Light probe for a near-infrared body chemistry measurement instrument

A light probe method and apparatus is provided for an infrared body chemistry measurement instrument. The light probe includes an illumination ring of a light-conducting material, having facets on an exterior circumferential surface, and an inner circumferential surface at about a forty-five degree angle, infrared light emitting devices positioned at each facet, a coaxially located optical detector, a shielding ring coaxially located between the optical detector and the illumination ring, and a cover having a central opening which exposes the optical detector, the shielding ring, and the illumination ring, wherein a length dimension of the light probe is less than a diameter dimension. The method includes radially illuminating an illumination ring with infrared light, redirecting the infrared light to an axial direction perpendicular to the radially inward direction, conducting the infrared light through the illumination ring and into a body part under test, and receiving reflected and scattered light in an optical detector concentric with the illumination ring.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a new and improved light probe for a 
near-infrared body chemistry measurement instrument. 
2. Description of Background Art 
Body chemistry measurement is a health field wherein the goal is to detect, 
monitor, or prevent health problems due to disease, illness, or genetic 
propensity by measuring analytes in the body. A large and important area 
of interest is in developing measurement devices that are inexpensive to 
produce, yet give fast and reliable results. The ultimate goal is an 
instrument that is reliable enough for medical use, yet inexpensive and 
reliable enough for use by ordinary persons. Through the use of such body 
chemistry measurement instruments, persons will be able to monitor their 
own health. 
Several body chemistry characteristics are vital to long term health, and 
are becoming easier to monitor. These are characteristics such as body fat 
percentage and body water percentage. Long term health can be improved by 
keeping both characteristics within widely-accepted ranges. It is well 
established that health risks increase for those who are more than twenty 
percent over optimal weight. Measurement of weight alone, however, is not 
sufficient. Body composition (i.e., body fat levels), is one preferred 
measure of health and fitness. Generally, body fat levels of fifteen to 
eighteen percent for men and twenty to twenty-five percent for women are 
considered acceptable. Body fat levels greater than twenty-six percent for 
men and twenty-nine percent for women are considered to be indicative of 
obesity and are a potential risk factor for the development of diseases 
such as cardiovascular disease, high blood pressure, and diabetes. Other 
important body function characteristics that often require regular 
measurement are blood pressure, pulse rate, blood glucose levels, etc. 
Body fat testing can be measured by several known methods, such as by 
measurement of body part circumferences, water immersion, bioelectrical 
impedance, or infrared light interactance. 
Each of the above measurements has particular problems or disadvantages. 
Measuring body part circumferences and using body fat calipers are two 
easy and cheap methods, but may be inaccurate due to a user's lack of 
knowledge on proper use, and may further suffer from differences between 
individuals, differences due to age, or differences due to gender. 
Numerous combinations of skinfold measurements taken at different sites 
are required. This data must be applied to regression equations to predict 
body fat levels. 
Water immersion body fat testing is widely accepted as the standard by 
which other body fat testing methods are measured. A person is immersed in 
water and the volume of displaced water is compared to the person's 
weight. Water immersion tests are expensive, somewhat complicated, require 
relatively expensive and bulky equipment, and must be performed by trained 
personnel. These limitations make it impractical for general use. 
Body fat composition may be measured by bioelectrical impedance, where body 
fat is indirectly measured by measuring the body's resistance to a small 
electrical current. This resistance is used to obtain body fat levels, as 
bones, muscle and tissue have a high level of electrical conductivity 
compared to body fat. In principle, the lower the electrical impedance, 
the greater an individual's lean body mass. This method can be 
incorporated into a testing device that is small and inexpensive, and 
available for general use. However, the accuracy of the bioelectrical 
impedance method can be affected by several critical factors. To make a 
valid measurement, the subject must be in a stable condition. The amount 
of hydration (i.e., the amount of water in the body) and the amount of 
electrolytes must be consistent every time a measurement is made. This is 
because bioelectrical impedance does not measure body fat, it measures the 
body's resistance to electrical current flow. Thus, for example, if the 
person is perspiring, the test results of the predicted body fat may be 
inaccurate. In fact, in order to obtain accurate measurements, the 
National Institutes of Health (NIH) insists that the person being tested 
with a bioelectrical impedance instrument have fasted (no food or drink) 
for a minimum of four hours, and preferably six hours. 
Near-infrared interactance measures body fat levels by measuring the 
absorption of infrared light at very specific wavelengths. All organic 
materials (i.e., fat or protein) absorb light in unique parts of the 
infrared light spectrum. Body fat can therefore be accurately and quickly 
measured by directing selected wavelengths of infrared or near-infrared 
light into a test area and measuring the amount of reflected light. 
Hereinafter, the term "infrared" will be used to encompass infrared as 
well as near-infrared wavelengths. Body fat will absorb the infrared 
light, while lean body mass will reflect it. Infrared light measurement 
instruments may also be used for other body chemistry measurements, such 
as blood analytes (e.g., glucose, hemoglobin), percentage of muscle (i.e., 
protein), pulse rate, etc. 
In operation, a long narrow light probe wand is connected to the infrared 
measurement instrument, with the light probe wand both emitting the 
infrared light and sensing the reflected light. The light probe wand must 
be used properly to avoid introducing errors into the measurement, as the 
operator may place the operative end of the light probe wand in a poor 
measurement site on the test subject or may apply an improper or 
inconsistent pressure on the light probe wand. 
The relatively large ratio between the light probe wand length in relation 
to its diameter presents a problem of incorporating a light probe into 
measurement equipment. Automated test instruments for measurements such as 
blood pressure are commonly available, and are popular due to their ease 
of use. They commonly use a cuff in which a person inserts his or her 
upper arm for testing. It has been found that the biceps or triceps 
muscles of the upper arm are good locations for infrared measurement of 
body fat levels. An infrared measurement employing a relatively thin, 
disc-shaped light probe could be easily incorporated into an existing 
automated measurement instrument. It is desirable to have an infrared 
light probe of a size and dimension that could be used in a pressure cuff, 
such as in a blood pressure tester, and would therefore be easy to use, 
consistent, and capable of being used without the help or expense of 
trained personnel. An infrared light probe could therefore be included as 
part of a blood pressure tester or other automated body chemistry 
measurement. 
What is needed, therefore, is a light probe method and apparatus of a small 
depth dimension that can be used for an infrared body chemistry 
measurement instrument. 
SUMMARY OF THE INVENTION 
It is therefore an object of the invention to provide a new and improved 
light probe for a body chemistry measurement instrument. 
It is another object of the invention to provide a light probe for a body 
chemistry measurement instrument with a low length to diameter ratio. 
It is yet another object of the invention to provide a light probe for a 
body chemistry measurement instrument wherein the infrared light is 
conducted onto the test subject via an illumination ring. 
It is yet another object of the invention to provide a light probe for a 
body chemistry measurement instrument wherein the infrared light enters 
the illumination ring from a radially inward direction. 
It is yet another object of the invention to provide a light probe for a 
body chemistry measurement instrument wherein the illumination ring 
redirects the infrared light from a radially inward direction to an axial 
direction. 
A light probe for a near-infrared measurement instrument is provided 
according to a first aspect of the invention. The light probe comprises an 
illumination ring of a light-conducting material, having a plurality of 
facets on an exterior circumferential surface and having an inner 
circumferential surface at about a forty-five degree angle, wherein 
infrared light radially entering the illumination ring from one of the 
plurality of facets is redirected by the inner circumferential surface in 
a radially perpendicular direction, a plurality of infrared light emitting 
devices positioned at each facet of the plurality of facets and capable of 
emitting the infrared light into the plurality of facets of the 
illumination ring, an optical detector coaxially located with the 
illumination ring, a shielding ring coaxially located between the optical 
detector and the illumination ring, and capable of preventing the infrared 
light from passing radially from the illumination ring to the optical 
detector, and a cover for enclosing a combination of the illumination 
ring, the plurality of infrared light emitting devices, the optical 
detector, and the shielding ring, with said cover having a central opening 
which exposes the optical detector, the shielding ring, and the 
illumination ring, wherein a length dimension of said light probe is less 
than a diameter dimension. 
A light probe for a near-infrared measurement instrument is provided 
according to a second aspect of the invention. The light probe comprises 
an illumination ring of a light-transmitting material, having a plurality 
of facets on an exterior circumferential surface, a plurality of infrared 
light emitting devices positioned at each facet of the plurality of facets 
and capable of emitting the infrared light into the plurality of facets of 
the illumination ring, an optical detector coaxially located with the 
illumination ring, a shielding ring coaxially located between the optical 
detector and the illumination ring, and capable of preventing the infrared 
light from passing directly from the illumination ring to the optical 
detector, and having an outer circumferential surface at about a 
forty-five degree angle, wherein the infrared light radially conducted 
through the illumination ring to the outer circumferential surface of the 
shielding ring is redirected by the outer circumferential surface in a 
radially perpendicular direction, and a cover for enclosing a combination 
of the illumination ring, the plurality of infrared light emitting 
devices, the optical detector, and the shielding ring, with said cover 
having a central opening which exposes the optical detector, the shielding 
ring, and the illumination ring, wherein a length dimension of said light 
probe is less than a diameter dimension. 
A method for illuminating a body part with an infrared light probe having a 
small length dimension is provided according to a third aspect of the 
invention. The method comprises the steps of radially illuminating an 
illumination ring with infrared light, redirecting the infrared light to 
an axial direction perpendicular to the radially inward direction, 
conducting the infrared light through the illumination ring and into a 
body part under test, and receiving reflected and scattered light in an 
optical detector concentric with the illumination ring. 
The above and other objects, features and advantages of the present 
invention will become clear from the following description of the 
preferred embodiment thereof, taken in conjunction with the accompanying 
drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIG. 1, there is shown a wand-type light probe 100 of the 
prior art. The prior art light probe 100 includes a cord 110 for 
connecting the prior art light probe 100 to a measurement instrument (not 
shown), an optical detector 120, a shielding ring 130, an illumination 
ring 140, and a cover 150. As can be seen from the drawing, the prior art 
light probe 100 has a high length (L) to diameter (D) ratio. Typical L/D 
ratios in the prior art are on the order of five or greater. Although the 
prior art light probe 100 performs its function, it is not dimensionally 
or physically well-suited for automated measurement instruments. One such 
instrument is the automated blood pressure measurement instrument commonly 
found in pharmacies and drugstores, wherein ordinary persons can insert an 
arm in a cuff and press a button to start the measurement. The machine 
automatically inflates the cuff, senses blood pressure and pulse rate, 
releases the cuff, and displays blood pressure and pulse rate readings. 
This machine could be readily used for other body chemistry tests by 
incorporating an infrared interactance measurement instrument. The 
infrared instrument could be easily incorporated if a light probe could be 
fitted in the cuff without size problems. 
FIG. 2 shows a new and improved light probe 200 of the present invention 
having a very low length to diameter (L/D) ratio. The light probe 200 
comprises a cord 220 for connecting to a measurement instrument (not 
shown), an optical detector 222, a shielding ring 227, an illumination 
ring 231, and a cover 236. Due to the design, function and positioning of 
the internal components, the light probe 200 of the present invention has 
a very low length to diameter (L/D) ratio. The light probe 200 is 
geometrically similar to the typical blood pressure sensor built into 
blood pressure cuffs. The shape of the light probe 200 therefore allows it 
to be used in an automated instrument or in a hand-held manner. 
The infrared light used for body chemistry measurement is emitted from the 
illumination ring 231 into the test subject. The light probe 200 is 
positioned so that a body part, preferably the biceps or triceps muscle of 
the upper arm, is pressed against the illumination ring 231 and the 
optical detector 222. The shielding ring 227 prevents infrared light from 
traveling directly from the illumination ring 231 to the optical detector 
222 without passing through the test subject. Light from the illumination 
ring 231 that has been reflected and scattered is received by the optical 
detector 222. 
FIG. 3A is a top view of the illumination ring 231. The illumination ring 
231 further includes an angled surface 248 (as best shown in FIG. 3B) and 
a central opening 252. The angled surface 248 is the area of the 
illumination ring 231 that is exposed and communicates with the body part 
under test. The illumination ring 231 has on its outer circumferential 
surface a plurality of facets 244. In the preferred embodiment the 
illumination ring 231 includes twelve of such aforementioned facets 244. 
In the preferred embodiment, the twelve facets 244 allow the use of six 
pairs of opposing infrared light emitting devices 400 (see FIGS. 4A-4B and 
FIGS. 5 and 6) with each pair preferably generating a selected wavelength 
of infrared light. The facets 244 enable infrared light emitting devices 
400 to be positioned around the outer circumferential surface of the 
illumination ring 231 and direct the infrared light radially inward. 
The material of the illumination ring 231 must be translucent and capable 
of conducting light. In the preferred embodiment, the illumination ring 
231 is formed from acrylic. One example of a suitable acrylic material is 
Plexiglas.RTM. #2447. 
FIG. 3B is a section view of the illumination ring 231 along the section 
line A--A of FIG. 3A. FIG. 3B illustrates the angled surface 248. The 
direction of infrared light entry and exit due to the angled surface 248 
can be seen from the arrows in FIG. 3B. In the preferred embodiment, the 
angled surface 248 is at an angle of forty-five degrees from the 
horizontal and consequently from the direction of light entry. In the 
preferred embodiment, the angled surface 248 does not have to be silvered 
(mirrored), as the angle plus the high refractive index of the acrylic to 
air boundary causes the entering infrared light to be refracted and as a 
result the infrared light is redirected in a direction perpendicular to 
the entry direction (i.e., it is redirected from a radially inward 
direction to an axial direction). The angled surface 248 can be either 
molded or machined and polished into the illumination ring 231. 
The area labeled with the descriptive numeral 255 is the annular region of 
the illumination ring 231 (corresponding to the angled surface 248) from 
which the redirected light emerges. 
FIGS. 4A and 4B show a typical infrared light emitting device 400 that may 
be used with the light probe 200 of the present invention. In the 
preferred embodiment, the infrared light emitting device 400 may be an 
infrared light emitting diode (IRED or LED) available from Stanley 
Electronics, part number AN505. Wide beam angle devices are preferred, as 
they provide nearly uniform illumination around the illumination ring 231. 
The infrared light emitting device 400 may include a narrow band pass 
optical filter 406, which may be fastened or attached to the radiating 
surface of the infrared light emitting device 400. The filter 406 
preferably has a band pass characteristic in the desired infrared light 
range, thereby eliminating all infrared light of wavelengths above and 
below the desired infrared light wavelength. In addition, the filter 406 
may have its edges painted or covered with an opaque material to prevent 
light leaks. The infrared light emitting device 400 may be attached to all 
facets 244 of the illumination ring 231, with the light radiating surface 
positioned radially inward on a facet 244 of the illumination ring 231. 
FIG. 5 shows a section view of a light probe 500 of a first embodiment of 
the invention along the section line B--B of FIG. 2. 
The light probe 500 comprises an optical sensor 222, a shielding ring 227, 
an illumination ring 231, a plurality of infrared light emitting devices 
400, a cover 236, and a compressible ring 536. 
The plurality of infrared light emitting devices 400 are positioned at each 
facet of the illumination ring 231 (see FIG. 3A). Light emitted by the 
infrared light emitting devices 400 (depicted by arrows in the figure) is 
redirected by the illumination ring 231 and is allowed to pass through the 
annular opening 543 defined by the shielding ring 227 and the cover 236. 
The shielding ring 227 contains the optical detector 222 and prevents 
light from reaching the optical detector 222 unless the light is reflected 
or scattered by a body part of a test subject. Not shown are the wires 
connecting electronic circuits to both the optical detector 222 and the 
infrared light emitting devices 400. The electronic circuits required for 
both are well known in the art, and may be incorporated into the light 
probe 500 or may be incorporated into the measurement instrument. Also 
shown is the compressible ring 536, which may be optionally included as 
part of the light probe 500. The compressible ring 536 is positioned 
around the outer circumference of the light probe 500, and extends above 
the cover 236 on the light probe face that contacts a body part under 
test. The compressible ring 536 may be made of a soft opaque foam, which 
when compressed in use prevents external light from entering the light 
probe 500. 
FIG. 6 shows a section view of a light probe 600 of a second embodiment of 
the invention along the section line B--B of FIG. 2. In this embodiment, 
the shape of the illumination ring 231 and the shielding ring 227 are 
different. The angled surface of the light probe 600 exists on the outer 
circumferential surface of the shielding ring 227 instead of on the inner 
circumferential surface of the illumination ring 231. The infrared light 
passes through the illumination ring 231 in a radially inward direction 
and is redirected in an axial direction by the shielding ring 227. In this 
embodiment, the angled surface of the shielding ring 227 may be silvered 
or may alternatively be made of aluminum having a polished angled surface 
for redirecting light. 
The light probe 200 can be standardized (calibrated) in a manner described 
in commonly owned U.S. Pat. No. 4,990,772, which is herein incorporated by 
reference. Alternatively, standardization may be performed by taking 
advantage of the small amount of infrared light that leaks directly 
through the angled surface 248 of the illumination ring 231. This small 
light leakage does not interfere with the measurement. The leaked light 
can be used to eliminate the need for an external optical standard. 
Internal standardization is accomplished by positioning a reference 
optical detector (not shown in the figures) inside the light probe 200 to 
pick up light leakage. When any infrared light emitting device 400 is 
activated (before or after the body part is placed on the probe), the 
leaked light is picked up by the reference optical detector. If the output 
of the infrared light emitting device 400 has drifted or diminished, a 
simple correction can be made according to the following equation: 
EQU E.sub.M CORRECTED =E.sub.M *(E.sub.RF /E.sub.RN); 
where E.sub.M CORRECTED =the value of the measurement of the optical 
detector 222 after being corrected by the reference detector, E.sub.M =the 
energy that reaches the optical detector 222 when a body part is placed on 
the light probe 200, E.sub.RF =the energy that reached the reference 
detector at the time the unit was originally calibrated, and E.sub.RN =the 
energy that reached the reference detector just prior to or just after the 
body part is placed on the probe. Therefore, the actual measurement is a 
ratio of the light that reaches the optical detector 222 after interacting 
with the body part, to the light captured by the reference detector built 
into the light probe 200. Multiple reference detectors may be employed if 
needed. This standardization approach would be highly valuable in a 
typical automated application where calibration by an external physical 
optical standard would be very inconvenient. 
While the invention has been disclosed in detail above, the invention is 
not intended to be limited to the invention as disclosed. It is evident 
that those skilled in the art may now make numerous uses and modifications 
of and departures from the specific embodiments described herein without 
departing from the inventive concepts.