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performing quantitative measurements of such organic

USING LED HARMONIC WAVELENGTHS FOR constituents in these lower wavelengths can be hin

NEAR-INFRARED QUANTITATIVE dered by interference with water absorption.

FIG. 2 illustrates the fact that, in lower wavelength

This application is a continuation-in-part of copend- 5 regions, infrared energy absorption by water signifi

ing application Ser. No. 544,580, filed Jun. 27, 1990, cantly overlaps with the absorption by other organic

now U.S. Pat. No. 5,086,229, which is a continuation-in- constituents. In contrast, water absorption at 1200 and

part of Ser. No. 298,904, filed Jan. 19, 1989, now U.S. between 1600 and 1800 nanometers do not significantly

Pat. No. 5,028,787. interfere which makes the measurements of protein,

„_ Tm- IM„CWT,nM 10 oil/fat, starch and other constituents considerably atBACKGROUND OF THE INVENTION tractjve m these regions

1. Field of the Invention For example, U.S. Pat. No. 5,028,787, incorporated This invention relates to instruments and methods for herein by reference, teaches a method of performing

the non-invasive quantitative measurement of constitu- near-infrared noninvasive measurement of blood glu

ents in material samples, such as protein in wheat and 15 cose levels using energy in the 600 to 1100 nanometer

glucose levels in a test subject's blood. Specifically, this spectrum region. Constituent absorptions in this region

invention relates to a novel near-infrared quantitative are weaker than in the 1200 nanometer region. As a

measurement instrument which utilizes harmonic wave- consequence, measurement of organic constituents in

lengths of light emitting diodes (LEDs). products containing water often result in major mutual

2. Description of the Background Art 20 interference from water. Thus, although glucose meaThe use of LEDs and IREDs as energy sources for surements in the 600 to 1100 nanometer region of the

near-infrared measurements is a well established art. spectrum are practical, such measurements are necesFor example, thousands of TREBOR-90/XL Wheat sarily more complex than potential measurement at and Barley Testers, which use IREDs as energy 1200 or 1600-1800 nanometers, sources, are currently being used in country elevators 25 Thus, there is a great need for a near-infrared quantifor measuring the protein and moisture content in wheat tative measurement instrument having a solid state enand barley. Similarly, over 10,000 FUTREX-5000 Body ergy source (IRED) which can provide reasonable Composition Analyzer Instruments, which also utilize energy in the 1200 to 1800 nanometer region and yet IREDs, are currently being used in medical institutions, which is reasonably priced, health clubs and sporting teams for measuring percent 30 Cttmiuapv Op Tuc Iwucmtitm body fat. Also, a combination of LEDs and IREDs are SUMMARY OF THE INVENTION currently being used in non-invasive near-infrared In accordance with the present invention, a nearquantitative analysis instruments to assess the chemical infrared quantitative analysis instrument for measuring composition of the blood, such as measurement of blood a constituent of a sample material comprises an introglucose levels. 35 ducing means including a near-infrared energy source One common limitation of the current generation of for introducing near-infrared energy into a sample mainstruments which use LEDs/IREDs is that they are terial wherein the energy source emits radiation at a generally limited to wavelengths below approximately peak wavelength and at harmonic wavelengths. The 1100 nanometers. This limitation is primarily due to the instrument further comprises a filter means for filtering fact that the longest wavelengths emitted by commer- 40 the near-infrared energy at all wavelengths except in cially available, low cost LEDs/IREDs is typically regions of a selected one of the harmonic wavelengths, approximately 950 nanometers. Even with the use of The instrument utilizes a detecting means for detecting narrow bandpass filters located outside the IRED's half the energy emerging from the sample and a processing power bandwidth (see U.S. Pat. No. 4,286,327, incorpo- means for processing an electric signal produced by the rated herein by reference), typical IREDs do not pro- 45 detecting means into a signal indicative of the constituvide a practical means of making measurements above ent present in the sample.

approximately 1050 nanometers. In accordance with another aspect of the present

Although there are commercially available IREDs invention, a near-infrared quantitative analysis instru

having wavelengths between 1000 and 1700 nanome- ment for measuring blood glucose comprises an introters, such energy sources are extremely expensive and 50 ducing means for introducing near-infrared energy into

have a very low power output. For example, Model blood present in a body part of a subject. The instru

IR-1300 (UDT Sensors, Inc.) is an IRED that emits 20 ment further comprises a filter means for selectively

microwatts of optical energy at 1300 nm and costs more filtering the near-infrared energy at all wavelengths

than $30. In comparison, a typical LED emits approxi- except in a region of one of the harmonic wavelengths mately 1000 times more energy and costs less than 55 of the introducing means. The Instrument utilizes a

$0.30. detecting means for detecting near-infrared energy

As illustrated in FIG. 1, the spectrum ranges in the emerging from the subject and means for converting an

vicinity of 1200 to 1800 nanometers can be very impor- electrical signal corresponding to the detected energy

tant in performing quantitative measurements. This into a signal indicative of the quantity of glucose presresults from the fact that some absorption peaks for fat, 60 ent in the blood of the subject,

starch and protein do not overlap the dominant water _____ __C_DTD_T„X1 A,.,TlkT„„

absorptions in this region. For example, at 1200 nm BRIEF DESCRIPTION OF THE DRAWINGS

there is a relatively strong fat absorption band with FIG. 1 is a plot of Log (1/1) versus wavelength illus

almost no interfering absorption occurring from water. trating near-infrared energy absorption spectra for wain most other regions of the spectrum, the infrared 65 ter, starch, oil and protein in the 1200 and 1600 nanome

energy absorption by water significantly overlaps with ter regions.

the infrared energy absorption by other organic constit- FIG. 2 is a plot of Log (1/1) versus wavelength illus

uents such as oil, starch and protein. Thus, accurately trating that the near-infrared energy absorption peaks of

3

water overlap with the absorption peaks of fat and protein in the 900 to 1050 nanometer region.

FIG. 3 illustrates the energy spectrum of a known IRED.

FIG. 4 illustrates the center wavelength and a har- 5 monic wavelength of a known IRED.

FIG. 5 is a near-infrared quantitative analysis instrument according to the present invention.

FIG. 6 is a near-infrared quantitative analysis instrument according to an second embodiment of the present 10 invention.

DETAILED DESCRIPTION OF THE
PREFERRED EMBODIMENTS

The near-infrared quantitative measurement instru- 15 ment according to the present invention effectively utilizes energy in the 1200 to 1800 nanometer regions by isolating and employing harmonic wavelengths emitted by typical, low cost commercially available LEDs. A typical LED is designed to emit energy at a center 20 wavelength which has a reasonably narrow half-power bandwidth. For example, FIG. 3 shows the spectrum of a typical LED, from Stanley Electronics Company Ltd. (Tokyo, Japan), which has a center wavelength at approximately 600 nanometers with a half power band- 25 width of 35 nanometers (Stanley Part Number MAA33685). Such LEDs are used in many commercial products and are very low priced, e.g. typical price is less than $0.30 each.

These typical LEDs also have been discovered to 30 emit light at a harmonic wavelength in the near-infrared region. For example, FIG. 4 shows the spectra of an "MAA" type LED, the same LED described in FIG. 3, measured with a precision spectrophotometer, i.e. a Cary-14 Spectrophotometer. FIG. 4 illustrates that 35 MAA the center wavelength of "MAA" type LED is approximately 608 nanometers which is reasonably identical to the 604 nanometer center shown in FIG. 3. FIG. 4 also illustrates that there is energy emitted form this low cost part which peaks at approximately 1200 40 nanometers with a half power bandwidth of approximately 180 nanometers. These figures show that the standard Stanley "MAA" type LED provides optical energy not only in the normal visible band of approximately 604 nanometers, but also in the near-infrared 45 1200 nanometer region.

The amount of energy at the 1200 nanometer region is approximately 5% of the peak energy at the 604 nanometer region. Although this number may not appear to be large, it is more than that generated by the custom 50 made IRED for 1200 nanometers. Moreover, because of the wide half-power bandwidth at 1200 nanometers, i.e. 180 nanometers, it means that many measurement wavelengths can be generated through use of either multiple MAA type LED's, each with its own narrow band pass 55 optical filter, or through use of a "filter wheel" which contains a number of optical filters and which is positioned in the light beam of the LED.

The spectrum of each "IRED" is limited by the use of suitable narrow bandpass optical filters both within a 60 half power bandwidth and outside the half power bandwidth, as taught in U.S. Pat. No. 4,286,327, incorporated herein by reference.

A near-infrared quantitative analysis instrument according to the present invention will be described with 65 reference to FIG. 5 which shows a lightweight handheld analysis instrument 10 which measures a blood analyte present in a body part, e.g. blood glucose levels.

4

The analysis instrument 10 includes an introducing means for introducing near-infrared energy into blood present in a body part of a test subject. The introducing means comprises at least one standard, low cost LED, such as the Stanley MAA type LED discussed above, which emits energy at a central wavelength and at harmonic wavelengths. Two such LEDs 16 and 17 are illustrated in FIG. 5 and are positioned within an upper flange 11. Each LED is optically isolated via opaque light baffle 19.

The upper flange 11 is hinged about shaft 12 to lower flange 15, and a spring 14 serves to maintain the flanges in a closed position. An optical detector 18 is disposed in lower flange 15 opposite the LEDs 16 and 17. The detector is disposed behind an optional window 21 which can be constructed of a material which is either optically clear or which excludes visible light yet permits near-infrared light to pass. A finger stop 23 helps place and maintain the subject's finger in its proper position within the instrument 10. Each of the flanges is provided with light-shielding barriers 24 (shown in phantom in FIG. 5) to block ambient light from entering the instrument.

A filtration means is positioned between the LEDs and a test subject's body part for selectively filtering the energy emitted by the introducing means and for passing only energy in the region of a selected harmonic wavelength of the LEDs. The filtration means can be any filter or system of filters which pass only energy in a selected wavelength Tegion. For example, filters 26 and 27, illustrated in FIG. 5, are narrow band pass filters which pass energy emitted by LEDs 16 and 17 only in the region of the harmonic wavelength, i.e. approximately 1200 nanometers. Any suitable narrow bandpass filters may be used.

Operation of the near-infrared quantitative analysis instrument 10 according to the present invention will be discussed as follows. The finger of a test subject is inserted between flanges 11 and 15 of the instrument 10. Light energy emitted from LEDs 16 and 17 is filtered by narrow bandpass filters 26 and 27 and is transmitted through the test subject's finger and is detected by optical detector 18. Detector 18 can be any suitable detector for detecting energy in near-infrared wavelength region, such as a lead sulfide (PbS) detector. An indium arsenide (InAs) detector can be used as well.

The electric signals produced by the detectors are transmitted via line 29 to a controller processor unit 28 where the signal is amplified and data processed using a suitable algorithm, such as those disclosed in U.S. Pat. No. 5,028,787 ("the '787 patent"), and displayed on a readout device. However, because there is less interference in these wavelength regions, an algorithm, such as those described in the '787 patent, can be used which has fewer regression terms. Using an algorithm having fewer regression terms makes the apparatus more simple and inexpensive. Also, potentiometer 50 is utilized to permit measurement of a patient's finger thickness.

A near-infrared quantitative analysis instrument according to another embodiment of the present invention will be described with reference to FIG. 6 which shows a near-infrared analysis instrument 30 for measuring the a constituent present in a sample material, such as protein in wheat. Analysis instrument 30 includes an introducing means for introducing near-infrared energy into a material sample. In the FIG. 6 embodiment, a wheat sample is shown supported by container means 36. The introducing means comprises at least one standard, low

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