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

Abstract

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 contrastenhanced 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.