Purpose or Case Report: Limiting radiation exposure while obtaining diagnostic-quality imaging is an essential goal of diagnostic radiology. This is particularly true for computed tomography (CT) scanning in children, who are more susceptible than adults to stochastic effects of radiation exposure. High-pitch technique with iterative reconstruction using modern dual-source CT scanners can reduce CT dose. This method uses some combination of peak kilovoltage (kVp) reduction and tube current modulation while also leveraging dual-source geometry to increase the pitch at which the images are acquired. Our institution recently transitioned to this method of performing CT scans. As part of a quality assurance study, we reviewed the dose exposure to our patients pre- and post-implementation.
Methods & Materials: All CT chest scans with intravenous contrast performed between November 2018 to October 2019 were reviewed retrospectively. This range included 6-month periods before and after our department transitioned to high-pitch scans as our routine method of acquisition in April 2019. Contrast-enhanced chest CT scans were chosen for this audit as they have already been well studied using high-pitch scanning. Scans were obtained using a SOMATOM Force dual-source scanner (Siemens, Germany). Low-pitch and high-pitch groups were compared. Data recorded included patient demographics; technical parameters including kVp, current-time product (mAs), and pitch; and dose measurements including CT volumetric dose index (32-cm phantom) (CTDI_vol32) and dose-length product (DLP).
Results: There were 29 low-pitch scans and 36 high-pitch scans. The two groups did not differ significantly with respect to demographics. Tube current-time product was significantly higher in the high-pitch group (70 mAs vs. 125.5 mAs, p=0.001), while kVp was similar between the two groups. Comparison of mean CTDI_vol32 between the low-pitch and high-pitch groups did not demonstrate any significant dose reduction (2.04 mGy vs. 1.72 mGy, p=0.817).
Conclusions: Early experience with high-pitch dual-source CT imaging at our institution has not demonstrated significant dose savings in pediatric patients. Potential reasons for this finding include already-low dose optimization with low-pitch scans at our site and small group numbers in this analysis. Our CTDI_vol32 average value for high-pitch scans is slightly higher than has been reported elsewhere, and individual scan-specific image quality optimizations may also be increasing dose.