Abstract 706: Detailed Distribution of Acute Pulmonary Thromboemboli: Direct Evidence for Reduction of Acquisition Length and Radiation Dose for Triple Rule Out Computed Tomographic Angiography
Purpose: To reduce the redundant acquisition range and total radiation dose for planning appropriate “Triple rule-out” computed tomographic (CT) angiography (CTA) for acute chest pain, we evaluated the detailed distribution of pulmonary thromboemboli (PTE) in subjects with acute pulmonary thromboembolism.
Materials and Methods: Retrospective review of CT pulmonary angiography (CTPA) (Light speed ultra 16, GE) in 75 subjects (48 females and 27 males; mean age, 57±16 years) with proven acute PTE was performed to determine whether PTE was present solely above the top of the aortic arch or below the undersurface of the heart.
Results: All 75 subjects demonstrated PTE in CT: 58 (77%) had PTE in the right upper lobe but none had PTE that were solely located higher than the top of the aortic arch; 55 (73%) had PTE in the right middle lobe; 60 (80%) had PTE in the right lower lobe, but none had PTE that were solely located lower than the undersurface of the heart. Of the 75 subjects, 61 (81%) had PTE in the left upper lobe and 2 (3%) of them had PTE solely located higher than the top of the aortic arch; both had PTE in the right upper, middle, and lower, and the left lower lobes of the lungs. Of the 75 subjects, 56 (75%) had PTE in the left lower lobe, but none had PTE that were solely located lower than the undersurface of the heart. As the acquisition length in limited CTPA in this population was reduced on average by 21.9% compared with full CTPA, the dose-length product for each examination, from which effective doses were then estimated, would be reduced in the limited CTPA in proportion, estimated at (21.9%) in comparison with full-length CTPA.
Conclusions: In subjects with acute PTE, there were none whose PTE was located solely in the upper lobes which were higher than the top of the arch, nor solely in the lower lobes which were lower than the undersurface of the heart. A limited range CTA for evaluation of PTE only between the top of the arch and the undersurface of the heart could reduce effective radiation doses approximately 22% relative to full chest CTA. A limited range triple rule-out CTA protocol for evaluation of PTE, aortic dissection, and coronary disease would decrease effective doses of CTA and may help the physician find all PE present.