948 research outputs found
Forward model for quantitative pulse-echo speed-of-sound imaging
Computed ultrasound tomography in echo mode (CUTE) allows determining the
spatial distribution of speed-of-sound (SoS) inside tissue using handheld
pulse-echo ultrasound (US). This technique is based on measuring the changing
phase of beamformed echoes obtained under varying transmit (Tx) and/or receive
(Rx) steering angles. The SoS is reconstructed by inverting a forward model
describing how the spatial distribution of SoS is related to the spatial
distribution of the echo phase shift. CUTE holds promise as a novel diagnostic
modality that complements conventional US in a single, real-time handheld
system. Here we demonstrate that, in order to obtain robust quantitative
results, the forward model must contain two features that were not taken into
account so far: a) the phase shift must be detected between pairs of Tx and Rx
angles that are centred around a set of common mid-angles, and b) it must
account for an additional phase shift induced by the error of the reconstructed
position of echoes. In a phantom study mimicking liver imaging, this new model
leads to a substantially improved quantitative SoS reconstruction compared to
the model that has been used so far. The importance of the new model as a
prerequisite for an accurate diagnosis is corroborated in preliminary volunteer
results
Fundamental issues in antenna design for microwave medical imaging applications
This paper surveys the development of microwave medical imaging and the fundamental challenges associated with microwave antennas design for medical imaging applications. Different microwave antennas used in medical imaging applications such as monopoles, bow-tie, vivaldi and pyramidal horn antennas are discussed. The challenges faced when the latter used in medical imaging environment are detailed. The paper provides the possible solutions for the challenges at hand and also provides insight into the modelling work which will help the microwave engineering community to understand the behaviour of the microwave antennas in coupling media
Application-Specific Broadband Antennas for Microwave Medical Imaging
The goal of this work is the introduction of efficient antenna structures on the basis of the requirement of different microwave imaging methods; i.e. quantitative and qualitative microwave imaging techniques. Several criteria are proposed for the evaluation of single element antenna structures for application in microwave imaging systems. The performance of the proposed antennas are evaluated in simulation and measurement scenarios
Approches tomographiques structurelles pour l'analyse du milieu urbain par tomographie SAR THR : TomoSAR
SAR tomography consists in exploiting multiple images from the same area acquired from a slightly different angle to retrieve the 3-D distribution of the complex reflectivity on the ground. As the transmitted waves are coherent, the desired spatial information (along with the vertical axis) is coded in the phase of the pixels. Many methods have been proposed to retrieve this information in the past years. However, the natural redundancies of the scene are generally not exploited to improve the tomographic estimation step. This Ph.D. presents new approaches to regularize the estimated reflectivity density obtained through SAR tomography by exploiting the urban geometrical structures.La tomographie SAR exploite plusieurs acquisitions d'une mĂȘme zone acquises d'un point de vue lĂ©gerement diffĂ©rent pour reconstruire la densitĂ© complexe de rĂ©flectivitĂ© au sol. Cette technique d'imagerie s'appuyant sur l'Ă©mission et la rĂ©ception d'ondes Ă©lectromagnĂ©tiques cohĂ©rentes, les donnĂ©es analysĂ©es sont complexes et l'information spatiale manquante (selon la verticale) est codĂ©e dans la phase. De nombreuse mĂ©thodes ont pu ĂȘtre proposĂ©es pour retrouver cette information. L'utilisation des redondances naturelles Ă certains milieux n'est toutefois gĂ©nĂ©ralement pas exploitĂ©e pour amĂ©liorer l'estimation tomographique. Cette thĂšse propose d'utiliser l'information structurelle propre aux structures urbaines pour rĂ©gulariser les densitĂ©s de rĂ©flecteurs obtenues par cette technique
Development of a Post-Processing Algorithm for Accurate Human Skull Profile Extraction via Ultrasonic Phased Arrays
Ultrasound Imaging has been favored by clinicians for its safety, affordability, accessibility, and speed compared to other imaging modalities. However, the trade-offs to these benefits are a relatively lower image quality and interpretability, which can be addressed by, for example, post-processing methods. One particularly difficult imaging case is associated with the presence of a barrier, such as a human skull, with significantly different acoustical properties than the brain tissue as the target medium. Some methods were proposed in the literature to account for this structure if the skull\u27s geometry is known. Measuring the skull\u27s geometry is therefore an important task that requires attention. In this work, a new edge detection method for accurate human skull profile extraction via post-processing of ultrasonic A-Scans is introduced. This method, referred to as the Selective Echo Extraction algorithm, SEE, processes each A-Scan separately and determines the outermost and innermost boundaries of the skull by means of adaptive filtering. The method can also be used to determine the average attenuation coefficient of the skull. When applied to simulated B-Mode images of the skull profile, promising results were obtained. The profiles obtained from the proposed process in simulations were found to be within 0.15 λ ± 0.11 λ or 0.09 ± 0.07 mm from the actual profiles. Experiments were also performed to test SEE on skull mimicking phantoms with major acoustical properties similar to those of the actual human skull. With experimental data, the profiles obtained with the proposed process were within 0.32 λ ± 0.25 λ or 0.19 ± 0.15 mm from the actual profile
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