Miniature Broadband-NIRS System to Measure CNS Tissue Oxygenation and Metabolism in Preclinical Research

In-vivo measurement of CNS tissue oxygenation and metabolism is critical in health and disease. Broadband-near infrared spectroscopy is a non-invasive optical technique which measures tissue oxygenation, haemodynamics and metabolism through in-vivo quantification of concentration changes of oxy- and deoxy-haemoglobin (Δ[HbO2] and Δ[HHb]) and oxidised cytochrome-c-oxidase (Δ[oxCCO]). Current commercially available NIRS systems only use a few wavelengths to measure concentration change that fails to provide accurate Δ[oxCCO] measurement. Broadband-NIRS instruments however, use more than 100 wavelengths which enables quantification of change in [oxCCO], an important marker of cellular oxidative metabolism. These systems tend to be bulky, requiring extensive calibrations and trained staff to operate them; making them less versatile and difficult to be adapted in the clinical environment. Furthermore, existing broadband-NIRS systems quantify chromophore concentration changes assuming a fixed optical pathlength across all the subjects using a previously measured DPF (differential pathlength factor) with time or frequency domain systems. This thesis describes the development of a portable broadband-NIRS system called mini-CYRIL “CYtochrome Research Instrument and appLication”, based on easily sourced components. A miniature white light source (HL-2000-HP) and miniature spectrometers (QE65pro and Ventana VIS-NIR) by Ocean Optics were customised for measuring CNS tissue oxygenation and metabolism. While having the features of commercially available NIRS systems in terms of portability, ease of use and no need for wavelength calibration, in terms of performance mini-CYRIL is comparable to broadband-NIRS instruments providing reliable Δ[oxCCO] measurements that have been validated and assessed through in-vivo tissue studies in (a) preclinical model of: (i) neonatal hypoxic-ischaemic (HI) encephalopathy, (ii) multiple sclerosis (MS) and (iii) low-light level therapy in the aged retina; (b) infants during brain functional activation. Mini-CYRIL is furthermore novel in offering calculation of absolute change in the concentration of chromophores based on real-time measurement of the optical path of light traversing the tissue. None of the current NIRS systems offer this feature which is crucial in case of changing pathology following an injury

Nasopharyngeal method for selective brain cooling and development of a time-resolved near-infrared technique to monitor brain temperature and oxidation status during hypothermia

Mild hypothermia at 32-35oC (HT) has been shown to be neuroprotective for neurological emergencies following severe head trauma, cardiac arrest and neonatal asphyxia. However, HT has not been widely deployed in clinical settings because: firstly, cooling the whole body below 33-34°C can induce severe complications; therefore, applying HT selectively to the brain could minimize adverse effects by maintaining core body temperature at normal level. Secondly, development of an effective and easy to implement selective brain cooling (SBC) technique, which can quickly induce brain hypothermia while avoiding complications from whole body cooling, remains a challenge. In this thesis, we studied the feasibility and efficiency of selective brain cooling (SBC) through nasopharyngeal cooling. To control the cooling and rewarming rate and because core body temperature is different from brain temperature, we also developed a non-invasive technique based on time-resolved near infrared spectroscopy (TR-NIRS) to measure local brain temperature. In normal brain, cerebral blood flow (CBF) and energy metabolism as reflected by the cerebral metabolic rate of oxygen (CMRO2) is tightly coupled leading to an oxygen extraction efficiency (OEF) of around ~33%. A decoupling of the two as in ischemia signifies oxidative stress and would lead to an increase in OEF beyond the normal value of ~33%. The final goal of this thesis is to evaluate TR-NIRS methods for measurements of CBF and CMRO2 to monitor for oxidative metabolism in the brain with and without HT treatment. Chapter 2 presents investigations on the feasibility and efficiency of the nasopharyngeal SBC by blowing room temperature or humidified cooled air into the nostrils. Effective brain cooling at a median cooling rate of 5.6 ± 1.1°C/hour compared to whole body cooling rate of 3.2 ± 0.7 was demonstrated with the nasopharyngeal cooling method. Chapter 3 describes TR-NIRS experiments performed to measure brain temperature non-invasively based on the temperature-dependence of the water absorption peaks at ~740 and 840nm. The TR-NIRS method was able to measure brain temperature with a mean difference of 0.5 ± 1.6°C (R2 = 0.66) between the TR-NIRS and thermometer measurements. Chapter 4 describes the TR-NIR technique developed to measure CBF and CMRO2 in a normoxia animal model under different anesthetics at different brain temperatures achieved by whole-body cooling. Both CBF and CMRO2 decreased with decreasing brain temperature but the ratio CMRO2:CBF (OEF) remained unchanged around the normal value of ~33%. These results demonstrate that TR-NIR can be used to monitor the oxidative status of the brain in neurological emergencies and its response to HT treatment. In summary, this thesis has established a convenient method for selective brain cooling without decreasing whole body temperature to levels when adverse effects could be triggered. TR-NIRS methods are also developed for monitoring local brain temperature to guide SBC treatment and for monitoring the oxidation status of the brain as treatment progresses

Non-invasive Multimodal Monitoring in Traumatic Brain Injury

Traumatic brain injury (TBI) is a leading cause of death and disability, often resulting in increased intracranial pressure (ICP) and cerebral ischemia. Current ICP measurement methods involve invasive, non-therapeutic procedures. This research aims to develop a non-invasive, continuous optical system for monitoring ICP and cerebral oxygenation. Using backscattered brain optical signals, it leverages cerebral pulsatile photoplethysmograms (PPGs) and non-pulsatile near-infrared spectroscopy (NIRS) signals to assess ICP and oxygenation. The innovation lies in using cerebral NIRS-PPGs to measure ICP, based on the hypothesis that changes in ICP affect cerebral PPG signal morphology. These changes in morphological features, with the support of advanced algorithms including Machine Learning (ML) models, could be utilised in translating the changes in the pulsatile signals in absolute measurements of ICP. The research firstly implemented Monte Carlo simulations to fully understand the effect of multi-source detector separations on brain light tissue interaction. Secondly, a novel reflectance, custom-made TBI multiwavelength and multisource-detector optical sensor and instrumentation, including advanced signal processing algorithms, was designed to acquire, pre-process, and analyse raw PPG signals (AC + DC) from the brain. Thirdly, a novel head phantom and an in vitro brain haemodynamic system were developed for evaluating the sensor. The phantom was the ideal tool for simulating different clinical scenarios that cannot be implemented in real in vivo studies. Fourthly, this research carried out three in vitro studies to investigate the sensor's capability to non-invasively monitor intracranial pressure and oxygenation. The first study evaluated the quality of the optical signals acquired from the developed probe at different source-detector (S-D) separations and multiple wavelengths. It was concluded that the optimal S-D separation to reach the cerebral tissue, and acquire good quality PPG signals, was within 3 cm and 4 cm. The second study assessed the central hypothesis of this research by recording PPG signals from the phantom’s brain at different intracranial pressure levels and implementing ML models utilising pertinent features from the PPG. Results from the second study showed a correlation coefficient of 0.86, mean absolute error of 3.7 mmHg, and limits of agreement of ±4 mmHg, which suggest that NIRS-PPG signals could estimate ICP non invasively. Finally, a third study demonstrated the sensor’s response to in vitro changes in blood oxygenation levels, with less than 33.8% error in half the measurements compared to the reference. This final implementation of spatially resolved spectroscopy algorithms actualize the proposed non-invasive multimodal monitoring sensor for traumatic brain injury. The novel technological developments and the new knowledge acquired from this research paves the way for the development of a transformative non-invasive optical sensor technology for the continuous monitoring of ICP and cerebral oxygenation in TBI patients and beyond

소형동물의 뇌신경 자극을 위한 완전 이식형 신경자극기

학위논문(박사)--서울대학교 대학원 :공과대학 전기·정보공학부,2020. 2. 김성준.In this study, a fully implantable neural stimulator that is designed to stimulate the brain in the small animal is described. Electrical stimulation of the small animal is applicable to pre-clinical study, and behavior study for neuroscience research, etc. Especially, behavior study of the freely moving animal is useful to observe the modulation of sensory and motor functions by the stimulation. It involves conditioning animal's movement response through directional neural stimulation on the region of interest. The main technique that enables such applications is the development of an implantable neural stimulator. Implantable neural stimulator is used to modulate the behavior of the animal, while it ensures the free movement of the animals. Therefore, stable operation in vivo and device size are important issues in the design of implantable neural stimulators. Conventional neural stimulators for brain stimulation of small animal are comprised of electrodes implanted in the brain and a pulse generation circuit mounted on the back of the animal. The electrical stimulation generated from the circuit is conveyed to the target region by the electrodes wire-connected with the circuit. The devices are powered by a large battery, and controlled by a microcontroller unit. While it represents a simple approach, it is subject to various potential risks including short operation time, infection at the wound, mechanical failure of the device, and animals being hindered to move naturally, etc. A neural stimulator that is miniaturized, fully implantable, low-powered, and capable of wireless communication is required. In this dissertation, a fully implantable stimulator with remote controllability, compact size, and minimal power consumption is suggested for freely moving animal application. The stimulator consists of modular units of surface-type and depth-type arrays for accessing target brain area, package for accommodating the stimulating electronics all of which are assembled after independent fabrication and implantation using customized flat cables and connectors. The electronics in the package contains ZigBee telemetry for low-power wireless communication, inductive link for recharging lithium battery, and an ASIC that generates biphasic pulse for neural stimulation. A dual-mode power-saving scheme with a duty cycling was applied to minimize the power consumption. All modules were packaged using liquid crystal polymer (LCP) to avoid any chemical reaction after implantation. To evaluate the fabricated stimulator, wireless operation test was conducted. Signal-to-Noise Ratio (SNR) of the ZigBee telemetry were measured, and its communication range and data streaming capacity were tested. The amount of power delivered during the charging session depending on the coil distance was measured. After the evaluation of the device functionality, the stimulator was implanted into rats to train the animals to turn to the left (or right) following a directional cue applied to the barrel cortex. Functionality of the device was also demonstrated in a three-dimensional maze structure, by guiding the rats to navigate better in the maze. Finally, several aspects of the fabricated device were discussed further.본 연구에서는 소형 동물의 두뇌를 자극하기 위한 완전 이식형 신경자극기가 개발되었다. 소형 동물의 전기자극은 전임상 연구, 신경과학 연구를 위한 행동연구 등에 활용된다. 특히, 자유롭게 움직이는 동물을 대상으로 한 행동 연구는 자극에 의한 감각 및 운동 기능의 조절을 관찰하는 데 유용하게 활용된다. 행동 연구는 두뇌의 특정 관심 영역을 직접적으로 자극하여 동물의 행동반응을 조건화하는 방식으로 수행된다. 이러한 적용을 가능케 하는 핵심기술은 이식형 신경자극기의 개발이다. 이식형 신경자극기는 동물의 움직임을 방해하지 않으면서도 그 행동을 조절하기 위해 사용된다. 따라서 동물 내에서의 안정적인 동작과 장치의 크기가 이식형 신경자극기를 설계함에 있어 중요한 문제이다. 기존의 신경자극기는 두뇌에 이식되는 전극 부분과, 동물의 등 부분에 위치한 회로부분으로 구성된다. 회로에서 생산된 전기자극은 회로와 전선으로 연결된 전극을 통해 목표 지점으로 전달된다. 장치는 배터리에 의해 구동되며, 내장된 마이크로 컨트롤러에 의해 제어된다. 이는 쉽고 간단한 접근방식이지만, 짧은 동작시간, 이식부위의 감염이나 장치의 기계적 결함, 그리고 동물의 자연스러운 움직임 방해 등 여러 문제점을 야기할 수 있다. 이러한 문제의 개선을 위해 무선통신이 가능하고, 저전력, 소형화된 완전 이식형 신경자극기의 설계가 필요하다. 본 연구에서는 자유롭게 움직이는 동물에 적용하기 위하여 원격 제어가 가능하며, 크기가 작고, 소모전력이 최소화된 완전이식형 자극기를 제시한다. 설계된 신경자극기는 목표로 하는 두뇌 영역에 접근할 수 있는 표면형 전극과 탐침형 전극, 그리고 자극 펄스 생성 회로를 포함하는 패키지 등의 모듈들로 구성되며, 각각의 모듈은 독립적으로 제작되어 동물에 이식된 뒤 케이블과 커넥터로 연결된다. 패키지 내부의 회로는 저전력 무선통신을 위한 지그비 트랜시버, 리튬 배터리의 재충전을 위한 인덕티브 링크, 그리고 신경자극을 위한 이상성 자극파형을 생성하는 ASIC으로 구성된다. 전력 절감을 위해 두 개의 모드를 통해 사용률을 조절하는 방식이 장치에 적용된다. 모든 모듈들은 이식 후의 생물학적, 화학적 안정성을 위해 액정 폴리머로 패키징되었다. 제작된 신경자극기를 평가하기 위해 무선 동작 테스트가 수행되었다. 지그비 통신의 신호 대 잡음비가 측정되었으며, 해당 통신의 동작거리 및 데이터 스트리밍 성능이 검사되었고, 장치의 충전이 수행될 때 코일간의 거리에 따라 전송되는 전력의 크기가 측정되었다. 장치의 평가 이후, 신경자극기는 쥐에 이식되었으며, 해당 동물은 이식된 장치를 이용해 방향 신호에 따라 좌우로 이동하도록 훈련되었다. 또한, 3차원 미로 구조에서 쥐의 이동방향을 유도하는 실험을 통하여 장치의 기능성을 추가적으로 검증하였다. 마지막으로, 제작된 장치의 특징이 여러 측면에서 심층적으로 논의되었다.Chapter 1 : Introduction 1 1.1. Neural Interface 2 1.1.1. Concept 2 1.1.2. Major Approaches 3 1.2. Neural Stimulator for Animal Brain Stimulation 5 1.2.1. Concept 5 1.2.2. Neural Stimulator for Freely Moving Small Animal 7 1.3. Suggested Approaches 8 1.3.1. Wireless Communication 8 1.3.2. Power Management 9 1.3.2.1. Wireless Power Transmission 10 1.3.2.2. Energy Harvesting 11 1.3.3. Full implantation 14 1.3.3.1. Polymer Packaging 14 1.3.3.2. Modular Configuration 16 1.4. Objectives of This Dissertation 16 Chapter 2 : Methods 18 2.1. Overview 19 2.1.1. Circuit Description 20 2.1.1.1. Pulse Generator ASIC 21 2.1.1.2. ZigBee Transceiver 23 2.1.1.3. Inductive Link 24 2.1.1.4. Energy Harvester 25 2.1.1.5. Surrounding Circuitries 26 2.1.2. Software Description 27 2.2. Antenna Design 29 2.2.1. RF Antenna 30 2.2.1.1. Design of Monopole Antenna 31 2.2.1.2. FEM Simulation 31 2.2.2. Inductive Link 36 2.2.2.1. Design of Coil Antenna 36 2.2.2.2. FEM Simulation 38 2.3. Device Fabrication 41 2.3.1. Circuit Assembly 41 2.3.2. Packaging 42 2.3.3. Electrode, Feedthrough, Cable, and Connector 43 2.4. Evaluations 45 2.4.1. Wireless Operation Test 46 2.4.1.1. Signal-to-Noise Ratio (SNR) Measurement 46 2.4.1.2. Communication Range Test 47 2.4.1.3. Device Operation Monitoring Test 48 2.4.2. Wireless Power Transmission 49 2.4.3. Electrochemical Measurements In Vitro 50 2.4.4. Animal Testing In Vivo 52 Chapter 3 : Results 57 3.1. Fabricated System 58 3.2. Wireless Operation Test 59 3.2.1. Signal-to-Noise Ratio Measurement 59 3.2.2. Communication Range Test 61 3.2.3. Device Operation Monitoring Test 62 3.3. Wireless Power Transmission 64 3.4. Electrochemical Measurements In Vitro 65 3.5. Animal Testing In Vivo 67 Chapter 4 : Discussion 73 4.1. Comparison with Conventional Devices 74 4.2. Safety of Device Operation 76 4.2.1. Safe Electrical Stimulation 76 4.2.2. Safe Wireless Power Transmission 80 4.3. Potential Applications 84 4.4. Opportunities for Further Improvements 86 4.4.1. Weight and Size 86 4.4.2. Long-Term Reliability 93 Chapter 5 : Conclusion 96 Reference 98 Appendix - Liquid Crystal Polymer (LCP) -Based Spinal Cord Stimulator 107 국문 초록 138 감사의 글 140Docto

Biomarkers of neurological tissue injury and inflammation in paediatric tuberculous meningitis

Includes bibliographical references.[Background] Tuberculous meningitis (TBM) in children has high mortality and neurological morbidity rates. The assessment of disease severity and prognostication are difficult because several factors influence initial presentation, and advanced tools for these are lacking. Biomarkers of neurological injury could help to assess severity and to prognosticate, but have not been assessed in paediatric TBM. This study examined serum and cerebrospinal fluid (CSF) biomarkers of neurological injury in paediatric TBM in association with clinical and physiological data, radiology, inflammatory markers, and outcome. [ Methods ] Serum and CSF (ventricular and lumbar) samples were taken on admission and over 3 weeks in children with probable TBM and hydrocephalus. These were analysed with ELISA for neuromarkers S100B, neuron-specific enolase (NSE) and glial fibrillary acidic protein (GFAP), and with Luminex multianalyte array assay for a panel of inflammatory markers. Results were compared with 2 controls groups. Computerized tomography was done on admission and magnetic resonance imaging (brain, spine and magnetic resonance angiography) at 3 weeks. Brain oxygenation was monitored invasively and non-invasively in selected patients. Clinical and neurodevelopmental outcomes were assessed at 6 months. Data were analysed with various statistical tools, including principal component analysis. [ Results ] Data were collected from 44 children. Of these, 16% died and 36% had disability (25% mildmoderate, 11% severe). S100B, NSE, GFAP and inflammatory markers were elevated in CSF on admission and for up to 3 weeks, but not in serum. Elevated neuromarkers were significantly associated with poor outcome and increased over time in patients who died, although combined inflammatory biomarkers decreased. Cerebral infarcts occurred in 66% of patients and were associated with neuromarker elevation. Novel findings on spinal MRI were the high frequency of asymptomatic disease. Cerebral vascular pathology was documented frequently on imaging but did not predict infarcts. Low brain oxygenation was common and in keeping with physiological events and outcome. [ Conclusion ] CSF neuro- and inflammatory markers are elevated in TBM. Neuromarkers were prognostic of clinical and radiological outcome and an increasing trend suggested ongoing injury. This does not appear to be related to ongoing inflammation as measured by cytokines but may reflect the ongoing secondary injury processes initiated by inflammation

Non-invasive techniques for predicting soft tissue during pressure induced ishaemia.

PhDSoft tissue breakdown occurs in association with biochemical changes that can be attributed to a reduction in blood and lymph flow to a localised tissue area in response to applied pressure. The resulting ischaemia can lead to a reduction in available oxygen and accumulation of waste products. Tissue breakdown leading to the development of pressure sores afflicts patients who are already debilitated, although not all patients appear to be equally susceptible. Measurement of sweat biochemistry and blood gas tensions may reflect the biochemical process in the underlying tissues and provide a simple and non-invasive method of investigating the status of soft tissues. The potential of specific sweat metabolites to act as markers of soft tissue status during and following loading has been investigated at a clinically relevant site in healthy volunteers, and in two clinically relevant patient groups. A range of validation procedures were undertaken and a series of parameters derived to investigate the temporal profile of sweat biochemistry, and identify various modes of gas tension response. Investigations at the loaded sacrum of healthy individuals showed a statistically significant increase in sweat lactate, urea, urate and chloride concentrations which were dependent upon the level of externally applied pressure. Mean increases of between 10%-60% were demonstrated for sweat metabolite concentrations at the loaded site compared to the control site for applied pressures in the range 40-120 mmHg. Similar increases were demonstrated in sweat collected from highly loaded tissue areas within the stump socket of lower limb amputees. A threshold value for P02 tension was identified, amounting to a 60% reduction from the unloaded value, which was associated with elevated tissue carbon dioxide levels as well as increased sweat metabolite concentrations in the loaded phase. This finding may provide a useful predictor of soft tissue status during prolonged loading. No pessimist ever discovered the secrets of the stars, or sailed to an uncharted land, or opened a new heaven to the human spirit. Helen Adam

Therapeutic modulation of liver ischaemia reperfusion injury

Liver Ischaemia Reperfusion Injury (IRI) leads to production of reactive oxygen species and cytokines, which affects hepatocellular function following liver resection and transplantation. This thesis examines 2 hypotheses: 1) The role of intravenous glycine in amelioration of liver IRI in a in vivo animal model of partial lobar liver IRI. 2) Does prophylactically administered N-acetylcysteine prevent liver IRI in patients undergoing elective liver resection. Materials and Methods 1) A rabbit model of hepatic lobar IRI was used to evaluate glycine. 3 groups (n=6) Sham group (laparotomy alone), ischaemia reperfusion (I/R) group (1 hour ischaemia and 6 hours of reperfusion), and glycine I/R group (IV glycine 5 mg/kg prior to the I/R protocol) were used. Portal blood flow, bile flow and bile was analysed by H1NMR spectroscopy. Hepatic microcirculation, intracellular tissue oxygenation, serum TNFα, IL-8, ALT, AST were measured at 1, 2, 4 and 6 hours following reperfusion. 2) A randomised double blind clinical trial was conducted to assess the effect of NAC on liver IRI following liver resections. The main outcomes were: morbidity and mortality, ICAM-1 expression in liver tissue, liver function tests. Patients were randomised to receive NAC as IV infusion (NACG) or a placebo group (PG) which received 5% dextrose only. Immunohistochemistry for ICAM-1 was carried out on perioperative liver biopsies. Results 1) Glycine normalised the bile flow, reduced phosphatidylcholine shedding, lactate surge, and stimulated bile acid, pyruvate, glucose and acetoacetate release. Glycine improved portal blood flow, hepatic microcirculation by the 2nd hour, and hepatic intracellular tissue oxygenation by the 4th hour of reperfusion. Glycine ameliorated serum TNFα at 1, 2 and 4 hours and serum Il- 8, AST and ALT up to 6 hours post reperfusion as compared to the I/R alone group. 2) Of the 43 patients, 15 received NAC, 16 were randomised to the PG, 12 were excluded due to inoperable tumours. Serum ALT was reduced in NACG (p=0.001), while serum ALP was higher in the NACG (p=0.003). ICAM-1 expression was up-regulated in 6/16 patients in the PG and in 3/15 patients in NACG. ICAM-1 was down-regulated in 1/15 patients in the NACG and none in the PG, the difference was not significant. Conclusions 1) Glycine ameliorated liver IRI, improved bile flow and composition. 2) NAC ameliorated parenchymal liver injury and enhanced liver regeneration in patients undergoing elective liver resection

Brain Injury

The present two volume book "Brain Injury" is distinctive in its presentation and includes a wealth of updated information on many aspects in the field of brain injury. The Book is devoted to the pathogenesis of brain injury, concepts in cerebral blood flow and metabolism, investigative approaches and monitoring of brain injured, different protective mechanisms and recovery and management approach to these individuals, functional and endocrine aspects of brain injuries, approaches to rehabilitation of brain injured and preventive aspects of traumatic brain injuries. The collective contribution from experts in brain injury research area would be successfully conveyed to the readers and readers will find this book to be a valuable guide to further develop their understanding about brain injury