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Dedicated Coronary CT Not Enough to Rule Out Pulmonary Embolism

December 11, 2009
Written by: , Filed in: Emergency Radiology
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Dedicated Coronary CT Not Enough to Rule Out Pulmonary Embolism

A recent study was conducted to assess a dedicated coronary CT protocol’s ability to evaluate for a pulmonary embolism (PE) and aortic dissection in addition to evaluating the coronary arteries.

The study, published in AJR, concludes that dedicated coronary CT scan protocol does not adequately depict the pulmonary arteries in order to exclude pulmonary embolism.

The Study
50 patients presented to the emergency department with suspected acute coronary syndrome (ACS) and underwent a dedicated coronary CT.

Methodology
Exclusion criteria included elevated cardiac biomarkers, ECG changes suggestive of myocardial infarction, and unstable hemodynamics.

All CTs were performed on a 64-MDCT scanner. Images were reconstructed with a slice thickness of 0.75 mm and 0.5-mm increment.

A cardiac field of view 12 to 16 cm from the carina to the apex of the heart was employed.

A beta-blocker was given as needed and sublingual nitroglycerin was given prior to scanning in all patients.

Retrospective ECG-gated reconstructions at 60% to 70% of the R-R interval were created.

In each scan, the coronary artery image quality was graded on a 3-point scale as excellent, adequate, or poor.

In each scan, image quality of the pulmonary arteries was evaluated quantitatively (by means of ROIs) and qualitatively by means of a 3-point scale.

The aorta was also evaluated quantitatively and qualitatively at the level of the aortic sinuses, most cranial level imaged, and most caudal level imaged.

Emergency Radiology The University of Washington School of Medicine, Harborview Medical Center, Department of Radiology * Features case-based presentations with extensive explanations – 15 hours of video * What, when, and how of imaging in relation to specific topics in emergency medicine * Stresses the interaction and communication required to be an effective part of the emergency medicine team * Provides guidance in diagnosis of polytrauma, commonly missed diagnoses, and when to change existing protocols Click here to read more or order: Emergency Radiology

Results
Coronary artery image quality was graded as excellent in 48 of 50 (96%) patients and adequate in the other 2 patients.

Eleven left main pulmonary arteries and 22 left upper lobar pulmonary arteries were not imaged.

Qualitatively, the visualized pulmonary arterial tree demonstrated good opacification with the exception of the right and left lower lobe lateral and posterior segmental pulmonary artery branches (52% to 54% rate of opacification graded as poor.)

Quantitatively, 4 central (8%), 6 lobar (8%), and 206 segmental (29%) pulmonary artery branches had poor contrast opacification (<200 HU).

Ninety-three percent of the upper lobe pulmonary arteries had >200 HU opacification compared with 73% of the lower lobe pulmonary arteries.

Mean contrast opacification of the visualized aorta was 300 +/- 34 HU.

Contrast homogeneity within the aorta was graded as excellent and significant motion or streak artifact limiting evaluation of the visualized aorta was not present.

Conclusions
A dedicated coronary CT protocol provides excellent image quality of the coronary arteries and visualized ascending aorta, but does not adequately show the pulmonary arteries to exclude pulmonary embolism.

Reviewer’s Comments

The authors also observe that a dedicated coronary CT protocol usually does not image the aortic arch, but they note that an isolated aortic arch dissection is rare.

Author: Vineet R. Jain, MD).

Dodd JD, Kalva S, et al. Emergency Cardiac CT for Suspected Acute Coronary Syndrome: Qualitative and Quantitative Assessment of Coronary, Pulmonary, and Aortic Image Quality. AJR; 2008; 191 (September): 870-877

Emergency Radiology The University of Washington School of Medicine, Harborview Medical Center, Department of Radiology * Features case-based presentations with extensive explanations – 15 hours of video * What, when, and how of imaging in relation to specific topics in emergency medicine * Stresses the interaction and communication required to be an effective part of the emergency medicine team * Provides guidance in diagnosis of polytrauma, commonly missed diagnoses, and when to change existing protocols Click here to read more or order: Emergency Radiology
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