Brain Temperature Monitoring Research Articles

Model-predicted brain temperature computational imaging by multimodal noninvasive functional neuromonitoring of cerebral oxygen metabolism and hemodynamics: MRI-derived and clinical validation.

Brain temperature, a crucial yet under-researched neurophysiological parameter, is governed by the equilibrium between cerebral oxygen metabolism and hemodynamics. Therapeutic hypothermia has been demonstrated as an effective intervention for acute brain injuries, enhancing survival rates and prognosis. The success of this treatment hinges on the precise regulation of brain temperature. However, the absence of comprehensive brain temperature monitoring methods during therapy, combined with a limited understanding of human brain heat transmission mechanisms, significantly hampers the advancement of hypothermia-based neuroprotective therapies. Leveraging the principles of bioheat transfer and MRI technology, this study conducted quantitative analyses of brain heat transfer during mild hypothermia therapy. Utilizing MRI, we reconstructed brain structures, estimated cerebral blood flow and oxygen consumption parameters, and developed a brain temperature calculation model founded on bioheat transfer theory. Employing computational cerebral hemodynamic simulation analysis, we established an intracranial arterial fluid dynamics model to predict brain temperature variations across different therapeutic hypothermia modalities. We introduce a noninvasive, spatially resolved, and optimized mathematical bio-heat model that synergizes model-predicted and MRI-derived data for brain temperature prediction and imaging. Our findings reveal that the brain temperature images generated by our model reflect distinct spatial variations across individual participants, aligning with experimentally observed temperatures.

An electrophysiological correlate of sleep in a shark.

Sleep is a prominent physiological state observed across the animal kingdom. Yet, for some animals, our ability to identify sleep can be masked by behaviors otherwise associated with being awake, such as for some sharks that must swim continuously to push oxygenated seawater over their gills to breathe. We know that sleep in buccal pumping sharks with clear rest/activity cycles, such as draughtsboard sharks (Cephaloscyllium isabellum, Bonnaterre, 1788), manifests as a behavioral shutdown, postural relaxation, reduced responsiveness, and a lowered metabolic rate. However, these features of sleep do not lend themselves well to animals that swim nonstop. In addition to video and accelerometry recordings, we tried to explore the electrophysiological correlates of sleep in draughtsboard sharks using electroencephalography (EEG), electromyography, and electrooculography, while monitoring brain temperature. The seven channels of EEG activity had a surprising level of (apparent) instability when animals were swimming, but also when sleeping. The amount of stable EEG signals was too low for replication within- and across individuals. Eye movements were not measurable, owing to instability of the reference electrode. Based on an established behavioral characterization of sleep in draughtsboard sharks, we offer the original finding that muscle tone was strongest during active wakefulness, lower in quietly awake sharks, and lowest in sleeping sharks. We also offer several critical suggestions on how to improve techniques for characterizing sleep electrophysiology in future studies on elasmobranchs, particularly for those that swim continuously. Ultimately, these approaches will provide important insights into the evolutionary confluence of behaviors typically associated with wakefulness and sleep.

Upconversion-Luminescent Fiber Microchannel Sensors for Temperature Monitoring at High Spatial Resolution in the Brains of Freely Moving Animals.

Brain temperature is a critical factor affecting neural activity and function, whose fluctuations may result in acute life-threatening health complications and chronic neuropathology. To monitor brain temperature, luminescent nanothermometry (LN) based on upconversion nanoparticles (UCNPs) with low autofluorescence has received extensive attention for its advantages in high temperature sensitivity and high response speed. However, most of current the LNs are based on optical imaging, which fails in temperature monitoring in deep brain regions at high spatial resolution. Here, the fiber microchannel sensor (FMS) loaded with UCNPs (UCNP-FMS) is presented for temperature monitoring at high spatial resolution in the deep brains of freely moving animals. The UCNP-FMS is fabricated by incorporating UCNPs in microchannels of optical fibers, whose diameter is ∼50µm processed by femtosecond laser micromachining for spatially resolved sensing. The UCNPs provide thermal-sensitive upconversion emissions at dual wavelengths for ratiometric temperature sensing, ensuring a detection accuracy of ± 0.3°C at 37°C. Superior performances of UCNP-FMS are demonstrated by real-time temperature monitoring in different brain regions of freely moving animals under various conditions such as taking food, undergoing anesthesia/wakefulness, and suffering external temperature changes. Moreover, this study shows the capability of UCNP-FMS in distributed temperature sensing in mammalian brains in vivo.

Abstract WP113: Feasibility Of Non-invasive Brain Temperature Measurement In Acute Ischemic Stroke: A Comparison Study Of MR Thermometry Vs. Zero-Heat-Flux Sensors

Introduction: Brain-selective hypothermia is a promising neuroprotectant in acute ischemic stroke. However, a non-invasive bedside method to monitor brain temperature during cooling is lacking. We tested the feasibility and accuracy of measuring brain temperature non-invasively using sensors designed to monitor core body temperature. Methods: In this prospective single-center study, 20 patients with large or medium vessel occlusion strokes were enrolled. Patients underwent a 3T MR spectroscopy imaging (MRSI, the reference standard) and zero heat flux (ZHF) core temperature sensor measurements (3M TM Bair Hugger TM ) within 12-72 hours from admission. Two ZHF sensors were placed on each side of the forehead on the side of stroke and contralateral side and the temperatures were checked before and after MRSI. A 2x2x2 cm voxel was centered on the infarct and matching contralateral location using diffusion weighted imaging. Brain temperature on MRSI was calculated using the relative chemical shifts of water and N-acetyl aspartate. Temperature measurements of the ZHF sensors were compared to MRSI measurements. Results: The brain temperature of stroke and contralateral sides were similar using MRSI or using ZHF sensors when each modality was compared to itself by hemisphere (all p>0.05). However, there was a significant difference for the ipsilateral side: median (SD) temperatures using MRSI was 36.0°C (1.8) vs 36.8°C (0.5) for sensor measurement. Bland-Altman plots showed that 95% of the observations fell within upper and lower limits of agreement of -2.1 to +3.7°C while 61% of observations fell within an agreement limit of +/- 1°C. There was an indication of an overall higher temperature measurements using the ZHF sensors compared to MRSI (Figure 1). Conclusions: More studies are needed to validate the use of ZHF thermometry in ischemic stroke including studies implementing hypothermia. Figure 1. Boxplot of stroke side MRSI compared to zero-heat-flux sensors.

Brain temperature monitoring in newborn infants: Current methodologies and prospects.

Brain tissue temperature is a dynamic balance between heat generation from metabolism, passive loss of energy to the environment, and thermoregulatory processes such as perfusion. Perinatal brain injuries, particularly neonatal encephalopathy, and seizures, have a significant impact on the metabolic and haemodynamic state of the developing brain, and thereby likely induce changes in brain temperature. In healthy newborn brains, brain temperature is higher than the core temperature. Magnetic resonance spectroscopy (MRS) has been used as a viable, non-invasive tool to measure temperature in the newborn brain with a reported accuracy of up to 0.2 degrees Celcius and a precision of 0.3 degrees Celcius. This measurement is based on the separation of chemical shifts between the temperature-sensitive water peaks and temperature-insensitive singlet metabolite peaks. MRS thermometry requires transport to an MRI scanner and a lengthy single-point measurement. Optical monitoring, using near infrared spectroscopy (NIRS), offers an alternative which overcomes this limitation in its ability to monitor newborn brain tissue temperature continuously at the cot side in real-time. Near infrared spectroscopy uses linear temperature-dependent changes in water absorption spectra in the near infrared range to estimate the tissue temperature. This review focuses on the currently available methodologies and their viability for accurate measurement, the potential benefits of monitoring newborn brain temperature in the neonatal intensive care unit, and the important challenges that still need to be addressed.

Multiplexed optical fiber sensors for dynamic brain monitoring

<h2>Summary</h2> Dynamic brain monitoring can mitigate traumatic brain injury (TBI) deterioration and enable precise treatment. Despite many studies on brain monitoring systems for neuroscience applications, current technologies are limited in providing a continuous and real-time readout of multiple brain biomarkers simultaneously because of limited sensor performance and signal interference. Regression modeling, being a subfield of machine-learning (ML) algorithm, offers great advantages in signal enhancement and prediction. However, studies on ML-integrated optical fiber sensors for precise brain monitoring have been rarely reported. Here, a multiplexed optical fiber sensor regulated by regression algorithms is developed for the dynamic monitoring of brain pH, temperature, dissolved oxygen, and glucose levels. The proposed sensor has demonstrated excellent sensing abilities and can perform dynamic monitoring of TBI stages in <i>ex vivo</i> brain models. The results indicate the capability of the multiplexed optical fiber sensor for continuous brain physiology reflection, suggesting a promising prospect for clinical applications.

Non-invasive Brain Temperature Measurement in Acute Ischemic Stroke.

Selective therapeutic hypothermia in the setting of mechanical thrombectomy (MT) is promising to further improve the outcomes of large vessel occlusion stroke. A significant limitation in applying hypothermia in this setting is the lack of real-time non-invasive brain temperature monitoring mechanism. Non-invasive brain temperature monitoring would provide important information regarding the brain temperature changes during cooling, and the factors that might influence any fluctuations. This review aims to provide appraisal of brain temperature changes during stroke, and the currently available non-invasive modalities of brain temperature measurement that have been developed and tested over the past 20 years. We cover modalities including magnetic resonance spectroscopy imaging (MRSI), radiometric thermometry, and microwave radiometry, and the evidence for their accuracy from human and animal studies. We also evaluate the feasibility of using these modalities in the acute stroke setting and potential ways for incorporating brain temperature monitoring in the stroke workflow.

Prolonged Automated Robotic TCD Monitoring in Acute Severe TBI: Study Design and Rationale.

Transcranial Doppler ultrasonography (TCD) is a portable, bedside, noninvasive diagnostic tool used for the real-time assessment of cerebral hemodynamics. Despite the evident utility of TCD and the ability of this technique to function as a stethoscope to the brain, its use has been limited to specialized centers because of the dearth of technical and clinical expertise required to acquire and interpret the cerebrovascular parameters. Additionally, the conventional pragmatic episodic TCD monitoring protocols lack dynamic real-time feedback to guide time-critical clinical interventions. Fortunately, with the recent advent of automated robotic TCD technology in conjunction with the automated software for TCD data processing, we now have the technology to automatically acquire TCD data and obtain clinically relevant informationin real-time. By obviating the need for highly trained clinical personnel, this technology shows great promise toward a future of widespread noninvasive monitoring to guide clinical care in patients with acute brain injury. Here, we describe a proposal for a prospective observational multicenter clinical trial to evaluate the safety and feasibility of prolonged automated robotic TCD monitoring in patients with severe acute traumatic brain injury (TBI). We will enroll patients with severe non-penetratingTBI with concomitant invasive multimodal monitoring including, intracranial pressure, brain tissue oxygenation, and brain temperature monitoring as part of standard of care in centers with varying degrees of TCD availability and experience. Additionally, we propose to evaluate the correlation of pertinent TCD-based cerebral autoregulation indicessuch as the critical closing pressure, and the pressure reactivity index withthe brain tissue oxygenationvaluesobtained invasively. The overarching goal of this study is to establish safety and feasibility of prolonged automated TCD monitoring for patients with TBI in the intensive care unit and identify clinically meaningful and pragmatic noninvasive targets for future interventions.

A Clinical Test for a Newly Developed Direct Brain Cooling System for the Injured Brain and Pattern of Cortical Brainwaves in Cooling, Noncooling, and Dead Brain.

To ensure the direct delivery of therapeutic hypothermia at a selected constant temperature to the injured brain, a newly innovated direct brain cooling system was constructed. The practicality, effectiveness, and safety of this system were clinically tested in our initial series of 14 patients with severe head injuries. The patients were randomized into two groups: direct brain cooling at 32°C and the control group. All of them received intracranial pressure (ICP), focal brain oxygenation, brain temperature, and direct cortical brainwave monitoring. The direct brain cooling group did better in the Extended Glasgow Outcome Scale at the time of discharge and at 6 months after trauma. This could be owing to a trend in the monitored parameters; reduction in ICP, increment in cerebral perfusion pressure, optimal brain redox regulation, near-normal brain temperature, and lessening of epileptic-like brainwave activities are likely the reasons for better outcomes in the cooling group. Finally, this study depicts interesting cortical brainwaves during a transition time from being alive to dead. It is believed that the demonstrated cortical brainwaves follow the principles of quantum physics.

Repeatability and Reproducibility of in-vivo Brain Temperature Measurements.

Background: Magnetic resonance spectroscopic imaging (MRSI) is a neuroimaging technique that may be useful for non-invasive mapping of brain temperature (i.e., thermometry) over a large brain volume. To date, intra-subject reproducibility of MRSI-based brain temperature (MRSI-t) has not been investigated. The objective of this repeated measures MRSI-t study was to establish intra-subject reproducibility and repeatability of brain temperature, as well as typical brain temperature range.Methods: Healthy participants aged 23–46 years (N = 18; 7 females) were scanned at two time points ~12-weeks apart. Volumetric MRSI data were processed by reconstructing metabolite and water images using parametric spectral analysis. Brain temperature was derived using the frequency difference between water and creatine (TCRE) for 47 regions of interest (ROIs) delineated by the modified Automated Anatomical Labeling (AAL) atlas. Reproducibility was measured using the coefficient of variation for repeated measures (COVrep), and repeatability was determined using the standard error of measurement (SEM). For each region, the upper and lower bounds of Minimal Detectable Change (MDC) were established to characterize the typical range of TCRE values.Results: The mean global brain temperature over all subjects was 37.2°C with spatial variations across ROIs. There was a significant main effect for time [F(1, 1,591) = 37.0, p < 0.0001] and for brain region [F(46, 1,591) = 2.66, p < 0.0001]. The time*brain region interaction was not significant [F(46, 1,591) = 0.80, p = 0.83]. Participants' TCRE was stable for each ROI across both time points, with ROIs' COVrep ranging from 0.81 to 3.08% (mean COVrep = 1.92%); majority of ROIs had a COVrep <2.0%.Conclusions: Brain temperature measurements were highly consistent between both time points, indicating high reproducibility and repeatability of MRSI-t. MRSI-t may be a promising diagnostic, prognostic, and therapeutic tool for non-invasively monitoring brain temperature changes in health and disease. However, further studies of healthy participants with larger sample size(s) and numerous repeated acquisitions are imperative for establishing a reference range of typical brain TCRE, as well as the threshold above which TCRE is likely pathological.

Non-invasive Monitoring of Brain Temperature during Rapid Selective Brain Cooling by Zero-Heat-Flux Thermometry

Introduction: Selective brain cooling can minimize systemic complications associated with whole body cooling but maximize neuroprotection. Recently, we developed a non-invasive, portable and inexpensive system for selectively cooling the brain rapidly and demonstrated its safety and efficacy in porcine models. However, the widespread application of this technique in the clinical setting requires a reliable, non-invasive and accurate method for measuring local brain temperature so that cooling and rewarming rates can be controlled during targeted temperature management. In this study, we evaluate the ability of a zero-heat-flux SpotOn sensor, mounted on three different locations, to measure brain temperature during selective brain cooling in a pig model. Computed Tomography (CT) was used to determine the position of the SpotOn patches relative to the brain at different placement locations.Methods and Results: Experiments were conducted on two juvenile pigs. Body temperature was measured using a rectal temperature probe while brain temperature with an intraparenchymal thermocouple probe. A SpotOn patch was taped to the pig’s head at three different locations: 1-2 cm posterior (Location #1, n=1), central forehead (Location #2, n=1); and 1-2 cm anterior and lateral to the bregma i.e., above the eye on the forehead (Location #3, n=1). This cooling system was able to rapidly cool the brain temperature to 33.7 ± 0.2°C within 15 minutes, and maintain the brain temperature within 33-34°C for 4-6 hours before slowly rewarming to 34.8 ± 1.1°C from 33.7 ± 0.2°C, while maintaining the core body temperature (as per rectal temperature probe) above 36°C. We measured a mean bias of -1.1°C, -0.2°C and 0.7°C during rapid cooling in induction phase, maintenance and rewarming phase, respectively. Amongst the three locations, location #2 had the highest correlation (R2 = 0.8) between the SpotOn sensor and the thermocouple probe.Conclusions: This SBC method is able to tightly control the rewarming rate within 0.52 ± 0.20°C/h. The SpotOn sensor placed on the center of the forehead provides a good measurement of brain temperature in comparison to the invasive needle probe.

Improved method for optical fiber temperature probe implantation in brains of free-moving rats

BackgroundThe localized monitoring of brain temperature is crucial to the understanding of the mechanisms underlying brain hyperthermia, such as that caused by stimulant drugs. Many animal studies investigating brain hyperthermia have utilized thermocouple electrodes for temperature measurement, however optical fiber sensors have proven to be an attractive alternative to conventional measurement techniques. Despite their advantages, optical fiber sensors in their current form have struggled to find effective use in studies involving free-moving animals. New methodWe have developed an improved optical fiber temperature probe and implantation method suitable for sensing in free-moving animals. By altering the structure of the probe, conventional guide cannulae can be used for stereotaxic implantation thus increasing ease-of-use and probe durability. ResultsThe new probe structure was easily implanted and extremely durable both pre-experimentation and during sampling in vivo. Probe re-usability also allowed for increased experimental workflow. Rats administered MDMA showed pathological increases in brain temperature. Comparison with existing method(s)Thermocouples commonly used for temperature measurement in deep brain structures lack the advantages offered by optical fiber sensors. Unlike our improved design, previous optical fiber temperature probes were unable to be removed from the brains of rats without removing the dental cement affixing it to the skull. This made the probe susceptible to breakage and often resulted in the complete loss of the animal from the experiment. ConclusionsOur fiber temperature probe and revised implantation technique can be easily employed in brain thermorecording using advantageous optical fiber sensors suitable for use in awake free-moving animals.

The effect of using a dielectric matching medium in focused microwave radiometry: an anatomically detailed head model study.

Microwave radiometry is a passive technique used to measure in-depth temperature distributions inside the human body, potentially useful in clinical applications. Experimental data imply that it may provide the capability of detecting in-depth local variations of temperature and/or conductivity of excitable tissues at microwave frequencies. Specifically, microwave radiometry may allow the real-time monitoring of brain temperature and/or conductivity changes, associated with local brain activation. In this paper, recent results of our ongoing research regarding the capabilities of focused microwave radiometry for brain intracranial applications are presented. Electromagnetic and thermal simulation analysis was performed using an anatomically detailed head model and a dielectric cap as matching medium placed around it, in order to improve the sensitivity and the focusing attributes of the system. The theoretical results were compared to experimental data elicited while exploring that the sensing depth and spatial resolution of the proposed imaging method at 2.1GHz areas located 3cm deep inside the brain can be measured, while at 2.5GHz, the sensing area is confined specifically to the area of interest. The results exhibit the system's potential as a complementary brain imaging tool for multifrequency in-depth passive monitoring which could be clinically useful for therapeutic, diagnostic, and research applications.

Postoperative monitoring of body temperature in patients with brain trauma: a prospective multicenter study

Objective To investigate the relationship of brain temperature (intra-ventricle, brain parenchyma, or subdural space) to axillary temperature, rectal temperature and bladder temperature in postoperative patients with brain trauma, and to explore the prognosis value of the brain temperature through a multicenter prospective observational study. Methods A total of 83 patients with brain trauma at 11 hospitals were enrolled to this study from March 2016 to December 2016. The data including patients' brain temperatures, axillary temperatures, rectal temperatures and bladder temperatures were hourly documented postoperatively until withdrawal of monitoring device of brain temperatures. The changes of the values were then further analyzed. Results Compared with the axillary temperature, the subdural temperature difference [0.10(-0.40, 0.40)℃] was less than intraventricular temperature difference [0.30(-0.20, 0.90)℃], which was less than parenchymal temperature difference [0.60(0.20, 1.00)℃](both P<0.05). Compared with rectal temperature and bladder temperature, the subdural temperature difference [-0.20(-0.40, 0.00)℃, -0.10(-0.30, 0.00)℃, respectively] was less than parenchymal temperature difference [0.10(-0.10, 0.20)℃, 0.10(0.00, 0.20)℃, respectively], which was less than intraventricular temperature difference [0.20(0.10, 0.30)℃, 0.20(0.10, 0.30)℃, respectively] (all P<0.05). No matter whether hypothermia treatment was administered, the difference between brain temperature and axillary temperature (ΔTBr-Ax) was larger than that between brain temperature and rectal temperature (ΔTBr-Re) and that between brain temperature and bladder temperature (ΔTBr-Bl) (both P<0.05). When brain temperature was higher than 38 ℃, ΔTBr-Ax was larger than ΔTBr-Re , which was larger than ΔTBr-Bl (both P<0.05). When brain temperature was less than or equal to 38 ℃, ΔTBr-Ax was larger than ΔTBr-Bl, which was larger than ΔTBr-Re (both P<0.05). When the fluctuation of brain temperature within 12 hours post operation was more than 1 ℃, the preoperative Glasgow coma scale (GCS) and the extended Glasgow outcome scale(GOS-E) at discharge were significantly lower compared with those of cases whose brain temperature fluctuation was less than or equal to 1 ℃ (both P<0.05). Conclusions For patients with brain trauma, brain temperature monitoring seems to have a very significant clinical value. When monitoring of brain temperature is not available, the bladder temperature might serve as the best reflection of brain temperature. Key words: Craniocerebral trauma; Body temperature; Multicenter study; Prospective studies

Simultaneous in vivo recording of local brain temperature and electrophysiological signals with a novel neural probe

Objective. Temperature is an important factor for neural function both in normal and pathological states, nevertheless, simultaneous monitoring of local brain temperature and neuronal activity has not yet been undertaken. Approach. In our work, we propose an implantable, calibrated multimodal biosensor that facilitates the complex investigation of thermal changes in both cortical and deep brain regions, which records multiunit activity of neuronal populations in mice. The fabricated neural probe contains four electrical recording sites and a platinum temperature sensor filament integrated on the same probe shaft within a distance of 30 µm from the closest recording site. The feasibility of the simultaneous functionality is presented in in vivo studies. The probe was tested in the thalamus of anesthetized mice while manipulating the core temperature of the animals. Main results. We obtained multiunit and local field recordings along with measurement of local brain temperature with accuracy of 0.14 °C. Brain temperature generally followed core body temperature, but also showed superimposed fluctuations corresponding to epochs of increased local neural activity. With the application of higher currents, we increased the local temperature by several degrees without observable tissue damage between 34–39 °C. Significance. The proposed multifunctional tool is envisioned to broaden our knowledge on the role of the thermal modulation of neuronal activity in both cortical and deeper brain regions.

Is Esophageal Temperature Better to Estimate Brain Temperature during Target Temperature Management in a Porcine Model of Cardiopulmonary Resuscitation?

Brain temperature monitoring is important in target temperature management for comatose survivors after cardiac arrest. Since acquisition of brain temperature is invasive and unrealistic in scene of resuscitation, we tried to sought out surrogate sites of temperature measurements that can precisely reflect cerebral temperature. Therefore, we designed this controlled, randomized animal study to investigate whether esophageal temperature can better predict brain temperature in two different hypothermia protocols. The results indicated that esophageal temperature had a stronger correlation with brain temperature in the early phase of hypothermia in both whole and regional body cooling protocols. It means that esophageal temperature was considered as priority method for early monitoring once hypothermia is initiated. This clinical significance of this study is as follows. Since resuscitated patients have unstable hemodynamics, collecting temperature data from esophagus probe is cost-efficient and easier than the catheter in central vein. Moreover, it can prevent the risk of iatrogenic infection comparing with deep vein catheterization, especially in survivors with transient immunoexpressing in hypothermia protocol.

Focused Ultrasound Treatment, Present and Future

The discovery that ultrasound waves could be focused inside the skull and heated to high temperatures at a focal point goes back to 1944. However, because the skull causes the ultrasound waves to attenuate and scatter, it was believed that application of this technology would be difficult, and that it would be impossible to use this approach in the surgical treatment of intracranial diseases. Eventually, magnetic resonance image guided focused ultrasound (MRgFUS) surgery began being used to treat uterine fibroids, breast cancer and bone metastasis and locally confined prostate cancer. In the first ten years of the 21st century, new developments in this technology have been achieved, broadening the scope of practical application, and treatment is now being performed in various countries around the world. In 2011, third-generation transcranial focused ultrasound made it possible to use thermocoagulation and create intracranial lesions measuring 2 to 6 mm in diameter with a precision of around 1 mm. It was also possible to produce MR images which relay information of temperature changes in real time, enabling a shift from reversible test heating to irreversible therapeutic heating. This gave rise to the possibility of a minimally-invasive treatment with outcomes similar to those of conventional brain surgery. This method is paving the way to a new future not only in functional neurosurgery, but in cranial neurosurgery targeting conditions such as epilepsy and brain tumors, among others. In this paper, we describe the current state and future outlook of magnetic resonance image guided focused ultrasound, which uses computed tomography (CT) bone images in combination with MRI monitoring of brain temperature.

Polysilicon-based flexible temperature sensor for brain monitoring with high spatial resolution

Temperature is one of the most important variables in brain monitoring, since changes of focal brain temperature are closely coupled to cerebral physiology and pathophysiological phenomena in injured brain. In this work, a highly accurate temperature sensor with polysilicon thermistors has been developed on flexible polyimide for monitoring brain temperature with high spatial resolution. The temperature sensors have a response time of 1.5 s and sensitivity of −0.0031 °C−1. Thermal hysteresis of the sensor in the physiological temperature range of 30–45 °C was found to be less than 0.1 °C. With silicon nitride as the passivation layer, the temperature sensor exhibits drift of less than 0.3 °C for 3 d in water. In vivo tests of the sensor show a low noise level of 0.025 ± 0.03 °C, and the expected transient increases in cortical temperature associated with cortical spreading depolarization. The temperature sensor developed in this work is suitable for monitoring brain temperature with the desired high sensitivity and resolution.

Polysilicon based flexible temperature sensor for high spatial resolution brain temperature monitoring.

In this paper, we present a flexible temperature sensor with ultra-small polysilicon thermistors for brain temperature monitoring. In vitro sensitivity, resolution, thermal hysteresis and long term stability tests were performed. Temperature coefficient of resistance (TCR) of -0.0031/ °C and resolution of 0.1 °C were obtained for the sensor. Thermal hysteresis for temperature range of 30~45 °C was less than 0.1 °C. With silicon nitride as the passivation layer, the temperature sensor showed a drift within 0.3 °C for 3 days long term stability test in water. In vivo tests showed a clear correlation between the localized brain temperature and electrocorticography (ECoG) signal during spreading depolarization. The developed flexible temperature sensor with small size polysilicon thermistors can be adopted for high resolution brain temperature mapping as well as multimodal monitoring with limited sensing space.

Polysilicon Thin Film Developed on Flexible Polyimide for Biomedical Applications

Flexible pressure and thermal sensors are the critical parts of the functional electronic skin of prostheses and robots, as well as flexible catheter/devices for multimodal biomedical monitoring. In this paper, a polysilicon thin film was developed on a flexible polyimide substrate using aluminum induced crystallization process for biomedical pressure and temperature sensing applications. The formation of polycrystalline structure was verified from the developed polysilicon film. Long term stability and real-time temperature tests were performed to evaluate potential application to the in vivo monitoring of brain or body temperature. The linear real-time change of polysilicon resistance with temperature was attained with the temperature coefficient of the resistance of −0.0027/°C and the resolution of 0.05 °C. With a gauge factor of 10.3, the polysilicon film developed in this paper represents a promising material for the development of high-sensitivity pressure sensors on flexible polyimide substrates. [2015-0106]