All patients underwent triphasic CT scanning on gemstone spectral CT (GE, Discovery HD750), including a TNC scan, a routine arterial contrast-enhanced scan, and a gemstone spectral venous contrast-enhanced scan. The scanning range was from the basis cranii to the upper edge of the aortic arch, according to the recommended thyroid scanning protocol in our institution. During the scanning, the patients were asked to raise the inferior jaw without swallowing and lower the shoulders to avoid clavicle interference. TNC and routine arterial contrast-enhanced scans were both performed with the following scan parameters: tube voltage: 120 kVp, automatic tube current modulation (auto mA), pitch: 0.984, rotation time: 0.8 s, detector coverage: 40.0 mm, slice thickness: 0.625 mm, and slice interval: 0.625 mm. The parameters used for the subsequent gemstone spectral venous contrast-enhanced scan were as follows: fast kV switching between 80 and 140 kVp, tube current: 260 mA, rotation time: 0.8 s, pixel spacing: 0.625 mm, field of view: 25 cm × 25 cm, pitch: 0.984, slice thickness: 5.0 mm, and slice interval: 5.0 mm. After the intravenous injection of contrast medium (3.0–3.5 ml/s, 1.5 ml/kg, Omnipaque, 350 mg·I/ml, GE) via a syringe pump (Bayer Healthcare), routine arterial contrast-enhanced and gemstone spectral venous contrast-enhanced were performed with delays of 30 s and 60 s, respectively. Adaptive statistical iterative reconstruction and automatic tube current modulation techniques were used for dose reduction. Axial images with a slice thickness and slice interval of 1.25 mm were reconstructed. In each scan, the volume CT dose index (CTDIvol, mGy) and dose-length product (DLP, mGy.cm) for each scan were obtained directly from the dosimetry metrics displayed in the CT scanner to estimate the radiation dose.
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