How Well Does Dual-energy CT with Fast Kilovoltage Switching Quantify CT Number and Iodine and Calcium Concentrations?

Publication date: Available online 21 December 2017
Source:Academic Radiology
Author(s): Shingo Ohira, Tsukasa Karino, Yoshihiro Ueda, Yuya Nitta, Naoyuki Kanayama, Masayoshi Miyazaki, Masahiko Koizumi, Teruki Teshima
Rationale and ObjectivesBecause it is imperative for understanding the performance of dual-energy computed tomography scanner to determine clinical diagnosis, we aimed to assess the accuracy of quantitative measurements using dual-energy computed tomography with fast kilovoltage switching.Materials and MethodsQuantitative measurements were performed for 16 reference materials (physical density, 0.965–1.550 g/cm³; diameter of rod, 2.0–28.5 mm; iodine concentration, 2–15 mg/mL; and calcium concentration, 50–300 mg/mL) with varying scanning settings, and the measured values were compared to their theoretical values.ResultsFor high-density material, the maximum differences in Hounsfield unit values in the virtual monochromatic images at 50, 70, and 100 keV were −176.2, 61.0, and −35.2 HU, respectively, and the standard deviations over short- and long-term periods were 11.1, 6.1, and 3.5 HU at maximum. The accuracy of the Hounsfield unit measurement at 50 and 70 keV was significantly higher (P < 0.05) with higher radiation output and smaller phantom size. The difference in the iodine and calcium measurements in the large phantom were up to −2.6 and −60.4 mg/mL for iodine (5 mg/mL with 2-mm diameter) and calcium (300 mg/mL) materials, and the difference was improved with a small phantom. Metal artifact reduction software improved subjective image quality; however, the quantitative values were significantly underestimated (P < 0.05) (−49.5, −26.9, and −15.3 HU for 50, 70, and 100 keV, respectively; −1.0 and −17 mg/mL for iodine and calcium concentration, respectively) compared to that acquired without a metal material.ConclusionsThe accuracy of quantitative measurements can be affected by material density and the size of the object, radiation output, phantom size, and the presence of metal materials.



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