JP2007236681A - Medical image diagnostic apparatus and control program of medical image diagnostic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a medical image diagnostic apparatus and a control program of the medical image diagnostic apparatus, especially for medical image diagnostic apparatus having the function of removing artifacts generated in images, which removes artifacts from images including artifacts and output only a real image. <P>SOLUTION: A plurality of pieces of image information including real image information and fake image information whose positions are different are collected, and the fake image information is removed by computation with a combination of addition and substraction of a plurality of image information and only real tissue image is displayed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a medical image diagnostic apparatus, and more particularly to a medical image diagnostic apparatus having a function of removing artifacts in an image in which artifacts are generated.

  A medical diagnostic imaging apparatus is an apparatus that detects an energy signal obtained by interaction with a living body and displays an internal organ as an image. An X-ray diagnostic apparatus that uses X-rays, an X-ray CT apparatus, and MRI that uses magnetic energy And an ultrasonic diagnostic apparatus using ultrasonic waves and a nuclear medicine diagnostic apparatus using gamma rays. These devices are now widespread and their performance is improving year by year.

  However, the internal organ images generated by these devices are not necessarily true organ images, and there may be a mixture of false images that do not actually exist due to various factors. This is usually called an artifact. If artifacts are mixed in the image, an accurate diagnosis cannot be made and this may lead to a misdiagnosis. The way in which artifacts appear differs depending on the type of diagnostic device, and the countermeasures have been taken for improvement methods specific to the device, but there are some that cannot be removed sufficiently. For example, linear streak artifacts in an X-ray CT apparatus and various artifacts in an ultrasonic diagnostic apparatus. In particular, artifacts due to multiple reflections, side lobes or grating lobes in an ultrasonic diagnostic apparatus are major obstacles in the ultrasonic water immersion method.

There is already an invention regarding the removal of artifacts in an ultrasonic diagnostic apparatus (Patent Document 1). In this invention, a plurality of data is collected by tilting the ultrasonic probe (at least two tilt angles according to the text), and a structure that depends on the direction around a predetermined threshold is defined via an evaluation program, It shows how to project in the scan direction, compare by subtraction and ignore artifacts. This evaluation program is complicated in processing, and it is difficult to set an appropriate threshold value. Since the evaluation result of whether or not an artifact differs depending on the threshold value, it is difficult to reliably remove the artifact. Further, as a simple method in the specification, when the true image A is subtracted from the image (A + B) in which the false image is superimposed on the true image, only the false image B is obtained, and the false image is superimposed on the true image. There is an explanation that the true image A can be obtained by subtracting the fake image B from the obtained image (A + B). However, if both of the two images include a fake image, this calculation process subtracts the fake image. It is not possible.
Special table 2002-512735 gazette Japanese Patent Publication No.62-4989 Japanese Examined Patent Publication No. 4-14015

  As described above, image artifacts obtained by a medical image diagnostic apparatus are a serious problem in diagnosis, and it is always important to reduce or eliminate the artifacts. The present invention is intended to solve such a conventional problem, and provides a medical image diagnostic apparatus that removes artifacts from an image including artifacts and outputs only a true image, and a control program for the medical image diagnostic apparatus. The purpose is to do. It is another object of the present invention to easily and surely remove artifacts of an ultrasonic diagnostic apparatus, which has been considered difficult in the past, to improve the image quality of the ultrasonic diagnostic apparatus and to put the ultrasonic water immersion method into practical use.

  In order to solve the above problems, a medical image diagnostic apparatus according to the present invention is a medical image diagnostic apparatus that displays an internal organ of a subject as an image, and includes true image information and false image information, and the true image information A plurality of pieces of image information for collecting a plurality of pieces of image information in which the positional relationship between the fake image information and the fake image information differs, and the plurality of pieces of image information Calculating means for removing the false image information and outputting only the true image information by subtracting information based on the difference between the plurality of pieces of image information from the sum of .

  The medical image diagnostic apparatus control program according to the present invention includes true image information and false image information in a medical image diagnostic apparatus that displays an internal organ of a subject as an image, and the true image information An image collection function for collecting a plurality of pieces of image information in which the positional relationship of the fake image information is different, and the sum of the plurality of pieces of image information so that the true image information has the same position for the plurality of pieces of image information. An arithmetic processing function for removing the false image information and outputting only the true image information by subtracting information based on the difference between the plurality of image information from .

  According to the present invention, it is possible to provide a medical image diagnostic apparatus that removes artifacts from an image including artifacts and outputs only a true image and a control program for the medical image diagnostic apparatus.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 illustrates an artifact removal method and principle of this embodiment common to medical image diagnostic apparatuses, and FIGS. 2 to 8 illustrate a case where the present embodiment is applied to an ultrasonic diagnostic apparatus.

  FIG. 1 shows two images (FIGS. 1a and 1b) collected by the medical image diagnostic apparatus and three images (FIGS. 1c to 1e) subjected to arithmetic processing. The internal organ display area 1 is indicated by a rectangular frame, and an image of the tissue is displayed in the inside. The tissue image 2a shown in FIGS. 1a and 1b is a true image. In FIG. 1a, the first artifact 3 is displayed so as to overlap the true image 2a, and in FIG. 1b, the true image 2a is overlapped. The second artifact 4 is displayed. The first artifact 3 and the second artifact 4 are at different positions with respect to the true image 2a. Assume that the signal intensity of the true image 2a is A, the intensity of the first artifact 3 is B1, and the intensity of the second artifact 4 is B2. Since the artifact is displayed so as to be superimposed on the true image, the magnitudes of the signals of the portion where the artifact is displayed are A + B1 and A + B2, respectively. Here, A, B1, and B2 are positive values.

  FIG. 1c is a sum image of FIG. 1a and FIG. 1b, the signal strength of the true image 2b is 2A, the strength of the first artifact 3 portion is 2A + B1, and the strength of the second artifact 4 portion. Is 2A + B2. Since the positions of B1 and B2 are different, the total is 2A + B1 + B2. FIG. 1d is an image of the absolute value of the difference between FIG. 1a and FIG. 1b. Since the true image 2a is the same, the difference is zero, and the portion of the first artifact 3 is | A + B1-A | = B1, The portion of the artifact 4 is | A− (A + B2) | = B2, and is B1 + B2 as a whole. That is, FIG. 1c is an image in which two artifacts overlap with two artifacts, and FIG. 1d is an image with only two artifacts. Therefore, subtracting FIG. 1d from FIG. 1c and dividing by 2 results in (2A + B1 + B2-B1-B2) / 2 = A, and both the first artifact 3 and the second artifact 4 are removed as shown in FIG. 1e. A true image 2a is obtained.

  Alternatively, a boundary 5 is provided at an intermediate position between the first artifact 3 and the second artifact 4 in the difference image (B1-B2) between FIG. 1a and FIG. 1b, and the first artifact 3 of the boundary 5 is provided. Multiplying the step function by +1 on the second side and -1 on the second artifact 4 side gives (B1 + B2), and the same image as in FIG. 1d is obtained. Therefore, by subtracting the image obtained by multiplying the difference by the step function from FIG. 1c, the false image is removed and a true image is obtained. However, in this case, A, B1, and B2 do not need to be positive values, and the application range is wide.

  Next, the case where this embodiment is applied to an ultrasonic diagnostic apparatus using a water immersion method will be described in detail.

  FIG. 2 is a block diagram of the ultrasonic diagnostic apparatus according to this embodiment. As shown in the figure, the ultrasonic diagnostic apparatus includes an ultrasonic probe 11, a probe moving mechanism 22, a moving distance measuring unit 27, a monitor 200, an ultrasonic transmitting unit 101, an ultrasonic receiving unit 102, and a B-mode processing unit 103. , A scan converter 105, a memory 106, and an arithmetic unit 107. Hereinafter, the function of each component will be described.

  The ultrasonic probe 11 is provided in a plurality of ultrasonic transducers that generate ultrasonic waves based on a drive signal from the ultrasonic receiving unit 101 and convert reflected waves from the subject into electrical signals, and the ultrasonic transducers. The matching layer includes a backing material that prevents the ultrasonic wave from propagating backward from the ultrasonic transducer. When an ultrasonic wave is transmitted from the ultrasonic probe 11 to the subject, the transmitted ultrasonic wave is reflected one after another on the discontinuous surface of the acoustic impedance, and is received by the ultrasonic probe 11 as an echo signal. The amplitude of this echo signal depends on the difference in acoustic impedance at the discontinuous surface that is to be reflected.

  The probe moving mechanism 22 is a mechanism for changing the distance between the ultrasonic probe 11 and the subject. For example, when the ultrasonic probe 11 immersed in a liquid container in contact with the subject is mechanically supported on the upper portion of the subject, a moving mechanism is incorporated in the mechanical support means, so that the subject of the ultrasonic probe 11 is covered. It is possible to move the specimen. The probe moving mechanism 22 is driven based on a command from the apparatus main body 100.

  The movement distance measurement unit 27 detects the movement distance of the probe. In the present embodiment, since the ultrasonic probe 11 is mechanically moved by the probe moving mechanism 22, the moving distance is detected by providing a known detection mechanism in the probe moving mechanism 22. Further, the movement distance measuring unit 27 may detect driving information from the apparatus main body 100 to the probe moving mechanism 22. In this case, the movement distance measurement unit 27 may be built in the apparatus main body 100.

  In addition, a known position sensor such as an optical sensor or a magnetic sensor may be used to detect a movement distance from a predetermined position. In the present embodiment, since position information with high accuracy is required by image processing, it is more preferable to use an optical sensor that can detect a position with higher accuracy than a magnetic sensor. The detected moving distance is transmitted to the calculation unit 107 and used for calculation for artifact reduction.

  The monitor 200 displays in-vivo morphological information as an image based on the video signal from the scan converter 105.

  The ultrasonic transmission unit 101 has a high voltage pulse generation circuit and the like. In the high voltage pulse generation circuit, a high voltage pulse for forming a transmission ultrasonic wave is repeatedly generated at a predetermined rate frequency fr Hz (cycle: 1 / fr second).

  The ultrasonic receiving unit 102 includes an amplifier circuit, an A / D converter, a delay circuit, an adder and the like not shown. The amplifier circuit amplifies the echo signal captured via the probe 12 for each channel. The A / D converter performs analog-digital conversion of the amplified echo signal. Then, the delay circuit gives a delay time necessary for determining the reception directivity, and then performs an addition process in the adder. By this addition, the reflection component from the direction corresponding to the reception directivity of the echo signal is emphasized, and a comprehensive beam for ultrasonic transmission / reception is formed by the reception directivity and the transmission directivity.

  The B-mode processing unit 103 receives echo signals from the ultrasonic receiving unit 102 and the arithmetic unit 107, performs detection processing, logarithmic amplification, envelope detection processing, and the like, and data whose signal intensity is expressed by brightness on the monitor 200 Is generated. This data is transmitted to the scan converter 105 and is displayed on the monitor 200 as a B-mode image in which the intensity of the reflected wave is represented by luminance.

  The scan converter 105 converts an ultrasonic scan scanning line signal sequence into a scanning line signal sequence of a general video format represented by a television or the like, and generates an ultrasonic diagnostic image as a display image. The scan converter 105 is equipped with a storage memory for storing image data. For example, an operator can call up an image recorded during an examination after diagnosis.

  The memory 106 stores the echo signal from the ultrasonic receiving unit 101. The memory 106 stores a plurality of sets of echo signals at a plurality of time points when the position of the probe is changed.

  The arithmetic unit 107 performs arithmetic processing such as addition / subtraction and absolute value processing based on the above-described method using a plurality of sets of echo signals stored in the memory 106 and information on the movement distance acquired from the movement distance measurement unit. The echo signal obtained by the arithmetic processing is input to the B-mode processing unit 103, and finally an ultrasonic image with reduced artifacts is displayed on the monitor 200. The arithmetic processing performed by the arithmetic unit 107 is a characteristic part of this embodiment. Hereinafter, the specific method of this arithmetic processing will be described in detail.

  FIG. 3 is an explanatory diagram for illustrating the state of multiple reflection artifacts displayed overlapping the tissue in the water immersion method and the movement of the position of the multiple reflection artifacts accompanying the movement of the probe.

  First, description will be made with reference to the left side of FIG. An ultrasonic probe 11 in which a large number of transducers 12 are arranged is placed in hot water 14 in a liquid container, and transmits and receives ultrasonic waves to a subject 16 such as a breast via the hot water. When a high voltage pulse is applied from the ultrasonic transmission unit 101 of FIG. 2 to the vibrator 12 through the cable 13, the ultrasonic wave is emitted, and when a reflected ultrasonic wave from the subject strikes the vibrator, a voltage is generated and the cable 13 passes through the cable 13. The cross-sectional image is generated by the scan converter 105 and displayed on the monitor 200. The ultrasonic probe 11 is moved in the ultrasonic beam direction so as not to cross the water surface 23 by the probe moving mechanism 22 indicated by an arrow in the drawing. The movement distance is detected by the movement distance detection unit 27.

  The surface of the subject, that is, the body surface 15 is usually skin, and a relatively strong reflection occurs due to a large difference in acoustic impedance with the hot water 14, and the first reflected wave is a cross section of the body surface on the image as the vibrator surface 12 Is displayed correctly at a distance of X from. The tissue 16 below the body surface is also displayed as a cross-sectional image.

  At this time, the reflection from the portion 19 of the body surface perpendicular to the ultrasonic beam is particularly strong, and the ultrasonic wave 20 that is reflected and reaches the vibrator surface 12 has a very large acoustic impedance of the vibrator compared to water. Therefore, strong reflection is caused, and it is reflected again by the body surface 19 toward the subject and reaches the vibrator. This becomes a multiple reflection signal. Since the arrival time of this signal reciprocates twice between the transducer 12 and the body surface 19, it is twice the arrival time of the first reflected wave, and the multiple reflection image 21a is twice as long from the transducer to the body surface. It is displayed at a distance, that is, at a position 2X from the vibrator. That is, it is displayed at a distance X from the body surface 19. The original tissue image 17 at this position is indicated by an ellipse, and the tissue image 17 and the multiple reflection image 21a are displayed in an overlapping manner.

  The right side of FIG. 3 shows a case where the ultrasonic probe is moved upward by Xs. At this time, the distance between the transducer surface 12 and the body surface 19 is X + Xs, but the multiple reflection image 21b is a distance of 2X + 2Xs from the transducer surface 2. When the display position of these entire images is returned to the transducer side by Xs, the body surface 15 and the tissue 16 and tissue image 17 thereunder are displayed at the same position as the left figure. On the other hand, the multiple reflection image 21 b is displayed below the body surface 15 and the tissues 16 and 17 by Xs. The tissue image 18 at this position is shown as a rectangle in the figure.

  Therefore, if the right-to-left images are subtracted, the body surface 15, tissue images 16, 17, and 18 displayed at the same position disappear, and only multiple reflection images 21a and 21b can be obtained. Conversely, when these images are added, the body surface 15, the tissue images 16, 17, and 18 and the multiple reflection images 21a and 21b are overlapped. If the image of only the multiple reflection of the former can be subtracted from the latter overlapping image, the multiple reflection image can be removed and a true tissue image can be obtained.

  However, in practice, multiple reflection images cannot be removed by simple subtraction and addition. Next, calculation processing for removing multiple reflections will be described in detail with reference to FIGS.

  FIG. 6 shows reflected wave waveforms of seven types of high-frequency signals (a) to (g). The horizontal axis is time (μs), and the vertical axis is the relative value of the reflected wave signal voltage. The envelope of the pulse waveform is approximated by a normal distribution curve, the ultrasonic frequency is 5 MHz, the half width of the ultrasonic pulse is about 0.6 mm, and the moving distance of the probe, that is, the distance between the positions of the tissue 17 and 18 is 2.3 mm. This is an example. When the distance corresponds to time, the half width of the pulse is about 0.8 μs, and the moving distance of the probe is about 3 μs. The amplitude ratio of the tissue 17, the tissue 18, and the multiple reflection 21a is 0.7: 1: 0.5, and the amplitude of the multiple reflection 21a is larger than the amplitude of the tissue 17 and the tissue 18.

  A waveform 31 in (a) is a reflected wave from the tissue 17 in FIG. 3, and a waveform 32 is a waveform of a reflected wave from the tissue 18. A waveform 33 of (b) is a waveform of the multiple reflection 21a of FIG. The waveform 34 of (c) is obtained by overlapping the waveform 31 of the tissue 17 and the waveform of the multiple reflection waveform 33. The waveform of the tissue 17 and the waveform 33 of multiple reflection are shifted by 1/8 wavelength. Waveforms (d) and (e) are waveforms of shift signals obtained by moving the probe by Xs and returning the obtained signal by a time corresponding to the distance Xs. A waveform 35 in (d) is a shift signal waveform of the multiple reflection 21b in the right side of FIG. 3, a waveform 36 in (e) is a shift waveform representing the tissue 17, and a waveform 37 is the tissue 18 and the multiple reflection 21b. Is a shift waveform of the superimposed waveform.

  Actually, only a waveform in which multiple reflections overlap with the tissues of (c) and (e) can be obtained as a reflection signal. (A), (b), (d), etc. The waveform cannot be measured. Therefore, it is a problem of this embodiment to obtain the true waveform (a) using the waveforms of (c) and (e).

  First, the waveforms of (c) and (e) are added. The reflected waveform 31 of the tissue 17 is T1, the reflected waveform 32 of the tissue 18 is T2, and the waveform of the multiple reflection 33 is M. Then, in the waveform obtained by adding (c) and (e), the position of the tissue 17 is (2T1 + M) and the position of the tissue 18 is (2T2 + M). Next, when the waveform of (e) is subtracted from (c), the position of the tissue 17 becomes M and the position of the tissue 18 becomes -M. If both subtracted waveforms are M, 2 (T1 + T2) is obtained by subtracting the subtracted waveform from the added waveform, and a true image of only the tissue is obtained, but this is not the case because one is M and the other is -M.

  FIG. 4F shows a step function 38 having a value of 1 before the distance corresponding to (X + Xs / 2) from the body surface and −1 thereafter. Assuming that the step function 38 is Kt, the product of Kt and the subtraction waveform is M at both the positions of the tissue 17 and the tissue 18. The calculation processing waveforms 39 and 40 in (g) are obtained by subtracting the product of the step function Kt and the subtraction waveform from the addition waveform and dividing by 2, and are equal to 31 and 32 of the tissue-only waveform (a). The multiple reflection signal is removed by arithmetic processing, and an image of only the tissue is obtained.

  The above arithmetic processing is performed on the reflected signal itself, that is, the high-frequency signal, but the present embodiment is not limited to this. The same result can be obtained by using a quadrature detection waveform having phase information. However, the detection signal that is normally used when displaying an ultrasonic tomographic image, that is, a high-frequency signal that has been rectified by both waves, does not have phase information, so multiple reflections cannot be removed by the above-described arithmetic processing. Comes out. Therefore, a method for removing multiple reflections using a detection signal will be described in detail.

  5 (h) to 5 (m) are detection waveforms, the ultrasonic frequency and other conditions are the same as those in FIG. 4, and the waveform of the tissue 17 and the waveform of the multiple reflection 21a are shifted by 1/8 wavelength.

  FIG. 5 (h) shows a composite waveform of the tissue 17, the tissue 18 and the multiple reflection 21a before moving the probe. In this case, the reflection from the tissue 17 and the multiple reflection 21a overlap to form a waveform 41. Only the reflected wave 42 from the tissue 18 is present at the position. As in FIG. 4, if the reflected waveform 41 of the tissue 17 is T1, the reflected waveform 42 of the tissue 18 is T2, and the waveform of the multiple reflection 43 is M, the waveform 41 is represented by | T1 + M |, and the waveform 42 is represented by | T2 | Is done. (I) is the shift waveform after the probe is moved, the waveform 43 is the waveform | T1 | of the tissue 17 only, and the waveform 44 is the waveform | T2 + M | in which the tissue 18 and the multiple reflection 21b overlap. Each of (h) and (i) is a composite waveform of tissue and multiple reflection, and is obtained from the received signal. (J) is an average of (h) and (i), waveform 45 is represented as (| T1 | + | T1 + M |) / 2], and waveform 46 is represented as (| T2 | + | T2 + M |). (K) is a waveform of an absolute value obtained by dividing the difference between (h) and (i) by 2, waveform 47 is || T1 + M | − | T1 || / 2, and waveform 48 is || T2 | −. | T2 + M || / 2.

  FIG. 5 (l) shows a processed waveform obtained by subtracting (k) from (j), and (m) shows a waveform of only the tissue. The processing waveform (l) only needs to be equal to the waveform (m) of the tissue only. In the example of FIG. 5, since the waveforms of the tissue 17 and the multiple reflection 21a are shifted by 1/8 wavelength but are almost in phase, the difference between (l) and (m) is almost zero, and multiple reflection artifacts are removed. The

  FIG. 6 shows the same thing as FIG. 5 in the case where the waveforms of the tissue 17 and the multiple reflection 21a are shifted by a half wavelength. The numbers in FIG. 5 and FIG. 6 correspond to the waveforms in FIG. 6, such as 41 and 61, 42 and 62, and the numbers in FIG. 5 plus 20.

  A waveform 61 in (n) of FIG. 6 is a waveform in which the tissue 17 and the multiple reflection 21a overlap each other. However, since the phase is inverted, the amplitude of the combined waveform is not the sum of each, but becomes a difference. Unlike (h), it is smaller than any waveform. The same applies to the waveform 64 in FIG.

  FIG. 6 (r) shows a processing waveform by the same method as FIG. 5, but when compared with the tissue-only waveform (s), the processing waveform 69 at the position of the tissue 17 is clearly compared with the true waveform 71. Strictly speaking, when the reflected wave of the tissue and the phase of multiple reflection are close to the opposite phase, multiple reflection artifacts are not removed by this calculation process. In other words, it can be seen that multiple reflection artifacts may or may not be removed depending on the phase relationship between the reflected wave of the tissue and multiple reflection.

  However, the phase relationship between the tissue and the multiple reflection can be changed by moving the probe. For example, when the probe is moved away by 1/8 wavelength, the round-trip distance becomes longer by 1/4 wavelength, and the phase of multiple reflection with respect to the reflected wave of the tissue changes by 1/4 wavelength before and after the movement. Therefore, the influence of the phase can be eliminated by performing the above-described arithmetic processing on a signal obtained by collecting and adding four types of signals while moving the probe by 1/8 wavelength.

  FIGS. 7 (t) to (y) show waveforms obtained by adding back the four waveforms obtained by moving the probe very slightly by 1/8 wavelength (in this example, 0.075 mm), respectively. After that, the above calculation processing is performed between the four waveforms obtained by moving the probe by 7.5 wavelengths (4.5 mm) and further moving by 1/8 wavelength, and the waveforms obtained by adding back the moved distances. It is the result of having gone. That is, in FIG. 5 or FIG. 6, a waveform obtained by moving 1/8 wavelength as a combined waveform before movement and adding four waveforms, and a shift waveform after movement by 7.5 wavelengths and further 1/8 wavelength. A waveform obtained by moving four by one and adding four waveforms is used.

  In this way, as shown in FIGS. 7 (x) and (y), the processing waveforms 89 and 90 and the reflected waveforms 91 and 92 only of the tissue not including multiple reflections are reflected from the tissue 17 and multiple reflections 21a. It is almost equal regardless of the phase relationship.

  For example, when the frequency of the ultrasonic wave is 5 MHz, the wavelength is about 0.6 mm, the 1/8 wavelength is 0.075 mm, and the corresponding times are 0.2 μs and 0.025 μs. A moving mechanism and a sensor for measuring the moving distance are required. However, such a precise mechanism is sufficient with the prior art. When returning only a small movement distance, it is necessary to accurately measure the movement distance and set an appropriate sound speed. For example, it is sufficient to make the water temperature constant at 37 degrees. Even if there is a measurement error in the movement distance, the approximate position where multiple reflections are present is known, so the position where the difference waveform before and after the movement of only the normal tissue is minimized is determined and fine adjustment is made. It can be performed.

  Further, here, a case has been described in which four waveforms obtained by shifting the probe by 1/8 wavelength are added, but the present invention is not limited to this. For example, it is also possible to use a signal obtained by adding a waveform shifted by an odd multiple of 1/8, such as a waveform shifted by 3/8 wavelength or a waveform shifted by 5/8 wavelength.

  So far, since the overlap of ultrasonic signals can be added or subtracted depending on the phase relationship of the reflected waves, the details have been examined and it has been explained that multiple reflections can be deleted in all cases. However, the internal organs generally have a tissue structure finer than the wavelength of ultrasonic waves (for example, about 0.3 mm when the frequency is 5 MHz), resulting in speckle patterns peculiar to ultrasonic waves and the phase relationship is broken. . Therefore, operations such as addition, subtraction, and absolute value may be performed without considering the phase. Even in this case, there is often no significant difference in the artifact removal effect.

  It is also possible to logarithmically compress the amplitude of the received signal as is normally done in an ultrasonic diagnostic apparatus, or to perform artifact removal calculation processing after nonlinear processing. Further, artifact removal calculation processing may be performed using an image obtained by performing special spatial processing for speckle removal or general filter processing on the image. That is, in this embodiment, the artifact removal calculation process is performed using the signal in the previous stage of the B-mode processing unit 103, but the present invention is not limited to this. The same processing may be performed on a signal generated by the B-mode processing unit 103, a signal input to the scan converter 105, or image data generated by the scan converter 105.

  Next, an example of an actual operation mode of the ultrasonic diagnostic apparatus according to the present embodiment will be described with reference to FIG.

  First, as step S1, the operator sets the subject and the apparatus at a predetermined position. Specifically, the subject is placed on his / her back on the bed, and the ultrasound probe 11 and a liquid container containing hot water 14 are set on the breast of the subject.

  Next, as step S2, collection of ultrasonic signals is started by the operator performing a predetermined input. Upon receiving this input, the process proceeds to step S3.

  In Step 3, the probe moving mechanism 22 is driven to move the ultrasonic probe 11 to a predetermined position. At the same time, the moving distance measuring unit 27 detects the moving distance of the ultrasonic probe 11 and stores it in the memory 106.

  In step S4, ultrasonic signals are collected. Specifically, ultrasonic waves are transmitted / received from the ultrasonic probe 11, and the obtained ultrasonic signals are stored in the memory 106 via the ultrasonic reception unit 102. The ultrasonic signals collected here are not limited to signals for one cross section. For example, ultrasonic signals in a three-dimensional region may be collected by rotating or translating the ultrasonic probe 11 in a direction different from the ultrasonic transmission / reception direction.

  In step S5, it is determined whether or not to collect ultrasonic signals at different positions based on the set conditions. Further, when collecting ultrasonic signals at different positions, the process returns to step S3, and when all the collections at the set positions are completed, the process proceeds to step S6. The condition set here is a condition of the moving distance of the probe for performing the above-described arithmetic processing, and may be set in the apparatus in advance. The operator may change the setting as appropriate. However, it is essential that the ultrasonic signal is set to be collected at at least two positions separated by at least the ultrasonic pulse width. By repeating the operations in steps S3 to S5, a plurality of ultrasonic signals having different positional relationships are collected.

  In step S <b> 6, the arithmetic unit 107 reads a plurality of ultrasonic signals stored in the memory 106 and information on the movement distance of the probe corresponding to each. The arithmetic unit 107 performs the above-described addition / subtraction, absolute value processing, and the like based on the acquired information.

  In step S7, the B-mode processing unit 103 and the scan converter 105 perform imaging processing based on the ultrasonic signal calculated by the calculation unit 107, and an ultrasonic image from which artifacts are removed is obtained.

  Here, although it has been described that the movement of the probe and the collection of ultrasonic signals are performed automatically, the present invention is not limited to this. An operator may input a moving amount as appropriate, or move manually. Further, in the collection of ultrasonic signals, the ultrasonic signals at the time when there is an input from the operator may be collected.

  Furthermore, in the above description, the removal of artifacts due to multiple reflection has been mainly described, but the present invention is not limited to this. Among the artifacts of an ultrasonic diagnostic apparatus, an artifact caused by a grating lobe is a major problem with multiple reflection. The grating lobe is generated in a specific direction such as 30 degrees with respect to the ultrasonic transmission / reception direction from the relationship between the vibration element interval and the ultrasonic frequency in an array transducer in which a large number of vibration elements are arranged. Due to the generation of the grating lobe, a reflected wave of a reflector in a direction of ± 30 degrees, for example, with respect to the ultrasonic transmission / reception direction is also received to some extent, which causes an artifact.

  The generation position of the grating lobe artifact is also changed by moving the ultrasonic probe in the direction of the ultrasonic beam as shown in FIG. 3, and the generation position is different even if the direction of the ultrasonic beam is changed as shown in FIG. . Therefore, the grating lobe artifact can be removed by moving the ultrasonic probe or changing the direction of the ultrasonic beam.

  Next, the effect of this embodiment will be described. According to this embodiment, it is possible to remove false image information and output only true image information.

  According to the present embodiment, by adapting to an ultrasonic diagnostic apparatus, it is possible to easily obtain a plurality of pieces of image information in which the positions of false image information are different particularly in the water immersion method. For example, by moving the ultrasonic probe in the direction of the ultrasonic beam, multiple pieces of image information including false image information due to multiple reflections and grating lobes can be obtained, and calculation processing is performed based on this information. Image information with reduced reflection and grating lobes can be output.

  Furthermore, by setting the moving distance of the ultrasonic probe to be equal to or greater than the ultrasonic pulse width, it is possible to generate false image information such as multiple reflections and grating lobes at different positions.

  Furthermore, according to the present embodiment, by performing arithmetic processing on a high-frequency signal or quadrature detection signal of an ultrasonic reflected wave, accurate arithmetic processing can be performed in consideration of phase information.

  Further, according to the present embodiment, it is possible to easily process even a normal apparatus by performing arithmetic processing on the detection signal of the reflected wave of the ultrasonic wave or a signal obtained by processing the signal.

  Furthermore, according to the present embodiment, noise generated by random phase information such as speckles or high spatial frequency noise can be reduced by performing arithmetic processing on spatially processed image information.

(Second Embodiment)
The second embodiment of the present invention will be described below with reference to FIGS. Here, the description will focus on parts that are different from the first embodiment, and redundant description will be omitted.

  In the first embodiment, the case where the ultrasonic probe 11 is moved in the beam direction has been described. However, as described in the principle diagram of FIG. 1, it is sufficient that the multiple reflections appear at different positions without necessarily moving the probe. The method will be described below.

  In FIG. 9, multiple reflections are generated at different positions by electronically changing the direction of the ultrasonic beam while the ultrasonic probe is fixed. In FIG. 3, the transmission / reception direction of the ultrasonic beam is a direction perpendicular to the transducer surface 12. In FIG. 9, the transmission / reception direction of the ultrasonic beam is a slightly oblique direction indicated by the scanning lines 24a and 24b. Transmission / reception is performed in a slightly right direction in the left diagram and slightly in the left direction in the right diagram.

  Multiple reflection occurs strongly at the part where the ultrasonic beam is perpendicularly incident on the body surface 15, that is, at the body surface part of the scanning lines 25a and 25b shown by the dotted lines in FIG. 9, and multiple reflected images 21c and 21d are generated. . As shown in FIG. 9, by changing the beam direction, the body surface part where multiple reflection occurs is different, and the position where multiple reflection occurs is also different. Therefore, if the above arithmetic processing is performed on these images, multiple reflections can be removed while the probe is fixed.

  FIG. 10 is a block diagram of the ultrasonic diagnostic apparatus according to this embodiment. The configuration of the present embodiment is different from the first embodiment in that the probe moving mechanism 22 and the moving distance measuring unit 27 are not necessary, and the beam direction control unit 108 is necessary.

  The beam direction control unit 108 controls the drive timing of the high voltage pulse generation circuit of the ultrasonic transmission unit 101 and the delay circuit of the ultrasonic reception unit 102. Thereby, the drive timing of each of the plurality of ultrasonic transducers arranged in the ultrasonic probe 11 is adjusted, and the beam direction of the ultrasonic wave transmitted and received from the ultrasonic probe 11 is determined. In the present embodiment, the inclination of the scanning line is controlled as described above with reference to FIG.

  Further, the beam direction control unit 108 transmits information on the beam direction, such as an angle of the beam direction with respect to the ultrasonic transducer surface, to the memory 106. The memory 106 stores a plurality of ultrasonic signals obtained by changing the beam directions. The arithmetic unit 107 reads out information related to the beam direction and a plurality of ultrasonic signals stored in the memory 106, and performs calculations for artifact removal. In the present embodiment, true image information is recorded on the same coordinates based on angle information in the beam direction. It goes without saying that the same arithmetic processing as in the first embodiment can be performed by using the image obtained in this way.

  Next, the operation mode of ultrasonic waves according to the present embodiment will be described with reference to FIG. In step S11 and step S12, as in the first embodiment, the setting of the apparatus and the input for starting the collection of ultrasonic signals are performed.

  In step S <b> 13, the beam direction control unit 108 determines the beam direction and transmits the information to the ultrasonic transmission unit 101, the ultrasonic reception unit 102, and the memory 106. The memory 106 stores information regarding this beam direction.

  In step S <b> 14, the ultrasonic transmission unit 101 and the ultrasonic reception unit 102 transmit and receive ultrasonic waves based on the beam direction information acquired from the beam direction control unit 108. The obtained ultrasonic signal is stored in the memory 106. In step S15, it is determined whether or not to collect at a different angle, and a plurality of ultrasonic signals and information on beam directions are stored in the memory 106 by the loop of step S13 to step S15.

  In step S16, the arithmetic unit 107 performs an operation based on a plurality of ultrasonic signals and beam direction information, and in step S17, an imaging process is performed. The time for collecting two pieces of image data at different angles shown in FIG. 9 within the same screen is, for example, about 0.05 seconds. It is also possible to collect ultrasonic signals in a three-dimensional region in a few tens of seconds while rotating and translating in different directions.

Here, in step S13, the beam direction control unit 108 transmits information on the beam direction to the memory 106 one by one, but the present invention is not limited to this. When predetermined conditions are set in advance and ultrasonic transmission / reception is performed in accordance with the predetermined conditions, it is not necessary to transmit information on the beam direction one by one, and calculation is possible based on the setting conditions.

  Next, the effect of this embodiment will be described. According to the present embodiment, in addition to the effects of the first embodiment described above, the following effects are obtained.

  According to this method, compared to the method of changing the tilt angle of the probe (Patent Document 1), the structure of the probe is simple because it does not require a probe moving mechanism, and the beam direction is changed electronically, for example, 0.05 seconds. Since data can be collected in a very short time, there is an advantage that it is not affected by body movement due to breathing.

  Here, also in the present embodiment, as in the first embodiment, it is possible to three-dimensionally acquire an ultrasonic signal by rotating or translating the ultrasonic probe 11. In such a case, the above-described effect is more remarkable. In the first embodiment, if a mechanism for parallel movement or rotational movement and a mechanism for vertical movement as in the first embodiment coexist with the support mechanism of the ultrasonic probe 11, the support mechanism becomes complicated. There are concerns. In contrast, in the present embodiment, the position of the artifact is changed by an electronic method, so that the mechanism is not complicated.

(Modification)
Below, the further modification of embodiment which concerns on this invention is demonstrated.

  FIG. 12 shows a case where the beam direction is mechanically changed as a first modification. In the configuration of the ultrasonic diagnostic apparatus according to this modification, the probe moving mechanism 22 in the configuration of the first embodiment is used as a mechanism for swinging and moving the probe, and the moving distance measuring unit 27 is swung by a known rotary encoder or the like. A mechanism for detecting a moving angle is used. The calculation performed by the calculation unit 107 may be substantially the same as the calculation in the second embodiment. It goes without saying that the same operation and effect as in the above-described embodiment can be obtained even with such a method. In this method, since the same cross section is ultrasonically transmitted and received at different angles, it is different from a mechanical rocking mechanism or the like for performing ultrasonic transmission and reception for a three-dimensional region.

  FIG. 13 shows a case where an ultrasonic image is obtained by sandwiching the breast 16 with a compression plate 26 used in mammography, as a second modification. From the top, the transducer surface 12, the hot water 14, the upper compression plate 26a, the breast surface 15, the breast tissue 16, and the lower compression plate 26b of the ultrasonic probe are arranged. The compression plate 26 is made of a hard plastic material such as polycarbonate having a thickness of about 3 mm. Since the acoustic impedance is much larger than that of water or skin, the compression plate 26 is strong in both the portion in contact with the water 14 and the portion in contact with the body surface 15. Multiple reflection 21e is caused. In FIG. 13, the strong multiple reflection 21e is represented by two lines.

  When the ultrasonic beam is electronically scanned in the arrangement of FIG. 13, a tomographic image parallel to the paper surface is obtained, and the tomographic image of the entire breast is obtained by mechanically moving the probe in the direction perpendicular to the paper surface. can get. In these tomographic images, as shown in FIG. 13, a line of strong multiple reflection 21e is displayed as an artifact and cannot be used for diagnosis as it is. Therefore, the probe is then moved upward to increase the distance between the probe surface and the compression plate, and the probe is returned perpendicularly to the paper surface from the back to the front. Then, the multiple reflection appears at a position lower than before, and a plurality of images are obtained at positions where the multiple reflection is different. If these images having different positions of multiple reflection are used, multiple reflection artifacts can be removed.

  Further, even in the case shown in FIG. 13, it goes without saying that images with different artifact positions can be obtained according to embodiments other than the vertical movement of the probe. For example, images with different artifact positional relationships can be acquired by electronically changing the beam direction as in the second embodiment. This eliminates the need to move the probe in the vertical direction, so it can be applied even when the probe is in direct contact with the compression plate or when the probe is fitted in the groove of one compression plate, or when it is different from the water immersion method. Is possible.

  In the case of the water immersion method using a compression plate, the method of electronically changing the beam direction of the second embodiment or the method of mechanically moving the beam direction of the first modification and the first embodiment are used. It is also possible to apply a combination of methods for moving the probe in the beam direction, whereby three-dimensional ultrasonic data with little influence of multiple reflection can be collected even when a compression plate is used.

  In all the embodiments and modifications described above, the memory 106, the arithmetic unit 107, the beam direction control unit 108, and the like may be provided in the apparatus main body 100 as a dedicated board in hardware or in software. May be. In the case of software, specifically, a program for realizing the functions of the present embodiment is stored in a storage medium built in the apparatus main body 100 or an external storage medium. It goes without saying that the same function and configuration are realized by developing this program in a memory built in the apparatus main body 100 and calculating it by a built-in CPU.

Explanatory drawing of the principle of embodiment which concerns on this invention 1 is a block diagram of an ultrasonic diagnostic apparatus according to a first embodiment of the present invention. Illustration of how to remove multiple reflection artifacts by moving the probe Reflected waveform and processed waveform of high-frequency signal obtained before and after probe movement Reflected waveform and processed waveform of detection signal obtained before and after probe movement (when tissue reflected wave and multiple reflection are in phase) Reflected waveform and processed waveform of detection signal obtained before and after probe movement (when tissue reflected wave and multiple reflection are in reverse phase) Waveforms with added detection signals before and after probe movement and their processed waveforms The flowchart for demonstrating the operation | movement aspect of embodiment of FIG. Explanatory diagram of a method for electronically changing the direction of ultrasonic beams to remove multiple reflection artifacts Block diagram of an ultrasonic diagnostic apparatus according to a second embodiment of the present invention Flowchart for explaining the operation mode of the embodiment of FIG. Explanatory drawing of the method of removing multiple reflection artifacts by mechanically changing the direction of the ultrasonic beam Explanatory drawing of the method of removing multiple reflection artifacts in the method of sandwiching the breast with a compression plate

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Display area of internal organ 2a True image 3 1st artifact 4 2nd artifact 11 Ultrasonic probe 12 Vibrator 14 Hot water 16 Subject 17 Tissue 18 overlapping with multiple reflection before probe movement 18 Overlapping with multiple reflection after probe movement Tissue 19 Body surface 10 perpendicular to ultrasonic beam Multiple reflection image 21d in water Multiple reflection image 21b before probe movement Multiple reflection image 21b after probe movement Multiple reflection image 21c Multiple reflection image 21d when the ultrasonic transmission / reception direction is tilted to the right Multiple reflection image 22 when transmission / reception direction is inclined leftward Probe moving mechanism 24a Scan line 24b when ultrasonic transmission / reception direction is inclined rightward Scanning line 24a ultrasonic transmission / reception direction when ultrasonic transmission / reception direction is inclined leftward Scanning line 24b where multiple reflection occurs when tilted to the right Multiple reflection occurs when the ultrasound transmission / reception direction is tilted to the left Inspection line 26 Compression plate 27 Movement distance measurement unit 31 Reflected waveform 32 from tissue 17 Reflected waveform 33 from tissue 18 Multiple reflected waveform 34 before probe movement Synthetic waveform 37 of tissue 7 and multiple reflection 37 Tissue 18 after probe movement Shift waveform 38 of multiple reflection composite waveform Step function 39, 40 Processing waveform 41, 42 by high frequency signal Synthetic detection waveform 43, 44 of tissue before probe movement and multiple reflection Synthetic detection shift waveform of tissue and multiple reflection after probe movement 49, 50 Processing waveform 51, 52 of detection signal Detection waveform of true reflected wave of tissue only 100 Main body 101 Ultrasonic transmission unit 102 Ultrasonic reception unit 103 B mode processing unit 105 Scan converter 106 Memory 107 Operation unit 108 Beam direction Control unit 200 Monitor

Claims (16)

In a medical diagnostic imaging apparatus that displays an internal organ of a subject as an image,
Image collecting means for collecting a plurality of pieces of image information including true image information and fake image information, wherein the positional relationship between the true image information and the fake image information is different;
The false image information is removed by subtracting information based on the difference between the plurality of image information from the sum of the plurality of image information so that the true image information is in the same position for the plurality of image information. Computing means for outputting an image of only the true image information;
A medical image diagnostic apparatus comprising: The computing means is
The medical image diagnostic apparatus according to claim 1, wherein an absolute value of a difference between the plurality of pieces of image information is subtracted from a sum of the plurality of pieces of image information. The computing means is
The medical image diagnostic apparatus according to claim 1, wherein a value obtained by multiplying a difference between the plurality of pieces of image information by a step function is subtracted from the sum of the plurality of pieces of image information. The step function is
Coefficients having opposite signs to the fake image information in the first image information of the plurality of image information and the fake image information in the second image information of the plurality of image information The medical image diagnostic apparatus according to claim 2, wherein The image collecting means includes
The medical image diagnostic apparatus according to claim 1, wherein the plurality of pieces of image information are collected based on an ultrasonic signal obtained by transmitting / receiving ultrasonic pulses to / from the subject. The image collecting means includes
6. The medical image diagnostic apparatus according to claim 5, wherein an ultrasonic probe that transmits and receives an ultrasonic pulse is moved in an ultrasonic beam direction to obtain the plurality of pieces of image information.   The medical image diagnostic apparatus according to claim 5, wherein the moving distance of the ultrasonic probe is equal to or greater than an ultrasonic pulse width. The image collecting means includes
6. The medical image diagnostic apparatus according to claim 5, wherein the plurality of pieces of image information obtained by changing an ultrasonic beam direction are obtained.   The medical image diagnostic apparatus according to claim 8, wherein the ultrasonic beam direction is electronically changed by controlling drive timings of a plurality of ultrasonic transducers arranged in an ultrasonic probe. The computing means is
6. The medical image diagnostic apparatus according to claim 5, wherein arithmetic processing is performed based on a high-frequency signal or orthogonal detection signal of an ultrasonic reflected wave. The computing means is
6. The medical image diagnostic apparatus according to claim 5, wherein arithmetic processing is performed based on a detection signal of an ultrasonic reflected wave or a signal obtained by processing the detection signal. The computing means is
The medical image diagnostic apparatus according to claim 1, wherein arithmetic processing is performed based on the spatially processed image information. The fake image information is
The ultrasonic pulse transmitted from the ultrasonic probe is an image that is reflected by an acoustic impedance mismatching surface and further reflected by an ultrasonic radiation surface of the ultrasonic probe. The medical image diagnostic apparatus described. An acoustic propagation material arranging means for arranging an acoustic propagation material between the ultrasonic probe and the subject surface;
The medical image diagnostic apparatus according to claim 13, wherein the acoustic impedance mismatching surface is a surface of the subject in contact with the acoustic propagation material or a film covering the surface. The acoustic impedance mismatch surface is:
The medical image diagnostic apparatus according to claim 13, wherein the medical image diagnostic apparatus is a compression plate for compressing the breast of the subject. In a medical diagnostic imaging device that displays the internal organs of a subject as an image,
An image collecting function for collecting a plurality of pieces of image information including true image information and fake image information, wherein the positional relationship between the true image information and the fake image information is different;
The false image information is removed by subtracting information based on the difference between the plurality of image information from the sum of the plurality of image information so that the true image information is in the same position for the plurality of image information. An arithmetic processing function for outputting an image of only the true image information;
A control program for a medical image diagnostic apparatus.

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