186 research outputs found
Review of photoacoustic imaging plus X
Photoacoustic imaging (PAI) is a novel modality in biomedical imaging
technology that combines the rich optical contrast with the deep penetration of
ultrasound. To date, PAI technology has found applications in various
biomedical fields. In this review, we present an overview of the emerging
research frontiers on PAI plus other advanced technologies, named as PAI plus
X, which includes but not limited to PAI plus treatment, PAI plus new circuits
design, PAI plus accurate positioning system, PAI plus fast scanning systems,
PAI plus novel ultrasound sensors, PAI plus advanced laser sources, PAI plus
deep learning, and PAI plus other imaging modalities. We will discuss each
technology's current state, technical advantages, and prospects for
application, reported mostly in recent three years. Lastly, we discuss and
summarize the challenges and potential future work in PAI plus X area
Compensating for visibility artefacts in photoacoustic imaging with a deep learning approach providing prediction uncertainties
Conventional photoacoustic imaging may suffer from the limited view and
bandwidth of ultrasound transducers. A deep learning approach is proposed to
handle these problems and is demonstrated both in simulations and in
experiments on a multi-scale model of leaf skeleton. We employed an
experimental approach to build the training and the test sets using photographs
of the samples as ground truth images. Reconstructions produced by the neural
network show a greatly improved image quality as compared to conventional
approaches. In addition, this work aimed at quantifying the reliability of the
neural network predictions. To achieve this, the dropout Monte-Carlo procedure
is applied to estimate a pixel-wise degree of confidence on each predicted
picture. Last, we address the possibility to use transfer learning with
simulated data in order to drastically limit the size of the experimental
dataset.Comment: main text 10 pages + Supplementary materials 6 page
On the importance of low-frequency signals in functional and molecular photoacoustic computed tomography
In photoacoustic computed tomography (PACT) with short-pulsed laser
excitation, wideband acoustic signals are generated in biological tissues with
frequencies related to the effective shapes and sizes of the optically
absorbing targets. Low-frequency photoacoustic signal components correspond to
slowly varying spatial features and are often omitted during imaging due to the
limited detection bandwidth of the ultrasound transducer, or during image
reconstruction as undesired background that degrades image contrast. Here we
demonstrate that low-frequency photoacoustic signals, in fact, contain
functional and molecular information, and can be used to enhance structural
visibility, improve quantitative accuracy, and reduce spare-sampling artifacts.
We provide an in-depth theoretical analysis of low-frequency signals in PACT,
and experimentally evaluate their impact on several representative PACT
applications, such as mapping temperature in photothermal treatment, measuring
blood oxygenation in a hypoxia challenge, and detecting photoswitchable
molecular probes in deep organs. Our results strongly suggest that
low-frequency signals are important for functional and molecular PACT
Towards ultrasound full-waveform inversion in medical imaging
Ultrasound imaging is a front-line clinical modality with a wide range of applications. However, there are limitations to conventional methods for some medical imaging problems, including the imaging of the intact brain. The goal of this thesis is to explore and build on recent technological advances in ultrasonics and related areas such as geophysics, including the ultrasound data parallel acquisition hardware, advanced computational techniques for field modelling and for inverse problem solving. With the significant increase in the computational power now available, a particular focus will be put on exploring the potential of full-waveform inversion (FWI), a high-resolution image reconstruction technique which has shown significant success in seismic exploration, for medical imaging applications. In this thesis a range of technologies and systems have been developed in order to improve ultrasound imaging by taking advantage of these recent advances.
In the first part of this thesis the application of dual frequency ultrasound for contrast enhanced imaging of neurovasculature in the mouse brain is investigated. Here we demonstrated a significant improvement in the contrast-to-tissue ratio that could be achieved by using a multi-probe, dual frequency imaging system when compared to a conventional approach using a single high frequency probe. However, without a sufficiently accurate calibration method to determine the positioning of these probes the image resolution was found to be significantly reduced. To mitigate the impact of these positioning errors, a second study was carried out to develop a sophisticated dual probe ultrasound tomography acquisition system with a robust methodology for the calibration of transducer positions. This led to a greater focus on the development of ultrasound tomography applications in medical imaging using FWI. A 2.5D brain phantom was designed that consisted of a soft tissue brain model surrounded by a hard skull mimicking material to simulate a transcranial imaging problem. This was used to demonstrate for the first time, as far as we are aware, the experimental feasibility of imaging the brain through skull using FWI. Furthermore, to address the lack of broadband sensors available for medical FWI reconstruction applications, a deep learning neural network was proposed for the bandwidth extension of observed narrowband data. A demonstration of this proposed technique was then carried out by improving the FWI image reconstruction of experimentally acquired breast phantom imaging data. Finally, the FWI imaging method was expanded for3D neuroimaging applications and an in silico feasibility of reconstructing the mouse brain with commercial transducers is demonstrated.Open Acces
Photoacoustic imaging in biomedicine and life sciences
Photo-acoustic imaging, also known as opto-acoustic imaging, has become a widely popular modality for biomedical applications. This hybrid technique possesses the advantages of high optical contrast and high ultrasonic resolution. Due to the distinct optical absorption properties of tissue compartments and main chromophores, photo-acoustics is able to non-invasively observe structural and functional variations within biological tissues including oxygenation and deoxygenation, blood vessels and spatial melanin distribution. The detection of acoustic waves produced by a pulsed laser source yields a high scaling range, from organ level photo-acoustic tomography to sub-cellular or even molecular imaging. This review discusses significant novel technical solutions utilising photo-acoustics and their applications in the fields of biomedicine and life sciences
The Feasibility of Using X-Ray Induced Acoustic Computed Tomography for Non-Destructive Testing of Aircraft Structural
Aviation safety is a very important aspect of the aviation industry. One of the most important methods for increasing aviation safety is the non-destructive testing method. The non-destructive testing method is considered to be the most effective method for checking defects, widely used in the aviation industry. X-ray induced Acoustic Computed Tomography (XACT) is a new novel imaging modality based on the X-ray induced acoustic effect. A short-pulsed of X-rays are required to achieve a thermal response and generate acoustic waves due to thermoelastic expansion. XACT takes advantage of X-ray absorption contrast with the ultrasonic spatial resolution for deep imaging. The goal of this work is to demonstrate the feasibility of XACT for defect detection in aircraft structures as a non-destructive testing method to overcome the limitations of most frequent techniques used non-destructive testing (NDT) methods are outlined in Chapter 1.
In this work, there are two main objectives to demonstrate the XACT technique are as follows, (1) introduce and proving the feasibility of XACT through simple models and (2) a full demonstration of XACT with three models from simple to complex structures.
This work demonstrates that XACT has the potential to be implemented in-field NDT for aircraft maintenance and inspection due to its feasibility in detect defects with accessibility to a single side of the object
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