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Evaluation of iodine detection and quantification limits in photon-counting CT-a phantom study
Rebecca Titternes1,2, Gavin Poludniowski3,4, Torkel Bo Brismar4,5
1Department of Nuclear Medicine and Medical Radiation Physics, Karolinska University Hospital, Stockholm, Sweden. rebecca.titternes@ki.se.
Objective:
Clinical decisions using CT iodine maps are based on evaluation of contrast enhancement, making it essential to understand how accurately CT systems detect and quantify iodine, yet quantitative evaluations remain scarce, and few studies treat iodine as an analyte for which detection threshold, quantification precision, and measurement linearity can be determined using standard laboratory-science concepts. No study has applied such concepts across photon-counting CT (PCCT) and dual-energy CT (DECT) systems.
Materials And Methods:
Using head and abdominal protocols, test tubes with iodine concentrations (0.0-2.0 mg/mL) were placed in a phantom providing head- and abdomen-equivalent attenuation. Scans were performed at two dose levels per protocol, on two DECT and one PCCT system. Iodine images were reconstructed for repeated scans using varying iterative reconstruction (IR) levels. Limit-of-detection (LoD), limit-of-quantification (LoQ), and lower-limit-of-linear-interval (LLLI) were calculated for two ROI sizes (3 and 10 mm), and differences between scanners were analyzed with Welch ANOVA and Games-Howell tests (α = 0.05).
Results:
PCCT demonstrated significantly lower LoD/LoQ values than the DECT systems across most protocols. For low-dose abdomen (3 mGy, medium-IR), LoD for 3 and 10 mm ROI size were 0.78 and 0.16 mg/mL (PCCT), 1.28 and 0.26 mg/mL (split-filter CT), and 1.42 and 0.57 mg/mL (dual-source CT). LoQ values were also lower for PCCT. Improvements were most pronounced in low-dose protocols, with LoD reductions up to 68% (brain) and 45% (abdomen). LLLI was similar across systems.
Conclusion:
PCCT outperformed DECT in iodine detection and quantification, particularly in low-dose protocols. These findings highlight the potential use of reduced iodine contrast and/or radiation dose.
Key Points:
Question Objective comparison of iodine detection and quantification performance between PCCT and DECT systems remains limited, particularly for low-iodine contrast media doses. Findings PCCT achieved significantly lower detection and quantification thresholds than conventional CT systems, particularly for small lesions and low-dose imaging protocols. Relevance statement Task-based LoD and LoQ metrics enable objective comparison of CT system performance and may provide clinically relevant thresholds for iodine detectability, quantification, and protocol optimization.