K-Edge imaging using a clinical dual-source photon-counting CT system

Photon-counting CT (PCCT) enables K-edge imaging, an advanced multi-material decomposition technique that requires multiple energy bins to perform decomposition unconstrained by physical assumptions. The clinical implementation of K-edge imaging applications like dual-contrast imaging could lead to reductions in radiation dose and motion artifacts between sequential scans.

To evaluate the feasibility and performance of K-edge imaging of iodine (I) and gadolinium (Gd) on a clinically available photon-counting computed tomography (PCCT) system.

A dual-source clinical PCCT scanner with four energy thresholds (20, 55, 72, 90 keV) was used to scan phantoms containing single and dual contrast solutions of I and Gd across multiple concentrations (1-10 mg/mL) and radiation doses (1-8 mGy). Multi-material decomposition was performed using a calibration-based, image-domain algorithm to generate material-specific maps. Quantitative accuracy was assessed using Bland-Altman analysis and contrast-to-noise ratio (CNR), while noise and bias trends were statistically analyzed using non-parametric tests.

K-edge imaging was successfully achieved on a clinical PCCT system with accurate decomposition of I and Gd across varying concentrations, solution compositions (single/dual contrast), and dose levels. Quantitative bias was significantly influenced by radiation dose, concentration, and solution composition (p < 0.0004). Increased radiation dose and contrast concentration improved quantification accuracy, with maximum bias reductions of 0.9 (I) and 0.3 mg/mL (Gd). CNR correlated linearly with concentration (R² > 0.99) and moderately with dose (R² = 0.85-0.94), achieving peak values of 13 (I) and 16 (Gd) at 8 mGy. Dual contrast solutions showed reduced performance compared to single contrast solutions, that is CNR of 5 mg/mL Gd solutions increased by 0.6 per mGy in single contrast solutions while by 0.5 per mGy in dual contrast mixtures. Noise was dependent on dose but not on concentration or solution composition.

This study establishes the feasibility of K-edge imaging using a clinical PCCT system and demonstrates accurate, simultaneous decomposition of I and Gd across composition of solution. These findings support the clinical translation of K-edge imaging and highlight PCCT's potential for advanced dual-contrast and molecular imaging applications.