  Purpose: Fast kV-switching (FKS) and dual-layer flat-panel detector (DL-FPD)
technologies have been actively studied as promising dual-energy solutions for
FPD-based cone-beam computed tomography (CBCT). However, CBCT spectral imaging
is known to face challenges in obtaining accurate and robust material
discrimination performance due to the limited energy separation. To further
improve CBCT spectral imaging capability, this work aims to promote a
source-detector joint spectral imaging solution which takes advantages of both
FKS and DL-FPD, and to conduct a feasibility study on the first tabletop CBCT
system with the joint spectral imaging capability developed. Methods: In this
work, the first FKS and DL-FPD jointly enabled multi-energy tabletop CBCT
system has been developed in our laboratory. To evaluate its spectral imaging
performance, a set of physics experiments are conducted, where the multi-energy
and head phantoms are scanned using the 80/105/130kVp switching pairs and
projection data are collected using a prototype DL-FPD. To compensate for the
slightly angular mismatch between the low- and high-energy projections in FKS,
a dual-domain projection completion scheme is implemented. Afterwards material
decomposition is carried out by using the maximum-likelihood method, followed
by reconstruction of basis material and virtual monochromatic images. Results:
The physics experiments confirmed the feasibility and superiority of the joint
spectral imaging, whose CNR of the multi-energy phantom were boosted by an
average improvement of 21.9%, 20.4% for water and 32.8%, 62.8% for iodine when
compared with that of the FKS and DL-FPD in fan-beam and cone-beam experiments,
respectively. Conclusions: A feasibility study of the joint spectral imaging
for CBCT by utilizing both the FKS and DL-FPD was conducted, with the first
tabletop CBCT system having such a capability being developed.
