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The triple-rule-out study (TRO) is commonly ordered in our ED to contemporaneously evaluate for obstructive CAD, pulmonary embolism and aortic dissection. Our objective is to assess if the incremental value of doing a triple-rule-out study over routine cardiac CT is high enough to rationalize the additional radiation burden.
Retrospective review of ED patients receiving cardiac CTA from 6/3/2010 to 12/31/2011 was performed. Out of 3267 cardiac CT's, 1079 (33%) triple rule out (TRO) studies were identified, all of which were performed on a 320 detector-row CT scanner utilizing a double volume acquisition technique. Standard demographic data were acquired. Specific review of all TRO studies positive for PE or aortic dissection were re-reviewed by a board certified cardiac imager, and specific determination was made if the cranial “volume” was needed to make a positive identification of acute pulmonary emboli.
Mean patient age was 51.2 years with 55.7% (601/1079) female. The average radiation dose was 10.1 msV. There were no new aortic dissections. Of studies deemed of adequate quality to assess for CAD, 12% (121/1001) demonstrated at least 50% diameter stenosis and were considered borderline obstructive, warranting further urgent workup. There were 9 cases of acute pulmonary embolism for a 0.8% (9/1079) yield. Of the nine new cases, one study demonstrated acute pulmonary emboli that were only detected within the cephalad volume, resulting in an incremental percentage of 0.09% (1/1079) for two volume over single caudal volume techniques. Assuming the cranial half E/DLP conversion factor is 30% less than the caudal half, the cranial half accounted for an average dose per person of 4.4mSv. Laboratory parameters and more patient demographics are being collected.
The majority of the pathology yield from triple rule out studies is from CAD, with a trivial contribution from new pulmonary embolism and none from new aortic dissections. Additionally, excluding the cephalad volume of the triple rule out cardiac CT would incur an effective dose savings to the population of 4748 mSV at the cost of missing less than 0.1% of acute pulmonary emboli and no aortic dissections.
Poster Sessions, Expo North
Saturday, March 09, 2013, 10:00 a.m.-10:45 a.m.
Session Title: Imaging: CT/Multimodality I
Abstract Category: 20. Imaging: CT/Multimodality
Presentation Number: 1140-331
- 2013 American College of Cardiology Foundation