JPS63266582A - Film image reader - Google Patents

Abstract

PURPOSE:To prevent an interference pattern from being formed and to improve diagnosing performance by forming a scanning optical system so that a laser beam for film scanning slants at a specific angle to a film. CONSTITUTION:A part of the laser beam 11 which travels in the film becomes primary emitting light 14, which emits the light and an angle theta1 from the light- emitting surface 13 of the film B, but the remaining light is reflected by the light-emitting surface 13 and reaches the incidence surface 12 as internal reflected light 15. This internal reflected light 15 is reflected by the incidence surface 12 except part of it emitted upward from the incidence surface 12 and reaches the light-emitting surface 13 again, where a part of the light is emitted downward similarly as secondary emitting light 16 and the remaining light is reflected by the light-emitting surface 13 to travel toward the incidence sur face 12. Thus the light is propagated in the film F. When l1<l1 holds for the gap l1 between the primary emitting light 14 and secondary emitting light 16 and the major axis l2 of the ellipse of the irradiating beam, there is no interference between the primary emitting light 14 and secondary emitting light 16.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention relates to a film image reading device used in the field of medical diagnosis, and particularly to a film image reading device on which an image is recorded using a laser beam. The present invention relates to an improvement of a film image reading device that scans a film, measures the amount of light transmitted through the film at that time, and measures the image density of the scanned portion.

(Prior art) When attempting to observe images recorded on film, especially images from X-ray film, conventionally, diagnosis was made by placing the film on a Scherkasten or the like and observing it directly. .

However, in recent years, with advances in photoelectric conversion technology, this image is scanned with a narrowly focused laser beam, converted into an electrical signal, and the resulting image signal is subjected to various types of image processing to produce information useful for medical diagnosis. A system has been established in which the image is emphasized and then reproduced, and this reproduced image is used for diagnosis. This system, as shown in FIG.
It has a basic configuration consisting of a laser beam scanning type film image reading device 22, a data processing device 23, and an appropriate display device 24.
By scanning the top with a laser beam, the image recorded thereon is converted into a digital amount, and this digitized image information is sent to the data processing device 23 at the subsequent stage.

(2) The data processing device 23 performs data processing such as frequency emphasis and edge emphasis on the sent image information so as to obtain a reproduced image with excellent diagnostic suitability.

■ The display device 24 uses the reproduced image information.
Displayed as a reproduced image above.

Through these steps, the visualized film image is provided for diagnosis by a doctor or the like.

In this case, the conventional film image reading device 22 used to read the image enlarges the aperture of the laser oscillator 25 and the laser beam incident from the oscillator 25 to an arbitrary size, as shown in FIG. A laser light source section includes a beam ink expander 26 that suppresses the spread angle of the laser beam, and a high-speed angular velocity changing mirror 27 such as a galvanometer or polygon mirror that reflects the incident laser beam in the main scanning direction with a constant angular velocity. , a scanning section consisting of an f/theta lens 28 that, when light with a constant angular velocity is incident, forms an image on the same plane with a constant linear velocity; a photographed film 21; A film portion consisting of a pair of film feed rollers 29a and 29b that run in the sub-scanning direction at a predetermined speed and a subsequent electronic circuit work together to convert the laser light that has passed through the film 21 into information about the position of each pixel. In order to efficiently guide the laser beam transmitted through the film 21 to the detector 30 and the detector 30, which are placed facing each other and convert into digital quantities in time series, the detector 30 is made of, for example, a bundle-shaped optical fiber or lens with a processed output end. The device is configured as a device having a measuring section consisting of a condenser 31 and a measuring section.

Therefore, to read a film image using this reading device @ 22, first, the diameter of the laser beam from the laser oscillator 25 is expanded, for example, five times by the beam expander 26, and the laser beam is spread over the film section in the sub-scanning direction. moving film 21
is scanned in the main scanning direction using this expanded laser beam and the scanning sections 27 and 28 to scan the entire surface of the film 21.

The optical signal obtained by this entire surface scanning is converted into target image data based on the following principle. That is, according to this principle, the reference light amount incident on the detector 30 is...=I.

The amount of light that enters the detector 30 when there is no film 21 in the film section...11 The density in that case...The amount of light that enters the detector 30 when the film 21 is placed in the D1 film section・・・・・・I2 When the density in that case is ・・・・・・D2, the relationship between the film density and the amount of detected light is Dl = -
! OgIt/Io, D2=-Iog■2/
I.

Then, the difference D3 between Dt and D2 at this time is D3
It can be expressed as =02-Dl =-IogIz/11.

Therefore, the density D1 "when there is no film 21" is measured in advance and stored in an appropriate storage means, and the value of the density D2 "when there is film 21" measured every time the diagnosis is made. By calculating the difference between E and the stored value, the density D3 of the film to be measured can be determined.

What is shown in FIG. 4 is a block diagram showing an electronic circuit connected to this film image reading device 22. This electronic circuit manages the entire circuit by a controller (not shown), and also controls the output of the controller (not shown). It is configured in advance so that continuous image information can be divided into each pixel by a clock signal corresponding to the main scanning speed.

In the figure, numeral 41 is a log amplifier for logarithmically converting the signal photoelectrically converted by the detector 30, which is a necessary measure for electrically processing film density having a logarithmic dimension. 42 is a sample/hold circuit for holding the output signal of the log amplifier 41 in the previous stage in synchronization with a clock signal input from the controller; 43 is a sample/hold circuit for converting the held signal of the sample/hold circuit 42 into a digital motherboard; The A/D converter 44 is a switch for switching the output from the A/D converter 43 and sending it to a calibration buffer 45 or a line buffer 46, which will be described later, based on instructions from the controller. Density D1 information when there is no film 21 is sent to the calibration buffer 45, and density D2 information when there is film 21 is sent to the line buffer 46.

These gear replacement buffers 45 and line buffers 46 are memory circuits that store digital signals of the number of pixels for one line, and advance the storage address using a clock signal from the controller to update the image. 47 is a difference calculation circuit that calculates the film density D3, which is the object to be measured, for each pixel according to a signal from the controller.
This function is necessary to subtract the film density D1 information stored in the calibration buffer 45 in advance from the film density D2 information stored in the line buffer 46 at the previous stage. 48 is an interface for sending the output signal of the difference calculation circuit 57 to the data processing device 23 mentioned above.

The operation of the film image reading device 22 controlled by this electronic circuit will be described below.

First, before measuring the density of a target film (for example, 21), the density of one line without the film is measured and the value is stored in the calibration buffer 45.

Next, in order to position the film 21 on the main scanning line by the high-speed angular velocity changing mirror 27, a film feed roller 29a,
29b is rotated to move the film 21 in the sub-scanning direction, the density of one line is measured with the film 21 in a certain state, and the measured value is stored in the line buffer 46.

Then, by the action of the controller, the values stored in the calibration buffer 45 and the values stored in the line buffer 146 are sent one after another to the difference calculation circuit 47, and after calculating the difference between the two values, that is, the film density D3, in the circuit 47, This calculation result is transferred to the data processing device 23 to complete the measurement for one line.

Thereafter, by rotating the film feed rollers 29a and 29b, the film 21 is moved by a predetermined distance in the sub-scanning direction, and the next line is measured.

(Problems to be Solved by the Invention) However, this conventional film image reading technology
Although it can be said to be an extremely superior technology in that it can convert film image information into density information with high precision, it does have the problem of reduced measurement accuracy due to optical interference. This problem needs to be solved in order to use the device more effectively. As a result of research into the problems faced by this conventional device, the inventor discovered that the problems were identified by Fabry-Perot.
I explained it using the principle of the interferometer and found out that the difference is 1q.

That is, in the conventional device, the laser beam oscillated from the laser oscillator 25 is incident perpendicularly on the surface of the film 21, so that the laser beam that passes through the film 21 and heads toward the condenser 31 is incident on the surface of the film. Light interference occurs on the back surface, and the resulting interference pattern (generally called moire pattern) is added to the image information when displayed on the display device 24, preventing accurate image formation and reducing measurement accuracy. It was discovered that this was causing a decrease in

Hereinafter, in order to facilitate further understanding of the present invention, the fifth section will be explained.
The principle of Fapley-Perot interferometer will be explained based on the figure.

In the figure, both 1a and 1b are semi-transmissive mirrors having highly reflective reflective surfaces capable of transmitting light, and are arranged so that the reflective surfaces are parallel to each other and face each other.

Now, if coherent light 2 such as a laser beam is incident from above these two semi-transmissive mirrors 1a and 1b (as shown in the top of the diagram), a portion of the beam 2 will be reflected by the upper half-transmissive mirror la surface. Most of the light is transmitted through both semi-transparent &'
The light propagates while being repeatedly reflected between the t18.1b planes, and the other part of the light passes through the lower half-transmitting mirror 1b.

This transmitted light includes primary transmitted light 3, which is the incident coherent light 2 that passes through as it is, and upper and lower semi-transparent mirrors 1a.
, multi-order (e.g., second-order) transmitted light 4a, 4b that repeats reflection an even number of times (e.g., two times) and passes through the lb plane.
Unfortunately, due to the difference in the length of each optical path, a phase difference naturally occurs between the two wavefronts. the result,
When the crests of both waves overlap, the amplitude of the transmitted light increases and the light becomes stronger, and when the crests and troughs overlap, the amplitudes cancel each other out and the light becomes darker.

Therefore, if the wavelength of the incident light 2 is λ, the amphoteric transmitting mirrors 1a, 1
When the interval between the reflective surfaces of b is d, 2nd=mλ
... (1) However, when n: the refractive index of the medium between the reflecting surfaces m: satisfies the formula of an integer, the combined light intensity on the lower semi-transmissive mirror 1b surface is sharp with a period of every λ/2 Interference effects appear.

Here, if we consider that the distance d between the front and back surfaces 2 of the film and the reflective surface of both semi-transmissive mirrors 1a and 1b is the film thickness, this interference effect will appear even in the case of film. In particular, in the case of X-ray film, the thickness is generally 175 μm, and although it appears uniform in appearance, the thickness d of the film changes slightly when viewed from the wavelength of 632.8 nm of the oscillation light of the He-Ne laser. ing. Therefore, if the laser beam incident on the film is a beam of a certain thickness, the intensity of the combined transmitted light will vary slightly depending on the position on the film. The present invention has been made in view of this point, and it is an object of the present invention to provide a novel film image reading device that prevents the occurrence of interference patterns as in the prior art and improves diagnostic performance.

[Structure of the Invention] (Means for Solving the Problems) The structure of the present invention for achieving this object scans an image on a film using a laser beam, and calculates the amount of light transmitted through the film at that time. In a film image reading device that can measure and process the image density in a scanning area as a digital quantity that corresponds to the position of each pixel, a scanning optical system in which a laser beam for film scanning is tilted at a predetermined angle with respect to the film is used. It's because it's configured.

(Function) The effect of the present invention based on this configuration is that when configuring the scanning optical system in a film image reading device, conditions for preventing the occurrence of interference patterns are made clear by tilting the laser light incident on the film. It is in.

(Example) Hereinafter, the present invention will be described in detail based on an example shown in the drawings. FIG. 1 is a diagram illustrating the principle of a film image reading apparatus according to the present invention, and in the figure, E indicates an X-ray film to be measured.

Now, when laser light 11 is incident on the incident surface 12 of the film F at an angle θ1, most of this light 11 is refracted at the incident surface 12 and enters the inside of the film at a refraction angle θ2. A portion of this laser light 11 traveling inside the film becomes primary emitted light 14 and is emitted from the exit surface 13 of the film F at an angle θ1.
The remaining light is reflected by the exit surface 13 and reaches the entrance surface 12 as internally reflected light 15 . This internally reflected light 15 is transmitted to the incident surface 12 except for a part of the light that is emitted upward from the incident surface 12.
2 and reaches the output surface 13 again, and here, as in the case described above, a part of the light becomes secondary output light 16 and is emitted downward, and the remaining light is reflected at the output surface 13. The light then travels toward the incident surface 12 again, repeating this process one after another and propagating within the film F.

Here, the interval 11 between the primary emitted light 14 and the secondary emitted light 16 is
．． If the maximum thickness of film F is dl, then A1=2dx
If the equation tanθ2 − (2) holds true and the beam diameter of the incident laser beam 11 in this case is d2, then the major axis 12 of the ellipse of the irradiation beam at the film incidence surface 12 is 1! 2 = d2 /cosθ1
... (3). Therefore, here! 22<I! 1... (4
), optical interference will not occur between the primary emitted light 14 and the secondary emitted light 16.

Therefore, the refractive indexes of air and film are nl, respectively,
If nl, then according to Snell's law, nl sinθt
= n2sinθ2 - Since the formula (5) holds true, the beam diameter d can be calculated using these formulas (2) to (5).
2 and the incident angle θ1. First, from equations (2) to (4), d2/CO3θ1 <2dl tanθ2d2. /2
d1< CO2O3x tanθ2 (6), and further, tanθ2 = sinθ2 / CO3θ2 = si
nθ2/FT: Pigeon V]Jun-. Therefore, if we substitute the above equation (5) into this equation, tanθ2= nl /√(n22x sinθ1/ −n1/√(
n22xsinθ1)2...(7) In this case, the refractive index of air is n1 = 1, so substituting equation (7) into equation (6) gives -5in2θ
1/2 nl-s+n2 1, and from this, d2/d1< 5in2θ1 / nl -5in2
8〒... (8) It becomes like this. In the case of this formula (8), the film thickness d
Since l and the refractive index n2 are constants, equation (8) is a relational expression between the beam diameter d2 and the incident angle θ1 of the laser beam, and if equation (8) is satisfied, the generation of interference patterns can be prevented. It will be possible. Although this equation (8) cannot be solved directly, it is an equation that can be solved by approximate calculation.

Now, since the base material of a general X-ray film is made of polyethylene terephthalate and has a thickness dl of 0.175 m and a refractive index n2 of 1.64, the beam diameter d2 is set to 0.
1. When set to , the incident angle θ1 is approximately 30 degrees.

Also, since the incident angle when the right side of equation (8) is maximum is approximately 50 degrees, the beam diameter at that time is approximately 0.12 m.
becomes.

Of course, these values vary widely depending on the film base material. For example, if the film base material is cellulose triacetate, its thickness dl is 0.2
1 to 0.24, the refractive index n2 is 1.48, but in any case, the beam diameter d2 and the incident angle θ1
Interference patterns can be prevented from occurring as long as the relationship satisfies equation (8).

Note that the object of the present invention can be achieved simply by tilting the laser beam with respect to the film surface.

As described above, in the present invention, the conditions for preventing the occurrence of interference patterns can be clearly expressed by tilting the laser beam incident on the film, or preferably by using the relational expression between the beam diameter of the laser beam and its angle of incidence. Therefore, by configuring the optical system to meet this condition, it has become possible to obtain an image reading device that does not generate interference patterns.

Although one embodiment has been described above, the present invention is not limited to this, and within the scope of not changing the gist thereof,
It is possible to implement various modifications. For example, although the illustrated embodiment describes processing of X-ray images, it should be noted that the present invention can also be applied to processing of images other than X-ray images.

[Effects of the Invention] As described above, when the present invention is used, it is possible to realize a film image reading device that prevents the generation of interference patterns as in the prior art and improves diagnostic performance.

[Brief explanation of drawings]

FIG. 1 is a diagram illustrating the principle of a film image reading device according to the present invention, FIG. 2 is a block diagram illustrating the basic configuration of a conventional image processing system, and FIG. 3 is a conventional diagram used in the image processing system. A schematic configuration diagram of a film image reading device of
FIG. 4 is a block diagram of an electronic circuit connected to this conventional film image reading device, and FIG. 5 is a diagram illustrating the principle of a Fapley-Perot interferometer. 1a, 1b... Semi-transparent mirror, 2... Coherent light,
3... Primary transmitted light, 4a, 4b... Multi-order transmitted light, F
... film, θ1... angle of incidence, θ2... angle of refraction, 11... laser beam, 12... plane of incidence, 13...
Output surface, 14...Primary output light, 15...Internally reflected light, 16...Secondary output light I Fig. 1

Claims (3)

[Claims] (1) Scan the image on the film using laser light,
By measuring the amount of light transmitted through the film at that time,
A film image reading device capable of processing image density in a scanning part as a digital quantity corresponding to the position of each pixel, characterized in that the laser beam for film scanning is tilted at a predetermined angle with respect to the film to form a scanning optical system. A film image reading device. (2) Diameter d_2 of the laser beam for scanning the film
and the incident angle θ_1 of the beam on the film are d_2/
d_1<sin2θ_1/√(n^2_2−sin^2
θ_1) The film image reading device according to claim 1, wherein the scanning optical system is configured to satisfy the following relational expression: d_1: maximum value of film thickness n_2: refractive index of the film. (3) The film image reading device according to claim 1, wherein the film is an X-ray film.