Computed tomography (CT) plays a vital role in medical diagnostics, often relying on iodinated contrast media (ICM) to enhance visualisation of anatomical structures. However, the use of ICM carries potential risks, particularly for patients with renal insufficiency, and contributes to healthcare costs and environmental waste. Recent advances in photon-counting computed tomography (PCCT) present an opportunity to mitigate these challenges. By leveraging virtual monoenergetic images (VMIs) and improved noise performance, PCCT may allow significant reductions in iodine dosage without compromising image quality. A phantom-based study published in European Radiology Experimental compared PCCT with traditional energy-integrating CT (EICT) to evaluate this potential in abdomen-pelvis protocols.
Improved Imaging Through Photon-Counting Technology
Photon-counting CT systems utilise detectors capable of measuring individual photon energies, resulting in enhanced spatial resolution and reduced electronic noise. These technological improvements yield superior image quality, particularly in VMIs generated at lower energy levels. In the study, VMIs at 40, 50, 60 and 70 keV were evaluated for both PCCT and EICT using a multi-energy abdominal phantom. At energy levels from 40 keV to 70 keV, PCCT consistently demonstrated lower noise values compared to EICT, with reductions ranging from approximately 49% to 25%. This noise suppression translated into significantly higher contrast-to-noise ratios (CNR) for iodine concentrations above 1 mg/mL, particularly at lower keV levels. The improved CNR is crucial for clinical diagnostics, as it directly influences the detectability of iodine-enhanced structures in abdominal imaging.
Quantifying the Potential for Iodine Reduction
The study assessed whether PCCT's improved CNR could be leveraged to reduce iodine concentration while maintaining diagnostic image quality. Using a linear correlation between iodine concentration and CNR, the researchers calculated the iodine reduction potential at different energy levels. The highest reduction was observed at 40 keV, with PCCT enabling a decrease of nearly 49% in iodine use while preserving the CNR equivalent to EICT. This potential diminished as the monoenergetic level increased, falling to about 24% at 70 keV. Moreover, using 40 keV with PCCT instead of 60 keV with EICT increased the iodine reduction potential to approximately 57%. These findings indicate that PCCT not only improves image quality at given energy levels but also expands flexibility in selecting lower keV settings, further amplifying contrast efficiency and enabling greater iodine conservation.
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Clinical Implications and Considerations
While the results demonstrate a strong case for PCCT's role in reducing ICM use, clinical translation requires cautious adaptation. The study used a controlled phantom setup, limiting direct applicability to patient imaging where anatomical variability and motion artifacts may affect outcomes. Furthermore, accurate tailoring of injection protocols will be essential to replicate phantom-based results in clinical settings. Ensuring similar contrast distribution across tissues during image acquisition will require adjustments in injection volume and rate, particularly when switching from EICT to PCCT protocols. Nevertheless, the findings align with previous research in pulmonary and cardiac imaging, suggesting consistent advantages of PCCT across multiple anatomical regions. The ability to maintain diagnostic quality while reducing iodine dosage also carries broader benefits, such as lowering the risk of contrast-induced complications and reducing the environmental burden from iodine waste.
The study confirms that photon-counting CT offers significant improvements over conventional energy-integrating CT in abdomen-pelvis imaging. By enhancing the contrast-to-noise ratio of virtual monoenergetic images, particularly at lower energy levels, PCCT enables substantial reductions in iodine contrast media without sacrificing image quality. These findings support the integration of PCCT into clinical practice, with the potential to improve patient safety, optimise resource use and support sustainable imaging practices. Further studies involving patient data will be crucial to validate and refine these findings for broader clinical implementation.
Source: European Radiology Experimental
Image Credit: Freepik
