JPH07103884A - Optical ct - Google Patents

Abstract

PURPOSE:To facilitate detection in a detection system connected with a light receiving point where the relative positional relationship with a light transmitting point varies. CONSTITUTION:Optical fibers are arranged annularly through a switch 12 at the light receiving part 10 disposed around a specimen 2. High speed photomultiplexer tubes 14, same in number as the light receiving ends at the light receiving part 10, are disposed at a detecting system section. The light receiving parts of the photomultiplexer tubes 14 are arranged annularly so that they are coupled optically with the outlets of optical fibers arranged annularly at the light receiving part while opposing thereto. A dimmer 18 is disposed at the light receiving part of each photomultiplexer tube 14 which is connected, at the post-stage thereof, with a time/voltage converter 20 and a peak analyzer 22 detects the time response waveform of received light pulse outputted from the time/voltage converter 20. A data processing section 24 collects output signal from the peak analyzer 22 and calculates an internal CT image of the specimen 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention irradiates a subject such as a living body with visible or near-infrared light and detects transmitted light or reflected light (including scattered light) to nondestructive information in the subject. Light C
It is related to T.

[0002]

2. Description of the Related Art In optical CT, measurement light is emitted from one point around the subject, and light transmitted or reflected inside the subject is received around the subject. Although the irradiation point is moved around the subject, if, for example, light is sequentially transmitted from the n point and is received at the n point, n ² data can be obtained, and thereby the internal tomographic image can be calculated. it can.

One method of optical scanning for obtaining information in the subject is to scan and irradiate the subject with measuring light in one direction from one direction, and the emission position of the measuring light is measured around the subject. There is a way to move it. As another method, there is also a method in which the measurement light is moved in parallel within a range including the subject, and the measurement light is moved around the subject.

However, in these methods, it is necessary to mechanically move the light-transmitting portion for measuring light or the light-receiving portion. In addition, since the light-transmitting end of the light-transmitting unit cannot be moved while it is in contact with the subject, the light-transmitting end is placed at a position away from the subject, and the tomographic image inside the subject can be calculated accurately. Not easy to do.

[0005]

As a light CT in which the measurement light can be sequentially irradiated from the periphery of the subject by eliminating the mechanically moving portion in the optical scanning mechanism around the subject,
A plurality of light-transmitting ends arranged around the subject, and a light-transmitting part that performs light-transmitting operations from the light-transmitting end to the subject in a fixed order, and around the subject. An optical fiber light receiving unit having light receiving ends arranged one by one between light transmitting ends is being considered.

FIG. 1 shows an example of a light-transmitting section and a light-receiving section of an optical CT, which is the object of the present invention. The light-transmitting ends I _{1 to} In of the optical fibers of the light-transmitting unit are arranged around the subject 2.
One light receiving end O _{1 to} On is arranged between the light transmitting ends. Measuring light is sequentially transmitted from the light-transmitting end by light-transmitting pulses, and is received by all the light-receiving ends. The measurement procedure is as follows. First, the subject 2 is irradiated with pulsed light from the light transmitting end I ₁ ,
All the light receiving ends O
By receiving light simultaneously in parallel at ₁ to On, n light receiving signals are obtained.

Next, the light transmitting unit is advanced by one step, that is, the light pulse is irradiated from the light transmitting end I ₂ to the subject 2 and all the light receiving ends O ₁ to On receive the light. By repeating this process and measuring n times by switching the n light-transmitting sections from the light-transmitting ends I _{1 to} In, it is possible to obtain a total of n ² light-receiving signals, from which a tomographic image can be obtained by calculation. it can. The light received at each light receiving end is guided to the detection system through the optical fiber. As an example, the detection system includes at least a dimmer that dims the incident light, a detector that detects the light that has passed through the dimmer, and a time-voltage converter that detects the photon detection time by the detector.

As shown in FIG. 2A, assuming that the object 2 is a sphere having a diameter of 100 mm, the light transmitting point A
When the light is received at point a (the distance from the light transmitting point is, for example, 20 mm) that is close to
The duration of the light-receiving pulse is significantly different from the case of receiving light at 00 mm). For example, as shown in FIG. 2 (B), at a point b separated by 100 mm, 0 to 0 after the light transmission pulse is generated.
Whereas it is necessary to measure the range of 20 nanoseconds,
It is necessary to measure a range of only 0 to 2 nanoseconds at a point separated by mm. Further, a time response curve having a high peak height at point a and a low peak height at point b is obtained. Figure 2
The vertical axis of (B) represents the relative intensity of the received light. In this way, the peak height and duration of the obtained time response curve greatly differ depending on the distance between the light transmitting point and the light receiving point.

As a method for detecting weak light, a received optical signal is converted into a pulse signal by a high-speed photomultiplier tube via a dimmer, and the detected pulse signal is converted into a time-voltage converter (T
There is known a method of detecting by a so-called time-correlated single photon detection method using an AC (Time-to-Amplitude Comverter) and a pulse height analyzer. However, the TAC has a narrow dynamic range and cannot be applied to the detection of light having significantly different peak heights and durations of the time response curve, such as the detection signals at the points a and b in FIG.

Therefore, a first object of the present invention is an optical CT provided with an optical scanning unit as shown in FIG. 1, in which the light sending points are switched relative to each other when the light sending points are sequentially switched. It is to facilitate detection by a detection system connected to a light receiving point whose positional relationship changes. A second object of the present invention is to provide a light receiving system with TA
This is to enable measurement even when an element having a narrow dynamic range such as C is included.

[0011]

The present invention has a plurality of light-transmitting ends arranged around a subject, and the light-transmitting operations from the light-transmitting ends to the subject are switched in a fixed order. Has a plurality of light-receiving ends arranged around the subject, and a detection system of the same number as the light-receiving ends, each of which receives light received by each light-receiving end. The detection system part to be detected by the detection system, is arranged between the optical fiber light receiving part and the detection system part, and the light emitting end of the optical fiber light receiving part and the light incident end of the detection system part are arranged in an annular shape, respectively, The light emitting end of the optical fiber light receiving part and the light incident end of the detection system part are opposed to each other and optically coupled, and at the same time, each light receiving end of the optical fiber light receiving part coupled to each detection system is transmitted. The light-transmitting end by the light-transmitting part is maintained so that the relative positional relationship with the light-transmitting end during the light-sending operation An optical CT with a sequentially switching switching unit coupling relationship between the optical fiber and the detection system of the optical fiber receiving portion in response to switching of al of transmission light.

In a preferred embodiment, each of the detection systems of the detection system section includes a dimmer for dimming incident light, a detector for detecting light passing through the dimmer, and a detector for transmitting light from a light transmitting end. At least one of a time-voltage converter that outputs the time until the photon detection by the detector is output as a voltage, and at least one of the extinction ratio of the dimmer, the sensitivity of the detector, and the time resolution of the time-voltage converter is a light transmitting unit. Is set or selected according to the relative positional relationship with the light-transmitting end during the light-transmitting operation.

[0013]

By introducing the switching unit, the coupling relationship between the optical fiber of the optical fiber light receiving unit and the detection system of the detection system unit can be sequentially switched in synchronization with the movement of the light transmitting point. Each detection system is only responsible for a specific distance between the light-transmitting end and the light-receiving end. Therefore, a high-speed photomultiplier tube with excellent time resolution and a time-voltage converter are used for short-distance detection, and a high-sensitivity detection system with low time resolution can be selected for long-distance detection. it can. Output to the detection system as a voltage, the dimmer that dims the incident light, the detector that detects the light that has passed through the dimmer, and the time from the sending of light from the sending end to the detection of photons by the detector. When equipped with a time-voltage converter, the measurement system should be set to the optimal conditions for the distance between the light-transmitting end and the light-receiving end, so that the time-voltage converter has a narrow dynamic range. Can also make measurements.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A light transmitting section and an optical fiber light receiving section which contact an object in an apparatus to which one embodiment is applied is schematically shown in FIG. FIG. 3 shows the whole one embodiment. The light-transmitting section has a light-transmitting side optical fiber 4 serving as a light-transmitting end arranged around the subject 2 with its tip in contact with the subject 2, and a pulse laser for generating picosecond pulse laser light in the near infrared. A device 6 and a light-transmitting-side fiber switch 8 for sequentially switching and guiding the laser light from the pulse laser device 6 to the light-transmitting-side optical fiber 4 are provided.

The optical fiber light receiving portion 10 is provided with an optical fiber whose tip is in contact with the subject 2 and one light receiving side optical fiber is provided between the light transmitting side optical fibers 4. The other end of the optical fiber of the optical fiber light receiving unit 10 is arranged in a ring shape by the switch 12 as shown in FIGS. 4 and 5 which will be specifically described later.

The detection system section is provided with the same number (n) of high-speed photomultiplier tubes 14 as the light-receiving ends of the optical fiber light-receiving section 10. The light-receiving section of the photomultiplier tube 14 is connected to the optical fiber by the switching unit 12. The light receiving portions 10 are arranged in a ring shape so as to face and optically couple with the emission ends of the optical fibers arranged in a ring shape. A light reducer 18 is arranged in the light receiving portion of each photomultiplier tube 14 to diminish the light entering the photomultiplier tube 14. In order to convert the arrival time of one photoelectron pulse generated in the photomultiplier tube 14 into a voltage value, each photomultiplier tube 1
A time-voltage converter 20 is connected to 4. Since the wave height analyzer 22 connected to the time-voltage converter 20 outputs a statistical distribution of arrival times of photoelectrons over a large number of times (for example, 10 ⁸ times), the time response for the corresponding “transmitter / receiver pair” is output. It becomes a waveform. A data processing unit 24 collects n time response waveforms output from the wave height analyzer 22 and calculates a tomographic image inside the subject 2.

The n photomultiplier tubes 14 are arranged 14-
1-14-n, photomultiplier tubes 14-1-14
Each of -n is coupled with each optical fiber of the optical fiber light receiving unit 10 having a specific positional relationship with the operating light transmitting end I ₁ when the light transmitting end I ₁ is operating, The light from the light receiving end of the fiber is detected. When the transmitting end in operation is switched from I ₁ to I ₂ , the photomultiplier tube 14
-1 to 14-n, the switch 12 is arranged so that the optical fibers of the optical fiber light receiving unit 10 maintain the same positional relationship as the light transmitting end I ₁ is in operation or close thereto. 10 optical fibers and photomultiplier tube 14-1
The connection relationship with 14 to 14-n is switched by one step. The optical fiber light receiving unit 10 is switched according to the switching of the light transmitting ends I _{1 to} In.
The coupling relationship between the optical fiber and the photomultiplier tubes 14-1 to 14-n is sequentially switched.

As described with reference to FIG. 2, when the distance between the light-transmitting point and the light-receiving point is different, the intensity and duration of the obtained time response waveform are significantly different, as in a and b, for example.
In the case of a, since the peak light intensity is strong, the extinction ratio of the dimmer is increased in order to reduce the photon count rate, and since the pulse is short, the time resolution of the time-voltage converter 20 is increased. On the other hand, in the case of b, the extinction rate is reduced, the time resolution of the time-voltage converter 20 is lowered, that is, the time resolution width of the time-voltage converter 20 is widened, and high sensitivity is set. The dimmer 18 and the time-voltage converter 20 are set to the dimming rate and time resolution corresponding to the relative positional relationship between the light-transmitting end and the light-receiving end of the light received by each. Further, the photomultiplier tube 14 is selected so as to have sensitivity according to the light received by each.

As the trigger signal of the time-voltage converter 20, for example, a pulse signal from a drive circuit when the pulse laser device 6 is oscillated is used. This pulse signal is an electric pulse that corresponds exactly to the generation of an optical pulse, is applied to the time-voltage converter 20, and becomes the start input of the time-voltage converter 20. When the photomultiplier tube 14 detects a photon through the light receiving end by the light pulse from one light sending end of the light sending side optical fiber 4, and the photoelectron pulse is generated, the time-voltage converter 2
0 outputs a voltage proportional to the time difference between the trigger signal and this photoelectron pulse as a pulse. The wave height analyzer 22 statistically collects the voltage distribution of this voltage pulse.

In the time-correlated single photon detection method, the pulse height analyzer 2
The distribution of the arrival times of photons at the time of repeated measurement, which is tabulated in 2, becomes the time response waveform as it is. For example, if the pulse laser device 6 is measured at 5 MHz for 20 seconds, 10
^Eight repeated measurements are performed in parallel on n channels, and the distribution curve of the arrival time of photons at that time is shown at each light receiving end O ₁
It will be obtained in parallel as a time response waveform of the received light signal at ~ On.

When the measurement at one light-transmitting end I _{1 is completed} , the light-transmitting end for irradiating the subject 2 with the light pulse from the pulse laser device 6 is advanced by one step by the fiber switching device 8, and the light-transmitting end I
_An optical pulse is applied to the subject ₂ from ₂ to obtain n time response waveforms from the light receiving signals of the light receiving ends O ₁ to On in the same manner as described above. By repeating this, a total of n ² time response waveforms can be obtained by measuring n times by switching the n light emitting ends from the light transmitting ends I _{1 to} In. The data processing unit 24 obtains a tomographic image inside the subject 2 by calculation from the n ² time response waveforms.

Next, a concrete example of the switch 12 will be described. Figure 4
Is the first example. The other end of the optical fiber of the optical fiber light receiving unit 10 whose one end is a light receiving end that contacts the subject 2 is arranged on the circumference of the rotating disk 30. Rotating disk 3
The photomultiplier tubes 14 are arranged in a ring shape so as to face the end faces of the optical fibers arranged in 0, and a neutral density filter 18 is arranged as a light attenuator in each light receiving portion of the photomultiplier tube 14.
The neutral density filter 18 and the photomultiplier tube 14 are fixed, and the neutral density filter 18 is set so that each photomultiplier tube 14 has a different neutral density.

The extinction ratio of the neutral density filter 18 and the sensitivity (time resolution) of the time-voltage converter connected to the photomultiplier tube 14.
Is set according to the distance between the light transmitting point and the light receiving point in the subject 2. In synchronism with the switching of the light-sending point in operation by the light-sending-side optical fiber 4 to I ₁ , I ₂ , ... In sequence, the rotating disk 30 causes the light incident on each photomultiplier tube 14 to be the light-sending point. Are rotated step by step so that the relative positional relationship between the light receiving point and the light receiving point is maintained. As a result, each detection system subsequent to the neutral density filter 18 receives a signal with a constant distance between the light transmitting point and the light receiving point, and can perform a required function. When the light-sending point makes one round with I _{1 to} In, the disk 30 of the switch also makes one round. At this time, in order to prevent the optical fiber 10 attached to the disk 30 from being twisted more than double, it is sufficient to make a reciprocating motion for each rotation.

FIG. 5 shows another example of the switch 12. In FIG. 5, the photomultiplier tube 14 and the neutral density filter 18 arranged in each light receiving portion thereof are fixed. The light emitting ends of the light-receiving side optical fibers 10 are connected by a closed chain of chains 32 and arranged so as to face the light-receiving part of the photomultiplier tube 14 via the neutral density filter 18. In FIG. 5A, the photomultiplier tube 14 and the neutral density filter 18 are arranged in the direction perpendicular to the paper surface so as to face the light emitting end of the optical fiber 10 connected by a chain. Also in this example, the light emitting end of the optical fiber 10 connected by the chain 32 is sequentially moved step by step as the light transmitting end is sequentially switched from I ₁ to In. This method has the advantage that it requires less space than using a rotating disk.

In FIGS. 4 and 5, the neutral density filter 18 is provided in the light receiving portion.
Switchers 30 and 32 are arranged immediately in front of the light receiving side of the photomultiplier tube 14 in which is arranged. However, an optical fiber may be arranged on the light incident side of the neutral density filter 18, and the switch may be arranged at a position intermediate between the optical fiber and the optical fiber 10.

[0026]

According to the present invention, the optical coupling between the light-receiving side optical fiber and the detection system is sequentially switched, so that the detection system after the switching unit can be fixed and dedicated. Therefore, each detection system can use the one having the optimum specifications for the output signal according to the distance between each light transmitting point and each light receiving point. Also, since the detection system can be fixed, all detection systems do not have to be the same, and a low-sensitivity, high-speed photoelectron amplification is used for a detection system that detects light with a short distance between the light-transmitting point and the light-receiving point. A photomultiplier tube with high sensitivity and slightly low speed can be selected as a detection system that uses a double tube and detects light having a long distance between a light transmitting point and a light receiving point.
As the time-voltage converter, it is possible to select one having a characteristic suitable for each detection light. Switching of the optical fibers on the receiving side is carried out in order of O ₁ , O ₂ , ... On- ₁ , On, O ₁ ,
Since it is carried out cyclically as O ₂ , ..., the mechanism of the switching unit is relatively simple.

[Brief description of drawings]

FIG. 1 is a schematic plan view showing an example of a light transmitting unit and a light receiving unit according to the present invention.

2A and 2B show propagation states of optical pulses in the light transmitting unit and the light receiving unit in FIG. 1, in which FIG. 2A is a schematic plan sectional view of the object portion, and FIG. 2B is a light receiving point close to the light transmitting point. It is a figure which shows the received light optical signal in the light receiving point far from.

FIG. 3 is a block diagram schematically showing an embodiment.

4A and 4B are diagrams showing a first example of a switching unit in one embodiment, FIG. 4A is a plan view showing a rotating disc portion, and FIG. 4B is a side view.

5A and 5B are diagrams showing a second example of the switching unit in one embodiment, FIG. 5A being a plan view and FIG. 5B being a side view.

[Explanation of symbols]

 2 specimen 4 light-transmitting side optical fiber 6 pulse laser device 8 light-transmitting side optical fiber switching unit 10 light-receiving side optical fiber 12 switching unit 14 photomultiplier tube 18 dimmer 20-hour voltage converter 22 wave height analyzer 24 data processing Part 30 rotating disk 32 chain

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hideo Eda Inventor Hideo Eda 1 Nishinokyo Kuwabara-cho, Nakagyo-ku, Kyoto Prefecture Kyoto Sanjo Factory Sanjo Factory (72) Inventor Yasushi Ito 1 Nishinokyo Kuwabara-cho, Nakagyo-ku, Kyoto Prefecture Kyoto Stock Company Shimadzu Sanjo factory (72) Inventor Ichiro Oda 1 Nishinokyo Kuwabara-cho, Nakagyo-ku, Kyoto-shi, Kyoto Shimazu Corporation Sanjo factory

Claims (2)

[Claims] 1. A light-transmitting section having a plurality of light-transmitting ends arranged around a subject, wherein light-transmitting operations from the light-transmitting ends to the subject are switched in a fixed order. An optical fiber light receiving unit having a plurality of light receiving ends arranged around the subject, and a detection system having the same number as the light receiving ends, and detecting light received by each light receiving end by each detection system. It is arranged between the system part and the optical fiber light receiving part and the detection system part, and the light emitting end of the optical fiber light receiving part and the light incident end of the detection system part are arranged in an annular shape, respectively, and the light of the optical fiber light receiving part is arranged. The emitting end and the light-incident end of the detection system section are opposed to each other one-to-one and are optically coupled, and at the same time, the respective light-receiving ends of the optical fiber light-receiving sections coupled to the respective detection systems and the light-transmitting section Switching the light emission from the light emitting end by the light transmitting unit so that the relative positional relationship with the light emitting end is maintained. An optical CT including a switching unit that sequentially switches the coupling relationship between the optical fiber of the optical fiber light receiving unit and the detection system unit. 2. Each of the detection systems of the detection system section includes a dimmer for dimming incident light, a detector for detecting light passing through the dimmer,
And at least a time-voltage converter that outputs, as a voltage, the time from the light transmission from the light-transmitting end to the photon detection by the detector, the extinction ratio of the dimmer, the sensitivity of the detector, and the time-voltage converter The optical CT according to claim 1, wherein at least one of the time resolutions is set or selected according to a relative positional relationship with a light-transmitting end of the light-transmitting unit during a light-transmitting operation.