JP6793352B2 - An imaging device including a light source, a photodetector, and a control circuit. - Google Patents

Description

The present disclosure relates to an imaging device.

In the fields of biometrics, material analysis, etc., a method of irradiating an object with light and acquiring internal information of the object from information of light transmitted through the inside of the object is used. In this method, mixing of a reflection component from the surface of the object and a scattering component immediately below the surface may become a problem. In particular, in biometric measurement, the surface reflection component and the subcutaneous scattering component have an intensity that is 4 to 5 orders of magnitude higher than that of the scattering component in the living body, and these surface reflection component and the subcutaneous scattering component are used to obtain the scattering component from the inside of the living body. It is desirable to remove as much as possible. As a method of removing these components and acquiring only desired internal information, for example, in the field of biometric measurement, there is a method disclosed in Patent Document 1. Patent Document 1 discloses a method in which a light source and a photodetector are spatially separated from each other at regular intervals and brought into close contact with a measurement site for measurement.

Japanese Unexamined Patent Publication No. 8-103434

The present disclosure provides a technique capable of measuring the internal information of a measurement target and the cerebral blood flow distribution with high resolution in a state where the internal information of the measurement target is not in contact with the target and noise due to the movement of the target is suppressed. .. The present disclosure also provides a technique capable of measuring an object by a method that is cheaper than a conventional method.

The imaging apparatus according to one aspect of the present disclosure includes a diffuser plate, a light source that emits pulsed light that spreads at a diffusion angle larger than 0 degrees toward an object, and photoelectric conversion that receives light from the object and converts it into electric charges. It includes a unit and a charge storage unit that stores the electric charge, and includes an optical detector that outputs an electric signal when the electric charge is read out, and a control circuit that controls the light source and the optical detector. The control circuit causes the light source to start emitting the pulsed light, and after a lapse of a predetermined time, starts the accumulation of the charge in the charge storage unit, whereby the inside of the target among the light from the target. The charge corresponding to the component scattered in is accumulated in the charge storage unit. Assuming that the distance from the diffusion plate to the object is R (mm), the diffusion angle is θ (degrees), and the spot size of the pulsed light on the diffusion plate is d (mm), the following equation is established.
81.5 ≦ R + d / (2tanθ)

FIG. 1 is a schematic view showing the image pickup apparatus of the first embodiment. FIG. 2 is a diagram showing the time response waveform of the optical signal reaching the photodetector 108, the relationship between the shutter timing and the detected optical signal, and the relationship between the shutter start phase and the detection intensity of the detected optical signal. is there. FIG. 3A is a diagram showing a change in the density of the irradiation light with the movement of the object. FIG. 3B is a diagram showing a time delay of the return light with respect to the same movement as in FIG. 3A. FIG. 4A is a diagram showing the relationship between the shutter start phase and the detected amount of change in the optical signal with respect to the movement of the target. FIG. 4B is a diagram showing the relationship between the movement of the target and the detected optical signal intensity. FIG. 5A is a diagram showing the relationship between the diffusion angle of the light source and the density change of the irradiation light. FIG. 5B is a diagram showing the relationship between the diffusion angle of the light source and the density change of the irradiation light. FIG. 5C is a diagram showing the optimum shutter start phase position under the conditions of FIGS. 5A and 5B. FIG. 6A is a diagram showing an example of an irradiation pattern. FIG. 6B is a diagram showing an example of an irradiation pattern. FIG. 7 is a diagram showing the relationship between the shutter start phase and the amount of change in the detected light signal due to fluctuations in the flight distance of light. FIG. 8 is a diagram showing the relationship between the diffusion angle of the irradiation light of the present embodiment and the distance to the target. FIG. 9 is a diagram showing an example of a value obtained by subtracting the right side from the left side of the mathematical formula 13.

According to a detailed study by the inventor of the present application, in the method of JP-A-8-1033434, the proportion of the subcutaneously scattered component contained in the detection signal is reduced, and the amount of the light scattered component that reaches the brain is detected. Can be done. However, in this method, it is necessary to separate the irradiation point and the detection point by 3 cm, and it is considered that the spatial resolution of the obtained brain activity distribution is lowered.

On the other hand, in recent years, an image sensor capable of high-speed photography has been developed for measuring the distance to an object by a TOF (Time-of-Flight) method. Since such an image sensor has a high time-dividing ability, it is conceivable that by controlling the shutter of the image sensor at high speed, the surface reflection and the subcutaneous scattering component having high intensity can be significantly reduced to detect the scattering component in the brain. Be done. Specifically, when pulsed light is directed toward a living body and the light reflected by the living body is photographed, the light reflected near the surface of the living body has a relatively short optical path, so that it reaches the image sensor quickly and the living body The light reflected inside the light path reaches the image sensor with a delay because the optical path is relatively long. Therefore, by adjusting the shutter so as to detect the rear end portion of the pulsed light returning to the image sensor, it is possible to efficiently detect the scattering component in the brain having a relatively long optical path length and a time delay. It is possible. Since this method of temporal separation detection can detect the brain signal immediately below the irradiation point, it is considered that a high-resolution brain activity distribution can be obtained as compared with the method of JP-A-8-103434. Be done.

However, when the signal from the target is detected in a non-contact manner, the amount of the optical signal detected by the sensor changes when the target moves, and an incorrect detection value is output. In particular, when detecting a very small amount of scattering components in the brain such as cerebral blood flow measurement, the influence of the noise component due to movement is high, and the SN in detecting the scattering components in the brain is lowered. In view of such problems, the inventor of the present application has conceived an imaging device having a novel structure. The outline of the image pickup apparatus of the present disclosure is as follows.

The imaging apparatus according to one aspect of the present disclosure includes a diffuser plate, a light source that emits pulsed light that spreads at a diffusion angle larger than 0 degrees toward an object, and photoelectric conversion that receives light from the object and converts it into electric charges. It includes a unit and a charge storage unit that stores the electric charge, and includes an optical detector that outputs an electric signal when the electric charge is read out, and a control circuit that controls the light source and the optical detector. The control circuit causes the light source to start emitting the pulsed light, and after a lapse of a predetermined time, starts the accumulation of the charge in the charge storage unit, whereby the inside of the target among the light from the target. The charge corresponding to the component scattered in is accumulated in the charge storage unit. Assuming that the distance from the diffusion plate to the object is R (mm), the diffusion angle is θ (degrees), and the spot size of the pulsed light on the diffusion plate is d (mm), the following equation is established.
81.5 ≦ R + d / (2tanθ)
Here, R, d, θ> 0.

The imaging apparatus according to one aspect of the present disclosure may further include a diffusion angle adjusting mechanism for adjusting the diffusion angle.

The imaging apparatus according to one aspect of the present disclosure may further include a pattern projection unit that converts the pulsed light into light having a desired pattern.

In the imaging apparatus according to one aspect of the present disclosure, the control circuit may remove a predetermined offset component from the electrical signal.

The image pickup apparatus according to another aspect of the present disclosure includes a light source that emits pulsed light toward an object, a photoelectric conversion unit, and a charge storage unit that stores charges generated by the photoelectric conversion unit. A control circuit includes an optical detector that outputs an electric signal by being read, and the control circuit transmits the pulsed light to the light source when the distance between the object and the light source is the first value. After a predetermined time has elapsed from the start of light emission, charge accumulation in the charge storage unit is started to generate a first electric signal, and the distance between the object and the light source is different from the first value. When the value is 2, the light source starts emitting the pulsed light, and after the lapse of the predetermined time, the charge accumulation in the charge storage unit is started to generate a second electric signal, and the predetermined time is This is the timing when the strength of the first electric signal and the strength of the second electric signal become the same.

The difference Δr between the first value r1 and the second value may satisfy the following equation.

Here, α is the attenuation coefficient of the phase change of the electric signal intensity of the return light from the object, and k is the ratio of the desired electric signal change amount to the initial electric signal intensity.

The difference Δr between the first value r1 and the second value may satisfy the following equation.

When the first value r1 is 100 cm, 50 cm, 25 cm, 20 cm, 16 cm, 15 cm and 10, 5 cm, the difference Δr between the first value and the second value is 0.
6 cm or more and 1.2 cm or less, 0.7 cm or more, 1.4 cm or less, 1.1 cm or more and 2.3 cm or less, 1.4 cm or more and 2.7 cm or less, 1.7 cm or more and 3.3 cm or less, 2.3 cm or more 4. It may be 6 cm or less and 3 cm or more and 5 cm or less.

In the present disclosure, all or part of a circuit, unit, device, member or part, or all or part of a functional block in a block diagram, refers to a semiconductor device, a semiconductor integrated circuit (IC), or an LSI (range scale integration). It may be executed by one or more electronic circuits including. The LSI or IC may be integrated on one chip, or may be configured by combining a plurality of chips. For example, functional blocks other than the storage element may be integrated on one chip. Here, it is called LSI or IC, but the name changes depending on the degree of integration, and it may be called system LSI, VLSI (very large scale integration), or ULSI (ultra large scale integration).

A Field Programmable Gate Array (FPGA) programmed after the LSI is manufactured, or a reconfigurable logistic device that can reconfigure the junction relationship inside the LSI or set up the circuit partition inside the LSI can also be used for the same purpose.

Further, all or part of the functions or operations of circuits, units, devices, members or parts can be performed by software processing. In this case, the software is recorded on a non-temporary recording medium such as one or more ROMs, optical discs, hard disk drives, and is identified by the software when it is executed by a processor. Functions are performed by the processor and peripherals. The system or device may include one or more non-temporary recording media on which the software is recorded, a processor, and the required hardware device, such as an interface.

Hereinafter, embodiments will be specifically described with reference to the drawings.

(Embodiment 1)
[Configuration of imaging device]
First, the configuration of the image pickup apparatus 100 according to the first embodiment will be described with reference to FIG.

The image pickup apparatus 100 includes a light source 106, a photodetector 108 including a photoelectric conversion unit 110 and a charge storage unit 112, and a control circuit 114. The light source 106 emits light 104, which is pulsed light, toward the target 102. A part of the light 104 that has reached the target 102 reaches the photoelectric conversion unit 110 on the photodetector 108 after optical phenomena such as reflection, diffusion, absorption, and scattering occur on the surface and inside of the target 102. The control circuit 114 includes a memory for storing the program and a computing device, and by reading and executing the program stored in the memory, the light source 106 is started to emit light 104 according to the procedure of the program for a predetermined time. After the lapse of time, the charge accumulation in the charge storage unit 112 is started to control the generation of an electric signal.

When the target 102 is a living body, a part of the light 104 emitted from the light source 106 reaches the inside of the target 102. Since the light 104 scattered inside the object 102 causes a time delay due to scattering, the pulsed light returning to the image pickup apparatus 100 includes a tail due to the component of the light 104 scattered inside. Information deep inside the target 102 (for example, the component that reached the brain in the measurement at the head) has a relatively longer optical path length than the light scattered near the surface of the target 102, so that it is larger than the rear end of the return pulse light. By starting the shutter at the timing when the slow tail reaches the image pickup apparatus 100, the ratio of information deep inside the living body (scattering component in the brain) contained in the detection signal can be increased. Here, starting the shutter means starting the charge accumulation in the charge accumulation unit 112. If the sensitivity is insufficient in one pulse light measurement, this operation is repeated a plurality of times to amplify the detected light amount by integration. For example, it is repeated hundreds to millions of times.

The light source 106 is composed of, for example, a fluorescent lamp, an LED, an LD, or the like. In order to separate the information deep inside the object 102 from the information near the surface, it is desirable that the rear end of the pulsed light falls sharply, so a light source that emits laser light such as LD may be used. When measuring the degree of oxygenation of the blood flow of the target 102, for example, near-infrared light that can pass through the living body to some extent is used as the light source 106. Further, in order to detect the change in the concentration of oxygenated hemoglobin and deoxygenated hemoglobin, light 104 having two wavelengths may be irradiated. For example, the light source 106 emits light 104 having a wavelength near 750 nm and light 104 having a wavelength near 850 nm. At this time, the photodetector 108 includes a plurality of charge storage units 112 for one photoelectric conversion unit 110, and is configured to store light of two wavelengths in each charge storage unit 112 in a time division manner. You may. By providing a plurality of charge storage units 112, it is possible to acquire a plurality of different information in one frame at substantially the same time. Further, not only the information of different wavelengths but also the information of different polarizations, the information of different intensities or the information of different phase differences can be acquired at the same time. As such a photodetector 108, for example, an image pickup apparatus disclosed in Japanese Patent Application Laid-Open No. 2008-89346 can be used.

The photodetector 108 used in the image pickup apparatus 100 includes a photoelectric conversion unit 110 and a charge storage unit 112. The photodetector 108 may be a photodiode, a photomultiplier tube, a CCD / CMOS type image sensor, a single photon counting type element, or an amplification type image sensor (EMCDD, ICCD).

The waveform (a) in FIG. 2 is a time response waveform of an optical signal reaching the photodetector 108. When the pulse width of the light source 106 is small to some extent, the waveform (a) can be regarded as an optical path length distribution. That is, the longer the optical path length, the later the time when the light reaches the photodetector 108, so that the light is detected at a relatively large t (late time). That is, the time response waveform has a spread according to the optical path length distribution.

The waveform (b) in FIG. 2 shows the shutter timing when the shutter start phase T is t1, t2, t3, and t4 (t1> t2> t3> t4), respectively. The shutter start phase T is a time difference between the emission timing of the pulsed light of the light source 106 and the timing of starting the shutter of the photodetector 108. The graph (c) in FIG. 2 is a diagram in which the horizontal axis is the shutter start phase T and the vertical axis is the detection intensity I of the detected optical signal. As shown in the waveform (b) and the graph (c), the detection intensity I of the detected optical signal 200 increases as the shutter start phase T is advanced. The setting of the shutter start phase T may be adjusted by the light emission start time of the illumination, or may be adjusted by the charge accumulation start time of the sensor.

FIG. 3A shows the density change of the irradiation light 210 with the movement of the object 102. In the case of synchrotron radiation in which the light source 106 has a spread, the illuminance (= light intensity density) decreases as the target 102 moves away from the light source 106. Therefore, when the target 102 moves to a distance r2 farther from the distance r1, the light intensity density of the irradiation light 214 on the target 102 when the target 102 exists at the distance r2 is such that the target 102 exists at the distance r1. It becomes smaller than the light intensity density of the irradiation light 212 on the target 102 at the time of

On the other hand, FIG. 3B is a diagram showing a time delay of the return light 220 with respect to the same movement of the object 102 as in FIG. 3A. When the target 102 moves from the distance r1 to the distance r2, the flight distance of the light that reaches the target 102 from the light source 106 and returns to the light source 106 again is that the return light 224 when the target 102 exists at the distance r2 has a distance r1. It is longer than the return light 222 when the target 102 is present in. Therefore, the return light 224 arrives at the photodetector 108 later than the return light 222. That is, when the shutter is started at a constant timing after emitting light from the light source 106, the amount of detected light increases as the target 102 moves from the distance r1 to the distance r2. In FIG. 3B, the rectangular frame represents the period during which the shutter is open.

Both the phenomena shown in FIGS. 3A and 3B cause an error in the detection signal with respect to the movement of the target 102, but have a negative correlation. That is, since the phenomenon shown in FIGS. 3A and 3B is an error factor contradictory to the movement of the target 102, FIGS. 3A and 3B due to the movement of the target 102 by controlling the shutter timing so as to cancel each other out of this phenomenon. The influence of the phenomenon shown in 3B can be offset.

Since the illuminance of the irradiation light 210 from the light source 106 on the target 102 is inversely proportional to the square of the distance between the light source 106 and the target 102, the detected optical signal intensity is also the square of the distance between the light source 106 and the target 102. Is inversely proportional to. Assuming that the light signal intensity detected when the distance 1 (initial distance) between the light source 106 and the target 102 is r ₁ is I ₁ , the light signal detected when the distance between the light source 106 and the target 102 is r ₁ The intensity I ^ill is expressed by the following equation.

と表すことができる。ここで、Δｒはｚ方向（光源１０６−対象１０２方向）の動き量である。つまり、ΔＩ^illは初期距離ｒ₁に反比例する。 Therefore, the amount of change in the optical signal ΔI ^ill detected due to the change in the illuminance of the irradiation light 210 on the object 102 is

It can be expressed as. Here, Δr is the amount of movement in the z direction (light source 106-target 102 direction). That is, ΔI ^ill is inversely proportional to the initial distance r ₁ .

On the other hand, the amount of change in the detected light signal due to the change in the flight distance of the return light 220 from the target 102 depends on the time response waveform of the return light 220 reaching the photodetector 108. Since it is known that when light passes through a scattering medium such as a living body, a time response of exponential intensity is observed according to Lambertbert's equation, it is a function of the flight time (shutter start phase) t of the return light 220. The detected optical signal intensity I ^dis is expressed by the following equation.

Here, t ₁ is the initial phase, and α is the absorption coefficient / scattering coefficient of the object 102 and the attenuation coefficient of the detection intensity of the return light, which depends on the dullness of the pulsed light emitted by the light source 106. For example, it is a coefficient when the waveform of the graph (c) of FIG. 2 is expressed by an exponential function.

と表すことができる。ここで、Δt=-２Δｒ/ｃ、ｃは光速である。数式４より、ΔＩ^dis
は光信号検出強度の位相変化の傾き（図２のグラフ（ｃ）の傾き）に比例することがわかる。 The amount of change in the detected light signal ΔI ^dis due to the change in the flight distance of the return light 220 from the target 102 is

It can be expressed as. Here, Δt = −2Δr / c and c are the speed of light. From Equation 4, ΔI ^dis
It can be seen that is proportional to the slope of the phase change of the optical signal detection intensity (the slope of the graph (c) of FIG. 2).

となる位相を初期位相とすればよい。すなわち、

を実現する位相位置である。 Therefore, in order to suppress the change in the detected optical signal with respect to the movement of the target 102,

The initial phase may be set as the initial phase. That is,

Is the phase position that realizes.

FIG. 4A shows the relationship between the shutter start phase T and the detected optical signal change amount ΔI with respect to the movement of the target 102. ΔI ^ill is the absolute value of the detected change in the optical signal due to the change in the illuminance of the irradiation light 210 on the target 102, and ΔI ^dis is the change in the detected light signal due to the change in the flight distance of the return light 220 from the target 102. It is an absolute value. For example, if the shutter start phase is too late (for example, it corresponds to t = t1 in the graph (c) of FIG. 2), the detected light is at a position where the change in the amount of light away from the rear end of the return light 220 is small, so that ΔI ^ill > ΔI ^dis . Further, when the shutter start phase is too early (for example, corresponding to t = t4 in the graph (c) of FIG. 2), the detected light is at a position where the change in the amount of light away from the rear end of the return light 220 is small, so that ΔI ^ill <ΔI ^dis .

FIG. 4B is a diagram showing the relationship between the movement amount Δr of the target 102 and the detection intensity I of the detected optical signal. By appropriately setting the shutter start phase, the detected optical signal intensity can be kept constant even if the target 102 moves. Specifically, when the target 102 is measured in the initial phase satisfying the formula 5 or the formula 6, the optical signal intensity obtained when the distance from the light source 106 to the target 102 is r1 (first value) and the light source 106 It is equal to the optical signal intensity obtained when the distance to the target 102 is r2 (second value). Therefore, the electric signal output from the photodetector 108 is also equal at the distance L1 and at the distance r2.

[Initial phase setting]
The initial phase can be set by calibration or by using a table prepared in advance. The calibration method can be further classified into a passive method and an active method. In the passive method, the target 102 is moved away from the light source 106, or if the target 102 is a person, it is instructed to do so. If the detected light amount decreases, the shutter start phase is advanced, and if it increases, the shutter start phase is decreased. .. This operation is efficiently repeated using Newton's method, dichotomy, or the like, and calibration is complete when there is no change in the amount of light. The same applies when the object 102 is brought closer to the light source 106. In the active method, the target 102 is freely moved (moved), and the direction of the movement is detected by distance measurement on the device side to determine whether the object 102 is moving away or approaching, and is matched with the increase or decrease in the amount of detected light. To determine the shutter start phase. The distance measurement can be realized by using the pulsed light of the imaging device and driving the TOF (Time of flight) mode by the control circuit 114, or by separately providing a distance measuring device such as a stereo ranging camera.

In the case of the method using a table prepared in advance, the relationship between the distance between the light source 106 and the target 102 and the optimum shutter start phase is tabulated in advance according to the optical characteristics of the target 102 and the waveform of the return light 220, and the target It is uniquely determined by referring to the table by measuring the distance to 102. According to this method, it is not necessary to perform calibration in advance.

When there are a plurality of measurement targets, if the materials and optical characteristics of the target 102 are similar, the initial phase may be determined by one of the target 102, and the other targets may follow it. On the other hand, when the material of the target 102 changes significantly, that is, when the scattering coefficient and the absorption coefficient are significantly different, the phase change of the optical signal intensity (the inclination change of the rear end of the return light 220) is also different. The initial phase may be determined.

[Allowable movement range]
Next, consider the allowable range of movement that can be corrected. If the amount of change in the detected signal due to movement is smaller than the amount of signal change to be detected (for example, the reaction of blood flow change due to a task from a calm state), the S / N ratio with respect to movement is 1 or more, and it can be said that measurement is possible. If the amount of signal change to be detected is set to ΔI ^task , the relationship of the following equation can be obtained under the condition that the S / N ratio is 1 or more.

In Equations 2 and 4, since both ΔI ^ill and ΔI ^dis are derived from the differential values, the applicable range is limited to the movement in the range where the linear approximation holds, but in order to obtain the margin of error, it is accurate again from Equations 1 and 3. calculate.

と、表される。一方、対象１０２からの戻り光２２０の飛行距離変化に起因する検出光信号変化量ΔＩ^disは、次式で示される。

Assuming that the distance between the light source 106 and the target 102 changes from the initial distance r ₁ to r ₂ , the amount of change in the optical signal ΔI ^ill detected due to the change in the illuminance of the irradiation light 210 on the target 102 is determined from Equation 1.

Is expressed. On the other hand, the amount of change in the detected light signal ΔI ^dis due to the change in the flight distance of the return light 220 from the target 102 is expressed by the following equation.

となる。したがって、数式８、数式９を数式７に代入すると、次式が得られる。

^Assuming that the signal change amount ΔI ^task to be detected is k times the initial detected optical signal intensity I ₁

Will be. Therefore, by substituting Equations 8 and 9 into Equation 7, the following equation is obtained.

If Δr is in the range satisfying Equation 11, the S / N ratio exceeds 1 and it can be said that motion correction is effective. That is, when the target 102 is measured at two distances r1 and r2 in which the distances from the light source 106 to the target 102 are different from each other using the initial phase satisfying the formula 5 or the formula 6, the difference Δr between r1 and r2 is the formula 11. If the above conditions are satisfied, the amount of change in the signal to be detected obtained from the target 102 becomes larger than the amount of change in the detection signal due to the movement of the target 102, and effective measurement can be performed.

In an experimental study by the inventor of the present application, the attenuation coefficient α of the return light when the rectangular pulse light was irradiated from the light source 106 toward the living body was 1.5 [1 / ns]. For example, assuming that the initial distance r ₁ is 16 cm, the ratio k of the amount of signal change to the task is 0.1, and the speed of light c is 300000000 m / s, the permissible range of motion Δr that can be corrected is ± 3.3 cm. The relationship between the initial distance r1 and the allowable movement range Δrb is shown below. As r1, it was set to 5 to 100 cm, which is a general measurement range.

Within the range of Table 1, a desired signal change can be detected with respect to the movement of the target 102. For example, if the difference between the distance 1 and the distance 2 in FIG. 3A is in the range of Δrb / 2 (= Δra) or more and Δrb or less, which is half of the limit value, and the light detection intensities of the distance 1 and the distance 2 are compared, S / N Can be confirmed to be 1 or more.

If the target 102 moves significantly beyond the range of Equation 11 or Table 1, the initial value may be reset. Whether or not the movement exceeds the permissible range is determined by using the image pickup device 100 capable of TOF, measuring the distance to the target 102 by the TOF periodically during the measurement period, and providing a separate distance detection mechanism such as stereo distance measurement. It can be realized by doing something like that. When resetting the initial value, the measurement may be continued with a new initial value, or when the target 102 is a person, the measurement may be restarted from the beginning or prompted.

When the internal scattering in the target 102 is small and an optical signal near the surface of the target 102 is detected, the rear end of the pulsed light generated from the light source 106 may be blunted in advance as shown in the waveform (a) of FIG. , It is effective for correcting the movement of the target 102. If it is blunted in advance, it can be used for adjusting the amount of increase / decrease in the detection signal due to the time delay of the optical signal due to the movement of the target even if the time delay due to scattering occurs in the target 102.

Although the present embodiment is correction of movement in the z direction, correction of x, y shift, pan, and tilt of the target 102 may also be combined. For these movements, motion tracking using a camera image, acceleration measurement provided on the target 102, or the like may be used. If the camera image is also used as the image of the image pickup apparatus 100, the number of sensing devices can be reduced. Three-dimensional motion correction of the target 102 becomes possible by matrix operation from the detected motion vector. The z direction may also be combined with the correction in motion tracking. In this case as well, optimizing the initial phase position of the present application in advance is effective because the load of motion tracking correction can be reduced.

(Embodiment 2)
The imaging device of the present embodiment is different from the imaging device of the first embodiment in that it further includes a diffusion angle adjusting mechanism 116 for adjusting the emission angle of the light emitted from the light source 106. Here, detailed description of the same contents as in the first embodiment in the present embodiment will be omitted.

FIG. 5A shows the relationship between the diffusion angle of the light source and the density change of the irradiation light 210. The diffusion angle adjusting mechanism 116 adjusts the spreading angle of the irradiation light 210 emitted by the light source 106. For example, it is formed of a diffuser plate and an optical lens. Comparing the cases where the target 102 exists at the positions A and B, the amount of change in illuminance due to movement is inversely proportional to the distance from the light source as shown in Equation 2, so even if the amount of movement is the same, the amount of change at position A The detected change in optical signal intensity is smaller than that of position B. Therefore, as shown in FIG. 5C, at position A, the position where the slope of the phase change of the optical signal detection intensity is relatively small is the optimum phase T2, and at position B, the position where the slope is relatively large is the optimum phase T1.

However, the optical signal 200 includes light having a long optical path length at the latest time, for example, t = t1, and light having a shorter optical path length toward the earlier time t = t4. Therefore, the later the shutter is disclosed, the greater the proportion of information in the deep part of the target 102 included in the optical signal 200. Therefore, in order to match the position where the ratio of the cerebral blood flow component is high with the optimum phase position of the motion correction, the diffusion angle of the light source may be adjusted by using the diffusion angle adjusting mechanism 116 as shown in FIG. 5B. .. In the case of FIG. 5B, since the spread angle is smaller than that in FIG. 5A, the change in illuminance due to the movement of the target 102 is small even at the position B. That is, the optimum phase at position B can be made the same as the optimum phase T2 at position A in FIG. 5A (FIG. 5C). The diffusion angle adjusting mechanism 116 may include a zoom lens mechanism. This is because the distance of the target 102 can be monitored and appropriately adjusted in real time according to the distance. Further, if the shutter start phase is too late, the absolute amount of light decreases and the S / N ratio decreases. In this case, it is preferable to increase the spreading angle of the diffusion angle adjusting mechanism 116 to advance the optimum phase position.

(Embodiment 3)
The image pickup apparatus of the present embodiment is different from the image pickup apparatus of the first embodiment in that the pattern projection unit 118 is provided on the exit surface of the light source 106. Here, detailed description of the same contents as in the first embodiment in the present embodiment will be omitted.

6A and 6B are diagrams showing an example of an irradiation pattern formed by the pattern projection unit 118. In the imaging devices of embodiments 1 and 2, the light source 106 projects uniform illumination light. On the other hand, in the present embodiment, the light emitted from the light source 106 is converted into light having a ring-shaped pattern by the pattern projection unit 118 and projected from the pattern projection unit 118. The light signal detection location in the projected irradiation pattern is inside the ring, for example, in the center of the ring. The ring-shaped pattern may have the same ring width or may have different widths depending on the distance. FIG. 6B shows an example of projecting a dot-shaped pattern of light from the pattern projection unit 118. The optical signal detection points are between the dots. The dot-shaped pattern may have the same dot diameter, or may have different diameters depending on the distance.

The pattern projection unit 118 includes a diffuser, a diffuser, an optical lens, a light-shielding plate, etc., and is converted into a desired pattern of light by blocking, converging, or reflecting a part of the light emitted from the light source 106. ..

(Embodiment 4)
The image pickup apparatus of this embodiment is different from the image pickup apparatus of this embodiment in that it has an arithmetic processing unit 120. Here, detailed description of the same contents as in the first embodiment in the present embodiment will be omitted.

The arithmetic processing unit 120 performs a process of removing an offset component from the signal obtained by the photodetector 108. The offset component is a constant noise component included regardless of the phase at which the shutter is started when the return light 220 is detected. The offset component is generated, for example, by leaking a part of the photoelectrically converted charge to the charge storage unit 112 even when the charge accumulation from the photoelectric conversion unit 110 to the charge storage unit 112 is stopped. It also contains components that pass through the gaps of the light-shielding film that blocks light so as to cover the charge storage unit 112. When a large offset component is generated, ΔI ^dis is significantly reduced as compared with ΔI ^ill , so that the optimum phase position is largely shifted or the optimum phase position does not exist. Therefore, the arithmetic processing unit 120 separately estimates the offset component and performs the processing of subtracting it by the arithmetic processing.

(Embodiment 5)
The image pickup apparatus of this embodiment satisfies a conditional expression having a diffusion angle of the irradiation light 210. Here, detailed description of the same contents as in the first embodiment in the present embodiment will be omitted.

FIG. 7 is a diagram showing the relationship between the shutter start phase and the amount of change in the detected light signal due to fluctuations in the flight distance of light. The horizontal axis of FIG. 7 represents the shutter start phase, and the vertical axis represents the amount of change in the detected optical signal ΔI ^dis due to the fluctuation of the flight distance of light. The variation in the flight distance of the light corresponds to the variation in the arrival time of the light to the image pickup apparatus 100. As shown in FIG. 7, when the rectangular pulsed light is emitted from the light source 106, the amount of change ΔI ^dis of the detected light signal due to the fluctuation of the flight distance of the light is constant even if the shutter is started before the rear end of the rectangular pulsed light. .. Further, as shown in FIG. 7, when the shutter start phase is after the rear end of the rectangular pulse light, the detected light signal change amount ΔI ^dis due to the flight distance variation of the light decreases as the shutter start phase increases. Therefore, there is an upper limit to the amount of change in the detected optical signal ΔI ^dis due to the variation in the flight distance of light.

Further, when the shutter start phase is after the start of decrease of the detected light signal change amount ΔI ^dis due to the fluctuation of the flight distance of the light at the rear end of the pulsed light, the image pickup apparatus 100 effectively acquires the internal scattering information of the target 102. Can be done. From the above, by canceling the detected light signal change amount ΔI ^ill caused by the illuminance change of the irradiation light 210 with the detected light signal change amount ΔI ^dis due to the fluctuation of the flight distance of the light, the change in the detected light amount due to the movement of the target 102 In the case of reducing the amount of ^light , the imaging device of the present embodiment at least satisfies the condition that ΔI ^ill ≤ ΔI ^dis .

となる。ただし、ｃは光速である。 FIG. 8 is a diagram showing the relationship between the diffusion angle θ of the irradiation light 210 irradiated from the light source 106 to the target 102 and the distance to the target 102 in the image pickup apparatus 100 of the present embodiment. The light source 106 includes a diffuser plate 300. If the diameter of the spot on the diffuser plate 300 of the irradiation light 210 is defined as d [mm] and the distance from the diffuser plate 300 to the target 102 is defined as R [mm], the above condition ΔI ^ill ≤ ΔI ^dis is ^satisfied .

Will be. However, c is the speed of light.

Here, alpha = 2.7 as a result of measurement in vivo [1 / ns], the speed of light ^{c = 3 × 10 8 [m} ], by substituting an average motion levels of human is 10 [mm] as Δr , Formula 13 is derived.
(Number 13)
81.5 ≦ R + d / (2tanθ) (Number 13)

However, R, d, θ> 0.

Here, Δr = 10 [mm] was substituted as the minute distance variation, which corresponds to the amount of variation when the person consciously stands still. If this condition is satisfied, there is a solution at the rear end of the pulsed light that can cancel the detected light signal change amount ΔI ^ill caused by the illuminance change of the irradiation light 210 with the detected light signal change amount ΔI ^dis due to the flight distance change of the light. To do.

FIG. 9 shows an example of the value obtained by subtracting the right side from the left side of the formula 13. Here, d = 5 mm, and the value when the distance R from the diffuser plate 300 to the target 102 and the diffusion angle θ of the irradiation light 210 are used as parameters is calculated. If the value in the table is negative, it means that the formula 13 is not satisfied. With reference to FIG. 9, for example, when the distance R to the target 102 is 50 mm, it can be seen that the equation 13 is satisfied if the diffusion angle θΘ of the irradiation light Ii is 4 ° or less.

The imaging device in the present disclosure is useful for a camera or a measuring device that acquires internal information of a measurement target in a non-contact manner. It can be applied to biomedical sensing, material analysis, food analysis, and in-vehicle sensing systems.

100 Imaging device 102 Target 104 Light 106 Light source 108 Photodetector 110 Photoelectric conversion unit 112 Charge storage unit 114 Control circuit 200 Optical signal 210, 212, 214 Irradiation light 220, 222, 224 Return light 116 Diffusion angle adjustment mechanism 118 Pattern projection unit 120 Arithmetic processing unit 300 Diffusing plate

Claims (4)

A light source that includes a diffuser and emits pulsed light that spreads at a diffusion angle greater than 0 degrees toward the target.
A photodetector that includes a photoelectric conversion unit that receives light from the object and converts it into an electric charge, and a charge storage unit that stores the electric charge, and outputs an electric signal when the electric charge is read out.
A control circuit that controls the light source and the photodetector,
With
The control circuit causes the light source to start emitting the pulsed light, and after a lapse of a predetermined time, starts the accumulation of the charge in the charge storage unit, whereby the inside of the target among the light from the target. The charge corresponding to the component scattered in is accumulated in the charge storage unit,
Assuming that the distance from the diffusion plate to the object is R (mm), the diffusion angle is θ (degrees), and the spot size of the pulsed light on the diffusion plate is d (mm), the following equation holds. ..
81.5 ≦ R + d / (2tanθ) A diffusion angle adjusting mechanism for adjusting the diffusion angle is further provided.
The imaging device according to claim 1. A pattern projection unit that converts the pulsed light into light having a desired pattern is further provided.
The imaging device according to claim 1. The control circuit removes a predetermined offset component from the electrical signal.
The imaging device according to claim 1.

Images