1,720,963 research outputs found
Multimodal imaging of holmium-loaded microsphere for internal Radiation therapy
No full textIn this dissertation, the qualitative and quantitative multimodal imaging possibilities of holmium-166 loaded poly(L-lactic acid) microspheres (166Ho-PLLA MS) are explored and exploited to improve biodistribution assessment and dose calculations for planning, image-guidance and evaluation of hepatic arterial radioembolization of liver malignancies. This relatively novel radiotherapy treatment modality represents a promising treatment option for patients with unresectable liver malignancies. In hepatic arterial radioembolization, radioactive microspheres are administered directly into the hepatic artery using a catheter. Targeting of tumors is accomplished by exploiting the predominance of the arterial blood supply to liver tumors, while normal parenchyma largely depends on portal blood supply. Ideally, this results in a high tumor-to-liver ratio, leading to an increased radiation dose to the tumor tissue while minimizing exposure to healthy liver parenchyma. An essential element of successful radioembolization of hepatic malignancies is preprocedural biodistribution assessment. The large variation in vascularity of tumor and liver tissue observed between patients necessitates extensive treatment planning to assure a favorable dose distribution in each individual patient. Due to their multimodal imaging properties, 166Ho-PLLA MS are believed to be an improvement as compared to the already clinically applied yttrium-90 microspheres, which lack high quality medical imaging possibilities. To fully exploit 166Ho-PLLA MS’ imaging opportunities and enable accurate biodistribution assessment and dose calculations, the qualitative and quantitative multimodal imaging possibilities of 166Ho-PLLA MS were investigated, focusing on magnetic resonance imaging (MRI), X ray computed tomography (CT) and Single Photon Emission Computed Tomography (SPECT). In vitro experiments demonstrated that SPECT has the highest sensitivity and lowest detection limit for 166Ho-PLLA MS, followed by MRI and CT, respectively. The development of highly-loaded holmium microspheres, with increased holmium content from 17% to 45% w/w, strongly increased the specific activity for therapeutic purposes and more than doubled the multimodal diagnostic properties for SPECT, MRI and CT. MicroCT imaging was demonstrated to enable high resolution 3D biodistribution assessment of 166Ho-PLLA MS in liver tissue after hepatic arterial radioembolization of a Vx2 tumor-bearing rabbit liver both qualitatively and quantitatively. Single microspheres were detectable using microCT. Microspheres mainly lodged in the periphery of the tumor, revealing a highly skewed cluster volume distribution towards small volumes. Macroscopically, MRI was demonstrated to enable selective depiction of Ho-PLLA MS with positive contrast in liver tissue in the presence of macroscopic magnetic field distortions, using a method called susceptibility gradient mapping. For MR-based quantitative assessment of the distribution of Ho-PLLA MS in liver tissue using T2* relaxometry, sampling of free induction decay (FID) was shown to be superior to sampling of the spin echo (SE), due to diffusion sensitivity of the SE signal decay time course. By means of MR experiments and Monte Carlo simulations FID signal behavior of a diffusive medium containing Ho-PLLA MS was shown to exhibit monoexponential signal decay. Both the static dephasing theory and the theory of strong field behavior accurately predicted transverse relaxivity, allowing MR-based quantification of the local concentration of HoMS. Furthermore, a method which increases the upper detection limit of the Ho-PLLA MS concentration by estimating the S0 value of the signal decay curve to be used in the quantitative fitting procedure was proposed. Finally, the feasibility to utilize quantitative MR data for dosimetric calculations of 166Ho-PLLA MS was demonstrated in an anthropomorphic gel phantom, indicating the potential of MR-based dosimetry for planning, guidance and evaluation of transcatheter radioembolization of hepatic malignancies
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Synthetic computed tomography: An artificial contrast for magnetic resonance imaging
No full textThe musculoskeletal (MSK) system provides support, stability and movement to the body. Disorders to the MSK system cause pain and stiffness, and can debilitate anatomical regions, hinder movement, or result in disability. As such, they are among the leading cause of activity limitation and absence from work and result in a major medical burden and economic cost.
Treatment and recommendations for diseases affecting the MSK system are very dependent on the type of disorder, the involvement of the affected soft tissues and bones, and the progression of the disease. In this context, medical imaging is crucial to localize a disorder, assess the stage of disease progression, support a diagnosis, or plan a treatment. For a comprehensive assessment and treatment planning of MSK pathologies, acquisition of both magnetic resonance imaging (MRI) and computed tomography (CT) is warranted, which is logistically complex and constitutes a high patient burden.
This work discusses the use of synthetic CT (sCT), a deep learning-enabled CT-like image generated from MR images, as a CT surrogate. Synthetic CT has been thoroughly investigated, from the acquisition and processing of the original MRI data to its clinical application, with a focus on orthopaedic care.
Synthetic CT has been found acceptable for bone visualization, simultaneously providing valuable information on soft tissues via the original MR acquisition. This paves the way to a purely MRI-based workflow with simplified logistics and radiation-free acquisition, and opens up new perspectives for diagnosis, treatment planning and disease understanding
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Computer-Assisted Osteotomy Planning: Medical Imaging Techniques for Orthopaedic Surgery
No full textIn this thesis, the ultimate goal has been to strive towards (automatic) computer assisted planning of reconstructive osteotomies. However, the quality of the output of such a workflow depends on the quality of all the intermediary steps, between the acquisition of a medical image, to the virtual reconstruction of the bone. In each chapter of this thesis, we have tried to overcome some of the challenges posed by these steps, and to evaluate the intermediate results.
First, a method to improve the registration of CT to MRI scans for knee joint images was developed. Large deformations can arise due to differences in patient positioning between scanners, making registration complex. The study showed that non-rigid registration using deformable B-Splines could be improved by initializing the registration with a rigid registration of bones and estimating soft tissue deformation using a dual quaternion-based interpolation step.
Second, an automatic and efficient deep learning-based method for semantic segmentation of six separate bones from lower extremity CT scans was proposed and validated. Existing deep learning segmentation algorithms were found to be slow and memory-intensive for this application. The optimized architecture of a cascaded U-net approach outperformed the state-of-the-art nn-Unet in memory efficiency, speed, and accuracy. Automated morphometric measurements on the hip joint were clinically validated, showing good to excellent correlation with measurements derived from manual segmentations.
Third, the impact of using CT and MRI to segment bone and/or cartilage on pre-operative osteotomy planning of the forearm in adolescent patients was evaluated. An automated, deterministic planning method was developed to directly compare planning outcomes and avoid inter- or intraoperator variation. Segmentations of bone from both CT and MRI were used to assess the impact of different modalities on planning. Additionally, segmentations of bone and bone combined with cartilage from MR images were analyzed to study the influence of cartilage on planning outcomes. Results showed excellent correlation between realignment parameters across different segmentations, with small significant differences in the translational part of realignment. A positive correlation was found between cartilage amount and differences in planning on bone and bone with cartilage, suggesting the importance of considering cartilage impact on joint shape in young patients. However, further research is needed to explore MRI as a potential replacement for CT in osteotomy planning due to the small sample size and time-consuming manual segmentation.
Lastly, a method to automatically quantify alignment parameters describing lower extremity morphology from 3D bone models was evaluated. A completely automatic pipeline was developed to extract these parameters using a CT scan as input. The alignment parameters were calculated using landmarks from previous studies and expanded upon to quantify all parameters needed for lower extremity realignment planning. This automatic method eliminated the need for manual operation and produced results that closely corresponded to intrarater variability. This advancement could pave the way for automatic realignment planning of lower extremities, addressing cases where a healthy contralateral example is unavailable for unilateral bone realignment planning
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