| 1. |
- Almquist, Helén, et al.
(författare)
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Quantitative SPECT by attenuation correction of the projection set using transmission data: evaluation of a method
- 1990
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Ingår i: European Journal Of Nuclear Medicine. - 1432-105X. ; 16:8-10, s. 587-594
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Tidskriftsartikel (refereegranskat)abstract
- A method for measuring attenuation coefficients in single-photon emission tomography (SPECT) is described and evaluated, together with a method for attenuation correction using these measured attenuation coefficients. Build-up, caused by scattered photons, is corrected for by a simple substitution in the algorithms. Transmission studies are performed with a 99mTc- or 57Co flood source, and emission phantom studies with 99mTc line sources. The method is evaluated with variable but well-defined phantoms. The result is accurate attenuation coefficients for different densities, dimensions and geometries, and an accuracy of corrected emission activities of better than +/- 10% in most cases. The present limitations of the method for attenuation correction are discussed.
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| 2. |
- Ljungberg, Michael, et al.
(författare)
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Attenuation correction in SPECT based on transmission studies and Monte Carlo simulations of build-up functions
- 1990
-
Ingår i: Journal of Nuclear Medicine. - 0161-5505. ; 31:4, s. 493-500
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Tidskriftsartikel (refereegranskat)abstract
- The quantitative information in SPECT images is distorted by photon attenuation and contribution of photons scattered in the object. It is, therefore, important to know the distribution of different attenuating tissues in order to be able to perform a proper attenuation correction. A correction method, based on correcting one pixel at a time by using density maps and build-up functions, has been developed. The density map has been produced by transmission measurements of the object using an external, solid 57Co flood source mounted on the scintillation camera head. The outline of the object is accurately defined by the map since the density values outside the object are very close to zero. The build-up of photons scattered in the object has been simulated by a Monte-Carlo code. SPECT-studies with 99mTc, 201T1 and 111In line sources in different parts of a non homogeneous Alderson phantom have been performed. The emission images have been corrected for photon attenuation using the measured density maps and the simulated build-up functions. The results show that quantitative measurements of the radioactivity in nonhomogeneous area can be accomplished to within +/- 10% for different radionuclides by using the attenuation correction described.
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| 3. |
- Ljungberg, Michael, et al.
(författare)
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Comparison of Dual-Window and Convolution Scatter Correction Techniques using the Monte Carlo Method
- 1990
-
Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 35:8, s. 1099-1110
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Tidskriftsartikel (refereegranskat)abstract
- In order to improve the accuracy of SPECT measurements, correction methods have to be used. Two different scatter correction techniques-the dual-window (DW) technique and the convolution (CV) technique-were compared using projection data, simulated by the Monte Carlo method. Comparison with measured data was also made to validate the accuracy of the Monte Carlo code. The main goal was to investigate how well the estimated scatter distributions, using these two scatter correction techniques, fit the simulated, true scatter distribution of the projection data obtained in the photo-peak window. The scatter distributions predicted by the CV technique were found to be consistently lower than those simulated by the Monte Carlo method in the part of the scatter distribution corresponding to the locations of the sources. The DW technique gives lower estimates of the scatter distribution. However, the scatter distribution estimated by the DW technique and the simulated scatter distribution bear a close resemblance to each other.
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| 4. |
- Ljungberg, Michael, et al.
(författare)
-
Scatter and attenuation correction in SPECT using density maps and Monte Carlo simulated scatter functions
- 1990
-
Ingår i: Journal of Nuclear Medicine. - 0161-5505. ; 31:9, s. 1560-1567
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Tidskriftsartikel (refereegranskat)abstract
- A new scatter and attenuation correction method is presented in which Monte Carlo simulated scatter line-spread functions for different depth and lateral positions are used. A reconstructed emission image is used as an estimate of the source distribution in order to calculate the scatter contribution in the projection data. The scatter contribution is then subtracted from the original projection prior to attenuation correction. The attenuation correction method uses density maps for the attenuation correction of projection data. Simulation studies have been done with a clinically realistic source distribution in cylindrical, homogeneous water phantoms of different sizes and with photon energies corresponding to 201T1, 99mTc, and 111In. The results show excellent quantitative results with an accuracy within +/- 10% for most of the source positions and phantom sizes. It has also been shown that the variation in the event distribution within the source region in the images has been significantly decreased and that an enhancement in the contrast has been achieved.
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