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Search Results: 1 - 10 of 211764 matches for " Nancy L. Ford "
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Phantom study of the impact of adaptive statistical iterative reconstruction (ASiRTM) on image quality for paediatric computed tomography  [PDF]
Angjelina Protik, Karen Thomas, Paul Babyn, Nancy L. Ford
Journal of Biomedical Science and Engineering (JBiSE) , 2012, DOI: 10.4236/jbise.2012.512A100
Abstract:

Quantitative analysis of image quality will be helpful for designing ASiRTM-enhanced paediatric CT protocols, balancing image quality and radiation dose. Catphan600 phantom studies were performed on a GE Discovery HD750 64-slice CT scanner. Images were reconstructed with 0% - 100% ASiRTM (tube current 150 mA, variable kVp 80 - 140) in order to determine the optimal ASiRTM-Filtered Back Projection (FBP) blend. Images reconstructed with a 50% ASiRTM-50% FBP blend were compared to FBP images (0% ASiRTM) over a wide range of kVp (80 - 140) and mA (10 - 400) values. Measurements of image noise, CT number accuracy and uniformity, spatial and contrast resolution, and low contrast detectability were performed on axial and reformatted coronal images. Improvements in CNR, low contrast detectability and radial uniformity were observed in ASiRTM images compared to FBP images. 50% ASiRTM was associated with a 26% - 30% reduction in image noise. Changes in noise texture were observed at higher %

Monitoring vascular changes induced by photodynamic therapy using contrast-enhanced micro-computed tomography  [PDF]
Otilia C. Nasui, Stuart K. Bisland, Nancy L. Ford
Journal of Biomedical Science and Engineering (JBiSE) , 2013, DOI: 10.4236/jbise.2013.62016
Abstract:

The aim of this study was to determine whether contrast-enhanced micro-computed tomography can be used for non-invasive imaging of the early-stage changes in the vasculature of tumours that have been treated with photodynamic therapy (PDT). The subjects used were C3H mice with an RIF-1 tumour implanted subcutaneously and allowed to grow for 3 weeks prior to treatment. The experimental groups were PDT-treated (150 J/cm2 and 50 J/cm2) and control (150 J/cm2 light-only and untreated). The laser light exposure was performed at 15 - 30 minutes after the administration of the photosensitizer (BPD-MA). The contrast-enhanced micro-computed tomography imaging procedure consisted of eight-second scans taking place before treatment and up to 24 hours after treatment. The 150 J/cm2 PDT group showed a significant increase in the ratio of blood volume to tumour volume at 2, 8 and 24 hours after treatment when compared to pre-treatment measurements (p < 0.01). The observed increase in the blood volume to tumour volume at the later time points corresponds to a decrease in epithelial coverage on immunohistochemical stained (CD31) slides for the 150 J/cm2 PDT group at 24 hours after treatment. This preliminary study indicates that micro-CT can detect compromised vasculature in tumours treated with high-fluence photodynamic therapy as early as 2 hours post treatment.

Does Resampled Image Data Offer Quantitative Image Quality Benefit for Pediatric CT?  [PDF]
Nancy L. Ford, Angjelina Protik, Paul Babyn, Karen Thomas
Journal of Biomedical Science and Engineering (JBiSE) , 2014, DOI: 10.4236/jbise.2014.76036
Abstract: Acquiring CT images with thin slices can improve resolution and detectability, but cause an increase in the image noise. To compensate for the additional image noise, the kVp or mA can be increased, which carries a dose penalty to the patient. We investigate the image quality achieved in MPR images reformatted from different slice thicknesses 0.625 mm and 5 mm, to determine if a thicker slice could be resampled to smaller thickness with minimal loss of image information. Catphan?600 phantom was imaged using selected kVp/mA settings (80 kVp/250 mA, 100 kVp/ 150 mA and 120 kVp/200 mA) to generate slices with thicknesses of 0.625 mm and 5 mm using a GE Discovery HD750 64-slice CT scanner to investigate the impact of the acquisition slice thickness on the overall image quality in MPRs. Measurements of image noise, uniformity, contrast-to-noise ratio (CNR), low contrast detectability and limiting spatial resolution were performed on axial and coronal multiplanar reformatted images (MPRs). Increased noise, reduced contrast-to-noise ratio, and improved limiting spatial resolution and low contrast detection were observed in 2 mm coronal MPRs generated with 0.625 mm thin slices when compared to the MPRs from 5 mm thick slices. If the 2 mm coronal MPRs acquired with 5 mm slices are resampled to 0.6 mm slice thickness, the reductions in limiting resolution and low contrast detection are compensated, although with reduced uniformity and increased image noise. Thick slice image acquisitions yield better CNR and less noise in the images, whereas thin slices exhibited improved spatial resolution and low contrast detectability. Retrospectively resampling into thinner slices before obtaining the coronal MPRs provided a balance between image smoothness and identifying fine image detail. Which approach provides the optimal image quality may also depend on the imaging task, size and composition of the features of interest, and radiologist preference.
Optimization of Image Quality in Retrospective Respiratory-Gated Micro-CT for Quantitative Measurements of Lung Function in Free-Breathing Rats  [PDF]
Nancy L. Ford, Andrew Jeklin, Karen Yip, Darren Yohan, David W. Holdsworth, Maria Drangova
Journal of Biomedical Science and Engineering (JBiSE) , 2014, DOI: 10.4236/jbise.2014.74020
Abstract: Objective: To optimize scan time and X-ray dose with no loss of image quality for retrospectively gated micro-CT scans of free-breathing rats. Methods: Five free-breathing rats were scanned using a dynamic micro-CT scanner over 10 continuous gantry rotations (50 seconds and entrance dose of 0.28 Gy). The in-phase projection views were selected and reconstructed, representing peak inspiration and end expiration from all 10 rotations and progressively fewer rotations. A least error method was also used to ensure that all angular positions were filled. Image quality and reproducibility for physiological measurements were compared for the two techniques. Results: The least error approach underestimated the lung volume, air content in the lung at peak inspiration, and tidal volume. Other measurements showed no differences between the projection-sorting techniques. Conclusions: Seven gantry rotations (35 seconds and 0.2 Gy dose) proved to be the optimal protocol for both the in-phase images and the least error images.
Design and Development of a High-Throughput System for Learning and Memory Research on Zebrafish  [PDF]
Hamed Hanafi Alamdari, Nancy Kilcup, Zachary Ford, Florentin Wilfart, David C. Roach, Michael Schmidt
Journal of Behavioral and Brain Science (JBBS) , 2018, DOI: 10.4236/jbbs.2018.86023
Abstract: Background: Since 2004, zebrafish have become the state-of-the-art, in vivo model for biomedical research due to their genetic and physiological homology with humans, inexpensive high-quantity breeding, and quick development in a highly-controlled environment suitable for longitudinal studies. New Method: To fully utilize the zebrafish model, a novel, automated, high-throughput system was designed. Shoals of five zebrafish were placed in 16 tanks and automatically fed over two days for a total of 16 training sessions. Color LED lights were used as the stimulus for each shoal coinciding with the release of food for a duration of 20 seconds. This system was tested on two age groups: 6- and 11-month-old. Results: After three training sessions, the median height of the school in the tank during stimulus was significantly higher than that of the naïve fish during the first training session. All subsequent training sessions demonstrated similar behaviour. A decline in memory retention, as defined by a reduction in the median height during light stimulus (i.e. no simultaneous food delivery), was observed 8 days post training. Comparison with existing methods: The high-throughput nature of this system allows for simultaneous training of 16 tanks of fish under identical conditions without human interaction and provides a means to rapidly assess their learning and memory behaviours. Conclusion: Results provide a baseline for understanding the normal cognitive processes of learning and memory retention in zebrafish. This work paves the way for future studies on the impacts of therapeutic agents on these cognitive processes.
An Independent Assessment of the Monthly PRISM Gridded Precipitation Product in Central Oklahoma  [PDF]
Jeanne M. Schneider, Donald L. Ford
Atmospheric and Climate Sciences (ACS) , 2013, DOI: 10.4236/acs.2013.32026
Abstract:

Accurate, long-term records of precipitation are required for the development of climate-informed decision support tools for agriculture. But rain gauges are too sparsely located to meet this need, and radar-derived precipitation measurements are too recent in duration. Using all readily available station records, spatiotemporally continuous estimates of precipitation were created by the PRISM Climate Group to address this problem. As with all interpolated data, the validity of the gridded PRISM product requires validation, and given the extreme spatiotemporal variability of precipitation, such validation is essential. Previous work comparing the monthly precipitation product against contributing rain gauge data revealed inconsistencies that prompted the analysis reported herein. As a basis for checking the accuracy of the PRISM product, independent precipitation data gathered at a USDA research laboratory in central Oklahoma were quality controlled, including comparison to a co-located automated rain gauge operated by the Oklahoma Mesonet. Results indicate that the independent USDA gauge data are of sufficient quality to use in the evaluation of the PRISM product. The area average of the independent USDA data over a matching size area was then used to validate colocated gridded PRISM estimates. The validation results indicate that the monthly gridded PRISM precipitation estimates are close to the independent observed data in terms of means (smaller by 3% to 4.5%) and cumulative probability distributions (within ~4%), but with variances too small by 7% to 11%. From the point of view of agricultural decision support, these results indicate that PRISM estimates might be useful for probabilistic applications, such as downscaling climate forecasts or driving weather generators, assuming appropriate corrections to the higher-order statistics were applied. However, the number of months with potentially significant differences precludes the use of PRISM estimates for any retrospective month-by-month analyses of possible interactions between climate, crop management, and productivity.

Transcriptional profiling of MnSOD-mediated lifespan extension in Drosophila reveals a species-general network of aging and metabolic genes
Christina Curtis, Gary N Landis, Donna Folk, Nancy B Wehr, Nicholas Hoe, Morris Waskar, Diana Abdueva, Dmitriy Skvortsov, Daniel Ford, Allan Luu, Ananth Badrinath, Rodney L Levine, Timothy J Bradley, Simon Tavaré, John Tower
Genome Biology , 2007, DOI: 10.1186/gb-2007-8-12-r262
Abstract: A doxycycline-regulated system was used to over-express manganese-SOD (MnSOD) in adult Drosophila, yielding increases in mean and maximal lifespan of 20%. Increased lifespan resulted from lowered initial mortality rate and required MnSOD over-expression in the adult. Transcriptional profiling indicated that the expression of specific genes was altered by MnSOD in a manner opposite to their pattern during normal aging, revealing a set of candidate biomarkers of aging enriched for carbohydrate metabolism and electron transport genes and suggesting a true delay in physiological aging, rather than a novel phenotype. Strikingly, cross-dataset comparisons indicated that the pattern of gene expression caused by MnSOD was similar to that observed in long-lived Caenorhabditis elegans insulin-like signaling mutants and to the xenobiotic stress response, thus exposing potential conserved longevity promoting genes and implicating detoxification in Drosophila longevity.The data suggest that MnSOD up-regulation and a retrograde signal of reactive oxygen species from the mitochondria normally function as an intermediate step in the extension of lifespan caused by reduced insulin-like signaling in various species. The results implicate a species-conserved net of coordinated genes that affect the rate of senescence by modulating energetic efficiency, purine biosynthesis, apoptotic pathways, endocrine signals, and the detoxification and excretion of metabolites.Reactive oxygen species (ROS) such as superoxide, hydrogen peroxide, and hydroxyl radical are produced as byproducts of normal cellular metabolism. These ROS, especially hydrogen peroxide, are participants in cellular signaling pathways [1]. In addition, ROS can damage macromolecules and this process is implicated in human aging and disease [2]. Among the most important regulators of ROS levels are the superoxide dismutase (SOD) enzymes [3,4]: Cu/ZnSOD in the cytoplasm and outer mitochondrial space, and MnSOD exclusively in th
Negative Energy Densities in Quantum Field Theory
L. H. Ford
Physics , 2009, DOI: 10.1142/S0217751X10049633
Abstract: Quantum field theory allows for the suppression of vacuum fluctuations, leading to sub-vacuum phenomena. One of these is the appearance of local negative energy density. Selected aspects of negative energy will be reviewed, including the quantum inequalities which limit its magnitude and duration. However, these inequalities allow the possibility that negative energy and related effects might be observable. Some recent proposals for experiments to search for sub-vacuum phenomena will be discussed. Fluctuations of the energy density around its mean value will also be considered, and some recent results on a probability distribution for the energy density in two dimensional spacetime are summarized.
Casimir Force between a Dielectric Sphere and a Wall: A Model for Amplification of Vacuum Fluctuations
L. H. Ford
Physics , 1998, DOI: 10.1103/PhysRevA.58.4279
Abstract: The interaction between a polarizable particle and a reflecting wall is examined. A macroscopic approach is adopted in which the averaged force is computed from the Maxwell stress tensor. The particular case of a perfectly reflecting wall and a sphere with a dielectric function given by the Drude model is examined in detail. It is found that the force can be expressed as the sum of a monotonically decaying function of position and of an oscillatory piece. At large separations, the oscillatory piece is the dominant contribution, and is much larger than the Casimir-Polder interaction that arises in the limit that the sphere is a perfect conductor. It is argued that this enhancement of the force can be interpreted in terms of the frequency spectrum of vacuum fluctuations. In the limit of a perfectly conducting sphere, there are cancellations between different parts of the spectrum which no longer occur as completely in the case of a sphere with frequency dependent polarizability. Estimates of the magnitude of the oscillatory component of the force suggest that it may be large enough to be observable.
Gravitons and Lightcone Fluctuations
L. H. Ford
Physics , 1994, DOI: 10.1103/PhysRevD.51.1692
Abstract: Gravitons in a squeezed vacuum state, the natural result of quantum creation in the early universe or by black holes, will introduce metric fluctuations. These metric fluctuations will introduce fluctuations of the lightcone. It is shown that when the various two-point functions of a quantized field are averaged over the metric fluctuations, the lightcone singularity disappears for distinct points. The metric averaged functions remain singular in the limit of coincident points. The metric averaged retarded Green's function for a massless field becomes a Gaussian which is nonzero both inside and outside of the classical lightcone. This implies some photons propagate faster than the classical light speed, whereas others propagate slower. The possible effects of metric fluctuations upon one-loop quantum processes are discussed and illustrated by the calculation of the one-loop electron self-energy.
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