| 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. |
- Ceberg, Crister, et al.
(författare)
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A new method for quantification of image distortion due to pile-up in scintillation cameras
- 1991
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Ingår i: European Journal Of Nuclear Medicine. - 1432-105X. ; 18:12, s. 959-963
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Tidskriftsartikel (refereegranskat)abstract
- Characterization of the count-rate performance of scintillation cameras should include not only the specification of count losses. At high count rates, there is also an image distortion due to the mispositioning of pile-up events. In this paper a simple and clinically relevant procedure to quantify this distortion is presented. The images of a square uniform technetium-99m phantom at high and low count rates are used. The fraction of the total counts being correctly positioned is determined as the peripheral count density divided by the total average count density. This ratio, corrected for the camera non-uniformity at low count rates, is called the 'positioning ability'. According to the National Electrical Manufacturers' Association (NEMA), the 'system count rate performance with scatter' should be reported as the measured count rate giving 20% count losses. In this paper it is suggested that this measure be complemented by a measure of the fraction correct positioned events at this count rate. This fraction, the 'high count rate positioning ability', can be easily and accurately measured using our method. The method has been tested on two different scintillation cameras. For one of them the high count rate positioning ability was determined as 91% at a measured count rate of 30,000 s-1 with 20% count losses. For the other camera, the corresponding figures were 88% at 59,000 s-1 and close to 100% at 38,000 s-1, before and after the installation of a new pile-up rejection circuit, respectively.
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| 3. |
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| 4. |
- Garkavij, Michael, et al.
(författare)
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Improving radioimmonotargeting of tumors. Variation in the amount of L6 MAb administered, combined with an immunoadsorption system (ECIA)
- 1993
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Ingår i: Acta Oncologica. - : Informa UK Limited. - 1651-226X .- 0284-186X. ; 32:7-8, s. 853-859
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Tidskriftsartikel (refereegranskat)abstract
- Extracorporeal immunoadsorption (ECIA) is a new method for the selective removal of circulating radiolabeled monoclonal antibodies (MAb) from plasma to increase the uptake in tumor versus normal tissues (T/N-ratio). To ascertain whether the amount of MAb affects T/N ratios immediately and 24 h after ECIA, we used a rat model with two tumor sites--one intramuscular (im) and one below the subrenal capsule (SR). Extracorporeal immunoadsorption was done with an avidin-agarose column after injection of 125I-labeled biotinylated L6 MAb. The animals received 10, 50 or 250 micrograms of L6 only (controls), or followed by ECIA. The efficacy of the procedure in removing plasma activity was 80-95%. For both tumor sites, the highest T/N-ratios were obtained with 10 micrograms L6. All T/N-ratios significantly improved for SR tumors by a factor ranging from 3.2 (lung) to 12.6 (bone marrow). The T/N-ratios were still elevated 24 h after ECIA. Injection of larger amounts of MAb, probably causing a higher degree of tumor saturation, will not necessarily improve the T/N ratio after ECIA.
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| 5. |
- Garkavij, Michael, et al.
(författare)
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Improving radioimmunotargeting of tumors: the impact of preloading unlabeled L6 monoclonal antibody on the biodistribution of 125I-L6 in rats
- 1994
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Ingår i: Journal of nuclear biology and medicine (Turin, Italy : 1991). - 0368-3249. ; 38:4, s. 594-600
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Tidskriftsartikel (refereegranskat)abstract
- In the radioimmunotherapy of malignancies the uptake of monoclonal antibodies (MoAb) is commonly low in tumors compared with normal tissue. Several methods have been suggested to increase the tumor-to-normal tissue (T/N) ratio. In this study we have investigated the biodistribution of different amounts of 125I-L6-biotin MoAb in combination with a preload of unlabeled L6 MoAb. Nude rats were injected with 50 micrograms or 250 micrograms of unlabeled L6 24 hours prior to the injection of 10 micrograms, 50 micrograms or 250 micrograms of 125I-L6, antipancarcinoma MoAb. Dissections were performed 24 hours after the injection of radiolabeled MoAb. The maximal enhancement of tumor uptake with simultaneously decreased uptake in normal tissues was with 250 micrograms of 125I-L6 preceded by a preload of 50 micrograms unlabeled L6. Mean T/N ratios were improved by a factor of 2.9 for bone marrow, 3.4 for liver, 3.7 for lungs and 2.3 for kidneys as compared with the corresponding controls. This study demonstrated that preinjection of optimal amounts of unlabeled L6 MoAb may increase the uptake of 125I-L6 by tumor and improve the T/N ratios. Based on present data, preloading with unlabeled MoAb should be considered in future clinical studies with immunoconjugates to improve the radioimmunotargeting of tumors. It is essential to titrate an appropriate amount of the preload, thus avoiding possible tumor antigen saturation of unlabeled MoAbs but simultaneously decreasing the uptake of subsequently injected radiolabeled MoAb in normal tissues.
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| 6. |
- Jönsson, Bo-Anders, et al.
(författare)
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A quantitative autoradiographic study of the heterogeneous activity distribution of different indium-111-labeled radiopharmaceuticals in rat tissues
- 1992
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Ingår i: Journal of Nuclear Medicine. - 0161-5505. ; 33:10, s. 1825-1833
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Tidskriftsartikel (refereegranskat)abstract
- In light of the increased interest in small scale dosimetry, this paper presents a quantitative autoradiographic method for evaluation of heterogeneous activity distribution in tissues. This was studied in rat tissues after administration of 111In-chloride, -oxine, -tropolone, 111In-labeled homologous blood cells and 111In-anti-CEA-F(ab')2, using quantitative whole-body autoradiography. Quantification was performed utilizing an image analyzing system designed for whole-body autoradiographs. Very heterogeneous activity distribution was found in several tissues including the liver, spleen, kidneys, bone marrow, lymph nodes and testes. Notable was the high 111In uptake in organs characterized as rapidly proliferating, and known to have numerous transferrin receptors. In the gastrointestinal tract, all activity was associated with the intestinal walls. The heterogeneous tissue distribution shown in this investigation accentuates the necessity for performing detailed studies of the tissue distribution of radiopharmaceuticals. This is especially important for the radiation dosimetry of radionuclides emitting beta-particles or low energy electrons. We suggest whole-body autoradiography as an excellent implement to determine local activity concentrations in organs and tissues necessary for accurate absorbed dose calculations
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| 7. |
- Jönsson, Bo-Anders, et al.
(författare)
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Radiation dosimetry for indium-111-labeled anti-CEA-F(ab')2 fragments evaluated from tissue distribution in rats
- 1992
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Ingår i: Journal of Nuclear Medicine. - 0161-5505. ; 33:9, s. 1654-1660
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Tidskriftsartikel (refereegranskat)abstract
- Accurate dosimetric investigations are important to be able to fulfill the ambition of radiation protection in nuclear medicine and to minimize the radiation burden to the patient. This paper presents human radiation absorbed dose estimates following an administration of an 111In-labeled anti-CEA-F(ab')2 (BW431/31) based on detailed biodistribution and elimination data in a rat model. Animals were followed from the time of injection up to 28 days after injection. A significant initial uptake of 111In in the bone marrow, 25% of injected activity, was evident after 6 hr. The kidneys showed a maximal uptake of 20% at 24 hr. At the end of the study, 27% of the activity was still retained in the whole body. The estimated humans absorbed dose to the kidneys, testes, spleen and bone marrow was 2.27, 0.80, 0.51 and 0.37 mGy MBq-1, respectively. The effective dose was estimated to 0.27 mSv MBq-1. The tissue distribution in rats was comparable to that in humans, which was confirmed by whole-body scintigrams and human biopsies
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| 8. |
- Ljungberg, Michael, et al.
(författare)
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Attenuation and scatter correction in SPECT for sources in a nonhomogeneous object: a monte Carlo study
- 1991
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Ingår i: Journal of Nuclear Medicine. - 0161-5505. ; 32:6, s. 1278-1284
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Tidskriftsartikel (refereegranskat)abstract
- Single-photon emission computed tomography (SPECT) is important for imaging radioactivity distributions in vivo. Quantitative SPECT is limited due to attenuation and scatter contribution. Approximations such as constant attenuation and mono-exponential scatter functions will not be valid for non-homogeneous regions. A correction method is described where non-uniform density-maps are used in the attenuation correction. Correction for non-uniform scatter is made by a convolution technique based on scatter line-spread functions (SLSF) calculated for different locations inside a clinically realistic, nonhomogeneous, computer phantom. Calculations have been made for a myocardiac source, a uniform source in the lungs and a tumor located in the lungs. Projections were simulated for photon energies corresponding to 201Tl, 99mTc, and 111In. The results show that quantitative images can be obtained in nonhomogeneous regions. An increased contrast has also been demonstrated in the SLSF-corrected images. Comparison with measurements have been made to validate the Monte Carlo code and the scatter and attenuation method.
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| 9. |
- 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
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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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| 10. |
- Ljungberg, Michael, et al.
(författare)
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Comparison of Dual-Window and Convolution Scatter Correction Techniques using the Monte Carlo Method
- 1990
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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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