Dose reduction at pediatric CT possible with ASIR

Radiation dose reduction at pediatric CT has been achieved with 40 percent adaptive statistical iterative reconstruction (ASIR) used as a dose reduction tool only, according to a study published in the January 2014 issue of Radiology.

Reducing dose for pediatric patients undergoing CT is often a difficult task, as substantial reduction leads to increased image noise. However, an ASIR technique was created in 2009 to reduce noise in reconstructed images. “By using the ASIR algorithm to improve image noise in a reconstructed image, ASIR can be used as a dose reduction tool by allowing more noise in an image, by decreasing radiation output, and then cleaning up the noisy, dose-reduced image with the ASIR algorithm,” wrote the study’s lead author, Samuel L. Brady, PhD, of the St. Jude Children’s Research Hospital in Memphis, Tenn., and colleagues,

Brady and colleagues thus designed a study in which they determined a comprehensive method for the implementation of ASIR for maximal dose reduction in pediatric CT without changing the magnitude of noise in the reconstructed image or the contrast-to-noise ratio (CNR) in the patient.

During the study, chest and abdominopelvic CT images performed before ASIR implementation from 183 patient examinations were analyzed for image noise and CNR. Utilizing these measurements with noise models derived from anthropomorphic phantoms, new beam current-modulated CT parameters to implement 40 percent ASIR at 120 and 100 kVp were created without changing noise texture or magnitude. Image noise was then assessed in images obtained after ASIR implementation in 492 patient exams. The study’s authors calculated dose reduction by comparing size-specific dose estimates in the pre- and post-ASIR patient groups.

Results revealed that the average relative dose reduction for chest CT was 39 percent with 40 percent ASIR implementation. The maximum reduction achieved for chest CT was 72 percent. The average relative dose reduction for abdominopelvic CT was 29 percent with a maximum reduction of 64 percent. The difference between zero percent and 40 percent ASIR noise magnitude was less than one HU. There were statistically nonsignificant increases in patient CNR at 100 kVp of eight perfect for chest CT and 13 percent for abdominopelvic CT.

Despite the study’s findings that ASIR can be implemented as a dose reduction-only tool by maintaining pre-ASIR image quality standards, it had several limitations. Of the post-ASIR population, only 19 patients weighed more than 100 kg. Patient dosimetry was performed using SSDE calculation methods, which makes comparison between the findings of other published works difficult. All aspects of image quality were not assessed in the study. One CT scanner from a manufacturer was used, so dose savings calculated in the research may vary among others.