WO2005034749A1 - 磁気共鳴イメージング装置及びこれを用いた造影アンジオグラフィー法 - Google Patents
磁気共鳴イメージング装置及びこれを用いた造影アンジオグラフィー法 Download PDFInfo
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- WO2005034749A1 WO2005034749A1 PCT/JP2004/014660 JP2004014660W WO2005034749A1 WO 2005034749 A1 WO2005034749 A1 WO 2005034749A1 JP 2004014660 W JP2004014660 W JP 2004014660W WO 2005034749 A1 WO2005034749 A1 WO 2005034749A1
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- 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
- G01R33/5601—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution involving use of a contrast agent for contrast manipulation, e.g. a paramagnetic, super-paramagnetic, ferromagnetic or hyperpolarised contrast agent
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- the present invention relates to a magnetic resonance imaging apparatus that obtains an image of a desired part of a subject using a nuclear magnetic resonance phenomenon, and in particular, a contrast angiography that uses a contrast agent to depict the movement of a vascular system.
- the present invention relates to a technique for acquiring a high-quality blood vessel image by a method.
- a magnetic resonance imaging (hereinafter abbreviated as "MRI") apparatus utilizes a nuclear magnetic resonance (hereinafter abbreviated as "NMR") phenomenon to produce a nuclear spin (hereinafter simply referred to as “spin”) at a desired examination site in a subject. ) Is measured, and an arbitrary cross section of the subject is displayed as an image from the measured data.
- NMR nuclear magnetic resonance
- MRI apparatuses include an MR angiography (hereinafter abbreviated as MRA) for drawing a blood flow and an MRI apparatus having an imaging function.
- MRA imaging function includes a contrast method without using a contrast agent and a method using a contrast agent.
- a contrast agent is superior in the ability to depict blood vessels, and a high-quality blood vessel image can be obtained. Can be.
- a method of using a contrast agent a method of combining a T1 shortened type contrast agent such as Gd-DTPA with a gradient echo sequence of short duration and TR (repetition time) is generally used.
- a contrast medium must be injected so as to stably maintain a high concentration in a blood vessel to be imaged. For this reason, the contrast medium is generally rapidly injected using an automatic injector.
- the measurement of the central portion (low-frequency region) of k-space, which governs the contrast of the image is adjusted to the timing when the contrast agent concentration reaches a peak.
- the timing is set according to. This timing setting technique is disclosed in Patent Document 1.
- the time from TE excitation to the echo center is set as short as possible in order to minimize signal attenuation due to T2 shortening due to the contrast agent and phase diffusion due to blood flow. (3 ms or less)
- For TR set the S / N as short as possible (10 ms or less) according to the injection speed of the contrast agent. That is, the method of changing the TR is changed according to the concentration of the contrast agent.
- Patent Document 1 US Pat. No. 5,553,619
- the concentration of the injected contrast agent in the blood vessel lumen changes every moment with time, and increases exponentially until the concentration peak is reached, and reaches this concentration peak. After that, it decays exponentially. For this reason, except during the peak concentration, Thus, there is a problem that a high signal from blood cannot be obtained during the entire measurement period.
- the imaging conditions are optimized according to the peak of the contrast agent concentration in the blood vessel lumen at the target site (see Patent Document 1). Technology).
- the measurement in the time period before and after the peak time of the contrast agent concentration other than the peak time is not always the optimal measurement.
- the acquisition time of the center data of the k space is adjusted at the time of the peak of the contrast agent concentration in the blood vessel lumen at the target site, so that the center of the k space for determining the image contrast is determined.
- the measurement of the part has been optimized and high signal acquisition is possible.
- the edge of the k-space which is a factor that determines the contour (sharpness) of an image, is out of the optimal state, and thus the optimal height is not obtained. No signal can be obtained.
- the present invention has been made in order to solve the above problems, and an object of the present invention is to always optimize an optimal condition by following a concentration of a contrast agent which is injected into a subject and changes every moment.
- An object of the present invention is to provide an MRI apparatus capable of obtaining a high-quality blood vessel image by imaging with an MRI, and a contrast angiography method using the MRI apparatus.
- the present invention is configured as follows.
- a contrast angiography method in which a blood vessel image of a subject is captured using a magnetic resonance imaging apparatus using a contrast agent, wherein (a) a desired region of the subject including the blood vessels is statically imaged. (B) injecting a contrast agent into the subject, (c) imaging the desired area based on a predetermined nose sequence having at least one imaging parameter, d) a step of reconstructing a blood vessel image from the photographing data obtained in the photographing step; and (e) a step of displaying the blood vessel image.
- the imaging step (C) during imaging, the value of at least one imaging parameter of the noise sequence is changed in accordance with the concentration of the contrast agent in the blood vessel.
- a first period and a second period are set in accordance with the concentration of the contrast agent, and the first period The value of the shooting parameter is different between and the second period.
- the photographing step (c) at least two photographing parameters are selected, and the photographing parameters are different between the first period and the second period. Select the shooting parameters.
- the value of the first shooting parameter is changed in the first period, and the value of the second shooting parameter is changed in the second period. .
- the first period is a concentration increasing period until the concentration of the contrast agent reaches a peak
- the first period is The concentration of the agent is the period during which the concentration decreases from the point when the S peak occurs.
- the first period is a high concentration period equal to or more than a predetermined threshold including a point in time when the concentration of the contrast agent reaches a peak, and The period is a low concentration period in which the concentration of the contrast agent is less than a predetermined threshold.
- the pulse sequence is a gradient echo type pulse sequence having a flip angle and a repetition time as the imaging parameters, and The value of at least one of the repetition times is changed, and the change of the flip angle is increased in accordance with the density increase in the density increase period, and is decreased in accordance with the density decrease in the density decrease period,
- the repetition time is changed so as to follow the increase in the density during the above-mentioned concentration increase period, and is increased following the decrease in the concentration during the above-mentioned concentration decrease period.
- the pulse sequence is a gradient echo-based pulse sequence having a flip angle and a repetition time as the imaging parameters.
- the first shooting parameter is one of the flip angle and the repetition time
- the second shooting parameter is the other
- the flip angle is set to the high angle.
- the flip angle of the concentration period is set to be larger than the flip angle of the low concentration period
- the repetition time is set so that the repetition time of the high concentration period is shorter than the repetition time of the low concentration period.
- the value of the first imaging parameter is changed in the opposite direction before and after the peak time, and the value of the second parameter is monotonously changed. Increase or decrease.
- the change of the flip angle is performed so that the flip angle becomes the Ernst angle, and the change of the repetition time is performed. , So that the flip angle becomes the Ernst angle.
- center data of k-space is acquired near a time point at which the concentration of the contrast agent reaches a peak.
- the start of the step (c) is instructed and the value of the photographing parameter is changed based on the density change information.
- start instruction includes: A signal reflecting the concentration information of the contrast agent in the blood vessel is extracted from the monitoring image, and the extraction is performed when the signal exceeds a predetermined threshold.
- the method of changing the value of the photographing parameter is changed during photographing.
- a static magnetic field generating means for applying a static magnetic field to the subject, a gradient magnetic field generating means for providing a gradient magnetic field, and a high-frequency magnetic field pulse for causing nuclear magnetic resonance to occur in nuclear spins in the subject
- High-frequency magnetic field transmitting means echo signal receiving means for detecting an echo signal emitted by the nuclear magnetic resonance
- a magnetic resonance imaging apparatus comprising: a control unit; a signal processing unit configured to reconstruct a blood vessel image using the echo signal detected by the echo signal receiving unit; and a display unit configured to display the blood vessel image.
- the pulse sequence control means (4) adjusts the concentration of the contrast agent injected into the subject in the blood vessel during the execution of the pulse sequence. Correspondingly, the value of at least one imaging parameter of the pulse sequence is changed.
- the signal processing means predicts the density based on the density change information of the contrast agent acquired in advance, and executes the pulse sequence control.
- the control unit captures the blood vessel image based on the predicted value of the density.
- an input unit for receiving an input for instructing the start of imaging of the blood vessel image
- the pulse sequence control means includes a monitor including the blood vessel. Images are continuously captured, the display means continuously displays the monitoring images, and the pulse sequence control means switches from monitoring the monitoring images to capturing the blood vessel images based on the start instruction. Switch.
- a contrast medium injection means is provided, and the contrast medium is injected by the contrast medium injection means.
- the present invention it is possible to obtain an image of a blood vessel with higher image quality by always capturing an image under optimal conditions, following the concentration of a contrast agent which is injected into a subject and changes every moment.
- a contrast angiography method can be realized.
- an MRI apparatus for performing the above-described contrast angiography method.
- the imaging condition is optimized by following the contrast agent concentration that changes with time in the blood vessel lumen.
- the flip angle and the repetition time TR can be optimally measured, and the lumen of the blood vessel can be acquired with a high signal over the entire measurement window.
- FIG. 1 is a block diagram showing a schematic overall configuration of an MRI apparatus to which the present invention is applied.
- FIG. 2 is a diagram illustrating control of a flip angle in contrast-enhanced MRA measurement performed by the MRI apparatus according to the present invention.
- FIG. 3 is a diagram showing flip angle versus signal intensity curves at various contrast agent concentrations.
- FIG. 4 is a schematic diagram illustrating a signal intensity obtained by a contrast MRA measurement according to the first embodiment of the present invention.
- FIG. 5 is a diagram illustrating TR control in contrast-enhanced MRA measurement according to the second embodiment of the present invention.
- FIG. 6 is a schematic explanatory diagram of a known three-dimensional gradient echo sequence.
- FIG. 7 is a diagram illustrating TR and FA control in contrast-enhanced MRA measurement according to the third embodiment of the present invention.
- FIG. 8 is a screen display example in the embodiment of the present invention.
- FIG. 1 is an overall schematic configuration diagram of an embodiment of an MRI apparatus to which the present invention is applied.
- This MRI apparatus obtains a tomographic image of the subject using the MR phenomenon, and as shown in Fig. 1, a static magnetic field generation system 2, a gradient magnetic field generation system 3, a transmission system 5, and A receiving system 6, a signal processing system 7, a sequencer 4, and a central processing unit (CPU) 8 are provided.
- a static magnetic field generation system 2 a gradient magnetic field generation system 3
- a transmission system 5 a transmission system 5
- a receiving system 6 a signal processing system 7, a sequencer 4, and a central processing unit (CPU) 8 are provided.
- the static magnetic field generation system 2 generates a uniform static magnetic field in the space around the subject 1 in the body axis direction or in a direction orthogonal to the body axis.
- a normal or superconducting magnetic field generating means is provided.
- the gradient magnetic field generation system 3 includes a gradient magnetic field coil 9 wound in three axial directions of X, Z, and Z, and a gradient magnetic field power supply 10 for driving the respective gradient magnetic field coils 9. . Then, the gradient magnetic field power supplies 10 of the respective coils are driven in accordance with a command from the sequencer 4 described later to apply the gradient magnetic fields Gz, GY, and Gx in three directions of X, ⁇ , and Z to the subject 1.
- a slice selection gradient field pulse (Gz) is applied in one of the X, ⁇ , and Z directions to set a slice plane for the subject 1, and the phase is set in the remaining two directions.
- Gz slice selection gradient field pulse
- GY encoding gradient magnetic field pulse
- Gx frequency encoding gradient magnetic field pulse
- the sequencer 4 is control means for repeatedly applying a high-frequency magnetic field pulse (hereinafter, referred to as “RF pulse”) and a gradient magnetic field pulse in a predetermined pulse sequence.
- RF pulse high-frequency magnetic field pulse
- the sequencer 4 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.
- the sequencer 4 includes means for performing measurement while changing the output of the RF pulse.
- the transmission system 5 irradiates the subject 1 with an RF pulse in order to cause nuclear spin of atoms constituting the living tissue of the subject 1 to generate nuclear magnetic resonance. It includes a modulator 12, a high-frequency amplifier 13, and a high-frequency coil 14a on the transmission side.
- the high-frequency signal 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. It is supplied to the high-frequency coil 14a placed close to the subject 1. As a result, the subject 1 is irradiated with the RF pulse.
- the receiving system 6 detects an echo signal (NMR signal) emitted by nuclear magnetic resonance of nuclear spins constituting the living tissue of the subject 1, and includes a high-frequency coil 14b on the receiving side, an amplifier 15 , An orthogonal phase detector 16 and an AZD converter 17.
- NMR signal nuclear magnetic resonance of nuclear spins constituting the living tissue of the subject
- a response MR signal from the subject 1 induced by the RF noise emitted from the high-frequency coil 14a on the transmitting side is detected by the high-frequency coil 14b arranged close to the subject 1. Then, the detected MR signal is amplified by an amplifier 15 and then divided into two orthogonal signals by a quadrature phase detector 16 at a timing according to a command from the sequencer 4. The signal is converted into a digital quantity and sent to the signal processing system 7.
- the signal processing system 7 includes an external storage device such as an optical disk 19 and a magnetic disk 18, and a display 20 including a CRT or the like.
- an external storage device such as an optical disk 19 and a magnetic disk 18, and a display 20 including a CRT or the like.
- the CPU 8 executes processing such as signal processing and image reconstruction, and displays the resulting tomographic image of the subject 1 on the display 20, and also stores the tomographic image in the external storage. Record on magnetic disk 18 etc. of device
- the high-frequency coils 14 a and 14 b on the transmitting side and the receiving side and the gradient magnetic field coil 9 are placed in the static magnetic field space of the static magnetic field generating system 2 into which the subject 1 is inserted. Installed facing Sample 1.
- an MRI apparatus for example, USP5553619
- a contrast medium injection means as shown in FIGS. 5A and 5B is provided.
- the nuclide to be imaged by the MRI apparatus is a hydrogen nucleus (proton), which is a main constituent substance of a subject, as being widely used clinically.
- proton a hydrogen nucleus
- the morphology or function of the human head, abdomen, limbs, etc. can be imaged in two or three dimensions.
- FIG. 6 is a diagram showing a gradient echo pulse sequence of the orthogonal sampling method.
- RF, Gz, GY, Gx, and Echo shown in FIG. 6 represent the axes of the RF pulse, the slice gradient magnetic field, the phase encoding gradient magnetic field, the frequency encoding gradient magnetic field, and the echo signal, respectively.
- 501 is RF noise
- 502 is a slice selection gradient magnetic field pulse
- 503 is a slice coil.
- 504 is a phase encoding gradient magnetic field pulse
- 505 is a frequency encoding gradient magnetic field pulse
- 506 is an echo signal.
- the RF pulse 501 is applied while the slice selection gradient magnetic field 502 is applied to select the three-dimensional volume, and then the slice encode gradient magnetic field pulse is applied.
- the number of slice encodes is selected to be a value such as 8, 16, 32, or 64
- the number of phase encodes is generally selected to be a value such as 64, 128, 256, or 512 per image.
- Each echo signal is usually obtained as a time-series signal composed of 128, 256, 512, and 1024 sampling data. These data are subjected to three-dimensional Fourier transform to create a three-dimensional image.
- the slice encode gradient magnetic field 503 and the slice encode gradient magnetic field 503 are set so that the application amount of the slice encode amount and the phase encode amount becomes 0 (zero) between TRs.
- a gradient magnetic field 510 of opposite polarity, a phase encoding gradient magnetic field 504 and a gradient magnetic field 511 of opposite polarity are applied, and at the same time, a spoiler 512 for dispersing the phase of transverse magnetization in the frequency encoding direction is applied.
- the phase of the RF pulse 501 is also changed by a fixed amount for each application.
- the amount of gradient magnetic field applied between TRs becomes constant in each axis, and if the repetition time TR is shorter than the magnetization relaxation time Tl of the region to be imaged, ⁇ 2, the magnetization of that region Becomes steady state
- the boiler 512 is inserted in the frequency encoding direction and the amount of the gradient magnetic field between TRs is not set to 0 (zero) in the frequency encoding direction, the contrast of the obtained image is 12 without emphasis. It becomes an emphasized image. This is because when the gradient magnetic field is set to 0 (zero) in the frequency encoding direction between TRs, the image becomes a ⁇ 2-weighted image, which is unsuitable for contrast MRA. This is to avoid the situation.
- the gradient magnetic fields 510 and 511 are applied corresponding to the gradient magnetic fields 503 and 504, respectively, so as to have a constant amount between TRs as in the case of a number encoding gradient magnetic field, a steady state is achieved and obtained.
- the image is a T1-weighted image suitable for contrast MRA.
- a gradient magnetic field that is, a gradient moment nulling for rephase. It is preferable to use a gradient echo.
- the contrast MRA will be briefly described.
- the blood containing the contrast agent can be visualized with a high signal by combining the Td-shortened contrast agent such as Gd-DTPA with the gradient echo system sequence of TR and TR.
- Td-shortened contrast agent such as Gd-DTPA
- the gradient echo system sequence of TR and TR the gradient echo system sequence of TR and TR.
- 3DMR—DSA Digital SubTRaction Angiography
- blood ejected from the heart circulates from the artery to each tissue, returns to the vein, and circulates from the heart to the lungs.
- blood pumped through the heart first contrasts the arterial system, and then the venous system is visualized via the capillaries.
- the subject 1 is placed in a measurement space in the static magnetic field generation system, an imaging region including a target blood vessel is determined, and a timing at which the concentration of the contrast agent reaches a peak in the target blood vessel is detected. To perform timing imaging.
- Test injection method A small amount of a contrast agent (about 11 to 2 ml) is test-injected into the subject 1 to obtain a time-signal curve at the target site, from which the arrival time of the contrast agent is determined. measure. Then, the main imaging is performed based on the result. In other words, the main imaging is started after the arrival time after the injection of the contrast agent for the main imaging.
- This method (M-1) generates a slight contrast of the background tissue by using a contrast agent prior to the main imaging, but at a level that does not cause a serious problem. The merit obtained by measuring is greater.
- the main imaging is performed after an appropriate time after the timing is acquired.
- (M-2) Fluoroscopic trigger method A region of interest (ROI) is set in a specific region within a monitor region, and real-time continuous imaging (fluoroscopic imaging) of the region is performed. Capture the signal change of the ROI. Then, when the signal value of the ROI exceeds a preset threshold value, the main imaging of the target part is automatically started (that is, an automatic trigger).
- ROI region of interest
- fluoroscopic imaging fluoroscopic imaging
- the target blood vessel is observed while performing real-time continuous imaging, and when an appropriate signal rise is obtained, the start of the main imaging of the target blood vessel is instructed via a user interface such as a keyboard. (That is, a manual trigger).
- Either a method of starting main imaging when the threshold value is exceeded (automatic trigger) or a method of instructing the start of main imaging when an appropriate signal rise is obtained (manual trigger) may be used.
- the main imaging is performed immediately after acquiring the imaging timing.
- measurement is continuously performed at the same slice or slab (that is, an imaging area in the slice direction in three-dimensional imaging).
- an arbitrary imaging sequence for example, it is preferable to use a two-dimensional sequence for timing imaging and a three-dimensional gradient echo method for main imaging.
- the measurement is started so that the measurement of the center data in the k-space is adjusted when the contrast agent concentration peaks in the target blood vessel.
- the k-space scanning method at this time may be a sequential system or a centric system.
- the sequential k-space scanning method uses a k-space ky-axis (phase encoding) direction from one high spatial frequency end to the other high spatial frequency end.
- the data in the central region of k-space (that is, the low spatial frequency region) mainly determines the contrast of the image, and the data in the high spatial frequency region mainly determines the contour (sharpness) of the image.
- a kz axis corresponding to slice encoding is added to a two-dimensional k space.
- the sequential or centric k-space running method in the ky-axis direction can be applied to the kz-axis direction.
- the optimal setting of the flip angle which is the first embodiment relating to the optimal imaging condition setting of the present invention, will be described.
- the blood at the target site is The flip angle is controlled so that the echo signal intensity increases according to the contrast agent concentration change in the tube.
- the echo signal is measured by controlling the flip angle so that the flip angle becomes the Ernst angle or close to the Ernst angle.
- the cardiac output of a general adult is about 5.51 / min, or about 97 ml / s, and the undiluted contrast medium is 500 mmol / ml.
- the estimated maximum concentration (concentration at peak) of the contrast agent in is estimated to be about 5 mmol / ml.
- the time-dependent change in concentration in the blood vessel after the injection of the contrast agent changes over time, for example, as shown in Fig. 2 (a).
- the time change b (t) is expressed by the following equation. Estimated in (2).
- these constants are obtained by test imaging based on the test injection method (M-1) performed before main imaging, for example, because individual differences between subjects are not small.
- the values of the constants ⁇ , C, C, and C may be determined for each individual from the actual contrast agent concentration change for each individual (that is, the signal intensity change at each elapsed time).
- a plurality of images reflecting the contrast agent concentration change obtained by the test imaging are temporarily stored in an external storage device or the like of the signal processing system 7.
- the CPU 8 calculates and estimates the contrast agent concentration at an arbitrary elapsed time based on the equation (2). I do.
- the T1 value of the lumen of the blood vessel into which the contrast agent has been injected can be calculated by the following equation (3).
- the T1 of the blood vessel lumen after contrast with respect to the time change of the contrast agent concentration can be obtained.
- the ability to estimate the value S is possible.
- a flip angle for maximizing an echo signal is called an Ernst angle.
- This Ernst angle ⁇ can be calculated by the following equation (4).
- TR is the repetition time
- T1 is the T1 value of the blood vessel lumen.
- FIG. 3 is a graph showing the relationship between the flip angle (horizontal axis) and the signal intensity (vertical axis) when the contrast agent concentration value is changed.
- the flip angle at which the signal intensity becomes maximum is the Ernst angle FA. Is
- the Ernst angle of the contrast agent concentration b3 is FA3
- the Ernst angle of the contrast agent concentration b2 is FA2
- the Ernst angle of the contrast agent concentration bl is FA1.
- Contrast agent concentration is lowest in bl, highest in b3, highest in Ernst angle FA1, highest in FA3.
- the signal intensity S1 of the Ernst angle FA1 of the contrast agent concentration bl is smaller than the signal intensity S2 of the Ernst angle FA2 of the contrast agent concentration b2.
- This signal intensity S2 is the signal intensity of the Ernst angle FA3 of the contrast agent concentration b3. Less than S3.
- the estimated T1 value after contrast obtained by equation (3) is used as T1 in equation (4).
- the Ernst angle following the time-dependent change in the concentration of the contrast agent in the blood vessel of the target site after the injection of the contrast agent into the subject can be estimated by following the contrast agent concentration.
- a method of estimating a flip angle that maximizes signal intensity following a contrast agent concentration is applied to three-dimensional contrast MRA measurement. That is, the actual flip angle is controlled so as to be the time change (t) of the flip angle calculated by the above equation (4) and the like.
- FIG. 2B is a graph showing the manner in which the flip angle is controlled by following the temporal change b (t) of the estimated contrast agent concentration b shown in FIG. 2A.
- the vertical axis represents the lip angle (FA1 ⁇ FA3)
- the horizontal axis represents the elapsed time t common to FIG. 2A.
- a curve 102 shows an example in which the flip angle is changed according to the contrast agent concentration according to the first embodiment of the present invention, and a straight line 101 is different from the present invention.
- An example is shown in which the flip angle irrespective of the change in the contrast agent concentration is fixed to, for example, FA3.
- the contrast agent concentration gradually increases according to a (t) calculated by the equation (4), and the period Da increases.
- the flip angle increases following the contrast agent concentration (FA1 ⁇ FA2 ⁇ FA3).
- the contrast agent concentration reaches its peak, it gradually decreases, and during the period Db (time t2-13), the flip angle is gradually reduced following the decreasing contrast agent concentration (FA3 ⁇ FA2). That is, the method of changing the flip angle is changed according to the concentration of the contrast agent.
- the sequencer 4 includes a high-frequency oscillator 11, a modulator 12, and a high-frequency amplifier 13 of the transmission system 5. To apply an RF pulse corresponding to the Ernst angle notified from the CPU 8 from the high-frequency coil 14a to the subject.
- FIGS. 4A and 4B are diagrams illustrating an example of the signal intensity obtained when the flip angle is controlled according to the contrast agent concentration.
- Fig. 4 (a) shows the time change of the contrast agent concentration
- Fig. 4 (b) follows the change of the contrast agent concentration in the blood vessel, and as shown in Fig. 2 (b), the flip angle. This shows the time change of the signal intensity obtained when is changed so as to always be close to the Ernst angle.
- a curve 111 is a time change of the signal intensity obtained by the conventional method without controlling the flip angle, and a curve 112 controls the flip angle according to the first embodiment of the present invention. It is a time change of the signal strength obtained by the method.
- the center data of the k-space is acquired when the contrast agent concentration reaches a peak.
- the signal intensity from a stationary region other than the target blood vessel changes in accordance with the change in the flip angle.
- difference processing is performed between images before and after contrast or temporally consecutive to remove tissues other than blood vessels, and a difference image that depicts only blood vessels is used. Therefore, since the change in the signal strength of the stationary portion is canceled by this difference processing, there is no particular problem.
- the TR is fixed and the flip angle is controlled to be the Ernst angle in accordance with the change in the contrast agent concentration.
- the second embodiment of the present invention controls the TR while fixing the flip angle.
- the flip angle is controlled to be the Ernst angle.
- the higher the contrast agent concentration the shorter T1 is. Therefore, according to the above equation (4), in order to keep the Ernst angle constant, the T1 is reduced during the period in which the contrast agent concentration increases. Shorten TR according to. Then, during the period in which the concentration of the contrast agent decreases, T1 is extended in reverse. Therefore, TR is lengthened in accordance with the extension of T1.
- the signal strength from a stationary region other than the intended blood vessel also changes with the change in the TR. This is because, as in the case of the first embodiment in which the flip angle is changed, since the difference image is used and TR is not changed abruptly, the influence of the change in the signal strength of the static area force is practically small. Therefore, there is no problem on the image.
- FIGS. 5A and 5B show examples of signal intensities obtained when TR is controlled to follow a contrast agent concentration according to the second embodiment of the present invention.
- FIG. 5 (a) shows the estimated contrast agent concentration change b (t) in the blood vessel in FIG. 2 (a).
- Fig. 5 (b) shows the time change of the signal intensity obtained when TR is changed to follow the contrast agent concentration change so that the constant flip angle is always equal to or close to the Ernst angle.
- the vertical axis in FIG. 5 (b) indicates the TR value, and the horizontal axis indicates the time corresponding to FIG. 5 (a).
- a straight line 201 in FIG. 5 (b) is a time change of the signal strength obtained by the conventional method without controlling the TR
- a curve 202 is a method for controlling the TR according to the second embodiment of the present invention. This is the time change of the signal strength obtained by the above.
- Specific control of the TR is performed by the sequencer 4 shown in FIG. That is, similarly to the first embodiment in which the flip angle is changed, the T1 value of the desired blood vessel lumen after the contrast is obtained, and the obtained T1 value is used to calculate the T1 value from the above equation (4).
- the sequencer 4 is notified of the TR at which the predetermined flip angle becomes the Ernst angle.
- the sequencer 4 controls a predetermined pulse sequence so that the repetition time interval becomes the calculated TR.
- the flip angle may be increased and the TR may be decreased following the increase in the concentration of the contrast agent.
- the flip angle may be reduced and TR may be increased in accordance with the decrease in the contrast agent concentration.
- a high-density period around the estimated contrast agent concentration including the peak time and a low-density period other than the high-density period are set. TR control is performed, and flip angle control is performed during a low concentration period.
- the high-density period is a period during which data near the center of the k-space is acquired, and therefore, in order to acquire a large amount of data, the shorter the TR period, the better. Therefore, TR control is performed so that the TR during the high concentration period is shorter than the TR during the low concentration period, and the flip angle becomes the Ernst angle.
- FIG. 7 indicates TR or FA (here, the TR control period is FA-constant, and the FA control period is TR-constant), and the horizontal axis is the elapsed time.
- TR the period of time tl-tla at the time point (b) in Fig. 7 is the first half of the low concentration period, as shown by the curve 701, TR is constant, and the value calculated by the above equation (4) is used. According to (t), the flip angle is controlled so as to follow the contrast agent concentration so that the flip angle becomes the Ernst angle.
- the third embodiment is an example in which different shooting parameters are changed during shooting.
- the determination of switching from the flip angle control to the TR control is made after switching from the flip angle control to the TR control for a certain period of time after the start of the measurement window, and further, after a predetermined time, from the TR control to the flip angle. Switching to control can be performed.
- a threshold may be set for the estimated contrast agent concentration, a period longer than the threshold may be defined as a high concentration period, and a period shorter than the threshold may be defined as a low concentration period.
- This threshold can be, for example, 80% of the peak value of the estimated contrast agent concentration.
- the signal intensity is monitored, flip angle control is performed until the monitored signal intensity reaches a constant value close to the peak, and switching to TR control is performed when the signal intensity reaches a constant value. It is also possible to do. Then, when the signal strength falls below a certain value, switch to flip angle control.
- TR control is performed in the high-density period and flip-angle control is performed in the low-density period.
- flip-angle control is performed in the high-density period.
- the TR control may be performed during the low concentration period.
- the value of the imaging parameter is changed in the opposite direction before and after the peak time of the contrast agent density.
- TR control TR is decreased until the peak time is reached, and TR is increased from the peak time.
- flip angle control the flip angle is increased until the peak point is reached, and the flip angle is decreased from the peak point.
- the value of the imaging parameter is monotonously decreased or increased.
- TR control TR is decreased during the concentration increase period before the peak time, and TR is increased during the concentration decrease period after the peak time.
- flip angle control In the density increase period, the flip angle is increased, and in the density decrease period after the peak point, the flip angle is reduced.
- the TR value may be changed to be convex downward around the peak point of the contrast agent concentration, and the flip angle value may be changed to be convex upward.
- the TR may be decreased while increasing the flip angle in the concentration increasing period before the peak time, and the flip angle may be decreased and TR may be increased in the concentration decreasing period after the peak time.
- the flip angle in the period from the high concentration period tla-t2b to the time tla-t2b is set to a fixed value, and the low concentration period t1-tla and t2b-13
- the flip angle in the period up to is set to another value.
- the flip angle during the high density period is set to a constant value larger than the flip angle during the low density period.
- TR during the period from the time tla to t2b, which is a high concentration period is set to a constant value, and the time from the time tl to tla, t2b-3, which is a low concentration period, is set.
- Set TR for the period is set to another value.
- the TR during the high concentration period is set to be shorter than the TR during the low concentration period. Note that the flip angle control described above may be performed with the flip angle set as described above.
- the flip angle or the value of TR as the first imaging parameter is changed before and after the peak time of the contrast agent concentration, in the opposite direction of small or large.
- the TR or flip angle value as the second photographing parameter can be monotonically increased or decreased.
- the fourth and fifth embodiments may be performed simultaneously, and the flip angle and TR may be set to different constant values during the high density period and the low density period.
- the TR during the high concentration period near the peak of the estimated contrast agent concentration is defined as a fixed period shorter than the TR during the other low concentration periods. It is also possible to perform flip angle control over the dough period. Or conversely, the flip angle during the high concentration period is set to a constant angle larger than the flip angle during the low concentration period, TR control may be performed over a period.
- the TR value and the flip angle value are displayed on the display screen as shown in FIG. It can display S power.
- the example shown in Fig. 8 is an example in which the average value of TR and the average value of flip angles are displayed together with the captured blood vessel image.
- the TR, the maximum value, the minimum value, the mode value of the flip angle, and the value at the time of measuring the center data in the k-space can also be displayed. Further, it is also possible to display a plurality of these together.
- the density of the contrast agent is increased during a period of time until the concentration reaches a peak. It is also possible to change the TR and change the flip angle during the concentration reduction period after the contrast agent concentration peaks.
- TR is decreased in the low-density period in the first half, and TR is decreased in the high-density period during the decreasing process. It is also possible to keep the closing price constant and to increase TR in the latter half of the low concentration period.
- the flip angle may be increased in the first half of the low density period, the flip angle may be fixed at the final value of the increasing process in the high density period, and the flip angle may be decreased in the second half of the low density period.
- the MRI apparatus according to the present invention is applicable not only to the vertical magnetic field method but also to the horizontal magnetic field method.
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Abstract
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JP2005514572A JP4807833B2 (ja) | 2003-10-07 | 2004-10-05 | 磁気共鳴イメージング装置及びこれを用いた造影アンジオグラフィー法 |
US10/575,159 US7467006B2 (en) | 2003-10-07 | 2004-10-05 | Magnetic resonance imaging system and contrast-enhanced angiography |
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JP2008538972A (ja) * | 2005-04-26 | 2008-11-13 | コーニンクレッカ フィリップス エレクトロニクス エヌ ヴィ | 時間変調されたコントラストの向上を備えた造影剤を伴うmri |
US8581585B2 (en) | 2008-02-12 | 2013-11-12 | Hitachi Medical Corporation | Magnetic resonance imaging apparatus, initial state creation method, optimum intensity determination method, and magnetic resonance imaging method |
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JPWO2005034749A1 (ja) | 2007-11-22 |
US20070078333A1 (en) | 2007-04-05 |
US7467006B2 (en) | 2008-12-16 |
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