Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves
  • A61B5/055—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R33/00—Arrangements or instruments for measuring magnetic variables
  • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
  • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
  • G01R33/48—NMR imaging systems
  • G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
  • G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
  • G01R33/563—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution of moving material, e.g. flow contrast angiography
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/02—Detecting, measuring or recording for evaluating the cardiovascular system, e.g. pulse, heart rate, blood pressure or blood flow
  • A61B5/026—Measuring blood flow
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R33/00—Arrangements or instruments for measuring magnetic variables
  • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
  • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
  • G01R33/48—NMR imaging systems
  • G01R33/483—NMR imaging systems with selection of signals or spectra from particular regions of the volume, e.g. in vivo spectroscopy
  • G01R33/4833—NMR imaging systems with selection of signals or spectra from particular regions of the volume, e.g. in vivo spectroscopy using spatially selective excitation of the volume of interest, e.g. selecting non-orthogonal or inclined slices
  • G01R33/4835—NMR imaging systems with selection of signals or spectra from particular regions of the volume, e.g. in vivo spectroscopy using spatially selective excitation of the volume of interest, e.g. selecting non-orthogonal or inclined slices of multiple slices

Definitions

• the present invention relates to a magnetic resonance imaging (hereinafter abbreviated as “MRI”) apparatus for obtaining a tomographic image of a desired site of a subject using a nuclear magnetic resonance (hereinafter abbreviated as “NMR”) phenomenon, and particularly to a vascular system.
• MRI magnetic resonance imaging
• NMR nuclear magnetic resonance
• the present invention relates to an MRI apparatus capable of recognizing the direction of a running of a vehicle.
• MRA MR angiography
• Typical methods of drawing blood flow in MRI equipment include time-of-flight (TOF) using the effect of inflow into the slice surface and phase diffusion of blood flow spin by a gradient magnetic field applied in the direction of movement.
• TOF time-of-flight
• phase methods that use the phase method.
• the main phase methods include the phase-sensitive (PS) method and the phase contrast (PC) method.
• PS phase-sensitive
• PC phase contrast
• phase contrast a pair of tilted field pulses (Froenco pulse) that give different phase rotations to blood flow spins is used, and a pair of data is obtained by applying these pulses to the 3 ⁇ 4S. Blood flow is drawn by taking the complex difference of the mouth data.
• each of these conventional blood flow drawing methods has advantages and disadvantages, and is used depending on the purpose.
• the gradient echo method is used as the imaging sequence. It is necessary to use a short TR sequence like this, and it is not possible to use a high-speed sequence like EPI.
• the blood spin flowing into the presaturated region from any direction is also increased in signal, the arteriovenous separation cannot be performed.
• T which can visualize only one direction of blood flow.
• the PC method also uses a technique of separating the artery and vein by taking the phase difference between flow-encoded phase images of different polarities.
• the sequence is not flow-phased, so it is vulnerable to turbulence and changes in flow velocity, and has the problem of easily causing blood vessel defects and artifacts.
• the two-dimensional PC method intended for quantitative measurement of blood flow velocity cannot increase the slice thickness including blood vessels, and is not suitable for observing the entire running of the vascular system at the same time. Was.
• an object of the present invention is to provide an MRI apparatus capable of observing an entire blood vessel, capable of separating arteries and veins (drawing the direction of blood flow), and having a novel blood flow drawing function with few artifacts.
• Another object of the present invention is to provide an MRI apparatus capable of applying a high-speed imaging sequence such as EPI, and thereby realizing blood flow drawing in a short imaging time.
• an MRI apparatus sequentially repeats excitation by high-frequency magnetic field irradiation and measurement of an echo signal on a plurality of slice planes, and reconstructs a blood flow image from the obtained echo signals.
• a first measurement for exciting a plurality of slice planes in a first order and a second measurement for exciting a plurality of slice planes in a reverse order to the first are performed, and each slice is executed.
• two types of data are obtained, and a difference operation between the two types of data of each slice is performed, and signals from blood flows in opposite directions are obtained as different types of data.
• the MRI apparatus comprises: a static magnetic field generating means for generating a static magnetic field in a space capable of accommodating a subject;
• the transmitting system that repeatedly applies a high-frequency panelless laser that causes nuclear magnetic resonance to the nuclei of the atoms constituting the TO of the subject's living body TO in a predetermined pulse sequence, and detects the echo signals emitted by the ItH self-nuclear magnetic resonance Receiving system, a signal processing system for performing an image reconstruction operation using the echo signal detected by the receiving system, and an obtained image.
• a control system for controlling the operation of the ri self-incident ⁇ !
• Field generating means means, the self-transmission system, the ii self-reception system, and the in-self signal processing system.
• the nuclear magnetic resonance blood flow drawing method (MRA) of the present invention sequentially repeats excitation by high frequency magnetic field irradiation and measurement of an echo signal on a plurality of slice planes, and reconstructs a blood flow image from the obtained echo signal.
• MRA nuclear magnetic resonance blood flow drawing method
• the blood flow flowing in that direction A is repeatedly excited with a relatively short repetition time.
• the signal from the blood flow spin becomes relatively weak.
• the blood flow flowing in the opposite direction (direction B) has a relatively long repetition time TR, and the signal intensity therefrom is almost the same as that of the stationary part.
• the second measurement when the same plurality of slices are sequentially generated in the direction B opposite to the first direction, a signal from the blood flow in the direction B is relatively generated, contrary to the above case. It becomes weaker, and the signal from the blood flow in the A direction becomes relatively stronger. Therefore, when the difference between the data obtained by these two types of measurements is taken, the pixel value (signal 5 daughter) of the stationary part becomes 0, and different data depending on the direction can be obtained in the blood flow.
• the MRA of the present invention includes, prior to the step (a), a step (c) of preliminarily saturating (presaturation) at least one of the regions adjacent to the imaging region composed of a plurality of slices by irradiation with a high-frequency magnetic field. Force, 'preferred.
• the blood flow spin flowing into the slice is multi-excited.
• the signal difference from the blood flow spinning out of the slice cannot be obtained because there is no signal suppression due to the rise, but by presaturating the area adjacent to the imaging area, Even in slices, the signal suppression effect by multiple excitation is obtained, and the difference between blood flow spins in different directions, that is, the difference between inflowing blood flow spins and outflowing blood flow spins, becomes clear. Can be improved. It is to be noted that, instead of pre-saturating an area adjacent to the imaging area, deleting data at both end slices in the data processing step (b) is also included in the present invention.
• the MRA of the present invention it is preferable to select an adjacent slice so that a part thereof overlaps in measurement of each slice.
• a gradient echo sequence can be used as the imaging sequence, and the number of echo signals measured for each excitation may be one or two or more. Since the blood flow signal can be drawn with a relatively high contrast to the stationary part without multiple excitations of the same slice, a March Czech (including EPI) sequence that measures multiple echo signals with one excitation Can also be adopted.
• FIG. 1 is an explanatory diagram showing an MR angography measurement method performed by the MRI apparatus of the present invention.
• FIGS. 2A and 2B are diagrams showing an example of an imaging sequence executed by the sequencer.
• FIG. 3 is a diagram illustrating the principle of the MR angiography measurement method according to the present invention.
• FIG. 4 is a diagram showing an example of image processing in the MRI apparatus of the present invention.
• FIG. 5 is a diagram illustrating a projection process in the MRI apparatus of the present invention.
• FIG. 6 is a diagram showing an example of image processing in the MRI apparatus of the present invention.
• FIG. 7 is a diagram showing another example of the MR angiography measurement method executed by the MRI apparatus of the present invention.
• FIG. 8 is a diagram showing an overall configuration of an MRI apparatus to which the present invention is applied.
• FIG. 8 is a block diagram showing the overall configuration of an MRI apparatus to which the present invention is applied.
• This MM device obtains a tomographic image of the subject by utilizing the NMR phenomenon, and as shown in FIG. 8, a static magnetic field generating magnet 2, a tilt field generating system 3, a transmitting system 5, and It comprises a receiving system 6, a signal processing system 7, a sequencer 4, and a central processing unit (CPU) 8.
• the static magnetic field generating magnet 2 generates a uniform static magnetic field around the subject 1 in the direction of its cage or in a direction perpendicular to the subject 1.
• a permanent magnet type space is provided around the subject 1 with a certain space.
• a normal-conducting or superconducting magnetic field generating means is provided.
• the gradient field generating system 3 is composed of a gradient coil 9 wound in three axes of ⁇ , ⁇ , and ⁇ , and a gradient and a gradient for each field coil!
• a gradient field power source 10 of each coil in accordance with a command from a sequencer 4 described later, a gradient magnetic field Gx, Gy, Gz in the X, Y, and Z directions is applied to the subject 1. It is applied.
• the slice plane for the subject 1 can be set by adding this inclination field.
• the sequencer 4 repeatedly applies a high-frequency magnetic field (RF) signal that causes (exciting) nuclear magnetic resonance to the nuclei of the atoms constituting the living tissue of the subject 1 in a predetermined panless sequence. It operates under the control of the CPU 8, and sends various commands necessary for data collection of tomographic images of the subject 1 to the transmission system 5, the gradient magnetic field generation system 3 and the reception system 6.
• RF radio frequency
• the transmission system 5 is an RF node sent from the sequencer 4.
• the RF field is irradiated by RF to generate nuclear magnetic resonance in the nuclei of the atoms constituting the living body ai3 ⁇ 4 of the subject 1.
• the high-frequency oscillator 11, the modulator 12, the high-frequency amplifier 13, and the high-frequency The high-frequency panel output from the high-frequency oscillator 11 is The amplitude is modulated by the modulator 12 according to the instruction of the sampler 4, and the amplitude-modulated RF pulse is amplified by the high-frequency amplifier 13 and then supplied to the high-frequency coil 14a arranged close to the subject 1.
• An electromagnetic wave is applied to the subject 1.
• the receiving system 6 detects an echo signal (NMR signal) emitted by nuclear magnetic resonance of the nucleus of the biological tissue of the subject 1, and includes a high-frequency coil 14b, an amplifier 15 and a quadrature phase detector 16 on the receiving side.
• the electromagnetic wave (NMR signal) of the response of the subject 1 due to the electromagnetic wave radiated from the high-frequency coil 14a on the transmitting side is transmitted by the high-frequency coil 14b arranged close to the subject 1.
• the data is collected in two series, and the signal is sent to the signal processing system 7.
• the signal processing system 7 includes a CPU 8, a recording device such as a magnetic disk 18 and a magnetic tape 19, and a display 20 such as a CRT, and a power.
• the CPU 8 performs a Fourier transform, a correction coefficient calculation image, and the like. Is performed, and a signal intensity distribution of an arbitrary cross section or a distribution obtained by performing an appropriate operation on a plurality of signals is imaged and displayed on the display 20 as a tomographic image.
• the high-frequency coils 14a and 14b on the transmission side and the reception side and the tilted field coil 9 are installed in the magnetic field space of the static magnetic field generating magnet 2 arranged in the space around the subject 1.
• FIG. 1 is a diagram schematically showing an area imaged by the MRI apparatus of the present invention.
• an imaging area including target blood vessels A and B of a subject is sliced so as to be substantially orthogonal to the blood vessels.
• the surface is set, and multi-slice imaging is performed on these multiple slice surfaces using two different jl enzymes.
• Fig. 2 (a) In multi-slice imaging, as shown in Fig. 2 (a), during the repetition time TR for one slice, excitation and echo signal measurement with RF pulses are sequentially repeated for each slice and the phase encoding step is changed. And repeat. In Fig. 2 (a), the repetition force of about one and a half times is not shown. The imaging sequence is repeated until an echo signal having the number of phase codes for image reconstruction is measured.
• imaging by the gradient echo method that generates one echo signal by reversing the gradient magnetic field after one slice selective excitation by RF and non-irradiation
• a sequence Fig. 2 (a)
• one slice selective excitation by RF and ° Loss irradiation the polarity of the readout gradient magnetic field is reversed several times while applying a phase encode gradient magnetic field in the form of a ° and ° Loss.
• a multi-shot or sync-releasing EPI sequence Fig. 2 (b)
• the sequence shown in FIG. 2 (b) is repeated while changing the offset amount of the phase code.
• excitation Z measurement is performed from the lowest slice 1 in Fig. 1 to slice N in order, for example, from the foot to the head in the case of a human body, and the second measurement Then, on the contrary, excitation measurement is performed sequentially from the upper slice N to the lower slice 1.
• the blood flow in the blood vessel A flowing in the excitation forward direction moves from slice 1 to slice 2 and slice 3
• the signal is much shorter than the repetition time TR and receives multiple excitations at intervals, and the signal 5 Sa decreases.
• the blood flow in the blood vessel B flowing in the direction opposite to the excitation order has a repetition time of the excitation that is almost the same as the TR of the stationary part, and has a relative length TR to the blood vessel A. That is, the signal is relatively high key.
• the order of excitation of the slices is reversed, so that the signal from the blood vessel A becomes a high signal and the signal from the blood vessel B becomes a low signal, contrary to the first measurement.
• the present invention makes it possible to draw blood vessels in different directions by utilizing the fact that the difference between the signal strength of the blood vessel A and the signal strength of the blood vessel B is reversed in the two different measurements.
• the signal boat is a weighted average of the ratio of the signals of the blood flow spins of these different eTRs.
• a signal decrease occurs in accordance with the ratio of the blood flow in which the eTR becomes TRN.
• the ratio of the blood flow that receives multiple excitations differs according to the blood flow velocity V, and the signal intensity is obtained by adding the ratio.
• the eTR can be regarded as almost the same as the stationary part. Therefore, even when there is overlap between slices, blood flow A, except for extremely high speeds, causes at least a part of the blood flow to undergo multiple excitations according to the blood flow velocity, and the signal determined by that ratio There is a 53 ⁇ 4 drop.
• the portion in the non-overlapping portion may be the repetition time before one phase encoding step, and the blood flow excited when the slice on the upstream side is excited may flow in that case.
• Typical repetition time e TR is
• n is an integer determined by TR, N, v, P, and is smaller than N
• the overlap amount should be 20 to 80% of the slice thickness, preferably 50% or less.
• the oval wrap amount may be increased in the artery of Katabe.
• the signal daughter can be made different depending on the direction of the blood flow. Can be different.
• One set of images obtained for the same slice shows blood vessel A with a low signal, blood vessel B with a high signal, and the other ( In the image obtained in the second measurement, blood vessel B is visualized with a low signal and blood vessel A is visualized with a high signal.
• a difference is made between these one set of data (for example, the image data obtained in the first measurement, and the image data obtained in the second measurement are subtracted).
• complex data or absolute value difference may be performed after each image is reconstructed, or reconstruction may be performed after complex difference using signal data before Uranari.
• the stationary part is deleted, and an image of only blood vessels is obtained.
• the pixel value of the blood vessel varies depending on the direction of the blood flow.
• the above-described difference processing is performed for each slice, whereby difference images for the number of slices are generated.
• a projection blood vessel image of the entire area is created by projecting the obtained difference image.
• MIP maximum value projection method
• MinIP minimum value projection method
• a threshold ⁇ is set for both positive and negative. If the absolute value is less than or equal to threshold a, it is regarded as a fiber other than a blood vessel, and is set to 0 and displayed in gray. If the value exceeds the threshold value, it is regarded as a blood vessel. If the value is positive, white is used, for example, and if negative, black is used. Thus, for example, the blood vessel A can be displayed in black on a gray background, and the blood vessel B flowing in the opposite direction can be displayed in white.
• the method of displaying the larger positive or negative value (Fig. 5 (b)) or the method that gives priority to either positive or negative is used.
• the method of the difference can be arbitrarily selected in consideration of the gender in diagnosis.
• the method (b) is suitable for preferentially rendering a blood vessel having a high signal value
• the method (c) is suitable for preferentially rendering an artery or a vein.
• the hue of the blood flow direction may be changed in addition to the black and white display described above. That is, for example, it may be possible to identify the two values by giving each hue that can be distinguished hue, such as red when the value is positive and blue when the value is negative. .
• the direction of projection can be set arbitrarily, such as a coronal section, a sagittal section, or a direction transverse to an axis.
• Fig. 6 by rotating around a certain axis C, for example, from a projection with an angle of ⁇ 45 °, create projection images every 5 ° to 10 ° and display them as moving images It is also possible.
• the MRI apparatus of the present invention utilizes the fact that the spins of the blood flow flowing in the excitation forward direction receive multiple excitations to reduce the signal, and the excitation orders are different. Based on the difference between the data obtained by the two measurements, the blood flow signal is acquired as data with different signs depending on the direction. In this case, referring to slice 1 which is first excited in FIG. 1, the blood flow in the excitation forward direction flowing into slice 1 does not receive a multiple excitation, so that the signal does not decrease. Similarly Even in the slice N excited first in the measurement of 2, the signal of the blood flow in the excitation forward direction does not have a low signal. Therefore, if the difference between two measurements in different excitation orders is taken, the difference in blood flow direction between the first and last slices 1 and N becomes unclear.
• the data of the first and last slices may be deleted, but more preferably, the area adjacent to the first excited slice is irradiated with RF in advance. Therefore, it is preferable to make it saturated (presaturation).
• FIG. 7 shows an embodiment in which the pre-saturation is added to the imaging sequence.
• multi-slice imaging is performed by dividing the imaging region into a plurality of slices substantially orthogonal to the target blood vessels A and B.
• the first measurement and the second The measurement is the same as in the example of FIG. 1.
• the region S 1 adjacent to the slice 1 to be excited first in the figure, The lower region is irradiated with RF to saturate the spin in this region.
• the area S 2 (upper area in the figure) adjacent to the slice n that is first excited is similarly pre-saturated to saturate the spin. Let it.
• Such presaturation can be performed irrespective of the imaging sequence, and the presaturation of the region S1 or S2 can be performed before the multislice sequence shown in FIGS. 2 (a) and (b). Steps may be inserted.
• the multi-slice imaging sequence of the present invention may be applied to a multi-slice imaging sequence other than the force described using the gradient echo method or the ⁇ I method.
• slice excitation is performed as a blood flow drawing function. This makes it possible to draw blood flows in different directions as signals of different polarities.
• EPI measures the echoes of all the phase encoders required for image reconstruction by one slice excitation, which enables blood to be collected in a very short time of about 10 seconds or less. Flow images can be obtained.
• the MRI apparatus of the present invention is not susceptible to turbulence, which is a problem in the conventional PC method, and can clearly recognize the direction of blood flow even when arteries and veins overlap.

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• 1998
  • 1998-03-04 JP JP05234198A patent/JP4127889B2/ja not_active Expired - Fee Related
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