Optical measuring instrument

Details Optical measuring instrument Optical measuring instrument

2001-05-24

2003-08-26

Walberg, Teresa (Department: 3742)

Surgery

Diagnostic testing

Measuring or detecting nonradioactive constituent of body...

C600S322000, C600S335000, C600S473000, C600S340000

Reexamination Certificate

active

06611698

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an optical measuring instrument and especially to the optical measuring instrument suited for optical measurement of in vivo information.
BACKGROUND OF THE INVENTION
The field of clinical medicine and brain science are eagerly expecting to have a measuring instrument which allows easy measurement of in-vivo blood circulation, hemodynamics and oxygen metabolism without giving much restriction to an examinee as a test object or being hazardous to a living body. In the case of cerebral measurement, for example, specific needs for such an instrument are found in the measurement and diagnosis of cerebral diseases such as brain infarction, intracerebral bleeding and dementia as well as high order cerebral functions such as thinking, language and bodily movement. Further, such objects for measurement are not restricted to the brain alone. Such a measuring instrument is needed for preventive diagnosis of such heart diseases as heart infarction on the pectoral region and viscera diseases related to kidney and liver on the abdominal region, as well as for the measurement of oxygen metabolism in limb muscles.
For simplicity, let us restrict the object to the cerebral region alone. In the measurement and diagnosis of intracerebral diseases or high order cerebral functions, it is necessary to specify the affected site or functional region clearly. This leads of the importance of cerebral image measurement. It goes without saying that the importance of image measurement is not restricted to the cerebral region. It also applies to the pectoral and abdominal region. Examples of showing its importance can be found in the positron emission tomographic equipment (PET), functional nuclear magnetic resonance tomographic equipment (fMRI) and magnetoencephalopgraphic equipment (MEG) which are placed in extensive use as image measuring instruments for cerebral functions in recent years.
These devices have an advantage of measuring intracerebral active areas in the form of images on the one hand. On the other hand, they have an disadvantage of being large-sized and requiring complicated handling procedures. For example, installation of these devices requires large room specifically designed for their use. It goes without saying that relocation of the devices is practically impossible. Further, an examinee is confined in a device and is required to keep the same posture for a long time during the measurement. Further, the examinee has to endure severe psychological pain in addition to this heavy physical restriction. Further, such devices require special personnel assigned for maintenance and management, with the result that huge costs will be involved in the operation of the system.
By contrast, optical measurement provides an effective means to ensure easy measurement of in-vivo blood circulation, hemodynamics and oxygen metabolism without giving much restriction to examinee or being hazardous to living body. The first reason is that the blood circulation and oxygen metabolism of the living body correspond to the concentration and its change of specific pigments (hemoglobin, cytochrome, mioglobin, etc.) in the living body, and the concentration of these pigments can be obtained from the light absorbency index of the wavelength from visible to infrared ray ranges. Said blood circulation and oxygen metabolism correspond to the normal/abnormal state of the in-vivo organs and activation of the brain with respect to high order cerebral functions. The second reason to account for effective optical measurement is that the device can be the downsized and simplified by the technologies related to semiconductor laser, light emitting diode and photodiode. Further, the head need not be fixed in position during measurement by use of flexible optical fiber for measurement. This greatly reduces the restriction on the examinee and minimizes psychological pains. The third reason is that light intensity is kept within the Safety Standard (ANSIZ 136-1973, JISC6802 Standard: 2 mW/mm
2
). Thus, the living body is not harmed by application of the light.
In addition to these advantages, optical measurement has advantages which cannot be found in said PET, MRI or MEG, for example, real time measurement, quantification of the concentration of pigment in the living body.
For example, the Japanese Patent Laid-Open NO. 115232/1982 and Japanese Patent Laid-Open NO. 275323/1988 disclose and claim a system wherein light with wave lengths from visible to infrared ray ranges is applied to the living body by effective use of the advantages of optical measurement, and in-vivo measurement is achieved by detecting the light passing through the living body by reflection therein. Further, a system of converting the living body in images by optical measurement is disclosed and claimed in the Japanese Patent Laid-Open NO. 19408/1997 and Japanese Patent Laid-Open NO. 149903/1997. The usefulness of image measurement of the living body using said light is also described, for example, in Atsushi Maki, et al. “Spatial and temporal analysis of human motor activity using noninvasive NIR topography”, 1995, Medical Physics, Vol. 22, P.P. 1997 to 2005).
Generally, high time resolution and high-precision measurement are essential factors in the measurement of living bodies. In the system disclosed in said Japanese Patent Laid-Open NO. 149903/1997, a high time resolution is achieved by simultaneous measurement of multiple wavelengths required to measure the image of changes in the concentration of the living body pigment such as hemoglobin and multiple channels at multiple positions.
FIG. 14
shows the over view of the system disclosed in the Japanese Patent Laid-Open NO. 149903/1997. This system allows light to be applied to multiple positions of the examinee, and detects light at the multiple positions.
In this case, the intensity of light is modulated at the frequency different for each of the positions where light is applied. For example, modulation frequencies for the light applied from light applied positions
1
,
2
,
3
and
4
in
FIG. 14
are assumed as f
1
, f
2
, f
3
and f
4
, respectively. Therefore, these modulation frequencies provide position information corresponding to each position where light is applied. Here the light detected at light detection position
1
includes all the modulated light. For signals output from the photodiode, however, light measurement signal on position information can be separately measured by selective measurement of each modulation frequency signal in a filter circuit of the lock-in amplifier or the like. For example, when each detection signal levels by modulation frequencies f
1
, f
2
, f
3
and f
4
detected by the photodiode corresponding to this light detection position
1
are assumed as I
1
, I
2
, I
3
and I
4
, each signal is completely separated from others in the output of each lock-in amplifier synchronized at each frequency. As a result, effective simultaneous multi-channel measurement can be implemented since there is no crosstalk between measurement signals.
To get the final image from such measurement, however, a high measurement precision is required for each signal. If these detection signals contains a signal whose precision or S/N ratio is considerably low, for example, reliability of the measurement site corresponding to the signal will be reduced on the image, and this will lead to reliability of the image itself. This requires high-precision measurement with satisfactory S/N balance for all detection signals. However, the conventional devices have the following problems with respect to this measurement precision:
The state in the living body is optically uneven in normal cases. If arrangement is so made that light is to be applied to the site containing a large quantity of hemoglobins as light absorbers such as large blood vessel or light is detected at such a site, there will be attenuation of light and a considerable reduction in said detection signal level. Thus, another cause for reduction of the detection signal level i

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