Abstract
A cone beam circular half-scan scheme is becoming an attractive imaging method in cone beam CT since it improves the temporal resolution. Traditionally, the redundant data in the circular half-scan range is weighted by a central scanning plane-dependent weighting function; FDK algorithm is then applied on the weighted projection data for reconstruction. However, this scheme still suffers the attenuation coefficient drop inherited with FDK when the cone angle becomes large. A new heuristic cone beam geometry-dependent weighting scheme is proposed based on the idea that there exists less redundancy for the projection data away from the central scanning plane. The performance of FDKHSCW scheme is evaluated by comparing it to the FDK full-scan (FDKFS) scheme and the traditional FDK half-scan scheme with Parker's fan beam weighting function (FDKHSFW). Computer simulation is employed and conducted on a 3D Shepp-Logan phantom. The result illustrates a correction of FDKHSCW to the attenuation coefficient drop in the off-scanning plane associated with FDKFS and FDKHSFW while maintaining the same spatial resolution.
Highlights
The use of the half-scan method in cone beam CT has been a hot topic in the recent years owing to the resultant improvement in temporal resolution [1, 2]
In order to correct this drop problem to a certain degree as well as to maintain spatial resolution, we propose an FDK half-scan scheme with a new weighting function that fits the cone beam geometry (FDKHSCW), where the weighting function is cone beam geometry dependent
We found that if we use β = β(1/ 1 + m2ξ2/so2) as the weighting angle for different row projection data, the weighting coefficients in the first redundant region away from the scanning plane are not much different from those calculated in the scanning plane; the biggest difference is below 0.2 percent if Δ = 15◦ and the half cone angle is 15◦
Summary
The use of the half-scan method in cone beam CT has been a hot topic in the recent years owing to the resultant improvement in temporal resolution [1, 2]. The CBFBP algorithm manipulates the redundant projection data in the radon domain; does the half-scan reconstruction in the structure of filtered backprojection (FBP) and achieves almost the same performance as FDKHSFW. The CBFBP-related halfscan and FDKHSFW showed obvious attenuation coefficient drop artifacts in the position of the reconstructed image farthest away from Z = 0, where Z is the rotation axis. In order to correct this drop problem to a certain degree as well as to maintain spatial resolution, we propose an FDK half-scan scheme with a new weighting function that fits the cone beam geometry (FDKHSCW), where the weighting function is cone beam geometry dependent.
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