The invention relates to a device and a method for the measurement of a glucose level according to the preamble of the independent claims.
It has been known to measure glucose concentrations in living tissue using electric fields. In particular, it has been found that the dielectric properties of the tissue vary with glucose concentration. Corresponding devices rely on the application of electrodes to the human body, which gives rise to various boundary problems, such as a dependence of the results on current skin condition.
Hence, it is a general object of the invention to provide a device and a method described above that is less prone to boundary problems.
This object is achieved by the device and method according to the independent claims.
Hence, the device of the present invention comprises a ring and a coil assembly. A coil of the coil assembly is wound around the ring, i.e. the ring is forming a substantially toroidal core of the coil. The coil may form part or all of the coil assembly. A current source is provided for generating an AC current in the coil. This current gives rise to an alternating magnetic field within and along the ring, which in turn generates an alternating electric field. A specimen is placed in the alternating electric field. In this way it is possible to generate an electric field within the specimen without using electrodes.
The dielectric properties of the specimen affect in turn the alternating electric field, which in turn affects the magnetic field and the inductance of the coil assembly. Hence, any parameter that depends on the inductance of the coil assembly also depends on the dielectric properties of the specimen and therefore on the glucose level. Therefore, by measuring a signal depending on the inductance of the coil assembly and by using suited calibration data, the glucose level can be determined.
The coil assembly may consist of a single coil, in which case the mentioned inductance is the coil's self inductance. Preferably, however, the coil assembly comprises two or more coils, and the mentioned inductance is a mutual inductance of the two coils, which can e.g. be measured by applying a voltage to a first one of the coils and measuring the induced voltage or current in the second coil.
The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings, wherein:
A coil assembly for a device according to a first embodiment of to the invention is shown in
For being placed on specimen 3, ring 1 can consist of two parts 1′, 1″ that can be separated at least at one point.
Ring 1 should be made of a material of high magnetic permeability μ, such as a ferrite. Materials with a permeability of at least 100, preferably of at least 1000, should be used.
An electronic circuit 10 such as shown in
The circuit comprises an AC voltage generator 11, which is preferred to be a sine wave generator operating at a given frequency f, preferably of at least 1 kHz. AC voltage generator 11 feeds a current through first coil 4, which generates an alternating magnetic field in ring 1. As mentioned above, this magnetic field gives in turn rise to an alternating electric field in opening 2 interacting with the dielectric properties of specimen 3. In particular; dipoles are oriented and ions are separated creating addition induced polarization, which affects the magnetic field in ring 1 and therefore induces additional current components in the coils 4 and 5.
In other words, the dielectric properties of specimen 3 affect the self inductances Lii as well as the mutual inductances Lij of the coils 4 and 5.
The voltage over second coil 5 is fed to a detector 12. Detector 12 can e.g. measure the ratio {tilde over (K)} between the voltage {tilde over (V)}2 and {tilde over (V)}1. As can be shown, this ratio is given by
wherein
Equation 2 is based on the assumption that the specimen is cylindrical with a diameter of 2·r1 and a height of h and is centered in opening 2 of ring 1. For a differently shaped specimen (as will be the rule for invivo measurements) a suited correction factor has to be applied. Such a correction factor is automatically accounted for when using the calibration technique described below.
The ratio {tilde over (K)} as measured by detector 12 is converted to a digital signal and fed to a microprocessor 13, which converts it to a glucose concentration using calibration data stored in a non-volatile memory 14. The glucose concentration can e.g. be displayed on a display 15.
For calibrating the present device, several measurements at known glucose levels cgl are carried out for a given patient. For each measurement, the known glucose level is stored together with the voltage ratio {tilde over (K)}. After a number of measurements, the relation between ration {tilde over (K)} and glucose level can be fitted to a function f using one or more parameters p1, p2, . . . , i.e. cgl=f({tilde over (K)}, p1, p2 . . . ). The parameters p1, p2 . . . can be stored as calibration data in memory 14. The function f({tilde over (K)}) can e.g. be a straight line (i.e. f({tilde over (K)}, p1, p2)=p1+{tilde over (K)}·p2) or any other function that is found empirically or theoretically to be suitable to describe the relation between {tilde over (K)} and cgl.
Instead of measuring the voltage ratio {tilde over (K)}, any other parameter depending on the mutual inductance Lij of the coils 4 and 5 can be measured. Similarly, any parameter depending on the self inductance of one of the coils can be measured, in which case only a single coil is required. For example, coil 4 may be part of an LC-circuit of an oscillator operating at approximately 50 MHz. A change in the coil's self inductance will lead to a change of the oscillator's frequency, which can be measured easily.
The advantage of the embodiment of
In the embodiments of
In the embodiments shown so far, ring 1 forms a circle and has rectangular cross section. However, ring 1 may e.g. also have a shape different from a perfect circle and may can e.g. be ellipsoidal or polygonal. Similarly, its cross section may be of any other shape.
While there are shown and described presently preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.
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Number | Date | Country | |
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Number | Date | Country | |
---|---|---|---|
Parent | PCT/IB02/03935 | Sep 2002 | US |
Child | 11070859 | US |