Effects of Closed Endotracheal Suctioning on Systemic and Cerebral Oxygenation and Hemodynamics in Children.

OBJECTIVES: To evaluate the effects of closed endotracheal tube suctioning on systemic oxygen saturation, cerebral regional oxygen saturation, and somatic regional (renal) oxygen saturation and hemodynamic variables in children. DESIGN: Prospective observational. SETTING: A tertiary care PICU. SUBJECTS: Children aged 0-18 years, requiring invasive mechanical ventilation and with an arterial line. INTERVENTIONS: Closed endotracheal suction. MEASUREMENTS AND MAIN RESULTS: The study included 19 sedated and intubated children, 0-18 years old. They were enrolled in an ongoing prospective observational study. We used near-infrared spectroscopy for cerebral regional oxygen saturation and somatic regional (renal) oxygen saturation. The timing of each closed endotracheal tube suctioning event was accurately identified from video recordings. We extracted systemic oxygen saturation, cerebral regional oxygen saturation, somatic regional (renal) oxygen saturation, heart rate, and systolic blood pressure and diastolic blood pressure for 5 minutes before and 5 minutes after each event and used these data for analysis. One-minute average values of these variables were used for repeated-measures analysis. We analyzed 287 endotracheal tube suctioning episodes in 19 children. Saline was instilled into the endotracheal tube during 61 episodes. The mean heart rate (107.0 ± 18.7 vs 110.2 ± 10.4; p < 0.05), mean arterial blood pressure (81.5 ± 16.1 vs 83.0 ± 15.6 mm Hg; p < 0.05), and the mean cerebral regional oxygen saturation (64.8 ± 8.3 vs 65.8 ± 8.3; p < 0.05) were increased after suctioning. The mean systemic oxygen saturation (96.9 ± 2.7 vs 96.7 ± 2.7; p = 0.013) was decreased, whereas the mean somatic regional (renal) oxygen saturation was not significantly different after endotracheal tube suctioning. Repeated-measures analysis revealed transient increases in heart rate, respiratory rate, systolic blood pressure, and diastolic blood pressure; a sustained increase in cerebral regional oxygen saturation; and transient decreases in systemic oxygen saturation and somatic regional (renal) oxygen saturation. Saline instillation did not affect oxygenation or hemodynamic variables. CONCLUSIONS: Closed endotracheal tube suctioning in sedated children is associated with transient but clinically insignificant changes in heart rate, blood pressure, cerebral regional oxygen saturation, systemic oxygen saturation, and somatic regional (renal) oxygen saturation. Saline instillation during endotracheal tube suctioning had no adverse effects on systemic or cerebral oxygenation.

Heart Rate Variability in Children Following Drowning Injury.

Heart rate variability (HRV) has been used as prognostic tool in various disorders in pediatric and adult patients. In our study we aimed to evaluate heart rate variability indices and their association with neurological outcome in three children with anoxic brain injury following drowning. Three children included in the study were admitted following drowning and required mechanical ventilation and targeted temperature management. All physiologic data, including electrocardiography (ECG) and EEG were collected for a period of 3-5 days after enrollment. ECG signals were analyzed in both time and frequency domains. The spectral power of the low-frequency (LF) band (0.04-0.15 Hz) and that of the high-frequency (HF) band (0.15-0.4 Hz), the standard deviation of the average R to R ECG intervals (SDANN) were calculated. Mean low-frequency/high-frequency power ratios (LF/HF) were compared using a two-tailed t-test and ANOVA with Tukey-Kramer multiple comparisons. The power in the LF band, the LF/HF power ratio, and the SDANN, were lower in children who had a poor outcome, and during periods of isoelectric or burst suppression EEG patterns.

The effect of lung recruitment maneuverer in COVID-19 induced acute respiratory distress syndrome.

Coronavirus disease-2019 (COVID-19) is a highly spread infectious disease around the world. This infectious disease impacts whole body systems, specifically on respiratory system. This 57-year-old women had diagnosed COVID-19 positive and progress to acute respiratory distress syndrome (ARDS) within 1 week. Mechanical ventilation with protective lung strategy, prone position could not reverse the worsen hypoxemia and bilateral lung infiltration. Recruitment manoeuvre was proceeded with 40-40 strategy and protective/ventilation tool (P/V tool). After 4 days (8 rounds) of recruitment manoeuvre, oxygenation level and lung compliance showed dramatic improvement. The patient was finally extubated at COVID-19 Day 40 and discharged with long term oxygen use at COVID-19 Day 60. In this case, we report how recruitment manoeuvre can improve severe hypoxemia and bilateral lung infiltration dramatically in ARDS.

The Effect of Electroencephalography Abnormalities on Cerebral Autoregulation in Sedated Ventilated Children.

Purpose: To determine the effects of non-ictal electroencephalogram (EEG) changes on cerebrovascular autoregulation (AR) using the cerebral oximetry index (COx). Materials and Methods: Mean arterial blood pressure (MAP), cerebral tissue oxygenation (CrSO2), and EEG were acquired for 96 h. From all of the EEG recordings, 30 min recording segments were extracted using the endotracheal suction events as the guide. EEG recordings were classified as EEG normal and EEG abnormal groups. Each 30 min segment was further divided into six 5 min epochs. Continuous recordings of MAP and CrSO2 by near-infrared spectroscopy (NIRS) were extracted. The COx value was defined as the concordance (R) value of the Pearson correlation between MAP and CrSO2 in a 5 min epoch. Then, an Independent-Samples Mann-Whitney U test was used to analyze the number of epochs within the 30 min segments above various R cutoff values (0.2, 0.3, and 0.4) in normal and abnormal EEG groups. A p-value < 0.05 was considered significant, and all analyses were two-tailed. Results: Among 16 sedated, mechanically ventilated children, 382 EEG recordings of 30 min segments were analyzed. The proportions of epochs in each 30 min segment above the R cutoff values were similar between the EEG normal and EEG abnormal groups (p > 0.05). The median concordance values for CSrO2 and MAP in EEG normal and EEG abnormal groups were similar (0.26 (0.17−0.35) and 0.18 (0.12−0.31); p = 0.09). Conclusions: Abnormal EEG patterns without ictal changes do not affect cerebrovascular autoregulation in sedated and mechanically ventilated children.

In vivo optical properties of cortical tubers in children with tuberous sclerosis complex (TSC): a preliminary investigation.

PURPOSE: Medically refractory epilepsy caused by cortical tubers resulting from tuberous sclerosis complex (TSC) often requires surgical intervention. The locations of cortical tubers generally are determined by preoperative magnetic resonance imaging (MRI). In this pilot study, we explored the feasibility of using the optical characteristics of cortical tubers as a potential means to guide their resection intraoperatively. METHODS: Optical characteristics of normal cortex and cortical tubers were measured intraoperatively using diffuse reflectance spectroscopy in three children undergoing epilepsy surgery for drug-resistant seizures. Unique diffuse reflectance spectroscopic features of cortical tubers were identified and their physiologic associations determined. KEY FINDINGS: Diffuse reflectance spectra revealed several features that distinguish cortical tubers from normal cortex. In tubers, diffuse reflectance intensities at oxy- and deoxyhemoglobin isobestic points, like 500, 530, and 570 nm, were consistently higher than those in normal cortex. According to the profile of diffuse reflectance spectra from 520-580 nm, hemoglobin oxygenation in tubers often was lower than in normal cortex. SIGNIFICANCE: Albeit preliminary, our findings suggest that the optical characteristics of cortical tubers differ from intervening normal cortex, likely reflecting the lower cerebral blood volumes and reduced hemoglobin oxygenation of cortical tubers. The results of this study can be used to design biomedical instruments that aid tuberectomies.

Advances in imaging and analysis of 4 fluorescent components through the rat cortical column.

BACKGROUND: Immunofluorescent staining coupled with axial optical sectioning allows for assessment of native three-dimensional structure of brain tissue. Typical challenges of analyzing network structure include limitations driven by magnification/field of view, spatial resolution, tissue thickness, staining quality of dense cell types, data quantifiability and the quantity of simultaneous staining targets. NEW METHOD: This manuscript demonstrates many methodological advancements. Software-aided alignment of the cortical slice and stereotaxic atlas maximizes ROI-identification accuracy. Tissue compression during antigen retrieval enhances epitope availability without damaging tissue. A thorough factorial experiment focusing on Smi-311 staining highlights the enhancements in image quality from our extended staining protocol. Mosaic scanning techniques and subsequent four-channel alignment ensures high data quality. RESULTS: Cortical column datasets [800µm x 3000µm x 70µm] utilizing sequential optical sectioning were successfully generated from three rats. Each rat provided three coronal sections in each of two regions, M1 and S1BF, from which data cubes were generated per hemisphere, totaling 36 high-magnification four-color datasets. COMPARISON WITH EXISTING METHOD(S): Typical confocal assessments of brain tissue do not utilize such thick tissue slices nor collect entire cortical columns from the cortical surface to the grey/white interface at a resolution that can map fine filamentous processes. The simultaneous collection of our four specific structural markers - neuronal, astrocytic, vascular and nuclear - is novel and the quantitative optimization of staining protocols through a factorial design rare. CONCLUSIONS: Building upon this preliminary success in protocol development, future work will encompass volumetric modeling and quantitative analysis of regional network architecture.

Optical spectroscopy for in-vitro differentiation of pediatric neoplastic and epileptogenic brain lesions.

The objective of this in vitro tissue study is to investigate the feasibility of using optical spectroscopy to differentiate pediatric neoplastic and epileptogenic brain from normal brain. Specimens are collected from 17 patients with brain tumors, and from 26 patients with intractable epilepsy during surgical resection of epileptogenic cerebral cortex. Fluorescence spectra are measured at excitations of 337, 360, and 440 nm; diffuse reflectance spectra are measured between 400 and 900 nm from each specimen. Pathological analysis is performed to classify abnormalities in brain specimens, and its findings are correlated with spectral data. Statistically significant differences (p<0.01) are found for both raw and normalized diffuse reflectance and fluorescence spectra between 1. neoplastic brain and normal gray matter, 2. epileptogenic brain and normal gray matter, and 3. neoplastic brain and normal white matter. However, no distinct spectral features are identified that effectively separate epileptogenic brain from normal white matter. The outcomes of the study suggest that certain unique compositional and structural characteristics of pediatric neoplastic and epileptogenic brain can be detected using optical spectroscopy in vitro.

Effects of probe contact pressure on in vivo optical spectroscopy.

The short- and long-term effects of probe contact pressure on in vivo diffuse reflectance and fluorescence spectroscopy were investigated using an animal model. Elevation in probe contact pressure induced major profile alterations in the diffuse reflectance spectra between 400 and 650 nm, and led to significant intensity increases in the fluorescence spectra. The pressure threshold that was required to induce statistically significant spectral alterations was dependent upon the type of tissue. The observed spectral alterations may be attributed to decreases in local blood volume, blood oxygenation, and tissue metabolism, resulting from high probe contact pressure.

The role of optical spectroscopy in epilepsy surgery in children.

OBJECT: Surgery is an important therapeutic modality for pediatric patients with intractable epilepsy. However, existing imaging and diagnostic technologies such as MR imaging and electrocochleography (ECoG) do not always effectively delineate the true resection margin of an epileptic cortical lesion because of limitations in their sensitivity. Optical spectroscopic techniques such as fluorescence and diffuse reflectance spectroscopy provide a nondestructive means of gauging the physiological features of the brain in vivo, including hemodynamics and metabolism. In this study, the authors investigate the feasibility of using combined fluorescence and diffuse reflectance spectroscopy to assist epilepsy surgery in children. METHODS: In vivo static fluorescence and diffuse reflectance spectra were acquired from the brain in children undergoing epilepsy surgery. Spectral measurements were obtained using a portable spectroscopic system in conjunction with a fiber optic probe. The optical investigations were conducted at the normal and abnormal cortex as defined by intraoperative ECoG and preoperative imaging studies. Biopsy samples were taken from the investigated sites located within the zone of resection. The optical spectra were classified into multiple subsets in accordance with the ECoG and histological study results. The authors used statistical comparisons between 2 given data subsets to identify unique spectral features. Empirical discrimination algorithms were developed using the identified spectral features to determine if the objective of the study was achieved. RESULTS: Fifteen pediatric patients were enrolled in this pilot study. Elevated diffuse reflectance signals between 500 and 600 nm and/or between 650 and 850 nm were observed commonly in the investigated sites with abnormal ECoG and/or histological features in 10 patients. The appearance of a fluorescent peak at 400 nm was observed in both normal and abnormal cortex of 5 patients. These spectral alterations were attributed to changes in morphological and/or biochemical characteristics of the epileptic cortex. The sensitivities and specificities of the empirical discrimination algorithms, which were constructed using the identified spectral features, were all > 90%. CONCLUSIONS: The results of this study demonstrate the feasibility of using static fluorescence and diffuse reflectance spectroscopy to differentiate normal from abnormal cortex on the basis of intraoperative assessment of ECoG and histological features. It is therefore possible to use fluorescence and diffuse reflectance spectroscopy as an aid in epilepsy surgery.

Histological Characterization of the Irritative Zones in Focal Cortical Dysplasia Using a Preclinical Rat Model.

Current clinical practice in focal epilepsy involves brain source imaging (BSI) to localize brain areas where from interictal epileptiform discharges (IEDs) emerge. These areas, named irritative zones, have been useful to define candidate seizures-onset zones during pre-surgical workup. Since human histological data are mostly available from final resected zones, systematic studies characterizing pathophysiological mechanisms and abnormal molecular/cellular substrates in irritative zones-independent of them being epileptogenic-are challenging. Combining BSI and histological analysis from all types of irritative zones is only possible through the use of preclinical animal models. Here, we recorded 32-channel spontaneous electroencephalographic data from rats that have focal cortical dysplasia (FCD) and chronic seizures. BSI for different IED subtypes was performed using the methodology presented in Bae et al. (2015). Post-mortem brain sections containing irritative zones were stained to quantify anatomical, functional, and inflammatory biomarkers specific for epileptogenesis, and the results were compared with those obtained using the contralateral healthy brain tissue. We found abnormal anatomical structures in all irritative zones (i.e., larger neuronal processes, glioreactivity, and vascular cuffing) and larger expressions for neurotransmission (i.e., NR2B) and inflammation (i.e., ILß1, TNFα and HMGB1). We conclude that irritative zones in this rat preclinical model of FCD comprise abnormal tissues disregarding whether they are actually involved in icto-genesis or not. We hypothesize that seizure perpetuation happens gradually; hence, our results could support the use of IED-based BSI for the early diagnosis and preventive treatment of potential epileptic foci. Further verifications in humans are yet needed.

A probability-based spectroscopic diagnostic algorithm for simultaneous discrimination of brain tumor and tumor margins from normal brain tissue.

This paper reports the development of a probability-based spectroscopic diagnostic algorithm capable of simultaneously discriminating tumor core and tumor margins from normal human brain tissues. The algorithm uses a nonlinear method for feature extraction based on maximum representation and discrimination feature (MRDF) and a Bayesian method for classification based on sparse multinomial logistic regression (SMLR). Both the autofluorescence and the diffuse-reflectance spectra acquired in vivo from patients undergoing craniotomy or temporal lobectomy at the Vanderbilt University Medical Center were used to train and validate the algorithm. The classification accuracy was observed to be approximately 96%, 80%, and 97% for the tumor, tumor margin, and normal brain tissues, respectively, for the training data set and approximately 96%, 94%, and 100%, respectively, for the corresponding tissue types in an independent validation data set. The inherently multi-class nature of the algorithm facilitates a rapid and simultaneous classification of tissue spectra into various tissue categories without the need for a hierarchical multi-step binary classification scheme. Further, the probabilistic nature of the algorithm makes it possible to quantitatively assess the certainty of the classification and recheck the samples that are classified with higher relative uncertainty.

Quantitative assessment of hemodynamic and structural characteristics of in vivo brain tissue using total diffuse reflectance spectrum measured in a non-contact fashion.

Here we present a new methodology that investigates the intrinsic structural and hemodynamic characteristics of in vivo brain tissue, in a non-contact fashion, and can be easily incorporated in an intra-operative environment. Within this methodology, relative total diffuse reflectance spectra (RTD(λ)) were acquired from targets using a hybrid spectroscopy imaging system. A spectral interpretation algorithm was subsequently applied to RTD(λ) to retrieve optical properties related to the compositional and structural characteristics of each target. Estimation errors of the proposed methodology were computationally evaluated using a Monte Carlo simulation model for photon migration under various conditions. It was discovered that this new methodology could handle moderate noise and achieve very high accuracy, but only if the refractive index of the target is known. The accuracy of the technique was also validated using a series of tissue phantom studies, and consistent and accurate estimates of µs'(λ)/µa(λ) were obtained from all the phantoms tested. Finally, a small-scale animal study was conducted to demonstrate the clinical utility of the reported method, wherein a forepaw stimulation model was utilized to induce transient hemodynamic responses in somatosensory cortices. With this approach, significant stimulation-related changes (p < 0.001) in cortical hemodynamic and structural characteristics were successfully measured.

Neuro-oncological applications of optical spectroscopy.

Advances in optics and molecular imaging have occurred rapidly in the past decade. One technique poised to take advantage of these developments is optical spectroscopy (OS). All optical spectroscopic techniques have in common tissue interrogation with light sources ranging from the ultraviolet (UV) to the infrared (IR) ranges of the spectrum, and collection of information on light reflected (reflectance spectroscopy) or light interactions with tissue and emergence at different wavelengths (fluorescence and Raman spectroscopy). OS can provide information regarding intrinsic tissue optical properties such as tissue structure, nuclear density, and the presence or absence of endogenous or exogenous fluorophores. Among other applications, this information has been used to distinguish tumor from normal brain tissues, to detect tumor margins in intrinsic, infiltrating gliomas, to identify radiation damage to tissues, and to assess tissue viability and predict the onset of apoptosis in vitro and in vivo. Potential applications of OS include detection of specific central nervous system (CNS) structures, such as brain nuclei, identification of cell types by the presence of specific neurotransmitters, and the detection of optically labeled cells or drugs during therapeutic interventions. All have potential utility in neuro-oncology, have been investigated in our laboratories, and will be the subject of this review.

Intraoperative optical mapping of epileptogenic cortices during non-ictal periods in pediatric patients.

Complete removal of epileptogenic cortex while preserving eloquent areas is crucial in patients undergoing epilepsy surgery. In this manuscript, the feasibility was explored of developing a new methodology based on dynamic intrinsic optical signal imaging (DIOSI) to intraoperatively detect and differentiate epileptogenic from eloquent cortices in pediatric patients with focal epilepsy. From 11 pediatric patients undergoing epilepsy surgery, negatively-correlated hemodynamic low-frequency oscillations (LFOs, ~ 0.02-0.1 Hz) were observed from the exposed epileptogenic and eloquent cortical areas, as defined by electrocorticography (ECoG), using a DIOSI system. These LFOs were classified into multiple groups in accordance with their unique temporal profiles. Causal relationships within these groups were investigated using the Granger causality method, and 83% of the ECoG-defined epileptogenic cortical areas were found to have a directed influence on one or more cortical areas showing LFOs within the field of view of the imaging system. To understand the physiological origins of LFOs, blood vessel density was compared between epileptogenic and normal cortical areas and a statistically-significant difference (p < 0.05) was detected. The differences in blood-volume and blood-oxygenation dynamics between eloquent and epileptogenic cortices were also uncovered using a stochastic modeling approach. This, in turn, yielded a means by which to separate epileptogenic from eloquent cortex using hemodynamic LFOs. The proposed methodology detects epileptogenic cortices by exploiting the effective connectivity that exists within cortical regions displaying LFOs and the biophysical features contributed by the altered vessel networks within the epileptogenic cortex. It could be used in conjunction with existing technologies for epileptogenic/eloquent cortex localization and thereby facilitate clinical decision-making.

Dysfunction of Neurovascular/Metabolic Coupling in Chronic Focal Epilepsy.

GOAL: We aim to evaluate the mechanisms underlying the neurovascular/metabolic coupling in the epileptogenic cortices of rats with chronic focal epilepsy. METHODS: We performed and analyzed intracranial recordings obtained from the seizure-onset zones during ictal periods on epileptic rats, and then, used these data to fit a metabolically coupled balloon model. Normal rats undergoing forepaw stimulation were used as control. RESULTS: We found a significant higher contribution from high local field potential frequency bands to the cerebral blood flow (CBF) responses in the epileptogenic cortices during ictal neuronal activities. The hemodynamic responses associated with ictal activities were distance-dependent with regard to the seizure focus, though varied in profiles from those obtained from acute seizure models. Parameters linking the CBF and relative concentration of deoxyhemoglobin to neuronal activity in the biophysical model were significantly different between epileptic and normal rats. CONCLUSION: We found that the coefficient associated with the strength of the functional hyperemic response was significantly larger in the epileptogenic cortices, and changes in hemoglobin concentration associated with ictal activity reflected the existence of a significantly higher baseline for oxygen metabolism in the epileptogenic cortices. SIGNIFICANCE: Introducing methods to estimate these physiological parameters would enhance our understanding of the neurovascular/metabolic coupling in epileptic brains and improve the localization accuracy on irritative zones and seizure-onset zones through neuroimaging techniques.

Peptide modified polymer poly (glycerol- dodecanedioate co-fumarate) for efficient control of motor neuron differentiation.

Neural tissue engineering is one of the most promising approaches for healing nerve damage, which bypasses the limits of contemporary conventional treatments. In a previous study, we developed a fibrous scaffold via electrospinning poly (glycerol dodecanedioate) (PGD) and gelatin that mimics the structure of a native extracellular matrix (ECM) for soft tissue engineering application. In this study, fumaric acid (FA) was incorporated into the PGD synthesis process, which produced a PGD derivative referred to as poly (glycerol dodecanedioate co-fumarate) (PGDF). This introduced a new functional group, a double bond, into the polymer thus providing new modification possibilities. Arg-Gly-Asp-Cys (RGDC) and laminin peptides were chosen as biomolecules to modify the fiber and facilitate cell attachment and differentiation efficiency. The release of FA into the medium was quantified to investigate the bioreactivity of the derived scaffolds. In combination with UV crosslinking, the developed PGDF fiber mats were able to withstand degradation processes for up to 2 months, which ensures that neural tissue engineering applications are viable. Cell viability and motor neuron differentiation efficiency were demonstrated to be significantly improved with the addition of FA, RGDC and laminin peptides.

Distributions of Irritative Zones Are Related to Individual Alterations of Resting-State Networks in Focal Epilepsy.

Alterations in the connectivity patterns of the fMRI-based resting-state networks (RSNs) have been reported in several types of epilepsies. Evidence pointed out these alterations might be associated with the genesis and propagation of interictal epileptiform discharges (IEDs). IEDs also evoke blood-oxygen-level dependent (BOLD) responses, which have been used to delineate irritative zones during preoperative work-up. Therefore, one may expect a relationship between the topology of the IED-evoked BOLD response network and the altered spatial patterns of the RSNs. In this study, we used EEG recordings and fMRI data obtained simultaneously from a chronic model of focal epilepsy in Wistar rats to verify our hypothesis. We found that IED-evoked BOLD response networks comprise both cortical and subcortical structures with a rat-dependent topology. In all rats, IEDs evoke both activation and deactivation types of BOLD responses. Using a Granger causality method, we found that in many cases areas with BOLD deactivation have directed influences on areas with activation (p<0.05). We were able to predict topological properties (i.e., focal/diffused, unilateral/bilateral) of the IED-evoked BOLD response network by performing hierarchical clustering analysis on major spatial features of the RSNs. All these results suggest that IEDs and disruptions in the RSNs found previously in humans may be different manifestations of the same transient events, probably reflecting altered consciousness. In our opinion, the shutdown of specific nodes of the default mode network may cause uncontrollable excitability in other functionally connected brain areas. We conclude that IED-evoked BOLD responses (i.e., activation and deactivation) and alterations of RSNs are intrinsically related, and speculate that an understanding of their interplay is necessary to discriminate focal epileptogenesis and network propagation phenomena across different brain modules via hub-based connectivity.

Fluorescence spectroscopy accurately detects irreversible cell damage during hepatic radiofrequency ablation.

BACKGROUND: A current limitation of hepatic radiofrequency ablation (RFA) is an inability to detect ablation margins in real time. Thermal injury from RFA alters the biochemical properties governing tissue fluorescence. We hypothesized that the changes in hepatic fluorescence measured during hepatic RFA could be used to detect irreversible hepatocyte damage accurately and to determine ablation margins in real time. METHODS: RFA was performed on healthy pig livers and monitored in vivo simultaneously for fluorescence and temperature by a fiberoptic micro-interrogation probe connected to a spectroscopy system. Ablations were stopped based on previously established real-time fluorescence spectral data, not based on temperature or time. To determine where in the ablated tissue cell death occurred, biopsies for transmission electron microscopy were taken from 4 areas of 3 specimens: (1) nonablated liver, (2) hemorrhagic zone/normal liver interface, (3) hemorrhagic zone/coagulated zone interface, and (4) coagulated zone. In vitro fluorescence emission intensity was determined at each biopsy site. RESULTS: Peak hepatic fluorescence intensity occurred at 470 nm and decreased as RFA progressed. Transmission electron microscopy evidence of irreversible hepatocyte damage occurred at the interface of the coagulation zone and the hemorrhagic zone and correlated with a 87.5% +/- 9% decrease in fluorescence emission intensity. Tissue fluorescent changes from thermal injury were unaffected by tissue cooling. CONCLUSION: Fluorescence spectroscopy accurately detected hepatocellular thermal injury from RFA in real time and can detect irreversible cell damage during tissue thermal therapy.

Feasibility study using surface-enhanced Raman spectroscopy for the quantitative detection of excitatory amino acids.

The release of excitatory amino acids (EAAs) from injured neurons has been associated with secondary injury following head trauma. The development of a rapid and sensitive method for the quantification of EAAs may provide a means for clinical management of patients affected by head trauma. We explore the potential application of surface-enhanced Raman spectroscopy (SERS) for rapid quantification of the concentration of EAAs in aqueous silver colloids. The EAAs glutamate (Glu) and aspartate (Asp) are released following head injury and have been observed to exhibit SERS spectra that should enable them to be distinguished in a complex aqueous media. Of the two EAAs, the concentration of Glu has been shown to be more indicative of injury to the central nervous system. Using 30-s scans and a 50-mW argon laser, aqueous Glu is quantifiable from 0.4 to 5 micromol/L and is spectrally distinguishable from Asp. In addition, initial in vivo microdialysis experiments suggest that this SERS system is capable of measuring chemical changes following head trauma in the rat brain. Compared with current high-performance liquid chromatography (HPLC) techniques for amino acid detection, the short scanning and processing time associated with the SERS approach enables measurement on a near-real-time basis, providing clinical information in anticipation of pharmaceutical intervention.

In vivo assessment of thermal damage in the liver using optical spectroscopy.

Resection is not a viable treatment option for the majority of liver cancer patients. Alternatives to resection include thermotherapies such as radio-frequency ablation; however, these therapies lack adequate intraoperative feedback regarding the degree and margins of tissue thermal damage. In this proof of principle study, we test the ability of fluorescence and diffuse reflectance spectroscopy to assess local thermal damage in vivo. Spectra were acquired in vivo from healthy canine liver tissue undergoing radio-frequency ablation using a portable fiber-optic-based spectroscopic system. The major observed spectral alterations on thermal coagulation were a red shift in the fluorescence emission peak at 480 nm, a decrease in the overall fluorescence intensity, and an increase in the diffuse reflectance from 450 to 750 nm. Spectral changes were quantified and correlated to tissue histology. We found a good correlation between the proposed spectral correlates of thermal damage and histology. The results of this study suggest that fluorescence and diffuse reflectance spectroscopy show strong potential as tools to monitor liver tissue thermal damage intraoperatively.