JP2001175844A - Medical image processing apparatus, medical image processing method, and computer-readable storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a medical image processor and a medical image processing method capable of efficiently compressing a fluorescent contrast image into the best state for use in medical site, and to provide a computer readable storage medium therefor. SOLUTION: When an infrared fluorescent contrasted image obtained by photographing, e.g. the eyeground is compressed, the quantization step of an quantization module included in an image compression module 2 is made different between the period (contrasting initial-period layer) from the appearance of a fluorescent image on a choroidal blood vessel to the arrival at a choroidal capillary vessel and the period (contrasting latter-period layer) after the penetration of fluorescence into the choroidal blood vessel. Consequently, a decoded image of the contrasting initial-period layer which is important for a medial treatment using the decoded image is compressed with low compressibility so that it can be displayed with excellent resolution, and an image of the contrasting latter-period layer which needs to only show a rough state when decoded is compressed with high compressibility.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a medical image processing apparatus, a medical image processing method, and a computer-readable storage medium. For example, the present invention is applied to an encoding apparatus for encoding a fluorescence contrast image of a fundus of a subject. The present invention relates to a medical image processing apparatus, a medical image processing method, and a computer-readable storage medium that are suitable.

[0002]

2. Description of the Related Art In recent years, an image of a subject (medical image) is often treated as digital image data even in a medical field. For this reason, in the medical field, by compressing a large amount of image data generated daily in the medical field by a compression method suitable for the use of medical images, it can be efficiently stored on a recording medium such as a magnetic disk or a magneto-optical disk. Attempts have been made to save.

For example, JPEG (Joint Photographic Ex)
A multi-level lossless compression method such as perts Group) -LS is known as a compression method suitable for medical images.

[0004] Among such medical fields, particularly in the field of ophthalmic medical care, a single measurement on a subject is required to be performed for several tens of times, for example, in the case of fluorescence contrast imaging for examining the state of blood flow on the retina or choroid. Because image data for the number of sheets is generated,
To save the generated image data efficiently,
Image compression technology is essential.

[0005] In the case of imaging the state of blood flow on the retina or choroid by fluorescence contrast imaging, infrared fluorescence contrast imaging using ICG (indocyanine green) as a fluorescent agent generally produces a fluorescent image on a choroidal blood vessel. Period from appearance to the choroid capillaries (early contrast layer)
And the period after the fluorescence has penetrated into the choroidal blood vessels (late-contrast layer). The period up to approximately 10 minutes is referred to as an early-contrast layer, and the subsequent steps are referred to as a late-contrast layer.

[0006] Depending on the case, in the initial contrast layer,
In general, the temporal change of the fluorescence image that appears on the choroidal blood vessels is drastic, so many images are taken to record the change, and especially the image at the beginning of the fluorescence is important for diagnosing the condition of the subject. Is seen. It is also a characteristic of the initial contrast enhancement layer to exhibit minute changes in fine blood vessels on the cerebral membrane.

On the other hand, in the late contrast layer, the fluorescent image generally changes slowly and the color of the fluorescent light also weakens, so that the captured image lacks contrast as a whole and becomes a dark and faint image. . The information required by the doctor or the like for the image captured at this stage is not a small change but rough information such as where a dark place (no fluorescent agent = no blood flow) is located. .

[0008]

However, an image compression method suitable for medical images in the field of ophthalmological medical care and the like has not yet been established.

Accordingly, an object of the present invention is to provide a medical image processing apparatus, a medical image processing method, and a computer-readable storage medium for compressing a fluorescence contrast image efficiently and in a state optimal for use in a medical field. And

[0010]

In order to achieve the above object, a medical image processing apparatus according to the present invention has the following configuration.

[0011] More specifically, image input means for inputting a plurality of contrast-enhanced fluorescence images of a predetermined part of a subject, and encoding for coding the contrast-enhanced fluorescence images output from the image input means using a wavelet transform method. Means, in the process of encoding the plurality of fluorescence contrast images, so that the quantization parameter used for the encoding is changed,
Control means for controlling the encoding means.

Further, for example, when the predetermined part is the fundus of the subject, the control means sets the quantization parameter to a different value between the period of the contrast enhancement initial layer and the period of the contrast enhancement late layer. (For example, the encoding means may be controlled so that the number of quantization steps in the period of the late contrast layer is smaller than the number of quantization steps in the period of the early contrast layer).

[0013] When the quantization step in the period of the late-stage contrast layer is changed as described above, of the plurality of fluorescent contrast-enhanced images, of the fluorescence-enhanced image encoded in the period of the late-stage contrast layer, It is better to change high frequency components.

In order to achieve the above object, an image processing method for a medical image processing apparatus according to the present invention has the following configuration.

That is, in the process of encoding a plurality of contrast-enhanced fluorescence images obtained by photographing a predetermined part of a subject using a wavelet transform method, a quantization parameter used for the encoding is changed.

For example, when the predetermined part is the fundus of the subject, the quantization parameter
Change to a different value between the period of the contrast early layer of the fluorescence contrast and the period of the late contrast layer (for example, the quantization step in the period of the late contrast layer is smaller than the quantization step in the period of the contrast early layer. Change it to be good).

Further, the present invention is characterized by a computer-readable storage medium storing a program code for realizing the medical image processing apparatus and the medical image processing method by a computer.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the medical image processing apparatus according to the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a schematic configuration of a medical image processing apparatus according to this embodiment. Each module described below in this embodiment includes a micro-illustration (not shown) provided in the medical image processing apparatus. Represents software or hardware functional units executed by a computer.

In FIG. 1, reference numeral 1 denotes an image input module;
2 is an image compression module, 3 is an image recording module, 4
Is an image expansion module, 5 is a monitor, 6 is a fluorescence timer,
Reference numeral 7 denotes a timer threshold storage module.

The image input module 1 is connected to a fundus camera (not shown) capable of performing fluoroscopic imaging.

Here, a procedure in the case where infrared fluorescence contrast imaging is performed using a fundus camera at a medical site will be described.

First, a fluorescent agent, indocyanine green, is injected into the arm vein of the eyeball of the subject, and at the same time, a start button (not shown) of the fluorescent timer 6 is depressed to start timing. Subsequently, the fundus of the subject to be photographed is aligned, and when fluorescence appears on the fundus, a photographing switch (not shown) is pressed to photograph a fluorescence contrast image as illustrated in FIG. 2. .

By this photographing operation, the fundus image signal of the subject input to the image input module 1 is converted into digital image data and then transferred to the image compression module 2.

FIG. 3 is a block diagram showing the internal configuration of the image compression module 2 in this embodiment.

The image compression module 2 includes a discrete wavelet transform module 10, a quantization module 11, and an encoding module 12, as shown in FIG.

Discrete wavelet transform module 10
Performs a two-dimensional discrete wavelet transform process on input image data, and outputs a transform coefficient to the quantization module 11 as a calculation result.

FIG. 4 is a diagram showing a basic configuration of the discrete wavelet transform module 10 shown in FIG. 3. Input image data is temporarily stored in the memory 101.
Then, the processing unit 102 sequentially reads out the image data stored in the memory 101 at a predetermined timing, performs a two-dimensional discrete wavelet transform process on the read out image data, and then writes the processed image data into the memory 201 again. The configuration of the processing of the processing unit 102 in the present embodiment will be described with reference to FIG.

FIG. 5 is a diagram showing the configuration of the discrete wavelet transform processing unit 102 in the present embodiment.

In FIG. 1, image data read from a memory 101 is separated into data of even addresses and odd addresses by a combination of a delay element and a downsampler, and is subjected to filter processing by filters p and u, respectively. . S and d shown in FIG. 5 represent low-pass coefficients and high-pass coefficients when one-level decomposition is performed on one-dimensional image data, respectively, and are calculated by the following equation (where x (n) Is image data to be converted).

D (n) = x (2 × n + 1) -floor ((x (2 × n) + x (2 × n + 2)) / 2) (Equation 1), s (n ) = x (2 × n) + floor ((d (n−1) + d (n)) / 4) (Equation 2) By the above processing, the image data read from the memory 101 is processed. One-dimensional discrete wavelet transform processing is performed. In the two-dimensional discrete wavelet transform, one-dimensional transform is sequentially performed in the horizontal direction and the vertical direction of the fluorescence contrast image (image data) to be processed. Is omitted.

FIG. 6 shows an example of the configuration of a two-level transform coefficient group obtained by a two-dimensional discrete wavelet transform process. The input image data includes coefficient sequences HH1, HL1, LH1,. LL (in the following description, these coefficient sequences are referred to as “subbands”). Then, the coefficients of each subband are output to the quantization module 11 at the subsequent stage.

The quantization module 11 quantizes the subband coefficients input from the discrete wavelet transform module 10 in a predetermined quantization step, and outputs an index for the quantized value. Here, the quantization process in the quantization module 11 is performed by the following equation (where c is a coefficient to be quantized).

Q = sign (c) floor (abs (c) / Δ) (expression 3), sign (c) = 1; c> = 0 (expression 4), sign (c) = -1; c <0 (Equation 5) In the present embodiment, the value of Δ is assumed to include 1, and when the value of Δ is 1, quantization is not performed and discrete wavelet transform is performed. The subband coefficients input from the module 10 are directly output to the entropy encoding module 12 at the subsequent stage.

FIG. 7 is a diagram exemplifying a time change of a frequency component in an arbitrary part of interest included in the infrared fluorescence contrast image.

The part of interest shown in the figure is the period from the appearance of the fluorescent image on the choroidal blood vessels to the end of the choroidal capillaries (early contrast layer), and the period after the fluorescence has penetrated into the choroidal blood vessels (late imaging phase). Layer). In the infrared fluorescence contrast image, a choroidal blood vessel image with a sharp edge appears as shown in FIG. 8A in the initial contrast layer, and locally in the late contrast layer as shown in FIG. 8B. Sites with different fluorescence concentrations (corresponding to sites where there is no blood flow due to thrombus or leakage)
Is appearing.

The threshold value (to) shown in FIG. 7 is the timer value of the fluorescence timer 6 that separates these early and late contrast layers. The threshold value is stored in the timer threshold storage module 7 in advance. .

In the period of the initial contrast layer up to the threshold value (to) shown in FIG. 7 from the start of the fluorescence contrast imaging, the value Δ in the above (Equation 3) is obtained by using a value common to each subband. In the present embodiment, quantization is performed in a uniform quantization step.

Then, in the period of the late-stage imaging step in which the timer value (elapsed time t) from the fluorescence timer 6 exceeds the threshold (to) stored in the timer threshold storage module 7,
The quantization module 11 performs a process of roughly quantizing the high-frequency component of the infrared fluorescence contrast image by changing the quantization step from the quantization process of the predetermined quantization step in the period of the contrast initial layer as described below. Is performed.

The LL included in the subband shown in FIG.
It shows the information of the lowest frequency component included in the fluorescent contrast image currently being processed, and the portion of interest included in the image of the late contrast layer illustrated in FIG. 8B is the information included in the LL. . Therefore, as described above, the information required by the doctor or the like for the image in the late contrast layer is not a small change but a rough information such as where a dark place (no fluorescent agent = no blood flow) exists. HH
Regarding 1, HL1, LH1, HH2, HL2, and LH2, even if compression is performed at a high compression rate by adopting a rough quantization step (that is, reducing the number of quantization steps), the diagnosis is not performed. It is considered that necessary information is not missing. Here, the above value Δ in LL is Δ
Assuming that ΔH other than L and LL is ΔH, the following relationship is established with the threshold value t0.

ΔL> ΔH (where t> t0) (Equation 6) That is, by performing the image quantization of the late-stage contrast layer using the condition of (Equation 6), it becomes possible to obtain a signal other than the low-frequency component. Only high compression can quantize.

The transform coefficients output from the quantization module 11 are encoded by the entropy encoding module 12 by a conventionally known general method.

Then, the entropy encoding module 12
(Compressed image data of the fluorescence contrast image) is recorded in the image recording module 3 and read out by the image decompression module 4, and decompression processing is performed in the module opposite to the image compression module 2. Is displayed on the monitor 5 as image data of the fluorescence contrast image.

In the above-described embodiment, the processing configuration in which quantization is performed by a quantization step common to each subband in the contrast initial layer has been described as an example. However, the present invention is not limited to this configuration. In contrast to the latter stage of contrast enhancement, only the low-frequency components of the target fluorescence-enhanced image are subjected to high compression (reducing the number of quantization steps), and other low-frequency components are subjected to low compression (take more quantization steps). May be adopted.

As another embodiment, in the late contrast layer, the coefficient in each of the above subbands is LL
Other than the above, a low weight (for example, 0.5 or the like) may be used.

Further, as shown in FIG. 9, quantization may be performed after repeating a two-dimensional discrete wavelet transform a plurality of times. In this case, the LL region is further frequency-decomposed, and comes closer to the DC component. As described above, since information required by a doctor or the like in an image of the late-stage contrast layer to find a part without blood flow is information representing light and dark, in order to execute efficient encoding to reduce the data amount, , Better encoding can be performed by performing an appropriate number of wavelet transforms.

In the above-described embodiment, the compressed image data encoded by the image compression module 2 is output to the image recording module 3 via the image recording module 3. The compressed image data (encoded data) obtained by the image compression module 2 is not limited to the device configuration, but may be converted to a LAN (Local Area Neighborhood), for example, in view of the recent networking between medical facilities.
twork) and WWW (WorldWide Web) and other networks,
A so-called telemedicine system is constructed by decoding the transferred compressed image data and displaying an image based on the decoded image data in an image processing device such as a computer provided with the image decompression module 4. You may.

As described above, according to the above-described embodiment, when compressing an infrared contrast-enhanced image, the compression ratio in the initial layer and the compression ratio in the later layer are automatically changed. Can generate compressed image data capable of realizing a display image with a sufficient resolution necessary for a doctor or the like performing a medical examination using the obtained image, and efficiently use the storage medium with a limited storage capacity such as a magnetic disk or a magneto-optical disk. Can be stored well.

Also, by adopting the wavelet transform method for encoding the photographed fluorescent contrast, it is possible to provide a hierarchical encoding technique with good compression efficiency.

[0050]

[Other Embodiments] Even if the present invention is applied to a system constituted by a plurality of devices (for example, a host computer, a fundus camera, etc.), an apparatus comprising one device (for example,
Copy machine, facsimile machine, etc.).

Further, an object of the present invention is to supply a storage medium (or a recording medium) in which a program code of software for realizing the functions of the above-described embodiments is recorded to a system or an apparatus, and to provide a computer (a computer) of the system or the apparatus. Alternatively, the present invention is also achieved when a CPU or an MPU reads and executes a program code stored in a storage medium. In this case, the program code itself read from the storage medium implements the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention. In addition, the computer executes the readout program code, so that not only the functions of the above-described embodiments are realized, but also an operating system (OS) running on the computer based on the instructions of the program code. This also includes a case where some or all of the actual processing is performed and the functions of the above-described embodiments are realized by the processing.

Further, after the program code read from the storage medium is written into a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer, based on the instruction of the program code. This also includes the case where the CPU or the like provided in the function expansion card or function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

[0053]

According to the present invention, there is provided a medical image processing apparatus, a medical image processing method, and a computer-readable storage medium for efficiently compressing a contrast-enhanced fluorescent image in a state optimal for use in a medical field. Is realized.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of a medical image processing apparatus according to an embodiment.

FIG. 2 is a diagram illustrating a fluorescence contrast image of a fundus oculi.

FIG. 3 is a block diagram illustrating an internal configuration of an image compression module 2 according to the embodiment.

FIG. 4 is a diagram showing a basic configuration of the discrete wavelet transform module 10 shown in FIG.

FIG. 5 is a diagram illustrating a configuration of a discrete wavelet transform processing unit 102 in the present embodiment.

FIG. 6 is a configuration example of a two-level transform coefficient group obtained by a two-dimensional discrete wavelet transform process.

FIG. 7 is a diagram illustrating a time change of a frequency component in an arbitrary part of interest included in the infrared fluorescence contrast image.

FIG. 8 is a diagram exemplifying a fluorescence contrast image in an early contrast layer and a fluorescence contrast image in a late contrast layer.

FIG. 9 is a configuration example of a two-level transform coefficient group obtained when the two-dimensional discrete wavelet transform process is repeated.

[Explanation of symbols]

 1: Image input module, 2: Image compression module, 3: Image recording module, 4: Image expansion module, 5: Monitor, 6: Fluorescence timer, 7: Timer threshold storage module, 10: Discrete wavelet conversion module, 11: Quantization module, 12: Entropy coding module,

Claims (16)

[Claims] 1. An image input means for inputting a plurality of fluorescence contrast images obtained by photographing a predetermined part of a subject, and encoding for coding a fluorescence contrast image output from the image input means by using a wavelet transform method. Means, in the process of encoding the plurality of fluorescence contrast images, so that the quantization parameter used for the encoding is changed, control means for controlling the encoding means, A medical image processing apparatus characterized by the following. 2. The method according to claim 1, wherein the predetermined part is a fundus of the subject, and the control unit changes the quantization parameter to a value different between a period of an initial contrast layer of fluorescence imaging and a period of a late imaging layer. 2. The medical image processing apparatus according to claim 1, wherein the encoding unit is controlled so as to be performed. 3. The control unit controls the encoding unit such that the number of quantization steps in the period of the late contrast layer is smaller than the number of quantization steps in the period of the early contrast layer. The medical image processing apparatus according to claim 2, wherein 4. The change of the quantization step in the period of the late contrast layer is performed on a high-frequency component of the fluorescence contrast image encoded in the period of the second contrast layer among the plurality of fluorescent contrast images. The medical image processing apparatus according to claim 3, wherein: 5. The medical image processing apparatus according to claim 1, wherein the fluorescence contrast is an infrared fluorescence contrast. 6. The medical image processing apparatus according to claim 1, wherein the change of the quantization parameter used in the encoding unit is applied to an image after wavelet transform. 7. The medical image processing apparatus according to claim 6, wherein the encoding unit performs the wavelet transform a plurality of times. 8. A medical apparatus characterized in that, in a process of encoding a plurality of contrast-enhanced fluorescence images obtained by photographing a predetermined part of a subject using a wavelet transform method, a quantization parameter used for the encoding is changed. Image processing method. 9. The method according to claim 8, wherein the predetermined part is a fundus of the subject, and the quantization parameter is changed to a different value between a period of an early-stage contrast layer of fluorescence imaging and a period of a late-stage contrast layer. The medical image processing method according to claim 8, wherein 10. The method according to claim 9, wherein when changing the quantization parameter, the number of quantization steps in the period of the late contrast layer is reduced as compared with the number of quantization steps in the period of the early contrast layer. The medical image processing method according to the above. 11. The method according to claim 7, wherein the change of the quantization step in the period of the late contrast layer is performed by using
11. The medical image processing method according to claim 10, wherein the method is performed on a high-frequency component of a fluorescence contrast image to be encoded during the period of the late imaging layer. 12. The medical image processing method according to claim 8, wherein infrared fluorescence contrast is adopted as said fluorescence contrast. 13. The medical image processing method according to claim 8, wherein the changed quantization parameter is applied to the image after the wavelet transform. 14. The medical image processing method according to claim 13, wherein the wavelet transform is performed a plurality of times. 15. A computer-readable storage medium storing a program code for operating a computer as the medical image processing apparatus according to claim 1. Description: 16. A computer readable storage medium storing a program code capable of realizing a medical image processing method according to claim 8 by a computer.