KEYWORDS: Glucose, Blood, Near infrared, Semiconductor lasers, Calibration, Optical fibers, In vivo imaging, Human subjects, Diffuse reflectance spectroscopy, Diodes
In the event of diabetes clinicians have advocated that frequent monitoring of a diabetic's blood
glucose level is the key to avoid future complications (kidney failure, blindness, amputations,
premature death, etc.,) associated with the disease. While the test-strip glucose meters available in
current consumer markets allow for frequent monitoring, a more convenient technique that is
accurate, painless and sample-free is preferable in a diabetic's daily routine. This paper presents a
non-invasive blood glucose measurement technique using diffuse reflectance near infrared (NIR)
signals. This technique uses a set of laser diodes, each operating at fixed wavelengths in the first
overtone region. The NIR signals from the laser diodes are channeled to the measurement site viz.,
the nail-bed by means of optical fibers. A series of in vivo experiments have been performed on eight
normal human subjects using a standard Oral Glucose Tolerance Test (OGTT) protocol. The
reflected NIR signals are inputs to a Partial Least Squares (PLS) algorithm for calibration and future
predictions. The calibration models used are developed using in vivo datasets and are unique to a
particular individual. The 1218 paired points collected from the eight test subjects plotted on the
Clarke Error Grid, revealed that 87.3% of these points fall within the A zone while the remainder,
within the B zone, both of which, are clinically accepted. The standard error of prediction was
±13.14mg/dL for the best calibration model. A Bland-Altman analysis of the 1218 paired points
yields a 76.3% confidence level for a measurement accuracy of ±20mg/dL. These results
demonstrate the initial potential of the technique for non-invasive blood glucose measurements in vivo.
The non-invasive measurement of blood sugar level was studied by use of near infrared laser diodes. The in vitro and in vivo experiments were carried out using six laser diodes having wavelengths range from 1550 nm to 1750nm. Several volunteers were tested for OGTT (Oral Glucose Tolerance Test) experiment. We took blood from a fingertip and measured its concentration with a glucose meter while taking signal voltage from laser diodes system. The data of signal voltage were processed to do calibration and prediction; in this paper PLS (Partial Least Square) method was used to do modeling. For in vitro experiment, good linear relationship between predicted glucose concentration and real glucose concentration was obtained. For in vivo experiments, we got the blood sugar level distributions in Clarke error grid that is a reference for doctors to do diagnosis and treatment. In the Clarke error grid, 75% of all data was in area A and 25 % was in area B. From the in vitro and in vivo results we know that multiple laser diodes are suitable for non-invasive blood glucose monitoring.
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