Impact of automatic exposure control on radiation dose and detectability in dual-source and fast kV switching dual-energy CT.

We evaluated radiation dose and detectability changes with automatic exposure control (AEC) according to object size in dual-source (DS) and fast kV switching (FS) dual-energy computed tomography (DECT). A phantom with five section diameters (16-36 cm) was scanned using different AEC settings (DS: Quality Reference mAs [QRmAs] 300-700; FS: Noise Index [NI] 8-12). Volume CT dose index (CTDIvol) and detectability index (d') for iodine were measured. Clinical CTDIvol data from 40 to 80 kg patients undergoing liver dynamic DECT were retrospectively analyzed. In DS-DECT, CTDIvol increased slightly with section diameter but plateaued at QRmAs 600-700 for 31-36 cm (31 cm: 24.1 mGy; 36 cm: 22.5-22.7 mGy), and d' decreased for larger sections. Clinical CTDIvol did not differ significantly among weight groups (40-<50 kg: 21.5 mGy; 50-<60 kg: 22.2 mGy; 60-<70 kg: 22.8 mGy; mean; p = 0.13). In FS-DECT, CTDIvol and d' varied with NI and section diameter: for the 26-cm section, CTDIvol ranged from 15.0 to 30.8 mGy and d' from 37.5 to 59.0; for 36-cm section, CTDIvol was 39.9 mGy and d' 24.0-27.8, with smaller variations than single-energy CT (SECT). Clinical CTDIvol increased with patient weight up to 70 kg (40-<50 kg: 20.3 mGy, 50-<60 kg: 25.8 mGy, 60-<70 kg: 29.2 mGy; mean; p < 0.05). AEC behavior in DECT differs from SECT, causing variations in dose and detectability. Appropriate AEC settings in DECT can achieve image quality comparable to SECT.