JP2009247773A - Magnetic resonance imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To quantitatively catch blood flow information such as a blood flow velocity, blood flow volume in capturing a blood vessel image by non-contrast radiography. <P>SOLUTION: This apparatus is provided with a measurement control means which controls measurement of an echo signal from an imaged area including blood vessels of a patient according to a predetermined sequence and an arithmetic processing means which captures the blood vessel image in the imaged area using the echo signal. The sequence is provided with a pre-saturation sequence section which pre-saturates at least the imaged area and a main measurement sequence section which measures the echo signal from a flow-in blood having flowed into the imaged area. The arithmetic processing means calculates the migration of the flow-in blood on the basis of the blood vessel image, calculates blood flow information on the flow-in blood from the migration, and colors the blood vessel image corresponding to the blood flow information. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention measures nuclear magnetic resonance (hereinafter referred to as `` NMR '') signals from hydrogen, phosphorus, etc. in a subject and images nuclear density distribution, relaxation time distribution, etc. In particular, the present invention relates to a technique for imaging blood flow dynamics.

  MRI equipment measures NMR signals (echo signals) generated by nuclear spins that make up the body of a subject, especially human tissue, and forms the shape and function of the head, abdomen, limbs, etc. in two or three dimensions. It is a device that images. In imaging, the echo signal is given different phase encoding depending on the gradient magnetic field and is frequency-encoded and measured as time-series data. The measured echo signal is reconstructed into an image by two-dimensional or three-dimensional Fourier transform.

  In the MRI apparatus, there is ASL (Arterial Spin Labeling) as one of the methods for imaging blood flow dynamics without contrast in the MRI apparatus. In this method, by applying an Inversion Recovery pulse (hereinafter referred to as IR pulse) in the region upstream of the region of blood flow from the region of interest, the longitudinal magnetization of the blood is reversed and labeled, and the TI (Inversion time) By setting the TI so that the labeled blood flows into the region of interest during the waiting time and the longitudinal magnetization reaches the Null Point, and imaging, the labeled blood signal and the blood that originally existed in the region of interest In this method, a high contrast is generated between tissue signals. In addition, by using the ASL method, images are taken at a plurality of object parts while sliding the area to which the IR pulse is applied, and the images obtained at each part are synthesized, so that a blood vessel image in a wide object area is obtained. Can be created (for example, Patent Document 1). Further, imaging is performed while changing TI, and a plurality of images having different blood flow arrival positions are acquired and continuously displayed, whereby blood flow dynamics can be observed as a cine image (for example, Patent Document 2).

Japanese Patent No. 03895972 JP 2001-252263 A JP 2003-144416 A JP 2007-029763 A "Considerations of Magnetic Resonace Angiography by Selective Inversion Recovery", D.G.Nishimura et al. , Magnetic Resonance in Medicine, Vol. 7,472-484,1988

  As described above, by using the ASL method, it is possible to acquire a blood vessel image using the blood inflow effect and observe blood flow dynamics using a cine image. However, in clinical practice, if blood flow information such as blood flow velocity and blood flow volume can be quantitatively grasped, it is easy to distinguish between healthy and non-healthy and helps interpretation.

  However, the above patent document and non-patent document do not take into account the quantitative analysis of blood flow information.

  Therefore, an object of the present invention is to quantitatively capture blood flow information such as a blood flow velocity and a blood flow volume in imaging for acquiring a blood vessel image without contrast.

  In order to achieve the above object, the MRI apparatus of the present invention is configured as follows. That is, measurement control means for controlling the measurement of echo signals from the imaging region including the blood vessels of the subject based on a predetermined sequence, and arithmetic processing means for acquiring blood vessel images in the imaging region using the echo signals, The sequence includes at least a pre-saturation sequence unit that pre-saturates the imaging region and a main measurement sequence unit that measures an echo signal from the inflowing blood that has flowed into the imaging region, and the arithmetic processing means is based on the blood vessel image. The movement amount of the inflowing blood is calculated, the blood flow information of the inflowing blood is calculated from the movement amount, and the blood vessel image is colored corresponding to the blood flow information.

  According to the MRI apparatus of the present invention, in imaging for acquiring a blood vessel image without contrast, blood flow information such as blood flow velocity and blood flow is calculated and imaged, thereby adding to the conventional blood vessel image form information. The blood vessel image to which the blood flow information is added can be provided.

  Hereinafter, each embodiment of the MRI apparatus of the present invention will be described with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiments of the invention, and the repetitive description thereof is omitted.

  First, an outline of an example of the MRI apparatus of the present invention will be described with reference to FIG. FIG. 1 is a block diagram showing the overall configuration of an example of the MRI apparatus of the present invention. This MRI apparatus uses a nuclear magnetic resonance (NMR) phenomenon to obtain a tomographic image of an object, and as shown in FIG. 1, a static magnetic field generation system 2, a gradient magnetic field generation system 3, and a transmission system 5 A receiving system 6, a signal processing system 7, a sequencer 4, and a central processing unit (CPU) 8.

  The static magnetic field generation system 2 generates a uniform static magnetic field in the space around the subject 1 in the direction of the body axis or in the direction perpendicular to the body axis. The permanent magnet method or the normal conduction method is provided around the subject 1 Alternatively, a superconducting magnetic field generating means is arranged.

  The gradient magnetic field generation system 3 (gradient magnetic field generation means) includes a gradient magnetic field coil 9 wound in three axial directions of X, Y, and Z, and a gradient magnetic field power source 10 that drives each gradient magnetic field coil 9, which will be described later. By driving the gradient magnetic field power supply 10 of each coil in accordance with the command from the sequencer 4, the gradient magnetic fields Gs, Gp, Gf in the three-axis directions of X, Y, Z are applied to the subject 1. More specifically, a slice selection gradient magnetic field pulse (Gs) is applied in one of X, Y, and Z directions to set a slice plane for the subject 1, and a phase encoding gradient magnetic field pulse is applied in the remaining two directions. (Gp) and a frequency encoding (or reading) gradient magnetic field pulse (Gf) are applied to encode position information in each direction into an echo signal.

  The sequencer 4 is measurement control means for controlling the measurement of echo signals by repeatedly applying a high-frequency magnetic field pulse (hereinafter referred to as “RF pulse”) and a gradient magnetic field pulse in a predetermined sequence. The sequencer 4 operates under the control of the CPU 8 and sends various commands for measuring echo signals necessary for the reconstruction of the tomographic image of the subject 1 to the transmission system 5, the gradient magnetic field generation system 3, and the reception system 6. By controlling these systems, echo signal measurement is controlled.

  The transmission system 5 irradiates an RF pulse to cause nuclear magnetic resonance to the nuclear spins of atoms constituting the biological tissue of the subject 1, and includes a high frequency oscillator 11, a modulator 12, a high frequency amplifier 13, and a transmission side It consists of a high frequency coil 14a. The high-frequency pulse output from the high-frequency oscillator 11 is amplitude-modulated by the modulator 12 at a timing according to a command from the sequencer 4, and the amplitude-modulated high-frequency pulse is amplified by the high-frequency amplifier 13 and then placed close to the subject 1. The subject 1 is irradiated with electromagnetic waves (RF pulses) by being supplied to the high frequency coil 14a.

  The receiving system 6 detects an echo signal (NMR signal) emitted by nuclear magnetic resonance of nuclear spins constituting the biological tissue of the subject 1, and receives a high-frequency coil 14b on the receiving side, an amplifier 15, and a quadrature detector 16 and an A / D converter 17. The response electromagnetic wave (NMR signal) of the subject 1 induced by the electromagnetic wave irradiated from the high-frequency coil 14a on the transmission side is detected by the high-frequency coil 14b arranged close to the subject 1 and amplified by the amplifier 15 Thereafter, the signals are divided into two orthogonal signals by the quadrature phase detector 16 at a timing according to a command from the sequencer 4, converted into digital quantities by the A / D converter 17, and sent to the signal processing system 7.

  The signal processing system 7 includes an external storage device (storage means) such as an optical disk 19 and a magnetic disk 18, and a display 20 made up of a CRT or the like, and when echo signal data from the reception system 6 is input to the CPU 8. The CPU 8 (arithmetic processing means) executes arithmetic processing such as signal processing and image reconstruction, and displays the tomographic image of the subject 1 as a result on the display 20 and records it on the magnetic disk 18 of the external storage device, etc. To do. The CPU 8 includes a memory corresponding to the K space, and stores echo signal data. Hereinafter, the description of arranging the echo signal data in the K space means that the echo signal data is written and stored in this memory.

  The operation system 25 is used to input various control information of the MRI apparatus and control information of processing performed in the signal processing system 7, and includes a trackball or mouse 23 and a keyboard 24. The operation system 25 is arranged close to the display 20, and the operator interactively controls various processes of the MRI apparatus through the operation system 25 while looking at the display 20.

  In FIG. 1, the transmission-side and reception-side high-frequency coils 14a and 14b and the gradient magnetic field coil 9 are installed in the static magnetic field space of the static magnetic field generation system 2 arranged in the space around the subject 1. .

  At present, the spin species to be imaged by the MRI apparatus are protons, which are the main constituents of the subject, as widely used in clinical practice. By imaging the spatial distribution of the proton density and the spatial distribution of the relaxation phenomenon in the excited state, the form or function of the human head, abdomen, limbs, etc. is photographed two-dimensionally or three-dimensionally.

  Next, an outline of a sequence according to the present invention provided in the MRI apparatus will be described with reference to FIG. FIG. 2A is a timing chart showing the timing of an ECG (ElectroCardioGraph) Trigger signal and an imaging sequence in electrocardiographic synchronization imaging. The imaging sequence is composed of a pre-saturation sequence unit 101 for suppressing a signal of a desired imaging region and a main measurement sequence unit 102 for collecting echo signals for images from the imaging region. It is shown in FIG. 2 (b) and FIG. 2 (c). Each time an ECG Trigger signal is detected, the pre-saturation sequence unit 101 and the main measurement sequence unit 102 are repeated until an echo signal necessary for image reconstruction is measured. FIG. 2 (a) shows an example in which one pre-saturation sequence unit 101 and a plurality of main measurement sequence units 102 are repeated for each ECT Trigger signal. Without being limited to such a combination, a combination in which at least one main measurement sequence unit 102 is executed after a plurality of pre-saturation sequence units 101 may be used.

The ECG Trigger signal shown in Fig. 2 (a) is an ECG monitor device that detects the ECG signal of the subject from the ECG electrode attached to the subject, and detects the R wave from the ECG signal. This is the Trigger signal output to the sequencer 4. The sequencer 4 controls the sequence start timing based on the ECG Trigger signal. The time from the ECG Trigger signal to start the pre-saturation sequence unit 101 Preset Delay (T _PD ) and the time from the ECG Trigger signal to start this measurement sequence Gate Delay (T _GD ) Set according to. For example, Preset Delay (T _PD ) = 50 msec and Gate Delay (T _GD ) = 500 msec.

  As shown in FIGS. 2 (b) and 2 (c), the imaging sequence includes an RF pulse (RF), a slice selection gradient magnetic field (Gs), a phase encoding gradient magnetic field (Gp), and a frequency encoding gradient magnetic field (Gr). And an echo signal (Signal) and a sampling period (A / D).

In the pre-saturation sequence unit 101, the sequencer 4 controls the transmission system 5, the gradient magnetic field generation system 2, and the reception system 6 based on the pre-saturation sequence as shown in FIG. That is, the sequencer 4 generates the slice selection gradient magnetic field 104 in the gradient magnetic field generation system 2 and the presaturation pulse 103 in the transmission system 5 to excite the longitudinal magnetization in a desired region (presaturation region) to generate the transverse magnetization. Magnetize. In order to disperse the phase of the transverse magnetization, the sequencer 4 causes the gradient magnetic field generation system 2 to generate spoiling gradient magnetic field pulses 105, 106, and 107 in the three axis directions of the slice direction, the phase encoding direction, and the frequency encoding direction, respectively. The spoil gradient magnetic field pulse may be applied in at least one direction. The sequencer 4 starts this pre-saturation sequence after Preset Delay (T _PD ) from the ECT Trigger signal.

  In this measurement sequence unit 102, by repeating RF pulse irradiation with a repetition time (TR) shorter than the longitudinal relaxation time T1 of the magnetization of the subject tissue, the magnetization is changed to a steady state (SSFP) and a desired region (slab region) is tertiary. The original imaging sequence is used (hereinafter referred to as SSFP sequence). Therefore, in the main measurement sequence unit 102, the sequencer 4 controls the transmission system 5, the gradient magnetic field generation system 2, and the reception system 6 based on the main measurement sequence as shown in FIG.

  That is, the sequencer 4 generates a slice selection gradient magnetic field 109 in the gradient magnetic field generation system 2 and generates an RF pulse 108 in the transmission system 5 to excite longitudinal magnetization in a desired region (slab region). Thereafter, the sequencer 4 causes the gradient magnetic field generation system 2 to generate a slice direction rephase gradient magnetic field 118 to align the phases of the excited transverse magnetization. Next, the sequencer 4 causes the gradient magnetic field generation system 2 to generate a slice encode gradient magnetic field 119 and a phase encode gradient magnetic field 110, and encodes position information in the slice direction and the phase encode direction, respectively, into the phase of transverse magnetization.

  In addition, the sequencer 4 generates a dephase gradient magnetic field 111 in the frequency encoding direction in the gradient magnetic field generation system 2, and disperses the phase of the transverse magnetization in advance so that the phases of the transverse magnetization are aligned at the echo time (TE). . Next, the sequencer 4 causes the reception system 6 to measure the echo signal 113 during the sampling period 114 while causing the gradient magnetic field generation system 2 to generate a frequency encoding gradient magnetic field 112 having a polarity opposite to that of the dephase gradient magnetic field 111. By this frequency encoding gradient magnetic field 112, position information in the frequency encoding direction is encoded into an echo signal.

  Next, in order to restore (ie, rewind) the phase of the transverse magnetization dispersed by the application of the slice encode gradient magnetic field 119, the phase encode gradient magnetic field 110, and the frequency encode gradient magnetic field 112, the sequencer 4 includes the gradient magnetic field generation system 2 In addition, a slice encode rewind gradient magnetic field 120 is generated in the opposite direction to the slice encode gradient magnetic field 119 in the slice direction. Similarly, the sequencer 4 sets the frequency of the phase encode rewind gradient magnetic field 116 to the opposite polarity to the phase encode gradient magnetic field 110 in the phase encode direction and the opposite polarity to the frequency encode gradient magnetic field 112 in the frequency encode direction. An encode rewind gradient magnetic field 117 is generated.

  Finally, the sequencer 4 causes the gradient magnetic field generation system 2 to generate a dephase gradient magnetic field 115 in the slice direction for selecting the next slice. The sequencer 4 generates the above RF pulse and each gradient magnetic field pulse and the echo signal measurement with a repetition time (TR) shorter than the longitudinal relaxation time T1 of the subject tissue, the slice encode gradient magnetic field 119 and the phase encode gradient magnetic field. 110 and the application amount of each of these rewind gradient magnetic fields 120 and 116 (the area surrounded by the gradient magnetic field waveform and the time axis) are repeated to repeat the magnetization of the subject tissue in the excitation region to a steady state (SSFP). At the same time, the phase applied to the transverse magnetization between TRs is completely rewound and is always constant at any repetition.

  Next, a blood vessel image capturing method according to the present invention using the above imaging sequence will be described. In the blood vessel image capturing method according to the present invention, in the presaturation sequence unit 101, a presaturation pulse is applied to a presaturation region including an imaging region (slab region), and the magnetization of the presaturation region is saturated, The measurement sequence unit 102 uses a method in which the blood flow newly flowing into the imaging region is depicted with a high signal.

As an example, FIG. 3 shows a method for imaging a lower limb artery blood vessel using such blood inflow effect. FIG. 3A shows a setting area of a slab area 301 that is an imaging area and a presaturation area 302 for suppressing unnecessary signals. As shown in FIG. Set as saturation area. Thereby, as shown in FIG. 3 (b), the background signal of the slab region 301, and the signal from the venous blood flowing into the slab region 301 from the peripheral side during the waiting time Preset delay (T _PD ), Are both suppressed.

On the other hand, as shown in FIG. 3C, arterial blood 303 flows into the slab region 301 from the trunk side during the waiting time Preset delay (T _PD ). Since the arterial blood 303 that has flowed into the slab region 301 has not received the presaturation pulse, its longitudinal magnetization has a maximum value. Therefore, the signal from the arterial blood 303 in this measurement sequence is measured as a high signal, and only the arterial blood 303 is imaged. The same applies to the case where venous blood is imaged. In this case, the pre-saturation region includes the slab region 301 and is set so as to include the trunk region that is the direction in which the venous flow flows.

  In addition, using FIG. 4, a wide range of arterial blood vessel images can be obtained by repeating the imaging of blood vessel images of each slab region 301 while the slab region 301 and the presaturation region are moved upstream of the arterial blood. An example is shown.

  As shown in FIG. 4, for part 1, the sequencer 4 controls the imaging of the slab region 301-1 (the number after the hyphen indicates the part number) based on the imaging sequence shown in FIG. One blood vessel image 401 is acquired. Next, in imaging of the part 2, the sequencer 4 moves the slab region 301-2 and the presaturation region 302-2 toward the trunk, which is upstream of the arterial blood. At this time, preferably, the slab regions 301-1 and 301-2 and the pre-saturation regions 302-1 and 302-2 are slightly overlapped with each other, so that the lab region 301-2 and the pre-saturation region 302-2 Is set. Then, based on the imaging sequence shown in FIG. 2 described above, the sequencer 4 images the region 2 and obtains the blood vessel image 402. Similarly, in the imaging of the parts 3 to 7, the sequencer 4 moves the slab area and the presaturation area to the upstream side of the arterial flow so as to overlap the previous slab area and the presaturation area, and Based on the imaging sequence shown in FIG. 2, each slab region is imaged, and blood vessel images 403 to 407 are acquired, respectively. Note that the movement of the slab region and the presaturation region is performed by shifting the transmission frequency of the RF pulses 103 and 108 (the detection frequency at the time of reception is also shifted accordingly) or by moving the subject.

Then, the CPU 8 synthesizes the acquired blood vessel images 401 to 407 so that the respective acquisition positions are held, and acquires one synthetic blood vessel image 410. When the blood vessel images of the individual parts are synthesized, for the overlapping regions, for example, the pixel value of the synthesized image can be obtained by calculating an average of the pixel values for each pixel.
(First embodiment)
Next, a first embodiment of the MRI apparatus of the present invention will be described. In the present embodiment, blood flow information is also acquired at the time of acquiring a blood vessel image, and this blood flow information is also displayed at the time of displaying the blood vessel image. Hereinafter, the present embodiment will be described in detail based on the flowchart showing the processing flow of the present embodiment shown in FIG. Note that the processing flow shown in FIG. 5 is stored in the hard disk in advance as a program, and is performed by the CPU 7 reading and executing the program as necessary.

  In step 501, a three-dimensional blood vessel image of the region of interest of the subject is acquired. The blood vessel image acquisition method is as described based on FIGS.

  In step 502, the three-dimensional blood vessel images 401 to 407 of each part are binarized. In the blood vessel image of each part, the inflowing blood signal is rendered as a high signal, and the background signal originally present in the region of interest is rendered as a low signal due to the presaturation effect. Therefore, the CPU 7 binarizes the blood vessel image of each part and completely removes the background signal from the blood vessel image of each part. In this binarization processing, the pixel value of a pixel whose pixel value is equal to or greater than a predetermined threshold is converted to the maximum value (for example, 255), and the pixel value of a pixel whose pixel value is less than the threshold is converted to the minimum value (for example, 0). The FIG. 7 (a) shows an example of a binarized three-dimensional blood vessel image. FIG. 7 (a) shows a binarized three-dimensional blood vessel image of the part 1, where the blood vessel is black (maximum value 255) and the background region is white (minimum value 0). In this image, the blood flow direction is the Z direction, and the directions perpendicular to this are the X and Y directions. The same applies to the binarized three-dimensional blood vessel images of other parts.

  In step 503, the CPU 7 divides the three-dimensional blood vessel image of each part binarized in step 502 in the blood flow direction (for example, the z direction) to generate a predetermined number N of two-dimensional images. The three-dimensional blood vessel image is divided for each pixel in the dividing direction. For example, in the case of a three-dimensional image acquired by a three-dimensional imaging sequence, the number of divisions is equal to the number of slice encodings. FIG. 7 (b) shows an example in which the binarized three-dimensional blood vessel image of FIG. 7 (a) is divided into N parts in the blood flow direction (Z direction) to obtain N binary two-dimensional blood vessel images.

  In step 504, the CPU 7 obtains the coordinates of the blood vessel center in the two-dimensional image for each two-dimensional image acquired in step 503. A method for obtaining the coordinates of the blood vessel center will be described later.

In step 505, the CPU 7 obtains the blood vessel length in the blood flow direction by connecting the coordinates of the blood vessel center in each two-dimensional image obtained in step 504 with a straight line between adjacent images. This blood vessel length becomes the moving distance D of arterial blood that flows during the waiting time Preset delay (T _PD ). Specifically, the CPU 7 connects the blood vessel centers on adjacent two-dimensional images with a straight line, and sets the length of the straight line between the nth image and the (n + 1) th image as dn. Then, the total sum Σdn of straight lines acquired between all adjacent two-dimensional images is set as the average amount D of blood that flows during the waiting time Preset delay (T _PD ). Using the movement amount D thus obtained, the average flow velocity V of arterial blood is calculated as follows.

Average blood flow velocity V (cm / s) = D / T _PD

In addition, the CPU 7 obtains the number of pixels constituting the blood vessel in each two-dimensional image, and sets the sum as the total number of pixels S on the three-dimensional blood vessel image. In addition, since the pixel size pixelsize of the three-dimensional blood vessel image is uniquely determined according to the imaging conditions, the average arterial blood flow is calculated as follows.

Average blood flow BV (cm ³ / s) = SX pixelsize / T _PD

When there are a plurality of blood vessels, the CPU 7 connects the closest blood vessel centers between the two-dimensional images with a straight line, performs the above processing for the number of blood vessels, and calculates the average blood flow velocity and the average blood flow volume. . FIG. 7 (e) shows an example in which each blood vessel center in each two-dimensional blood vessel image is connected by a straight line, and the average moving distance of blood flow is obtained for each blood vessel. FIG. 7 (e) shows that for blood vessels 1 and 2, the centers of blood vessels 1 and 2 in each two-dimensional image are straight lines d11, d12, d13, d14,... And d21, d22, d23, In this example, the average moving distance D1 = Σd1n of the blood vessel 1 and the average moving distance D2 = Σd2n of the blood vessel 2 are obtained.

  In step 506, the CPU 7 colors the blood vessel image of each part based on the values of the average blood flow velocity and the average blood flow obtained in step 505, and acquires a composite image of the colored blood vessel images.

  The coloring method is, for example, RGB color, and B (Blue) can correspond to a value with a low average blood flow velocity, and R (Red) can correspond to a high value. Thereby, the color is made to correspond to the average blood flow velocity according to the value, and based on this correspondence, the CPU 7 colors each point of the blood vessel image according to the average blood flow velocity at that point. FIG. 8 shows an example of coloring the blood vessel image of each part (401 to 407) according to the blood flow information, and an example of a composite image 801 obtained by synthesizing the blood vessel image of each colored part. The mean blood flow velocity or mean blood flow is colored from blue to red as it goes from the downstream part 1 (401) to the upstream part 7 (407) because the upstream trunk is larger than the lower leg part. Yes. The same applies to the composite image 801.

  The above is the description of the processing flow related to the acquisition of the blood vessel image including the blood flow information and the blood vessel image coloring process according to the blood flow information according to the present embodiment. In this way, by acquiring blood flow information together when acquiring a blood vessel image, the blood flow information can also be displayed when displaying the blood vessel image.

  Next, the processing flow for obtaining the coordinates of the blood vessel center in each two-dimensional image in step 504 will be described in detail based on the flowchart shown in FIG. The processing flow shown in FIG. 6 is stored in advance in the hard disk as a program, and is performed by the CPU 7 reading and executing the program as necessary.

  In step 601, the CPU 7 sets the operation loop counter i to 1. Within this loop, center coordinates for each two-dimensional blood vessel image are calculated.

  In step 602, the CPU 7 extracts a region where a maximum number of pixels are adjacently gathered by a predetermined number (for example, 10 pixels) in the binarized i-th two-dimensional blood vessel image. Then, the CPU 7 determines that the extracted region is a blood vessel, and assigns numbers 1 to n to each blood vessel. The numbering method is arbitrary. FIG. 7 (c) shows an example of the extracted blood vessel. FIG. 7 (c) shows an example in which the blood vessel 1 and the blood vessel 2 are extracted for each two-dimensional blood vessel image, and each is shown by a black region.

  In step 603, the CPU 7 sets the operation loop counter j to 1. The center coordinates for each blood vessel are calculated in this loop.

  In step 604, the CPU 7 calculates the total number of pixels for the j-th blood vessel ij in the i-th two-dimensional blood vessel image.

  In step 605, the CPU 7 copies a set of pixels constituting the blood vessel ij onto another two-dimensional coordinate space, counts the number of pixels in the y direction at each x coordinate, and sets the horizontal axis to the x coordinate, A one-dimensional profile is created with the vertical axis representing the number of pixels in the y direction. Then, the CPU 7 integrates the number of pixels in order in the x direction based on this profile, and the x coordinate at which the integration value is half the total number of pixels of the blood vessel ij calculated in step 604 is determined for the blood vessel ij. The x coordinate value of the center is xij.

  In step 606, the CPU 7 counts the number of pixels in the x direction at each y coordinate on the two-dimensional coordinate space copied in step 605 for the blood vessel ij, the horizontal axis is the y coordinate, and the vertical axis is the pixel in the x direction. Create a one-dimensional profile with numbers. Then, the CPU 7 integrates the number of pixels sequentially in the y direction based on this profile, and sets the y coordinate at which the integration value is half the total number of pixels of the blood vessel ij calculated in step 604 to the blood vessel ij. The center y coordinate value is yij. FIG. 7 (d) shows an example of the blood vessel center of the blood vessel obtained in steps 605 and 606. FIG. 7 (d) shows the centers of the blood vessel 1 and the blood vessel 2 that are represented in white in the blood vessel.

  In step 607, the CPU 7 increments the calculation loop counter j and performs the processing of steps 603 to 606 for all blood vessels (total number of blood vessels n).

In step 608, the CPU 7 increments the calculation loop counter i, and performs the processing in steps 602 to 607 for all the two-dimensional blood vessel images (two-dimensional blood vessel image total number N).
The above is the description of the process for obtaining the coordinates of the blood vessel center in each two-dimensional image.

As described above, according to the MRI apparatus of the present embodiment, when the slab region is imaged, by pre-saturating the region including the slab region and extending in the downstream direction of the blood flow of interest, the inflow from the downstream side is performed. The blood flow signal can be suppressed, and only the blood flow signal flowing from upstream can be depicted. Further, such imaging of the slab region is repeated while moving the slab region and the presaturation region in the upstream direction of the blood flow. Accordingly, a wide range of blood vessel images can be acquired by synthesizing the acquired blood vessel images of the respective slab regions, and blood flow information such as an average blood flow velocity and an average flow rate can be acquired together. Then, by coloring the blood vessel image based on the blood flow information, blood flow information such as average blood flow and average blood flow can be visually represented in the blood vessel image representing the blood vessel morphology information. Become.
(Second embodiment)
Next, a second embodiment of the MRI apparatus of the present invention will be described. In the present embodiment, the blood vessel center in the blood flow direction is obtained, and blood flow information such as the average blood flow velocity and the average blood flow is colored as the blood vessel center in the blood flow direction. Then, colors other than the blood vessel center in the blood flow direction are obtained by linear interpolation processing using the color at the blood vessel center of the adjacent part. The difference from the first embodiment described above is that blood flow information for each slab region is a value at the blood vessel center, and blood flow information at points other than the blood vessel center is obtained by interpolation. Hereinafter, only differences from the above-described first embodiment will be described, and descriptions regarding the same points will be omitted.

  First, a method for obtaining a blood vessel center in a blood flow direction of a blood vessel in a slab region and a blood vessel image coloring method according to the present embodiment will be described with reference to FIG. Since this embodiment is different from the first embodiment described above only in the blood vessel image coloring method in step 506 of the flowchart in FIG. 5, the flowchart in FIG. 9 is only the blood vessel image coloring method according to this embodiment. And a description of the same processing flow as in the first embodiment is omitted.

  In step 901, the CPU 7 initializes the operation loop counter i to 1. By this loop, the blood vessel center in the blood flow direction for each blood vessel is calculated for each three-dimensional blood vessel image in the slab region.

  In step 902, the CPU 7 initializes the operation loop counter j to 1. By this loop, the blood vessel center in the blood flow direction is calculated for each blood vessel.

  In step 903, on each two-dimensional blood vessel image formed by dividing the three-dimensional blood vessel image of the slab region j in step 503, the number of pixels constituting the blood vessel ij counted in step 604 is used, and the CPU 7 Creates a one-dimensional profile with the horizontal axis representing the two-dimensional blood vessel image number and the vertical axis representing the number of pixels of the blood vessel ij on the two-dimensional blood vessel image.

  In step 904, the CPU 7 integrates the number of pixels in the two-dimensional blood vessel image number order (that is, in the blood flow direction) with respect to the one-dimensional profile created in step 903. Then, the integrated value is a half of the total number of pixels of the blood vessel ij in the three-dimensional blood vessel image of the slab region i acquired in the above-described step 503, and the sequential two-dimensional blood vessel image includes the blood vessel center in the blood flow direction. And

  In step 905, the CPU 7 sets the coordinates (in the division direction) of the two-dimensional blood vessel image obtained in step 904 as the blood vessel center in the blood flow direction in the slab region i.

  In step 906, the CPU 7 sets the blood flow information of the blood vessel obtained in step 505 described above as a value at the blood vessel center obtained in step 905, and assigns a color corresponding to the blood flow information to the blood vessel center.

  FIG. 10 shows an example in which a blood vessel center of each blood vessel in a three-dimensional blood vessel image of each slab region and a color corresponding to the blood flow information are assigned to the blood vessel center. Each blood vessel center is indicated by a circle, and the color of the circle is a color assigned corresponding to blood flow information. Since the slab region of the region 1 (401) is on the lower limb side, the blood flow velocity is slow, the blood flow is reduced, and blue is assigned. On the other hand, since the slab region of the part 7 (407) is on the trunk side, the blood flow velocity is high, the blood flow volume is increased, and red is assigned. As the slab region in between goes from the lower limb side to the trunk side, the blood flow velocity increases and the blood flow volume increases, and it is understood that the assigned color gradually changes from blue to red.

  In step 907, the CPU 7 increments the calculation loop counter j and performs the processing of steps 903 to 906 for all blood vessels (blood vessel total number n).

  In step 908, the CPU 7 increments the calculation loop counter i, and performs the processing in steps 902 to 907 for the three-dimensional blood vessel images in all the slab regions (slab total number M).

  In step 909, the CPU 7 synthesizes the three-dimensional blood vessel image of each slab region to which the color is assigned to obtain a synthesized image. An example of the composite image is shown in FIG. In the composite image 1001, the blood vessel centers of the slab areas represented by circles are arranged along the traveling direction of the blood vessels, and each circle has a color corresponding to blood flow information in the slab area.

  In step 910, in the composite image obtained in step 909, the CPU 7 changes the color of the region other than the blood vessel center in the blood flow direction in each slab region to the blood flow in the blood vessel center in the slab region adjacent to the blood vessel center in the slab region. Obtained by interpolation using information or colored colors. Finally, the circle at the center of each blood vessel is deleted, and a composite image in which the blood flow information distribution is displayed in color is acquired. An example of a composite image in which the blood flow information distribution is displayed in color is shown in FIG. In the composite image 1002, blood vessels are colored so that the color changes monotonously from red to blue as it goes from the trunk side to the lower limb side.

  The foregoing is the description of the method for obtaining the blood vessel center in the blood flow direction of the blood vessel in the slab region and the method for coloring the blood vessel image. When the operator designates a desired point on the colored composite image acquired in step 910 with a mouse or the like, blood flow information at that point may be displayed in a pop-up manner. An example is shown in FIG. An arrow pointer linked to the mouse operation is displayed on the display 20 together with the composite image. When the operator operates the mouse to position the arrow pointer on a desired blood vessel and clicks the right mouse button at that position, the average of the points is displayed. The blood flow velocity and average blood flow values are popped up. FIG. 11 shows an example in which the left lower limb blood vessel is pointed and the average flow velocity is 20 cm / s.

  As described above, according to the MRI apparatus of the present embodiment, blood flow information of a wide range of blood vessels of a subject is displayed in color, so that an operator can easily obtain blood flow information of a wide range of blood vessels of a subject. It becomes possible to grasp. In addition, since the color step between the parts is smoothed by the interpolation, the change in the blood flow direction can be grasped visually without a sense of incongruity. In addition, blood flow information at a desired position can be acquired as necessary.

1 is a block diagram showing a schematic configuration of an MRI apparatus according to the present invention. The sequence diagram which shows the sequence which concerns on this invention. (a) is a timing chart showing the timing of an ECG (ElectroCardioGraph) Trigger signal and an imaging sequence in electrocardiographic synchronization imaging. (b) is a sequence diagram showing a pre-saturation sequence unit for suppressing a signal of a desired imaging region. (c) is a sequence diagram showing a main measurement sequence unit for collecting echo signals for images from a desired imaging region. The figure explaining the imaging method of the blood vessel using the inflow effect based on this invention. (a) is a figure which shows a slab area | region and a pre-saturation area | region. (b) is a diagram showing that both the background signal of the slab region and the signal from venous blood flowing into the slab region from the peripheral side during the waiting time are suppressed. (c) is a diagram showing that arterial blood flowing into the slab region 301 from the trunk side is imaged during the waiting time. The present invention relates to an example in which a wide range of blood vessel images are acquired by repeatedly capturing blood vessel images of each slab region while the slab region and the presaturation region are moved upstream of the blood flow of interest. Figure. 3 is a flowchart showing a processing flow of the first embodiment of the present invention. 6 is a flowchart showing detailed processing of step 504 in the flowchart of FIG. The figure which shows the example which extracts the blood vessel for every two-dimensional blood vessel image in the 1st Embodiment of this invention, and connects the center with a straight line. FIG. 4 is a diagram showing an example of coloring blood vessel images of each part according to blood flow information and an example of a synthesized image obtained by synthesizing the blood vessel images of colored parts in the first embodiment of the present invention. 9 is a flowchart showing a processing flow of a second embodiment of the invention. The figure which shows the example which assigned the color according to the blood-flow information to the blood vessel center of each blood vessel in the three-dimensional blood vessel image of each slab area | region in the 2nd Embodiment of this invention, and the blood vessel center. The figure which shows the example which the left leg blood vessel is pointed and the average flow velocity is 20 cm / s.

Explanation of symbols

  1 subject, 2 static magnetic field generation system, 3 gradient magnetic field generation system, 4 sequencer, 5 transmission system, 6 reception system, 7 signal processing system, 8 central processing unit (CPU), 9 gradient magnetic field coil, 10 gradient magnetic field power supply, 11 High frequency transmitter, 12 modulator, 13 high frequency amplifier, 14a high frequency coil (transmitting coil), 14b high frequency coil (receiving coil), 15 signal amplifier, 16 quadrature detector, 17 A / D converter, 18 magnetic disk, 19 optical disc, 20 display, 21 ROM, 22 RAM, 23 trackball or mouse, 24 keyboard

Claims (8)

Based on a predetermined sequence, a measurement control unit that controls measurement of an echo signal from an imaging region including a blood vessel of a subject, an arithmetic processing unit that acquires a blood vessel image of the imaging region using the echo signal, A magnetic resonance imaging apparatus comprising: display means for displaying a blood vessel image;
The sequence includes at least a pre-saturation sequence unit that pre-saturates the imaging region, and a main measurement sequence unit that measures an echo signal from the inflowing blood that has flowed into the imaging region.
The arithmetic processing means calculates a movement amount of the inflowing blood based on the blood vessel image, calculates blood flow information of the inflowing blood from the movement amount, and calculates the blood vessel image corresponding to the blood flow information. A magnetic resonance imaging apparatus characterized by coloring. The magnetic resonance imaging apparatus according to claim 1.
The magnetic resonance imaging apparatus, wherein the pre-saturation sequence unit includes the imaging region, and pre-saturates a region expanded in a blood flow direction in the blood vessel. The magnetic resonance imaging apparatus according to claim 1 or 2,
The measurement control means controls the measurement of echo signals from a plurality of imaging regions by moving the imaging region so that at least a part thereof overlaps in the upstream direction of blood flow in the blood vessel.
The said arithmetic processing means acquires the blood vessel image for every said imaging area, and synthesize | combines several blood vessel images and acquires a synthesized image, The magnetic resonance imaging apparatus characterized by the above-mentioned. The magnetic resonance imaging apparatus according to any one of claims 1 to 3,
The arithmetic processing means extracts the blood vessel from the blood vessel image, sets the length of the extracted blood vessel as the movement, and uses the time between the pre-saturation sequence unit and the main measurement sequence unit to perform the inflow. A magnetic resonance imaging apparatus characterized by calculating an average blood flow velocity of blood and coloring the blood vessel image corresponding to the calculated average blood flow velocity. The magnetic resonance imaging apparatus according to any one of claims 1 to 3,
The arithmetic processing means extracts the blood vessel from the blood vessel image, calculates an average blood flow from the total number of pixels constituting the extracted blood vessel, and pixel size, and corresponds to the calculated blood flow A magnetic resonance imaging apparatus characterized by coloring an image. The magnetic resonance imaging apparatus according to any one of claims 1 to 5,
The arithmetic processing means calculates a center position in the blood flow direction of the blood vessel for each blood vessel image, and colors the center position corresponding to the blood flow information, and between the center positions of adjacent blood vessel images. A magnetic resonance imaging apparatus characterized by obtaining a color of a blood vessel region by interpolation. The magnetic resonance imaging apparatus according to any one of claims 1 to 6,
The measurement control means controls the measurement of echo signals having different cardiac phases by changing the time from the ECG Trigger to the main measurement sequence unit,
The magnetic resonance imaging apparatus, wherein the arithmetic processing unit acquires blood vessel images having different cardiac phases using echo signals having different cardiac phases. The magnetic resonance imaging apparatus according to any one of claims 1 to 7,
Input means for inputting position information for designating a desired point on the composite image;
The arithmetic processing means displays blood flow information at the designated desired point on the display means.

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