CT image acquisition

The following scanning parameters were used: scan mode, helical; helical pitch, 51.0; gantry rotation time, 0.5 s; detector configuration, 0.5 × 80 mm; tube voltage, 120 kVp. For tube current, automatic exposure control with a fixed noise index was used, and the mean CT dose index volume and dose–length product (with scan range) were as follows: 22.8 ± 12.7 mGy and 690.8 ± 286.7 mGy cm (neck only, 18 patients) and 12.4 ± 5.2 mGy and 655.8 ± 320.1 mGy cm (neck to chest, 4 patients). Contrast materials with a concentration of 300 mg I ml⁻¹ were used. The total volume of the contrast material was determined by multiplying the body weight by two with an upper limit of 100 ml (for example, 90 ml for patients weighing 45 kg and 100 ml for patients weighing 60 kg). For patients with renal function impairment, the dose of the contrast material was reduced appropriately. The contrast material was injected within 60 s, and the scan was performed for 60 s (for a scanning range of the neck only) or 90 s (for a scanning range of neck to chest) after initiating the injection of contrast materials.