Purpose: Spectral CT is not available on all diagnostic systems because of its hardware requirements. A recent proposal is to achieve spectral CT by combining flying focal spot (FFS) with a fixed grating acting as a filter. We demonstrate that standard anti-scatter grid fabrication technologies can be used for this task, and we estimate the spectral separation that could be achieved.
Methods: We envision an anti-scatter grid placed 100 mm from the source and focused at a first FFS focal spot. With a 10:1 grid ratio, the second FFS focal spot should be displaced 10 mm from the first spot to maximize spectral separation. We estimated spectral separation assuming 20 cm of water object filtration, 1.5 mm grid thickness, 0.036 mm lamellae at 60 lp/cm, 120 kVp, and several candidate materials. We provide an experimental tabletop system demonstration. A short focal distance grid was not easily available, so the concept was emulated by placing the grid at focus 105 cm from the source and acquiring two sequential scans with a 9.2 cm shift in source position.
Results: Our experimental demonstration showed separation of multiple materials in a dual energy phantom, including adipose tissue and bone. We estimate 13 keV, 6 keV, and 2 keV spectral separation using a grid with tin, lead, or tungsten lamellae, respectively, with differences due to material K-edge. For comparison, a dual source CT system operating at 100 and 140 kVp provides a spectral separation of 12 keV.
Conclusion: Anti-scatter grids could be combined with FFS for spectral imaging. The grid would need to be modified to have a short focal distance. A respectable spectral separation can be achieved using tin lamellae.