| 31. |
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| 32. |
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| 33. |
- Pan, Tin-Su, et al.
(författare)
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Segmentation of the Body and Lungs from Compton Scatter and Photopeak Window Images in SPECT: A Monte Carlo Investigation
- 1996
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Ingår i: IEEE Transactions on Medical Imaging. - 1558-254X. ; 15:1, s. 13-24
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Tidskriftsartikel (refereegranskat)abstract
- In SPECT imaging of the chest, nonuniform attenuation correction requires use of a patient specific attenuation (p)map. Such a map can be obtained by estimating the regions of 1)the lungs and 2) the soft tissues and bones, and then assigning an appropriate value of attenuation coefficient (p) to each region. We proposed a method to segment such regions from the Compton scatter and photopeak window SPECT slices of Tc-99m Sestamibi studies. The Compton scatter slices are used to segment the body outline and to estimate the regions of the lungs. Locations of the back bone and sternum are estimated from the photopeak window slices to assist in the segmentation. To investigate the accuracy of using Compton scatter slices in estimating the regions of the body and the lungs, a Monte-Carlo SPECT simulation of an anthropomorphic phantom with an activity distribution and noise characteristics similar to patient data was conducted. Energy windows of various widths were simulated for use in locating a suitable Compton scatter window for imaging. The effects of attenuation correction using a p map based on segmentation were also studied. The results demonstrated for the activity and p maps studied herein that: 1) reasonable contrast could be obtained from Compton scatter data for the segmentation of the lung regions, 2) true positive rates of 99% and 89% for determining the body and lung regions, respectively, with total error rates of 4% and 29%, could be achieved, 3) usage of a p map based on segmentation for attenuation correction improved relative quantification over filtered backprojection, 4) variations in the assigned p value of 40% smaller or 40% larger in the lung regions had an insignificant impact on the results of relative quantification, 5) a wide energy window away from the photopeak window for recording scattered events could benefit both the segmentation of the lung regions and the attenuation correction of the activity in the myocardium region, and 6) usage of a smaller than true p value in the lung regions of an assigned p map might benefit attenuation correction for absolute quantification.
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| 34. |
- Sampson, Joshua N., et al.
(författare)
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Analysis of Heritability and Shared Heritability Based on Genome-Wide Association Studies for 13 Cancer Types
- 2015
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Ingår i: Journal of the National Cancer Institute. - : Oxford University Press (OUP). - 0027-8874 .- 1460-2105. ; 107:12
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Tidskriftsartikel (refereegranskat)abstract
- Background: Studies of related individuals have consistently demonstrated notable familial aggregation of cancer. We aim to estimate the heritability and genetic correlation attributable to the additive effects of common single-nucleotide polymorphisms (SNPs) for cancer at 13 anatomical sites. Methods: Between 2007 and 2014, the US National Cancer Institute has generated data from genome-wide association studies (GWAS) for 49 492 cancer case patients and 34 131 control patients. We apply novel mixed model methodology (GCTA) to this GWAS data to estimate the heritability of individual cancers, as well as the proportion of heritability attributable to cigarette smoking in smoking-related cancers, and the genetic correlation between pairs of cancers. Results: GWAS heritability was statistically significant at nearly all sites, with the estimates of array-based heritability, h(l)(2), on the liability threshold (LT) scale ranging from 0.05 to 0.38. Estimating the combined heritability of multiple smoking characteristics, we calculate that at least 24% (95% confidence interval [CI] = 14% to 37%) and 7% (95% CI = 4% to 11%) of the heritability for lung and bladder cancer, respectively, can be attributed to genetic determinants of smoking. Most pairs of cancers studied did not show evidence of strong genetic correlation. We found only four pairs of cancers with marginally statistically significant correlations, specifically kidney and testes (rho = 0.73, SE = 0.28), diffuse large B-cell lymphoma (DLBCL) and pediatric osteosarcoma (rho = 0.53, SE = 0.21), DLBCL and chronic lymphocytic leukemia (CLL) (rho = 0.51, SE = 0.18), and bladder and lung (rho = 0.35, SE = 0.14). Correlation analysis also indicates that the genetic architecture of lung cancer differs between a smoking population of European ancestry and a nonsmoking Asian population, allowing for the possibility that the genetic etiology for the same disease can vary by population and environmental exposures. Conclusion: Our results provide important insights into the genetic architecture of cancers and suggest new avenues for investigation.
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| 35. |
- Strand, Sven-Erik, et al.
(författare)
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Radio-immunotherapy dosimetry with special emphasis on SPECT quantification and extracorporeal immuno-adsorption
- 1994
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Ingår i: Medical & Biological Engineering & Computing. - 0140-0118. ; 32:5, s. 551-561
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Forskningsöversikt (refereegranskat)abstract
- Results from therapeutic trials with radiolabelled monoclonal antibodies are difficult to compare, because of lack of accurate macroscopic and microscopic dosimetry for both tumours and normal tissues. Requirements for such a dosimetry are covered in the paper. Accurate in vivo dosimetric measurement techniques for verification of calculated absorbed doses are also needed to verify treatment planning. In the review, important topics related to dosimetry in therapeutic trials in RIT are covered, such as, absorbed-dose calculations and activity-quantification techniques for planar imaging and SPECT. The latter is particularly discussed, including a summary of different correction techniques. Absorbed-dose calculations and treatment-planning techniques are also discussed. Possible ways of enhancing the therapeutic ratio are reviewed, especially the novel technique with extracorporeal immuno-adsorption. The review could form the basis of the development of future treatment-planning protocols and for dosimetry calculations in radio-immunotherapy, considering some of the most important parameters for approaching an accurate in vivo dosimetry.
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| 36. |
- Tran-Gia, Johannes, et al.
(författare)
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A multicentre and multi-national evaluation of the accuracy of quantitative Lu-177 SPECT/CT imaging performed within the MRTDosimetry project
- 2021
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Ingår i: EJNMMI Physics. - : Springer Science and Business Media LLC. - 2197-7364. ; 8:1
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Patient-specific dosimetry is required to ensure the safety of molecular radiotherapy and to predict response. Dosimetry involves several steps, the first of which is the determination of the activity of the radiopharmaceutical taken up by an organ/lesion over time. As uncertainties propagate along each of the subsequent steps (integration of the time–activity curve, absorbed dose calculation), establishing a reliable activity quantification is essential. The MRTDosimetry project was a European initiative to bring together expertise in metrology and nuclear medicine research, with one main goal of standardizing quantitative 177Lu SPECT/CT imaging based on a calibration protocol developed and tested in a multicentre inter-comparison. This study presents the setup and results of this comparison exercise. Methods: The inter-comparison included nine SPECT/CT systems. Each site performed a set of three measurements with the same setup (system, acquisition and reconstruction): (1) Determination of an image calibration for conversion from counts to activity concentration (large cylinder phantom), (2) determination of recovery coefficients for partial volume correction (IEC NEMA PET body phantom with sphere inserts), (3) validation of the established quantitative imaging setup using a 3D printed two-organ phantom (ICRP110-based kidney and spleen). In contrast to previous efforts, traceability of the activity measurement was required for each participant, and all participants were asked to calculate uncertainties for their SPECT-based activities. Results: Similar combinations of imaging system and reconstruction lead to similar image calibration factors. The activity ratio results of the anthropomorphic phantom validation demonstrate significant harmonization of quantitative imaging performance between the sites with all sites falling within one standard deviation of the mean values for all inserts. Activity recovery was underestimated for total kidney, spleen, and kidney cortex, while it was overestimated for the medulla. Conclusion: This international comparison exercise demonstrates that harmonization of quantitative SPECT/CT is feasible when following very specific instructions of a dedicated calibration protocol, as developed within the MRTDosimetry project. While quantitative imaging performance demonstrates significant harmonization, an over- and underestimation of the activity recovery highlights the limitations of any partial volume correction in the presence of spill-in and spill-out between two adjacent volumes of interests.
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| 37. |
- Tran-Gia, Johannes, et al.
(författare)
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On the use of solid 133Ba sources as surrogate for liquid 131I in SPECT/CT calibration : a European multi-centre evaluation
- 2023
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Ingår i: EJNMMI Physics. - 2197-7364. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- Introduction: Commissioning, calibration, and quality control procedures for nuclear medicine imaging systems are typically performed using hollow containers filled with radionuclide solutions. This leads to multiple sources of uncertainty, many of which can be overcome by using traceable, sealed, long-lived surrogate sources containing a radionuclide of comparable energies and emission probabilities. This study presents the results of a quantitative SPECT/CT imaging comparison exercise performed within the MRTDosimetry consortium to assess the feasibility of using 133Ba as a surrogate for 131I imaging. Materials and methods: Two sets of four traceable 133Ba sources were produced at two National Metrology Institutes and encapsulated in 3D-printed cylinders (volume range 1.68–107.4 mL). Corresponding hollow cylinders to be filled with liquid 131I and a mounting baseplate for repeatable positioning within a Jaszczak phantom were also produced. A quantitative SPECT/CT imaging comparison exercise was conducted between seven members of the consortium (eight SPECT/CT systems from two major vendors) based on a standardised protocol. Each site had to perform three measurements with the two sets of 133Ba sources and liquid 131I. Results: As anticipated, the 131I pseudo-image calibration factors (cps/MBq) were higher than those for 133Ba for all reconstructions and systems. A site-specific cross-calibration reduced the performance differences between both radionuclides with respect to a cross-calibration based on the ratio of emission probabilities from a median of 12–1.5%. The site-specific cross-calibration method also showed agreement between 133Ba and 131I for all cylinder volumes, which highlights the potential use of 133Ba sources to calculate recovery coefficients for partial volume correction. Conclusion: This comparison exercise demonstrated that traceable solid 133Ba sources can be used as surrogate for liquid 131I imaging. The use of solid surrogate sources could solve the radiation protection problem inherent in the preparation of phantoms with 131I liquid activity solutions as well as reduce the measurement uncertainties in the activity. This is particularly relevant for stability measurements, which have to be carried out at regular intervals.
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| 38. |
- Zimmerman, Brian E, et al.
(författare)
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Multi-centre evaluation of accuracy and reproducibility of planar and SPECT image quantification : An IAEA phantom study
- 2017
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Ingår i: Zeitschrift für Medizinische Physik. - : Elsevier BV. - 1876-4436 .- 0939-3889. ; 27:2, s. 98-112
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Tidskriftsartikel (refereegranskat)abstract
- Accurate quantitation of activity provides the basis for internal dosimetry of targeted radionuclide therapies. This study investigated quantitative imaging capabilities at sites with a variety of experience and equipment and assessed levels of errors in activity quantitation in Single-Photon Emission Computed Tomography (SPECT) and planar imaging. Participants from 9 countries took part in a comparison in which planar, SPECT and SPECT with X ray computed tomography (SPECT-CT) imaging were used to quantify activities of four epoxy-filled cylinders containing 133Ba, which was chosen as a surrogate for 131I. The sources, with nominal volumes of 2, 4, 6 and 23mL, were calibrated for 133Ba activity by the National Institute of Standards and Technology, but the activity was initially unknown to the participants. Imaging was performed in a cylindrical phantom filled with water. Two trials were carried out in which the participants first estimated the activities using their local standard protocols, and then repeated the measurements using a standardized acquisition and analysis protocol. Finally, processing of the imaging data from the second trial was repeated by a single centre using a fixed protocol. In the first trial, the activities were underestimated by about 15% with planar imaging. SPECT with Chang's first order attenuation correction (Chang-AC) and SPECT-CT overestimated the activity by about 10%. The second trial showed moderate improvements in accuracy and variability. Planar imaging was subject to methodological errors, e.g., in the use of a transmission scan for attenuation correction. The use of Chang-AC was subject to variability from the definition of phantom contours. The project demonstrated the need for training and standardized protocols to achieve good levels of quantitative accuracy and precision in a multicentre setting. Absolute quantification of simple objects with no background was possible with the strictest protocol to about 6% with planar imaging and SPECT (with Chang-AC) and within 2% for SPECT-CT.
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| 39. |
- Abu-Ghanem, Yasmin, et al.
(författare)
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Limitations of Available Studies Prevent Reliable Comparison Between Tumour Ablation and Partial Nephrectomy for Patients with Localised Renal Masses : A Systematic Review from the European Association of Urology Renal Cell Cancer Guideline Panel
- 2020
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Ingår i: European Urology Oncology. - : Elsevier. - 2588-9311. ; 3:4, s. 423-442
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Forskningsöversikt (refereegranskat)abstract
- The European Association of Urology (EAU) Renal Cell Carcinoma (RCC) Guideline Panel performed a protocol-driven systematic review (SR) on thermal ablation (TA) compared with partial nephrectomy (PN) for T1N0M0 renal masses, in order to provide evidence to support its recommendations. The Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines were followed, and only comparative studies published between 2000 and 2019 were included. Twenty-six nonrandomised comparative studies were included, recruiting a total of 167 80 patients. Risk of bias (RoB) assessment revealed high or uncertain RoB across all studies, with the vast majority being retrospective, observational studies with poorly matched controls and short follow-up. Limited data showed TA to be safe, but its long-term oncological effectiveness compared with PN remains uncertain. A quality assessment of pre-existing SRs (n = 11) on the topic, using AMSTAR, revealed that all SRs had low confidence rating, with all but two SRs being rated critically low. In conclusion, the current data are inadequate to make any strong and clear conclusions regarding the clinical effectiveness of TA for treating T1N0M0 renal masses compared with PN. Therefore, TA may be cautiously considered an alternative to PN for T1N0M0 renal masses, but patients must be counselled carefully regarding the prevailing uncertainties. We recommend specific steps to improve the evidence base based on robust primary and secondary studies.Patient summary: In this report, we looked at the literature to determine the effectiveness of thermoablation (TA) in the treatment of small kidney tumours compared with surgical removal. We found that TA could cautiously be offered as an option due to many remaining uncertainties regarding its effectiveness.
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| 40. |
- Agin, Sol, 1989-
(författare)
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Communicating climate action : Combining action repertoires and linguistic repertoires in social movement message construction
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The climate crisis is one of the largest global challenges that humanity has ever faced. Despite the scientific consensus on the threat, action is not occurring on the pace or level needed to stave off the consequences. As climate change is made up by complex and conjoined causes and effects, the issue is also riddled with communicative challenges which those calling for action need to tackle. Climate change communication research has, however, mainly focus on how traditional news media frame the climate change issue and overlooks climate activist and movement groups. This despite these actors being key for shifting public perceptions and public opinion. Although research on other communication actors exist, it is far from extensive and the research field overlooks the publics perceptions of the sender in relation to the construction of climate messages. Through survey data and an experiment, this doctoral thesis explores the public’s inclination towards different protest action repertoires and addresses the research gap in the climate movement message construction. Herein, the actions and words of three subgroups within the larger environmental movement is considered as one part of a larger message whole. The groups chosen action repertoires are viewed as part of the activists’ performed message and the linguistic communication styles created by lexical choices related to emotional appeals are part of the activists’ verbal/textual message. The results indicate that there is much to be gained from adhering to an alignment between lexical choices and action repertoires. Alignment may be key for understanding why some movement subgroups are successful in inspiring certain actions whilst others inspire other actions. Communication-action alignment is a way to approach the interconnectedness of actions and words for complex and abstract issues that require message recipients to construct consonant mental models to break potential cognitive dissonance.
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