Focal spot rotation for improving CT resolution homogeneity

Focal spot characteristics are one of the key determinants for system resolution. Focal spot size drives source blurring, focal spot aspect ratio using the line focus principle drives resolution loss away from isocenter, and focal spot deflection improves sampling. The purpose of this work is to introduce focal spot rotation as a possible new mechanism to fine-tune resolution tradeoffs. A conventional design orients a rectangular focal spot towards isocenter, with resolution decreasing with distance from isocenter. We propose rotating the focal spot so that it is pointed a small distance from isocenter (for example, to a point 10 cm right of isocenter). This improves resolution to the right of isocenter, decreases resolution slightly at isocenter and decreases resolution significantly to the left of isocenter. In a full scan, each ray passing through a point far from isocenter will be sampled twice, once with a larger and once with a smaller effective focal spot. This data can be appropriately combined during reconstruction to boost the limiting radial resolution of the scan, improving the resolution homogeneity of the scanner. Dynamic rotation of the focal spot, similar to dynamic deflection, can be implemented using electromagnetic steering and has other advantages.