KR100904227B1 - Apparatus and method for visualizing object by using tomography - Google Patents

Abstract

The present invention is to stably change the optical path length and to improve the variable speed in order to detect reliable image data in imaging the tomography of the measurement target, and divides the light output from the light source into the first and second light Making a step; Varying a length of the first and second light paths through which the first and second light pass, respectively; Irradiating the first light to a measurement object through the first optical path to obtain a reflected signal light; Generating a reference light using the second light passing through the second light path; Detecting image data representing the tomogram of the measurement object from the signal light and the reference light; And correcting the data for the image by using a function in which the variable speeds of the first and second optical paths are considered.

Optical coherence tomography, piezoelectric element, sine wave

Description

Tomographic imaging method and apparatus {Apparatus and method for visualizing object by using tomography}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging apparatus, and more particularly, to an imaging apparatus and method for photographing a tomography of a measurement target using optical interference.

Widely used imaging techniques in basic medical research and clinical medicine include X-ray computed tomography (CT), ultrasound imaging, and positron emission tomography (PET). These imaging techniques are based on different principles but are widely used in the medical field and complement each other. That is, these techniques are complementary to each other in various fields according to different physical properties, resolutions, penetration depths, and the like.

Optical coherence tomography (OCT) is a new imaging technique that enables the measurement of biological tissue in micrometer-wide cross-sectional images using low coherence reflectometry. OCT is somewhat similar to ultrasound imaging or radar. However, the technology using light rather than ultrasonic waves or radio waves has a resolution (resolution) of about 10 times that of conventional ultrasound images, and allows the tissue to be measured to be examined in a non-contact manner. This technology uses a light source in the near-infrared region to observe the inside of the living body in a non-incision manner, which is harmless to the human body and enables real-time tomography imaging. In addition, it is possible to obtain a high resolution tomography image capable of physiological and deradiative diagnosis, and to manufacture a small and low-cost device. The optical signal detected from the biological tissue has spatial information inside the tissue and is used for skin surface examination, retina measurement, and eye structure measurement. In addition, OCT is being researched for industrial use to be applied to large storage media.

In order to detect an accurate optical signal using the OCT imaging technique, an element capable of varying the length of an optical path inside an OCT apparatus is required. However, when using a beam splitter or a mirror to vary the length of the optical path, multiple interference modes occur, and thermal drift may occur when the optical path is changed using an optical fiber. . Interference modes and thermal fluctuations give errors to the detected optical signal. In addition, mechanical movement by a linear motor or the like for shifting the position of the mirror is not only limited to improving the optical path variable speed but also involves a loss of light due to unstable (incorrect) movement.

Disclosure of Invention An object of the present invention is to provide a tomography imaging method and apparatus capable of stably varying an optical path length and improving a variable speed by devising to compensate for the shortcomings of the existing technologies.

Another object of the present invention is to provide a tomography imaging method and apparatus capable of eliminating errors caused by interference modes or thermal fluctuations.

Tomographic imaging method of the present invention for achieving the above object comprises the steps of: dividing the light output from the light source into first and second light; Varying a length of the first and second light paths through which the first and second light pass, respectively; Irradiating the first light to a measurement object through the first optical path to obtain a reflected signal light; Generating a reference light using the second light passing through the second light path; Detecting image data representing the tomogram of the measurement object from the signal light and the reference light; Correcting the data for the image by using an inverse function of a function for the variable speeds of the first and second optical paths.

In the adjusting of the lengths of the first and second light paths, the diameter of the piezoelectric element is changed by supplying a sine wave voltage to the cylindrical piezoelectric element wound with the optical fiber.

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A tomography imaging apparatus according to the present invention comprises: a light splitter for dividing light output from a light source into first and second lights; First and second optical path retarders for varying lengths of the first and second optical paths through which the first and second light respectively pass; A meter reading unit which irradiates the measurement object with the first light passing through the first optical path, and transmits the signal light reflected from the measurement object to the light splitter; A reference light generator for generating a reference light using the second light passing through the second light path; A photodetector for detecting tomographic image data indicating a tomography of the measurement target from the signal light and the reference light output from the light splitter; And a signal corrector for correcting the detected tomographic data by using an inverse function of a function of the variable speeds of the first and second optical paths.

The tomography imaging apparatus further includes an optical path retarder driver configured to supply sinusoidal voltages having different polarities to the piezoelectric elements of the first optical path retarder and the piezoelectric elements of the second optical path retarder, respectively. The optical path retarder driver supplies a-voltage to the piezoelectric elements of the first optical path retarder and supplies a + voltage to the piezoelectric elements of the second optical path retarder, respectively.

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The present invention is not limited to the above-described embodiments, and can be modified by those skilled in the art as can be seen from the appended claims, and such modifications are within the scope of the present invention. Reveal.

As described above, in the present invention, since the optical path length is changed by using a piezoelectric element, the variable speed is improved, and the optical path may be changed to the correct length according to the linear optical path variable speed. In addition, since the transfer function is used to exclude error factors such as interference mode and thermal fluctuation, accurate data can be obtained.

Hereinafter, with reference to the accompanying drawings, the present invention will be described in detail. In the following description, the same components are given the same names and the same reference numerals for convenience of description.

In addition, the terminology used in the present invention was selected as a general term that is widely used at present, but in some cases, the term is arbitrarily selected by the applicant, and in this case, since the meaning is described in detail in the corresponding part of the present invention, a simple term is used. It is to be understood that the present invention is to be understood as a meaning of terms rather than names.

1 is a block diagram showing the configuration of a tomography imaging apparatus according to the present invention. As shown in FIG. 1, the tomography imaging apparatus of the present invention includes a light source 100, an optical circulator 101, an optical coupler 103, a first optical path retarder 104, and a first polarization controller 105. , Condenser 106, second optical path retarder 109, second polarization controller 110, free space (linear) optical path retarder 111, optical fiber mirror 112, waveform generator 113, sight The furnace retarder driver 114, the photodetector 115, the signal amplifier 116, the signal rectifier 117, the AD converter (analog-to-digital converter) 118, and the signal compensator 119 are included.

Here, a portion consisting of the first optical path retarder 104, the first polarization controller 105, and the condenser 106 is called a probe stage, and the second optical path retarder 109 and the second A portion consisting of the polarization controller 109, the free space optical path retarder 110, and the optical fiber mirror 111 is called a reference stage. The reading stage detects an optical signal for tomography images from the measurement target 108, and the reference stage generates a reference optical signal that interferes with the optical signal for tomography images.

The light source 100 is a low-intensity super-bright light source, for example, a diode light source having a center wavelength of 1300 nm, a bandwidth of 50 nm, and a maximum output of 20 mW. Here, the center wavelength, bandwidth, maximum output, etc. of the light source 100 may be variously changed / set according to the design of the imaging apparatus. Light emitted from the diode light source 100 is transmitted to the optical coupler 103 through the optical circulator 101 through the optical fiber 102.

The light combiner 103 includes a bidirectional light splitter for dividing the amount of light into a ratio of 5: 5, 7: 3, 9: 1, and the like. The optical combiner 103 bisects the light output from the light source 100 and outputs the light to the meter reading stage and the reference stage, respectively. In addition, the optical coupler 103 receives light fed back through the metering stage and the reference stage, that is, the first and second optical path delayers 104 and 109.

In the case of the light proceeding to the meter reading stage, the optical path length is varied by the first optical path retarder 104, and the polarization direction of the light is adjusted by the first polarization controller 105. The light output from the first polarization controller 105 is concentrated and irradiated from the light collector 106 to the measurement target (eg, the body) 108. The light irradiated onto the measurement target 108 is reflected with a specific scattering value according to the structure / shape of the tissue to be measured. The reflected light proceeds in the reverse process and is transmitted to the optical coupler 103.

In the case of the light traveling to the reference stage, the path length of the light is changed by the second optical path retarder 109. The light output from the second optical path retarder 109 is controlled by the second polarization controller 110, and the polarization direction of the optical fiber is adjusted to adjust the total length of the probe stage and the reference stage and the measurement start position. It is reflected by the optical fiber mirror 112 via the third optical path retarder 111 that changes the length linearly. The light reflected by the optical fiber mirror 112 is transmitted to the optical coupler 103 while undergoing a reverse process from the optical coupler 103 to the optical fiber mirror 112.

In the optical coupler 103, two light fed back through the metering end and the reference end interfere with each other, and the interference is divided into a first carrier interference light and a second carrier interference light. The first carrier interference light is transmitted to the photodetector 115 via the optical circulator 101, and the second carrier interference light is directly transmitted to the photo detector 115. Then, the photo detector 115 compares the first and second carrier interference light and detects whether the two lights have the same intensity, phase, or the like. If the first and second carrier interference light are not equal to each other, since the noise is included, the noise is removed, and the noise-removed light is converted into a current or voltage value.

The electrical signal output from the photo detector 115 is very weak and amplifies the electrical signal by the signal amplifier 116, and the noise included in the amplified signal is removed by the signal rectifier 117. Since the noise-free electrical signal is an analog signal, this signal is converted into a digital value by the A-D converter (analog-to-digital converter) 118. The converted digital signal is transmitted and stored in the signal compensator 119, for example, a computer. The digital signal transmitted to the signal compensator 119 includes information on a depth (light propagation) direction of the measurement target 108, that is, one-dimensional image data. At this time, while obtaining information about the depth direction of the measurement target 108 and continuously obtaining information about the depth direction while moving the light collector 106 in the horizontal direction perpendicular to the depth direction to the measurement target 108 2D tomography images can be implemented. The two-dimensional tomography image thus obtained is stored in the signal correcting apparatus 119.

2 is a diagram illustrating an example of the first optical path retarder 104. As shown in FIG. 2, the first optical path retarder 104 is wound around the cylindrical piezoelectric element 104a at a predetermined length and force with a cylindrical piezoelectric transducer (PZT) 104a. A single mode optical fiber 104b. The cylindrical piezoelectric element 104a has the same characteristics as a capacitor and has a characteristic in which its diameter changes according to an input voltage. For example, the cylindrical piezoelectric element 104a has a capacitance of several nF, and may be configured in various sizes of cylindrical shapes, and its diameter change has a characteristic of several μm / 100V. Here, the capacitance, the size, the shape, the length of the optical fiber 104b, the number of turns, etc. of the piezoelectric element 104a may be variously modified within the scope of the invention.

The configuration and function of the second optical path delay unit 109 is the same as that of the first optical path delay unit 104. By arranging the same optical path retarder in each of the metering end and the reference end, it is possible to equalize thermal changes / errors that may occur due to the continuous length change of the optical fiber to the metering end and the reference end.

The waveform generator 113 generates a sine wave (sine wave) and provides it to the optical path retarder driver 114. The optical path retarder driver 114 receives a sine wave from the waveform generator 113 and controls the first and second optical path retarders 104 and 109 using the input sine wave. In this case, the waveform generator 113 and the optical path retarder driver 114 transmit a synchronization signal used for generating and outputting the sine wave to the signal correction device 119.

When the optical path retarder driver 114 controls the first and second optical path retarders 104 and 109 by using a triangular wave instead of a sine wave, the first and second optical path retarders 104 and 109 are controlled. An image of the object to be measured 108 may be obtained from an optical signal that is linearly variable with time and is output through the adjusted optical path. However, when the first and second optical path delayers 194 and 109 are driven by a triangular wave, there is a possibility that a nonlinear phenomenon may occur at the maximum-minimum point of the driving waveform. 3 is a view showing the relationship between the optical path length change and the delay time (variable time) when using a triangular wave. Here, the slope of the measurement depth graph of the measurement object according to the delay time represents the variable speed of the optical path. The nonlinearity of the variable speed of the optical path shown in FIG. 3 not only brings about the limitation of the variable speed of the first and second optical path retarders 104 and 109 but also causes an inaccurate measurement result. Accordingly, the waveform generator 113 generates a sine wave and inputs it to the optical path retarder driver 114. In this case, nonlinear phenomenon is eliminated at the maximum-minimum point of the driving waveform, and faster driving is possible.

The optical path retarder driver 114 may selectively supply a sine wave to only one of the first and second optical path retarders 103 and 109, but the first and second optical path retarders 103 and 109 may be used. The maximum effect can be obtained when the sinusoidal voltages of the same magnitude and different polarity are respectively supplied to the piezoelectric elements of. For example, the optical path retarder driver 114 supplies a negative voltage (−200 V) to the piezoelectric element of the first optical path retarder 103 and the piezoelectric of the second optical path retarder 109. Supply + voltage (+ 200V) to the device. At this time, the diameter of the piezoelectric element is reduced when the voltage is applied to the piezoelectric element, and the diameter of the piezoelectric element is increased when the + voltage is applied. The length of the optical fiber wound on the piezoelectric element of the second optical path retarder 109 is increased. Therefore, the optical path length of the reference stage can be obtained by varying twice.

The signal compensator 119 receives a synchronization signal from the optical path delay driver 114 and receives and stores the digital signal including an image from the A-D converter 118. The signal correction device 119 transmits the digital signal (one-dimensional image data) received from the AD converter 118 to eliminate a position value error of interference light according to time that may occur by driving with a sine wave. Correct using a function.

4 is a diagram illustrating a method of coordinate transformation of the received 1D image data using the transfer function. New one-dimensional depth data 203 whose position is corrected by correcting the position of the one-dimensional image data 201 according to the sinusoidal driving of the first and second optical path delayers 104 and 109 through the transfer function 202. Convert to

5 is a graph showing the transfer function 202 of the imaging device of the present invention. Since the waveform input to the first and second optical path retarders 104 and 109 as the transfer function 202 may be a sine wave, an inverse function thereof may be taken, but the sine wave input to the optical path retarder driver 114 is accurate. Since it may not be a sinusoidal wave, it is preferable to use the transfer function 202 based on the measured value.

The signal correction device 119 is an optimization function (a function that depends on the variable speed of the first and second optical path delayers) indicating a position value (delay time) according to the depth measured using the following equation. Find and use its inverse function (2) as the transfer function (202). The signal correction device 119 may set the optimization function and the transfer function at an initialization time of the imaging device or through a test immediately before scanning the measurement object 108.

(1)

(One)

(2)

(2)

Here, x is an array position factor of the one-dimensional depth direction data, C ₁ and C ₂ are constant values according to the sampling rate of the AD converter 118, and x ₀ is a value for determining the start position of the transfer function.

6 is a graph showing a variable speed of a light path based on image data corrected through spatial coordinate transformation in the imaging apparatus of the present invention. As shown in FIG. 6, the slope of the measurement depth graph of the measurement object according to the optical path delay time shown through the spatial coordinate transformation represents an average variable speed. In this way, high linearity can be secured through spatial coordinate transformation, and the optical path length according to the sine wave driving can be quickly changed.

1 is a block diagram showing the configuration of a tomography imaging apparatus according to the present invention;

FIG. 2 is a diagram illustrating an example of the optical path retarder of FIG. 1; FIG.

3 is a graph showing a relationship between a change in optical path length and a delay time using a triangular wave;

4 is a diagram illustrating a method of converting image data using a transfer function;

5 is a graph showing an example of a transfer function value;

6 is a glyph illustrating a relationship between an optical path length change and a delay time using a sine wave.

Claims (9)

Dividing the light output from the light source into first and second lights; Varying a length of the first and second light paths through which the first and second light pass, respectively; Irradiating the first light to a measurement object through the first optical path to obtain a reflected signal light; Generating a reference light using the second light passing through the second light path; Detecting image data representing the tomogram of the measurement object from the signal light and the reference light; And correcting the image data using an inverse function of a function of the variable speeds of the first and second optical paths. The method of claim 1, In the step of adjusting the length of the 1, 2 light path, And a sine wave voltage supplied to the cylindrical piezoelectric element wound by the optical fiber to change the diameter of the piezoelectric element. The method of claim 1, In generating the reference light by using the second light, And reflecting the second light to a mirror to generate the reference light. The method of claim 1, In the detecting of the tomographic image data from the signal light and the reference light, And detecting the intensity of the interference light caused by the signal light and the reference light. delete A light splitter for dividing the light output from the light source into first and second lights; First and second optical path retarders for varying lengths of the first and second optical paths through which the first and second light respectively pass; A meter reading unit which irradiates the measurement object with the first light passing through the first optical path, and transmits the signal light reflected from the measurement object to the light splitter; A reference light generator for generating a reference light using the second light passing through the second light path; A photodetector for detecting tomographic image data indicating a tomography of the measurement target from the signal light and the reference light output from the light splitter; And a signal compensator for correcting the detected tomographic data by using an inverse function of a function of a variable speed of the first and second optical paths. The method of claim 6, And a light path retarder driver configured to supply sinusoidal voltages having different polarities to the piezoelectric elements of the first optical path retarder and the piezoelectric elements of the second optical path retarder, respectively. The method of claim 7, wherein The optical path retarder driver, And a-voltage is supplied to the piezoelectric elements of the first optical path delay unit, and a + voltage is supplied to the piezoelectric elements of the second optical path delay unit, respectively. delete

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