Pattern identification of biomedical images with time series: contrasting THz pulse imaging with DCE-MRIs

Objective We provide a survey of recent advances in biomedical image analysis and classification from emergent imaging modalities such as terahertz (THz) pulse imaging (TPI) and dynamic contrast-enhanced magnetic resonance images (DCE-MRIs) and identification of their underlining commonalities. Methods Both time and frequency domain signal pre-processing techniques are considered: noise removal, spectral analysis, principal component analysis (PCA) and wavelet transforms. Feature extraction and classification methods based on feature vectors using the above processing techniques are reviewed. A tensorial signal processing de-noising framework suitable for spatiotemporal association between features in MRI is also discussed. Validation Examples where the proposed methodologies have been successful in classifying TPIs and DCE-MRIs are discussed. Results Identifying commonalities in the structure of such heterogeneous datasets potentially leads to a unified multi-channel signal processing framework for biomedical image analysis. Conclusion The proposed complex valued classification methodology enables fusion of entire datasets from a sequence of spatial images taken at different time stamps; this is of interest from the viewpoint of inferring disease proliferation. The approach is also of interest for other emergent multi-channel biomedical imaging modalities and of relevance across the biomedical signal processing community

On the integration of deformation and relief measurement using ESPI

The combination of relief and deformation measurement is investigated for improving the accuracy of Electronic Speckle-Pattern Interferometry (ESPI) data. The nature of sensitivity variations within different types of interferometers and with different shapes of objects is analysed, revealing significant variations for some common interferometers. Novel techniques are developed for real-time measurement of dynamic events by means of carrier fringes. This allows quantification of deformation and relief, where the latter is used in the correction of the sensitivity variations of the former

Project OASIS: The Design of a Signal Detector for the Search for Extraterrestrial Intelligence

An 8 million channel spectrum analyzer (MCSA) was designed the meet to meet the needs of a SETI program. The MCSA puts out a very large data base at very high rates. The development of a device which follows the MCSA, is presented

An electromagnetic imaging system for metallic object detection and classification

PhD ThesisElectromagnetic imaging currently plays a vital role in various disciplines, from engineering to medical applications and is based upon the characteristics of electromagnetic fields and their interaction with the properties of materials. The detection and characterisation of metallic objects which pose a threat to safety is of great interest in relation to public and homeland security worldwide. Inspections are conducted under the prerequisite that is divested of all metallic objects. These inspection conditions are problematic in terms of the disruption of the movement of people and produce a soft target for terrorist attack. Thus, there is a need for a new generation of detection systems and information technologies which can provide an enhanced characterisation and discrimination capabilities. This thesis proposes an automatic metallic object detection and classification system. Two related topics have been addressed: to design and implement a new metallic object detection system; and to develop an appropriate signal processing algorithm to classify the targeted signatures. The new detection system uses an array of sensors in conjunction with pulsed excitation. The contributions of this research can be summarised as follows: (1) investigating the possibility of using magneto-resistance sensors for metallic object detection; (2) evaluating the proposed system by generating a database consisting of 12 real handguns with more than 20 objects used in daily life; (3) extracted features from the system outcomes using four feature categories referring to the objects’ shape, material composition, time-frequency signal analysis and transient pulse response; and (4) applying two classification methods to classify the objects into threats and non-threats, giving a successful classification rate of more than 92% using the feature combination and classification framework of the new system. The study concludes that novel magnetic field imaging system and their signal outputs can be used to detect, identify and classify metallic objects. In comparison with conventional induction-based walk-through metal detectors, the magneto-resistance sensor array-based system shows great potential for object identification and discrimination. This novel system design and signal processing achievement may be able to produce significant improvements in automatic threat object detection and classification applications.Iraqi Cultural Attaché, Londo

Quantitative subsurface defect evaluation by pulsed phase thermography: depth retrieval with the phase

La Thermographie de Phase Pulsée (TPP) est une technique d’Évaluation Non-Destructive basée sur la Transformée de Fourier pouvant être considérée comme étant le lien entre la Thermographie Pulsée, pour laquelle l’acquisition de données est rapide, et la Thermographie Modulée, pour laquelle l’extraction de la profondeur est directe. Une nouvelle technique d’inversion de la profondeur reposant sur l’équation de la longueur de diffusion thermique : μ=(α /πf)½, est proposée. Le problème se résume alors à la détermination de la fréquence de borne fb, c à d, la fréquence à laquelle un défaut à une profondeur particulière présente un contraste de phase suffisant pour être détecté dans le spectre des fréquences. Cependant, les profils de température servant d’entrée en TPP, sont des signaux non-périodiques et non-limités en fréquence pour lesquels, des paramètres d’échantillonnage Δt, et de troncature w(t), doivent être soigneusement choisis lors du processus de discrétisation du signal. Une méthodologie à quatre étapes, basée sur la Dualité Temps-Fréquence de la Transformée de Fourier discrète, est proposée pour la détermination interactive de Δt et w(t), en fonction de la profondeur du défaut. Ainsi, pourvu que l’information thermique utilisée pour alimenter l’algorithme de TPP soit correctement échantillonnée et tronquée, une solution de la forme : z=C1μ, peut être envisagée, où les valeurs expérimentales de C1 se situent typiquement entre 1.5 et 2. Bien que la détermination de fb ne soit pas possible dans le cas de données thermiques incorrectement échantillonnées, les profils de phase exhibent quoi qu’il en soit un comportement caractéristique qui peut être utilisé pour l’extraction de la profondeur. La fréquence de borne apparente f’b, peut être définie comme la fréquence de borne évaluée à un seuil de phase donné φd et peut être utilisée en combinaison avec la définition de la phase pour une onde thermique : φ=z /μ, et le diamètre normalisé Dn=D/z, pour arriver à une expression alternative. L'extraction de la profondeur dans ce cas nécessite d'une étape additionnelle pour récupérer la taille du défaut.Pulsed Phase Thermography (PPT) is a NonDestructive Testing and Evaluation (NDT& E) technique based on the Fourier Transform that can be thought as being the link between Pulsed Thermography, for which data acquisition is fast and simple; and Lock-In thermography, for which depth retrieval is straightforward. A new depth inversion technique using the phase obtained by PPT is proposed. The technique relies on the thermal diffusion length equation, i.e. μ=(α /π·f)½, in a similar manner as in Lock-In Thermography. The inversion problem reduces to the estimation of the blind frequency, i.e. the limiting frequency at which a defect at a particular depth presents enough phase contrast to be detected on the frequency spectra. However, an additional problem arises in PPT when trying to adequately establish the temporal parameters that will produce the desired frequency response. The decaying thermal profiles such as the ones serving as input in PPT, are non-periodic, non-band-limited functions for which, adequate sampling Δt, and truncation w(t), parameters should be selected during the signal discretization process. These parameters are both function of the depth of the defect and of the thermal properties of the specimen/defect system. A four-step methodology based on the Time-Frequency Duality of the discrete Fourier Transform is proposed to interactively determine Δt and w(t). Hence, provided that thermal data used to feed the PPT algorithm is correctly sampled and truncated, the inversion solution using the phase takes the form: z=C 1 μ, for which typical experimental C 1 values are between 1.5 and 2. Although determination of fb is not possible when working with badly sampled data, phase profiles still present a distinctive behavior that can be used for depth retrieval purposes. An apparent blind frequency f’b , can be defined as the blind frequency at a given phase threshold φd , and be used in combination with the phase delay definition for a thermal wave: φ=z /μ, and the normalized diameter, Dn=D/z, to derive an alternative expression. Depth extraction in this case requires an additional step to recover the size of the defect.La Termografía de Fase Pulsada (TFP) es una técnica de Evaluación No-Destructiva basada en la Transformada de Fourier y que puede ser vista como el vínculo entre la Termografía Pulsada, en la cual la adquisición de datos se efectúa de manera rápida y sencilla, y la Termografía Modulada, en la que la extracción de la profundidad es directa. Un nuevo método de inversión de la profundidad por TFP es propuesto a partir de la ecuación de la longitud de difusión térmica: μ=(α /π·f)½. El problema de inversion se reduce entonces a la determinación de la frecuencia límite fb (frecuencia a la cual un defecto de profundidad determinada presenta un contraste de fase suficiente para ser detectado en el espectro de frecuencias). Sin embargo, las curvas de temperatura utilizadas como entrada en TFP, son señales no-periódicas y no limitadas en frecuencia para las cuales, los parámetros de muestreo Δt, y de truncamiento w(t), deben ser cuidadosamente seleccionados durante el proceso de discretización de la señal. Una metodología de cuatro etapas, basada en la Dualidad Tiempo-Frecuencia de la Transformada de Fourier discreta, ha sido desarrollada para la determinación interactiva de Δt y w(t), en función de la profundidad del defecto. Así, a condición que la información de temperatura sea correctamente muestreada y truncada, el problema de inversión de la profundidad por la fase toma la forma : z=C 1 μ, donde los valores experimentales de C 1 se sitúan típicamente entre 1.5 y 2. Si bien la determinación de fb no es posible en el caso de datos térmicos incorrectamente muestreados, los perfiles de fase exhiben de cualquier manera un comportamiento característico que puede ser utilizado para la extracción de la profundidad. La frecuencia límite aparente f’b , puede ser definida como la frecuencia límite evaluada en un umbral de fase dado φd , y puede utilizarse en combinación con la definición de la fase para una onda térmica: φ=z /μ, y el diámetro normalizado Dn , para derivar una expresión alternativa. La determinación de la profundidad en este caso, requiere de una etapa adicional para recuperar el tamaño del defecto

Optophone design: optical-to-auditory vision substitution for the blind

An optophone is a device that turns light into sound for the benefit of blind people. The present project is intended to produce a general-purpose optophone to be worn on the head about the house and in the street, to give the wearer a detailed description in sound of the'scene he is facing. The device will therefore consist'of an'electronic camera, some signal-processing electronics, earphones`, and a battery. The two major problems are the derivation of (a) the most suitable mapping from images to sounds, and (b) an algorithm to perform the mapping in real'time on existing electronic components. This thesis concerns problem (a). Chapter 2 goes into the general scene-to-sound mapping problem in some detail'and presents the work of earlier investigators. Chapter 3 1- discusses the design of tests to evaluate the performance of candidate mappings. A theoretical performance test (TPT) is derived. Chapter 4 applies the TPT to the most obvious mapping, the cartesian piano transform. Chapter 5 applies the TPT to a mapping based on the cosine transform. Chapter 6 attempts to derive a mapping by principal component analysis, using the inaccuracies of human sight and hearing and the statistical properties of real scenes and sounds. Chapter 7 presents a complete scheme, implemented in software, for representing digitised colour scenes by audible digitised stereo sound. Chapter 8 tries to decide how'many numbers are required to specify a steady spectrum with no noticeable degradation. Chapter 9 looks'at a scheme designed to produce more natural-sounding sounds related to more meaningful portions of the scene. This scheme maps windows in the scene to steady spectral patterns of short duration, the location of the window being conveyed by simulated free-field listening. Chapter 10 gives detailed recommendations as to further work

Modal Analysis of Millimetre-wave and Terahertz Imaging Systems

This thesis presents the theory and applications of electromagnetic field calculation using orthogonal Gaussian beam modes within the context of far-infrared imaging systems. Laguerre and Hermite-Gaussian modes have been frequently reported in the analysis of paraxial millimetre-wave propagation in astronomical optical systems. Here the method of Gaussian beam mode analysis (GBMA) is extended to fields of optical research that have until recently been associated with wavelengths in the visible band. Using recently derived expressions for the non-paraxial diffraction of Hermite-Gaussian modes, the author demonstrates the modal calculation of far-field intensity distributions with less angular restriction on the accuracy of the method compared to the conventional paraxial description of orthogonal Gaussian modes. This method shows excellent agreement with predictions from more rigourous fullwave numerical methods such as the finite-difference time-domain algorithm, which is also described as a software tool in the modelling of horn and lens antennas. The properties of diffraction limited Bessel beams is described using the Laguerre-Gaussian expansion of conical lenses, and experimental measurements of a conical lens is presented to explore the validity of the use of these optical elements as horn coupled devices in millimetre wave imaging systems. A study of diffractive Fresnel lenses has been undertaken with a comparison of experimentally measured fields with those predicted by the modal techniques. The effects of such lenses on ultrashort paraxial pulses are also investigated using a novel numerical description of few-cycle fields as a superposition of pulsed Laguerre- Gaussian modes. The application of digital holography in the far-infra red band has the prospect of diffraction limited imaging systems without creating distortions and aberrations which is a common problem in conventional techniques using lenses and mirrors. The author presents results from a simple proof-of-concept system which exhibits the potential of this technique for application in, for example, mm-wave security imaging

Modal Analysis of Millimetre-wave and Terahertz Imaging Systems

This thesis presents the theory and applications of electromagnetic field calculation using orthogonal Gaussian beam modes within the context of far-infrared imaging systems. Laguerre and Hermite-Gaussian modes have been frequently reported in the analysis of paraxial millimetre-wave propagation in astronomical optical systems. Here the method of Gaussian beam mode analysis (GBMA) is extended to fields of optical research that have until recently been associated with wavelengths in the visible band. Using recently derived expressions for the non-paraxial diffraction of Hermite-Gaussian modes, the author demonstrates the modal calculation of far-field intensity distributions with less angular restriction on the accuracy of the method compared to the conventional paraxial description of orthogonal Gaussian modes. This method shows excellent agreement with predictions from more rigourous fullwave numerical methods such as the finite-difference time-domain algorithm, which is also described as a software tool in the modelling of horn and lens antennas. The properties of diffraction limited Bessel beams is described using the Laguerre-Gaussian expansion of conical lenses, and experimental measurements of a conical lens is presented to explore the validity of the use of these optical elements as horn coupled devices in millimetre wave imaging systems. A study of diffractive Fresnel lenses has been undertaken with a comparison of experimentally measured fields with those predicted by the modal techniques. The effects of such lenses on ultrashort paraxial pulses are also investigated using a novel numerical description of few-cycle fields as a superposition of pulsed Laguerre- Gaussian modes. The application of digital holography in the far-infra red band has the prospect of diffraction limited imaging systems without creating distortions and aberrations which is a common problem in conventional techniques using lenses and mirrors. The author presents results from a simple proof-of-concept system which exhibits the potential of this technique for application in, for example, mm-wave security imaging