Fan-beam reconstruction algorithm for a spatially varying focal length collimator
- Univ. of Utah, Salt Lake City, UT (United States). Dept. of Radiology
- Duke Univ., Durham, NC (United States). Dept. of Radiology
Fan-beam collimators are used in single photon emission computed tomography to improve the sensitivity for imaging of small organs. The disadvantage of fan-beam collimation is the truncation of projection data surrounding the organ of interest or, in those cases of imaging large patients, of the organ itself producing reconstruction artifacts. A spatially varying focal length fan-beam collimator has been proposed to eliminate the truncation problem and to maintain good sensitivity for the organ of interest. The collimator is constructed so that the shortest focal lengths are located at the center of the collimator and the longest focal length is located at the periphery. The variation of the focal length can have various functional forms but in the authors work it is assumed to increase monotonically toward the edge of the collimator. The authors have derived a reconstruction algorithm for this type of fan-beam collimation. The algorithm is expressed as an infinite series of convolutions followed by one backprojection. However, simulations show that only a small number of N terms in the series are needed to obtain high quality reconstructions. The weighting and convolution are executed N times, then N convolved projections are summed up and one backprojection is performed to obtain the final reconstructed image. The algorithm was tested for two spatially varying focal length formulations. Through computer simulations it is found that if the focal length function is not smooth, a singular artifact is seen in the reconstruction, whereas for smooth functions, the reconstructions are free of artifacts.
- OSTI ID:
- 5641317
- Journal Information:
- IEEE Transactions on Medical Imaging (Institute of Electrical and Electronics Engineers); (United States), Vol. 12:3; ISSN 0278-0062
- Country of Publication:
- United States
- Language:
- English
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