| 11. |
- Ljungberg, Michael, et al.
(author)
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Comparison of four scatter correction methods using Monte Carlo simulated source distributions
- 1994
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In: Journal of Nuclear Medicine. - 0161-5505. ; 35:1, s. 143-151
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Journal article (peer-reviewed)abstract
- Scatter correction in SPECT is important for improving image quality, boundary detection and the quantification of activity in different regions. This paper presents a comparison of four scatter correction methods, three using more than one energy window and one convolution-subtraction correction method using spatial variant scatter line-spread functions. METHODS: The comparison is based on Monte Carlo simulated data for point sources on- and off-axis, hot and cold spheres of different diameters, and a clinically realistic source distribution simulating brain imaging. All studies were made for a uniform cylindrical water phantom. Since the nature of the detected photon is known with Monte Carlo simulation, separate images of primary and scattered photons can be recorded. These can then be compared with estimated scatter and primary images obtained from the different scatter correction methods. The criteria for comparison were the normalized mean square error, scatter fraction, % recovery and image contrast. RESULTS: All correction methods significantly improved image quality and quantification compared to those obtained with no correction. Quantitatively, no single method was observed to be the best by all criteria for all the source distributions. Three of the methods were observed to perform the best by at least one of the criteria for one of the source distributions. For brain imaging, the differences between all the methods were much less than the difference between them and no correction at all. CONCLUSION: It is concluded that performing scatter correction is essential for accurate quantification, and that all four methods yield a good, but not perfect, scatter correction. Since it is hard to distinguish the methods consistently in terms of their performance, it may be that the choice should be made on the basis of ease of implementation.
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| 12. |
- Ljungberg, Michael, et al.
(author)
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Scatter and attenuation correction in SPECT using density maps and Monte Carlo simulated scatter functions
- 1990
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In: Journal of Nuclear Medicine. - 0161-5505. ; 31:9, s. 1560-1567
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Journal article (peer-reviewed)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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| 13. |
- Norrgren, Kristina, et al.
(author)
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A general, extracorporeal immunoadsorption method to increase the tumor-to-normal tissue ratio in radioimmunoimaging and radioimmunotherapy
- 1993
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In: Journal of Nuclear Medicine. - 0161-5505. ; 34:3, s. 448-454
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Journal article (peer-reviewed)abstract
- The aim of this study was to investigate a new extracorporeal immunoadsorption method to improve tumor-to-normal tissue ratios in radioimmunoimaging (RII) and radioimmunotherapy (RIT). We have developed and investigated a general method using biotinylated antibodies and an agarose-avidin column for extracorporeal immunoadsorption. The studies were made in an animal model and extracorporeal immunoadsorption (ECIA) was performed 24 or 48 hr after the injection of 125I-labeled biotinylated antibodies. In athymic rats, heterotransplanted with human malignant melanoma, 90%-95% of the circulating activity was removed with ECIA. The tumor-to-normal tissue ratios at 24 hr was increased 4 times (from 1.2 to 5.1) in the liver, 2.5 times (0.7 to 1.8) in the lung, 4 times (1 to 4) in the kidneys and 4 times (1.4 to 5) in the bone marrow. Whole body activity was reduced by 40%-50%. Tumor-to-organ ratios at 48 hr were increased 3.5 times (from 1.5 to 5.2) in the liver, 2 times (0.9 to 1.7) in the lung, 3 times (1.3 to 3.8) in the kidneys and 4 times (1.4 to 5.5) in the bone marrow. Whole body activity was reduced by 35% when ECIA was performed 48 hr after injection. This study proves that an important reduction in background activity, and thereby an improvement in the tumor-to-background ratio, can be achieved by using this generally applicable, biotin-avidin ECIA method. For RII, the improved ratio increases the possibilities of detecting tumors and metastases in blood-rich organs. For RIT, the procedure may lead to a decreased absorbed dose to bone marrow and other critical organs.
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