Harri K. Kopola

Assessment of skin erythema by eye, laser Doppler flowmeter, spectroradiometer, two-channel erythema meter and Minolta chroma meter

Visual grading, a laser Doppler flowmeter, a spectroradiometer, a two-channel erythema meter and a Minolta chroma meter were compared in the measurement of erythemas arising from immediate contact reactions produced either by 250 mM benzoic acid or 10 mM methyl nicotinate in petrolatum in an open application test or by ultraviolet irradiation. A good correlation between visual grading and objectively measured values was found for all the instruments, buth the laser Doppler flowmeter gave proportionally lower values for the ultraviolet erythemas than the skin reflectance meters, suggesting that these differ from erythemas induced by benzoic acid or methyl nicotinate. The laser Doppler flowmeter gave less repeatable results than other meters when measuring moderate and pronounced erythemas produced by ultraviolet irradiation. Measuring both the blood flow and the actual erythema may give more information about the reaction than either measurement system alone.

Non-invasive glucose measurement based on selective near infrared absorption; requirements on instrumentation and spectral range

Abstract A tight control of the level of blood glucose is known to reduce the long-term complications of diabetic patients. A non-invasive measurement method suitable for home use would allow a more accurate and frequent control of glucose level, along with reducing the long-term health care costs of diabetic patients and improving their quality of life. In clinical use, the non-invasive method would be suitable for several applications, such as rapid monitoring of glucose levels in emergency rooms [G. Cote, J. Clin. Engrg. 22 (4) (1997) 253–259]. In this work, the potential of near infrared (NIR) spectroscopy as a non-invasive method has been evaluated on the basis of theoretical considerations and measurements on water–glucose solutions and a test person. The partial least squares (PLS) algorithm was used in calibration. The standard deviation of the error of prediction was 0.97 and 1.14 mmol/l for measurements from water–glucose solutions and the test person respectively.

Comparison of distributed fiber optic sensing methods for location and quantity information measurements

A state-of-the-art review of distributed optical fiber sensor technologies has been carried out. The studied methods include polarization-modulation-based, Brillouin-scattering-based, and frequency-modulated continuous-wave (FMCW) methods as well as optical coherence domain reflectometry (OCDR) and interferometric distributed sensing techniques. A classification of the methods with their main properties for measuring quantity information continuously from a long sensor fiber is carried out. The main emphasis is on the comparison of the methods with respect to their spatial resolution, measurement time, and measurement range. The FMCW methods are found to be the most versatile techniques for various applications, due to their short measurement times with measurement ranges extending up to tens of kilometers and location sensing resolution better than 0.1%. The OCDR methods are fast and compete with the FMCW methods in versaility, especially when the measurement range is shorter than 1 to 2 km.

Two-channel fiber optic skin erythema meter

The skin erythema meter is a fiber optic, dual-wavelength reflectance meter that measures the reflectance of the skin on two wavelengths, one the blood/hemoglobin absorption band (555 nm) and another a reference (660 nm). The instrument consists of a fiber optic sensor head, a microprocessor-based control and analysis unit, and a plotter, and it presents the relation between the measured reflectance results in terms of a reflectance index [R(555 nm):R(660 nm)]. The measurement cycle, including printing, takes 5 s. Stability tests on the erythema meter (constant distance, reference object) showed the standard deviation of the reflectance index to be ± 0.1%, whereas that in repeatability tests was less than ± 0.5% for skin and less than ± 0.2% for paper with handheld positioning and repetition. The dynamic change in the reflectance index was about 30% with strong irritation. Results of various irritation test series on human skin are also presented. Finally, the performance and applicability of the skin erythema meter with respect to allergy test procedures, irritancy testing, and measurement of uv-induced erythema are discussed.

Instrument for measuring human biting force

Alongside EMG activity, biting force is the primary parameter used for assessing the biting problems of dentulous patients and patients with dentures. In a highly conductive oral cavity, dielectric measurement methods are preferred, for safety reasons. The maximum biting force for patients with removable dentures is not more than 100 ... 300 N. We report here on an instrument developed for measuring human biting force which consists of three units: a mouthpiece, a signal processing and interface unit (SPI), and a PC. The mouthpiece comprises a sensor head of thickness 3.4 mm, width 20 mm and length 30 mm constructed of two stainless steel plates and with a fiber optic microbending sensor between them. This is connected to the SPI unit by a three-meter fiber optic cable, and the SPI unit to the PC by an RS connection. A computer program has been developed that includes measurement, display, zeroing, and calibration operations. The instrument measures biting force as a function of time and displays the time-dependent force profile and maximum force on a screen or plots it in hard copy. The dynamic measurement range of the mouthpiece is from 0 to 1000 N, and the resolution of the instrument is 10 N. The results of preliminary clinical measurements and repeatability tests are reported.

Fiber optic sensors for traffic monitoring applications

A novel fiber optic sensors for traffic monitoring applications are presented. They are useful for monitoring the traffic entering and leaving guarded areas, counting traffic on public roads as well as in determining lane occupancy at traffic lights. When installing sensor arrays, the sensors may also be used to provide additional information: measure the speed, wheel base of a vehicle and also to determine the number of axles and vehicle type. The sensors are based on optical fiber or cable, installed inside the asphalt layer of the road, to measure compression or vibrations near the road surface. Two sensor principles were used. One based on the microbending effect and another that utilizes the speckle phenomenon. In both cases the whole length of the fiber acts as a sensor. The microbending sensor requires a special fiber and special set-up, whereas in the speckle sensor a standard cable may be used. Both sensor types were tested in field applications where the harsh environment, especially the heat, sets great demands on installation. In these experiments, speed and vehicle type measurements were carried out with good results. In the paper, we will discuss the advantages and disadvantages of both sensor types and present some field test results. We will also show the benefits of these particular fiber optic sensors over traditional sensors.

Indicating cure and stress in composite containers using optical fibers

Long optical fibers embedded inside a composite material enable on-line monitoring of the manufacturing process and can also be used to assess damage by monitoring strain and cracks in the structure. We report on measurements of the microbending loss in long single-mode and multimode telecommunication fibers that were successfully installed inside the walls of composite containers during the normal manufacturing process. The work was largely empirical, and theoretical aspects were not investigated thoroughly. The measurements were carried out using the optical through power technique and a commercial optical time-domain reflectometer that gives not only the attenuation but also spatial information. We found that the coating material and its thickness have an effect on loading sensitivity and on the applicability of the method for cure monitoring. Although we discovered that repeatability issues are a problem, the measurement data indicate that the end-of-curing process of the composite can be determined by optical sensing fibers and damaging external loading of the structure can be detected.

Information of circulation from soft tissue and dental pulp by means of pulsatile reflected light: Further development of optical pulp vitalometry

OBJECTIVES To show experimentally and clinically that information of blood circulation patterns can be obtained through dentin and enamel by means of reflected light. STUDY DESIGN Several different experimental techniques were developed in vitro leading up to in vivo tests. RESULTS Pulsatile information of back-scattered light at 560 nm was obtained in an experiment in which a thread with white and red sections was pulled through the empty pulp cavum. The pulsatile information of back-scattered light of 560 nm wavelength was detected from a forefinger of a volunteer through dental hard tissue plates. There was a difference in the radiant flux of back-scattered light in extracted teeth filled with various materials. Photoplethysmograms obtained from the vital pulp of a 24-year-old woman were analyzed with Fast Fourier Transformation (FFT). The analyzed data showed a dominant amplitude of heart rate near 1 Hz. CONCLUSIONS Tests indicated that reliable information of circulation can be obtained from the dental pulp chamber by means of the optical reflection method. This could serve as a model for a new type of pulp vitalometer.

Main characteristics of a miniaturized multipurpose infrared spectrometer

This paper describes the main characteristics of a miniaturized multipurpose IR spectrometer. The miniaturized spectrometer comprise of three silicon micromachined devices: an electrically modulated thermal IR emitter, and electrically tunable Fabry-Perot interferometer and a photodetector. The IR emitter and the detector are monolithically integrated into a silicon substrate. In addition, the silicon substrate carries an integrated circuit die-bonded and wire-bonded on the silicon substrate. The whole spectrometer assembly is packaged in a DIL package having holes for the incoming and outgoing radiation. The dimensions of the package are 12 mm X 23 mm X 5 mm. This concept enables the realization of a miniaturized spectrometer for high-volume and low-cost products. In the miniaturization, the critical optical characteristic is the throughput of a system. In addition, the S/N-ratio and crosstalk of the module are the main electrical characteristics to be considered in the miniaturization. In this paper, the performance of the spectrometer module is presented via measurements including the radiometric analysis, S/N-ratio analysis and crosstalk analysis.

Novel fiber optic dental pulp vitalometer

Since the diagnosis of the intradental blood supply is difficult in dental trauma, we have designed and built a new dental pulp vitalometer based on optical reflectance measurement and exploiting the different absorption spectra of haemoglobins. The device comprises light transmitters, a receiver, electronics and a PC. Pulsed light is transmitted along the fiber optic probe, which illuminates the tooth being tested. The same probe collects the reflected light from the tooth pulp and transfers the light to the receiver. The received signal is divided into AC and DC components and a data acquisition card reads these signals, performs an A/D conversion and writes the results in a text file. A reference plethysmogram signal from a finger is used to help in processing the measured dental signal. The computer program calculates an estimate for the oxygen saturation.