676 research outputs found

    Adolescent Idiopathic Scoliosis. The Role of Low Dose Computed Tomography.

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    Continuous implementation of new operative methods for correction and stabilization of spinal deformities in young patients with AIS demands a detailed morphological analysis of the vertebral column. CT spine according to protocols available in daily clinical practice means high radiation dose to these young individuals. All examinations included in this thesis were performed on a 16-slice CT scanner. Examination of the chest phantom in paper I showed that the radiation dose of the spine (including 15 vertebrae) was 20 times lower than that of routinely used protocols for CT examination of the spine in children (0.38 mSv vs 7.76 mSv). In paper II the radiation dose and the impact of dose reduction on image quality were evaluated in 113 consecutive examinations with low-dose spine CT and compared with that of 127 CTs after trauma and 15 CTs performed according to a previously used ANV-protocol of a limited part of the vertebral column. The effective dose of the low-dose spine CT (0.01 mSv/cm scan length) was 20 times lower than that of the standard CT for trauma (0.20 mSv/cm scan length). The absorbed doses to the breasts, genital organs, and thyroid gland in the low-dose spine CT was 8, 265, and 22 times lower than the corresponding doses in CT for trauma. This significant dose reduction conveyed no impact on image quality with regard to answering the clinical questions at issue for the preoperative CTs and for the postoperative CTs after posterior corrective surgery. In paper III the low-dose CT showed to be a reliable method in the evaluation of screw placement in patients with AIS after posterior scoliosis surgery with titanium implants, using the new grading system for screw misplacement. Our proposed grading system for screw misplacement has shown to be feasible, practical, and easy to perform and is in line with the general agreement about the harmlessness of misplacement with minor pedicle breach. In paper IV the evaluation of the clinical and radiological outcome of 49 patients with AIS operated on with titanium “all-pedicle screw construct” showed an overall misplacement rate of 17 %. No evidence of neurovascular complications was reported. In parity with most of the reports in the literature the lateral- and medial cortical perforation were the most common types of screw misplacement (8 % and 6.1 % respectively)

    Investigating the ability to use the CT scan projection radiograph to monitor adolescent idiopathic scoliosis

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    Introduction: Adolescent idiopathic scoliosis (AIS) is a spinal deformity that causes the spine to bend laterally. Patients with AIS undergo frequent X-ray examinations to monitor the progression of the deformity through the measurement of the Cobb angle, increasing the risk of developing radiation-induced cancer. The aim of this study was to investigate the use of scan projection radiograph (SPR) in computed tomography (CT) to assess AIS by quantifying radiation dose from the SPR acquisitions and comparing it to those of digital radiography (DR) and a dedicated scoliosis imaging system (EOS) and by evaluating the accuracy of Cobb angle measurements on SPR images using a bespoke validated phantom. Methods: A dosimetry phantom representing a 10-year-old child and thermoluminescent dosimeters were used for measuring organ dose to calculate effective dose (ED) and effective risk (ER). Twenty-seven CT SPR protocols were used. A comparison was made to doses from imaging protocols using DR and the EOS system. The effectiveness of a scoliosis shawl for selected projections was also tested. To test the accuracy of Cobb angle measurements on SPR images, a scoliotic phantom was constructed and validated. Poly-methyl methacrylate (PMMA) and plaster of Paris (PoP) were used to represent human soft tissue and bone tissue, respectively, to construct a phantom exhibiting a 15° lateral curve of the spine. The phantom was validated by comparing the Hounsfield unit (HU) of its vertebrae with those of a human and an animal. Additionally, comparisons of signal-to-noise ratio (SNR) to those from a commercially available phantom were made. The angle of the curve in the phantom was measured directly to confirm that it was 15°. The constructed phantom was scanned in CT SPR mode, and the resulting images were visually evaluated against set criteria to determine their suitability for Cobb angle measurements. Those deemed of insufficient quality were excluded. Cobb angle measurements were then performed on the remaining images (n = 10) by 13 observers.Results: EOS had the lowest ED and ER when it was used to irradiate the phantom in AP positions. Five SPR AP imaging protocols and seven PA imaging protocols delivered significantly lower radiation dose and risk than their corresponding imaging positions in DR (p < 0.05). The scoliosis shawl significantly lowered the ED and ER of SPR and DR AP imaging protocols (p < 0.05). The validation of the PoP phantom revealed that the HU of the PoP vertebrae was 628 (SD= 56), human vertebrae was 598 (SD= 79) and sheep vertebra was 605 (SD= 83). The SNR values of the two phantoms correlated strongly (r = 0.93 [(p < 0.05]). The measured scoliosis angle was 14 degrees. When the phantom was imaged using SPR, the difference between the measured Cobb angle and the known angle was, on average, –2.75° (SD = 1.46°). The agreement among the observers was good (p = 0.861, 95% CI [0.70–0.95]) and comparable to similar studies on other imaging modalities which are used for Cobb angle estimation.Conclusion: EOS had the lowest dose. Where this technology is not available, there is a potential for organ dose (OD) reduction in AIS imaging using CT SPR compared with DR. The PoP phantom has physical characteristics (in terms of spinal deformity) and radiological characteristics (in terms of HU and SNR values) of the spine of a 10-year-old child with AIS. CT SPR images can be used for AIS assessment with the 5° margin of error that is clinically acceptable. A few SPR imaging protocols (CT4, 8 and 11) had the lower radiation risk compared with the DR and provided the most accurate Cobb angle measurements.Implications for practice: The bespoke phantom can be used to investigate new X-ray imaging techniques and technology in the assessment of scoliosis and has utility for the optimisation of X-ray imaging techniques in 10-year-old children. Overall, the outcome is promising for patients and health providers because it provides an opportunity to reduce patient dose and achieve clinically acceptable Cobb angle measurements whilst using existing CT technology

    Development and validation of a bespoke phantom to test accuracy of Cobb angle measurements

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    Introduction: Adolescent idiopathic scoliosis (AIS) is a spinal deformity that causes the spine to bend laterally. Patients with AIS undergo frequent X-ray examinations to monitor the progression of the disorder by through the measurement of the Cobb angle. Frequent exposure of adolescents poses the risk of radiation-induced cancer. The aim of this research was to design and build a bespoke phantom representing a 10-year-old child with AIS to allow optimisation of imaging protocols for AIS assessment through the accuracy of Cobb angle measurements. Method: Poly-methyl methacrylate (PMMA) and plaster of Paris (PoP) were used to represent human soft tissue and bone tissue, respectively, to construct a phantom exhibiting a 15olateral curve of the spine. The phantom was validated by comparing the Hounsfield unit (HU)of its vertebrae with that of human and sheep. Additionally, comparisons of signal-to-noise ratio (SNR) to those from a commercially available phantom. An assessment of the accuracy of the radiographic assessment of the Cobb angle measurement was performed. Results: The HU of the PoP vertebrae was 628 (SD= 56), human vertebrae was 598 (SD= 79) and sheep vertebra was 605 (SD= 83). The SNR values of the two phantoms correlated strongly (r = 0.93 (p = 0.00)). The measured scoliosis angle was 14 degrees. Conclusion:The phantom has physical characteristics (in terms of spinal deformity) and radiological characteristics (in terms of HU and SNR values) of the spine of a 10-year-old child with AIS. This phantom has utility for the optimisation of x-ray imaging techniques in 10 year old children. Implications for practice: A phantom to investigate new x-ray imaging techniques and technology in the assessment of scoliosis and to optimise currently used protocols

    OPTIMAX 2014 - Radiation dose and image quality optimisation in medical imaging

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    Medical imaging is a powerful diagnostic tool. Consequently, the number of medical images taken has increased vastly over the past few decades. The most common medical imaging techniques use X-radiation as the primary investigative tool. The main limitation of using X-radiation is associated with the risk of developing cancers. Alongside this, technology has advanced and more centres now use CT scanners; these can incur significant radiation burdens compared with traditional X-ray imaging systems. The net effect is that the population radiation burden is rising steadily. Risk arising from X-radiation for diagnostic medical purposes needs minimising and one way to achieve this is through reducing radiation dose whilst optimising image quality. All ages are affected by risk from X-radiation however the increasing population age highlights the elderly as a new group that may require consideration. Of greatest concern are paediatric patients: firstly they are more sensitive to radiation; secondly their younger age means that the potential detriment to this group is greater. Containment of radiation exposure falls to a number of professionals within medical fields, from those who request imaging to those who produce the image. These staff are supported in their radiation protection role by engineers, physicists and technicians. It is important to realise that radiation protection is currently a major European focus of interest and minimum competence levels in radiation protection for radiographers have been defined through the integrated activities of the EU consortium called MEDRAPET. The outcomes of this project have been used by the European Federation of Radiographer Societies to describe the European Qualifications Framework levels for radiographers in radiation protection. Though variations exist between European countries radiographers and nuclear medicine technologists are normally the professional groups who are responsible for exposing screening populations and patients to X-radiation. As part of their training they learn fundamental principles of radiation protection and theoretical and practical approaches to dose minimisation. However dose minimisation is complex – it is not simply about reducing X-radiation without taking into account major contextual factors. These factors relate to the real world of clinical imaging and include the need to measure clinical image quality and lesion visibility when applying X-radiation dose reduction strategies. This requires the use of validated psychological and physics techniques to measure clinical image quality and lesion perceptibility

    Craniofacial growth and development in modern humans and Neanderthals

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    This thesis assesses craniofacial growth, development and the dynamics of developmental interactions among cranial regions in modern humans and Neanderthals. To these ends, virtual segmentation, landmarking and Geometric Morphometrics (GM) are applied to an ontogenetic series of the whole crania of 68 H. sapiens and 12 H. neanderthalensis. First, the ontogenetic shape and form changes in the cranial vault, base and face are explored, and the locations and magnitudes of these changes are discussed. Secondly, allometric scaling is tested for differences among different age classes in the three regions of the cranium. In addition, the degree of covariation among these and how it changes over time is investigated.The study then focuses on interactions among facial regions. First, similar analyses as those used in the study of the cranium are applied to compare growth, development and covariation among parts of the face in different age classes. Additionally, a sample of 227 modern humans from 0 to 6 years of age is analysed using path analysis, to investigate the cascade of interactions and relative contributions of soft tissue and skeletal elements to the overall growth and development of the face. Last, the facial morphology of H. sapiens is compared to that of H. neanderthalensis and their ontogenetic trajectories are tested for divergence. Novel method registration-free colour maps are used to visualise regional changes during growth and development and to compare the morphologies of the two species. Covariation among facial elements is also compared to assess potential differences in developmental interactions. In modern humans, the results show that allometry and covariation change significantly among age classes and between cranial regions during ontogeny and that covariation is stronger in younger subadults than in older subadults and adults. Among modern humans, significantly divergent trajectories are observed between age classes during ontogeny in all three cranial regions. In the modern human face, allometric scaling also differs among age stages in each region. Interestingly, covariation among facial regions becomes progressively non-significant with time, with the exception of those including the nose and maxilla. Path analysis in modern humans shows a large contribution of the proxy used for nasal septum to the overall facial development. Soft tissues contribute only locally to the development of some skeletal elements of the face. Major aspects of the differences between adult modern humans and Neanderthals are already present in the youngest individuals. However, additional differences arise through differences in the degree of change in facial size and significantly divergent allometric trajectories. Analyses of covariation among Neanderthal facial regions suffer from small sample size but, where significant, suggest that the interactions among cranial components are similar to those in modern humans, with some differences

    Aerospace Medicine and Biology: A continuing supplement 180, May 1978

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    This special bibliography lists 201 reports, articles, and other documents introduced into the NASA scientific and technical information system in April 1978

    Aerospace Medicine and Biology: A cumulative index to the 1981 issues

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    The aeromedical research reported considers the safety of the human component in manned space flight. The effects of spacecraft environment, radiation and weightlessness on human biological and psychological processes are covered

    The clinical impact of multidetector SPET technology

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    Introduction: Single photon emission tomography (SPET) is an established technique in Nuclear Medicine. Recent advances in SPET technology have now permitted the development of multidetector gamma cameras. This thesis evaluates some of these new gamma cameras and their impact on clinical practice. Aim: (a) To assess four new multidetector SPET gamma cameras (IGE Neurocam, Toshiba GCA-9300A, IGE Optima and Sopha DST). (b) To establish appropriate acquisition and analytical clinical protocols. Methodology: For each instrument, the tomographic spatial resolution, contrast and sensitivity were measured. The capability of a new slant hole collimator (IGE Optima) to perform radionuclide ventriculography (RNV) was assessed. To evaluate the utility of these systems, a total of 1215 patient studies were performed (1007 cardiac, 85 skeletal, 73 renal and 50 brain studies). The effect of 8, 16 and 32 minutes data acquisition on image quality and clinical relevance was evaluated. In addition, a new cardiac SPET protocol for rest/stress myocardial perfusion scintigraphy (thallium-201/Tc-99m tetrofosmin) was tested. Results: Tomographic spatial resolution of the order of 10 mm FWHM was achieved by all four systems. System sensitivity was related to the number of detectors and ranged between 9.2–11.2 Kcps/(MBq/ml)/cm per detector. The slant hole collimator with cephalic tilt gave highly reproducible results (r=0.98,SEE=+2) for ejection fraction measurements in 75 patients. There was no significant difference in the clinical information obtained using 8 min, 16 min and 32 min acquisitions. Based on patient studies and experience with these multidetector SPET systems, optimum acquisition and analysis protocols for commonly performed SPET studies were documented for routine clinical use. Artefacts due to patient movement during Tl-201 myocardial SPET studies were less frequent on a dual-detector system compared with a single detector system (0.7% and 4% respectively); while artefacts due to poor positioning or shift in centre of rotation were more. The rest/stress thallium-201/Tc-99m tetrofosmin study protocol (acquisition and analysis) was completed in 90 min. This protocol gave a sensitivity of 80% and specificity of 70% for the detection of coronary artery disease. Conclusion: For the first time a comprehensive comparison of multidetector SPET systems has been documented. Optimum acquisition and analysis protocols have been identified. The study also shows that the new generation of multidetector SPET systems offer adequate resolution and sensitivity for routine clinical imaging. Increased sensitivity can be translated into an increased patient throughput. This can increase the cost-effectiveness of this new technology

    Application of next generation sequencing in genetic and genomic studies

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    Genetic variants that spread along the human genome play vital roles in determining our traits, affecting development and potentially causing disorders. Most common disorders have complex underlying mechanisms involving genetic or environmental factors and the interaction between them. Over the past decade, genome-wide association studies (GWAS) have identified thousands of common variants that contribute to complex disorders and partially explain the heritability. However, there is still a large portion that is unexplained and the missing heritability may be caused by several factors, such as rare or low-frequency variants with high effect that are not covered by GWAS and linkage analysis. With the development of next generation sequencing (NGS), it is possible to rapidly detect large amount of novel rare and low-frequency variants simultaneously at a low cost. This new technology provides vast information on studying the association of genetic variations and complex disorders. Once the susceptibility gene is mapped, model organisms such as zebrafish (Danio rerio) are popular for further investigating the possible function of diseaseassociated gene in determining the phenotype. However, the genome annotation of zebrafish is not complete, which affects the characterization of gene functions. Accordingly, highthroughput RNA sequencing can be employed for identifying new transcripts. In our studies, pooled DNA samples were used for whole genome sequencing (WGS) and exome sequencing. In Paper I, we evaluated minor allele frequency (MAF) estimates using three variant detection tools with two sets of pooled exome sequencing and one set of pooled WGS data. The MAFs from the pooled sequencing data demonstrated high concordance (r = 0.88-0.94) with those from the individual genotyping data. In Paper II, exome sequencing implementing pooling strategy was performed on 100 idiopathic scoliosis (IS) patients for mapping susceptibility genes. After validating 20 candidate single nucleotide variants (SNVs), we did not find associations between them and IS. However, the previously reported common variant rs11190870 near LBX1 was validated in a large Scandinavian cohort. In Paper III, we analyzed WGS of pooled DNA samples performed on 19 affected individuals who shared a phenotype-linked haplotype in a dyslexic Finish family. Two of the individuals were sequenced for the whole genome individually as well. The screen for causative variants was narrowed down to a rare SNV, which might affect the binding affinity of LHX2 that regulated dyslexia associated gene ROBO1. In Paper IV, RNA sequencing (RNA-seq) data were analyzed for identifying novel transcripts in zebrafish early development using an inhouse pipeline. We discovered 152 novel transcribed regions (NTRs), validated more than 10 NTRs and quantified their expression in early developmental stages. In our studies, we evaluated and applied a pooling approach for identifying variants susceptible to disease using high-throughput DNA sequencing. Based on RNA sequencing data, we provided new information for genome annotation on model organism zebrafish, which is valuable for studying the function of disease causative genes. In summary, the whole series of studies demonstrate how NGS can be applied in studying the genetic basis of complex disorders and assisting in follow-up functional studies in model organisms
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