Commissioning of a Compton camera for medical imaging

The interest of using hadron-therapy in cancer treatment, particularly for tumors in the vicinity of critical organs-at-risk, is continuously growing due the ability of this treatment modality to provide high precision dose delivery. In order to fully exploit this beneficial property, it is mandatory to ensure that the well-localized dose deposition (Bragg peak) is located in the tumor volume. This calls for a precise in-vivo monitoring of the particle (proton, ion) beam stopping range. Therefore, the purpose of our project is to develop an in-vivo imaging system based on a Compton camera to verify the particle beam range by detecting (multi-MeV) prompt γ rays, generated as a result of nuclear reactions between the particle beam and biological tissue. In the context of this thesis the prototype of the LMU Compton camera was considerably improved and upgraded, and characterized both in the laboratory as well as under online conditions with particle beams at various accelerator facilities. The Compton camera consists of two main components: a scatterer (tracker), formed by a stack of six double-sided Si-strip detectors (DSSSD), and a monolithic LaBr 3 :Ce scintillation detector (5x5x3 cm 3 ), acting as absorber. The highly segmented DSSSD detectors, each with 128 strips per side (strip pitch: 0.39 mm), is processed by a compact ASIC-based electronics (1536 signal channels), while the scintillation detector is read out by a 256-fold segmented, position-sensitive multi-anode photomultiplier tube, providing energy and time information for each PMT segment. The stacked design of the LMU Compton camera scatter detector allows not only to reconstruct the incident photon origin, but it also allows to track Compton scattered electrons, thus enhancing the reconstruction efficiency compared to the conventional design. The Compton camera absorber (LaBr 3 :Ce scintillator crystal) was characterized in two different side-surface wrapping scenarios, absorptive and reflective. (Position-dependent) energy resolution and time resolution were determined for both coating scenarios, revealing the superior properties of the advanced scintillator material in case of the reflectively coated crystal, providing excellent energy (position independent: ∆E/E =3.8 % at 662 keV) and time resolution (273(6) ps FWHM). In addition, the impact of the crystal wrapping options on the scintillation light distribution was studied by extracting the Light Spread Function (LSF) from the crystal irradiation with a collimated 137 Cs source. Here, as can be expected, the absorptively coated crystal reveals a slightly better FWHM value of the LSF compared to the reflectively coated detector. Nevertheless, the drastic improvement of the other properties with reflective coating motivated this choice for the Compton camera absorber. The capability of the monolithic LaBr 3 :Ce scintillator to provide the γ-ray interaction position, which is a mandatory prerequisite for the targeted photon source reconstruction based on Compton scattering, was determined by applying two specific algorithms (’k-nearest neighbor’(k-NN) and ’Categorical Average Pattern’ (CAP)). These algorithms require a large reference data base of 2D scintillation light amplitude distributions, acquired by perpendicularly irradiating the scintillator front surface with a tightly (1 mm diameter) collimated photon source on a fine grid (0.5 mm step size). Two γ-ray sources, 137 Cs and 60 Co, were used to generate the required reference libraries in order to study the energy-dependent spatial resolution of the LaBr 3 :Ce scintillator. Systematic parameter studies were performed as a function of the photon energy, PMT granularity, irradiation grid size and number of photopeak events acquired in each of the 10 4 irradiation positions. Optimum values for the spatial resolution were achieved with 4.8(1) mm (FWHM) at 662 keV and 3.7(1) mm (FWHM) at 1.3 MeV using the CAP algorithm,thus almost reaching the final design goal of 3 mm envisaged for the prompt-γ energy region of 4-6 MeV. With the observed trend of improving spatial resolution with increasing photon energy, it will be interesting to study this property beyond the realm of γ-ray calibration sources in the higher energy region beyond 4 MeV, provided the availablility of an intense, monoenergetic and collimated photon beam. Furthermore, the Compton camera has been commissioned at different particle beam facilities. The camera components were first calibrated and characterized with monoenergetic 4.44 MeV γ rays generated via the nuclear 15 N(p,αγ) 12 C ∗ reaction at the Helmholtz-Zentrum Dresden Rossendorf (HZDR). The response of both the scatter and absorber detectors was found in good agreement with Monte-Carlo simulations. Moreover, the time-of-flight (TOF) measurement capability of the absorbing scintillator was studied at the Garching Tandem accelerator, using a 20 MeV pulsed (400 ns) deuteron beam hitting a water phantom, showing prompt γ rays well separated from the slower neutron background. The camera was finally commissioned with different clinical proton beams (100 MeV, 160 MeV and 225 MeV) at the research area of the Universitäts Protonen Therapie Dresden, stopping either in a water or a PMMA phantom. Energy spectra were acquired and separated into their prompt and delayed components, extracting the prompt photon contribution via TOF. The Compton electron energy deposit in each DSSSD layer was determined and found in very good agreement with simulation expectations. Hit multiplicities and the correlated electron tracking capability of the scatter/tracker array were investigated and limitations imposed by the present ASIC-based readout electronics, as well as options for further improvements, were identified

Decolonizing Approaches to Human Rights and Peace Education Higher Education Curriculum

While the project of decolonization within higher education has become important in recent years (Kester et al., 2019), human rights and peace education specifically have undergone critique (Coysh, 2014; Al-Daraweesh and Snauwaert, 2013; Barreto, 2013; Zembylas, 2018; Williams, 2017; Cruz and Fontan, 2014). This critique has focused on the delegitimization of non-Western epistemologies around peace and human rights and the reliance on Eurocentric structures of thought and power within curricular and pedagogical practices (Kester et al., 2019). The decolonization of academic human rights curricula is the primary focus of this research; through interviews and content analysis with U.S. human rights professors, professors’ curricular approaches were analyzed to understand how and to what extent they aligned with, incorporated, or utilized decolonial theory. The findings demonstrate that a decolonial curricular approach is only just emerging; these findings, which have significant implications for both human rights and peace education programs, indicate the need for further research into decolonial approaches to higher education curriculum

Women Leaders in Social Entrepreneurship: Leadership Perception, And Barriers

Social entrepreneurship increases women’s social inclusion and empowerment by providing self-employment opportunities (Datta & Gailey, 2012). There is growing attention, locally and globally, to social entrepreneurship from economic, social, environmental, and industrial lenses (Cornforth, 2014.) Grounded by feminist and empowerment theories, this phenomenological case study investigated the perceptions of women social entrepreneurs about leadership. In addition, the study explored the barriers to effective leadership in social entrepreneurship. A total of five participants participated in this study. The participants were five women leaders in social enterprise with experience in the field ranged from 3-40 years. Data was collected through multiple avenues including the researcher, semi-structured interviews, reflective journaling, and demographic survey questionnaire. The thematic Constant comparison coding was used to analyze the data collected. To ensure accuracy, the researcher shared the data transcripts with the participants and received feedback (Creswell, 2017). The overall findings of this study support that the participants in this study perceive leadership as an act of empowerment and advocacy. The participants also shared their perception of leadership as a process of contusions learning. The study identified one main barrier to effective leadership as the intersection of race-gender-ethnicity. Based on the findings of this study, implications, and recommendations to support and enhance the practice for women leaders were developed

Elementary Special Education Teachers\u27 Perceptions of Using the Best Practices of Video Modeling, Social Stories, and Peer Mediated Interventions to Teach Social Skills for Individuals With Autism Spectrum Disorder

Statistical data from the Centers for Disease Control (2018) indicated autism spectrum disorder (ASD) affects 1 out of 59 children in American schools. The purpose of this study was to explore the perceptions of special education teachers regarding teaching social skills for K-5 students with ASD; specifically, to see how teachers viewed the effective use of two promising practices (i.e., peer-mediated interventions and social stories) and one evidence-based intervention (i.e., video modeling). The experiences of special education teachers regarding teaching social skills to K-5 students with ASD were explored. Seven special education teachers from school districts in Colorado were interviewed and their responses were coded. After reading the transcripts and reviewing the responses to the questions as demonstrated above, the researcher found the following themes emerged from the contextual descriptions: collaboration, using pictures, using peers, equipment, training, and using social stories. For each core theme, there were sub-themes. A discussion of how the teachers implemented interventions revealed a possible lack of fidelity and understanding of how to use specific interventions as they had been defined

Spring-Guided Electromagnetic Vibrations Energy Harvester

In recent years, vibration based energy harvesting techniques showed a promising alternative to power wireless sensor networks (WSN). Billions of low power sensors are currently used widely in wireless sensor networks (WSN) and the Internet of Things environment (IoT). These sensors are currently powered by a traditional power source, i.e. a disposable battery. Vibrations are an abundant source of kinetic energy that can serve as the power source for these sensor nodes. This approach eliminates the necessity for frequent battery replacement due to their short-life span and hazardous disposal process. The adverse and irreversible effect from the disposal of these batteries have an alarming impact on the environment. In order to limit the severity of this impact, the vibration energy harvesting alternative is proposed as a solution. Vibration energy harvesting provides on site power sources for these small sensors by utilizing kinetic vibrations from its surroundings. This was the drive for much of the research done in vibration based energy harvesting. Most of the work that has been done so far focused on linear resonators with limited operational bandwidth. This limitation opposes a challenge, considering that vibrations exist on a wide frequency spectrum. This challenge was met by the invention of levitation based magnetic energy harvester. In a traditional magnetic levitation design, two stationary magnets are fixated in an orientation to repel a center magnet to allow it to float in between. This mechanism shows considerable lever in terms of power generation and operational bandwidth over linear counterparts. The traditional design shows superior performance over linear generators. Nonetheless, it remains deficient in power output as well as operational bandwidth. This work introduces an Enhanced Energy Harvester (EEH) design over the traditional design (TEH) based on dual mass moving magnets. The proposed design shows significant increase in power output and a wider frequency response bandwidth. The presented EEH design consists of a levitated magnet, an FR4 spring-guided magnet, and coils. Prototypes of the EEH have been fabricated and characterized experimentally. Nonlinear dynamical models of the EEH are developed and validated against experimental data. The results show excellent agreement between model simulations and experimental data. The figure of merits shows that the presented EEH design significantly outperforms the commonly studied magnetic spring based vibration energy harvesters. The EEH generates 1.97 mW/cm3 g 2 at 0.4 g[m/s2] which is approximately 400% the amount of power generated by the traditional magnetic spring based harvester, i.e. 0.5 [mW/cm3 g 2 ]. At lower acceleration, i.e. 0.1 g[m/s2], the enhanced harvester exhibits 4000% increase in power density compared to the traditional harvester. This makes the presented enhanced harvester design exceptionally suitable for applications where low acceleration oscillations are abundant, including harvesting vibrations from highway bridges and human body motion. Additionally, the half-power frequency bandwidth of the EEH is 90% wider than the bandwidth of its rival traditional magnetic spring based energy harvester

Linguistic Choices for Literary Dialectics: A Coming Together of Divergent Entities

Literature involves the manipulation of language for creative purposes and the discipline which fosters this synergic relationship between literature and language is termed stylistics. The purpose of this article is to show how it is possible to bridge the divide between language and literature by using the analytical techniques available within this sub-discipline of language study. Stylistics aims to interconnect linguistic form and literary effect, and also account for what it is that readers respond to when they praise the quality of a particular piece of writing. This article attempts to depict how the knowledge of linguistic intricacies can affect the reader’s interpretation. It also discusses how linguistic form relates to literary effect by analysing “Domination of Black”, by the renowned American poet Wallace Stevens. We aim to show that a linguistic approach to the analysis of a literary text does not have to mean that interpretation is disregarded. On the contrary, stylistic analysis can often illuminate why a particular literary text is regarded so highly

Commissioning of a Compton camera for medical imaging

The interest of using hadron-therapy in cancer treatment, particularly for tumors in the vicinity of critical organs-at-risk, is continuously growing due the ability of this treatment modality to provide high precision dose delivery. In order to fully exploit this beneficial property, it is mandatory to ensure that the well-localized dose deposition (Bragg peak) is located in the tumor volume. This calls for a precise in-vivo monitoring of the particle (proton, ion) beam stopping range. Therefore, the purpose of our project is to develop an in-vivo imaging system based on a Compton camera to verify the particle beam range by detecting (multi-MeV) prompt γ rays, generated as a result of nuclear reactions between the particle beam and biological tissue. In the context of this thesis the prototype of the LMU Compton camera was considerably improved and upgraded, and characterized both in the laboratory as well as under online conditions with particle beams at various accelerator facilities. The Compton camera consists of two main components: a scatterer (tracker), formed by a stack of six double-sided Si-strip detectors (DSSSD), and a monolithic LaBr 3 :Ce scintillation detector (5x5x3 cm 3 ), acting as absorber. The highly segmented DSSSD detectors, each with 128 strips per side (strip pitch: 0.39 mm), is processed by a compact ASIC-based electronics (1536 signal channels), while the scintillation detector is read out by a 256-fold segmented, position-sensitive multi-anode photomultiplier tube, providing energy and time information for each PMT segment. The stacked design of the LMU Compton camera scatter detector allows not only to reconstruct the incident photon origin, but it also allows to track Compton scattered electrons, thus enhancing the reconstruction efficiency compared to the conventional design. The Compton camera absorber (LaBr 3 :Ce scintillator crystal) was characterized in two different side-surface wrapping scenarios, absorptive and reflective. (Position-dependent) energy resolution and time resolution were determined for both coating scenarios, revealing the superior properties of the advanced scintillator material in case of the reflectively coated crystal, providing excellent energy (position independent: ∆E/E =3.8 % at 662 keV) and time resolution (273(6) ps FWHM). In addition, the impact of the crystal wrapping options on the scintillation light distribution was studied by extracting the Light Spread Function (LSF) from the crystal irradiation with a collimated 137 Cs source. Here, as can be expected, the absorptively coated crystal reveals a slightly better FWHM value of the LSF compared to the reflectively coated detector. Nevertheless, the drastic improvement of the other properties with reflective coating motivated this choice for the Compton camera absorber. The capability of the monolithic LaBr 3 :Ce scintillator to provide the γ-ray interaction position, which is a mandatory prerequisite for the targeted photon source reconstruction based on Compton scattering, was determined by applying two specific algorithms (’k-nearest neighbor’(k-NN) and ’Categorical Average Pattern’ (CAP)). These algorithms require a large reference data base of 2D scintillation light amplitude distributions, acquired by perpendicularly irradiating the scintillator front surface with a tightly (1 mm diameter) collimated photon source on a fine grid (0.5 mm step size). Two γ-ray sources, 137 Cs and 60 Co, were used to generate the required reference libraries in order to study the energy-dependent spatial resolution of the LaBr 3 :Ce scintillator. Systematic parameter studies were performed as a function of the photon energy, PMT granularity, irradiation grid size and number of photopeak events acquired in each of the 10 4 irradiation positions. Optimum values for the spatial resolution were achieved with 4.8(1) mm (FWHM) at 662 keV and 3.7(1) mm (FWHM) at 1.3 MeV using the CAP algorithm,thus almost reaching the final design goal of 3 mm envisaged for the prompt-γ energy region of 4-6 MeV. With the observed trend of improving spatial resolution with increasing photon energy, it will be interesting to study this property beyond the realm of γ-ray calibration sources in the higher energy region beyond 4 MeV, provided the availablility of an intense, monoenergetic and collimated photon beam. Furthermore, the Compton camera has been commissioned at different particle beam facilities. The camera components were first calibrated and characterized with monoenergetic 4.44 MeV γ rays generated via the nuclear 15 N(p,αγ) 12 C ∗ reaction at the Helmholtz-Zentrum Dresden Rossendorf (HZDR). The response of both the scatter and absorber detectors was found in good agreement with Monte-Carlo simulations. Moreover, the time-of-flight (TOF) measurement capability of the absorbing scintillator was studied at the Garching Tandem accelerator, using a 20 MeV pulsed (400 ns) deuteron beam hitting a water phantom, showing prompt γ rays well separated from the slower neutron background. The camera was finally commissioned with different clinical proton beams (100 MeV, 160 MeV and 225 MeV) at the research area of the Universitäts Protonen Therapie Dresden, stopping either in a water or a PMMA phantom. Energy spectra were acquired and separated into their prompt and delayed components, extracting the prompt photon contribution via TOF. The Compton electron energy deposit in each DSSSD layer was determined and found in very good agreement with simulation expectations. Hit multiplicities and the correlated electron tracking capability of the scatter/tracker array were investigated and limitations imposed by the present ASIC-based readout electronics, as well as options for further improvements, were identified

Ability of Caries Detection Methods to Determine Caries Lesion Activity

Indiana University-Purdue University Indianapolis (IUPUI)Background: Non-cavitated caries lesions form due to acid diffusion and demineralization of enamel subsurface with an intact surface layer (SL). Caries lesions progress when the outcome of demineralization and remineralization processes over time is net mineral loss. Lesions that continue to demineralize are called active, while those that display no evidence of further demineralization are called inactive. Micro-computed-tomography (µCT) analysis provides objective non-destructive measurements of the thickness of the surface layer (SL) and severity of caries lesions. Aims: 1) To investigate if visual/tactile suspected active non-cavitated early white spot lesions present a thinner surface layer than inactive ones; 2) To investigate if there is an association between the thickness of the surface layer (SLT) and caries activity, as determined by QLF during dehydration (△QD); 3) To determine lesion severity by comparing lesion volume and maximum depth correlation with △Q value at 15 s from QLF during dehydration. Materials and Methods: Thirty extracted human premolars exhibiting non-cavitated approximal white spot early lesions stored in 0.1.-percent thymol/4C and treated with 5.0-percent NaOCl/30 min were included in the study. Fifteen active and 15 inactive lesions were determined by visual/tactile examinations by consensus of two experienced examiners. Roughness measurements (Ra) were acquired using non-contact optical profilometry. Two-dimensional minimum (2D-min), maximum (2D-max), average (2D-avg) SL and three-dimensional (3D) analyses, volume and depth of lesions were determined from µCT image analysis. A series of fluorescence images were acquired at baseline (hydrated), at 1 s, at 5 s, at 10 s and at 15 s by QLF. During image acquisition, surfaces were dehydrated with continuous-compressed-air. △Q and △Q/s (△QD) were calculated. Data were analyzed using two-sample t-tests and Pearson correlation coefficients (p < 0.05). Results: Surface roughness of active and inactive lesions was not significantly different (p > 0.08). Overall lesion volume and depth in dentin were significantly larger in active lesions (p = 0.022, p = 0.009). SL thickness of active and inactive lesions was not significantly different (2D = 0.121, 3D = 0.080, 2D-avg = 0.446, 2D-min = 0.197, 2D-max = 0.122). △QD at 1s was significantly larger for active lesions (p = 0.046). ΔQ at 15 s of dehydration had a moderate positive association with lesion volume (r = 0.56). △QD had a weak negative association with SL thickness (2D-avg) and (2D-min). Conclusions: 1) Active and inactive non-cavitated lesions show no difference in SL thickness; 2) QLF during dehydration (△QD) does not correlate well with SL thickness; 3) ΔQ at 15 s of dehydration correlates moderately well with lesion volume and is consistent with caries activity assessed by visual/tactile examination

Notes on Ants of the genus Strumigenys F. Smith, 1860 (Hymenoptera: Formicidae) in the Arabian Peninsula, with a key to species.

The ant genus Strumigenys in the Arabian Peninsula is treated. Three species are recognized, S. arnoldi Forel, S. emmae (Emery) and S. membranifera Emery. The invasive species S. membranifera and the Afrotropical species S. arnoldi are recorded for the first time from Saudi Arabia and the Arabian Peninsula. A key to the Arabian species based on the worker caste is presented. Biological, ecological and distribution notes for each species are given. A regional distribution map for the three species is also presented