Browsing by Subject "Imaging"

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Advancements in Imaging of Concrete Members Using Shear Waves
(2018-12) Asadollahi, Aziz
The emergence of linear array devices employing dry point contact transducers emitting horizontal shear waves significantly increased the efficiency of data acquisition and enabled using imaging techniques for nondestructive evaluation of concrete members. Reverse time migration (RTM) is a mechanics-based imaging technique that has gained the attention of researchers in the context of nondestructive testing (NDT) in recent years. RTM offers a better focusing over synthetic aperture focusing technique (SAFT), a well-established real-time imaging method for NDT of concrete members, and enables locating reflectors with steep slopes and the bottom boundaries of embedded objects. Despite all advantages, RTM suffers from some limitations. It is computationally costly and demands a massive memory. In addition, RTM algorithm generates images with high-amplitude artifacts and assigns amplitudes to the points of a reconstructed image that are not a true representative of the reflectivity of the scanned medium at those points. This dissertation develops an analytical approach to resolve the computational cost and memory demand bottlenecks of the RTM when dry point contact transducers emitting horizontal shear waves are used for data acquisition. Horizontal shear waves preserve more energy than longitudinal waves after emission allowing inspection of concrete members in deeper depths. However, the lower wavelength of shear waves increases the potential of scattering by aggregates and air voids that affects the quality of the reconstructed images. This dissertation develops a 3D numerical tool to study the scattering attenuation of shear waves in concrete. An efficient algorithm is introduced to generate non-overlapping aggregates and air voids to study the effect of size, shape, and material properties of aggregates as well as the porosity of concrete on the scattering attenuation of shear waves. Moreover, it develops novel techniques to mitigate the high-amplitude artifacts of RTM images and to adjust the amplitudes assigned to the points of an image reconstructed by RTM for homogeneous and concrete members.
The Applied Use of Technology in Phenotyping Apple (Malus × domestica Borkh.) Fruit and Trees
(2019-07) Anderson, Joshua
Current phenotyping methods for apple (Malus × domestica Borkh.) fruit and trees are destructive, time and labor intensive and can be subjective. Fruit: A handheld NIR spectrometer was used to collect spectra along with traditional phenotyping of several fruit quality traits. Two trait spectral models (starch pattern index, and soluble solids concentration) had sufficient predictive ability across 15 cultivars. Temperature and outdoor limitations of the spectrometer were minimal compared to the importance of collecting more than a single scan per fruit to control for individual fruit heterogeneity. Trees: A low-cost RGB-D sensor was used to characterize trees of a rootstock experiment. The relationship between image-derived metrics and hand-measured was highest for tree height R2=0.93, and TCA R2=0.71. The predictive ability of cumulative yield by image based-tree volume was lower than by manual-measured tree volume. Tree volume, in general, did not improve upon other mixed models when estimating cumulative yield.
Characterizing the impact of genetic and environmental variation on maize utilizing phenomic approaches
(2020-08) Tirado, Sara
To gain a better understanding of how genotypic elements interact with the environment, we need to develop more efficient ways of monitoring plant phenotypes so that we can gather phenotypic data through time. Remote sensing technologies provide effective means to do this. Sensor, computational, and platform technologies keep evolving and provide avenues to evaluate how plants grow and respond to environmental conditions. The goals of this thesis were to develop methods and analytical procedures to evaluate maize plant phenotypic performance under varied environmental conditions. The first set of experiments were geared towards utilizing unmanned aerial vehicles equipped with RGB cameras to assess how maize plants grow in response to various field management conditions, including various planting dates and densities, and weather events. These tools were used to assess variation for lodging responses and downstream impacts on productivity. More generally, results from this thesis demonstrate that measurements collected early in development can be useful for improving predictions of end-season traits. The second set of experiments provided insights into using hyperspectral technologies for genotypic differentiation and abiotic stress detection. There is a large amount of variation in reflectance throughout maize leaves that can be useful in distinguishing different maize genotypes at the seedling stage and for detecting and quantifying abiotic stress conditions including cold, heat, and salt stress early in development. By documenting phenotypic differences across genotypes and environments through time in a more efficient manner by taking advantage of available remote sensing technologies, we can improve our understanding of how different environmental and genetic elements impact plant productivity and facilitate advancements in crop improvement and production.
Computational Modeling of Cardiac Devices Implanted in Specimens Preserved within the Visible Heart® Laboratories’ Human Heart Library
(2022-01) Cham, Nyimatoulie
The Visible Heart® Laboratories’ (VHL) Atlas of Cardiac Anatomy is an open public resource to students, medical professionals, and individuals in medical device companies that contains expansive cardiac anatomy and physiology information. Within this website is the human heart library, which contains 835 specimens overall, including perfusion-fixed and pre-fixed specimens collected from the Advanced Cardiac Anatomy and Physiology Course, as well as donated hearts received from LifeSource. The physical specimens are housed within the VHL (Minneapolis, Minnesota), and individuals that utilize the library can take pictures, make measurements, and perform device draping studies as long as these procedures are non-destructive. In this project, the main aim was to identify heart specimens within the VHL human heart library and build a database of the hearts that had associated implanted cardiac devices within. With the successful imaging of a large number of hearts with a variety of cardiac devices, these images will be made available on the free-access Atlas of Human Cardiac Device website: this will include photos and unity flythrough movies, as well as the resultant generated computational models.
Developing a Predictive Model and Novel Imaging Technique for the Failure of Polyethylene Insulators
(2019-08) Zoltek, Daniel
Polyethylene is the most widespread polymer used in insulative cable housings due to its low cost, high chemical resistivity and low permeability to liquids and gases. This does not mean, however, that the material is not susceptible to failure under environmental working conditions. Many techniques for monitoring both chemical and physical changes have been developed, though no attempts have been made to integrate these findings. Here, we put forth a model for the failure of polyethylene cable housings under thermooxidative conditions. This model revealed an absence of data on the monitoring of polyethylene crystalline structure during the aging process, which in part controls the insulative properties of the polyethylene. Polyethylene films (30 µm) were aged at 110°C for 24-hour periods in an oven and carbonyl content, a common aging indicator, was monitored. An ATR-FTIR crystallinity monitoring technique was developed and revealed a 3-phase change of crystalline structure upon thermal aging. To better visualize the hypothesized pore formation in the polyethylene, which follows aging, EIS was used to saturate pores with gold nanoparticles before elemental analysis and imaging with SEM. Results suggest the existence of these pores and the ability for ions to penetrate the aged films.
Diagnostic accuracy of panoramic radiograph and MRI for detecting signs of TMJ degenerative joint disease
(2016-07) Kaimal, Shanti
Background: To determine the diagnostic accuracy of panoramic radiograph and magnetic resonance imaging (MRI) for detection of signs of temporomandibular joint (TMJ) degenerative joint disease (DJD). Methods: Panoramic radiographs, bilateral TMJ MRI and bilateral TMJ computed tomography (CT) were performed on 705 subjects. Three calibrated board-certified radiologists blinded to the subjects’ clinical findings interpreted all images. Assessment of diagnostic accuracy of panoramic radiographs and MRI for detecting signs of DJD was compared to the reference-standard diagnoses derived from the CTs. DJD was defined by the presence of subcortical cyst, surface erosion, osteophyte or generalized sclerosis. Target sensitivity and specificity were > 70% and > 95%, respectively. Results: For panoramic radiographs, sensitivity and specificity were: subcortical cysts - 14%, 100% respectively; erosion - 20%, 100% respectively; osteophyte - 12%, 100% respectively and generalized sclerosis - 33%, 100%, respectively. For MRI, sensitivity and specificity were: subcortical cysts - 32%, 100% respectively; erosion - 35%, 99% respectively; osteophyte 71%, 98% respectively and generalized sclerosis 50%, 100% respectively. For diagnosis of signs of DJD based on panoramic radiographs, radiologists’ inter-examiner reliability was slight (k=0.16), moderate (k=0.47) when using MRI and substantial with CT images (k=0.71). Conclusions: Panoramic radiographs and MRI had below target sensitivity but above target specificity in detecting all CT-depicted signs of DJD with the exception of detection of MRI-depicted osteophytes, which had adequate diagnostic accuracy. Practical Implications: Use of CT to diagnosis signs of TMJ DJD is recommended to address the false negatives that can occur with panoramic radiographs and MRI.
Imaging Skins and Threads: An Exploration of Far-field Optical Imaging Systems Confined to a Two-dimensional or One-dimensional Form-factor
(2016-08) Burch, Jordan
The resolution diffraction limit of an imaging system is inversely proportional to the width of its aperture. The depth of these systems, however, is determined by the choice of architecture. To show that an imaging system can be confined to a plane or a line, while maintaining high far-field resolution, two new architectures are presented. The planar device, referred to as an imaging skin, uses a grating coupler to map points in the far-field to guided modes in a slab waveguide. Similarly, an imaging thread is a nearly one-dimensional device which uses a tilted fiber Bragg grating to couple points into a guided mode of an optical fiber. The diffraction gratings introduce a high degree of chromatic aberration. To maintain their resolution, imaging skins and threads must use a narrow spectral filter. When these devices are used at finite conjugates, only sources very near the object plane have high coupling efficiency. Both systems, despite their extreme form factors, are shown to have far-field resolution near the diffraction limit of a lens with a similar diameter.
Lanthanide-Based Probes for Oxidative Stress
(2014-06) Peterson, Katie
Oxidative stress, or the imbalance of reactive oxidative species and antioxidants, is implicated in a wide variety of physiological functions and diseases. Currently, little is known about the biological concentrations and the exact roles of individual species. In particular, the cellular concentration of hydroxyl radical and the etiology of this reactive oxygen species in disease states are unclear. The photophysical properties of luminescent lanthanide-based imaging agents and the magnetic properties of fluorinated contrast agents make them favorable candidates to monitor oxidative species in biological environments. Luminescent lanthanide-based probes for hydroxyl radical are presented. These probes utilize aromatic acid pre-antennas that sensitize terbium emission upon hydroxylation. The ability of hydroxylated and non-hydroxylated aromatic acids including benzoate, benzamide, isophthalate, isophthalamide, trimesate, and trimesamide to sensitize Tb DO3A was evaluated by time-delayed luminescence spectroscopy. The formation of a weak ternary complex between hydroxytrimeasamide and Tb-DO3A was confirmed by temperature-dependent titrations. The luminescence response of the bimolecular Tb DO3A and trimesamide probe to hydroxyl radical generated by the photolysis of hydrogen peroxide was investigated. The system exhibits excellent selectivity for hydroxyl radical over other biologically relevant reactive oxygen and nitrogen species. Next, fluorinated magnetic resonance imaging contrast agents responsive to hydroxyl radical are described. The 3,5-difluorobenzoic acid probe is water soluble and ratiometrically responds to hydroxyl radical. Upon hydroxylation, a fluoride ion is released. The relative signal intensity of the product and that of the unreacted contrast agent can then be used to monitor the analyte in a ratiometric manner by 19F NMR and 19F MRI. The selectivity of the system towards hydroxyl radical compared to other reactive oxygen and nitrogen species is also measured. Paramagnetic, lanthanide-based contrast agents incorporating the sensing moiety are also evaluated for increased sensitivity of detection compared to the diamagnetic analogs. Additionally, a family of lanthanide-based luminescent complexes based on a macrocyclic core featuring different sensitizing antennas and variable pendant arms are investigated in terms of their biological compatibility. The cellular uptake of Tb-DOTA complexes containing hydroxyisophthalamide (IAM), methoxyisophthalamide (IAM(OMe)), or phenathridine (Phen) antenna were comparable despite their differences in hydrophobicity. The luminescence quenching of Tb-DOTA-IAM(OMe) was also investigated in cell lysate by time-delayed spectroscopy. Pendant arms varying in hydrophobicity and charge were used to evaluate the effect of structural and electronic properties on cellular viability and cell association as measured by a MTT assay and ICP-MS, respectively. Regardless of the amide substituents, complexes based on Tb-DOTAm-IAM(OMe) core exhibited low cytotoxicity and low cellular association. Thus, complexes based on this platform are well-suited for the detection of extracellular analytes.
Neurocircuitry of Generalization of Avoidance Behavior following Pavlovian Conditioning in Adults with High and Low Trait Anxiety
(2016-08) van Meurs, Brian
One of the cardinal features of many anxiety disorders is maladaptive avoidance. While behavioral avoidance is important for survival and adaptive when danger is present, in the absence of a threat it is maladaptive. Signaled avoidance depends on Pavlovian learning that a neutral conditioned stimulus signals an ensuing aversive unconditioned stimulus. Maladaptive signaled avoidance could therefore result from abnormalities in Pavlovian conditioning. Overgeneralization of conditioned fear is one such abnormality that has been demonstrated in several anxiety disorders. To assess the relationship between anxiety and generalization of signaled avoidance behavior, 22 participants, with a range of trait anxiety scores split into two group of high and low anxiety, completed a generalization gradient, approach-avoidance fMRI task following Pavlovian discrimination conditioning. Results indicated the expected curvilinear generalization gradient in avoidance responses and ratings of risk, with group differences in avoidance responses. There were several functional regions of interest which also demonstrated the expected curvilinear gradient as well as group differences in percent BOLD signal change across the gradient. This was true for both Pavlovian trials, as well as during the decision making stage of the Instrumental trials. There were also several regions in which activations were significantly related to avoidance behavior. These results indicate that individuals with higher levels of trait anxiety are at increased risk of ‘maladaptive’ avoidance of safe stimuli that resemble danger-cues. Moreover brain areas such as the anterior insula and subgenual anterior cingulate cortex, and primary visual cortex, which are involved in the Pavlovian generalization of fear, are also involved in the overgeneralization of the avoidance response. Additional unexpected findings highlight the role of the cerebellum, somatosensory cortex, and gender in production and maintenance of an avoidance response.
Noninvasive imaging of three-dimensional ventricular electrical activity
(2012-08) Han, Chengzong
Noninvasive imaging of cardiac electrical activity is of great importance and can facilitate basic cardiovascular research and clinical diagnosis and management of various malignant cardiac arrhythmias. This dissertation research is aimed to investigate a novel physical-model-based 3-dimensional cardiac electrical imaging (3DCEI) approach. The 3DCEI approach is developed by mathematically combining high-density body surface electrocardiograms (ECGs) with the anatomical information. Computer simulation study and animal experiments were conducted to rigorously evaluate the performance of 3DCEI. The simulation results demonstrate that 3DCEI can localize the origin of activation and image the activation sequence throughout the three-dimensional ventricular myocardium. The performance of 3DCEI was also experimentally and rigorously evaluated through well-controlled animal validation studies in both the small animal model (rabbit) and large animal model (canine), with the aid of simultaneous intramural recordings from intra-cardiac mapping using plunge-needle electrodes inserted in the ventricular myocardium. The clinical relevance of 3DCEI was further demonstrated by investigating 3DCEI in cardiac arrhythmias from animal models with experimentally-induced cardiovascular diseases. The consistent agreement between the non-invasively imaged activation sequences and its directly measured counterparts in both the rabbit heart and canine heart implies that 3DCEI is feasible in reconstructing the spatial patterns of ventricular activation sequences, localizing the arrhythmogenic foci, and imaging dynamically changing arrhythmia on a beat-to-beat basis. The promising results presented in this dissertation study suggest that this cardiac electrical imaging approach may provide an important alternative for non-invasively imaging cardiac electrical activity throughout ventricular myocardium and may potentially become an important tool to facilitate clinical diagnosis and treatments of malignant ventricular arrhythmias.
Optimizing Metal Complexes as Bacteria-Specific Tracers for in vivo Nuclear Molecular Imaging and Modulators of the Nuclease Resistance of DNA Nanostructures
(2023-05) Joaqui Joaqui, Michel Andrey
Infectious diseases caused by bacteria remain one of the major global threats to human health. Rapid and precise diagnosis is thus crucial for preventing the propagation of these bacterial pathogens and achieving favorable treatment results for impacted patients. To achieve this, diagnostic methods must possess the ability to accurately detect the bacterial pathogen with high selectivity, while also being prompt to facilitate rapid containment and informed treatment decisions. In vivo nuclear molecular imaging modalities such as PET and SPECT have gained importance as alternative diagnostics techniques, especially in scenarios where the site of infection is unknown, or the extraction of sample is anatomically challenging rendering well-established in vitro diagnostic techniques impractical. The effectiveness of these in vivo imaging techniques heavily relies on the utilization of proper radiolabeled probes that target bacteria. Currently, there are no radiotracers available that can be swiftly and easily prepared and that exhibit the necessary selectivity for bacterial cells to enable clear and definitive diagnosis. The first part of this dissertation presents an investigation regarding the use of artificial siderophore analogs of enterobactin, a bacterial virulence factor, as promising scaffolds for the development of metal-based radiopharmaceutical agents suitable for the detection of bacteria in vivo. The study covers the rationale behind the design of the artificial enterobactin analogs, the study of the in vitro and in vivo stability of the 68Ga and 45Ti-labeled enterobactin analogs, their suitability as nuclear imaging agents, as well as the evaluation of their abilities to image a bacterial infection in vivo.The second part of this dissertation, on the other hand, is dedicated to exploring the stability challenges faced by DNA nanotechnology in biologically relevant environments, particularly the instability of DNA-based nanomaterials. DNA nanostructures exhibit unique properties and hold great potential in areas such as biotechnology, nanoelectronics, and nanomedicine. However, these materials encounter numerous hurdles, such as degradation by nucleases and enzymes when introduced into biological environments like blood, tissues, or cells. Such degradation significantly impairs the stability and performance of DNA nanomaterials, curtailing their effectiveness in biological and biomedical applications. Hence, the field of DNA nanotechnology is currently grappling with the critical challenge of devising techniques to enhance the stability and performance of DNA nanomaterials under such conditions. The second section of this dissertation describes a methodical exploration of the modulation of the degradation of DNA nanocages through reversible supramolecular functionalization with metal complexes. The study encompasses the development and synthesis of several coordination compounds featuring metal centers such as EuIII, TbIII, PtII, CuII, CoII, and RuII, as well as a diversity of ligands. Further, the binding affinities of these metal complexes for DNA nanostructures are assessed, and their ability to mitigate the degradation of DNA nanostructures in biologically relevant media is evaluated.
Polarization-sensitive optical coherence tomography using polarization-maintaining fibers
(2010-12) Al-Qaisi, Muhammad K.
Optical Coherence Tomography (OCT) is a sensitive imaging technique that generates cross-sectional images of turbid tissues with a micrometer-scale resolution. Polarization-Sensitive (PS) OCT adds additional contrast to OCT by detecting polarization alterations within tissues, and provides accurate OCT images in polarization-altering tissues. Common approaches to build PSOCT are either: simple but difficult to incorporate in clinics and laboratories, or fiber-based and flexible but expensive, sophisticated, and computationally demanding. We have developed a new approach to build PSOCT using Polarization-Maintaining Fibers (PMF). A single depth scan is sufficient to calculate reflectivity, retardance, and axis orientation information using computationally-inexpensive algorithms. We present novel PMF-based PSOCT systems and demonstrate sensitivity figures larger than 100 dB, equivalent to common approaches. The developed PMF-based interferometers are used to measure minute Faraday rotations in tissue-mimicking phantoms, and the polarization properties of unmyelinated nerves. A novel algorithm is also developed to correct for errors calculating the birefringence of samples, and generate interpretable PSOCT images.
Powerful Association Testing with Application to Neuroimaging Genetics
(2017-05) Xu, Zhiyuan
In spite of the huge success of the standard single-nucleotide polymorphism (SNP) based analysis in genome-wide association studies (GWASs), it has some limitations. First, it suffers power loss from a stringent significance level due to multiplicity adjust- ment for up to millions of tests. In addition, it has low power since the effect sizes of SNPs are usually small. Instead, gene-based testing might improve statistical power by aggregating moderate to weakly associated SNPs within each gene while greatly re- ducing the burden of multiple testing adjustment from millions to thousands. Second, almost all existing analyses do not explicitly account for (unknown) genetic hetero- geneity, leading to possible loss of power as convincingly shown in simulation studies (Londono et al., 2012; Qian and Shao, 2013; Zhou and Pan, 2009). Moreover, as there are many other data resources available (e.g. neuroimaging phenotypes, molecular phenotypes like gene expression) besides GWAS/DNA sequencing data, integrating them into GWAS is expected to boost statistical power. We first introduce a flexible framework to extend score-based testing in generalized linear models to more complex models, for example, mixed effect models. Second, we show that by accounting for genetic heterogeneity, more associated SNPs can be detected than the standard one-degree-of-freedom trend test in single SNP-based testing. Third, we propose a new adaptive aSPC test to detect associations between two random vectors in moderate to high dimensions; we also point out its connections to some existing association testing for multiple SNPs and multiple traits. Finally, we propose a novel gene-based association testing approach by incorporating weights derived from other data resources (e.g. from another eQTL dataset). We show the power gain of the new approach over two existing methods PrediXcan and TWAS, pointing out that both PrediXcan and TWAS are special cases of our new test.
A Single-Element Fiber Transducer for All-Optical Ultrasound and Photoacoustic Sensing
(2019-12) Vilanguppam Thathachary, Supriya
The past few decades have seen a rapid rise in minimally invasive medical procedures performed around the globe. These procedures have been made possible largely because of innovations in medical imaging and sensing to guide physicians in performing the interventions safely. Ultrasound technology has remained highly popular through this transition due to its safety and efficacy. However, the demand for miniature flexible devices for increased accessibility has prompted a shift toward all-optical ultrasound devices. Additionally, photoacoustic imaging and sensing have emerged as a promising technology with abilities to enhance diagnostic capabilities in several clinical applications, most significantly in the imaging of atherosclerotic plaque. The Fabry-perot ultrasound detector, being one of the more widespread optical ultrasound detection technologies, has been explored significantly in this context. This thesis presents a novel wave-guided configuration for fiber Fabry-Perot ultrasound detectors. This work demonstrates 16 times higher sensitivity than traditional piezoelelectric technology at comparable size scales. The chapters that follow present the simulations and experiments conducted around (a) optimizing the fabrication of the wave-guided fiber Fabry-Perot devices, (b) the complete optical and acoustic characterization of the fabricated devices, and (c) the potential improvements that can be made with incorporating dielectric mirrors. The thesis concludes with a discussion on the possible configurations for creating a complete ultrasound and photoacoustic probe for guiding minimally invasive interventions.
Temporal and spatial properties of the BOLD fMRI response to first and second order contrast in V1.
(2010-01) Thompson, Serena Kainoa Au
Our ability to detect, discriminate, and identify objects, to extract depth information through the use of stereopsis, and to learn about and classify different surface properties and textures are all secondary to first extracting useful cues about the local contrast within a visual scene. Contrast can be made by a change in a variety of visual features. We will specifically consider the contrast made by first-order and second-order luminance changes, specifically the contrast between local pixel luminance, and the contrast between local pixel luminance variance. There are a variety of tools available to `observe' cortical modulation to contrast, such as electrophysiological recordings of spike rate or local field potentials, fMRI BOLD modulation, magnetic encephalography (MEG), or visually evoked potentials (VEP), or through behavioral markers such as detection thresholds and discrimination thresholds. BOLD fMRI modulation provides a unique tool to measure the early visual response to local changes in image contrast with superior spatial specificity and minimal subject invasiveness, while psychophysics allows us to quantify the information human observers use to detect contrast. We will use both BOLD fMRI and psychophysics to explore three components of the human response to contrast: 1) how much do we use contrast when it forms the edge of a target shape compared to when it composes the interior area of the shape; 2) how well does second-order contrast modulate early visual cortex compared to the modulation elicited by first-order contrast; and 3) how accurate is the timing information of functional magnetic resonance imaging (fMRI) of the blood oxygen-level dependent (BOLD) modulation. Human observers do not always use contrast in the same way, and in the first experiment we study how human observers use first-order contrast in an image region versus second-order contrast at a region boundary when accomplishing a difficult detection task. We may expect V1 response to differ when contextual cues suggest that contrast is contained within an object border compared to when it fills in the interior texture of an object. Consider the case of two Holstein (black and white spotted) cows standing together, one partially occluding the other. We can use contrast cues to both identify which parts belong to which cow, as well as to determine the type of cow based on the spotted character of its hide. Both the segmentation task and the identification task require use of the same type of contrast information. However, optimal processing may change the way that low-level cues are handled in early visual cortex by modulation through context-dependent feedback as well learned information about cows. This may give rise to similar low-level cues producing different neural signals in early cortical areas, and subsequently, different sensitivity to cues in a border compared to a region. Our first experiment explores observers' use of contrast contained within the edge of a detectable target compared to the contrast that makes up the entire interior region of the target. Extraction of local image contrasts occurs at an early stage of visual processing, however, which types of contrast and how strongly they modulate early visual cortex remains undetermined. There are a variety of contrasts that could be compared. The first-order versus second-order contrast comparison is appealing because, with images generated by locally changing either average pixel luminance or pixel variance in white noise, we can create stimuli that are equal in orientation and spatial frequency information, contain detectable boundaries, and still require independent information to be extracted for detection. Our second experiment quantifies the response in primary visual cortex (V1) to first- and second-order using fMRI to acquire a spatially specific edge response in human subjects. Finally, it would be ideal to acquire both spatially and temporally specific measurements of cortical modulation in response to contrast changes. Several research groups around the world have begun using the relative timing between BOLD fMRI events to assign causal significance to the temporal order of modulation across different cortical areas using dynamic causal modeling. If, however, the timing of the modulation depends on the strength of the modulation, we could draw false conclusions from relative timing comparisons. Therefore, in our third experiment we measured three temporal characteristics of the BOLD hemodynamic response function (HRF) as a function of stimulus contrast: onset latency, time to peak, and full-width half-maximum. These explorations into the human and BOLD fMRI response to contrast are aimed at developing the current knowledge about how we perceive and parse the world around us, as well as how we can better interpret one of our measurement tools, fMRI, as a correlate of the neuronal activity occurring in early visual cortex. Both aims guide us toward a better understanding of the mechanisms we employ to process the rich information our visual systems acquire.
There’s a Lump in My Breast…Now What?
(2009-05-01) Martin, Angela Beale
When a patient finds a breast lump either accidentally or by breast self exam, there are many different imaging modalities and/or invasive procedures that may be done to determine if breast disease is present. This pamphlet describes many of the possible options a patient and physician may face to “work-up” a breast lump.
Three-Dimensional Imaging of Ventricular Electrical Activity: Method, Animal Validation and Clinical Evaluation
(2017-02) Yu, Long
Non-invasive cardiac electrical imaging techniques aim to directly visualize the intra-cardiac electrical activities and promise to assist in clinical diagnosis and treatment of cardiac arrhythmias, a family of highly dangerous disease leading to a hundreds of thousands of deaths and disabilities in the United States alone. In this dissertation, a line of investigations is included regarding cardiac electrical sparse imaging - a novel three dimensional cardiac imaging technique – from mathematical formulation of the imaging problem to validations studies covering numerical models, animal healthy and pathological models and patients with ventricular arrhythmias both during and before cardiac ablative procedures. With its spatiotemporal sparse problem, the novel imaging method incorporate cardiac electrophysiological features into the imaging process in order to achieve improvements in spatiotemporal resolution and, consequentially, general performance of the imaging technique. Simulation studies were conducted using a cardia automaton based heart-torso numerical model to verify the performance of the technique against various disturbances resembling the clinical challenges. Based on the numerical studies, rigorous animal studies using intra-cardiac simultaneous mapping technique were conducted to further validate the technique in biological systems such as canine and swine under healthy and pathological conditions such as myocardial infarction and congestive heart failure. Moreover, to evaluate the performance and compatibility of the technique in real life clinical challenges, further in-procedural and pre-procedural clinical studies were carried out on patients with ventricular arrhythmias. High accuracy and strong robustness can be observed by comparing the imaged activations with the mapped ones. The imaging technique achieved good performance not only in numerical simulations, but also in animal models with complex pathological conditions. Strong correlation was observed from the comparisons on ventricular arrhythmias with both focal and reentrant patterns. In further clinical studies, the technique also achieved good performance in localizing the arrhythmia foci and imaging the 3D activation pattern during the arrhythmias. The promising results shown in the studies indicate that the technique has good capability in visualizing the whole heart electrical activities and in providing key information such as arrhythmia foci and reentry pathways to assist in clinical practice in various pathological conditions.
Tracking your twin pregnancy using ultrasound
(2012-04-09) Kelley, Kyrsten

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