21 research outputs found

    Ultrasound and Photoacoustic Techniques for Surgical Guidance Inside and Around the Spine

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    Technological advances in image-guidance have made a significant impact in surgical standards, allowing for safer and less invasive procedures. Ultrasound and photoacoustic imaging are promising options for surgical guidance given their real-time capabilities without the use of ionizing radiation. However, challenges to improve the feasibility of ultrasound- and photoacoustic-based surgical guidance persists in the presence of bone. In this thesis, we address four challenges surrounding the implementation of ultrasound- and photoacoustic-based surgical guidance in clinical scenarios inside and around the spine. First, we introduce a novel regularized implementation of short-lag spatial coherence (SLSC) beamforming, named locally-weighted short-lag spatial coherence (LW-SLSC). LW-SLSC improves the segmentation of bony structures in ultrasound images, thus reducing the hardware and software cost of registering pre and intra-operative volumes. Second, we describe a contour analysis framework to characterize and differentiate photoacoustic signals originating from cancellous and cortical bone, which is critical for a safety navigation of surgical tools through small bony cavities such as the pedicle. This analysis is also useful for localizing tool tips within the pedicle. Third, we developed a GPU approach to SLSC beamforming to improve the signal-to-noise ratio of photoacoustic targets using low laser energies, thus improving the performance of robotic visual servoing of tooltips and enabling miniaturization of laser systems in the operating room. Finally, we developed a novel acoustic-based atlas method to identify photoacoustic contrast agents and discriminate them from tissue using only two laser wavelengths. This approach significantly reduces acquisition times in comparison to conventional spectral unmixing techniques. These four contributions are beneficial for the transition of a combined ultrasound and photoacoustic-based image-guidance system towards more challenging scenarios of surgical navigation. Focusing on bone structures inside and surrounding the spine, the newly combined systems and techniques demonstrated herein feature robust, accurate, and real-time capabilities to register to preoperative images, localize surgical tool tips, and characterize biomarkers. These contributions strengthen the range of possibilities for spinous and transthoracic ultrasound and photoacoustic navigation, broaden the scope of this field, and shorten the road to clinical implementation in the operating room

    Patient-Specific Polyvinyl Alcohol Phantoms for Applications in Minimally Invasive Surgery

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    In biomedical engineering, phantoms are physical models of known geometric and material composition that are used to replicate biological tissues. Phantoms are vital tools in the testing and development of novel minimally invasive devices, as they can simulate the conditions in which devices will be used. Clinically, phantoms are also highly useful as training tools for minimally invasive procedures, such as those performed in regional anaesthesia, and for patient-specific surgical planning. Despite their widespread utility, there are many limitations with current phantoms and their fabrication methods. Commercial phantoms are often prohibitively expensive and may not be compatible with certain imaging modalities, such as ultrasound. Much of the phantom literature is complicated or hard to follow, making it difficult for researchers to produce their own models and it is highly challenging to create anatomically realistic phantoms that replicate real patient pathologies. Therefore, the aim of this work is to address some of the challenges with current phantoms. Novel fabrication methods and frameworks are presented to enable the creation of phantoms that are suitable for use in both the development of novel devices and as clinical training tools, for applications in minimally invasive surgery. This includes regional anaesthesia, brain tumour resection, and percutaneous coronary interventions. In such procedures, imaging is of key importance, and the phantoms developed are demonstrated to be compatible across a range of modalities, including ultrasound, computed tomography, MRI, and photoacoustic imaging

    Biomedical Photoacoustic Imaging and Sensing Using Affordable Resources

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    The overarching goal of this book is to provide a current picture of the latest developments in the capabilities of biomedical photoacoustic imaging and sensing in an affordable setting, such as advances in the technology involving light sources, and delivery, acoustic detection, and image reconstruction and processing algorithms. This book includes 14 chapters from globally prominent researchers , covering a comprehensive spectrum of photoacoustic imaging topics from technology developments and novel imaging methods to preclinical and clinical studies, predominantly in a cost-effective setting. Affordability is undoubtedly an important factor to be considered in the following years to help translate photoacoustic imaging to clinics around the globe. This first-ever book focused on biomedical photoacoustic imaging and sensing using affordable resources is thus timely, especially considering the fact that this technique is facing an exciting transition from benchtop to bedside. Given its scope, the book will appeal to scientists and engineers in academia and industry, as well as medical experts interested in the clinical applications of photoacoustic imaging

    PLGA Based Drug Carrier and Pharmaceutical Applications

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    Poly(lactic-co-glycolic acid) (PLGA) is one of the most successful polymers used for producing therapeutic devices, such as drug carriers (DC). PLGA is one of the few polymers that the Food and Drug Administration (FDA) has approved for human administration due to its biocompatibility and biodegradability. In recent years, DC produced with PLGA has gained enormous attention for its versatility in transporting different type of drugs, e.g., hydrophilic or hydrophobic small molecules, or macromolecules with a controlled drug release without modifying the physiochemical properties of the drugs. These drug delivery systems have the possibility/potential to modify their surface properties with functional groups, peptides, or other coatings to improve the interactions with biological materials. Furthermore, they present the possibility to be conjugated with specific target molecules to reach specific tissues or cells. They are also used for different therapeutic applications, such as in vaccinations, cancer treatment, neurological disorder treatment, and as anti-inflammatory agents. This book aims to focus on the recent progress of PLGA as a drug carrier and their new pharmaceutical applications

    High-resolution 3D printing enabled, minimally invasive fibre optic sensing and imaging probes

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    Minimally invasive surgical procedures have become more favourable to their traditional surgical counterparts due to their reduced risks, faster recovery times and decreased trauma. Despite this, there are still some limitations involved with these procedures, such as the spatial confinement of operating through small incisions and the intrinsic lack of visual or tactile feedback. Specialised tools and imaging equipment are required to overcome these issues. Providing better feedback to surgeons is a key area of research to enhance the outcomes and safety profiles of minimally invasive procedures. This thesis is centred on the development of new microfabrication methods to create novel fibre optic imaging and sensing probes that could ultimately be used for improving the guidance of minimally invasive surgeries. Several themes emerged in this process. The first theme involved the use and optimisation of high-resolution 3D injection of polymers as sacrificial layers onto which parylene-C was deposited. One outcome from this theme was a series of miniaturised parylene-C based membranes to create fibre optic pressure sensors for physiological pressure measurements and for ultrasound reception. The pressure sensor sensitivity was found to vary from 0.02 to 0.14 radians/mmHg, as the thickness of parylene was decreased from 2 to 0.5 μm. The ultrasound receivers were characterised and exhibited a noise equivalent pressure (NEP) value of ~100 Pa (an order of magnitude improvement compared to similarly sized piezoelectric hydrophones). A second theme employed high-resolution 3D printing to create microstructures of polydimethylsiloxane (PDMS) and subsequently formed nanocomposites, to create microscale acoustic hologram structures. This theme included the development of innovative manufacturing processes such as printing directly onto optical fibres, micro moulding and precise deposition which enabled the creation of such devices. These microstructures were investigated for reducing the divergence of photoacoustically-generated ultrasound beams. Taken together, the developments in this thesis pave the way for 3D microfabricated polymer-based fibre optic sensors that could find broad clinical utility in minimally invasive procedures

    Minimally invasive photoacoustic imaging:Current status and future perspectives

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    Photoacoustic imaging (PAI) is an emerging biomedical imaging modality that is based on optical absorption contrast, capable of revealing distinct spectroscopic signatures of tissue at high spatial resolution and large imaging depths. However, clinical applications of conventional non-invasive PAI systems have been restricted to examinations of tissues at depths less than a few cm due to strong light attenuation. Minimally invasive photoacoustic imaging (miPAI) has greatly extended the landscape of PAI by delivering excitation light within tissue through miniature fibre-optic probes. In the past decade, various miPAI systems have been developed with demonstrated applicability in several clinical fields. In this article, we present an overview of the current status of miPAI and our thoughts on future perspectives.status: publishe

    Imaging of human peripheral blood vessels during cuff occlusion with a compact LED-based photoacoustic and ultrasound system

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    Non-invasive imaging plays an important role in diagnosing and monitoring peripheral artery disease (PAD). Doppler ultrasound imaging can be used for measuring blood flow in this context. However, this technique frequently provides low contrast for flow in small vessels. Photoacoustic imaging can allow for the visualization of blood in small vessels, with direct contrast from optical absorption of hemoglobin. In this work, we investigate the potential applications of a compact LED-based photoacoustic (850 nm) and ultrasound imaging system for visualizing human peripheral blood vessels during cuff occlusion. Each measurement comprised three stages. First, a baseline measurement of a digital artery of a human finger from a volunteer without a diagnosis of PAD was performed for several seconds. Second, arterial blood flow was stopped using an occlusion cuff, with a rapid increase of pressure up to 220 mm Hg. Third, the occlusion cuff was released rapidly. Raw photoacoustic and ultrasound image data (frame rate: 70 Hz) were recorded for the entire duration of the measurement (20 s). The average photoacoustic image amplitude over an image region that enclosed the digital artery was calculated. With this value, pulsations of image amplitudes from the arteries was clearly visualized. The average photoacoustic image amplitude decreased during the increase in cuff pressure and it was followed by a rapid recovery during cuff release. With real-time non-invasive measurements of peripheral blood vessel dynamics in vivo, the compact LED-based system could be valuable for point-of-care imaging to guide treatment of PAD

    Enhancing photoacoustic visualization of medical devices with elastomeric nanocomposite coatings

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    Ultrasound (US) imaging is widely used for guiding minimally invasive procedures. However, with this modality, there can be poor visibility of interventional medical devices such as catheters and needles due to back-reflections outside the imaging aperture and low echogenicity. Photoacoustic (PA) imaging has shown promise with visualising bare metallic needles. In this study, we demonstrate the feasibility of a light emitting diode (LED)-based PA and US dual-modality imaging system for imaging metallic needles and polymeric medical catheters in biological tissue. Four medical devices were imaged with the system: two 20-gauge spinal needles with and without a multi-walled carbon nanotube / polydimethylsiloxane (MWCNT/PDMS) composite coating, and two 18-gauge epidural catheters with and without the MWCNT/PDMS composite coating. These devices were sequentially inserted into layers of chicken breast tissue within the US imaging plane. Interleaved PA and US imaging was performed during insertions of the needle and catheter. With US imaging, the uncoated needle had very poor visibility at an insertion angle of 45°. With PA imaging, the uncoated needle was not visible, but its coated counterpart was clearly visualised up to depths of 35 mm. Likewise, both catheters were not visible with US imaging. The uncoated catheter was not visible on PA images, but its coated counterpart was clearly visualised up to depths of 35 mm. We conclude that the highly absorbing CNT/PDMS composite coating conferred excellent visibility for medical devices with the LED-based PA imaging system and that it is promising for translation in minimally invasive procedures
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