Calculation of Stopping-Power Ratio from Multiple CT Numbers Using Photon-Counting CT System: Two- and...

Area of Science:

• Medical Physics
• Radiological Imaging
• Computational Science

Background:

• The two-parameter-fitting method (PFM) is standard for calculating stopping-power ratios (SPR), crucial for radiation dosimetry.
• Accurate SPR determination is essential in medical imaging, particularly in computed tomography (CT) for dose estimation and material characterization.

Purpose of the Study:

• To introduce and evaluate a novel three-parameter-fitting method (three-PFM) for SPR calculation in multi-spectral CT.
• To compare the accuracy and noise robustness of the three-PFM against the conventional two-PFM using photon-counting CT data.

Main Methods:

• Utilized a photon-counting CT system with various material phantoms (aluminium, graphite, PMMA, biological) at 150 kVp.
• Developed a semi-empirical correction for CT values and applied both two- and three-PFMs to derive effective atomic number, electron density, and mean excitation energy.
• Simulated CT noise to assess the robustness of both fitting methods.

Main Results:

• The three-PFM demonstrated significantly lower maximum relative errors in SPR calculations compared to the two-PFM across all tested materials.
• For aluminium and graphite, maximum relative errors were 7.1% (three-PFM) vs. 17.1% (two-PFM).
• For PMMA and biological materials, maximum relative errors were 2.0% (three-PFM) vs. 5.5% (two-PFM).

Conclusions:

• The three-PFM provides more accurate SPR values, closely matching theoretical predictions.
• The three-PFM exhibits superior robustness against noise in CT data compared to the two-PFM.
• The proposed three-PFM formalism is a promising advancement for quantitative multi-spectral CT applications.