Purpose or Case Report: Patients undergoing lung and stem cell transplants require serial CT examinations and hence dose reduction techniques are mandatory. The newest 3^rd generation dual-source CT scanner incorporates spectral beam shaping at 100 kilovoltage (kVp) using a dedicated tin filter (100 kVp Sn), which improves dose efficiency by removing low-energy photons that contribute little to noncontrast image quality. The purpose of this study was to compare radiation exposure in non-contrast-enhanced pediatric chest CT at 100 kVp Sn imaging and at conventional low kVp imaging in the same patient cohort.
Methods & Materials: This is an institutional review board-approved, retrospective study of 61 children with lung or stem cell transplants (median age 12 years, range 1 month to 21 years) who underwent standard of care, non-contrast chest CT at 2 techniques. Baseline scans were acquired on a 2^nd generation dual-source scanner using conventional 80 or 100 kVp and follow-up scans were performed on a 3^rd generation scanner using 100 kVp Sn. Patients served as their own controls. Scanned volume CT dose index (CTDI_vol) values were recorded and compared. Quantitative image quality metrics, including mean CT attenuation, noise and signal-to-noise ratio (SNR) in the lung parenchyma were calculated in a subset of 37 patients. Subjective image quality was assessed on a 4 point scale (excellent, good, poor, non-diagnostic). Parametric testing of paired samples was performed.
Results: In the same patients, the mean ± standard deviation CTDI_vol was significantly lower in the 100-kVp SN group compared with the conventional CT group (2.35 ± 1.51 mGy vs 0.84 ± 0.18 mGy, P<.0001), representing an average CTDI_vol reduction of 55.5%. Compared to conventional scans, spectral filtration CT had similar lung attenuation (-790 HU vs -804 HU, P > 0.05), reduced noise (70.5 HU vs 59.4 HU, P < .001), and increased SNR (11.6 vs 14.5, P < .001). Subjective image quality was similar for both examinations (P > 0.05).
Conclusions: Pediatric chest CT performed at 100 kVp with tin filtration for spectral shaping allows for significant radiation dose reduction compared with CT performed at 80 or 100 kVp while maintaining image quality. The results support the use of 100 kVp Sn non-contrast enhanced pediatric chest CT in evaluation of the lung parenchyma.