Pairing low-dose CT angiography, model-based iterative reconstruction reduces dose

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Low-dose CT angiography with model-based iterative reconstruction can facilitate a dose reduction up to 73 percent while maintaining diagnostic accuracy for patients who have undergone endovascular aneurysm repair of thoracic and abdominal aortic aneurysms (EVAR), according to a study published in the March issue of the American Journal of Roentgenology.

Though the preferred method of treatment is EVAR for the majority of patients, lifelong imaging surveillance is then necessary. This surveillance is often performed with CT angiography, which emits a large radiation dose. Lead author Neil J. Hansen, MD, of the Nebraska Medical Center in Omaha, and colleagues aimed to evaluate the image quality and overall adequacy of low-dose CT angiography studies reconstructed with model-based iterative reconstruction in patients examined after EVAR. They then compared the imaging method with that of standard dose CT angiography with adaptive statistical iterative reconstruction.

The study included 30 patients whose studies were randomly evaluated by two radiologists. The maximal aneurysm diameter, image noise, and contrast-to-noise ratio were measured.

Results indicated that the mean image score for low-dose CT angiography was acceptable to very good in all categories of assessment. No significant difference was seen between the low-dose CT angiography and the standard dose CT angiography in evaluation of the stent lumen.

The radiologists’ subjective assessments of stent configuration, aneurysm outline, adequacy of vascular imaging, and overall adequacy of solid organ imaging were superior on standard dose CT angiography. No significant difference in the mean aneurysm diameter was seen between the two.

The effective dose of the low-dose CT angiography was 4.4 mSv, while the effective dose of the standard dose was 16.2 mSv during the arterial phase acquisitions. During the delayed phase acquisitions, the effective dose was 2.4 mSv versus 6.7 mSv, respectively. The measured image noise was 14.7 HU for the low-dose CT angiography and was 19.3 HU for the standard dose. The contrast-to-noise ratio, however, was higher for the low-dose CT angiography (25.6 versus 17.1).

“This technique could have a substantive impact on cumulative radiation exposure for patients who will undergo potentially lifelong CT surveillance,” wrote Hansen and colleagues.