Liver imaging plays a crucial role in diagnosing and monitoring hepatic conditions. While conventional computed tomography (CT) relies on iodine-based contrast agents, these have limitations, particularly in visualising hepatocyte-specific features. Gadolinium-based contrast agents (GBCAs), commonly used in magnetic resonance imaging (MRI), offer potential for liver-specific imaging but are not typically effective for CT due to their lower doses. Recent advancements in photon-counting detector (PCD) CT provide improved spectral resolution, opening new possibilities for visualising GBCAs in liver imaging. A recent study has explored the feasibility of using gadoxetate disodium with PCD CT to achieve enhanced hepatic contrast.
Optimising Contrast in PCD CT
Conventional CT contrast agents primarily use iodine, which provides high X-ray attenuation but lacks hepatocyte specificity. Gadoxetate disodium, a hepatocyte-specific GBCA, accumulates in liver cells and has a prolonged enhancement phase. However, its low clinically approved dose results in insufficient attenuation in traditional CT imaging. The PCD-CT system, with its ability to differentiate photon energies, offers a novel approach to amplify the visibility of GBCAs. This study conducted a phantom analysis to evaluate attenuation levels of various gadoxetate disodium concentrations using PCD CT at different energy levels, including virtual monoenergetic imaging (VMI) reconstructions.
The study employed an anthropomorphic abdominal phantom to simulate in vivo conditions. A series of diluted gadoxetate disodium solutions was tested at concentrations ranging from 0.25 to 2.5 µmol/ml, corresponding with potential in vivo doses of 25 to 200 µmol/kg. Attenuation values were measured across multiple energy levels, with a focus on low-keV virtual monoenergetic images to determine whether PCD CT could enhance visualisation of GBCAs. By analysing the resulting attenuation data, the study aimed to determine whether a meaningful contrast improvement could be achieved within clinically relevant dose ranges.
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Findings and Attenuation Trends
The study demonstrated that attenuation increased with both concentration and decreasing energy levels in PCD CT. At 40 keV, the highest gadoxetate disodium concentration tested (2.5 µmol/ml) achieved an attenuation of 45.2 Hounsfield units (HU), while the clinically approved 0.25 µmol/ml dose reached only 13.0 HU. Extrapolating these results to estimated in vivo conditions suggested that a dose of 200 µmol/kg could theoretically achieve a meaningful hepatic enhancement. However, this dose is significantly higher than the current clinical standard. Despite the promising results, noise levels were notably higher in an anthropomorphic phantom, indicating challenges for real-world applications.
A linear regression model was applied to estimate in vivo hepatic enhancement at different gadoxetate disodium doses. The results indicated that for the standard clinical dose of 25 µmol/kg, estimated hepatic enhancement at 40 keV was only 4.9 HU. This increased to 19.9 HU for a dose of 100 µmol/kg and reached 30.8 HU at 200 µmol/kg. These findings highlight that while PCD CT can enhance GBCA attenuation, the clinically approved dose remains insufficient for reliable contrast enhancement in the liver. Furthermore, image noise was significantly greater in the anthropomorphic phantom, emphasising the need for further refinement of PCD CT acquisition parameters.
Implications and Future Considerations
While PCD CT significantly improves the attenuation of gadoxetate disodium at lower energy levels, clinical translation remains limited by the high doses required for effective imaging. Safety concerns regarding GBCA accumulation and nephrogenic systemic fibrosis necessitate further research into optimising contrast agent formulations and refining PCD CT postprocessing techniques. Potential applications include enhanced liver lesion characterisation, prolonged biliary imaging and alternative imaging options for patients unable to undergo MRI. Future developments in artificial intelligence-driven image processing and dose optimisation may enable the integration of hepatocyte-specific contrast agents into routine CT protocols.
Additionally, refining PCD CT acquisition techniques to minimise image noise and improve contrast-to-noise ratio (CNR) will be essential for clinical implementation. While the findings demonstrate significant potential for hepatocyte-specific contrast enhancement, current limitations necessitate further studies on dose reduction and safety evaluation. The use of artificial intelligence in image reconstruction may help address these challenges by optimising contrast at lower doses. If future research can bridge the gap between necessary and clinically feasible GBCA doses, PCD CT could offer an alternative for liver imaging in cases where MRI is contraindicated or unavailable.
The combination of gadoxetate disodium and PCD CT holds promise for hepatocyte-specific imaging but is currently constrained by dose limitations. While the study demonstrated substantial improvements in attenuation at low keV levels, clinically approved doses remain insufficient for meaningful contrast. Continued research into PCD CT technology, contrast agent refinement and image reconstruction techniques may eventually bridge this gap, allowing CT to leverage liver-specific contrast agents effectively.
Future investigations should focus on optimising GBCA delivery and reducing the required doses while maintaining safety and efficacy. By leveraging PCD CT’s enhanced spectral capabilities, it may become possible to use lower doses of GBCAs while achieving clinically useful contrast. Until then, MRI remains the preferred modality for hepatocyte-specific imaging. However, with further advancements, PCD CT may provide an alternative for liver assessment, expanding diagnostic possibilities and improving accessibility to hepatocyte-specific imaging in clinical practice.
Source: American Journal of Radiology
Image Credit: iStock
