Validation of the use of calibration factors between the iodine concentration and the computed tomography number measured outside the objects for estimation of iodine concentration inside the objects: phantom experiment.

Purpose: The aim of this study was to validate the use of a calibration factor measured outside the object for estimating the iodine concentration inside the object to improve the accuracy of the quantitative contrast-enhanced computed tomography (CT).

Materials and methods: Several known concentrations (0, 6, 9, and 12 mg I/ml) of iodine contrast material (CM) samples were placed inside and outside cylindrical acrylic phantoms of two sizes and were imaged under various combinations of the tube voltages and currents (kV/mAs-80/200, 100/200, 120/200, 140/200) to obtain K factors. The K factors were compared between the phantoms and among the tube voltages. Each CM concentration was estimated from the CT number using the K factor measured outside the phantom.

Results: The K factors varied between the phantoms or among the tube voltages (P < 0.05). Although there were statistically significant variations in K factors among the different regions in a phantom, the mean variation coefficient was 3%-4%. The mean error of the estimated concentration was -5.5%.

Conclusion: The CM concentration should be accurately estimated at the region within a patient's body using the K factor measured at the surface of the body regardless of body size and tube voltage.