JP2001236492A - Method and device for image processing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accelerate selective projecting process of an MRI. SOLUTION: When a pixel having a maximum or a minimum value is retrieved from each pixel array, extending in the direction where a three- dimensional image composed of pixels arrayed in three dimensions should be projected, only the pixels object pixels are retrieved as only a part of the pixels in the pixel array are retrieved as the pixels of retrieval.

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 method and apparatus for tomographic imaging.

[0002]

2. Description of the Related Art In recent years, medical image diagnostic apparatuses such as CT apparatuses, MRI apparatuses, and ultrasonic apparatuses have been able to display not only two-dimensional images but also three-dimensional images. . It is also possible to create a two-dimensional image from a three-dimensional image.

More specifically, when a projection image is obtained by visualizing only a necessary tissue such as a blood vessel from a 3D signal (three-dimensional image signal) obtained by a medical image diagnostic apparatus, the visualization overlaps the projection direction. There is known a method (hereinafter, referred to as a selective projection method) of removing unnecessary signals (for example, fat or the like) of a tissue that does not need to be extracted and extracting only necessary signals.

[0004] In the selective projection method, an image projected in several different directions is created using the acquired 3D data, displayed on a display, and an operator can view unnecessary signals while observing the displayed image. And go. Usually, in order to shorten the processing time, the projection directions are AP direction (body front-back direction), HF direction (body up-down direction), and RL
It is a three-axis direction (a body left-right direction).

[0005] By this processing, 3
In order to confirm the unnecessary signal removal effect on the D data, images projected again in several different directions (even in this case, usually projected only in the three-axis directions) are created and displayed on a display. Here, for example, when an unnecessary signal to be removed still exists or when a necessary signal or the like is removed by mistake, the unnecessary signal removing process is repeated as necessary, and the unnecessary signal is correctly removed. Final 3
Obtain D data.

[0006]

In the above-described selective projection method, a process of searching a pixel having a maximum or minimum value from an image to extract a necessary signal is performed. When the signal and the signal overlap in the projection direction in a complicated manner or when the unnecessary signal is to be completely removed, the number of times of performing the unnecessary signal removing process is increased, and it takes a long time to obtain the final 3D data. Takes time.

An object of the present invention is to reduce the time required for selective projection processing.

[0008]

SUMMARY OF THE INVENTION The object of the present invention is to provide, for each pixel column, a pixel having a predetermined value from each pixel column extending in a projection direction of a three-dimensional image composed of three-dimensionally arranged pixels. The method includes a step of searching, and a step of forming a projection image from the searched pixels. In the step of searching for the pixels, a pixel to be searched is a part of pixels in a pixel column. It is solved by an image processing method.

In this image processing method, the search time is reduced because only some of the pixels are searched without searching all the pixels. Therefore, for example, only the pixel having the maximum value is extracted. Processing, that is, the maximum intensity projection method
d) can be performed at high speed.

In this way, in the medical image diagnostic apparatus, for example, processing for removing unnecessary signals from tissue such as fat is repeatedly performed while confirming the effect of the removal processing on the screen to form an image of only blood vessels. Can be performed in a short time.

A step of setting the number n of thinned pixels is provided, and pixels in a pixel row are thinned every n pixels to be used as a search target pixel. Further, it is preferable that the position of a pixel to be searched be shifted between adjacent pixel columns. By doing so, it is possible to prevent all the pixels of the thin blood vessels from being excluded from the search target.

[0012]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 2 is a block diagram showing the overall configuration of an MRI apparatus to which the method of the present invention is applied. This MRI apparatus obtains a tomographic image of a subject by using a magnetic resonance phenomenon. As shown in FIG. 2, a static magnetic field generating magnetic circuit 1, a gradient magnetic field generating system 2, a transmitting system 3, and a receiving system The system includes a system 4, a signal processing system 5, a sequencer 6, a central processing unit (CPU) 7, and an operation unit 8.

The static magnetic field generating magnetic circuit 1 generates a uniform static magnetic field around the subject 9 in the body axis direction or in a direction perpendicular to the body axis, and has a certain spread around the subject 9. And a permanent magnet type, a normal conduction type, or a superconducting type magnetic field generating means disposed in a closed space.

The gradient magnetic field generating system 2 includes a gradient magnetic field coil 10 wound in three axes of X, Y, and Z, and a gradient magnetic field power supply 11 for driving each coil. The gradient magnetic field power supplies 11 of the respective coils are driven in accordance with the instructions to apply the gradient magnetic fields Gs, Gp, and Gf in the X, Y, and Z directions to the subject 9. The slice plane of the subject 9 can be set by how to apply the gradient magnetic field.

The transmission system 3 irradiates a high-frequency signal to cause nuclear magnetic resonance in the nuclei of the atoms constituting the living tissue of the subject 9 by a high-frequency magnetic field pulse transmitted from a sequencer 6 described later. High-frequency oscillator 12, modulator 13, high-frequency amplifier 14, transmission-side high-frequency coil 15
Consists of After the high-frequency pulse output from the high-frequency oscillator 12 is amplified by the high-frequency amplifier 14,
The electromagnetic wave is applied to the subject 9 by supplying the electromagnetic wave to the reception-side high-frequency coil 16 disposed close to the object 9.

The receiving system 4 includes an echo signal (NMR signal) emitted by nuclear magnetic resonance of an atomic nucleus of a living tissue of the subject 9.
And comprises a receiving-side high-frequency coil 16, an amplifier 17, a quadrature phase detector 18, and an A / D converter 19. A response electromagnetic wave (NMR signal) from the subject 9 to the electromagnetic wave emitted from the transmitting high-frequency coil 15 is detected by the receiving high-frequency coil 16 disposed close to the subject 9, and transmitted to the amplifier 17 and the quadrature phase detector 18. Via A /
Input to the D converter, where it is converted to a digital quantity,
Further, the data is sent to the signal processing system 5 as two series of collected data sampled by the quadrature phase detector 18 at a timing according to a command from the sequencer 6.

The signal processing system 5 performs an operation for image reconstruction by using the echo signal detected by the receiving system 4 and displays an image.
A CPU 7 for performing processing such as correction coefficient calculation and image reconstruction and controlling a sequencer 6 to be described later, and a ROM for storing a program for image analysis processing and measurement over time and certain parameters used for executing the program (Read-only memory) 20 for temporarily storing and storing measurement parameters obtained by preceding measurement, echo signals detected by the receiving system 4, images used for setting a region of interest, parameters for setting a region of interest, and the like. RAM (Random Access Memory) 21, Magneto-optical disk 22 and Magnetic Disk 23 as data storage for storing image data reconstructed by CPU 7, and images read from these Magneto-optical Disk 22 and Magnetic Disk 23 And a display 24 for displaying data as a tomographic image.

The sequencer 6 executes an operation of repeatedly applying a high-frequency magnetic field pulse for causing nuclear magnetic resonance to the nuclei of the atoms constituting the living tissue of the subject 9 in a predetermined pulse sequence. And sends various commands necessary for data collection of tomographic images of the subject 9 to the transmission system 3, the gradient magnetic field generation system 2, and the reception system 4. The operation unit 8 is for inputting information necessary for controlling processing performed by the signal processing system 5.
A keyboard 26 is included.

Next, a procedure for removing unnecessary signals from the 3D data obtained by the above-described MRI apparatus and creating a projection image of only necessary tissues such as blood vessels will be described with reference to FIG.

First, using the 3D data acquired in step 101, a plurality of different projection directions, for example, an AP direction (body longitudinal direction), an HF direction (body vertical direction), and RL
An image projected in three axial directions (lateral directions of the body) is created, displayed on a display in step 102, and an operator deletes unnecessary signals while observing the image displayed in step 103.

In order to confirm the effect of the unnecessary signal removal processing, in step 104, projection images in a plurality of different directions are created again using the data from which the unnecessary signal has been removed. In this step, MIP processing for searching for a pixel having the maximum value in each projection direction is executed. In the conventional MIP processing, all pixels are set as search targets. Here, in order to speed up the processing, the maximum value search is thinned out every n (n is a positive integer) pixels in each projection direction. The value of n can be set, for example, by inputting a numerical value at a predetermined position on the screen or displaying a slide bar on the screen and operating with a mouse. Thus, each time the MIP processing (MIP performed to confirm an unnecessary signal removal effect) in the selective projection processing is performed, the thinning width n used in the MIP processing can be set.

The position of the pixel for which the maximum value search is performed in the RL direction is i (0 ≦ i <x), the position in the HF direction is j (0 ≦ j <y), and the position in the AP direction is k (0 ≦ k <z). ), The maximum value search in the RL direction is performed according to the following equation.

W (j, k) _max = max (W (j, k) [i]) where i = 0 (n + 1), 1 (n + 1), 2 (n + 1), 3 ( n + 1) (Equation 1) Here, max (W (j, k) [i]) represents the maximum value of the data sequence W (j, k) [i]. W calculated for all combinations of j and k
A pixel corresponding to (j, k) _max forms a selected projection image in the RL direction.

When the number n of thinned pixels is 1,
That is, when the maximum value search is performed every other pixel, i is an even number (i = 0,
2,4, ...) are all subjected to the maximum value search.
Are all odd numbers (i = 1, 3, 5,...) Are excluded from the maximum value search. For this reason, information on thin tissues such as blood vessels may not be extracted well. In order to cope with this problem, it is preferable to thin out pixels so that pixels adjacent to the pixel for which the maximum value search is to be performed are excluded from the maximum value search target. Such a maximum value search can be performed, for example, according to the following equation.
P processing can be speeded up.

W (j, k) _max = max (W (j, k) [i]) where i is 0 when the remainder of (k + j) / (n + 1) is m. (n + 1) + m, 1 (n + 1) + m, 2 (n + 1) + m, 3 (n + 1) + m (Equation 2) FIG. 3 shows an example of a pixel arrangement pattern for n = 2. As long as the pixels for which the maximum value search is performed are arranged every n pixels, the same processing speed-up effect can be obtained with any arrangement pattern.

At step 104, the MI
After performing P processing and creating a projection image, step 10
In step 5, an image from which unnecessary signals have been removed is displayed on the display. In step 106, for example, when the operator determines that the unnecessary signal to be removed still exists or determines that the necessary signal has been removed by mistake, the operator returns to step 103 and performs the unnecessary signal removing process again. If it is determined that this effect is sufficient, the area from which unnecessary signals have been removed is reflected in the 3D data in step 107.

In step 108, the operator finally determines whether to continue or terminate the processing. If the processing is continued, the operation returns to step 103, and if it is completed, an image in a desired projection direction is created.

In the above embodiment, the coordinate position of each pixel to be searched for the maximum is obtained by calculation. However, those position patterns can be prepared in advance as a table. In the present embodiment, the image data of the MRI apparatus is used as the 3D data, but an image such as a CT or an ultrasonic wave may be used.

[0029]

According to the present invention, in each projection direction,
Since the maximum value search is performed only on pixels extracted in advance, a selected projection image can be formed at high speed, and the time required for unnecessary signal removal processing can be reduced.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a procedure of selective projection according to the present invention.

FIG. 2 is a block diagram of an MRI apparatus to which the method of the present invention is applied.

FIG. 3 is a diagram illustrating an arrangement pattern of pixels to be searched for a maximum value.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Static magnetic field generation magnetic circuit 2 Gradient magnetic field generation system 3 Transmission system 4 Receiving system 5 Signal processing system 6 Sequence 7 CPU 8 Operation unit 9 Subject 10 Gradient magnetic field coil

Claims (6)

[Claims] 1. A three-dimensional array composed of three-dimensionally arranged pixels.
Searching for a pixel having a predetermined value for each pixel row from each pixel row extending in the direction in which the three-dimensional image is to be projected, and forming a projection image from the searched pixels; An image processing method, wherein, in the step, a pixel to be searched is a part of pixels in a pixel column. 2. The image processing method according to claim 1, further comprising the step of setting the number n of thinned pixels, wherein the pixels in the pixel column are thinned out every n pixels to be a search target pixel. 3. The image processing method according to claim 1, wherein a search target pixel position is shifted between adjacent pixel columns. 4. A means for obtaining a three-dimensional image of an object composed of three-dimensionally arranged pixels, and a method of converting a pixel having a predetermined value from each pixel row extending in a direction in which the three-dimensional image is to be projected. An image processing apparatus comprising: means for searching for each column; and means for forming a projection image from the searched pixels, wherein the searching means uses a part of pixels in the pixel row as search target pixels. . 5. The image processing apparatus according to claim 4, further comprising means for setting the number n of thinned pixels, wherein pixels in a pixel column are thinned every n pixels to be a search target pixel. 6. The image processing apparatus according to claim 4, wherein a search target pixel position is shifted between adjacent pixel columns.