Tin filters and lung nodule CT at x-ray exposure levels: Accurate?

Thursday, December 3 | 11:10 a.m.-11:20 a.m. | SSQ19-05 | Room S403B

How well does CT equipped with a tin filter measure lung nodule volumes at radiation dose levels similar to those of a chest x-ray? Pretty well, most of the time, Mayo Clinic researchers will report in this Thursday presentation.

Using an x-ray beam with an added tin filter may allow lung cancer screening CT to be performed at a dose level approaching that of a chest x-ray, according to Chi Ma, PhD, and colleagues from the Mayo Clinic in Rochester, MN.

The study sought to evaluate the accuracy of lung nodule volume measurements at very low dose levels.

"The use of a tin filter to shape the x-ray beam may improve the dose efficiency of a CT system by removing low-energy photons that do not contribute to image quality," explained study co-author Dr. Joel Fletcher in an email to AuntMinnie.com. "We examined this approach using a tin filter for patients of different sizes at routine lung cancer screening chest CT, compared to routine acquisition, and the estimated potential reduction both in terms of image noise and radiation dose."

Using the tin filter maintained the accuracy of automated volume measurements of high-contrast nodules within 2% of the accuracy of the standard dose, the team found. However, accuracy degraded for low-contrast nodules at -800 Hounsfield units due to increased noise.