JPH0698890A - Optical ct apparatus - Google Patents

Abstract

PURPOSE:To enable the learning of the position of an object within a scattering/ absorbing object, a density distribution of a chemical substance and the like by admitting a pulse light with a multiple wavelength to analyze a hourly difference of an output waveform. CONSTITUTION:A relationship between the elapsed time from the incidence of light and a quantity of light emitted is determined to be converted to a time solving intensity waveform. The existence of substances 3 different in absorption coefficient affects a quantity of light greatly in a scatting/absorbing object 2. Hence, when DELTAt represents time to the moment at which an absorption difference appears from the shortest arrival time, a distance L' can be learned between a straight line aligning the incident position and a detection position and the object 3. An optical CT image of a sample 2, namely, a tomographic image is obtained when a measurement is performed varying the incident direction with detectors 1 arranged on the entire circumference of the sample 2. A curve 7 of values obtained by dividing a difference between a detection waveform 5 with a wavelength of 803nm and the detection waveform 6 with the wavelength of 810nm by an output of 803nm indicates a certain fixed value, namely, a ratio of absorption values in the 803nm and 810nm (existence ratio in object between Hb and HbO2) when the elapsed time is large enough.

Description

Detailed Description of the Invention

[0001]

The present invention relates to the shape, position, concentration distribution of chemical substances, etc. of an object having different properties from the surrounding object inside an opaque scattering / absorbing object in the medical and industrial fields. The present invention relates to an optical CT device that measures based on the optical properties of an object.

[0002]

2. Description of the Related Art Conventionally, an ultrasonic diagnostic apparatus, an X-ray CT apparatus, and the like are known as methods for measuring the internal structure or state of a scattering / absorbing object such as living tissue using light. Among these, an optical CT device that has recently been attracting attention is an optical CT device that performs internal measurement by utilizing the optical properties of a substance. The reason why optical CT is attracting attention in spite of poor resolution compared to X-rays is that conventional CT such as X-ray CT can only understand the structure of tissue, but optical CT provides new information on the activity status of tissue. Is obtained.

Utilization of the optical properties of an object is made by paying particular attention to the light absorption characteristic of the substance to be inspected. In the case of optical CT, a wavelength in the near-infrared region of 700 to 1300 nm, which has appropriate transmittance in living tissue and has little scattering and absorption by water, is usually used for measurement. By using this wavelength range, it is possible to know the amount of oxygen that is closely related to the function of the living body. The problem in the case of biometrics is that the target object not only simply transmits and absorbs light, but also has a scattering characteristic, and the light is mixed in the detection signal to deteriorate the SN.

The methods proposed so far are, for example, Japanese Patent Laid-Open No. 2-290534 or Japanese Patent Laid-Open No. 3-11.
There is a method such as Japanese Patent No. 1737 in which continuous or pulsed parallel light is made incident on a scattering / absorbing body which is an object, and the light which reaches a detector in the shortest time or the shortest distance is detected. That is, a time gate method, a heterodyne method, etc. have been proposed for only the light that has gone straight without being scattered internally.

[0005]

However, in the above-mentioned conventional example, as the thickness and the concentration of the scatterer increase,
There is a problem in that the light that travels straight without being scattered inside is sharply reduced. Since the decrease occurs exponentially, the drop of the light amount is serious and often becomes undetectable, which is a major obstacle to practical use. Apart from being applied to experimental small animals, solving the problem of light quantity is an essential requirement for full-scale introduction to human body measurement. The present invention has been made in view of the above problems, and an object of the present invention is to provide an optical CT apparatus that can be applied to a thick and dense scattering object.

[0006]

Therefore, the present invention is capable of measuring an object by analyzing a waveform while detecting scattered light over time, instead of detecting straight light which is difficult to detect in practice. Is characterized by. More specifically, a scattering / absorbing material sample such as a living body is irradiated with ultrashort pulsed light of multiple wavelengths, scattered / absorbed inside, and scattered light emitted out of the sample is time-sequentially. The position of an object inside the sample, the concentration of the chemical substance, the optical characteristics, etc. are obtained by analyzing the relationship between the detected light amount, which is the obtained waveform, and the arrival time. In order to detect scattered light, measurements are made at several locations on the sample in opposition to the incident light. Further, the light used has a known wavelength that is absorbed by the target sample and another wavelength that receives a different amount of absorption.

The analysis of the obtained waveform is performed using a straight-ahead light, that is, a signal in the time domain delayed by a predetermined value from the signal obtained in the shortest time. The time range delayed from the straight-ahead light is closely related to the object position and optical characteristics inside the sample, and affects the amount of scattered light. It is difficult to detect non-scattering straight-ahead light with a high-concentration scattering / absorbing body, but it is possible to know the internal state of the sample by using the signal of scattered light with much higher intensity and calculating backward from the signal. is there.

[0008]

Embodiment 1 FIG. 1 is a schematic view of the essential portions of Embodiment 1 of the present invention, which best shows the features of the present invention. In the figure, 1 is a photodetector, 2 is a scattering / absorbing material sample, 3 is 2
Is an object with different absorption from the outside in the sample of
This corresponds to the internal structure of the sample. For example, in the above configuration, Hb (hemoglobin) and Hb in the biological tissue
When the concentration distribution of O ₂ (oxygenated hemoglobin) is measured, 2 corresponds to muscle tissue and 3 corresponds to the blood-rich liver.

In biological measurement, an object having a scattering / absorption coefficient different from that of the sample is contained in the sample of the scattering / absorbing material, and the measurement is performed using a special wavelength whose absorption characteristic for the object is known in advance. . Since Hb carries oxygen, the concentration of Hb and HbO ₂ is measured, and the ratio of the concentrations of both is calculated to obtain the oxygen saturation of Hb. The oxygen saturation is an amount indicating the supply state of oxygen to the living tissue, which indicates whether or not blood normally carries oxygen, and is an index for determining a functional change occurring in the living body. The absorption characteristics of HbO ₂ combined with Hb and oxygen in the near infrared region are different,
This characteristic is used in this embodiment.

In the case of FIG. 1, 803 nm is used as the wavelength and 810 nm, which is a wavelength slightly deviated from the wavelength, is used, and the light of the two wavelengths becomes an extremely short pulse light of the psec order, and the sample 2 is obtained. It is incident from the left. A laser light source (not shown) is used as the light source. 803 nm is Hb
At a special wavelength corresponding to the isosbestic wavelength of HbO ₂ and HbO ₂ , absorption does not change whether Hb is oxygenated or deoxygenated. At 810 nm, Hb and HbO ₂ have different absorption amounts,
It can be considered that the scattering aspect is almost the same as 803 nm because the wavelengths are close.

The incident light propagates in the sample while being scattered and absorbed. Since it is the information about the object 3 that is desired to be detected, the 810 nm light having a difference in absorption gives the main information, and the output of the 803 nm light serves as a reference signal output.

Light emitted from the sample after being diffused while being scattered / absorbed inside the sample is detected by a photodetector arranged around the sample, and the relationship between the elapsed time after the incidence and the amount of emitted light is captured and It is converted into a decomposition intensity waveform. FIG. 2 shows incident light, light having different wavelengths reaching the detector, and time-resolved intensity waveforms of the differences.

The vertical axis represents the intensity of light in which the peak of the amount of incident light is normalized to 1, and the horizontal axis represents time. Detection is performed separately for each wavelength, but it is also possible to perform detection by dividing the incident pulse for each wavelength in time, or prepare detection elements for each wavelength and place a filter in front of the detector. Signals may be separated. When using a filter, incident light may be emitted simultaneously.

Reference numeral 4 is the waveform of the incident pulsed light, and 5 is the wavelength 803.
nm is a detection waveform, 6 is a detection waveform having a wavelength of 810 nm, and 7 is a difference between the waveforms of the detection waveform 5 and the detection waveform 6 divided by the output of 803 nm. When the light emission is not performed simultaneously, the pulse of the waveform 4 is applied to the sample independently for each wavelength and superposed during signal processing.

Different wavelengths, in this case 803 nm and 8
The difference between 10 nm shows the relationship of the difference due to the wavelength of the absorption amount received by the object in the sample at a certain time. By analyzing the time on the obtained waveform,
It is possible to know the time from the incidence until the absorption difference first appears.

FIG. 3 shows the range of trajectories that can be traced in the scattering / absorbing body within the delay Δt from the shortest time until the incident light reaches the detector. It is known that L is given by the following equation, where L is the maximum width on one side of the deviation amount from the straight-ahead light.

[0017]

[Equation 1] Here, c is the speed of light in the medium, LA is the distance from the incident position to the detector position, and Δt is the elapsed time from the shortest arrival time. Existence like substance 3 with different absorption coefficient
It has a great influence on the amount of light in the absorbing body. Therefore, if Δt is the time from the shortest arrival time to the time when the absorption difference appears, the distance from the straight line connecting the incident position and the exit position to the object in the sample can be known.

Returning to FIG. 2 again, T ₀ is set to 803 nm and 81
Let T ₁ be the time at which 0 nm light starts to be detected, and T ₁ be the time at which the output difference between the two wavelengths begins to appear. As described in FIG. 3, the output 7 has information about the object 3, and T ₁ −T
₀ corresponds to Δt in equation (1). Taking the difference is equivalent to removing the straight-ahead light, which can be said to be the zero-order component, in the signal processing.

From the above relationship, L'in FIG. 1, that is, the distance between the object 3 and the straight line connecting the incident position and the detection position can be known. Optical CT of the sample is measured by changing the incident direction with the detectors arranged all around the sample.
An image, that is, a tomographic image can be obtained.

It can be seen that curve 7 also exhibits a certain value when the elapsed time is sufficiently large. This value is 803nm
And the ratio of absorption at 810 nm, that is, the abundance ratio of Hb and HbO _{2 in} the object.

In the following description of FIG. 1, the absorption characteristics of Hb and HbO ₂ are mainly used as an example of analysis of oxygen saturation. INDUSTRIAL APPLICABILITY The present invention is characterized by being non-destructive, non-contact inspection, and harmless unless it illuminates the human body too strongly, and can be applied in a wide range. Therefore, the present invention is not limited to the application to the liver by the measurement of Hb and HbO ₂ , and can be applied to other parts of the living body such as the examination of the brain of a newborn baby and the use of any dyes that the living body has. Further, the present invention is applicable not only to the living body but also to the measurement of the optical characteristics of an object in slag, sewage, or other turbid medium.

[0022]

As described above, according to the present invention, pulsed light having a plurality of wavelengths is incident on a scattering / absorbing object which is an object, and the light emitted from the object is received by a detector and converted into a time-resolved intensity signal. By analyzing the difference in the output waveforms of a plurality of wavelengths over time, it is possible to know the position of an object inside the object, the concentration distribution of chemical substances, and the like. In addition, by analyzing the time-resolved intensity signal, it has become possible to simultaneously measure the optical properties of internal substances or chemical substances.

Other known methods for obtaining the internal structure of a scattering / absorbing body such as a living body are PET and MRI.
However, the method according to the present invention is much cheaper than the conventional method and is easy to implement only by using, for example, a near infrared pulse laser and a waveform detector. Also, regarding the harmfulness to the human body, there is no possibility of radiation exposure such as X-ray CT and PTE, and magnetic interference such as MRI, and extremely safe non-contact and non-destructive CT can be realized.

[Brief description of drawings]

FIG. 1 is a schematic view of a main part showing an embodiment in which the present invention is applied to a cylindrical sample.

2 is an explanatory diagram showing an incident signal and an outgoing signal obtained in the system of FIG.

FIG. 3 is an explanatory diagram showing a range of a trajectory of light propagating in a scattering / absorbing object.

[Explanation of symbols]

1 Photodetector 2 Scattering / absorbing object sample 3 Object or chemical substance in sample 4 Time-resolved intensity waveform of incident pulsed light 5 Time-resolved intensity waveform of emitted light of first wavelength 6 Time of emitted light of second wavelength Resolved intensity waveform 7 Time-resolved intensity waveform normalized to the difference between the detection lights of two wavelengths

Claims (1)

[Claims] 1. An optical CT apparatus for measuring the internal structure of a light scattering / absorbing object by means of light that has passed through the object, the apparatus comprising: a pulse laser light source for emitting a plurality of light beams having different wavelengths; A detection device for separately detecting the light incident on and passing through the object for each of the plurality of wavelengths, and processing the time-resolved intensity signals of the plurality of wavelengths detected by the detection device, An optical CT device characterized by measuring a structure inside an object.