No description available.

It is well known that lead is toxic. Since the full effects, particularly of long term, low level exposure are not well understood, further knowledge of lead metabolism has significant public health implications. Traditionally, clinical studies of lead's effect on health have relied heavily on blood lead levels as an indicator of lead exposure. However, this is unsatisfactory, because blood lead levels principally reflect only recent exposure and lead in serum is more readily bioavailable than whole blood. Over 90% of the lead body burden is in bone, where it has a long residence time. Therefore, bone lead measurements are reflective of cumulative exposure. The bone lead detection system at McMaster University uses a ¹⁰⁹Cd source, which is positioned at the centre of the detector face (HPGE). This arrangement allows great flexibility, since one can sample lead in a range of different bone sites due to a robust normalization technique that eliminates the need to correct for bone geometry, thickness of overlying tissue, and other related factors. Lead in both the tibia and the calcaneus, whole blood lead, and serum lead have been measured in a group of 49 active lead workers (Nova Pb bone lead survey). Before studying the interrelationships between the above measurements, work was done to improve the programs which fit the bone lead spectra. That is, work was done to link the amplitudes of the alpha and beta peaks and to investigate the sensitivity of the analysis on the channel ranges and start parameters. The main goal of this project was to carefully study the interrelationships between the major components of any human lead metabolism model, bone, whole blood, and serum, in order to establish a solid basis for computer modelling of lead metabolism. / Thesis / Master of Science (MSc)

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)

This report describes the industrial research work done during the summer of 1986. The main objective of this research was to develop a high resolution X-ray imaging system for mammographic applications. The basic set up of such system is quite simple: it consists of an x-ray tube; an x-ray sensor (which is coupled to the read out electronics), and the optical scanner assembly which serves as the reading device. Based on the feasibility studies carried out two years ago, much of the work during the past summer was targeted to improve the existing prototype, and to test out the new x-ray sensors. A new optical assembly was built for this system, which was used to examine the optical resolution of the new sensors. Experimental results were analysed using calculations of the resolution (MTF) of the sensors, and the results indicate that the latest sensors are capable of resolving a 1mm diameter object. Unfortunately, due to the limitation of time, no x-ray exposure test were done on test targets. However, a theoretical model describing the x-ray sensors responses to x-ray radiation and laser light (based on previous work carried out by A. Zermeno et al, 1979) is presented here. Also, the results of the research work, carried out since the feasibility study up until the end of the summer of 1986, indicate that the sensors have a great potential for achieving limiting resolutions in the range of "0.1mm" objects. / Thesis / Master of Engineering (ME)

This thesis explores the use of skin iron concentration, assessed using a portable x- ray fluorescence (PXRF) analyzer, as an indicator of liver iron concentration. Ultrasound images were acquired from four sites on human cadavers: thenar eminence (TE), between the metacarpophalangeal joint 1 and 2 (MJ), patella (P), and plantar arch (PA). Skin thickness was subsequently measured using boundary detection software applied to the ultrasound images. Skin iron concentrations, from the same sites, were obtained directly from 13 cadavers using a PXRF analyzer. As the iron concentrations determined using PXRF may have been impacted due to beam attenuation through the skin, these iron concentrations were subsequently corrected using the Beer-Lambert Law accounting for the skin thickness at each site. Huber XRF is a bulk tissue measurement system that was used to measure iron concentrations from the extracted samples of the four sites. The skin iron concentrations determined using both PXRF and Huber XRF were compared to evaluate the agreement between the two methods. As such, samples from the four sites were extracted and the iron concentrations of the extracted samples were measured using a Huber X-Ray Fluorescence (XRF) analyzer as the control. A statistically significant relationship with a p-value of <0.01 and a strong correlation with a R2 value of 0.87 was seen between the corrected skin iron concentrations determined using PXRF and the skin iron concentrations determined using Huber XRF analysis of the extracted samples. Thus, the skin iron concentrations obtained using PXRF are representative of the skin iron concentrations collected by Huber XRF. For further validation, liver samples were obtained from 6 of the 13 cadavers and the liver iron concentrations were assessed using Huber XRF. The non- corrected PXRF, corrected PXRF and the Huber XRF skin iron concentrations were then compared with the liver iron concentrations. The relationships between iron concentrations measured at the PA site and in the liver were found to be statistically significant with strong correlations (R2 = 0.94 for Huber XRF, R2 = 0.87 for non-corrected PXRF, and R2 = 0.95 for corrected PXRF). Therefore, the skin iron concentrations at the PA site determined by PXRF and determined by Huber XRF analysis of skin samples could be used in the future as a surrogate marker for the liver iron concentrations in humans. / Thesis / Master of Science (MSc)

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 / 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.

Yes / The purpose of this work is to report on a machine vision approach for the automated measurement of x-ray image contrast of coronary arteries lled with iodine contrast media during interventional cardiac procedures. A machine vision algorithm was developed that creates a binary mask of the principal vessels of the coronary artery tree by thresholding a standard deviation map of the direction image of the cardiac scene derived using a Frangi lter. Using the mask, average contrast is calculated by tting a Gaussian model to the greyscale pro le orthogonal to the vessel centre line at a number of points along the vessel. The algorithm was applied to sections of single image frames from 30 left and 30 right coronary artery image sequences from di erent patients. Manual measurements of average contrast were also performed on the same images. A Bland-Altman analysis indicates good agreement between the two methods with 95% con dence intervals -0.046 to +0.048 with a mean bias of 0.001. The machine vision algorithm has the potential of providing real-time context sensitive information so that radiographic imaging control parameters could be adjusted on the basis of clinically relevant image content. / Project PANORAMA, funded by grants from Belgium, Italy, France, the Netherlands, and the United Kingdom, and the ENIAC Joint Undertaking.