The aim of this study was to discover a simple/convenient geometrical arrangement of radiation sources and detector to acquire finger-photoplethysmograms (PPGs) with wavelength regions of blood glucose (BGL) absorption, toward practical noninvasive BGL measurement. First, we compared PPGs with three wavelengths: 808 nm (without water absorption), 1160 nm (with weak water absorption), and 1600 nm (with nearly peak BGL absorption and strong water absorption), while the source-detector spacing was successively increased circumferentially around a fingertip. In 10 healthy subjects, we observed clear cardiac-related pulsatile components of PPG signals at 808 and 1160 nm in any incident positions with more than 15 dB of signal-to-noise ratio (S/N), but reliable PPG detections at 1600 nm with more than 10 dB of S/N was only possible when the source-detector distance was less than 3 mm around the fingertip circumference. Second, with this arrangement, an experiment was performed using six wavelengths to cover glucose absorption bands (from 1550 to 1749 nm), obtaining pulsatile PPG signals with more or less 15 dB of S/N. Through the present experiments, this orthogonal arrangement of the source and detector to detect forward- and side-scattered radiation through the tissue is appropriate for PPG measurements with wavelength regions where there is potential for BGL measurement.
Brain activity can be monitored non-invasively by functional near-infrared spectroscopy (fNIRS), which has several advantages in comparison with other methods, such as flexibility, portability, low cost and fewer physical restrictions. However, in practice fNIRS measurements are often contaminated by physiological interference arising from cardiac contraction, breathing and blood pressure fluctuations, thereby severely limiting the utility of the method. Hence, further improvement is necessary to reduce or eliminate such interference in order that the evoked brain activity information can be extracted reliably from fNIRS data. In the present paper, the multi-distance fNIRS probe configuration has been adopted. The short-distance fNIRS measurement is treated as the virtual channel and the long-distance fNIRS measurement is treated as the measurement channel. Independent component analysis (ICA) is employed for the fNIRS recordings to separate the brain signals and the interference. Least-absolute deviation (LAD) estimator is employed to recover the brain activity signals. We also utilized Monte Carlo simulations based on a five-layer model of the adult human head to evaluate our methodology. The results demonstrate that the ICA algorithm has the potential to separate physiological interference in fNIRS data and the LAD estimator could be a useful criterion to recover the brain activity signals.
This paper concerns the study and use of biological cells in which there is a need for sensors and assemblies for the
measurement of a diverse range of physical and chemical variables. In this field cell culture is used for basic research
and for applications such as protein and drug synthesis, and in cell, tissue and organ engineering. Metabolic processes
are fundamental to cell behaviour and must therefore be monitored reliably. Basic metabolic studies measure the
transport of oxygen, glucose, carbon dioxide, lactic acid to, from, or within cells, whilst more advanced research requires
examination of energy storage and utilisation. Assemblies are designed to incorporate bioreactor functions for cell
culture together with appropriate sensing devices. Oxygen consumption by populations of cells is achieved in a flowthrough
assembly that incorporates O2 micro-sensors based on either amperometry or fluorescence. Measurements in
single cell are possible with intra-cellular fluorophores acting as biosensors together with optical stimulation and
detection. Near infra-red spectroscopy (NIRS) is used for analysis within culture fluid, for example for estimation of
glucose levels, as well as within cell populations, for example to study the respiratory enzymes.£
A diverse range of sensors and instruments is available for use in the critical care of acutely ill patients and it is not
always straightforward to decide which technologies should be used. Clinicians have their own priorities for the
physiological variables that they consider need to be monitored in order to provide optimum medical care. Alongside this,
consideration must be given to the choice of available technologies. This choice may be influenced by performance
criteria, cost, and ease of use. It is also necessary to consider the physical status of the patients, the measurement
instruments and any potential risks for the patients so as to provide the best measurement scheme. This paper explores
the use of decision support tools that may be used in critical care situations. The care of ill newborn babies requiring
mechanical ventilation is considered as a case study. The choice of invasive and non-invasive techniques for blood gas
and pH assessment is evaluated and decision trees and hierarchical clustering are considered as possible decision support
methodologies.
Optical methods continue to play significant roles in medical and biological research. In recent times cell and tissue engineering have emerged rapidly and are now well recognised as important multi-disciplinary endeavours within the medical and biological spheres. This paper describes applications of optical science and technology in cell and tissue engineering, ranging from the basic visualization of organeeles, cells and tissues through to probing the structure and function of cells and tissues being cultured in bioreactors. The development of tissue engineering for the fabrication of cell-based systems, for example for the repair or replacement of damaged or diseased tissues and organs, is first described. Then, interactions of light propagating through cells and tissues are considered, both theoretically and practically, as a prelude to the description of means for optical interrogation. Scattering and absorption of light by cells and tissues is shown to provide useful opportunities for measurement, for example via spectrophotometric analysis or small angle light scattering. Optical sensors for chemical analysis based on immobilised fluorophores and chromophores are also presented, these being particularly useful in bioreactors. In this application the continuous monitoring of a variety of chemical and physical variables may lead to optimised cell and tissue culture.
Cell culture using bioreactors is a vital part of Cellular and Tissue Engineering. Bioreactor design continues to advance, in order to allow control over physical and chemical parameters as well as continuous assessment of cell behaviour, gene expression, and tissue formation and growth. Measurement or monitoring of many such parameters or features can be achieved with optical techniques. The current aim of cell culture is to re-create in vivo conditions and in order to achieve this control of the chemical environment is required and some cell types must be subjected to shear stress and/or axial loads. For creating tissue engineered cartilage chondrocytes are cultured within a biodegradable scaffold. Influences of cyclic loading and of oxygen supply on phenotype are studied. Vascular endothelial cells are subjected to fluid shear stress and the influence on prostacyclin production is measured. Optical interrogation of culture fluid, attached cells, cells in suspension and tissue constructs is carried out using a combination of spectrophotometry, analysis of scattering, and chemical sensing. Insertion of sensing probes within the culture vessel presents problems of protein adsorption to sensing surfaces. Approaches based on cell membrane mimicry are being evaluated for their potential to overcome this problem. Sensors based on immobilised fluorophores and chromaphores within either wall-mounted membranes or within optical fibres are assessed. Culture fluid turbidity is evaluated with scattering determinations and circulating glucose concentration is measured spectrophotometrically. Formed tissue is interrogated with NIR radiation and in the future will include the use of OCT.
A novel algorithm is demonstrated to determine the reduced scattering and absorption coefficients from time-resolved reflectance measurements at two positions on the surface of biotissue. The algorithm is very straightforward and fast, in which only some simple mathematical operations are involved, avoiding complicated iterative non-linear fitting to the time- resolved curve. The derived reduced scattering coefficient is not affected by whatever boundary condition is applied. The algorithm was verified using the time-resolved data from the Monte-Carlo model. Both the semi-infinite medium and the turbid slab medium were tested. In contrast to the non-linear fitting method, it is found using this algorithm that both the scattering and absorption coefficients can be determined to a high accuracy.
Human newborns can suffer from neuro-developmental abnormalities, when they are born as preterms. With near infrared spectroscopy (NIRS) it is possible to investigate any brain disease occurring together with these neuro- abnormalities. The specific absorption properties of haemoglobin and oxygenated haemoglobin in the near infrared region allow to measure the oxygenation status and several other variables. Local variations in cerebral blood volume (CBV) and blood oxygenation is important for a better understanding of these abnormalities.
Near infrared spectroscopy (NIRS) is a relatively new method which is suitable for monitoring oxygenation in blood and tissue in the brain of the fetus and the neonate. The technique involves in-vivo determination of the absorption of light in the wavelength range 775 to 900 nm through such tissue and converting such changes in absorbance to provide information about the changes in the concentration of oxygenated and de-oxygenated haemoglobin (HbO2 and Hb). Recent developments of the methodology now enable the calculation of changes in cerebral blood volume (CBV) as well as absolute CBV and cerebral blood flow (CBF). The attraction of this method is its applicability to monitor cerebral function in a wide variety of patient groups. Although primarily developed for neonatal use it is today applied on the fetus to investigate fetal hypoxia and on adults undergoing surgery.
A miniature optical sensor based on the fluorescent indicator, 8-hydroxyl-1,3,6-pyrene trisulfonic Acid Trisodium Salt (HOPSA), was developed for physiological pH measurement. Dowex-1 strongly basic anion exchange resin was used as a medium to immobilize the indicator on the end of an optical fiber to form a pH sensing layer. Polyetherurethane was dip- coated onto the sensing layer as the permeable membrane for H+. The properties of the sensor were assessed and found to be suitable for monitoring physiological pH values.
KEYWORDS: Tissues, Sensors, Reconstruction algorithms, Photon transport, Monte Carlo methods, Scattering, Photodetectors, Detection and tracking algorithms, Near infrared, Algorithm development
Monte Carlo simulation technique is used to study photon migration in biological tissues. On a 36 mm diameter cylinder, temporal point spread function is simulated for each of the seven detectors around the model. Information such as mean-time-of-flight, differential pathlength factor, and detected photon number are recorded. Two back-projection algorithms have been proposed to reconstruct tomographic images of phantom.
KEYWORDS: Spatial resolution, Scattering, Tissue optics, Near infrared, Light scattering, Photons, Signal detection, Absorption, Time metrology, Modulation transfer functions
A preliminary study into the spatial resolution that may be achieved for time resolved near infrared imaging through highly scattering media has been performed. The spatial resolution, for time gated images, has been investigated quantitatively by measuring the edge-spread function for scattering media of different properties and at different depths. Transmission scans of two absorbing rods, spaced by different distances, were used to qualitatively study the contrast obtained at different integration periods or using the measured mean time-of-flight. Both spatial resolution and contrast are improved as the time gating interval is reduced. However, for thick tissue sections it may not be possible to reduce the spatial resolution below about 10 mm, because of the small amount of light arriving at these early times.
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