[Monte Carlo Simulation Analysis of Beam Hardening and Iodine Contrast CT Values: Effects of Body Size and Tube Voltage].

PURPOSE: The quantitative accuracy of computed tomography (CT) values in contrast-enhanced CT is affected by tube voltage, body size, and scattered radiation. This study aimed to analyze the influence of these factors on CT values using Monte Carlo simulation and to clarify the usefulness of tube voltage optimization considering body size.

METHODS

The Particle and Heavy Ion Transport code System was used to analyze transmitted X-ray spectra at 80-140 kV in water phantoms (16-32 cm in diameter) containing contrast medium. Sinograms were generated under conditions that included both primary and scattered radiation, and images were reconstructed using the filtered back projection method. CT values in the contrast medium region were then evaluated.

RESULTS

As body size increased, beam hardening progressed, and CT values in the contrast medium region decreased. This decrease in CT values was more pronounced at higher tube voltages, whereas higher CT values were maintained at lower tube voltages even in large phantoms. Scattered radiation further reduced CT values, with a greater effect observed in larger phantoms.

CONCLUSION

Beam hardening and scattered radiation are major factors that reduce the quantitative accuracy of CT values, particularly in larger body sizes. Low tube voltage imaging is effective for stabilizing CT values and maintaining contrast enhancement. These findings support the optimization of tube voltage tailored to body size.