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Научни трудове на Съюза на учените в България-Пловдив, Серия Г. Медицина, фармация и дентална медицина т. XIX. ISSN 1311-9427 юни 2016. Scientific works of the Union of Scientists in Bulgaria-Plovdiv, series G. Medicine, Pharmacy and Dental medicine, Vol. XIX, ISSN 1311-9427 Medicine and Dental medicine June 2016.
OPTICAL METHODS IN BIOMETRY FOR VEIN IDENTIFICATION AND MEDICAL DIAGNOSTICS
G. Dyankov1*, T. Eftimov2, T. L. Dimitrova2
institute of Optical Materials and Technology, BAS, 109, Acad. G. Bontchev Str., 1113 Sofia,*[email protected]
2Plovdiv University "Paisii Hilendarski", Tzar Assen Str. 24, Plovdiv
Abstract
Nowadays the personal identification is world sizable security problem. Hence, various biometric technologies for individual verification are widely spread. Fingerprint is one of the most often used techniques due to its easy and fast performance and relatively low cost. Recently, the efforts to increase the access reliability led to development of finger vein pattern authentication technology and its rapid commercialization.
As far as the vein identification is based on optical method, the technology can be extended for performing measurement of other characteristics giving information about the personal health and emotional status. Thereby, the biometric devices for identification can be used for permanent medical check-in after appropriate hardware and software modification.
Here we present some experimental results on development of a vein reader device, vein tracking and pulse rate measurement. We consider further improvement of our system regarding oximetry application. A potential method of implementation is proposed.
1. Introduction
Personal identification is everyday practices at custom service, public offices etc. Digital identification is daily used for credit card authentication, automated teller machine, automobile security, computer and network authentication, employee time tracking, attendance registration, end point security etc. There are several biometrical technics used for personal identifications such as fingerprint, iris pattern, facial futures, voice recognition, blood vessels structure etc. Every of them is used depending on its security level and convenience. In Table 1 is presented the rating of different biometric technologies [1]. From the table is obvious that vein recognition is one of the most reliable biometric technologies ensuring good security and normal convenience.
Table 1 Rating of different biometric technologies
Biometrics SECURITY CONVENINCE
Anti-Forgery Accuracy Speed Enrolment rates Resistance Cost Size
Fingerprint I N N I I G G
Iris N G N N I I I
Face N I N N G I I
Voice N I N N G N N
Vein Pattern G G G N N N N
G- good; N- normal; I - insufficient
The common understanding for biometry is related to „digitally scanning of the physiological or behavioural characteristics of individuals as a means of identification" [2], but it may be successfully applied in medicine too. Vein identification technology is very suitable in this direction.
The first paper about use of vascular patterns for biometric recognition was published in 2000 [3]. During the last two years one can observe fast movement towards commercialization of this technique. A few companies have already launched on the market vein pattern reading devices.
In comparison to the other hand-based biometric authentication techniques, the finger vein recognition demonstrates some advantages such as:
1) Non-contact measurement: Finger vein patterns are not influenced by surface conditions. By deriving non-invasive and contactless data capture it ensures both convenience and cleanliness for the users.
2) Live body identification: Finger vein patterns can only be identified on a live body, so, it can be used as vitality indicator too.
3) High security: Finger vein pattern is placed inside of the tissue and protected by the skin, so that, it is more difficult to be destroyed or damaged by external factors.
4) Small size devices: The small size devises can be portable what allows their use in casual conditions.
Here, we present a vein reader device, developed by following the options for extending vein identification technology towards application to medical diagnostic.
2. Experimental setup
The principle of the blood vessels patterning is based on the selective light absorption of blood hemoglobins. One can distinguish several hemoglobins like: oxy-hemoglobin or Hb02
when the the hemoglobin molecule is bound to oxygen; carboxy-hemoglobin (HbCO) - the hemoglobin molecule is bound to carbon monoxide; deoxy-hemoglobin (Hb) - the hemoglobin molecule is bound to nothing and, met-hemoglobin in the case when the hemoglobin molecule has broken down. Every kind of hemoglobin has different absorption spectra [4]. In general, the different blood hemoglobins absorb in the range between 300 nm and 1300 nm.
There are known three different experimental setups for finger vein pattern registration:
1) Transmission of near-infrared light through the finger - the light is partially absorbed by veins haemoglobin, forming thus the veins pattern shadow on the registered picture. This is light transmission leading-edge technology developed by Hitachi.
2) Light diffusion from one light source - the light source and the detector are placed on the same side of the finger.
3) Light diffusion from two light sources - the two light sources are placed on the opposite sides of the finger and the detector is placed on the orthogonal side.
Objective Finger
Fig. 1 Experimental setup of vein reading device
Our vein reader, shown in Fig. 1 is constructed in transmission mode. LEDs emit infrared light at 910 nm. The radiation passes through the tissue and it is absorbed by both oxy- and deoxyhemoglobin of the blood. The image of the finger vein structure is obtained by CCD camera equipped with infrared down-cut transmission filter. The image tracking the veins positions is
extracted by freeware software after some modifications.
3. Results and discussion
3.1 Finger vein pattern recognition
In Fig.2 is shown a finger image obtained by infrared light. Vein structure is clearly observed. It is worthy to mention that the choice of LED emitting at 910 nm was done after careful study the quality of pictures at different wavelength into the infrared range. We have found that at this wavelength the tradeoff between the tissue penetration and blood absorption provides the best contrast.
The contrast also depends on tissue density which is an individual characteristic. Aiming to get images with compatible contrast and quality adapted to the personal particulars of the different users, it is necessary to control the intensity of the LED light emission. A feedback from image quality (evaluated according to proper criteria) toward the LED current controlling unit is provided.
In Fig.3 is shown vein structure extracted from the photo in Fig.2. Several methods for vein tracking have been tested and, as it may be expected, we have found that its efficiency depends from the image quality. The selection of the most effective method is going to be done.
Fig. 2 Infrared finger photo Fig. 3 Extracted veins structure at 910 nm
1.2 Finger pulse pattern recognition
Vein identification technology can be used for pulse rate detection after appropriate modification of the software controlling the CCD. In Fig. 4 is shown the pulse of an individual measured on the base of the image brightness variation at selected area. The measurement is provided by images capturing for 10 seconds at speed of 25 frames per second. The construction of the vein reader and the software ensures reliable pulse rate detection.
Pulse rate provides information for one of the most important phenomena related to the health and to the emotional status - Heard Rate Variability (HRV) [5, 6]. The methodology for determination of HRV and its interpretations are well known. They are used in many smartphone and tablet apps that provide HRV reading [7]. Vein identification technology ensures very reliable detection of pulse rate and HRV determination will be much more accurate compared to the tablet apps. The integration of HRV software with vein identification software is going to be done
150-1---,-.-1-.-,-.-,---,
0 2 4 6 8 10
Second
Fig. 4 Brightness variation with the time of selected area from the image
1.3 Oximetry
Oximetry is a procedure for measuring the blood oxygen concentration. The first optical oximetry measurement is made by the German physician Karl Matthes in 1935. In 1972 the Japonees bioengineers Takuo Aoyagi and Michio Kishi have extended the technology to pulse oximetry. Nowadays, the intensive research in this field has reviled new applications [8-11] which has been brought to the market. However, the oximetry suffers from lack of selectivity. For example, trivial rheum may cause the same oximetry parameters deviation like drugging.
It is very simple to extend the vein pattern technology to oximetry implementation. In the vein recognition technology is used finger illumination at one wavelength only. The oximetry measurement is based on two light sources - one infrared and one red. The selection of the wavelengths is due to the different absorption of the oxy- and deoxyhemoglobin. While the oxyhemoglobin absorbs more infrared and transmits more red light, the deoxyhemoglobine, in the opposite, absorbs more red and transmits more infrared light.
In our case, an additional emitting at 660 nm embedded in vein reader unit. The combination of 910 nm infrared and 660 nm red light gives reasonable difference between the oxy- and deoxyhemoglobin absorption [12].
Oximetry measurement procedure is the next. Firstly, the reader measures the sum of the intensities of the infrared and of the red light. That represents the contribution of both blood components - with and without oxygen. The constant skin and tissue absorption should be considered. In oximetry regime the reader detects the pulse, and then subtracts the light intensities when the pulse is absent. The difference of intensity represents only the oxygenated blood. The ratio between the intensities of the red and infrared transmitted light serves as an indicator for the blood oxygen saturation.
The feasibility of our system was confirmed by simultaneous measurements provided with standard commercially available pulse oximeter.
We intend to combine the vein pattern recognition with oximetry measurement for personal control. For example, one can appraise the eligibility for performing particular activities related to official duties. The appraisal is based on surveillance of a few physiological parameters by means of oximetry together with HRV surveillance. Such security system is much needed for securing
objects sensitive to the personal's health and emotional status such as, for example, manipulation with specific machines etc.
Summary
We present some experimental results on development of a vein reader device. Our experience shows that the vein pattern recognition technology can be use for surveillance of health and emotional status. We demonstrate that the pulse rate is reliability detected and the application of vein reader for SHV is very effective. The application of vein reader for access control means that statistically significant data base can be used for analysis. A personal profile can be build and survey of deviations from normal status can be performed. In this case correlation analysis can help for increasing oximetry selectivity. This could be a first step towards a complex reliable technology for clinical use.
Ascknowledgements
The authors thank BIODIT Ltd for the financial support.
References:
1. Finger vein authentication: White paper; Hitachi, 2008.
2. Encyclopedia of Biometrics; Editors: Stan Li, A. Jain; Springer; ISBN: 978-1-48997487-7; Springer, New York, 2015.
3. Sang-Kyun Im, Hyung-Man Park, Young-Woo Kim, Sang-Chan Han, Soo-Won Kim, and Chul-Hee Kang, "Biometric Identification System by Extracting Hand Vein Patterns," Journal of the Korean Physical Society, Vol. 38, No. 3, March 2001: 268-272.
4. Prahl, Scott. "Optical absorption of hemoglobin." Oregon Medical Laser Center, http:// omlc. ogi. edu/spectra/hemoglobin/index. html 15 (1999).
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