A method for measuring the resolution of medical endoscopes based on the contrast sensitivity of the human eye

Abstract

The present invention discloses a method for measuring the resolution of a medical endoscope based on the contrast sensitivity of the human eye. The method is based on a human eye contrast sensitivity function model, and weights the obtained spectrum to obtain the Michelson interference fringe spectrum actually perceived by the human eye retina, thereby realizing non-artificial intervention measurement and calculation of the endoscope angular resolution. At the same time, the method characterizes the endoscope's imaging capability for object edges and details, introduces a step function for boundary analysis, and obtains the slope of the brightness distribution curve of the black and white fringe boundaries collected by the endoscope by deriving the step function to calibrate the display capability of edges and details.

Description

Technical Field

[0001] The invention relates to a method for measuring the resolution of a medical endoscope based on the contrast sensitivity of human eyes. Background Art

[0002] An endoscope is a diagnostic instrument that integrates traditional optics, ergonomics, precision mechanics, modern electronics, mathematics, and software. Equipped with an image sensor, optical lens, light source, and mechanical mechanisms, it can be inserted through the mouth into the stomach or other natural orifices. Endoscopes are extremely useful to doctors because they can reveal lesions that X-rays cannot.

[0003] Rigid tube endoscope is the most convenient, direct and effective medical device for medical personnel to observe the diseased tissue inside the human body. It has the advantages of high image clarity, realistic colors, and is easy to operate. As the scope of use of rigid tube endoscopes expands, doctors in various fields use rigid tube endoscopes more and more frequently. Since the quality inspection standards for endoscopes have not yet been unified, it has brought certain troubles to the quality inspection standards for endoscopes on the market and the market entry standards. At the same time, it has also caused some unqualified products to enter the market, bringing harm to society. Summary of the Invention

[0004] The purpose of the present invention is to overcome the above-mentioned deficiencies in the prior art and to provide a method for measuring the resolution of a medical endoscope based on the contrast sensitivity of the human eye with a rational structural design.

[0005] The technical solution adopted by the present invention to solve the above problems is: a method for measuring the resolution of a medical endoscope based on the contrast sensitivity of the human eye, characterized by:

[0006] (1) Collecting Michelson interference fringes through the endoscope;

[0007] (2) Using machine vision recognition technology, the two-dimensional brightness distribution at specific positions on and off the axis of the endoscope under test is obtained;

[0008] (3) Perform linear smoothing on the two-dimensional brightness distribution curve using a Gaussian filter to eliminate Gaussian noise; then perform Fourier transform on the curve to obtain the spectrum;

[0009] (4) Using the contrast sensitivity function of the human eye, the spectrum is weighted to obtain the Michelson interference fringe spectrum actually perceived by the human retina;

[0010] (5) According to formula (1), the modulation contrast at this time is obtained,

[0011] (1)

[0012] Where, is the modulation contrast; is the brightness of the white lines; is the brightness of the black line;

[0013] By changing the width of the Michelson interference fringes, the angular resolution of the endoscope can be measured and calculated without human intervention.

[0014] Further preferably, the imaging capability of the endoscope for the edge and details of the object is characterized, a step function is introduced for boundary analysis, and the brightness distribution function of the Michelson interference fringes is represented by the step function shown in formula (2):

[0015] (2)

[0016] Where, is brightness; n is an integer (1, 2, 3...); is the Michelson interference fringe width;

[0017] By taking the derivative of the step function, the slope of the brightness distribution curve of the black and white stripe boundaries acquired by the endoscope is obtained.

[0018] Compared with the existing technology, the present invention has the following advantages and effects: based on the human eye contrast sensitivity function model, the present invention weights the obtained spectrum to obtain the Michelson interference fringe spectrum actually perceived by the human eye retina, thereby realizing non-artificial intervention measurement and calculation of the endoscope angular resolution. At the same time, the method characterizes the endoscope's imaging ability for object edges and details, introduces a step function for boundary analysis, and obtains the slope of the brightness distribution curve of the black and white stripe boundaries collected by the endoscope by deriving the step function to calibrate the display ability of edges and details. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a flow chart of a method for measuring the resolution of a medical endoscope according to an embodiment of the present invention. DETAILED DESCRIPTION

[0020] The present invention will be further described in detail below with reference to the accompanying drawings and through examples. The following examples are intended to explain the present invention but the present invention is not limited to the following examples.

[0021] See also Figure 1 This embodiment provides a method for measuring the resolution of a medical endoscope based on the contrast sensitivity of the human eye, comprising:

[0022] (1) Collecting Michelson interference fringes through the endoscope;

[0023] (2) Using machine vision recognition technology, the two-dimensional brightness distribution at specific positions on and off the axis of the endoscope under test is obtained;

[0024] (3) Perform linear smoothing on the two-dimensional brightness distribution curve using a Gaussian filter to eliminate Gaussian noise; then perform Fourier transform on the curve to obtain the spectrum;

[0025] (4) Using the contrast sensitivity function of the human eye, the spectrum is weighted to obtain the Michelson interference fringe spectrum actually perceived by the human retina;

[0026] (5) According to formula (1), the modulation contrast at this time is obtained,

[0027] (1)

[0028] Where, is the modulation contrast; is the brightness of the white lines; is the brightness of the black line;

[0029] By changing the width of the Michelson interference fringes, the non-human intervention measurement and calculation of the endoscope angular resolution can be achieved. The specific method is to obtain a series of CM values ​​by continuously changing the width of the fringes. This series of CM values ​​can be used to draw a curve. The larger the slope of the curve, the higher the angular resolution.

[0030] In the above method, it is necessary to characterize the endoscope's ability to image the edges and details of objects. A step function is introduced for boundary analysis. The brightness distribution function of the Michelson interference fringes is represented by the step function shown in formula (2):

[0031] (2)

[0032] Where, is brightness; n is an integer (1, 2, 3...); is the Michelson interference fringe width;

[0033] By taking the derivative of the step function, the slope of the brightness distribution curve of the black and white stripe boundaries acquired by the endoscope is obtained.

[0034] Specifically, a medical rigid endoscope was selected for testing. Michelson interference fringes with a line width of 59.9 μm were collected, and a region of the same size at the center of the field of view was selected to obtain a sampled image.

[0035] The central axis of the sampling image and the average brightness of the transverse lines at intervals of 100 μm, 200 μm, ..., 1000 μm above and below the central axis are selected as the brightness of the stripe, and the two-dimensional brightness distribution is extracted.

[0036] The modulation contrast of the sample under test is calculated by combining the above methods;

[0037] Then, based on the number of distinguishable line pairs of the human eye and the following domestic and international standard angular resolution formulas, the angular resolution can be calculated;

[0038] (3)

[0039] (4)

[0040] In the above formula: is the number of variable line pairs per millimeter, is the distance from the end of the endoscope to the entrance pupil, is the optical working distance.

[0041] The above contents described in this specification are merely examples of the present invention. Those skilled in the art may make various modifications, additions, or substitutions to the described embodiments, without departing from the contents of this specification or exceeding the scope defined by the claims, and such modifications, additions, or substitutions may be made to the described embodiments. Such modifications, additions, or substitutions may be made by persons skilled in the art. As long as such modifications do not depart from the contents of this specification or exceed the scope defined by the claims, such modifications shall fall within the scope of protection of the present invention

Claims

1. A method for measuring the resolution of a medical endoscope based on the contrast sensitivity of the human eye, characterized by: include (1) Collecting Michelson interference fringes through the endoscope; (2) Using machine vision recognition technology, the two-dimensional brightness distribution at any position on or off the axis of the endoscope under test is obtained; (3) Perform linear smoothing on the two-dimensional brightness distribution curve using a Gaussian filter to eliminate Gaussian noise; then perform Fourier transform on the curve to obtain the spectrum; (4) Using the contrast sensitivity function of the human eye, the spectrum is weighted to obtain the Michelson interference fringe spectrum actually perceived by the human retina; (5) According to formula (1), the modulation contrast at this time is obtained, (1) Where, is the modulation contrast; is the brightness of the white lines; is the brightness of the black line; By changing the width of the Michelson interference fringes, a series of CM values ​​are obtained and a curve is drawn. The greater the slope of the curve, the higher the angular resolution. Based on this, the non-artificial intervention measurement and calculation of the angular resolution of the endoscope can be achieved.

2. The method for measuring the resolution of a medical endoscope based on the contrast sensitivity of the human eye according to claim 1, wherein: In order to characterize the imaging capability of the endoscope for the edge and details of the object, a step function is introduced for boundary analysis. The brightness distribution function of the Michelson interference fringes is represented by the step function shown in formula (2): (2) Where, is brightness; n is an integer (1, 2, 3...); is the Michelson interference fringe width; By taking the derivative of the step function, the slope of the brightness distribution curve of the black and white stripe boundaries acquired by the endoscope is obtained.

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