Reproducibility and sensitivity of detecting brain activity by simultaneous electroencephalography and near-infrared spectroscopy

The aims were (1) to determine the sensitivity and reproducibility to detect the hemodynamic responses and optical neuronal signals to brain stimulation by near-infrared spectroscopy (NIRS) and evoked potentials by electroencephalography (EEG) and (2) to test the effect of novel filters on the signal-to-noise ratio. This was achieved by simultaneous NIRS and EEG measurements in 15 healthy adults during visual stimulation. Each subject was measured three times on three different days. The sensitivity of NIRS to detect hemodynamic responses was 55.2% with novel filtering and 40% without. The reproducibility in single subjects was low. For the EEG, the sensitivity was 86.4% and the reproducibility 57.1%. An optical neuronal signal was not detected, although novel filtering considerably reduced nois

Detection of hyperbilirubinaemia in jaundiced full-term neonates by eye or by bilirubinometer?

The aim of this study was to compare predictions of hyperbilirubinaemia by eye, performed by trained physicians and nurses, with predictions obtained using two commercial bilirubinometers. Jaundice was assessed in 92 white and 48 non-white healthy full-term neonates using three non-invasive methods and by total serum bilirubin as the reference method. Clinical assessment of cephalocaudal progression of jaundice was carried out independently by a physician and by nurses. Simultaneously, the Minolta Airshields JM-102 was applied on the sternum, the BiliCheck on both the forehead and the sternum, and finally, serum bilirubin concentrations were determined. The Minolta JM-102 showed the best performance with r2=0.90, an intraclass correlation coefficient (ICC) of 0.93, and a 95% confidence interval (CI) of ±4units (approx. 56µmol/l). The BiliCheck performed slightly better on the forehead than over the sternum with r2=0.90, an ICC of 0.88, and a CI of ±62µmol/l. Assessment of jaundice by eye was least accurate with r2=0.74, an ICC of 0.67, and a CI of ±1.5 zones (corresponding to ±75µmol/l). Skin pigmentation and ambient light both adversely affected non-invasive bilirubin estimation. Conclusion:All three non-invasive methods are well suited for estimation of serum bilirubin but show large confidence intervals. In healthy term newborns, hyperbilirubinaemia (>250µmol/l) can be safely ruled out by eye if jaundice does not reach the abdomen or the extremities (Kramer zones 1 and 2), with <22 units (<230µmol/l) for the Minolta JM-102, or with a cut-off of 190µmol/l for the BiliCheck. If these respective thresholds are exceeded, serum bilirubin concentrations should be measure

Wireless miniaturized in-vivo near infrared imaging

Our group measures tissue oxygenation and the cortical hemodynamic response to sensory stimuli applying continuous wave near-infrared imaging (NIRI). To improve the method's quality and applicability and to explore new fields in clinical practice and research, we developed a miniaturized wireless NIRI system. It was validated by measuring muscle oxygenation in a blood-flow occlusion experiment and brain activity in adults

Multifrequency frequency-domain spectrometer for tissue analysis

In this paper we describe the modification and assessment of a standard multidistance frequency-domain near infrared spectroscopy (NIRS) instrument to perform multifrequency frequency-domain NIRS measurements. The first aim of these modifications was to develop an instrument that enables measurement of small volumes of tissue such as the cervix, which is too small to be measured using a multidistance approach. The second aim was to enhance the spectral resolution to be able to determine the absolute concentrations of oxy-, deoxy- and total hemoglobin, water, and lipids. The third aim was to determine the accuracy and error of measurement of this novel instrument in both in vitro and in vivo environments. The modifications include two frequency synthesizers with variable, freely adjustable frequency, broadband high-frequency amplifiers, the development of a novel avalanche photodiode (APD) detector and demodulation circuit, additional laser diodes with additional wavelengths, and a respective graphic user interface to analyze the measurements. To test the instrument and algorithm, phantoms with optical properties similar to those of biological tissue were measured and analyzed. The results show that the absorption coefficient can be determined with an error of <10%. The error of the scattering coefficient was <31%. Since the accuracy of the chromophore concentrations depends on the absorption coefficient and not on the scattering coefficient, the <10% error is the clinically relevant parameter. In addition, the new APD had similar accuracy as the standard photomultiplier tubes. To determine the accuracy of chromophore concentration measurements we employed liquid Intralipid® phantoms that contained 99% water, 1% lipid, and an increasing concentration of hemoglobin in steps of 0.010 mM. Water concentration was measured with an accuracy of 6.5% and hemoglobin concentration with an error of 0.0024 mM independent of the concentration. The measured lipid concentration was negative, which shows that the current setup is not suitable for measuring lipids. Measurements on the forearm confirmed reasonable values for water and hemoglobin concentrations, but again not for lipids. As an example of a future application, chromophore concentrations in the cervix were measured and comparable values to the forearm were found. In conclusion the modified instrument enables measurement of water concentration in addition to oxy- and deoxyhemoglobin concentrations with a single source-detector distance in small tissue samples. Future work will focus on resolving the lipid component

Changes in cerebral oxygenation during early postnatal adaptation in newborns delivered by vacuum extraction measured by near-infrared spectroscopy

Background: Newborns delivered by vacuum extraction quite often show clinical signs of a hemodynamic compromise, which is difficult to assess in terms of severity. The conventional means to measure the hemodynamic status are not sensitive enough to appreciate the severity of general, and more specifically of cerebral circulatory imbalance. The aim was to study cerebral tissue oxygenation during postnatal adaptation in these infants using near-infrared spectroscopy. Methods: The tissue hemoglobin index (THI), tissue oxygenation index (TOI), arterial oxygen saturation (pre-ductal SaO₂) and heart rate (HR) were recorded immediately after birth, and again after 12-24 hours of life in 15 newborns delivered by vacuum extraction due to fetal distress. A comparison with 19 healthy newborns delivered by elective cesarean section was performed. Results: Newborns delivered by vacuum extraction had significantly higher THI 10 to 15 minutes after birth. TOI and HR were significantly higher in the first 5 min and SaO₂ in the first 10 minutes but then did not differ from those after cesarean section. Conclusion: Infants delivered by vacuum extraction following fetal distress show transient deviations in cerebral oxygenation and perfusion after birth which were not detectable after 24 hours

Near-infrared spectroscopy measurements of cerebral oxygenation in newborns during immediate postnatal adaptation

OBJECTIVE: In view of growing concerns regarding the optimal supplementation of oxygen at birth, we measured cerebral oxygenation during the first minutes of life. STUDY DESIGN: Using near-infrared spectroscopy, changes in cerebral oxygenated hemoglobin (O(2)Hb), dexoxygenated hemoglobin (HHb), and tissue oxygenation index (TOI) were measured during the first 15 minutes of life in 20 healthy newborn infants delivered at term by elective cesarean section. RESULTS: O(2)Hb and TOI increased rapidly within the first minutes of life (median slope for O(2)Hb, 3.4 micromol/L/min; range, 1.4 to 20.6 micromol/L/min; median slope for TOI, 4.2 %/min; range, -0.4 to 27.3%/min), and cerebral HHb decreased (median slope, -4.8 micromol/L/min; range, -0.2 to -20.6 micromol/L/min). O(2)Hb, TOI, and HHb all reached a plateau within 8 minutes. CONCLUSIONS: A significant increase in cerebral O(2)Hb and TOI and a significant decrease in HHb occur during immediate adaptation in healthy term newborns, reaching a steady plateau at around 8 minutes after birth

Reproducibility and sensitivity of detecting brain activity by simultaneous electroencephalography and near-infrared spectroscopy

The aims were (1) to determine the sensitivity and reproducibility to detect the hemodynamic responses and optical neuronal signals to brain stimulation by near-infrared spectroscopy (NIRS) and evoked potentials by electroencephalography (EEG) and (2) to test the effect of novel filters on the signal-to-noise ratio. This was achieved by simultaneous NIRS and EEG measurements in 15 healthy adults during visual stimulation. Each subject was measured three times on three different days. The sensitivity of NIRS to detect hemodynamic responses was 55.2 % with novel filtering and 40 % without. The reproducibility in single subjects was low. For the EEG, the sensitivity was 86.4 % and the reproducibility 57.1 %. An optical neuronal signal was not detected, although novel filtering considerably reduced noise