The authors studied the artifacts generated by the application of methods of crystal efficiency calculation based on the fan-sum, to situations of high variability of efficiency, namely the cases of a ring with defective blocks and acquisitions using narrow energy windows. The authors propose two efficiency calculation methods to reduce these artifacts: one method discriminates the crystals with an efficiency very different from the average, and then uses a modification of the fan-sum to estimate the efficiency; the other method calculates iteratively the fan-sum of each crystal, weighted by the efficiencies of the opposed detectors. The effect of using an off-center uniform cylinder is also discussed, since it influences the performance of the algorithms. The proposed algorithms are compared with the more conventional fan-sum method and with an algorithm used in commercial tomograph, using measurements and simulations. The results show a significant reduction of the efficiency estimation errors, in severe situations where detectors in a ring have very different detection efficiency.
[1]
Magnus Dahlbom,et al.
PET system calibrations and corrections for quantitative and spatially accurate images
,
1989
.
[2]
Calibration of detector sensitivity in positron cameras
,
1990
.
[3]
A Geissbuhler,et al.
A normalization technique for 3D PET data.
,
1991,
Physics in medicine and biology.
[4]
Calculation of single detector efficiencies and extension of the normalization sinogram in PET.
,
1997,
Physics in medicine and biology.
[5]
P K Marsden,et al.
Algorithms for calculating detector efficiency normalization coefficients for true coincidences in 3D PET.
,
1998,
Physics in medicine and biology.
[6]
E. Hoffman,et al.
Quantitation in positron emission computed tomography: 7. A technique to reduce noise in accidental coincidence measurements and coincidence efficiency calibration.
,
1986,
Journal of computer assisted tomography.