  As photon counting detectors are being explored for medical and industrial
imaging applications, there is a critical need to understand spectral
characteristics of scattered x-ray photons. Scattered radiation is detrimental
to x-ray imaging by reducing image quality and quantitative accuracy. While
various scatter correction techniques have been proposed for x-ray imaging with
conventional energy-integrating detectors, additional efforts are required to
develop approaches for spectral x-ray imaging with energy-resolving PCDs. We
show the benefits of accurate scatter estimation and correction for each energy
bin when using a photon counting detector. We propose a scatter estimation
model that accounts for the energy-dependent scatter characteristics in
projection x-ray imaging. This can then be used to restore quantitative
accuracy for spectral x-ray imaging with PCDs. Results are shown in the context
of contrast-enhanced spectral mammography using dual-energy subtraction to
digitally isolate iodine targets. In the presence of scatter, the projected
iodine densities are increasingly underestimated as the object thickness
increases. The energysensitive scatter correction improves the iodine density
estimation. These results suggest that our scatter estimation model can
accurately account for the energy-dependent scatter distribution, which can be
an effective tool for scatter compensation in spectral x-ray imaging.
Implementing this scatter estimation model does not require any modifications
to the acquisition parameters and is transferable to other x-ray imaging
applications such as tomosynthesis and CT.
