Ultralow-Dose CT Chest = CXR Radiation Dose?
July 10, 2019
Written by Clay Smith
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Ultralow-dose chest CT (ULCT) had perfect diagnostic accuracy for minor traumatic injury to the chest. It was superior to plain CXR and delivered the same, or in several cases, a lower radiation dose.
Why does this matter?
We often obtain a CXR in patients with blunt thoracic trauma as a screening tool. But as CT technology improves, lower-dose techniques may more accurately detect injuries with the same or lower radiation dose than an x-ray. Is that the case here?
CT vs. x-ray = same radiation dose? Yup…
This was a comparison of patients with chest trauma that were hemodynamically stable and had traditional CXR +/- rib series and ULCT. CT was done with a 64 slice scanner without contrast, with iterative reconstruction (which reduces the “noise” from a lower dose scan). A reference CT, with a 1-2 mSv dose, was also done and read by the radiologists in real time as the gold standard. ULCT performed perfectly, with sensitivity 100%, specificity 100% for detecting all patients with at least one finding on reference CT, with no false positives. Plain x-ray had sensitivity 79%, specificity 89%. The radiation dose of ULCT was the same or lower than plain x-ray. ULCT is more expensive than x-ray. It also may or may not change management to find a small pneumothorax, hemothorax, or a couple rib fractures, but it depends. Might it be best to use ULCT instead of CXR in patients for whom we want to screen but not do a full trauma CT chest?
Here are two example images from the supplemental material.
From cited article. “Chest radiographs AP view (A), lateral view (B), and rib series (C). AP view demonstrates fractures that are not completely assessed due to structure superimposition (black arrow) (A), hence, rib series were performed (arrowheads). Lateral view discloses a pneumothorax of which side is not confidently attributable (B). Ultralowdose-CT (D, E, and F) with a single acquisition allows a thorough assessment in every plane thanks to multi planar reformatting. Coronal plane demonstrating 9th rib fracture (arrowhead) (D). Axial plane depicting 7th (arrowhead) and 9th rib fractures (arrow), pneumothorax (asterisk) (E). Moreover, a right pleural effusion is also visible. Sagittal plane showing the displacement of the 8th rib lateral aspect fracture (arrow) (F). Note that the radiograph work-up delivered 200% radiation dose more than ultralowdose-CT.”
From cited article. “Chest radiographs AP view (A) and rib series (B). AP view demonstrates extensive subcutaneous emphysema and pneumomediastium (A). Fracture of the 3rd and 4th ribs were better visualized on rib series view (arrow) as well as pneumomediastinum (arrowheads) (B). Ultralowdose-CT (C, D, E, and F) enables in-depth assessment with a single acquisition. Coronal view demonstrates para-aortic pneumomediastinum (arrows) and subcutaneous emphysema (arrowheads) (C). Magnified axial plane showing 4th rib posterior aspect fracture (arrow) and pneumomediastinum (arrowhead) is also well imaged (D). Note the small circle region circle region of interest within the pleural effusion demonstrating that no hemorrhagic component is within (mean 8.9 HU). Such evaluation would not be feasible on a simple radiograph. Axial plane demonstrating 4th rib lateral aspect fracture (arrow), subcutaneous emphysema (arrowhead), and tracheal bifurcation fluid accumulation (asterisk) (E). Axial oblique plane obtained with multiplanar reconstruction demonstrating a bifocal fracture (arrows) of the 5th rib, not detected on the chest radiograph (F). The radiographic work-up delivered 46.6% radiation dose more than ultralowdose-CT.”
Source
Minor Blunt Thoracic Trauma in the Emergency Department: Sensitivity and Specificity of Chest Ultralow-Dose Computed Tomography Compared With Conventional Radiography. Ann Emerg Med. 2019 Jun;73(6):665-670. doi: 10.1016/j.annemergmed.2018.11.012. Epub 2019 Jan 18.
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