Improving the Accuracy and Detectability of HafO₂ Nanoparticles
Abstract
Purpose
High–atomic number hafnium oxide (HafO₂) nanoparticles have demonstrated potential as radio-enhancers, but their detectability using standard CT calibration is limited. This work aims to (1) establish CT calibration curves for HafO₂ solutions of known concentration and (2) evaluate dual-energy CT’s capability to improve the minimum detectable concentration of standard CT.
Methods
RMI body phantom inserts were filled with aqueous HafO₂ solutions of known concentrations ranging from 0.1% to 10% by weight. CT imaging was performed using a thoracic free-breathing protocol and dual-energy acquisitions. For dual-energy scans, monoenergetic images were reconstructed at multiple energies. Regions of interest corresponding to each insert were analyzed across all image slices, and for each ROI the slice with the maximum mean Hounsfield Unit (HU) value was identified. The corresponding mean HU and noise were recorded.
Results
In thoracic free-breathing images (120 kVp), mean HU increased from 51.5 ±76 at 0.1% concentration to 2,722.6 ± 68.2 at 10%. Dual energy mono energetic images demonstrated enhanced contrast, with 50 keV images yielding mean HU values of 30.2 ± 14.7 at 0.1% and 3,777.5 ± 245.1 at 10%. Noise increased modestly with concentration and did not offset the gain in signal. Dual-energy CT improved the minimum detectability slightly from 0.5% to 0.1%-0.5% range, under sample preparation uncertainties and single-slice image analysis, which need further prudent revision.
Conclusion
CT calibration curves for HafO₂ nanoparticle solutions were successfully established. Dual-energy CT improved nanoparticle detectability by increasing contrast while maintaining acceptable noise levels, supporting its use for improved visualization and quantification of HafO₂ nanoparticles in radiotherapy applications.