Spectral Beam Shaping in Unenhanced Chest CT Examinations: A Phantom Study on Dose Reduction and Image Quality

Rationale and Objectives This study aimed to determine the optimal tube potential for unenhanced chest computed tomographies (CTs) with age-related phantoms. Materials and Methods Three physical anthropomorphic phantoms (newborn, 5-year-old child, and adult) were scanned on a third-generation dual-source CT using CAREkV in semi-mode and CAREDose4D (ref. KV: 120; ref. mAs 50). Scans were performed with all available tube potentials (70–150 kV and Sn150 kV). The lowest volume computed tomography dose index (CTDI vol ) was selected to perform additional Sn100-kV scans with matched and half (Sn100-half) CTDI vol value. Image quality was evaluated on the basis of contrast-to-noise ratio (CNR). Results For the newborn phantom, 70–110 kV was selected as the optimal range (0.36–0.37 mGy). Using Sn150 kV led to an increase in radiation dose (0.75 mGy) without improving CNR (96.9 vs 101.5). Sn100-half showed a decrease in CNR (73.1 vs 101.5). The lowest CTDI vol for the child phantom was achieved between 100 and 120 kV (0.78–0.80 mGy). Using Sn150 kV increased radiation dose (1.02 mGy) without improvement of CNR (92.4 vs 95.8). At Sn100-half CNR was decreased (61.4 vs 95.8). For adults, 140 and 150 kV revealed the lowest CTDI vol (2.68 and 2.67 mGy). The Sn150 kV scan delivered comparable CNR (54.4 vs 56.6), but a lower CTDI vol (2.08 mGy). At Sn100-half CNR was comparable to the 150 kV scan (58.1 vs 56.6). Conclusion Unenhanced chest CT performed at 100 kV or 150 kV with tin filtration enables radiation dose reduction for the adult phantom, but not for the pediatric phantoms.