Measurement System and Method for Measuring Living Bodies

Abstract

A living body measurement system including a cerebral blood volume measurement unit for measuring a regional cerebral blood volume of a subject, an arterial pressure/heart rate measurement unit for measuring an arterial pressure and/or a heart rate of the subject, an analysis unit for analyzing signals measured by the cerebral blood volume measurement unit and the arterial pressure/heart rate measurement unit, an extraction unit for extracting information concerning a regional cerebral vascular state of the subject on the basis of an output of the analysis unit, and a display unit for displaying a measurement result measured by the cerebral blood volume measurement unit and/or the arterial pressure/heart rate measurement unit, an analysis result analyzed by the analysis unit, or an extraction result extracted by the extraction unit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a configuration of a living body measurement system;

FIG. 2 shows an input screen of the living body measurement system;

FIG. 3 shows an example of a measurement probe;

FIGS. 4A and 4B show low frequency components of a power spectrum;

FIG. 5 shows a result display example;

FIG. 6 shows a processing flow in an analysis unit and an extraction unit;

FIG. 7 is a standard vascularity diagram;

FIG. 8 shows result display with sensitivity distribution information attached;

FIG. 9 shows an adjustment procedure for thresholds TH1 and TH2; and

FIG. 10 shows utilization of history information of the same subject.

DESCRIPTION OF THE EMBODIMENTS

(1) FIG. 1 shows a configuration of a system. The present system includes an input unit, an analysis unit, a storage unit and an extraction unit included in a computer 112, a cerebral blood volume measurement unit 120, an arterial pressure/heart rate measurement unit 130 and a display unit 113. If the computer 112 has the display function, the computer 112 can be substituted for the display unit 113.

In the input unit, information required for the test, for example, the age, the distinction of sex and the handedness of the subject, diagnosis information such as a diagnosis at the current time point and treatment history, in particular, whether there is a confirmed diagnosis result are input by an operator. How an input screen is displayed is shown in FIG. 2. In this example, the subject is identified by using a patient No. However, the name may be used. If there is a confirmed diagnosis result, a square in item No. 1 is checked. In that case, test results are stored in a database automatically.

The regional cerebral blood volume (oxyhemoglobin, deoxyhemoglobin, and total hemoglobin) is obtained in the cerebral blood volume measurement unit 120 by exposing a head of the subject to light having a wavelength belonging to the visible region to the infrared region, and detecting and measuring light beams of a plurality of signals passed through the inside of the subject by using the same photodetector.

A plurality of light sources 102a to 102d have wavelengths that are different from each other. (The light sources 102a and 102c have a wavelength of 780 nm, and the light sources 102b and 102d have a wavelength of 830 nm.) Modulators conduct strength modulation on light beams emitted from the light sources 102a and 102b (102c and 102d) by using oscillators 101a and 101b (101c and 101d) having different frequencies. A coupler 104a (104b) couples light beams subjected to strength modulation, through optical fibers 103a and 103b (103c and 103d). A plurality of light irradiation means applies a light beam from the coupler 104a (104b) to different positions on a scalp of a subject 106 via a light irradiation optical fiber 105a (105b). A plurality of light sensing optical fibers 107a to 107f are provided so as to have tips positioned in the vicinity of light irradiation positions of the light irradiation means and at equal distances (which are supposed to be 30 mm here) from the light irradiation means. A plurality of light sensing means formed of light sensors 108a to 108f are provided respectively for the light sensing optical fibers 107a to 107f. Light beams transmitted through the living body are collected by using the six light sensing optical fibers 107a to 107f, and subjected to photoelectric conversion in the light sensors 108a to 108f. The light sensing means detect light beams reflected within the subject and convert them to electric signals. As the light sensors 108, photoelectric conversion elements represented by photomultipliers or photodiodes are used.

The electric signals (hereafter referred to as living body passed light strength signals) representing living body passed light strength obtained by photoelectric conversion conducted in the light sensors 108a to 108f are input to lock-in amplifiers 109a to 109h. The light sensors 108c and 108d detect the living body passed light strength collected by the light sensing optical fibers 107c and 107d located at equal distances from the light irradiation optical fibers 105a and 105b. Therefore, each of signals from the light sensors 108c and 108d is separated into two systems. Thus, the signal from the light sensor 108c is input to the lock-in amplifiers 109c and 109e, and the signal from the light sensor 108d is input to the lock-in amplifiers 109d and 109f. Strength modulation frequencies from the oscillators 101a and 101b are input to the lock-in amplifiers 109a to 109d as reference frequencies. Strength modulation frequencies from the oscillators 101c and 101d are input to the lock-in amplifiers 109e to 109h as reference frequencies. Therefore, living body passed light strength signals for the light sources 102a and 102b are separated and output from the lock-in amplifiers 109a to 109d, and living body passed light strength signals for the light sources 102c and 102d are separated and output from the lock-in amplifiers 109e to 109h.

The separated passed light strength signals for respective wavelengths output from the lock-in amplifiers 109a to 109h are subjected to analog-digital conversion in an analog-digital converter 110, and resultant digital signals are sent to a measurement control computer 111. The measurement control computer 111 computes relative change quantities of the oxyhemoglobin concentration, deoxyhemoglobin concentration, and total hemoglobin concentration from signals detected at the detection points according to the procedure described in the non-patent document 1 by using the passed light intensity signals, and stores them in the storage unit as information at the plurality of measurement points with time.

Herein an embodiment in which a plurality of light beams are separated by using the modulation method has been described. However, this is not restrictive, but, for example, a time division method of discriminating a plurality of light beams by shifting timing of applying a plurality of light beams in time can also be used.

On the other hand, the arterial pressure/heart rate measurement unit 130 measures the heart rate and/or the arterial pressure by using the photoplethysmography. A cuff 122 is attached to a finger tip, and the heart rate is detected by optical detection and the arterial pressure (systolic arterial pressure, diastolic arterial pressure, and average arterial pressure) are detected simultaneously. The arterial pressure value is interpolated at a sampling frequency of 200 Hz in a signal processing unit 121, and sent to the analysis unit in the computer 112. Herein, the arterial pressure/heart rate measurement unit 130 for measuring the heart rate and the arterial pressure is shown. However, it is sufficient if either the heart rate or the arterial pressure can be measured. Herein, the photoelectric volume pulse wave recording is used because of easiness of handling. However, it is also possible to use an electrocardiograph for the hear rate and use an invasive sphygmomanometer for the arterial pressure.

The analysis unit analyzes the power spectra of the measured regional cerebral blood volume and the arterial pressure or heart rate. Results of them are delivered to the storage unit in the computer 112.

The storage unit temporarily stores the measurement information on the subject to make subsequent processing possible. On the other hand, for example, if there is a confirmed diagnosis, it is also possible to store the measured information as a database. The database information is used not only when the parameter automatic adjustment is conducted as described later, but also when making a diagnosis on the basis of results of the test conducted by the present system.

The extraction unit in the computer 112 extracts information concerning the cerebrovascular disease from the power spectrum of the signal analyzed by the analysis unit and quantitative information concerning the power spectrum according to a method described later. The information concerning the cerebrovascular disease extracted by the extraction unit is displayed by the display unit 113.

In FIG. 1, the computer 111 and the computer 112 are drawn separately. However, it is a matter of course that one computer may be used instead of the computer 111 and the computer 112.

FIG. 3 schematically shows a probe for measuring the cerebral blood volume. Cz, T3 and T4 are characters indicating standard positions for electroencephalogram measurement, and represent the vertex, a part located immediately above the left ear, and a part located immediately above the right ear, respectively. C3 and C4 denote the middle point between Cz and T3 and the middle point between Cz and T4, respectively. Measurement is possible for 12 left channels and 12 right channels, i.e., 24 channels in total. Each channel is identified by a number (hereafter referred to as channel number) given to a measurement point.

Examples of the power spectrum obtained by the analysis unit are shown in FIGS. 4A and 4B. FIG. 4A shows an average value (represented as AP/HR) of a power spectrum obtained from the arterial pressure (AP) and heart rate (HR). FIG. 4B shows a power spectrum of the regional cerebral blood volume (CBV). The ordinate represents the power spectral density (PSD). The power spectral density is normalized so as to yield unity when power is integrated with respect to the frequency. The frequency on the abscissa is a coordinate corresponding to a time axis obtained by conducting Fourier transform on the arterial pressure & heart rate which is time series data, and includes a range from zero Hz to the Nyquist frequency (half of the sampling frequency). FIGS. 4A and 4B show a part thereof. The arterial pressure & heart rate shown in FIG. 4A has been measured by attaching a probe to the third finger of the left hand and using the arterial pressure/heart rate measurement unit 130. A result shown in FIG. 4B has been calculated from the regional cerebral blood volume measured on the channel 4 in FIG. 3. The arterial pressure & heart rate is compared with the regional cerebral blood volume with respect to a power ratio R_p. Here, the power ratio R_p is represented as R_p=P_LF/P_VLF and it is the ratio of average power P_LF in a low-frequency (LF) region (0.07-0.11 Hz) to average power P_VLF in a very-low-frequency (VLF) region (0.01-0.05 Hz). As a result, it is appreciated that the arterial pressure & heart rate is greater in power ratio R_p than the regional cerebral blood volume. Fluctuations in these regions deeply relate to the regulation function of the vascular system. The regulation is dominated by a vasomotor center, a sympathetic nerve, a parasympathetic nerve (vagus nerve) or the like. However, the fluctuations are partly neurogenic and partly myogenic. According to the non-patent documents 2 and 3 written by Schroeter etc., the LF region component of the cerebral blood volume is weakened by aging, whereas a large change is not noticed in the VLF region component, and both the LF region component and the VLF region component of the cerebral blood volume are weakened by the microangropathy, but the LF region component is weakened more violently. Changes caused by aging have deep relations to the fiberization of a smooth muscle, and changes caused by the microangropathy have deep relations to an occlusion and sclerosis phenomenon caused in a thin small blood vessel by a thrombus. Any change is considered to have been caused by degeneration in a smooth muscle. The power ratio R_P tends to be decreased in value by either of aging and the microangropathy. In other words, it can be said that fluctuations in the LF region are more myogenic than those in the VLF region. Results in FIGS. 4A and 4B indicate that on average the blood vessel in the finger tip is softer as to the vascular stiffness.

In the present invention, the power ratio R_p, which is the ratio of the average power P_LF in the LF region (0.07-0.11 Hz) to the average power P_VLF in the VLF region (0.01-0.05 Hz), is used as an index for the vascular stiffness. For the above-described reason, the power ratio R_p becomes a parameter reflecting the vascular stiffness. As described above, the power ratio R_p is calculated on the basis of the average power values in respective regions. Or the power ratio R_p may be calculated from a ratio between power integral values in corresponding frequency regions. In addition, if the 1/f spectrum component in the power spectrum is previously removed at that time, the vascular property can be evaluated more accurately. The 1/f spectrum component is a spectrum structure that does not have a characteristic frequency and that is often observed in the power spectrum of a living body, especially the artery pressure & heart rate. It is considered that the 1/f spectrum component represents that the variabilities in artery pressure and heart rate are generated from a complicated feedback structure. However, details of the generation mechanism are still unknown.

The method for previously removing the 1/f spectrum component will be described hereafter. First, the power spectrum is plotted in full logarithmic exhibition, and the low frequency part is approximated by a straight line.

log P(f)=−α log f+β  [Expression 1]

A slope a represents an exponent of the 1/f spectrum component. These parameters α and β are determined by using the least square method, and a spectrum with the straight line part removed is calculated. When conducting the least square calculation, the data of the LF region and the VLF region are not included. In FIGS. 4A and 4B, this processing has been conducted.

The vessel in that region is judged to be stiffer as the power ratio R_p thus found becomes smaller. In addition, power ratios respectively obtained from the arterial pressure & heart rate and the regional cerebral blood volume are denoted by R_p(AP/HR) and R_p(CBV), respectively. Hereafter, AP, HR and CBV in a parenthesis represent a relation to the artery pressure, the heart rate and the regional cerebral blood volume, respectively. As for the arterial pressure & heart rate, a power spectrum is found from each of the arterial pressure and the heart rate independently. An average of resultant power spectra is found and regarded as a power spectrum of the arterial pressure & heart rate. The power ratio R_p is calculated on the basis of the averaged power spectrum. Instead of using both the arterial pressure and the heart rate, only either the arterial pressure or the heart rate may be used. At that time, indication AP or HR is used so as to correspond to actually used data, instead of the indication AP/HR. The power ratios obtained from the arterial pressure & heart rate and the regional cerebral blood volume are represented by the following expressions.

R _p(AP/HR)=P_LF(AP/HR)/P_VLF(AP/HR)   [Expression 2]

R _p(CBV)=P_LF(CBV)/P_VLF(CBV)   [Expression 3]

In the present embodiment, the test for the vascular disease is conducted by using these relations (the expressions 2 and 3) and the following two criteria.

<1>

When

R _p(AP/HR)<TH1   [Expression 4]

or

R _p(CBV)<TH1,   [Expression 5]

a cerebral vascular disease tends to occur.<2>

In a region satisfying the (expression 4 or 5) and

R _p(CBV)/R_p(AP/HR)<TH2,   [Expression 6]

a cerebral vascular disease especially tends to occur.

The extraction unit extracts information concerning the cerebral vascular disease in accordance with the two criteria. The threshold TH1 is set equal to 0.1. This is determined on the basis of a preliminary study conducted on subjects that are medically sufficient in number. Automatic parameter adjustment based on some data of a confirmed diagnosis will be described later. The criterion <1> detects general vascular stiffness. Although it is difficult to determine which of the genetic condition and living custom causes the stiffness, it is guessed that a subject satisfying this criterion is in a state in which a cerebral vascular disease is apt to occur. On the other hand, in the criterion <2>, a preventive diagnosis of the cerebral vascular disease is conducted paying attention to an especially small power ratio which is seen in the cerebral blood volumes of some subjects. A very great deal of blood is circulating through the brain as compared with other organs. It is considered that this is apt to cause the sclerosis phenomenon of the cerebrovascular system and this relates to an especially small power ratio seen in the cerebral blood volume. The threshold is set equal to TH2=0.2, and this criterion is regarded as being satisfied when the power ratio found by using the arterial pressure and/or the heart rate is at least five times large. This value has also been determined on the basis of a preliminary study conducted on a comparatively small number of subjects. If data of confirmed diagnoses are stored as database in the future, improvement can be made by the automatic parameter adjustment function described later.

In the present embodiment, one left channel and one right channel satisfy the criterion <1>. The display unit displays the results as shown in FIG. 5. Here, the risk of the cerebral vascular disease is displayed in the following three stages. A first stage is displayed with white to indicate that there is no problem. A second stage is displayed with gray to indicate that care must be taken and the progress should be observed. A third stage is displayed with black to indicate that a close test is required. In this example, a great part is in the first stage and only two channels are in the second stage.

FIG. 6 shows a flow of processing conducted especially in the analysis unit and the extraction unit ranging from the acquisition of measured data to the result display. The power spectra are calculated from the measured data of the cerebral blood volume and the arterial pressure or the heart rate by using the Fast Fourier Transform (FFT). As for the power spectrum calculation method, there are various methods such as nonparametric methods like the Welch method and parametric methods like the Yule method. Any of these methods may be used. Subsequently, the 1/f spectrum component is removed from the obtained power spectra by using the above-described method, and the power ratios R_P(AP/HR) and R_P(CBV) are calculated according to the above-described method. The extraction unit extracts information concerning the cerebral vascular disease on the basis of the obtained power ratios and the criteria <1> and <2>. The display unit displays results.

(2) However, these results are susceptible to the influence of the vascularity. It is important to conduct an analysis with the influence of the vascularity taken into consideration. Hereafter, a measurement method with the influence of the vascularity taken into consideration will be described.

First, a sensitivity map is created according to the measurement regions from a standard vascularity diagram previously stored in the storage unit. An example of the standard vascularity diagram is shown in FIG. 7. A dotted line roughly represents the distribution of the cerebral tissue. Here, arterial distribution is represented by thick solid lines. The anterior cerebral artery, the middle cerebral artery and their terminal branches are included. The standard vascularity diagram is bisymmetrical. The standard vascularity diagram is prepared for the frontal, the parietal and the occipital areas as well besides the temporal area. A procedure for creating a sensitivity map on the basis of the standard vascularity diagram will now be described. In the present embodiment, a sensitivity map of two stages is created. The standard sensitivity is set equal to 1, and the sensitivity is set equal to 0.5 in a region where a comparatively thick artery is located. The power ratio R_P appearing in the expression 2 or 3 is corrected with the sensitivity. The correction is conducted by dividing the measured power ratio by the sensitivity. According to the non-patent documents 2 and 3, a motion of a thickish blood vessel is apt to appear in the VLF region strongly, and the VLF region variation is nerval motion and is hardly susceptible to the influence of aging and the microangropathy. The above-described correction has been determined by taking such facts into consideration. Especially thick blood vessels show a marked trend toward absorption of the light beam, and it is necessary to conduct measurements while avoiding positions of them as far as possible. It is possible in the display unit 113 to display sensitivity distribution obtained from the standard vascularity information together. In the case of the present embodiment, the display becomes as shown in FIG. 8. It is indicated that the sensitivity becomes 0.5 at channel Nos. 8 and 22.

In a region having a thick blood vessel, detected light tends to become weak, and consequently it can be denied that the reliability becomes low. Therefore, such information is information that is useful to the user.

(3) The thresholds used in extraction of the information concerning the cerebral vascular disease can be improved by storing data. The present system has an automatic adjustment function for that purpose. A threshold adjustment procedure is summarized in FIG. 9. First, channels of data obtained from a confirmed diagnosis are classified into three stages: “no problem”; “care must be taken (progress should be observed)”; and “close test is required”. The threshold TH1 is optimized on the basis of the information of the power ratio stored in the storage unit. TH1 is a threshold for separating the first stage from the rest. TH1 is determined so as to maximize the average of the correct answer rates in respective groups. The threshold TH2 is optimized. TH2 is a threshold for separating the second stage from the third stage. TH2 is determined so as to maximize the average of the correct answer rates in respective groups. It is possible to change the thresholds to more suitable values by thus conforming to the confirmed diagnosis information.

(4) In the present system, it is possible to provide information useful to the diagnosis and treatment by suitably displaying serially stored history information such as measured, analyzed and extracted information of the same subject. One example is shown in FIG. 10. Measurements are conducted on the subject once per month for half a year, i.e., six times in total. Until July, the risk is in the second stage (care must be taken). From August on, the risk is in the first stage (no problem). It is considered to be an effect of treatment conducted during that time. It is also possible to evaluate an effect of a specific treatment by thus utilizing the history information.

The present invention can be applied to a measurement system and method for measuring living bodies to conduct noninvasive cerebrovascular disease tests.

It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.

Claims

1. A living body measurement system comprising: a cerebral blood volume measurement unit for measuring a regional cerebral blood volume of a subject;an arterial pressure/heart rate measurement unit for measuring an arterial pressure and/or a heart rate of the subject;an analysis unit for analyzing signals measured by the cerebral blood volume measurement unit and the arterial pressure/heart rate measurement unit;an extraction unit for extracting information concerning a regional cerebral vascular state of the subject on the basis of an output of the analysis unit; anda display unit for displaying a measurement result measured by the cerebral blood volume measurement unit and/or the arterial pressure/heart rate measurement unit, an analysis result analyzed by the analysis unit, or an extraction result extracted by the extraction unit.

2. The living body measurement system according to claim 1, wherein the analysis unit analyzes power spectra of signals measured by the cerebral blood volume measurement unit and the arterial pressure/heart rate measurement unit.

3. The living body measurement system according to claim 2, wherein the extraction unit calculates a first power strength ratio in a first frequency band and a second frequency band of an artery pressure and/or a heart rate and a second power strength ratio in the first frequency band and the second frequency band of a regional cerebral blood volume on the basis of the output of the analysis unit, and extracts information concerning a cerebral vascular state on the basis of whether the first power strength ratio and/or the second power strength ratio is greater than a first threshold.

4. The living body measurement system according to claim 3, wherein the extraction unit extracts information concerning the cerebral vascular state on the basis of whether the first power strength ratio and the second power strength ratio is greater than a second threshold.

5. The living body measurement system according to claim 3, wherein the first frequency band is in a range of 0.01 to 0.05 Hz, and the second frequency band is in a range of 0.07 to 0.11 Hz.

6. The living body measurement system according to claim 2, wherein the analysis unit conducts processing of removing a 1/f spectrum component from the power spectra.

7. The living body measurement system according to claim 1, further comprising an input unit for inputting living body information and/or diagnosis information of the subject.

8. The living body measurement system according to claim 1, wherein the display unit classifies the information concerning the regional cerebral vascular state of the subject into classes for each region in the head.

9. The living body measurement system according to claim 1, wherein the display unit displays history of past diagnosis information of the subject.

10. The living body measurement system according to claim 1, further comprising a storage unit for storing a measurement result measured by the cerebral blood volume measurement unit and/or the arterial pressure/heart rate measurement unit, an analysis result analyzed by the analysis unit, or an extraction result extracted by the extraction unit as a database,wherein the extraction unit extracts the information concerning the regional cerebral vascular state of the subject on the basis of the database stored in the storage unit and an output of the analysis unit.

11. The living body measurement system according to claim 10, wherein the database stores standard cerebral vascularity information, andthe extraction unit conducts sensitivity correction in each cerebral region for the subject on the basis of the standard cerebral vascularity information.

12. The living body measurement system according to claim 4, further comprising a storage unit for storing confirmed diagnosis information of a plurality of subjects,wherein the extraction unit determines magnitude of the first threshold and/or the second threshold so as to maximize a correct answer rate of the extraction on the basis of the confirmed diagnosis information.

13. The living body measurement system according to claim 1, wherein the cerebral blood volume measurement unit comprises: a plurality of light irradiation means for applying light beams to a head of the subject;a plurality of light sensing means for detecting light beams applied from the light irradiation means and passed through a head of the subject; anda computing unit for calculating a blood volume change of the head of the subject on the basis of light beams detected by the light sensing means.

14. A living body measurement method comprising the steps of: measuring a regional cerebral blood volume of a subject;measuring an arterial pressure and/or a heart rate of the subject;analyzing the measured regional cerebral blood volume and the measured arterial pressure and/or heart rate; andextracting information concerning a regional cerebral vascular state of the subject on the basis of information obtained by the analysis.

15. The living body measurement method according to claim 14, wherein the analyzing step comprises a step of analyzing power spectra of the measured regional cerebral blood volume and the measured arterial pressure and/or heart rate.

16. The living body measurement method according to claim 15, wherein the extracting step comprises a step of calculating a first power strength ratio in a first frequency band and a second frequency band of the artery pressure and/or the heart rate and a second power strength ratio in the first frequency band and the second frequency band of the regional cerebral blood volume on the basis of an analysis result obtained at the analyzing step, and extracting information concerning the cerebral vascular state on the basis of whether the first power strength ratio and/or the second power strength ratio is greater than a first threshold.

17. The living body measurement method according to claim 16, wherein the extracting step comprises a step of extracting information concerning the cerebral vascular state on the basis of whether the first power strength ratio and the second power strength ratio is greater than a second threshold.

18. The living body measurement method according to claim 16, wherein the first frequency band is in a range of 0.01 to 0.05 Hz, and the second frequency band is in a range of 0.07 to 0.11 Hz.

19. The living body measurement method according to claim 15, wherein the analyzing step comprises a step of conducting processing of removing a 1/f spectrum component from the power spectra.