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Designing non-invasive blood glucose monitor

04 Nov 2013  | Masab Ahmad, Awais Kamboh, Ahmed Khan

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The lower limit of detection using NIR in this setup is 55mg/dl. A sugar level below this cannot be accurately measured. However, this can be improved by increasing the power output of the LEDs. The upper limit is set to 355mg/dl, although higher levels can be measured easily.

Display
Although the final glucose value can be displayed on a simple LCD, in this design it is also displayed on an android phone using Bluetooth connectivity. The Universal Asynchronous Receiver Transmitter (UART) of the PSoC is connected to the Bluetooth device. A simple communication protocol was implemented inside the PSoC and the mobile device. When a user asks for a glucose value, the Android platform sends a 'get' to the PSoC, which waits for glucose computation after which it sends the glucose value and an acknowledgement. The Android device displays the glucose value upon receiving it. The whole process takes about 2s.


Figure 4: Snap-shots of the Android device.


Figure 5: Complete setup.


Results
To determine the accuracy of the device described above, its readings were compared against an off-the-shelf handheld home-use invasive glucometer available in the market. A Clarkson Error Grid [1] is a standard specifically used to determine the accuracy of glucose monitoring devices. The y-axis represents the values read by the non-invasive device, and the x-axis represents the values recorded by the invasive off-the-shelf device, for the same patient, at the same time. Over 100 test points were taken on 80 patients. The error grid is shown in figure 6. Around 75% of the data points lie in region A, while all the remaining points lie in region B. No data point lies in the other regions. The correlation coefficient between measurements from non-invasive glucometer and reference glucometer is equal to 0.85, which is very good. This accuracy is better than most non-invasive glucose meters present in the literature (although the sample size presented in this study may not be large enough and further testing and calibration may be required). This high performance is made possible in part due to the fact that PSoC-5LP provides highly integrated analogue and digital capabilities, with a low noise floor, and high-resolution analogue-to-digital conversion. Further improvements in accuracy can be made by increasing the LED power, by using more sensitive photodiodes, and by including further parameters like ambient and body temperatures.

Figure 6: Clarkson Error Grid for the PSoC based non-invasive glucometer.


Conclusions
In this article we have presented a non-invasive blood glucose meter that can provide glucose measurements painlessly, without a blood sample or finger pricks, within a few seconds. The device can be easily adapted to provide continuous blood glucose monitoring and blood oxygen level and maintain a history of these measurements. The device algorithm can also be modified to provide other capabilities like heart rate using the same devices and sensors.


Caution
The device presented here is only a proof of concept, showing good correlation between NIR transmittance and blood glucose. However, as such an experimental device is not FDA approved, it should only be used for academic or informative purposes, and should not be used to make any medical decisions including but not limited to administrating medicine.


References
[1] V. A. Saptari,"A Spectroscopic system for Near Infrared Glucose Measurement," PhD Thesis, MIT, 2004.
[2] A. Tura, A. Maran, and G. Pacini, "Non-invasive glucose monitoring: Assessment of technologies and devices according to quantitative criterion," Elsevier J. of Diabetes Research and Clinical Practice, vol. 77, no. 6, pp. 16-40, 2007.


About the authors
Masab Ahmad received his BE degree in Electrical Engineering from School of Electrical Engineering and Computer Science, National University of Sciences and Technology, Islamabad, Pakistan in 2013. He is currently a Research Assistant at the same institution. His research interests include signal processing and digital design.

Awais M. Kamboh received his BE degree in Electrical Engineering with honours from National University of Sciences and Technology, Islamabad, Pakistan, in 2003, his MS degree in Electrical Engineering: Systems from University of Michigan, Ann Arbor, USA in 2006, and his Ph.D. in Electrical Engineering from Michigan State University, East Lansing, USA in 2010. Since the beginning of 2011 he is serving as an Assistant Professor in the School of Electrical Engineering and Computer Science, National University of Sciences and Technology, Islamabad, Pakistan.

Ahmed Majeed Khan is an experienced engineer seasoned in working with cross-functional groups to continually push the envelope of technology implemented in the electronic products. Mr. Khan is from consumer electronics background and his expertise includes embedded systems and wireless multimedia communication. With his expertise, he personally developed and led teams to develop several high volume, high quality products. Currently, Mr. Khan holds an engineering role at Cypress Semiconductor Corp.

To download the PDF version of this article, click here.


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