Power Approaches for Implantable Medical Devices.

Implantable medical devices have been implemented to provide treatment and to assess in vivo physiological information in humans as well as animal models for medical diagnosis and prognosis, therapeutic applications and biological science studies. The advances of micro/nanotechnology dovetailed with novel biomaterials have further enhanced biocompatibility, sensitivity, longevity and reliability in newly-emerged low-cost and compact devices. Close-loop systems with both sensing and treatment functions have also been developed to provide point-of-care and personalized medicine. Nevertheless, one of the remaining challenges is whether power can be supplied sufficiently and continuously for the operation of the entire system. This issue is becoming more and more critical to the increasing need of power for wireless communication in implanted devices towards the future healthcare infrastructure, namely mobile health (m-Health). In this review paper, methodologies to transfer and harvest energy in implantable medical devices are introduced and discussed to highlight the uses and significances of various potential power sources

Editorial

In recent years, we have observed spectacular advancements in the area of nano-circuits and systems at several levels, from the fabrication material and device levels to the system and application levels. New emerging materials provide us with a wealth of new devices such as (silicon) nanowires, graphene, and carbon nanotubes fabricated in various technologies. Applications of these devices are vast and include, but are not limited to, new computing and memory structures, super-capacitors, as well as nano-bio-sensors based on the molecular combination of molecular probes to electronic devices. This special issue of the Journal on Emerging and Selected Topics in Circuits and Systems (JETCAS) has the purpose to collect some selected contributions to the workshop as well as other works in this domain, all subject to peer review. In particular, this issue focuses on two specific topics: biomedical circuits and systems, and 3-D integrated circuits and systems. This choice is motivated by a synergy of the spontaneous contributions in these areas as well as by the importance of these fields. We will review these two areas at large before briefly summarizing the contributions

Development of three-dimensional, ex vivo optical imaging

The ability to analyse tissue in 3-D at the mesoscopic scale (resolution: 2-50 µm) has proven essential in the study of whole specimens and individual organs. Techniques such as ex vivo magnetic resonance imaging (MRI) and X-ray computed tomography (CT) have been successful in a number of applications. Although MRI has been used to image embryo development and gene expression in 3-D, its resolution is not sufficient to discriminate between the small structures in embryos and individual organs. Furthermore, since neither MRI nor X-ray CT are optical imaging techniques, none of them is able to make use of common staining techniques. 3-D images can be generated with confocal microscopy by focusing a laser beam to a point within the sample and collecting the fluorescent light coming from that specific plane, eliminating therefore out-of-focus light. However, the main drawback of this microscopy technique is the limited depth penetration of light (~1 mm). Tomographic techniques such as optical projection tomography (OPT) and light sheet fluorescence microscopy (also known as single plane illumination microscopy, SPIM) are novel methods that fulfil a requirement for imaging of specimens which are too large for confocal imaging and too small for conventional MRI. To allow sufficient depth penetration, these approaches require specimens to be rendered transparent via a process known as optical clearing, which can be achieved using a number of techniques. The aim of the work presented in this thesis was to develop methods for threedimensional, ex vivo optical imaging. This required, in first instance, sample preparation to clear (render transparent) biological tissue. In this project several optical clearing techniques have been tested in order to find the optimal method per each kind of tissue, focusing on tumour tissue. Indeed, depending on its structure and composition (e.g. amount of lipids or pigments within the tissue) every tissue clears at a different degree. Though there is currently no literature reporting quantification of the degree of optical clearing. Hence a novel, spectroscopic technique for measuring the light attenuation in optically cleared samples is described in this thesis and evaluated on mouse brain. 5 Optical clearing was applied to the study of cancer. The main cancer model investigated in this report is colorectal carcinoma. Fluorescently labelled proteins were used to analyse the vascular network of colorectal xenograft tumours and to prove the effect of vascular disrupting agents on the vascular tumour network. Furthermore, optical clearing and fluorescent compounds were used for ex vivo analysis of perfusion of a human colorectal liver metastasis model

Physical principles for scalable neural recording

Simultaneously measuring the activities of all neurons in a mammalian brain at millisecond resolution is a challenge beyond the limits of existing techniques in neuroscience. Entirely new approaches may be required, motivating an analysis of the fundamental physical constraints on the problem. We outline the physical principles governing brain activity mapping using optical, electrical, magnetic resonance, and molecular modalities of neural recording. Focusing on the mouse brain, we analyze the scalability of each method, concentrating on the limitations imposed by spatiotemporal resolution, energy dissipation, and volume displacement. Based on this analysis, all existing approaches require orders of magnitude improvement in key parameters. Electrical recording is limited by the low multiplexing capacity of electrodes and their lack of intrinsic spatial resolution, optical methods are constrained by the scattering of visible light in brain tissue, magnetic resonance is hindered by the diffusion and relaxation timescales of water protons, and the implementation of molecular recording is complicated by the stochastic kinetics of enzymes. Understanding the physical limits of brain activity mapping may provide insight into opportunities for novel solutions. For example, unconventional methods for delivering electrodes may enable unprecedented numbers of recording sites, embedded optical devices could allow optical detectors to be placed within a few scattering lengths of the measured neurons, and new classes of molecularly engineered sensors might obviate cumbersome hardware architectures. We also study the physics of powering and communicating with microscale devices embedded in brain tissue and find that, while radio-frequency electromagnetic data transmission suffers from a severe power–bandwidth tradeoff, communication via infrared light or ultrasound may allow high data rates due to the possibility of spatial multiplexing. The use of embedded local recording and wireless data transmission would only be viable, however, given major improvements to the power efficiency of microelectronic devices

Physical principles for scalable neural recoding

Simultaneously measuring the activities of all neurons in a mammalian brain at millisecond resolution is a challenge beyond the limits of existing techniques in neuroscience. Entirely new approaches may be required, motivating an analysis of the fundamental physical constraints on the problem. We outline the physical principles governing brain activity mapping using optical, electrical, magnetic resonance, and molecular modalities of neural recording. Focusing on the mouse brain, we analyze the scalability of each method, concentrating on the limitations imposed by spatiotemporal resolution, energy dissipation, and volume displacement. Based on this analysis, all existing approaches require orders of magnitude improvement in key parameters. Electrical recording is limited by the low multiplexing capacity of electrodes and their lack of intrinsic spatial resolution, optical methods are constrained by the scattering of visible light in brain tissue, magnetic resonance is hindered by the diffusion and relaxation timescales of water protons, and the implementation of molecular recording is complicated by the stochastic kinetics of enzymes. Understanding the physical limits of brain activity mapping may provide insight into opportunities for novel solutions. For example, unconventional methods for delivering electrodes may enable unprecedented numbers of recording sites, embedded optical devices could allow optical detectors to be placed within a few scattering lengths of the measured neurons, and new classes of molecularly engineered sensors might obviate cumbersome hardware architectures. We also study the physics of powering and communicating with microscale devices embedded in brain tissue and find that, while radio-frequency electromagnetic data transmission suffers from a severe power–bandwidth tradeoff, communication via infrared light or ultrasound may allow high data rates due to the possibility of spatial multiplexing. The use of embedded local recording and wireless data transmission would only be viable, however, given major improvements to the power efficiency of microelectronic devices

An ultrasonic system for intravascular measurement and visualisation of anatomical structures and blood flow

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Platform Independent, Illumination aware Reconfigurable Switch Capacitor based 3.3 Volt Energy Harvester IC

This dissertation presents a platform independent illumination aware fully on chip microscale energy harvester for powering 3.3V sensor nodes and smart IOT devices. The programmable switched capacitor DC-DC converter for fully on chip applications is discussed and implemented

'ACOUSTO-OPTIC SENSING FOR SAFE MRI PROCEDURES'

In this work, a novel sensor platform is developed for safer and more effective magnetic resonance imaging (MRI). This is achieved by tracking interventional devices, such as guidewires and catheters during interventional MRI procedures, and by measuring the radio frequency (RF) field to assess RF safety of patients with implants, such as pacemakers, during diagnostic MRI. The sensor is based on an acousto-optic modulator coupled with a miniature antenna. This structure is realized on an optical fiber which is immune to the RF field and eliminates the need for conducting lines. The acousto-optic modulator consists of a piezo-electric transducer and a fiber Bragg grating (FBG). The piezoelectric transducer is electrically connected to the miniature antenna and mechanically coupled to the FBG. Local RF signal received by the miniature antenna is converted to acoustic waves by the piezoelectric transducer. Acoustic waves change the grating geometry on the FBG, thus the reflected light from the FBG is modulated. For diagnostic imaging, short dipole antennas are used for sensing the local electric field, which is the primary cause of RF induced heating. For tracking purposes, small loop antennas are used for capturing local MRI signal which contains the location information. In this thesis, a comprehensive model for the acousto-optic modulator is developed and validated through sensitivity and linearity tests. Prototype RF field sensors are built and characterized: sensitivity of 1.36mV/nT and 98 μV/V/m with minimum detectable field strength of 8.2pT/√Hz and 2.7V/m/√Hz and dynamic range of 117dB/√Hz at 23MHz are achieved with 4mm single loop and 8mm short dipole antennas, respectively. These figures are competitive with commercial sensors with much larger form factors. Catheter tracking capability of the sensor under MRI is demonstrated in-vivo in swine in a 0.55T scanner using an 8F catheter in addition to phantom studies under 0.55T and 1.5T clinical MRI systems.Ph.D

MEMS Technology for Biomedical Imaging Applications

Biomedical imaging is the key technique and process to create informative images of the human body or other organic structures for clinical purposes or medical science. Micro-electro-mechanical systems (MEMS) technology has demonstrated enormous potential in biomedical imaging applications due to its outstanding advantages of, for instance, miniaturization, high speed, higher resolution, and convenience of batch fabrication. There are many advancements and breakthroughs developing in the academic community, and there are a few challenges raised accordingly upon the designs, structures, fabrication, integration, and applications of MEMS for all kinds of biomedical imaging. This Special Issue aims to collate and showcase research papers, short commutations, perspectives, and insightful review articles from esteemed colleagues that demonstrate: (1) original works on the topic of MEMS components or devices based on various kinds of mechanisms for biomedical imaging; and (2) new developments and potentials of applying MEMS technology of any kind in biomedical imaging. The objective of this special session is to provide insightful information regarding the technological advancements for the researchers in the community

Agile and Bright Intracardiac Catheters

Intracardiac imaging catheters represent unique instruments to diagnose and treat a diseased heart. While there are imminent advances in medical innovation, many of the commercially available imaging catheters are outdated. Some of them have been designed more than 20 years and therefore they lack novel sensor technology, multi-functionality, and often require manual assembly process. Introduction chapter of this thesis discusses clinical needs and introduces new technological concepts that are needed to progress the functionality and clinical value of the intracardiac catheters along with efficient and simple designs to make the catheters affordable for the patients. The following chapters are grouped into two parts that explore complementary transducer technology and a novel optical fiber-link solution for catheter-based intracardiac imaging. _Part I_ focuses on developing a new intracardiac catheter that has an advanced functionality, which provides clinician with high penetration or close-up high resolution ultrasound imaging in a single device. This agile ultrasound visualization is enabled by a capacitive-micromachined ultrasound transducer (CMUT), operated in collapse-mode, of which the operating frequency can be tuned. Acoustic performance of a fabricated CMUT is modelled and measured. Imaging performance of the CMUT array is quantified on a tissue-mimicking phantom and demonstrated both ex vivo and in vivo experiments. It is found that the combination of the forward-looking design, frequency-tuning and agile deflectability of the catheter allow for visualizing intracardiac structures of various sizes at different distances relative to the catheter tip, providing both wide overviews and detailed close-ups. _Part II_ is devoted to a novel optical technology for transmitting signals and transferring power inside catheters. A novel concept of an all-optical fiber link is introduced. A key insight obtained is that a blue light-emitting diode (LED) may be used as a photo-voltaic converter. Used in reverse under illumination with violet light, it converts significant amount of photonic energy to electricity and at the same time it may emit blue light back, which makes it a unique miniature power and communication channel for catheters. A pressure-sensing catheter prototype is built to demonstrate the concept of transmitting signals and delivering power using a single optical fiber and an LED. The potential of the power and signal fiber link solution is exploited further for ultrasound imaging. A bench-top demonstrator scalable to catheter dimensions is built, in which electrical wires for ultrasound-sensor signal and power tra