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Empirical timing protocol versus bolus tracking for optimal CT pulmonary angiography
Poster Title: Empirical timing protocol versus bolus tracking for optimal CT pulmonary angiography
Submitted on 07 Sep 2018
Author(s): N Gandy, N Tyagi, M Arora, H Taufik, P Ettienne-Chen, P Karia, HS Chana
Affiliations: Northwick Park Hospital
Poster Views: 733
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Poster Information
Abstract: Method:
All CTPAs performed on three different scanners within a 5 month period were retrospectively reviewed on PACS by a cardiothoracic radiology consultant and four radiology registrars. Reviewers were blinded to the scanning methodology. In both the ET and BT groups, opacification density (OD) of the main pulmonary artery (MPA), segmental pulmonary arteries (SPA), and ascending aorta (AA) were assessed. Image quality, contrast dose and radiation dose-length-product (DLP) were recorded.

A total of 145 scans were evaluated: 74 in the BT group; 71 in the ET group. Mean patient age was 63 years in both groups. Mean ODs in the MPA, SPA and AA were 375±131 HU, 343±144 HU and 259±105 HU for BT; 364±131 HU, 335±133 and 347±133 HU for ET (p=0.61, 0.71 and 0.00002). Average DLP was 428±177 mGycm in the BT group; 333±124 mGycm in the ET group (p=0.0002). Pulmonary embolism positivity rates were 20% and 17% for BT and ET (p=0.42).

Similar contrast opacification can be obtained in the MPA and SPA using either the BT or ET method, but aortic opacification is superior using the ET method with possible implications where aortic assessment is deemed necessary. Radiation doses conferred by the ET method were 23% lower than in the BT group, a feature which may be relevant, particularly in young female patients.
Summary: There is no clear consensus as to the optimal CTPA acquisition method regarding diagnostic accuracy for pulmonary artery emboli (PE). We aim to evaluate empirical timing (ET) and bolus tracking (BT) methods in optimising image quality and radiation dose.

“According to published studies conducted at regional centres CTPA should detect pulmonary emboli in between 15.4 & 37.4% of patients.” RCR
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