The Bionic Clicker Mark I &amp; II

In this manuscript, we present two 'Bionic Clicker' systems, the first designed to demonstrate electromyography (EMG) based control systems for ...

University College London

We report a dual-wavelength passive mode locking regime where picosecond pulses are generated from both ground (lambda = 1263 nm) and excited state transitions (lambda = 1180 nm), in a GaAs-based monolithic two-section quantum-dot laser. Moreover, these results are reproduced by numerical simulations which provide a better insight on the dual-wavelength mode-locked operation.

Dual-wavelength mode-locked quantum-dot laser, via ground and excited state transitions: experimental and theoretical investigation.

Precise device guidance is important for interventional procedures in many different clinical fields including fetal medicine, regional anesthesia, interventional pain management, and interventional oncology. While ultrasound is widely used in clinical practice for real-time guidance, the image contrast that it provides can be insufficient for visualizing tissue structures such as blood vessels, nerves, and tumors. This study was centered on the development of a photoacoustic imaging system for interventional procedures that delivered excitation light in the ranges of 750 to 900 nm and 1150 to 1300 nm, with an optical fiber positioned in a needle cannula. Coregistered B-mode ultrasound images were obtained. The system, which was based on a commercial ultrasound imaging scanner, has an axial resolution in the vicinity of 100  μm and a submillimeter, depth-dependent lateral resolution. Using a tissue phantom and 800 nm excitation light, a simulated blood vessel could be visualized at a maximum distance of 15 mm from the needle tip. Spectroscopic contrast for hemoglobin and lipids was observed with ex vivo tissue samples, with photoacoustic signal maxima consistent with the respective optical absorption spectra. The potential for further optimization of the system is discussed.

Performance characteristics of an interventional multispectral photoacoustic imaging system for guiding minimally invasive procedures.

Optical clearing, in combination with recently developed optical imaging techniques, enables visualization and acquisition of high-resolution, three-dimensional images of biological structures deep within the tissue. Many different approaches can be used to reduce light absorption and scattering within the tissue, but there is a paucity of research on the quantification of clearing efficacy. With the use of a custom-made spectroscopy system, we developed a way to quantify the quality of clearing in biological tissue and applied it to the mouse brain. Three clearing techniques were compared: BABB (1:2 mixture of benzyl alcohol and benzyl benzoate, also known as Murray’s clear), pBABB (peroxide BABB, a modification of BABB which includes the use of hydrogen peroxide), and passive CLARITY. We found that BABB and pBABB produced the highest degree of optical clearing. Furthermore, the approach allows regional measurement of light attenuation to be performed, and our results show that light is most attenuated in regions with high lipid content. We provide a way to choose between the multiple clearing protocols available, and it could prove useful for evaluating images that are acquired with cleared tissues.

Quantification of light attenuation in optically cleared mouse brains.

Ultrasound phantoms are invaluable as training tools for vascular access procedures. We developed ultrasound phantoms with wall-less vessels using 3-dimensional printed chambers. Agar was used as a soft tissue-mimicking material, and the wall-less vessels were created with rods that were retracted after the agar was set. The chambers had integrated luer connectors to allow for fluid injections with clinical syringes. Several variations on this design are presented, which include branched and stenotic vessels. The results show that 3-dimensional printing can be well suited to the construction of wall-less ultrasound phantoms, with designs that can be readily customized and shared electronically.

Construction of 3-Dimensional Printed Ultrasound Phantoms With Wall-less Vessels.

Accurate and efficient guidance of medical devices to procedural targets lies at the heart of interventional procedures. Ultrasound imaging is commonly used for device guidance, but determining the location of the device tip can be challenging. Various methods have been proposed to track medical devices during ultrasound-guided procedures, but widespread clinical adoption has remained elusive. With ultrasonic tracking, the location of a medical device is determined by ultrasonic communication between the ultrasound imaging probe and a transducer integrated into the medical device. The signal-to-noise ratio (SNR) of the transducer data is an important determinant of the depth in tissue at which tracking can be performed. In this paper, the authors present a new generation of ultrasonic tracking in which coded excitation is used to improve the SNR without spatial averaging.

Coded excitation ultrasonic needle tracking: An in vivo study.

Image guidance plays a central role in minimally invasive fetal surgery such as photocoagulation of inter-twin placental anastomosing vessels to treat twin-to-twin transfusion syndrome (TTTS). Fetoscopic guidance provides insufficient sensitivity for imaging the vasculature that lies beneath the fetal placental surface due to strong light scattering in biological tissues. Incomplete photocoagulation of anastamoses is associated with postoperative complications and higher perinatal mortality. In this study, we investigated the use of multi-spectral photoacoustic (PA) imaging for better visualization of the placental vasculature. Excitation light was delivered with an optical fiber with dimensions that are compatible with the working channel of a fetoscope. Imaging was performed on an ex vivo normal term human placenta collected at Caesarean section birth. The photoacoustically-generated ultrasound signals were received by an external clinical linear array ultrasound imaging probe. A vein under illumination on the fetal placenta surface was visualized with PA imaging, and good correspondence was obtained between the measured PA spectrum and the optical absorption spectrum of deoxygenated blood. The delivery fiber had an attached fiber optic ultrasound sensor positioned directly adjacent to it, so that its spatial position could be tracked by receiving transmissions from the ultrasound imaging probe. This study provides strong indications that PA imaging in combination with ultrasonic tracking could be useful for detecting the human placental vasculature during minimally invasive fetal surgery.

Interventional Photoacoustic Imaging of the Human Placenta with Ultrasonic Tracking for Minimally Invasive Fetal Surgeries.

Anatomical models are important training and teaching tools in the clinical environment and are routinely used in medical imaging research. Advances in segmentation algorithms and increased availability of three-dimensional (3D) printers have made it possible to create cost-efficient patient-specific models without expert knowledge. We introduce a general workflow that can be used to convert volumetric medical imaging data (as generated by Computer Tomography (CT)) to 3D printed physical models. This process is broken up into three steps: image segmentation, mesh refinement and 3D printing. To lower the barrier to entry and provide the best options when aiming to 3D print an anatomical model from medical images, we provide an overview of relevant free and open-source image segmentation tools as well as 3D printing technologies. We demonstrate the utility of this streamlined workflow by creating models of ribs, liver, and lung using a Fused Deposition Modelling 3D printer.

Article	Year
Dual-wavelength mode-locked quantum-dot laser, via ground and excited state transitions: experimental and theoretical investigation. Optics express\| PubMed ID: 20588412	2010
Performance characteristics of an interventional multispectral photoacoustic imaging system for guiding minimally invasive procedures. Journal of biomedical optics\| PubMed ID: 26263417	2015
Quantification of light attenuation in optically cleared mouse brains. Journal of biomedical optics\| PubMed ID: 26277988	2015
Construction of 3-Dimensional Printed Ultrasound Phantoms With Wall-less Vessels. Journal of ultrasound in medicine : official journal of the American Institute of Ultrasound in Medicine\| PubMed ID: 27162278	2016
Coded excitation ultrasonic needle tracking: An in vivo study. Medical physics\| PubMed ID: 27370125	2016
Interventional Photoacoustic Imaging of the Human Placenta with Ultrasonic Tracking for Minimally Invasive Fetal Surgeries. Medical image computing and computer-assisted intervention : MICCAI ... International Conference on Medical Image Computing and Computer-Assisted Intervention\| PubMed ID: 28101537	2015
From medical imaging data to 3D printed anatomical models. PloS one\| PubMed ID: 28562693	2017

Daniil Nikitichev

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