CN100346739C - Real-time imaging optical coherent endoscope system - Google Patents

Abstract

An optical coherent endoscopic system for real-time imaging belongs to the technical field of medical optical coherent imaging. The invention includes a broadband light source, a fiber coupler, a sample arm and a reference arm, a position detector and a computer acquisition and processing system, and the system structure is based on Michelson interferometer. The reference arm adopts a scanning turntable connected with a motor, and the scanning turntable is composed of a central axis and at least one fan blade whose surface shape is an equidistant helical surface arranged on the central axis; the sample arm adopts a micro-optical transmission based on an ultrasonic motor and scanning devices. The invention utilizes a fast motor to drive a scanning turntable to perform scanning, and has a simple structure. It can provide a scanning range greater than 3mm, provide variable scanning speed, have good linearity and repeatability, and perform real-time compensation for the difference in return light intensity caused by the manufacturing accuracy of the turntable. Real-time detection of vascular diseases and the like can be performed (imaging speed>4 images/s), and no additional dispersion is introduced.

Description

Optical coherent endoscopy system for real-time imaging

technical field

The invention relates to a technology for performing tomographic imaging by using optical coherence, in particular to an optical coherence endoscopic system for real-time imaging, which belongs to the technical field of medical optical imaging.

Background technique

In the last few decades, biological imaging technology has developed rapidly. MRI, XCT, ultrasound, etc. have been widely used in biomedicine. However, these technologies are far from sufficient in applications requiring high resolution (~1um) such as biological slices and tissue analysis. Coronary artery disease is a common disease in modern times, and its early prevention requires high-resolution examination of tissues. OCT is an imaging technology that has been developed in the past ten years. It has many advantages: it can perform micron-resolution cross-sectional imaging of organisms; it can be imaged in real time; It is easy to combine with existing medical devices, so it is suitable for early diagnosis and prevention of high incidence of coronary artery disease.

Optical coherence tomography (OCT) technology was invented by Professor J.Fujimoto of MIT in 1991 (Huang et al, Science1991). Simply put, OCT is similar to ultrasound, except that the probe returns light waves instead of sound waves. OCT can point the light beam at the organism, and detect the backscattered light when scanning the light beam to form a one-dimensional, two-dimensional or three-dimensional image. In medical imaging, OCT images represent differences in the scattering properties of different layers of organisms on the micron scale. Typical OCT systems are based on a Michelson interferometer. One of the arms is the sample arm, which scans the sample, while the other arm is the reference arm, which scans longitudinally and rapidly. When the optical path of the reference arm is the same as that of the sample arm, the light returning to the detector from the two arms interferes. The interference signal is detected, demodulated and processed, so that an image whose scattered light intensity corresponds to the longitudinal scanning depth can be obtained. A reference arm that provides longitudinal scanning is an important part of an OCT system. The reference arm needs to be evaluated from the following indicators: scanning speed, scanning repeatability, effective scanning specific gravity, scanning linearity, etc. Today, most commercial OCT systems use moving mirrors, scanning with galvanometers, or stretching optical fibers with PZT for scanning. These technologies cannot meet the requirements of real-time imaging. For example, in a real-time endoscopy system, in order to avoid blurring of the image caused by the peristalsis of biological tissues, the imaging speed close to that of video is required.

Use a linear motor to drive the mirror to scan. If you want to increase the scanning frequency, you need to increase the acceleration accordingly. Therefore, using this method generally can only obtain a scanning frequency of 30 Hz in a scanning range of 2-3 mm. Although high scanning speeds can be obtained using PZT stretching, the scanning range is severely limited. The resonant galvanometer can reach the scanning frequency of KHz, but because its optical path change has a sinusoidal relationship with time, the Doppler modulation of the coherent signal is related to the scanning depth; and the bandwidth of the signal will increase, which will introduce more noise. Optical delay lines can make group delay and phase delay independent of each other. The scanning speed of 2000s/second can be achieved by using the vibrating mirror (1KHz triangular wave). However, its structure is complex, requiring precise adjustment of devices such as vibrating mirrors, gratings, and prisms, and its stability is difficult to adapt to commercial use. It has also been reported in the literature that cube glass is used for scanning, and the scanning speed can reach 28.5KHz. However, the effective scanning range of this method is very low, and there are many nonlinear factors in the scanning. At the same time, the selection of the reference arm scanning method also has a great relationship with the field of application. Fast scanning delay line (USPatent6111645A) is more used now in the endoscopy system. Because of the large difference in fiber length between the sample arm and the reference arm in the endoscopy system, it will cause serious dispersion problems. Dispersion not only degrades resolution, but also affects the signal-to-noise ratio of the system. The use of delay lines in endoscopy systems therefore requires compensation for dispersion, which in turn increases system complexity and instability. The use of optical coherence for imaging in the endoscopic system also has great requirements for the sample arm, especially for the detection of vascular diseases, the diameter of the sample arm is required to be 1-2 mm. Endoscopic probes less than 2mm have been reported in the MIT group so far (J.Fujimoto et al, Science 1997). The probe is geared to drive the rotation of the optical fiber to achieve lateral scanning. Although the volume is suitable for blood vessel detection, it is not enough for commercial use because the meshing of gears and the optical coupling efficiency between optical fibers are sensitive to position.

Contents of the invention

The purpose of the present invention is to provide a real-time imaging optical coherent endoscopic system aimed at the deficiencies and defects of the prior art: it can perform linear scanning within a scanning range of several millimeters, and the scanning speed is high without affecting the quality; and it does not Dispersion compensation is required, it is easy to install, has a large effective scanning range, and can be used stably for a long time.

The technical scheme of the present invention is as follows: an optical coherent endoscopic system for real-time imaging, including a broadband light source, an optical fiber coupler, a sample arm and a reference arm, a photodetector and a computer acquisition and processing system, and the light of the broadband light source passes through the described After being coupled by the fiber coupler, it enters the sample arm and the reference arm in two ways, and the light reflected by the sample arm and the reference arm returns to the fiber coupler and enters the photodetector through the optical fiber. The photodetector communicates with the computer through the signal line. The acquisition and processing system are connected, and it is characterized in that: the reference arm adopts a scanning turntable connected with the motor, and the turntable is composed of a central axis and at least one fan blade whose surface shape is an equidistant helical surface arranged on the central axis; The outgoing parallel light of the arm is parallel to the central axis of the turntable; the system also includes a position detector for detecting the position of the fan blade, and the incident point of the detection light of the position detector on the turntable is the same as that of the collimator in the reference arm The incident point of the outgoing light is symmetrical about the central axis of the turntable, and the position detector is connected with the computer acquisition and processing system through the processor.

The technical feature of the present invention is that: a frequency shifter or a modulator is respectively arranged between the sample arm and the coupler and between the reference arm and the coupler.

The sample arm of the present invention uses a micro-optical transmission and scanning device based on an ultrasonic motor.

Another technical feature of the present invention is that the real-time imaging optical coherent endoscopic system also includes a voltage control board, which is connected with the ultrasonic motor of the sample arm, the motor of the reference arm and the computer through the control circuit to collect and process system connection.

Compared with the prior art, the present invention has the following advantages and outstanding effects: the present invention can provide a scanning range larger than 3mm, can provide variable scanning speed, and has good linearity and repeatability. Real-time detection of vascular diseases and the like can be performed (imaging speed>4 images/s), and no additional dispersion is introduced. The invention uses a fast motor to drive the turntable to scan, and has a simple structure. Doppler shift can be reduced to lower frequencies, simplifying data acquisition and processing. The scanning of the turntable can be synchronized with the data acquisition. The scanning speed of the sample arm and the reference arm can be adjusted to obtain the optimal scanning mode. Real-time compensation for the difference in return light intensity caused by the manufacturing accuracy of the turntable.

Description of drawings

FIG. 1 is a schematic structural diagram of the entire imaging system provided by the present invention.

Figure 2 is a schematic diagram of the structure of an equidistant helicoid.

Fig. 3 is a structural schematic diagram of a fan blade of the turntable.

Figure 4 shows the secondary reflection structure of the turntable in the system.

Fig. 5 is a miniature optical transmission and scanning device based on an ultrasonic motor.

In the figure: 1-broadband light source; 2-fiber coupler; 3-sample arm; 4-collimator; 5-secondary mirror; 6-frequency shifter; 7-scan turntable; 8-motor; 9-sample ;10-photoelectric detector; 11-data acquisition; 12-computer processing system; 13-processor; 14-position detector; 15-power control board; 16-parallel light; 17-reflected light; 18-reference arm; 19-computer acquisition and processing system; 20-blade; 51-optical fiber;, 52-sleeve; 53-right-angle prism; 54-rotor;

Detailed ways

Figure 1 shows a schematic diagram of the entire imaging system. The system comprises a broadband light source 1, an optical fiber coupler 2, a sample arm 3 and a reference arm 18, a photodetector 10 and a computer acquisition and processing system 19, and the reference arm adopts a scanning turntable 7 connected with a motor 8, and the scanning turntable It consists of a central shaft and at least one fan blade 20 whose surface shape is an equidistant helical surface arranged on the central shaft. The broadband light source 1 can use SLD, fiber laser and other light sources, and the central wavelength of the biological tissue light source should be selected around 1.0um. The broadband light source 1 is coupled into the optical fiber through the fiber coupler 2 , and then one is led to the sample arm 3 and the other is led to the reference arm 18 . The light is incident on the fan blade 20 of the scanning turntable through the collimator 4, and is reflected by the fan blade to a secondary reflector to return in the same way; wherein, the scanning turntable includes a plurality of fan blades with equidistant helical surfaces, and the output of the reference arm The parallel light is parallel to the central axis of the turntable; the sample arm 3 is focused on the sample 9 . The light backscattered by the sample is collected by the sample arm and returns to the fiber coupler 2. The outgoing light of the collimator 4 is parallel light 16 , which strikes the scanning turntable 7 driven by the motor 8 , and strikes the secondary reflector 5 through the reflected light 17 . The secondary reflection mirror 5 is perpendicular to the reflected light 17, so that the reflected light 17 returns through the original path. The light returned by the sample arm and the scanning turntable interferes in the fiber coupler 2, and the photodetector 10 collects the interference signal and converts it into an electrical signal with modulation. The electrical signal is converted into a digital signal through data acquisition 11, and sent to a computer for data processing system 12 to obtain a longitudinal section view of the sample. In FIG. 1 , the processor 13 is for coordinating the timing of the position of the scanning turntable 7 and the acquisition time of the data acquisition 11 . The system also includes a position detector for detecting the position of the fan blade. The detection light direction of the position detector is parallel to the central axis of the turntable. The incident point of the detection light of the position detector 14 on the turntable is the same as that of the collimator in the reference arm. The incident point of the outgoing light is symmetrical about the central axis of the turntable, and the position detector passes through the processor and the computer processing system. The position detector 14 can notify the data processing system 12 in real time of the serial number of the fan blade currently in use by counting.

The optical coherent endoscopic system of the present invention also includes a voltage control board 15, which is respectively connected with the ultrasonic motor of the sample arm, the motor 8 of the scanning turntable and the computer processing system 12 through control lines. The voltage control board 15 can change the voltage of the ultrasonic motor in the sample arm 3 and the motor 8 of the scanning turntable 7 according to the instruction of the data processing system 12 so as to change the speed of horizontal scanning and vertical scanning.

The sample arm 3 uses a miniature optical transmission and scanning device based on an ultrasonic motor. Figure 5 shows a schematic structural view of the device (see Chinese Patent Publication: CN1586402A). The optical fiber 51 is connected with the gradient index lens 56, and the right-angle prism 53 is glued on the rotor 54 connected with the ultrasonic motor 55. The hypotenuse of the right-angle prism can focus the focused light emitted by the gradient index lens on the sample. Gradient index lenses, prisms, rotors, and ultrasonic motors are packaged in a sleeve 52 .

The light intensity returned by the sample arm and the reference arm is incident on the photodetector 10 through one branch of the fiber coupler. The electrical signal output by the photodetector is sent to the computer acquisition and processing system 19 again. In the above system, the scanning carousel of the reference arm is connected to a position detector 14 . The position detector is connected with the computer acquisition and processing system 19 . The computer processing system can provide a trigger signal for data acquisition according to the signal of the position detector, and can also detect the moving position of the scanning turntable in real time. At the same time, the computer processing system is connected with the voltage control board 15, and the horizontal and vertical scanning speeds can be changed by controlling the motor voltages of the reference arm and the sample arm.

Figure 2 is a schematic diagram of an equidistant helicoid. Among them, Z represents the distance that the curved surface advances along the axial direction, and Φ represents the angle that the curved surface turns around the axis at the same time. There is a relationship between Z and Φ as shown in Formula 1: Z=(a/2π)Φ(1). It can be seen that the distance that the equidistant helix protrudes along the axial direction is in a linear relationship with the angle through which the curved surface turns. So when the turntable rotates at a constant speed, it can be used for linear scanning.

Fig. 3 is a schematic diagram of a fan blade of an actual scanning turntable. AB is the tangent at a certain point from the axis R, and BC is parallel to the axis. The angle between the tangent line AB and the axis is θ. According to the geometric relationship in the figure, Tanθ=AC/BC=(R*δΦ)/δZ(2), from Z=(a/2π)Φ we know that δΦ/δZ=2π/a, so Tanθ=R*2π/a , θ=arctan(R*2π/a)(3). It can be seen from formula 3 that the tangential direction on a surface equidistant from the axis is a constant. That is, the reflection direction of the incident light along the axial direction has nothing to do with the rotation of the helicoid.

Figure 4 shows a reference arm made of such a scanning carousel. The light 16 is incident on the scanning turntable 7 along the axial direction, and the reflected light 17 returns to the original path through the secondary reflection mirror 5 . Such a structure can perform longitudinal scanning, and the Doppler frequency shift brought about at the same time can be used as the modulation of the OCT signal. The scanning range is determined by the protruding distance of the fan blades on the scanning turntable. OCT generally requires a scanning range of about 3mm. By increasing the coefficient a in formula (1), a larger scanning range can be obtained. The scanning speed is determined by the scanning speed of the motor 8 and the number of repetitions of the fan blades on the scanning turntable, and the modulation frequency is determined by the rotational speed of the motor 8 . When the rotating speed of the motor 8 is 100r/s and there are 10 fan blades on the turntable, the scanning speed is 1KHz. When using a light source with a center wavelength of 1.3um, the modulation frequency is 2v/λ=4.6MHZ. If a faster rotation speed is selected, the modulation frequency will be higher. However, such a high modulation frequency brings difficulties to later data collection and processing, so the present invention provides a frequency shifter or modulator 6 between the reference arm 18 and the fiber coupler 2 . A frequency shifter 6 is added to the system to lower the modulation frequency. In order to maintain the dispersion matching of the two arms, the same frequency shifter or modulator 6 is added between the sample arm 3 and the fiber coupler 2 . The frequency shifter 6 of the reference arm reduces the reference Doppler modulation frequency, and the frequency shifter of the sample arm is only for dispersion matching. The simplest form of the position detector 14 is to judge the position by scanning the gap between the adjacent fan blades of the turntable. Parallel and axial light can be applied at a position where the parallel and incident light 16 is symmetrical with respect to the center of the scanning turntable, and then the intensity of the reflected light can be converted into an electrical signal. When the incident light 16 enters a new line of scanning through the gap between adjacent fan blades, the light intensity received by the position detector will suddenly decrease, and an electrical pulse will be formed. Processor 15 monitors this pulse to determine the position of the turntable. The coming of the falling edge of the pulse indicates the start of a new vertical scan. At this time, the processor 15 will provide a trigger signal to the data collection device, so that the data collection device collects new first-line data. The time from when the processor 15 detects the falling edge to when the acquisition trigger is given can be set by the computer processing system 12, so that an effective scanning range can be conveniently selected. At the same time, because receiving a falling edge means starting to turn to a new position, so the current position of the turntable can be judged according to this pulse signal. For example, for a turntable with 10 fan blades, the fan blade turned for the first time is marked as fan blade 1, then the 11th pulse signal represents the position of the fan blade 1 turned again. Because the turntable may have different reflection properties due to different degrees of polishing during production. After knowing the position of the specific turntable rotation, the signal returned by each fan blade can be compensated.

The voltage control board can provide the specified voltage to the ultrasonic motor in the sample arm and the motor 8 in the reference arm according to the instructions of the computer so as to control the horizontal and vertical scanning speeds.

Claims (4)

1. the optical coherent endoscope system of a realtime imaging, comprise wideband light source (1), fiber coupler (2), sample arm (3) and reference arm (18), photodetector (10) and computer acquisition and processing system, the light of wideband light source divides two-way to enter sample arm (3) and reference arm respectively after described fiber coupler coupling, light after sample arm and reference arm reflection returns fiber coupler again, enter photodetector through optical fiber, described photodetector links to each other with processing system with computer acquisition by holding wire, it is characterized in that: described reference arm adopts the scanning rotating disk (7) that links to each other with motor, and this rotating disk is that the flabellum of equidistant helicoid is formed by central shaft with being arranged at least one surface configuration on the central shaft; The outgoing directional light of reference arm and the central axes of rotating disk; This system also comprises a position sensor that the flabellum position is surveyed, the incidence point of detection light on rotating disk of described position sensor is with the incidence point of the emergent light of collimator in the reference arm central shaft centrosymmetry about rotating disk, and position sensor links to each other with processing system with computer acquisition by processor.

2. according to the optical coherent endoscope system of the described realtime imaging of claim 1, it is characterized in that: be respectively equipped with a frequency shifter or manipulator (6) between described sample arm (3) and the fiber coupler and between reference arm (18) and the fiber coupler (2).

3. according to the optical coherent endoscope system of claim 1 or 2 described realtime imagings, it is characterized in that: described sample arm adopts micro-optical transmission and the scanning means based on ultrasonic motor.

4. according to the optical coherent endoscope system of the described realtime imaging of claim 3, it is characterized in that: described optical coherent endoscope system also comprises a Control of Voltage plate (15), and this Control of Voltage plate is connected with processing system with the ultrasonic motor of sample arm and the motor (8) and the computer acquisition of scanning rotating disk respectively by control circuit.

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