Non-invasive Measurement Method Research Articles

In situ measurement of liquid-liquid equilibria by medium field nuclear magnetic resonance

A new method for non-invasive measurement of liquid-liquid equilibria (LLE) using a compact medium field nuclear magnetic resonance (NMR) spectrometer is presented. Mixing of all components, phase separation, and analysis of the composition of the coexisting phases is performed in situ in an NMR glass tube. Thus, the experimental effort is reduced and errors caused by sampling are eliminated. Furthermore, calibration of the analysis method is not necessary as quantitative information is obtained directly from the NMR spectra. The proposed method for studying LLE in situ can be swiftly conducted in standard chemical laboratories as medium field NMR spectrometer do not require dedicated laboratory infrastructure but enable convenient handling and fast analysis of the samples. In the present work, four non-reactive ternary solvent systems with closed miscibility gap (toluene + acetone + water, diethyl ether + acetone + water, diethyl ether + methanol + water, and acetonitrile + ethanol + cyclohexane) and one reactive ternary system (water + acetic acid + acetic anhydride) were investigated at a temperature of 22.0 °C using 1H medium field NMR spectroscopic measurements. For comparison, the composition of the coexisting phases is also examined for one non-reactive system (acetonitrile + ethanol + cyclohexane) using 13C medium field NMR spectroscopy as well as spatially resolved spectroscopy in a conventional high field NMR spectrometer. The comparison of the results of the present work to literature data shows that the new proposed method enables swift and reliable investigations of LLE.

Inter-method agreement in retinal blood vessels diameter analysis between Dynamic Vessel Analyzer and optical coherence tomography

To analyze the inter-methods agreement in arteriovenous ratio (AVR) evaluation between spectral-domain optical coherence tomography (SD-OCT) and Dynamic Vessel Analyzer (DVA). Healthy volunteers underwent DVA and SD-OCT examination. AVR was measured by SD-OCT using the four external lines of the optic nerve head-centered 7-line cube and by DVA using an automated AVR estimation. The mean AVR was calculated, twice, separately by two independent readers for each tool. Twenty-two eyes of 11 healthy subjects (five women and six men, mean age 35) were included. AVR analysis by DVA showed high inter-observer agreement between reader 1 and 2, and high intra-observer agreement for both reader 1 and reader 2. With regard to AVR analysis on SD-OCT, we found high inter-observer agreement between reader 1 and 2, and low intra-observer agreement for reader 2 but high intra-observer agreement for reader 1. Overall, the mean AVR measured on SD-OCT turned out to be significantly higher than mean AVR measured through DVA (reader 1, 0.9023 ± 0.06 vs 0.8036 ± 0.08; p < 0.001, and reader 2, 0.9067 ± 0.06 vs 0.8083 ± 0.05; p= 0.003). No inter-method agreement in AVR could be detected in the present study due to bias in measurements (shift between DVA and SD-OCT). We found significant difference in the two noninvasive methods for AVR measurement, with a tendency for SD-OCT to overestimate retinal vascular caliber in comparison to DVA. This may be useful for achieving greater accuracy in the evaluation of retinal vessel in ocular as well as systemic diseases.

NOVEL APPROACHES TO NON-INVASIVE BLOOD GLUCOSE MEASUREMENT

Aim. Development of a novel method for non-invasive blood glucose measurement based on the hemodynamics parameters, and implementation of non-invasive glucometer. Material and methods. Totally, 170 persons studied, of the age 20-75 y.o.: with arterial hypertension (n=70), diabetes type 2 (n=70), healthy (n=30). Blood pressure (BP) was measured on both arms of patient, fasting and after a meal. The mean values of systolic BP, diastolic BP, pulse BP were calculated, and BP coefficient as their relation. At the same time chemistry was done for glucose levels. Results. The case was being resolved by the method of mathematical modelling using Statistica software. Correlational and functional multifactorial tests were done, in all groups. The highest correlational coefficients in all dimensions represent the relations of glucose level with BP response (0,75-0,85), which was selected for regression equations for BP and glucose relation. Optimal regression equations were used for the device measuring glycemia non-invasively. Conclusion. A novel method for non-invasive glycemia diagnostics is developed, based on the modelling of correlation of systemic hemodynamics and blood glucose concentration. The relations obtained, are used for invention of automatic non-invasive glucometer by the pulse wave parameters. Novelty has been proved by RF patents: “Method for non-invasive glucose concentration measurement in blood”; “Equipment for non-invasive assessment of blood glucose concentration”. Non-invasive glucometer can be used in healthcare institutions and for individual use.

Relation between foot pain and plantar pressure in pregnancy

Background/aim: Hormonal and structural changes that occur during pregnancy cause alterations in body biomechanics. These alterations reach their peak in the last trimester. Adaptive changes that appear in the foot result in pain in the foot and ankle. Pedobarography is a noninvasive measurement method that can be used to understand the origin of such pain. Materials and methods: One hundred and thirty-one pregnant women who did not have a foot or ankle problem prior to pregnancy volunteered to take part in the study. Pain was quantified by a visual analog scale (VAS). A cut-off value of 2.95 was taken to divide the subjects into two groups: Group 1 (n = 70) with VAS scores of <2.95 and Group 2 (n = 61) with VAS scores of ?2.95. Plantar pressure measurements were taken by Tekscan HR Mat using midgait protocol. Results: Forces experienced by the total right foot area, right forefoot, and the midfoot for both feet were significantly higher in Group 2 (P < 0.05). Contact area was significantly larger in Group 2 (P < 0.05). Conclusion: Results indicate that presence and severity of foot pain during pregnancy are related to the force distribution along the foot, especially at midfoot and the contact area.

Noninvasive photoacoustic measurement of glucose by data fusion.

We proposed a novel noninvasive method for glucose detection using a photoacoustic (PA) technique utilizing both the peak-to-peak value and peak arrival time delay information. Without increasing apparatus and system complexity, we demonstrated the accuracy enhancement of 29.5% and 33.63% for high (0-7 g dL-1) and low (0-350 mg dL-1) concentration of glucose solution, compared to conventional amplitude-based prediction.

Measurements of glucose concentration in aqueous solutions using reflected THz radiation for applications to a novel sub-THz radiation non-invasive blood sugar measurement method.

The terahertz (THz) frequency range corresponds to molecular vibrations or relaxation modes such as those for the hydrogen bond. Most biomolecules are activated only in aqueous solutions, thus, to understand the function and structure of biomolecules, it is necessary to investigate the characteristics of electromagnetic waves in hydrated samples. THz radiation causes little damage to the human body, thus it is expected that it can be applied for noninvasive examinations. However, spectrometry of the transmitted light is difficult, since the absorption of THz radiation in water is extremely high. In this study, we used sub-THz radiation (frequencies near to 0.1 THz), where the absorption is lower than for THz radiation, to measure the reflectance of a glucose water solution. We found that the reflectance decreases in proportion with the glucose concentration. These results suggest that sub-THz radiation can be used in the noninvasive measurement of blood glucose levels.

A Noninvasive Measurement of Blood Glucose Concentration by UWB Microwave Spectrum

A noninvasive blood glucose measurement method based on ultrawideband (UWB) microwave detecting technique is proposed for monitoring the patients' blood glucose level. With this method, a noninvasive measurement for the blood glucose determination can be realized by analyzing the received UWB microwave signals. This method is very convenient and is harmless to the patients. The time-frequency features are used to analyze the received signals. The correctness of the method is testified by successfully obtaining the regularity of the energy of the received signals with the range of blood glucose concentration 0-4000 mg/dl in the dispersion case of the configuration. The reliability of the method is also confirmed by obtaining the regularity of the energy of experimental signals at 6.5 GHz for the realistic earlobe phantom with the step of 50 mg/dl in the range of human blood glucose concentration 0-400 mg/dl. The results verify the sensitivity and efficiency of this method.

Non-invasive method of blood hemoglobin measurement based on time-resolved transmission spectroscopy

Objective To theoretically study the non-invasive measurement method of blood hemoglobin in vivo based on the time-resolved approach combined with occlusion spectroscopy. Methods The dynamic dual wavelength time-resolved transmission was analyzed based on the artificial blood flow kinetics condition on a human finger model. The sensitivity of hemoglobin measurement was improved by Laplace transforming of time-domain data. The method was validated using hemoglobin with a mass concentration range of 6~16 g/dl. Results The simulation results showed that compared with the continuous wave method, the time-resolved method could provide higher detection sensitivity using Laplace transform parameter p=5×1010 s-1. Conclusions The sensitivity of hemoglobin measurement can be enhanced when early arriving photons are emphasized by Laplace transformingthe time-resolved transmission with a small positive parameter. Key words: Time-resolved transmission spectroscopy; Blood hemoglobin; Non-invasive measurement

Photoplethysmography for an independent measure of pulsatile pressure under controlled flow conditions

Noninvasive continuous blood pressure measurements are desirable for patients and clinicians. This work proposes and validates a method for transmural pressure measurement using photoplethysmography (PPG) in an in vitro setup that allows control of pressure and flow conditions. The optimum pulsatile volume measure is obtained by comparing parameters extracted from the photoplethysmographic signal (AC amplitude, normalized pulse volume (NPV) and adjusted pulse volume (APV)). Pulsatile volume can then provide pressure measurements using the exponential pressure–volume (P–V) relationship and validated using the gold standard catheter pressure measurement. Pressure, red (R) and infrared (IR) PPG signals were recorded continuously in two arterial models with different cross-sectional areas (Model 1 and Model 2) utilising a pulsatile pump. Flow rates were controlled by varying pumping frequencies at low and high stroke volumes. The optimum method for estimation of the pulsatile volume is through APV, which had a highly significant correlation (r2 = 0.99, p < 0.001) for Model 1 and (r2 = 0.98, p < 0.001) for Model 2. APV obtained a significantly better fit when compared to NPVIR (r2 = 0.73, z = 25.85, p < 0.001), NPVR (r2 = 0.95, z = 12.26, p < 0.001), IRAC (r2 = 0.52, z = 28.29, p < 0.0001) and RAC (r2 = 0.92, z = 15.27, p < 0.0001) in Model 1, and when compared to NPVIR (r2 = 0.92, z = 10.23, p < 0.0001), NPVR (r2 = 0.96, z = 5.08, p < 0.001) IRAC (r2 = 0.63, z = 22.47, p < 0.0001) and RAC (r2 = 0.92, z = 17.70, p < 0.0001) in Model 2. These preliminary findings suggest that APV could be used as a potential non-invasive continuous method of blood pressure measurement at different flow conditions.

Distant Measurement of Plethysmographic Signal in Various Lighting Conditions Using Configurable Frame-Rate Camera

Abstract Videoplethysmography is currently recognized as a promising noninvasive heart rate measurement method advantageous for ubiquitous monitoring of humans in natural living conditions. Although the method is considered for application in several areas including telemedicine, sports and assisted living, its dependence on lighting conditions and camera performance is still not investigated enough. In this paper we report on research of various image acquisition aspects including the lighting spectrum, frame rate and compression. In the experimental part, we recorded five video sequences in various lighting conditions (fluorescent artificial light, dim daylight, infrared light, incandescent light bulb) using a programmable frame rate camera and a pulse oximeter as the reference. For a video sequence-based heart rate measurement we implemented a pulse detection algorithm based on the power spectral density, estimated using Welch’s technique. The results showed that lighting conditions and selected video camera settings including compression and the sampling frequency influence the heart rate detection accuracy. The average heart rate error also varies from 0.35 beats per minute (bpm) for fluorescent light to 6.6 bpm for dim daylight.

A novel unconstrained cardiorespiratory monitoring system during sleep

ABSTRACTAs one of the basic means of assessing human health conditions, cardiorespiratory monitoring during sleep has been widely used in diagnosis of sleep disorders. In this paper, a novel method for unconstrained and non-invasive measurement of respiration and heartbeat is proposed. The method is based on the intelligent combination of two sensor systems for respiratory and pulse monitoring. In order to wear comfortable, polyvinylidene fluoride (PVDF) film was taken as the sensor material. For improving the sensor sensitivity, a “double-sided arch” spring and a “thin-shell” spring were designed as the substrate of respiratory sensor and pulse sensor, respectively. To obtain clear cardiorespiratory responses from the sensor probe, hardware filter circuit is applied for further data filtering. Relative cardiorespiratory signal parameters such as respiratory cycle (RC) and heart rate (HR) could be displayed by LabVIEW. The fabrication steps and some experiments results for human monitoring system are described. The results show that respiration and pulse signal can be obtained accurately and the method lays the foundation for medical diagnosis.

Age-related changes in dermal fiber-like structures in facial cheeks.

Despite recent progress in non-invasive measurement methods, such as in vivo laser confocal microscopy (CLSM), it is difficult to quantitatively measure age-related changes in dermal fibrous structures in the face using these methods and qualitative characteristics. We used characteristics extracted from the analysis of CLSM images to quantitatively investigate the effects of aging on dermal fibrous structures in the face. CLSM images of dermal fibrous structures were obtained from 90 Japanese females, ranging in age from 20 to 60 years. The feature values of CLSM images were extracted using image analysis methods, such as short-line segment-matching processing and spatial frequency analysis. The qualitative characteristics of the dermal fibrous structures in the CLSM images were obtained by principal component analysis (PCA) of these feature values. The fibrous structures were scored on the basis of qualitative characteristics and then age-related changes in the scores among the subjects were quantitatively evaluated. The PCA results showed that there were two characteristics in the images of fibrous structures: clearness and directionality. The clearness of fibrous structures decreased and directionality isotropy increased with age.

Synergistic efficacy of salicylic acid with a penetration enhancer on human skin monitored by OCT and diffuse reflectance spectroscopy.

Salicylic acid (SA) has been frequently used as a facial chemical peeling agent (FCPA) in various cosmetics for facial rejuvenation and dermatological treatments in the clinic. However, there is a tradeoff between therapeutic effectiveness and possible adverse effects caused by this agent for cosmetologists. To optimize the cosmetic efficacy with minimal concentration, we proposed a chemical permeation enhancer (CPE) azone to synergistically work with SA on human skin in vivo. The optical properties of human skin after being treated with SA alone and SA combined with azone (SA@azone) were successively investigated by diffuse reflectance spectroscopy (DRS) and optical coherence tomography (OCT). Our results revealed that as the SA concentration increased, the light reflectance decreased and the absorption increased. We also found that SA@azone exhibited a synergistic effect on enhancing light penetration and OCT imaging depth. We demonstrated that the combination of DRS and OCT techniques could be used as a noninvasive, rapid and accurate measurement method to monitor the subtle changes of skin tissue after treatment with FCPA and CPE. The approach will greatly benefit the development of clinical cosmetic surgery, dermatosis diagnosis and therapeutic effect inspection in related biomedical studies.

Effects of tissue susceptibility on brain temperature mapping

A method for mapping of temperature over a large volume of the brain using volumetric proton MR spectroscopic imaging has been implemented and applied to 150 normal subjects. Magnetic susceptibility-induced frequency shifts in gray- and white-matter regions were measured and included as a correction in the temperature mapping calculation. Additional sources of magnetic susceptibility variations of the individual metabolite resonance frequencies were also observed that reflect the cellular-level organization of the brain metabolites, with the most notable differences being attributed to changes of the N-Acetylaspartate resonance frequency that reflect the intra-axonal distribution and orientation of the white-matter tracts with respect to the applied magnetic field. These metabolite-specific susceptibility effects are also shown to change with age. Results indicate no change of apparent brain temperature with age from 18 to 84 years old, with a trend for increased brain temperature throughout the cerebrum in females relative for males on the order of 0.1°C; slightly increased temperatures in the left hemisphere relative to the right; and a lower temperature of 0.3°C in the cerebellum relative to that of cerebral white-matter. This study presents a novel acquisition method for noninvasive measurement of brain temperature that is of potential value for diagnostic purposes and treatment monitoring, while also demonstrating limitations of the measurement due to the confounding effects of tissue susceptibility variations.

Towards Bio-impedance Based Labs: A Review

In this paper are summarized some of the main contributions to BioImpedance (BI) parameter-based systems for medical, biological and industrial fields, oriented to develop micro laboratory systems. These small systems are enabled by the development of new measurement techniques and systems (labs), based on the impedance as biomarker. The electrical properties of the life mater allow the easy, cheap and usually non-invasive measurement methods to define its status or value, with the possibility to know its time evolution. In this work, it is proposed a review of bio-impedance based methods being employed to develop new Lab-on-a-Chips (LoC) systems, and some open problems identified as main research challenges, such us, the accuracy limits of measurements techniques, the role of the microelectrode-biological impedance modelling in measurements and system portability specifications demanded for many applications.

Physical capacity in LVAD patients: hemodynamic principles, diagnostic tools and training control.

Over time left ventricular assist devices (LVAD) have become an alternative to heart transplantation because of enormous technical development and miniaturization. Most patients present a significant improvement in clinical conditions and exercise capacity. Nevertheless, exercise tolerance remains markedly limited even after LVAD implantation compared to a control group. The complex physiological and hemodynamic changes in LVAD patients, both at rest and during exercise, are not yet understood, or at least not completely.It is the aim of the present paper to describe the current state of scientific knowledge. Furthermore, the spectrum of diagnostic tools, including the noninvasive inert gas rebreathing method for measurement of cardiac output and associate parameters, are discussed. Options for training control in this special patient group are presented.

Blood pressure measurement on the cheek

Abstract In a large group of patients, it is impossible to measure blood pressure using an upper arm cuff. An alternative, non-invasive method of blood pressure measurement is required for patients with severe limb deformities or obesity, for amputees, and in the emergency medicine. The device proposed here measures blood pressure in the cheek using a small pressure pad and a pump to occlude the cheek artery – arteria facialis – and assesses blood flow with an infrared light source and a detector. The infrared light signal is analysed to assess the systolic and diastolic blood pressure of the patient. Manual evaluation of the light intensity signal showed a good agreement between cheek blood pressure measurement and a reference measurement using an upper arm cuff.

Variability in the amount of fluorine-18 fluorodeoxyglucose excreted in urine measured from oncology patients during PET/computed tomography imaging.

The objectives of this work were to estimate the amount of fluorine-18 fluorodeoxyglucose (F-FDG) excreted (AFE) in the patient urine during the uptake phase as percentage of the injected activity and to examine the effect of blood glucose levels (BGL) on the excreted amount and whether it varies among men and women using statistical analysis methods. Radiation dose rates were measured at 1 m from 50 patients, 24 men and 26 women, before and after the first void using a calibrated ionization chamber. The F-FDG was injected in the patients using a calibrated automatic dose injection system. Statistical analysis using hypothesis testing was carried out. Patients with BGL above 5 mmol/l had a higher AFE of 12.3% in comparison with 8.3% of the patients with BGL below 5 mmol/l. A statistically nonsignificant correlation (r=0.183, P<0.249) between AFE and BGL was found; a nonsignificant difference was found in the AFE measured among the male and female patients. The AFE measured was 12±6%, with a range of (2-30%). There was a wide variation in the first void time of 39±8 min, with a range of (17-68) min. A simple noninvasive measurement method is presented that enabled the estimation of the amount of F-FDG excreted from the patient during voiding. Statistical analysis concluded that the amount of F-FDG excreted does not depend on sex, but is perhaps influenced by BGL.

Sacral Skin Elasticity - Establishing a Non-Invasive Mechanical Method for Measurement

Some patients with sacral scars, e. g. those developing after pilonidal sinus surgery, report discomfort when sitting or putting strain on the scars. In order to establish objective criteria for the assessment of this kind of discomfort and for the evaluation of scar quality after various types of surgical interventions, it is of interest to provide a method which enables physicians to assess skin quality in the sacral region. For this purpose, we developed a mechanical, non-invasive, fast and cost-neutral method for the measurement of skin distensibility and mobility. We examined a healthy sample of 100 study participants to establish benchmark values for scar-free skin in the sacral region and to identify the factors which impact skin quality, e. g. age, weight and sex. With the participant in a standing position, 4 vertically arranged measurement points, which are exactly spaced in cranial to caudal direction by 10 mm-100 mm-10 mm, are marked in the lumbar and sacral region, respectively. The participant is then asked to bend forward and - with arms and legs fully stretched on both sides - to touch both their patellae with the balls of their hands so that the distance between the measurement points can be measured in this position as well. Then, with the participant standing upright again, another measurement is taken to establish the distance by which the lowest point can be manually moved in cranial direction. The sacral-lumbar skin distension quotient (lumbar skin distension / sacral skin distension×100), which can easily be calculated from the measurements, is independent of age and BMI and has a standard range of about 80-93%. Sacral skin mobility ranges from 11 to 18 mm, but is slightly negatively influenced by a high BMI. By comparing lumbar and sacral skin distension in the same study participant, we are able to obtain intraindividually valid findings about possible changes in skin and scar quality. Owing to the lack of known published data about sacral skin elasticity, the proposed measurement method, while restricted to a number of special cases, seems to be practicable and independent of the patient's general condition. Compared with devices that have been used for the measurement of elasticity in other skin areas, our procedure is generally available and cost-neutral.

Photoplethysmography: Towards a non-invasive pressure measurement technique.

There is a need for non-invasive and continuous blood pressure measurements. This study explored the relationship between Photoplethysmography (PPG) and Pressure-Volume (P-V) changes in an in vitro model. We proposed and compared methods for an estimation of the pulsatile volume, termed as Normalized Pulse Volume (NPV) and Adjusted Pulse Volume (APV). To validate the methods, pressure, Red (R) and InfraRed (IR) PPG signals were recorded continuously in an arterial model utilizing a pulsatile pump. Flow rates were controlled by varying pumping frequencies at low and high stroke volumes. It was found that the optimum method for estimation of the pulsatile volume is through APV, which had a high correlation (r2=0.99, p<;0.001) with the assumed exponential P-V model. APV obtained a significantly better fit when compared to NPVIR (r2=0.73, z=25.85, p<;0.001) and NPVR (r2=0.95, z=12.26, p<;0.001). These preliminary findings suggest that APV could be used as a potential non-invasive continuous method of blood pressure measurement.