KEY POINTS
- Technical feasibility study proposing an algorithm to generate effective atomic number and effective physical density images from clinical photon-counting computed tomography virtual monoenergetic images.
- The method used virtual monoenergetic images at 70 and 100 keV and fitted mass attenuation coefficient data to measured linear attenuation coefficients.
- Low-density phantom testing showed effective physical density correlated strongly with reference density, with root mean square error 0.016 g/cm³ and relative root mean square error 5.5%.
- In representative clinical chest images from 2 patients, effective physical density provided clearer contrast for lung lesion assessment than effective atomic number.
- In a lung metastasis example, the nodule had effective physical density 1.07 ± 0.01 g/cm³ versus 0.06 ± 0.02 g/cm³ in surrounding lung tissue; in a pneumonia example, effective physical density decreased by 58% at follow-up.
CLINICAL TAKEAWAY
This study shows that photon-counting computed tomography can generate quantitative effective atomic number and physical density images without a calibration phantom, using virtual monoenergetic images. The concept may be useful for lung lesion characterization because density-based contrast appeared more informative than atomic-number contrast in the examples shown. But the evidence is early: single scanner, phantom validation, only representative clinical cases, and no diagnostic accuracy study.