JP6071591B2 - Optical scanning endoscope - Google Patents

Description

  The present invention relates to an optical scanning endoscope using a swingable fiber.

  Conventionally, as an optical scanning observation apparatus that scans an observation object with a laser beam and converts the transmitted light, reflected light, or fluorescence from the observation object into an electrical signal by a photoelectric conversion unit to form image data, An optical scanning endoscope that obtains an image by irradiating an observation target with laser light from the tip of a swingable fiber and sequentially scanning the laser light on the observation target by vibrating the fiber. Known (for example, refer to Patent Document 1 and Patent Document 2).

  As a means for vibrating the fiber of the optical scanning endoscope, a method of attaching a piezoelectric element to the fiber to vibrate (for example, refer to Patent Document 1), or an electromagnetic coil for vibrating a permanent magnet attached to the fiber by an electromagnetic coil. There is a method (for example, see Patent Document 2). When a fiber is driven to vibrate, a large deflection (displacement, amplitude) of the fiber can be obtained with a small amount of energy by driving a drive element such as a piezoelectric element or an electromagnetic coil near the resonance frequency of the oscillated fiber.

  However, when the fiber is actually driven near the resonance frequency, the locus is not stable due to nonlinear vibration. For example, even if it is desired to vibrate so that the locus of the irradiation position of the laser beam on the observation object is a straight line, if it is driven in the vicinity of the resonance frequency, it becomes an elliptical locus. This means that even when scanning is performed in the X-axis direction, scanning is also performed unintentionally in the Y-axis direction perpendicular to the X-axis direction. Even when two-dimensional scanning is performed, the scanning trajectory is distorted. Bring. For example, when two-dimensional spiral scanning is performed, the phase difference between the X-axis scanning and the Y-axis scanning is shifted from 90 °, and the circular scanning is distorted into the elliptical scanning. Moreover, even when the amplitude of spiral scanning is the smallest, it does not become zero, so that a phenomenon occurs such that the center of the screen is not scanned, that is, an image at the center of the screen cannot be obtained (see Non-Patent Document 1).

  In contrast to the waveform distortion caused by driving near the resonance frequency, when driving at a frequency shifted by several percent from the resonance frequency, the fiber tip trajectory becomes straight and stable when driven by vibration. Has been reported (see Non-Patent Document 2). In Non-Patent Document 2, the frequency at which the locus becomes a straight line from an ellipse when the fiber is vibrated one-dimensionally is called a quasi-resonant frequency.

US Pat. No. 6,294,775 JP 2008-116922 A

Quinn Y. J. Smithwick et. Al. “An Error Space Controller for a Resonating Fiber Scanner: Simulation and Implementation” Jounal of Dynamic Systems, Measurement, and Conrol Vol.128, pp899, 2006 (University of Washington) Sucbei Moon et. Al. "Semi-resonant operation of a fiber-cantilever piezotube scanner for stable optical coherence tomography connector imaging" Optics Express Vol.18, pp21183, 2010 (University of California, Irvine)

  As described in Non-Patent Document 2, it is expected that the locus of the irradiation position of the laser beam can be stabilized by shifting the drive frequency of the drive element to the quasi-resonant frequency of the fiber. However, as a result of diligent experimentation and verification by the present inventors, when scanning with amplitude modulation such as spiral scanning is performed, even when the driving element is driven at a quasi-resonant frequency, the scanning trajectory of the laser beam is distorted. I found it to happen. In particular, when performing spiral scanning, there is a problem that even if scanning is performed at a quasi-resonant frequency, even when the amplitude of spiral scanning is the smallest, it does not become zero and the scanning center is not scanned.

  Therefore, the object of the present invention, which has been made by paying attention to these points, is that the scanning trajectory in the case of performing the spiral scan of the observation object is stabilized, and the signal is also emitted from the scanning center portion of the observation object by the laser light irradiation. An object of the present invention is to provide a detectable optical scanning endoscope.

The invention of an optical scanning endoscope that achieves the above object is as follows.
A fiber having a fixed portion and a swingable portion swingable with respect to the fixed portion, and irradiating an observation object with laser light from the tip of the swingable portion;
A drive unit for oscillating and driving the oscillating unit of the fiber;
A detection unit that detects light obtained by irradiation of the laser light from the observation object and converts the light into an electrical signal; and
The drive unit is substantially a maximum and a predetermined zero Rutotomoni, the amplitude of the vibration of the fiber is scanned the swinging portion of the fiber respectively to vibrate at a constant driving frequency different 2 axially helically The drive frequency is fluctuated depending on the modulation frequency between values.
Upper limit frequency ≧ drive frequency ≧ high frequency side quasi-resonance frequency + modulation frequency or lower limit frequency ≦ drive frequency ≦ low frequency side quasi-resonance frequency−modulation frequency.
Here, the upper limit frequency and the lower limit frequency are respectively the high frequency side and the low frequency side of the resonance frequency, and the amplitude of the vibration of the fiber due to the driving of the drive unit is driven at the resonance frequency. Ri frequency der when a minute of 1,
The quasi-resonant frequency is a frequency at which the orbits reciprocating in the long axis direction partially overlap when the drive unit is driven to vibrate in a one-dimensional direction and the drive frequency is shifted from the resonance frequency .

More preferably, the drive frequency is
It is preferable that drive frequency = high frequency side quasi-resonance frequency + modulation frequency or drive frequency = low frequency side quasi-resonance frequency−modulation frequency.

Further, the driving unit, it is preferable to vibrate with a phase difference of approximately 90 ° in two directions perpendicular to each other physician.

Further, when the drive frequency of the drive unit is changed, the amplitude of the oscillating unit with respect to the drive frequency exhibits asymmetry around the resonance frequency,
When the amplitude at the high-frequency side quasi-resonant frequency is greater than the amplitude at the low-frequency side quasi-resonant frequency, the drive frequency,
Upper limit frequency ≧ drive frequency ≧ high frequency side quasi-resonant frequency + modulation frequency
When the amplitude at the low-frequency side quasi-resonant frequency is larger than the amplitude at the high-frequency side quasi-resonant frequency, the drive frequency,
More preferably, lower limit frequency ≦ drive frequency ≦ low frequency side quasi-resonant frequency−modulation frequency

  Note that the quasi-resonant frequency of the present application is a frequency at which the locus becomes a straight line from an ellipse when the optical fiber is driven to vibrate in a one-dimensional direction and is shifted from the resonant frequency. Present on both sides of the frequency side. The quasi-resonant frequency on the high frequency side is called the high-frequency side quasi-resonant frequency, and the quasi-resonant frequency on the low-frequency side is called the low-frequency side quasi-resonant frequency. Here, the frequency at which the locus becomes a straight line from the ellipse is a frequency when the ellipticity of the locus is 3.5% or less. The reason is as follows. That is, in order to obtain an angle of view of about 90 degrees with an optical scanning endoscope, it is preferable that the fiber amplitude is 0.1 mm or more in consideration of the optical resolution depending on the lens magnification. On the other hand, the mode field diameter (MFD) of a single mode fiber generally used for visible light is 3.5 μm. Therefore, if the ellipticity is about 3.5% (the major axis is 100 μm and the minor axis is 3.5 μm, the ellipticity (E) = 3.5 / 100) or less, the orbits reciprocating in the substantially major axis partly overlap. Therefore, the elliptical orbit can be regarded as a straight line. Further, in this application, the resonance frequency of the oscillating part of the fiber means that when a part of the member of the driving part is attached to a part of the oscillating part of the fiber, the resonance frequency in a state where the member is attached. Means.

According to the present invention, the drive unit vibrates the oscillation unit of the fiber at the drive frequency, and varies the amplitude of the vibration of the fiber substantially between zero and a predetermined maximum value according to the modulation frequency, The
Since the upper limit frequency ≧ drive frequency ≧ high frequency side quasi-resonant frequency + modulation frequency or lower limit frequency ≦ drive frequency ≦ low frequency side quasi-resonance frequency−modulation frequency, the scanning locus when scanning the observation object is stable, It is possible to detect and observe a signal from the scanning center portion of the observation object by irradiating the laser beam.

1 is a block diagram illustrating a schematic configuration of an optical scanning endoscope according to a first embodiment. FIG. FIG. 2 is an overview diagram schematically showing the optical scanning endoscope main body of FIG. 1. It is a figure which expands and shows the front-end | tip part of the optical scanning endoscope main body of FIG. It is a figure which expands and shows the drive part of FIG. 3, (a) is the whole, (b) is a figure which shows the general view of the optical fiber for illumination, and a magnet. It is a figure which shows schematic structure of the light source part of the optical scanning endoscope of FIG. It is a figure which shows schematic structure of the detection part of the optical scanning endoscope of FIG. FIGS. 2A and 2B are diagrams for explaining scanning by the driving unit in FIG. 1, in which FIG. 1A shows a time change in vibration in the x direction, FIG. 1B shows a time change in vibration in the y direction orthogonal to the x direction, and FIG. It is a figure explaining the scanning locus in a plane, respectively. It is a figure explaining the frequency spectrum in spiral scanning. It is a figure explaining the relationship between the frequency spectrum in the case of performing a spiral scan by using a quasi-resonance frequency as a drive frequency, and the unstable region near the resonance frequency. It is a figure explaining the relationship between the frequency spectrum of spiral scanning by 1st Embodiment, and the unstable area | region of the resonance frequency vicinity. It is a figure explaining the measuring method of the change of the amplitude by an amplitude modulation, and a phase, Fig.11 (a) demonstrates the measurement of the scanning locus | trajectory which is not accompanied by an amplitude modulation, FIG.11 (b) is the scanning in case an amplitude modulation is accompanied. It is a figure explaining the measurement of a locus. It is a figure which shows the measurement result of the change of the amplitude and phase by amplitude modulation about a different modulation frequency and a drive frequency, (a) is a case where a drive part is not oscillated at an quasi-resonance frequency without amplitude modulation, (b) is a drive When the part is amplitude-modulated at 3.7 Hz and is vibrationally driven at a quasi-resonant frequency, (c) is when the drive part is amplitude-modulated at 3.7 Hz and is vibrationally driven at a driving frequency that is 3.7 Hz lower than the quasi-resonant frequency. ) When the drive unit is amplitude-modulated at 7.4 Hz and vibration driven at a drive frequency lower than the quasi-resonant frequency by 3.7 Hz, FIG. The cases where vibration driving is performed at a low driving frequency are shown. It is a figure explaining selection of a drive frequency in case nonlinear vibration arises. It is a graph which shows an example of the amplitude of the front-end | tip part of the illumination optical fiber with respect to the drive frequency obtained from the experimental result. It is a figure which expands and shows the front-end | tip part of the optical scanning type endoscope main body which concerns on 2nd Embodiment. 16A is a side view showing the vibration drive mechanism at the tip of FIG. 15 and the swinging portion of the optical fiber for illumination, and FIG. 16B is a cross-sectional view taken along the line AA in FIG. is there.

  Embodiments of the present invention will be described below with reference to the drawings.

(First embodiment)
FIG. 1 is a block diagram showing a schematic configuration of the optical scanning endoscope according to the first embodiment. The optical scanning endoscope 10 includes an optical scanning endoscope main body 20, a light source unit 30, a detection unit 40, a drive control unit 50, a control unit 60, a display unit 61, and an input unit 62. Consists of. The light source unit 30 and the optical scanning endoscope main body 20 are optically connected by the illumination optical fiber 11 that is a single mode fiber, and the detection unit 40 and the optical scanning endoscope main body 20 are multi-connected. They are optically connected by a plurality of optical fibers for detection 12 constituted by mode fibers. The light source unit 30, the detection unit 40, the drive control unit 50, and the control unit 60 may be housed in the same housing or may be housed in separate housings.

  The light source unit 30 combines, for example, light from three laser light sources that emit CW (continuous oscillation) laser light of three primary colors of red, green, and blue, and emits it as white light. The optical scanning endoscope main body 20 scans the laser light emitted from the light source unit 30 by the illumination optical fiber 11 on the observation object 100 by the driving unit 70, and uses the signal light obtained by this scanning. The light is condensed on the detection optical fiber 12 and transmitted to the detection unit 40 via the detection optical fiber 12. Here, based on the control from the control unit 60, the drive control unit 50 applies a drive current to the drive unit 70 via the wiring cable 13.

  The detection unit 40 decomposes the signal light that has passed through the detection optical fiber 12 into spectral components, and converts the signal light into an electrical signal by a photodetector using a photodiode. The control unit 60 synchronously controls the light source unit 30, the detection unit 40, and the drive control unit 50, processes the electrical signal output by the detection unit 40, combines the images, and displays the images on the display unit 61. Further, various settings such as the scanning speed and the brightness of the display image can be performed on the optical scanning endoscope 10 from the input unit 62.

  FIG. 2 is a schematic view schematically showing the optical scanning endoscope body 20. The optical scanning endoscope main body 20 includes an operation unit 22 and an insertion unit 23, and one end of the operation unit 22 and one end of the insertion unit 23 are connected and integrated. The operation unit 22 is connected to the illumination optical fiber 11 from the light source unit 30, the plurality of detection optical fibers 12 from the detection unit 40, and the wiring cable 13 from the drive control unit 50. The illumination optical fiber 11, the detection optical fiber 12, and the wiring cable 13 pass through the inside of the insertion portion 23, and a distal end portion 24 that is different from the end portion connected to the operation portion 22 of the insertion portion 23 (see FIG. 2 to a portion within a broken line portion).

  3 is an enlarged cross-sectional view of the distal end portion 24 of the insertion portion 23 of the optical scanning endoscope main body 20 of FIG. 4 is an enlarged view of the drive unit 70 shown in FIG. 3. FIG. 4A is an overall view, and FIG. 4B is an overview of the illumination optical fiber 11 and the magnet. The distal end portion 24 includes a drive unit 70 and a projection lens 25, and an illumination optical fiber 11 that passes through the insertion unit 23, a detection optical fiber 12, and forceps holes 27 through which various treatment tools are inserted. doing. Here, although not shown, a detection lens may be provided at the tip of the detection optical fiber 12.

  The illumination optical fiber 11 is a fixed portion 11 a partially fixed by an attachment ring 26 fixed inside the distal end portion 24, and laser light is emitted from the fixed portion 11 a toward the observation object 100. Up to the tip portion 11c is a swinging portion 11b supported so as to be swingable. On the other hand, each of the plurality of detection optical fibers 12 is disposed so as to pass through the outer peripheral portion of the insertion portion 23 and extends to the tip of the tip portion 24.

  A permanent magnet 73 that is magnetized in the axial direction of the illumination optical fiber 11 and has a through-hole is provided in a part of the swinging portion 11b of the illumination optical fiber 11, and the swinging portion 11b of the illumination optical fiber 11 is a through-hole. It is combined in the state of passing through. In addition, a square tube 71 having one end fixed to the mounting ring 26 is provided so as to surround the swinging portion 11b, and each of the four side surfaces of the portion of the square tube 71 facing the two poles of the permanent magnet 73 is provided. Are provided with helical coils 72a to 72h for generating a deflection magnetic field. The electromagnetic coils 72 a to 72 h are connected to the wiring cable 13 and connected to the drive control unit 50. The drive control unit 50 can scan the laser light on the observation object 100 in a plane composed of the X direction and the Y direction orthogonal to the X direction by applying a current to the electromagnetic coils 72a to 72h.

  Further, the projection lens 25 is disposed at the forefront of the distal end portion 24. The projection lens 25 is configured so that laser light emitted from the distal end portion 11 c of the illumination optical fiber 11 is substantially condensed on the observation object 100. In addition, when a detection lens is disposed, the light (the light that interacts with the observation object 100) that is reflected, scattered, refracted, or the like by the observation object 100 from the laser light collected on the observation object 100. ) Or fluorescence or the like as detection light, and is arranged so as to be condensed and coupled to the detection optical fiber 12 arranged after the detection lens.

  FIG. 5 is a diagram showing a schematic configuration of the light source unit 30 of the optical scanning endoscope 10 of FIG. The light source unit 30 includes laser light sources 31R, 31G, and 31B that emit CW (continuous oscillation) laser light of three primary colors of red, green, and blue, dichroic mirrors 32a and 32b, and an AOM (acousto-optic modulator) 33, respectively. And a lens 34. For example, an LD (semiconductor laser) can be used as the red laser light source 31R. Further, as the green laser light source 31G, for example, a DPSS laser (semiconductor excitation solid-state laser) can be used. Furthermore, as the blue laser light source 31B, for example, an LD can be used.

  The optical path of the laser light emitted from the laser light source 31R and the optical path of the laser light emitted from the laser light source 31G are arranged so as to intersect at a predetermined point, and a dichroic mirror 32a is provided at the intersecting position. The dichroic mirror 32a has an optical characteristic of transmitting light in the red wavelength band and reflecting light in the green wavelength band. The red laser light emitted from the laser light source 31R and transmitted through the dichroic mirror 32a, and the laser light source The green laser light emitted from 31G and reflected by the dichroic mirror 32a is arranged at an angle to be combined.

  Furthermore, the optical path of the laser beam obtained by combining the red laser beam and the green laser beam and the optical path of the blue laser beam emitted from the laser light source 31B are arranged so as to intersect at a predetermined point. A dichroic mirror 32b is provided at the intersecting position. The dichroic mirror 32b has optical characteristics of transmitting light in the red wavelength band and light in the green wavelength band and reflecting light in the blue wavelength band, and is combined by the dichroic mirror 32a and transmitted through the dichroic mirror 32b. And the blue laser light emitted from the laser light source 31B and reflected by the dichroic mirror 32b are arranged at an angle to be combined. In this way, the laser light of the three primary colors of red, green, and blue emitted from the laser light sources 31R, 31G, and 31B are combined to become white laser light.

  The AOM 33 is an element that modulates the intensity of incident light, and can switch between a light shielding state and a light transmitting state continuously and at high speed. The white laser light combined by the dichroic mirrors 32 a and 32 b is transmitted through the AOM 33 when the AOM 33 is in a light transmitting state, and is incident on the incident end of the illumination optical fiber 11 by the lens 34. The AOM 33 is electrically connected to the control unit 60 in FIG. The arrangement of the laser light sources 31R, 31G, and 31B and the dichroic mirrors 32a and 32b is not limited to this. For example, after combining green and blue laser beams, the red laser beams are combined. Also good.

  FIG. 6 is a diagram illustrating a schematic configuration of the detection unit 40 of the optical scanning endoscope 10 of FIG. The detection unit 40 includes light receivers 41R, 41G, and 41B, dichroic mirrors 42a and 42b, and a lens 43 that use photodiodes for detecting light corresponding to red, green, and blue colors. A plurality of detection optical fibers 12 are bundled and connected to the detection unit 40.

  The signal light that is reflected by the observation object 100 or emitted from the observation object 100 by the irradiation of the laser light and passes through the detection optical fiber 12 and exits from the exit end thereof becomes a substantially parallel light flux by the lens 43. Dichroic mirrors 42a and 42b are disposed on the optical path of the signal light that has become a substantially parallel light beam so as to be inclined with respect to the direction of the optical path. The dichroic mirror 42b has an optical characteristic of reflecting light in the blue wavelength band and transmitting light in the red and green wavelength bands, and separates the blue signal light from the signal light that has become a parallel light flux by the lens 43. . The separated blue signal light is detected by the light receiver 41B and converted into an electric signal. The dichroic mirror 42a has an optical characteristic of reflecting light in the green wavelength band and transmitting light in the red wavelength band, and separates the signal light transmitted through the dichroic mirror 42b into red and green signal lights. To do. The separated red and green signal lights are detected and converted into electrical signals by the light receiver 41R and the light receiver 41G, respectively.

  The light receivers 41R, 41G, and 41B are electrically connected to the control unit 60 of FIG. The arrangement of the light receivers 41R, 41G, and 41B and the dichroic mirrors 42a and 42b is not limited to this. For example, after the red light is separated from the signal light, the green and blue signal lights are further separated. It is good also as arrangement.

The control unit 60 vibrates and drives the drive unit 70 of the optical scanning endoscope main body 20 via the drive control unit 50 to spirally emit the laser light emitted from the illumination optical fiber 11 on the observation object 100. Scan (spiral scan). Specifically, a current is applied to the electromagnetic coils 72a to 72h to cause the following vibrations in the x and y directions, respectively.
x = sin (ω _m t) · sin (ω _x t)
y = sin (ω _m t) · sin (ω _y t + 90 °)
Here, ω _x , ω _y, and (ω _x = ω _y ) are drive angular frequencies, and ω _m is a modulation angular frequency of amplitude modulation. (A) of FIG. 7 is a figure which shows the time change of the vibration of x direction, (b) is a figure which shows the time change of the vibration of the y direction orthogonal to x direction, (c) is a figure which shows the vibration of x direction and y direction. It is a figure explaining the scanning locus | trajectory of the target laser beam in xy plane obtained by combining. The scanning locus in FIG. 7C corresponds to a half cycle of amplitude modulation. As shown in FIG. 7C, the scanning trajectory of the laser beam is spiral. In this way, a scanning locus close to rotational symmetry (periphery is close to a circle) can be obtained by vibrating the oscillating portion of the fiber with a phase difference of 90 ° in two orthogonal axes.

As described above, when the oscillating portion 11b of the illumination optical fiber 11 is vibrated, in the frequency space, as shown in FIG. 8, the driving frequency (f _x = ω _x / 2π = ω _y / 2π) on the high frequency side and low Sideband waves (f _x ± f _m , f _m = ω _m / 2π) appear on the frequency side. According to the study by the present inventors, even if the drive frequency of the illumination optical fiber 11 is shifted to the quasi-resonant frequency of the fiber, the reason why the scanning locus is distorted is that this sideband is more resonant than the quasi-resonant frequency. Exists in an unstable region located in the vicinity of. This will be described with reference to FIG. FIG. 9 is a diagram for explaining the relationship between a frequency spectrum and an unstable region near the resonance frequency when spiral scanning is performed using the low frequency side quasi-resonance frequency f _ql as a drive frequency. The curve graph of FIG. 9 shows the change in the amplitude of the distal end portion 11c of the illumination optical fiber 11 when the drive frequency is changed by the drive unit 70 with the same drive energy without amplitude modulation. Amplitude of the graph is the largest becomes the frequency is the resonant frequency f _r. The frequencies f _ql and f _qh are the quasi-resonant frequencies on the low frequency side and the high frequency side of the resonance frequency, respectively. The region near the resonance frequency between the frequencies f _ql and f _qh is an unstable region where the vibration waveform becomes unstable. As shown in FIG. 9, by setting the driving frequency f _x to the low frequency side of the semi-resonant frequency f _ql, sideband of the high-frequency side (frequency f _{x +} f _m) belongs to an unstable region in the vicinity of the resonance frequency It will be. Also, the driving frequency is set to f _x on the high frequency side semi-resonant frequency f _qh, similarly sideband of the low frequency side (frequency f _x -f _m) belongs to an unstable region in the vicinity of the resonance frequency It will be.

Therefore, in the present invention, the drive frequency (f _x ) is set in consideration of the modulation frequency (f _m ) so as to be located outside the unstable region of the resonance frequency including the sideband as shown in FIG. That is,
If drive frequency ≧ high-frequency side quasi-resonant frequency + modulation frequency or drive frequency ≦ low-frequency side quasi-resonance frequency−modulation frequency, the frequency spectrum including the sidebands on the high-frequency side and low-frequency side quasi-resonant frequency (f Since there is no unstable region near the resonance frequency between _qh and f _ql ), the scanning trajectory of spiral scanning is stabilized.

On the other hand, as the drive frequency moves away from the resonance frequency, the amplitude of the illumination optical fiber 11 rapidly decreases. As for the amplitude of the optical fiber 11 for illumination, it is desirable that it has an amplitude of 1/10 or more of the amplitude (A) when it is driven to vibrate at the resonance frequency. If the amplitude is less than this, the energy efficiency of the vibration drive is poor. When the amplitude is 1/10 or less, in order to obtain a desired amplitude, it is necessary to pass a current 10 times or more that when the coil is driven at the resonance frequency. In this case, the increase in the amount of generated heat is 10 times or more. Therefore, in consideration of practicality, it is preferable that there is an amplitude of 1/10 or more. Therefore, the drive frequency is
It is preferable that upper limit frequency ≧ drive frequency ≧ high frequency side quasi-resonance frequency + modulation frequency or lower limit frequency ≦ drive frequency ≦ low frequency side quasi-resonance frequency−modulation frequency. Here, the upper limit frequency and the lower limit frequency are on the high frequency side and the low frequency side of the resonance frequency, respectively, and the amplitude of the vibration of the fiber driven by the drive unit 70 is one tenth of that when driving at the resonance frequency. Frequency (f _max , f _min ).

Furthermore, from the viewpoint of energy efficiency, the drive frequency is preferably closer to the resonance frequency. Therefore, it is preferable that the drive frequency is drive frequency = high frequency side quasi-resonant frequency + modulation frequency or drive frequency = low frequency side quasi-resonant frequency−modulation frequency.

  Next, in order to show that the scanning trajectory accompanied by amplitude modulation is stabilized when the drive frequency satisfies the conditions of the present invention, changes in the amplitude and phase of the scanning trajectory due to amplitude modulation of the drive signal were measured. The results will be described. 11A and 11B are diagrams illustrating a method for measuring changes in amplitude and phase by amplitude modulation. FIG. 11A illustrates measurement of a scanning trajectory without amplitude modulation, and FIG. 11B illustrates amplitude modulation. It is a figure explaining the measurement of the scanning locus in the case where it accompanies. First, as procedure 1, as shown in FIG. 11A, the position of the point indicating the scanning position is plotted with time for every fixed period (vibration period) in one direction without amplitude modulation. Here, it is confirmed that the points plotted at the center of the amplitude are linearly arranged. Next, as procedure 2, as shown in FIG. 11B, amplitude modulation is performed between the amplitude 0 (the amplitude at the upper end and the lower end in FIG. 11B) and the maximum amplitude by a triangular wave or a sine wave or the like. While performing, the points are plotted at regular intervals as in the case of FIG. A curve formed by a set of points obtained in this way is called a phase curve. Here, if the plotted phase curve does not become a straight line, it means that the phase has changed. Such a phase change leads to distortion of the trajectory, and in the case of linear vibration, the shape of the scanning trajectory is changed to an elliptical shape.

  FIG. 12 is a diagram showing measurement results of changes in amplitude and phase due to amplitude modulation for different modulation frequencies and drive frequencies. In this measurement, first, the amplitude curve of the drive unit 70 is not modulated and the vibration is driven at a quasi-resonant frequency to measure the phase curve. As shown in FIG. 12A, when amplitude modulation is not performed, waveform distortion does not occur, so the phase curve is almost a straight line.

  Next, when the drive unit 70 is amplitude-modulated at 3.7 Hz and is driven to vibrate at the low frequency side quasi-resonant frequency, it is confirmed that the phase curve is curved and a phase change occurs as shown in FIG. It was done. Further, the minimum amplitude (node portion of the scanning trajectory) of the scanning trajectory (showing the envelope of the trajectory in FIG. 12) located at the upper end and the lower end of FIG. 12B did not fall to zero. That the minimum value of the amplitude of the scanning trajectory does not drop to zero means that when spiral scanning is performed, a region that is not scanned at the scanning center remains in a circular shape. As a result, when the obtained signal is imaged, the center of the image is lost, resulting in an image like a donut shape. Therefore, when the drive unit 70 is amplitude-modulated at 3.7 Hz and is vibrated at a drive frequency that is 3.7 Hz lower than the low-frequency side quasi-resonant frequency, the curve of the phase curve becomes considerably large as shown in FIG. As the phase became smaller, that is, the phase shift became smaller, the minimum value of the amplitude of the scanning locus became substantially zero. As a result, it is possible to scan up to the scanning center of the observation object 100, and the omission of the center of the image can be eliminated. Note that the fact that the scanning locus is substantially zero is defined that the minimum value of the amplitude is within 3.5% of the maximum amplitude. As described above, the maximum amplitude of the fiber is preferably 0.1 mm or more, whereas the MFD of the single mode fiber is 3.5 μm, so the minimum amplitude is 3.5% or less of the maximum amplitude. This is because the orbit of the laser beam at the minimum amplitude almost overlaps the scanning center.

  FIG. 12D shows a case where the drive unit 70 is amplitude-modulated at 7.4 Hz and is oscillated at a drive frequency that is 3.7 Hz lower than the low-frequency side quasi-resonant frequency. In this case, the phase curve is curved as in FIG. 12B, and the minimum value of the amplitude at the upper end and the lower end of the scanning locus does not become zero. For this reason, a region that is not scanned at the scanning center of the observation object 100 remains circular, and when the obtained signal is imaged, an image with a hole like a donut shape is formed. Therefore, when the drive unit 70 is amplitude-modulated at 7.4 Hz and vibrationally driven at a drive frequency 7.4 Hz lower than the quasi-resonant frequency on the low frequency side, as shown in FIG. It becomes considerably small, that is, the phase shift becomes small, and the minimum value of the amplitude of the scanning locus is substantially zero. As a result, it is possible to scan up to the scanning center, and the omission of the center of the image can be eliminated. Note that the measurement was also performed when the drive unit 70 was amplitude-modulated at 7.4 Hz and was driven to vibrate at a quasi-resonant frequency. However, in this case, the waveform became extremely unstable and is not shown in FIG. .

  The above example is an example in which the modulation frequencies are 3.7 Hz and 7.4 Hz, but the same effect is expected even when other modulation frequencies are used. For example, when acquiring a moving image by performing amplitude modulation at a frame rate of 30 Hz by spiral scanning, the modulation frequency may be 30 Hz and the drive frequency may be 30 Hz lower than the low-frequency resonance frequency.

As described above, when the drive frequency is set to drive frequency = low-frequency side quasi-resonant frequency−modulation frequency, the curvature of the phase curve is reduced and the minimum value of the amplitude of the scanning locus is substantially zero.

The above explanation is for the case where the drive frequency is shifted from the low-frequency side quasi-resonant frequency to the low-frequency side, but similar results are obtained even when the drive frequency is shifted from the high-frequency side quasi-resonant frequency to the high-frequency side. It is done. And
If the driving frequency = high frequency side quasi-resonance frequency + driving frequency satisfying the modulation frequency, the observation object 100 can be scanned to the scanning center by spiral scanning.

Further, in order to obtain a frequency spectrum that does not overlap with an unstable region near the resonance frequency and has an amplitude of 1/10 or more when driven by the resonance frequency, the drive frequency of the scanning endoscope 1 is set to an upper limit frequency ≧ By setting drive frequency ≧ high frequency side quasi-resonant frequency + modulation frequency or lower limit frequency ≦ drive frequency ≦ low frequency side quasi-resonance frequency−modulation frequency, the laser light emitted from the light source unit 30 is on the observation object 100. With respect to the predetermined region, the entire predetermined region can be repeatedly scanned in a spiral manner by the modulation frequency. As a result, reflected light, scattered light, fluorescence, or the like obtained from the observation target object 100 by the laser light irradiation is detected by the detection unit 40 via the detection optical fiber 12, and is removed to the center by the control unit 60. It is possible to repeatedly generate an image with no modulation frequency and output it to the display unit 61.

  Next, a case where the influence of nonlinear vibration is large in the first embodiment will be described. When the influence of nonlinear vibration in the vicinity of the resonance frequency is large, the graph of the amplitude with respect to the driving frequency of the distal end portion 11c of the illumination optical fiber 11 shows that the larger the amplitude, the lower the frequency side or the higher the frequency as shown in FIG. The shape is bent to the frequency side. In FIG. 13, the unstable region near the resonance frequency is indicated by a region sandwiched by broken lines. At this time, the unstable region near the resonance frequency is further expanded in the bending direction of the graph. Since the graph is not symmetrical between the low frequency side and the high frequency side, the oscillating portion 11b of the illumination optical fiber 11 is driven with the same energy at the low frequency side quasi-resonant frequency and the high frequency side quasi-resonant frequency. However, the obtained amplitude is different. In FIG. 13, a higher amplitude is obtained on the high frequency side (the non-curved side of the graph).

Therefore, when the drive frequency by the drive unit 70 is changed, the graph created by taking the drive frequency on the horizontal axis and the amplitude of the tip 11c of the illumination optical fiber 11 on the vertical axis shows asymmetry around the resonance frequency, When the amplitude at the high frequency side quasi-resonant frequency is larger than the amplitude at the low frequency side quasi-resonant frequency,
Upper limit frequency ≧ drive frequency ≧ high frequency side quasi-resonant frequency + modulation frequency, and when the amplitude at the low frequency side quasi-resonant frequency is larger than the amplitude at the high frequency side quasi-resonant frequency,
Lower limit frequency ≦ drive frequency ≦ low frequency side quasi-resonant frequency−modulation frequency. As a result, the oscillating portion 11b of the illumination optical fiber 11 can be oscillated and driven by the drive frequency belonging to the range of the drive frequency from which the amplitude of the tip portion 11c of the larger illumination optical fiber 11 is obtained. It becomes possible to drive the illumination optical fiber 11 with high energy efficiency.

FIG. 14 is a graph showing an example of the amplitude of the distal end portion 11c of the illumination optical fiber 11 with respect to the drive frequency obtained from the experimental results. In this example, the drive frequencies of 373.5 Hz and 376 Hz are the quasi-resonant frequencies (f _ql , f _qh ) on the low frequency side and the high frequency side, respectively. That is, the region between 373.5 Hz and 376 Hz is an unstable region. In this case, the drive frequency on the high frequency side can obtain a larger amplitude than the low frequency side with less drive energy.

(Second Embodiment)
FIG. 15 is an enlarged view of the distal end portion 24 of the scanning endoscope according to the second embodiment. In this embodiment, the scanning endoscope according to the first embodiment uses a piezoelectric element instead of a drive unit that uses a permanent magnet and an electromagnetic coil. FIG. 16A is a side view showing a vibration driving mechanism including the piezoelectric elements 82a to 82d of the distal end portion 24 of FIG. 15 and the swinging portion 11b of the illumination optical fiber 11, and FIG. It is AA sectional drawing of Fig.16 (a).

  The drive unit 80 includes an actuator tube 81 fixed inside the insertion unit 23 of the optical scanning endoscope body 20 by the mounting ring 26, piezoelectric elements 82a to 82d disposed in the actuator tube 81, and an internal The optical fiber 11 for illumination is comprised including the fiber holding member 83 which penetrated. The illuminating optical fiber 11 is supported by a fiber holding member 83, and a fixed end 11a supported by the fiber holding member 83 to a tip end portion 11c is a swinging portion 11b that is swingably supported. The four side surfaces of the fiber holding member 83 are oriented in the + X direction and the + Y direction and in the opposite directions, respectively. A pair of piezoelectric elements 82a and 82c for driving in the X direction are fixed in the + X direction and the −X direction of the fiber holding member 83, and a pair of piezoelectric elements 82b and 82d for driving in the Y direction in the + Y direction and −Y direction. Is fixed.

  Moreover, the wiring cable 13 from the drive control part 50 is connected to each piezoelectric element 82a-82d. The drive control unit 50 applies vibration voltage to the piezoelectric elements 82a and 82c in the X direction and the piezoelectric elements 82b and 82d in the Y direction, and drives the swinging part 11b of the illumination optical fiber 11 to vibrate. Similar to the first embodiment, the observation object 100 can be spirally scanned by causing the X direction and the Y direction to be 90 degrees out of phase with each other and performing amplitude modulation with the modulation frequency in each direction. . Since other configurations and operations are the same as those of the first embodiment, the same or corresponding components are denoted by the same reference numerals and description thereof is omitted.

According to the present embodiment, the oscillating portion 11b of the illumination optical fiber 11 can be driven to vibrate using the piezoelectric elements 82a to 82d instead of the combination of the permanent magnet and the electromagnetic coil as the driving portion 80. Therefore, as in the first embodiment, the oscillating portion 11b of the illumination optical fiber 11 is vibrated at the drive frequency, and the vibration amplitude of the illumination optical fiber 11 is between zero and a predetermined maximum value. Fluctuate according to the modulation frequency and drive frequency
By setting upper limit frequency ≧ drive frequency ≧ high frequency side quasi-resonant frequency + modulation frequency or lower limit frequency ≦ drive frequency ≦ low frequency side quasi-resonant frequency−modulation frequency, the scanning trajectory when scanning the observation object 100 is stable. In addition, the signal can be detected by irradiating the laser beam from the scanning center portion of the observation object.

  In addition, this invention is not limited only to the said embodiment, Many deformation | transformation or a change is possible. For example, in the above embodiment, lasers having three different wavelengths are used for the light source unit, but the light source unit may be a single laser. Furthermore, pulse laser light may be used instead of CW (continuous oscillation) laser light. Further, the scanning method of the laser beam is not limited to scanning that is oscillated and driven with the same amplitude in two orthogonal directions. For example, a scanning method in which the scanning locus is long in one axis direction is also possible. Further, the amplitude modulation is not limited to a sine wave, but may be any one that repeatedly vibrates between zero amplitude and the maximum amplitude like a triangular wave.

DESCRIPTION OF SYMBOLS 10 Optical scanning endoscope 11 Illumination optical fiber 11a Fixing part 11b Oscillating part 11c Tip part 12 Detection optical fiber 13 Wiring cable 20 Optical scanning type endoscope main body 22 Operation part 23 Insertion part 24 Tip part 25 For projection Lens 26 Mounting ring 27 Forceps hole 30 Light source part 31R, 31G, 31B Laser light source 32a, 32b Dichroic mirror 33 AOM (acousto-optic modulator)
34 Lens 40 Detection unit 41R, 41G, 41B Light receiver 42a, 42b Dichroic mirror 43 Lens 50 Drive control unit 60 Control unit 61 Display unit 62 Input unit 70 Drive unit 71 Square tube 72a-72h Electromagnetic coil 73 Permanent magnet 80 Drive unit 81 Actuator tube 82a to 82d Piezoelectric element 83 Fiber holding member 100 Object to be observed

Claims (4)

A fiber having a fixed portion and a swingable portion swingable with respect to the fixed portion, and irradiating an observation object with laser light from the tip of the swingable portion;
A drive unit for oscillating and driving the oscillating unit of the fiber;
A detection unit that detects light obtained by irradiation of the laser light from the observation object and converts the light into an electrical signal; and
The drive unit is substantially a maximum and a predetermined zero Rutotomoni, the amplitude of the vibration of the fiber is scanned the swinging portion of the fiber respectively to vibrate at a constant driving frequency different 2 axially helically The drive frequency is fluctuated depending on the modulation frequency between values.
Upper limit frequency ≧ drive frequency ≧ high frequency side quasi-resonance frequency + modulation frequency or lower limit frequency ≦ drive frequency ≦ low frequency side quasi-resonance frequency−modulation frequency.
Here, the upper limit frequency and the lower limit frequency are respectively the high frequency side and the low frequency side of the resonance frequency, and the amplitude of the vibration of the fiber due to the driving of the drive unit is driven at the resonance frequency. Ri frequency der when a minute of 1,
The quasi-resonant frequency is a frequency at which the orbits reciprocating in the long axis direction partially overlap when the drive unit is driven to vibrate in a one-dimensional direction and the drive frequency is shifted from the resonance frequency . The drive frequency is
2. The optical scanning endoscope according to claim 1, wherein driving frequency = high frequency side quasi-resonance frequency + modulation frequency or driving frequency = low frequency side quasi-resonance frequency−modulation frequency. The drive unit includes an optical scanning-type endoscope according to claim 1 or 2, characterized in that vibrate with a phase difference of approximately 90 ° in two directions perpendicular to each other physician. When the drive frequency of the drive unit is changed, the amplitude of the oscillating unit with respect to the drive frequency exhibits asymmetry around the resonance frequency,
When the amplitude at the high-frequency side quasi-resonant frequency is larger than the amplitude at the low-frequency side resonant frequency, the drive frequency,
Upper limit frequency ≧ drive frequency ≧ high frequency side quasi-resonant frequency + modulation frequency
When the amplitude at the low-frequency side quasi-resonant frequency is larger than the amplitude at the high-frequency side resonant frequency, the drive frequency,
2. The optical scanning endoscope according to claim 1 , wherein lower limit frequency ≦ drive frequency ≦ low frequency side quasi-resonant frequency−modulation frequency.

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