| 1. |
- Wang, Chunliang, 1980-
(författare)
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Computer Assisted Coronary CT Angiography Analysis : Disease-centered Software Development
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The substantial advances of coronary CTA have resulted in a boost of use of this new technique in the last several years, which brings a big challenge to radiologists by the increasing number of exams and the large amount of data for each patient. The main goal of this study was to develop a computer tool to facilitate coronary CTA analysis by combining knowledge of medicine and image processing.Firstly, a competing fuzzy connectedness tree algorithm was developed to segment the coronary arteries and extract centerlines for each branch. The new algorithm, which is an extension of the “virtual contrast injection” method, preserves the low density soft tissue around the coronary, which reduces the possibility of introducing false positive stenoses during segmentation.Secondly, this algorithm was implemented in open source software in which multiple visualization techniques were integrated into an intuitive user interface to facilitate user interaction and provide good over¬views of the processing results. Considerable efforts were put on optimizing the computa¬tional speed of the algorithm to meet the clinical requirements.Thirdly, an automatic seeding method, that can automatically remove rib cage and recognize the aortic root, was introduced into the interactive segmentation workflow to further minimize the requirement of user interactivity during post-processing. The automatic procedure is carried out right after the images are received, which saves users time after they open the data. Vessel enhance¬ment and quantitative 2D vessel contour analysis are also included in this new version of the software. In our preliminary experience, visually accurate segmentation results of major branches have been achieved in 74 cases (42 cases reported in paper II and 32 cases in paper III) using our software with limited user interaction. On 128 branches of 32 patients, the average overlap between the centerline created in our software and the manually created reference standard was 96.0%. The average distance between them was 0.38 mm, lower than the mean voxel size. The automatic procedure ran for 3-5 min as a single-thread application in the background. Interactive processing took 3 min in average with the latest version of software. In conclusion, the presented software provides fast and automatic coron¬ary artery segmentation and visualization. The accuracy of the centerline tracking was found to be acceptable when compared to manually created centerlines.
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| 2. |
- Deyhle Jr, Richard
(författare)
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Cross-modal Imaging in Lung Research: From µCT dosimetry to synchrotron phase contrast microtomography biomechanical insights in preclinical lung injury models
- 2024
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lung diseases continue to present a large burden to public health, especially in industrialized countries. For abetter understanding of the underlying patho-mechanisms in lung related diseases as well as for testing theefficacy of novel therapies, preclinical studies in animal models are indispensable. The significance of preclinical X-ray based micro-computed tomography (µCT) research lies in its ability to provide high-resolution, non-invasive lung imaging of small animals as the air inside the lung acts as a natural contrast and to image the lung parenchyma longitudinally to assess functional and morphological alterations and test efficacy of therapeutic interventions. This often requires requires imaging protocols that balance between sufficient image quality and clinically relevant radiation absorbed doses. A reproducible method for evaluation of absorbed radiation absorbed doses is desirable. Absorbed radiation absorbed doses were measured in a polymethyl methacrylate (PMMA) phantom using standard TLD and a novel type of OSLD made form household salt. Four imaging protocols from MILabs “xUHR-µCT” scanner were tested. A large discrepancy was observed from results compared to vendor-provided values. The results indicate a need for thorough empirical dose measurements prior to performing longitudinal studies. Four-dimensional imaging, allows for investigation of the dynamics of regional lung functional parameters simultaneously with structural deformation of the lung as a function of time. It is of significant interest to have direct visualization and quantification of interstitial lung diseases at spatial resolutions beyond the capabilities of clinical and conventional absorption-based only CT. Thus far, the high intensity of synchrotron X-ray light sources offer a tool to investigate dynamic morphological and mechanistic features, enabling dynamic in-vivo microscopy. This investigation elucidates the direct effects of interventions targeting the pathophysiology of Acute Respiratory Distress Syndrome (ARDS) and Ventilator-Induced Lung Injury (VILI) on the terminal airways and alveolar microstructure within intact lungs. In such conditions, the relationship between microscopic strain within the mechanics of the alveolar structure and the broader mechanical characteristics and viscoelastic properties of the lungs remains poorly understood. A time-resolved synchrotron phase-contrast micro-computed tomography imaging acquisition protocol based on the synchronization between the mechanical ventilation and the cardiac activity was used to resolve the lung parenchyma motion with an effective isotropic voxel size of 6 µm. Quantitative maps of microscopic local lung tissue strain within aerated lung alveolar tissue under protective mechanical ventilation in anesthetized rats were obtained. This approach was used to assess the effect of alterations in lung tissue biomechanics induced by lung injury at 7 days after single-dose, intratracheal bleomycin instillation in combination with short-term high-tidal volume (VT) mechanical ventilation. Overall, this work address the aspects of radiation exposure to in experimental imaging of small animals and lays a foundation for a more nuanced understanding of lung injury and mechanical ventilation. In the future, it may result in a more effective and less injurious respiratory support for patients with acute lung injury or chronic lung diseases.
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| 3. |
- Adjeiwaah, Mary, 1980-
(författare)
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Quality assurance for magnetic resonance imaging (MRI) in radiotherapy
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Magnetic resonance imaging (MRI) utilizes the magnetic properties of tissues to generate image-forming signals. MRI has exquisite soft-tissue contrast and since tumors are mainly soft-tissues, it offers improved delineation of the target volume and nearby organs at risk. The proposed Magnetic Resonance-only Radiotherapy (MR-only RT) work flow allows for the use of MRI as the sole imaging modality in the radiotherapy (RT) treatment planning of cancer. There are, however, issues with geometric distortions inherent with MR image acquisition processes. These distortions result from imperfections in the main magnetic field, nonlinear gradients, as well as field disturbances introduced by the imaged object. In this thesis, we quantified the effect of system related and patient-induced susceptibility geometric distortions on dose distributions for prostate as well as head and neck cancers. Methods to mitigate these distortions were also studied.In Study I, mean worst system related residual distortions of 3.19, 2.52 and 2.08 mm at bandwidths (BW) of 122, 244 and 488 Hz/pixel up to a radial distance of 25 cm from a 3T PET/MR scanner was measured with a large field of view (FoV) phantom. Subsequently, we estimated maximum shifts of 5.8, 2.9 and 1.5 mm due to patient-induced susceptibility distortions. VMAT-optimized treatment plans initially performed on distorted CT (dCT) images and recalculated on real CT datasets resulted in a dose difference of less than 0.5%. The magnetic susceptibility differences at tissue-metallic,-air and -bone interfaces result in local B0 magnetic field inhomogeneities. The distortion shifts caused by these field inhomogeneities can be reduced by shimming. Study II aimed to investigate the use of shimming to improve the homogeneity of local B0 magnetic field which will be beneficial for radiotherapy applications. A shimming simulation based on spherical harmonics modeling was developed. The spinal cord, an organ at risk is surrounded by bone and in close proximity to the lungs may have high susceptibility differences. In this region, mean pixel shifts caused by local B0 field inhomogeneities were reduced from 3.47±1.22 mm to 1.35±0.44 mm and 0.99±0.30 mm using first and second order shimming respectively. This was for a bandwidth of 122 Hz/pixel and an in-plane voxel size of 1×1 mm2. Also examined in Study II as in Study I was the dosimetric effect of geometric distortions on 21 Head and Neck cancer treatment plans. The dose difference in D50 at the PTV between distorted CT and real CT plans was less than 1.0%.In conclusion, the effect of MR geometric distortions on dose plans was small. Generally, we found patient-induced susceptibility distortions were larger compared with residual system distortions at all delineated structures except the external contour. This information will be relevant when setting margins for treatment volumes and organs at risk. The current practice of characterizing MR geometric distortions utilizing spatial accuracy phantoms alone may not be enough for an MR-only radiotherapy workflow. Therefore, measures to mitigate patient-induced susceptibility effects in clinical practice such as patient-specific correction algorithms are needed to complement existing distortion reduction methods such as high acquisition bandwidth and shimming.
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| 4. |
- de Lazzari, Mattia, 1996
(författare)
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Practical Implementation of Quality Assurance Guidelines for Hyperthermia Therapy
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Hyperthermia therapy (HT) has been proven to be a potent enhancer of chemotherapy and radiotherapy in numerous clinical trials. The effectiveness of HT is strictly dependent on the administered thermal dose, which, in turn, is dependent on the quality of the therapeutic heat applied to the patient. Quality Assurance (QA) protocols in HT exist to ensure that heating devices can consistently deliver controlled, reproducible, and high-quality treatments. The physical characterization of HT devices requires specific procedures and instrumentation as well as adequate tissue-mimicking phantoms to perform QA experimental procedures. However, the implementation of QA guidelines is hampered due to the unavailability of suitable phantom materials and limited equipment for the QA experimental evaluation. This work addresses these gaps by (i) proposing the design of tissue-mimicking materials for routine use in HT QA procedures and (ii) demonstrating the practical implementation of the latest QA guidelines for both superficial and deep HT. A novel fat-mimicking material was developed to mimic superficial fatty tissue. This fat phantom is based on an ethylcellulose stabilized glycerol in oil emulsion and is intended to be used in superficial HT QA procedures. Measured dielectric and thermal properties were consistent with fatty tissue properties, with an acceptable variability in most of the frequency range used in HT. This fat-mimicking material was then used in the experimental implementation of HT guidelines. The physical characterization of a superficial HT device (Lucite Cone Applicator, LCA) was conducted by assessing the quality metrics defined in the HT guidelines, demonstrating acceptable performance. These findings were further validated through computational studies. For deep HT, a comparative study engaged six HT centers across Europe to assess the performance of commonly used deep regional heating devices. Preliminary results in experimental phantoms showed a good performance in terms of device heating capability and steerability. This study provided practical insights into implementing QA guidelines involving phantom properties, experimental setup, temperature acquisition, and time constraints. We are positive this research will benefit the routine implementation of deep HT guidelines in a clinical setting.
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| 5. |
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| 6. |
- Selim, Marianne, 1954-
(författare)
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Från anlogt till digitalt : digitaliseringen av svensk radiologi i ett produktions- och organisationsperspektiv
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Syfte: Att beskriva den organisationsförändring som fem röntgenkliniker i Sverige genomgick i samband med att radiologin digitaliserades.Frågeställningar:Hur förändrades antalet genomförda radiologiska undersökningar och undersökningstyper från tidpunkten två år före digitaliseringen till två, fyra och sex år efter digitaliseringen?Hur förändrades antalet arbetade timmar och fördelningen av arbetade timmar mellan de olika personalkategorierna från tidpunkten två år före digitaliseringen till två, fyra och sex år efter digitaliseringen?Hur förändrades arbetsuppgifterna inom och mellan de olika personalkategorierna på röntgenklinikerna efter digitaliseringen?Hur beskriver personal med en nyckelfunktion genomförandet av digitaliseringen och eventuell förändring av arbetet efter digitaliseringen?Metod: Kvantitativ och kvalitativ metod har använts och kombinerats för att besvara studiens frågeställningar. Fem svenska röntgenkliniker ingick i studien och material avseende produktionsutfall samlades in från respektive röntgenklinik. Totalt intervjuades 22 personer, med tre till sex intervjuer per röntgenklinik.Teoretiska ramverk: För att försöka förstå de positiva fynden, avseende utökade antalet undersökningar och minskning av arbetade timmar, efter digitaliseringen, genomfördes vid en av röntgenklinikerna en fallstudie med ytterligare två frågeställningar: Hur genomfördes digitaliseringen? Hur har uppföljningen vad avser arbetsflöden, genomförandet och förändringar i detalj genomförts efter digitaliseringen? Delar av Bramson m.fl. (2005) perspektiv och Kotter och Cohens (2002) framgångsfaktorer har applicerats vid analysen av det resultatet.Resultat: Samtliga röntgenkliniker uppvisade en liten ökning av antalet radiologiska undersökningar, medan datortomografi- och magnetkameraundersökningarna ökade markant under den studerade tiden. Efter digitaliseringen genomförs således fler komplicerade undersökningar, vilket anses ha medfört en kvalitativt bättre och säkrare diagnosticering. Övriga undersökningstyper uppvisar varierande resultat. Vid tre av röntgenklinikerna minskade den totala arbetade tiden, och vid två ökade den. Antalet arbetade timmar ökade för röntgenläkare och röntgensjuksköterskor, men minskade för sekreterare och undersköterskor under den studerade tiden. Generellt utför röntgenläkarna och röntgensjuksköterskorna fler arbetsuppgifter efter digitaliseringen, och många av de traditionella arbetsuppgifterna för sekreterare och undersköterskor har försvunnit eller tagits över av datorn. Bättre tillgänglighet, förhöjd kvalitet och utökad diagnostik, tydligare arbetslistor som styr arbetsflödet, förbättrad ergonomi och miljö samt samordning med andra har möjliggjorts efter digitaliseringen. Utifrån intervjuerna i fallstudien framkom teman som beskriver: information, superanvändare, utbildning, tydliga arbetsflöden och rutiner, personalbehov och motivation, liksom ett tydligt ledarskap som genomsyrat förändringsprocessen. Dessa teman är, enligt Bramson och Bramson (2005) och Kotter och Cohen (2002), viktiga att beakta för att lyckas med en förändring.Konklusion: Ingen av de intervjuade vill återgå till ett analogt arbetssätt. Digitaliseringen har inneburit att mycket förändrats för de berörda personalkategorierna, men fördelarna anses uppväga nackdelarna. För att lyckas med en förändring bör Bramsons perspektiv och Kotters framgångsfaktorer tas i beaktande.
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| 7. |
- Dahlström, Nils, 1969-
(författare)
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Magnetic Resonance Imaging of the Hepatobiliary System Using Hepatocyte-Specific Contrast Media
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- There are two Gadolinium-based liver-specific contrast media for Magnetic Resonance Imaging on the market, Gd-BOPTA (MultiHance®, Bracco Imaging, Milan, Italy) and Gd-EOB-DTPA (Primovist®, Bayer Schering Pharma, Berlin, Germany). The aim of this study in two parts was to evaluate the dynamics of biliary, parenchymal and vascular enhancement using these contrast media in healthy subjects. Ten healthy volunteers were examined in a 1.5 T magnetic resonance system using three-dimensional Volumetric Interpolated Breath-Hold (VIBE) sequences for dynamic imaging with both contrast media – at two different occasions – until five hours after injection. The doses given were 0.025 mmol/kg for Gd-EOB-DTPA and 0.1 mmol/kg for Gd-BOPTA. The enhancement over time of the common biliary duct in contrast to the liver parenchyma was analyzed in the first study. This was followed by a study of the image contrasts of the hepatic artery, portal vein and middle hepatic vein versus the liver parenchyma.While Gd-EOB-DTPA gave an earlier and more prolonged enhancement of the biliary duct, Gd-BOPTA achieved higher image contrast for all vessels studied, during the arterial and portal venous phases. There was no significant difference in the maximal enhancement obtained in the liver parenchyma.At the obtained time-points and at the dosage used, the high contrast between the common biliary duct and liver parenchyma had an earlier onset and longer duration for Gd-EOB-DTPA, while Gd-BOPTA achieved higher maximal enhancement of the hepatic artery, portal vein and middle hepatic vein than Gd-EOB-DTPA. Diseases of the liver and biliary system may affect the vasculature, parenchyma, biliary excretion or a combination of these. The clinical context regarding the relative importance of vascular, hepatic parenchymal and biliary processes should determine the choice of contrast media for each patient and examination.
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| 8. |
- Morén, Björn, 1987-
(författare)
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Mathematical Modelling of Dose Planning in High Dose-Rate Brachytherapy
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cancer is a widespread type of diseases that each year affects millions of people. It is mainly treated by chemotherapy, surgery or radiation therapy, or a combination of them. One modality of radiation therapy is high dose-rate brachytherapy, used in treatment of for example prostate cancer and gynecologic cancer. Brachytherapy is an invasive treatment in which catheters (hollow needles) or applicators are used to place the highly active radiation source close to or within a tumour.The treatment planning problem, which can be modelled as a mathematical optimization problem, is the topic of this thesis. The treatment planning includes decisions on how many catheters to use and where to place them as well as the dwell times for the radiation source. There are multiple aims with the treatment and these are primarily to give the tumour a radiation dose that is sufficiently high and to give the surrounding healthy tissue and organs (organs at risk) a dose that is sufficiently low. Because these aims are in conflict, modelling the treatment planning gives optimization problems which essentially are multiobjective.To evaluate treatment plans, a concept called dosimetric indices is commonly used and they constitute an essential part of the clinical treatment guidelines. For the tumour, the portion of the volume that receives at least a specified dose is of interest while for an organ at risk it is rather the portion of the volume that receives at most a specified dose. The dosimetric indices are derived from the dose-volume histogram, which for each dose level shows the corresponding dosimetric index. Dose-volume histograms are commonly used to visualise the three-dimensional dose distribution.The research focus of this thesis is mathematical modelling of the treatment planning and properties of optimization models explicitly including dosimetric indices, which the clinical treatment guidelines are based on. Modelling dosimetric indices explicitly yields mixedinteger programs which are computationally demanding to solve. The computing time of the treatment planning is of clinical relevance as the planning is typically conducted while the patient is under anaesthesia. Research topics in this thesis include both studying properties of models, extending and improving models, and developing new optimization models to be able to take more aspects into account in the treatment planning.There are several advantages of using mathematical optimization for treatment planning in comparison to manual planning. First, the treatment planning phase can be shortened compared to the time consuming manual planning. Secondly, also the quality of treatment plans can be improved by using optimization models and algorithms, for example by considering more of the clinically relevant aspects. Finally, with the use of optimization algorithms the requirements of experience and skill level for the planners are lower.This thesis summary contains a literature review over optimization models for treatment planning, including the catheter placement problem. How optimization models consider the multiobjective nature of the treatment planning problem is also discussed.
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| 9. |
- Sterlingova, Tatiana
(författare)
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Women’s participation in mammography screening
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This dissertation focuses on women’s participation in mammography screening, which is a vital component of early detection and effective management of breast cancer. All Swedish women in the age group of 40-74 receive an invitation by mail at regular intervals of 18-24 months. However, about 20% of Swedish women fail to attend the mammography screening they were offered. The impact on mortality within a population is contingent on theparticipation rate, underscoring the importance of making efforts to attain a high level of participation. This thesis is an attemt to improve understanding and awareness of the women’s choices and actions that can influence life or death, especially considering that being a woman is the most significant risk factor for breast cancer. The overall aim of this thesis was to explore the phenomenon of women’s participation in mammography screening by exploring the reasons why women refrain from mammography screening from the perspective of non-attending women (Paper I) and factors that affect women’s participation in mammography screening in the Nordic countries.The research was conducted through qualitative and mixed studies review method studies. The data collection methods comprised ten personal interviews (Paper I), and 16 articles (Paper II).Qualitative content analysis was used to analyse the interviews in an indictive approach (Paper I). A deductive approach with segregated mixed research synthesis was used to analyse and summarise findings from articles in systematic review (Paper II). Health Promotion Model by N. Pender was used as a theoretical framework.Participation in mammography screening is a complex phenomenon that has many dimensions. The thesis results underscore the significance of comprehending the unique and subjective encounters of women in the context of mammography screening. These experiences hold substantial sway over their perspectives and actions regarding this procedure. Additionally, the research suggests that effective communication and prior experiences, whether positive or negative, play pivotal roles in shaping women's knowledge and attitudes towards mammography. These findings align with the biopsychosocial perspective, which underscores the intricate interplay of biological, psychological, and social factors in individuals' lives. Mammography screening, as demonstrated in Paper I, operates as a standardized system aimed at addressing the diverse and individual needs of women. Various factors, such as individual characteristics, past experiences, cognitive factors related to behavior, emotional aspects, competing priorities, and the organizational aspects of screening, collectively influence women's participation in both positive and negative ways (Paper II). Promotional efforts are essential to motivate women to actively engage in their healthcare.
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| 10. |
- Cros, Olivier, 1975-
(författare)
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Image Analysis and Visualization of the Human Mastoid Air Cell System
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- From an engineering background, it is often believed that the human anatomy has already been fully described. Radiology has greatly contributed to understand the inside of the human body without surgical intervention. Despite great advances in clinical CT scanning, image quality is still related to a limited amount X-ray exposure for the patient safety. This limitation prevents fine anatomical structures to be visible and, more importantly, to be detected. Where such modality is of great advantage for screening patients, extracting parameters like surface area and volume implies the bone structure to be large enough in relation to the scan resolution.The mastoid, located in the temporal bone, houses an air cell system whose cells have a variation in size that can go far below current conventional clinical CT scanner resolution. Therefore, the mastoid air cell system is only partially represented on a CT scan. Any statistical analysis will be biased towards air cells of smaller size. To allow a complete representation of the mastoid air cell system, a micro-CT scanner is more adequate. Micro-CT scanning uses approximately the same amount of X-rays but for a much longer exposure time compared to what is normally allowed for patients. Human temporal bone specimens are therefore necessary when using such scanning method. Where the conventional clinical CT scanner lacks level of minutes details, micro-CT scanning provides an overwhelming amount of fine details.Prior to any image analysis of medical data, visualization of the data is often needed to learn how to extract the structures of interest for further processing. Visualization of micro-CT scans is of no exception. Due to the high resolution nature of the data, visualization of such data not only requires modern and powerful computers, but also necessitates a tremendous amount of time to adjust the hiding of irrelevant structures, to find the correct orientation, while emphasising the structure of interest. Once the quality of the data has been assessed, and a strategy for the image processing has been decided, the image processing can start, to in turn extract metrics such as the surface area or volume and draw statistics from it. The temporal bone being one of the most complex in the human body, visualization of micro-CT scanning of this bone awakens the curiosity of the experimenter, especially with the correct visualization settings.This thesis first presents a statistical analysis determining the surface area to volume ratio of the mastoid air cell system of human temporal bone, from micro-CT scanning using methods previously applied for conventional clinical CT scannings. The study compared current resul s with previous studies, with successive downsampling the data down to a resolution found in conventional clinical CT scanning. The results from the statistical analysis showed that all the small mastoid air cells, that cannot be detected in conventional clinical CT scans, do heavily contribute to the estimation of the surface area, and in consequence to the estimation of the surface area to volume ratio by a factor of about 2.6. Such a result further strengthens the idea of the mastoid to play an active role in pressure regulation and gas exchange.Discovery of micro-channels through specific use of a non-traditional transfer function was then reported, where a qualitative and a quantitative preanalysis was performed are described. To gain more knowledge about these micro-channels, a local structure tensor analysis was applied where structures are described in terms of planar, tubular, or isotropic structures. The results from this structural tensor analysis, also reported in this thesis, suggest these micro-channels to potentially be part of a more complex framework, which hypothetically would provide a separate blood supply for the mucosa lining the mastoid air cell system.
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