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Glycerol-3-phosphate cytidylyltransferase from 𝘚𝘵𝘢𝘱𝘩𝘺𝘭𝘰𝘤𝘰𝘤𝘤𝘶𝘴 𝘢𝘶𝘳𝘦𝘶𝘴 complexed with CTP (TarDₛₐ-CTP) was crystallized by the hanging drop-vapor diffusion method at 22°C. Determination of crystallization condition included examination of the amount of precipitant, investigation of the effects of small molecules, and alteration of the rate of diffusion. With these three optimization steps, crystals suitable for x-ray diffraction study were produced. During data processing, TarDₛₐ-CTP was determined to belong to the space group P3₁21, with unit-cell dimensions a=b=92.2 and c=156.1Å. The crystal structure of TarDₛₐ-CTP was solved to 3.0Å by molecular replacement, using TagD from 𝘉𝘢𝘤𝘪𝘭𝘭𝘶𝘴 𝘴𝘶𝘣𝘵𝘪𝘭𝘪𝘴 as a search model. Unlike the search model, TarDₛₐ appears as a tetramer in the asymmetric unit. This result also confirms the gel-filtration and ultracentrifugation studies that were done previously. Although TarDₛₐ crystals were grown in the presence of CTP, the crystal structure does not reveal convincing data for the location and position of this co-factor. However, the data suggests a possible location for CTP in one of the four subunits in an orientation that differs from that of TagD_Bₛ. Unfortunately, the resolution of this data set at 3.0Å is not high enough to corroborate this finding. / Thesis / Master of Science (MS)

X-ray devices have demonstrated the ability to characterize a material at the molecular and atomic levels. This ability is particularly important for detecting plastic explosives, where object shape information cannot be used. X-ray devices are relatively inexpensive compared to many other detection technologies. X-ray technology is considered as the technology for detecting illicit materials. Using x-ray technology, a material's <i>density-</i> and <i>effective atomic number</i> or <i>Z_eff</i>-related information can be determined. In theory, an illicit material can be identified using those two pieces of information. This dissertation discusses explosives detection in passenger luggage bags. The x-ray technology used is called <i>R-L</i> multi-sensing technology. The <i>R-L</i> technology was developed by researchers at Virginia Tech. It is the first true multisensing technology used for explosive detection. It uses dual-energy transmission and scatter technologies to obtain characteristic values of an object, i.e., <i>R</i> and <i>L</i>. The material type of this object can then be determined using <i>R-L</i> plane. The characteristic value <i>R</i> is computed using signals from dual-energy transmission modality. <i>R</i> is related to <i>Z_eff</i>. The characteristic value L is computed using signals from low-energy transmission and scatter modalities. <i>L</i> is related to density. Compared to single-sensing technologies and pseudo multi-sensing technologies, the detection accuracy of <i>R-L</i> technology should be much higher. The <i>R</i> and <i>L</i> values of an object can only be computed from an object's <i><b>true</b></i> gray levels. <i><b>True</b></i> gray level refers to the measured gray level of an object when it is not overlapped with any other objects. The problem is objects in a bag almost always overlap with other objects. Being able to identify the object of interest and remove the overlap effects becomes the key issue that needs to be solved. The discussion in this dissertation focuses on the development of the image-processing system used on this multiple sensor system. This image-processing system is comprised of four steps. The first step is to spatially register images from all the sensing modalities. The second step is to remove noise using the edge-preserving smoothing algorithm. The third step is to segment image into regions with relatively uniform gray levels. The fourth step is to compute the true gray levels for objects of interest using the mathematical models for removing overlapping effects. Most of the research focuses on developing a robust segmentation algorithm for segmenting x-ray bag images and developing mathematical models for removing object overlapping effects. The unique contribution of this dissertation includes the development of those mathematical models used for removing object-overlapping effects, and the development of the algorithm for determining an object's true gray levels. The experimental verification shows that the algorithms for registration, smoothing, and segmentation work well. The algorithm that computes the true gray levels of an object can perform the computation quite precisely in transmission modality. However, the methods that were developed for computing an object's true gray levels in scatter images are much less accurate. / Ph. D.

Yes / In relation to wrist imaging, the accepted requirement is two orthogonal projections obtained at 90°, each with the wrist in neutral position. However, the literature and anecdotal experience suggests that this principle is not universally applied. Method: This multiphase study was undertaken across eight different hospitals sites. Compliance with standard UK technique was confirmed if there was a change in ulna orientation between the dorsi-palmar (DP) and lateral wrist projections. A baseline evaluation for three days was randomly identified from the preceding three months. An educational intervention was implemented using a poster to demonstrate standard positioning. To measure the impact of the intervention, further evaluation took place at two weeks (early) and three months (late). Results: Across the study phases, only a minority of radiographs demonstrated compliance with the standard technique, with an identical anatomical appearance of the distal ulna across the projections. Initial compliance was 16.8% (n = 40/238), and this improved to 47.8% (n = 77/161) post-intervention, but declined to 32.8% (n = 41/125) within three months. The presence of pathology appeared to influence practice, with a greater proportion of those with an abnormal radiographic examination demonstrating a change in ulna appearances in the baseline cohort (p

Yes / The properties of nitrogen centres acting either as hydrogen-bond or Brønsted acceptors in solid molecular acid–base complexes have been probed by N 1s X-ray photoelectron spectroscopy (XPS) as well as 15N solid-state nuclear magnetic resonance (ssNMR) spectroscopy and are interpreted with reference to local crystallographic structure information provided by X-ray diffraction (XRD). We have previously shown that the strong chemical shift of the N 1s binding energy associated with the protonation of nitrogen centres unequivocally distinguishes protonated (salt) from hydrogen-bonded (co-crystal) nitrogen species. This result is further supported by significant ssNMR shifts to low frequency, which occur with proton transfer from the acid to the base component. Generally, only minor chemical shifts occur upon co-crystal formation, unless a strong hydrogen bond is formed. CASTEP density functional theory (DFT) calculations of 15N ssNMR isotropic chemical shifts correlate well with the experimental data, confirming that computational predictions of H-bond strengths and associated ssNMR chemical shifts allow the identification of salt and co-crystal structures (NMR crystallography). The excellent agreement between the conclusions drawn by XPS and the combined CASTEP/ssNMR investigations opens up a reliable avenue for local structure characterization in molecular systems even in the absence of crystal structure information, for example for non-crystalline or amorphous matter. The range of 17 different systems investigated in this study demonstrates the generic nature of this approach, which will be applicable to many other molecular materials in organic, physical, and materials chemistry. / EPSRC, Sanofi-Aventis

Yes / An automated closed-loop dose control system balances the radiation dose delivered to patients and the quality of images produced in cardiac x-ray imaging systems. Using computer simulations, this study compared two designs of automatic x-ray dose control in terms of the radiation dose and quality of images produced. The first design, commonly in x-ray systems today, maintained a constant dose rate at the image receptor. The second design maintained a constant image quality in the output images. A computer model represented patients as a polymethylmetacrylate phantom (which has similar x-ray attenuation to soft tissue), containing a detail representative of an artery filled with contrast medium. The model predicted the entrance surface dose to the phantom and contrast to noise ratio of the detail as an index of image quality. Results showed that for the constant dose control system, phantom dose increased substantially with phantom size (x5 increase between 20 cm and 30 cm thick phantom), yet the image quality decreased by 43% for the same thicknesses. For the constant quality control, phantom dose increased at a greater rate with phantom thickness (>x10 increase between 20 cm and 30 cm phantom). Image quality based dose control could tailor the x-ray output to just achieve the quality required, which would reduce dose to patients where the current dose control produces images of too high quality. However, maintaining higher levels of image quality for large patients would result in a significant dose increase over current practice. / This work has been performed in the project PANORAMA, funded by grants from Belgium, Italy, France, the Netherlands, and the United Kingdom, and the ENIAC Joint Undertaking.

No / The aim of this research was to explore x-ray beam parameters with intent to optimize pediatric x-ray settings in the cardiac catheterization laboratory. This study examined the effects of peak x-ray tube voltage kVp and of copper Cu x-ray beam filtration independently on the image quality to dose balance for pediatric patient sizes. The impact of antiscatter grid removal on the image quality to dose balance was also investigated. Methods: Image sequences of polymethyl methacrylate phantoms approximating chest sizes typical of pediatric patients were captured using a modern flat-panel receptor based x-ray imaging system. Tin was used to simulate iodine-based contrast medium used in clinical procedures. Measurements of tin detail contrast and flat field image noise provided the contrast to noise ratio. Entrance surface dose ESD and effective dose E measurements were obtained to calculate the figure of merit FOM , CNR2 / dose, which evaluated the dose efficiency of the x-ray parameters investigated. The kVp, tube current mA , and pulse duration were set manually by overriding the system’s automatic dose control mechanisms. Images were captured with 0, 0.1, 0.25, 0.4, and 0.9 mm added Cu filtration, for 50, 55, 60, 65, and 70 kVp with the antiscatter grid in place, and then with it removed. Results: For a given phantom thickness, as the Cu filter thickness was increased, lower kVp was favored. Examining kVp alone, lower values were generally favored, more so for thinner phantoms. Considering ESD, the 8.5 cm phantom had the highest FOM at 50 kVp using 0.4 mm of Cu filtration. The 12 cm phantom had the highest FOM at 55 kVp using 0.9 mm Cu, and the 16 cm phantom had highest FOM at 55 kVp using 0.4 mm Cu. With regard to E, the 8.5 and 12 cm phantoms had the highest FOM at 50 kVp using 0.4 mm of Cu filtration, and the 16 cm phantom had the highest FOM at 50 kVp using 0.25 mm Cu. Antiscatter grid removal improved the FOM for a given set of x-ray conditions. Under aforesaid optimal settings, the 8.5 cm phantom FOM improved by 24% and 33% for ESD and E, respectively. Corresponding improvements were 26% and 24% for the 12 cm phantom and 6% and 15% for the 16 cm phantom. Conclusions: For pediatric patients, using 0.25–0.9 mm Cu filtration in the x-ray beam while maintaining 50–55 kVp, depending on patient size, provided optimal x-ray image quality to dose ratios. These settings, adjusted for x-ray tube loading limits and clinically acceptable image quality, should provide a useful strategy for optimizing iodine contrast agent based cardiac x-ray imaging. Removing the antiscatter grid improved the FOM for the 8.5 and 12 cm phantoms, therefore grid removal is recommended for younger children. Improvement for the 16 cm phantom declined into the estimated margin of error for the FOM; the need for grid removal for older children would depend on practical feasibility in the clinical environment. / Philips Healthcare

Yes / Modern cardiac x-ray imaging systems regulate their radiation output based on the thickness of the patient to maintain an acceptable signal at the input of the x-ray detector. This approach does not account for the context of the examination or the content of the image displayed. We have developed a machine vision algorithm that detects iodine-filled blood vessels and fits an idealized vessel model with the key parameters of contrast, diameter, and linear attenuation coefficient. The spatio-temporal distribution of the linear attenuation coefficient samples, when appropriately arranged, can be described by a simple linear relationship, despite the complexity of scene information. The algorithm was tested on static anthropomorphic chest phantom images under different radiographic factors and 60 dynamic clinical image sequences. It was found to be robust and sensitive to changes in vessel contrast resulting from variations in system parameters. The machine vision algorithm has the potential of extracting real-time context sensitive information that may be used for augmenting existing dose control strategies. / Project PANORAMA, funded by grants from Belgium, Italy, France, the Netherlands, United Kingdom, and the ENIAC Joint Undertaking.