE literature is pretty clear about one thing: a CT with well-timed opacification of the pulmonary arteries is very sensitive for detecting pulmonary embolism. This means that there needs to be enough contrast in the central pulmonary arteries to be able to detect clot. So how can you be really sure the PE Protocol CT you ordered is adequate? Have you really ruled out PE?
What does this mean for the emergency physician?
- The pulmonary arteries on CT should be approximately 200 or so Hounsefield units (HU).
- What this means is that you slide the cursor over the pulmonary arteries and see what their HUs are. On the computer screens at UMMS, Hounsefield units are on the bottom of the screen and change as you roll the cursor over different densities (bone, soft tissue, calcium, etc).
- If the central pulmonary arteries are a lot less than 200 Hounesfield units (e.g. 100 HU) the scan would be considered suboptimal.
Some predict that in the future WE (the emergency physician) may in fact be held accountable for knowing whether or not a CTPA (CT Pulmonary Angiography) is optimal or not.
References:
(1) Kline-Carolinas Medical Center (2) Journal of Thrombosis and Hemostasis 2007 (3) AJR 2006,2007