Diode laser spectroscopy for noninvasive monitoring of oxygen in the lungs of newborn infants.

BACKGROUND: Newborn infants may have pulmonary disorders with abnormal gas distribution, e.g., respiratory distress syndrome. Pulmonary radiography is the clinical routine for diagnosis. Our aim was to investigate a novel noninvasive optical technique for rapid nonradiographic bedside detection of oxygen gas in the lungs of full-term newborn infants. METHODS: Laser spectroscopy was used to measure contents of oxygen gas (at 760 nm) and of water vapor (at 937 nm) in the lungs of 29 healthy newborn full-term infants (birth weight 2,900-3,900 g). The skin above the lungs was illuminated using two low-power diode lasers and diffusely emerging light was detected with a photodiode. RESULTS: Of the total 390 lung measurements performed, clear detection of oxygen gas was recorded in 60%, defined by a signal-to-noise ratio of >3. In all the 29 infants, oxygen was detected. Probe and detector positions for optimal pulmonary gas detection were determined. There were no differences in signal quality with respect to gender, body side or body weight. CONCLUSION: The ability to measure pulmonary oxygen content in healthy full-term neonates with this technique suggests that with further development, the method might be implemented in clinical practice for lung monitoring in neonatal intensive care.

Development of a compact multipass oxygen sensor used for gas diffusion studies in opaque media.

A highly scattering porous ceramic sample is employed as a miniature random-scattering multipass gas cell for monitoring of oxygen content in opaque media, that is, wood materials in the present work. Gas in scattering media absorption spectroscopy is used by employing a 760 nm near-infrared laser diode to probe the absorption of molecular oxygen enclosed in the pores of the ceramic material working as the multipass gas cell, with a porosity of 75%. A path length enhancement of approximately 26 times and a signal-to-noise ratio of about 60 were obtained for the ceramic sample used in this work. The gas sensor was then used in a case study of the gas diffusion in wood materials, namely, oak, spruce, and mahogany samples. Differences depending on whether gas diffusion was studied longitudinal or radial to the tree annual rings are demonstrated, with very little gas diffusing in the radial direction. We can also observe that the gas diffusion for the densest material-oak-had the fastest diffusion time, and mahogany, which had the lowest density, showed the slowest diffusion time.

Tea classification and quality assessment using laser-induced fluorescence and chemometric evaluation.

Laser-induced fluorescence was used to evaluate the classification and quality of Chinese oolong teas and jasmine teas. The fluorescence of four different types of Chinese oolong teas-Guangdong oolong, North Fujian oolong, South Fujian oolong, and Taiwan oolong was recorded and singular value decomposition was used to describe the autofluoresence of the tea samples. Linear discriminant analysis was used to train a predictive chemometric model and a leave-one-out methodology was used to classify the types and evaluate the quality of the tea samples. The predicted classification of the oolong teas and the grade of the jasmine teas were estimated using this method. The agreement between the grades evaluated by the tea experts and by the chemometric model shows the potential of this technique to be used for practical assessment of tea grades.

Gas spectroscopy and optical path-length assessment in scattering media using a frequency-modulated continuous-wave diode laser.

Simultaneous assessment of the spectroscopic absorption signal of gas enclosed in a scattering medium and the corresponding optical path length of the probing light is demonstrated using a single setup. Sensitive gas absorption measurements are performed by a tunable diode laser using wavelength-modulation spectroscopy, while the path length is evaluated by the frequency-modulated cw technique commonly used in the field of telecommunication. Proof-of-principle measurements are demonstrated with water vapor as the absorbing gas and using polystyrene foam as an inhomogeneously scattering medium. The combination of these techniques opens up new possibilities for straightforward evaluation of gas presence and exchange in scattering media.

Active feedback regulation of a Michelson interferometer to achieve zero-background absorption measurements.

An active phase-controlling scheme based on a proportional-integral-derivative-controlled piezoelectric transducer is presented with the purpose of stabilizing a quasi-zero-background absorption spectrometer. A fiber-based balanced Michelson interferometer is used, and absorption due to a gas sample in one of its arms results in an increased light signal to a detector, which otherwise, thanks to destructive interference, experiences a very low light level. With the presented approach, the sensitivity of already potent absorption measurement techniques, e.g., based on modulation, could be improved even further.

Remote nocturnal bird classification by spectroscopy in extended wavelength ranges.

We present optical methods at a wide range of wavelengths for remote classification of birds. The proposed methods include eye-safe fluorescence and depolarization lidar techniques, passive scattering spectroscopy, and infrared (IR) spectroscopy. In this paper we refine our previously presented method of remotely classifying birds with the help of laser-induced ß-keratin fluorescence. Phenomena of excitation quenching are studied in the laboratory and are theoretically discussed in detail. It is shown how the ordered microstructures in bird feathers induce structural "colors" in the IR region with wavelengths of around 3-6 µm. We show that transmittance in this region depends on the angle of incidence of the transmitted light in a species-specific way and that the transmittance exhibits a close correlation to the spatial periodicity in the arrangement of the feather barbules. We present a method by which the microstructure of feathers can be monitored in a remote fashion by utilization of thermal radiation and the wing beating of the bird.

Optical porosimetry by gas in scattering media absorption spectroscopy (GASMAS) applied to roller compaction ribbons.

Currently, there is a need for new technology for in-line or fast at-line assessment of solid material porosity. One specific gap is a fast technology to be used in connection to roller compaction (RC) manufacturing, where the porosity of the RC ribbons is critical to the manufacturing of tablets of the right tensile strength and disintegration properties. In this paper, the development of an at-line technology for fast, non-destructive assessment of porosity of RC ribbons is reported. The technology is based on a diode laser spectroscopic technique called Gas in scattering media absorption spectroscopy (GASMAS). GASMAS measures the sample voids by laser light, giving the distance through air. The total distance the light travels is measured using time-of-flight spectroscopy (TOFS). The ratio of these measures gives an "optical porosity", which through theory relates to the porosity of the sample. We present a description of the technology, evaluations of measurement robustness and results from an experimental design where roller compactor, roll force, roll gap and formulation were varied. It is concluded that the data from two different pharmaceutical formulations is supported by the same calibration curve, which indicates that optical porosimetry is a general technique for pharmaceutical materials that does not require frequent calibrations.

Feasibility study: fluorescence lidar for remote bird classification.

We present a method for remote classification of birds based on eye-safe fluorescence lidar techniques. Mechanisms of quenching are discussed. Plumage reflectance is related to plumage fluorescence. Laboratory measurements on reflectance and fluorescence are presented, as well as test-range measurements. Also we present examples of birds' in-flight lidar returns. The methods are suitable for studies of night migrating species and high-altitude classification with implications for the detailed understanding of bird migration and global virus spread.

Insect monitoring with fluorescence lidar techniques: field experiments.

Results from field experiments using a fluorescence lidar system to monitor movements of insects are reported. Measurements over a river surface were made at distances between 100 and 300 m, detecting, in particular, damselflies entering the 355 nm pulsed laser beam. The lidar system recorded the depolarized elastic backscattering and two broad bands of laser-induced fluorescence, with the separation wavelength at 500 nm. Captured species, dusted with characteristic fluorescent dye powders, could be followed spatially and temporally after release. Implications for ecological research are discussed.

Assessment of photon migration in scattering media using heterodyning techniques with a frequency modulated diode laser.

A novel technique for studying photon propagation in scattering media is proposed and demonstrated, as is believed, for the first time. Photons propagating through the medium, from a frequency-ramped single-mode diode laser, meet a reference beam from the same source, at a common detector, and beat frequencies corresponding to various temporal delays are observed by heterodyne techniques. Fourier transformation directly yields the temporal dispersion curve. Proof-of-principle experiments on polystyrene foam and a tissue phantom suggest, that the new method, when fully developed, may favorably compete with the more complex time-correlated single-photon counting (TCSPC) and the phase-shift methods, now much employed.

Computer simulation analysis of source-detector position for percutaneously measured O2 -gas signal in a three-dimensional preterm infant lung.

Further improvements in the clinical care of our most vulnerable patients-preterm infants-are needed. Novel diagnostic and surveillance tools facilitate such advances. The GASMAS technique has shown potential to become a tool to, noninvasively, monitor gas in the lungs of preterm infants, by placing a laser source and a detector on the chest wall skin. It is believed that this technology will become a valuable clinical diagnostic tool for monitoring the lung function of these patients. Today, the technology is, for this application, in an early stage and further investigations are needed. In the present study, a three-dimensional computer model of the thorax of an infant is constructed, from a set of CT images. Light transport simulations are performed to provide information about the position dependence of the laser- and detector probe on the thorax of the infant. The result of the simulations, based on the study method and the specified model used in this work, indicates that measurement geometries in front and on the side of the lung are favorable in order to obtain a good gas absorption signal.

Development of a 3-dimensional tissue lung phantom of a preterm infant for optical measurements of oxygen-Laser-detector position considerations.

There is a need to further improve the clinical care of our most vulnerable patients-preterm infants. Novel diagnostic and treatment tools facilitate such advances. Here, we evaluate a potential percutaneous optical monitoring tool to assess the oxygen and water vapor content in the lungs of preterm babies. The aim is to prepare for further clinical studies by gaining a detailed understanding of how the measured light intensity and gas absorption signal behave for different possible geometries of light delivery and receiver. Such an experimental evaluation is conducted for the first time utilizing a specially developed 3-dimensional-printed optical phantom based on a geometry model obtained from computer tomography images of the thorax (chest) of a 1700-g premature infant. The measurements yield reliable signals for source-detector distances up to about 50 mm, with stronger gas absorption signals at long separations and positions related to the lower part of the lung, consistent with a larger relative volume of this. The limitations of this study include the omission of scattering tissue within the lungs and that similar optical properties are used for the wavelengths employed for the 2 gases, yielding no indication on the optimal wavelength pair to use.

Sensitivity enhancement and fringe reduction in tunable diode laser spectroscopy using hemispherical diffusers.

The use of diffuse, highly reflective optical components, in particular, a hemispherical BaSO4 diffuser, at the point of light injection into non-transparent or turbid media was evaluated as a means to increase the measurement sensitivity of spectroscopic absorption measurements. By performing the light injection from, e.g., an optical fiber through a component designed to make the light diffuse and to reflect (and thereby re-inject) light scattered from the sample, the total amount of light delivered into the sample is increased. Further, the occurrence of possible interference fringes is strongly reduced.

Noninvasive monitoring of gas in the lungs and intestines of newborn infants using diode lasers: feasibility study.

Preterm newborn infants have a high morbidity rate. The most frequently affected organs where free gas is involved are the lungs and intestines. In respiratory distress syndrome, both hyperexpanded and atelectatic (collapsed) areas occur, and in necrotizing enterocolitis, intramural gas may appear in the intestine. Today, these conditions are diagnosed with x-ray radiography. A bed-side, rapid, nonintrusive, and gas-specific technique for in vivo gas sensing would improve diagnosis. We report the use of noninvasive laser spectroscopy, for the first time, to assess gas content in the lungs and intestines of three full-term infants. Water vapor and oxygen were studied with two low-power diode lasers, illuminating the skin and detecting light a few centimeters away. Water vapor was easily detected in the intestines and was also observed in the lungs. The relatively thick chest walls of the infants prevented detection of the weaker oxygen signal in this study. However, results from a previous phantom study, together with scaling of the results presented here to the typical chest-wall thickness of preterm infants, suggest that oxygen also should be detectable in their lungs.