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

Abstract

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 (CTDI_vol) and detectability index (d') for iodine were measured. Clinical CTDI_vol data from 40 to 80 kg patients undergoing liver dynamic DECT were retrospectively analyzed. In DS-DECT, CTDI_vol 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 CTDI_vol 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, CTDI_vol and d' varied with NI and section diameter: for the 26-cm section, CTDI_vol ranged from 15.0 to 30.8 mGy and d' from 37.5 to 59.0; for 36-cm section, CTDI_vol was 39.9 mGy and d' 24.0-27.8, with smaller variations than single-energy CT (SECT). Clinical CTDI_vol 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.