Influence of object size on beam hardening in dual energy images: A study using different dual-energy CT systems

Dual-energy CT (DECT) enables material decomposition and artifact reduction. However, beam hardening effects, which vary by DECT system and object size, can impact measurement accuracy. This study investigates the influence of beam hardening across various DECT systems and object sizes.

A polyethylene Mercury phantom with five diameters (16, 21, 26, 31, and 36 cm) was scanned using three DECT systems: fast kilovolt-switching CT (FKSCT), dual-source CT (DSCT), and dual-layer CT (DLCT). Measurements included CT numbers and standard deviations (SD) of virtual monochromatic images (VMI) at 70 keV for iodine inserts, iodine concentrations, and artifact indices (AI) to assess beam hardening artifacts.

CT numbers and iodine concentrations decreased with increasing phantom size for FKSCT and DLCT, with DLCT showing a larger decrease. DSCT exhibited relatively stable CT numbers and iodine concentrations across all sizes. Noise levels (SD) increased significantly with phantom size for DSCT and DLCT, while FKSCT showed a smaller increase. Beam hardening artifacts, as assessed by AI, were the lowest for FKSCT, while DSCT and DLCT exhibited greater artifacts compared to FKSCT, particularly at larger phantom sizes.

The effect of beam hardening varies among DECT systems. FKSCT demonstrated the most stable performance across object sizes, while DSCT and DLCT were more sensitive to object size, affecting measurement accuracy and stability. These findings emphasize the importance of understanding system-specific characteristics to ensure optimal DECT use.

In clinical practice, when using DECT to measure CT numbers and iodine concentration, it is important to understand that the size of the object may be affected by beam hardening, depending on the DECT system.