WO2014126134A1 - 磁気共鳴イメージング装置及び不要コントラスト低減方法 - Google Patents
磁気共鳴イメージング装置及び不要コントラスト低減方法 Download PDFInfo
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- 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
- G01R33/561—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution by reduction of the scanning time, i.e. fast acquiring systems, e.g. using echo-planar pulse sequences
- G01R33/5615—Echo train techniques involving acquiring plural, differently encoded, echo signals after one RF excitation, e.g. using gradient refocusing in echo planar imaging [EPI], RF refocusing in rapid acquisition with relaxation enhancement [RARE] or using both RF and gradient refocusing in gradient and spin echo imaging [GRASE]
- G01R33/5617—Echo train techniques involving acquiring plural, differently encoded, echo signals after one RF excitation, e.g. using gradient refocusing in echo planar imaging [EPI], RF refocusing in rapid acquisition with relaxation enhancement [RARE] or using both RF and gradient refocusing in gradient and spin echo imaging [GRASE] using RF refocusing, e.g. RARE
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- 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
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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
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
- G01R33/36—Electrical details, e.g. matching or coupling of the coil to the receiver
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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
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
- G01R33/385—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using gradient magnetic field coils
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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
- G01R33/4818—MR characterised by data acquisition along a specific k-space trajectory or by the temporal order of k-space coverage, e.g. centric or segmented coverage of k-space
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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
- G01R33/543—Control of the operation of the MR system, e.g. setting of acquisition parameters prior to or during MR data acquisition, dynamic shimming, use of one or more scout images for scan plane prescription
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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
- G01R33/5602—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution by filtering or weighting based on different relaxation times within the sample, e.g. T1 weighting using an inversion pulse
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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
- G01R33/546—Interface between the MR system and the user, e.g. for controlling the operation of the MR system or for the design of pulse sequences
Definitions
- 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.
- ⁇ NMR '' nuclear magnetic resonance
- the present invention relates to image contrast adjustment technology.
- the MRI device measures NMR signals generated by the spins of the subject, especially the tissues of the human body, and visualizes the form and function of the head, abdomen, limbs, etc. in two or three dimensions Device.
- the NMR signal is given different phase encoding depending on the gradient magnetic field, frequency-encoded, and measured as time series data.
- the measured NMR signal is reconstructed into an image by two-dimensional or three-dimensional Fourier transform.
- FSE Fast Spin Echo
- FSE applies multiple refocusing RF pulses (refocus RF pulse; 180 degree pulse) to one excitation RF pulse (90 degree pulse) to obtain multiple echoes (echo train) to reduce imaging time.
- This is a shortened imaging method.
- Such an imaging method is called multi-echo imaging.
- T2 transverse relaxation time
- VRFA Variable Refocus Flip Angle
- the signal strength is prolonged by changing the FA appropriately so that the echo signal also has a component of longitudinal magnetization.
- Longitudinal magnetization is recovered at the longitudinal relaxation time T1, but is attenuated at T1 when a component contributing to the generation of an echo signal in the echo train is considered. This is referred to herein as T1 attenuation. Since T1 is sufficiently longer than T2 in many tissues, the attenuation in the echo train can be slowed by providing a longitudinal magnetization component in VRFA.
- T1 and T2 Relaxation times T1 and T2 are specific to the organization and are determined by the organization. Using this, there are T1-weighted (T1W) imaging that images the difference in relaxation time T1 (T1 contrast) of two different tissues, and T2-weighted (T2W) imaging that images the difference between T2 (T2 contrast) .
- T1W T1-weighted
- T2W T2-weighted
- T1-weighted imaging that images the difference in relaxation time T1 (T1 contrast) of two different tissues
- T2W T2-weighted imaging that images the difference between T2 (T2 contrast) .
- T1-weighted images it is important to maximize T1 contrast and reduce T2 contrast.
- T2-weighted image it is necessary to maximize the T2 contrast and reduce the T1 contrast.
- VRFA since the echo signal also has a component of longitudinal magnetization, the change in signal intensity in the echo train is caused by T1 attenuation in addition to that due to T2 attenuation, and both effects are mixed. Therefore, in VRFA, TE affects both T1 contrast and T2 contrast.
- VRFA is a technique intended to make the echo train as long as possible. However, if the echo train is made too long, T2 attenuation within the echo train will affect the T2 contrast. Therefore, the length of the echo train is also limited in this respect.
- Patent Document 1 is to increase only T1 contrast or to create contrast close to T1 contrast using the influence of T2, and consider that T2 contrast is reduced by T1 weighted imaging. Not a thing. Therefore, with the technique disclosed in Patent Document 1, it is considered difficult to obtain a normal T1 contrast for various tissues.
- the second issue is the mixing of T1 contrast in T2 weighted imaging. Since the relaxation time T1 is longer than the lateral relaxation time T2, in general, a change in contrast due to the influence of T1 attenuation is not regarded as important in T2-weighted imaging. In practice, however, this change cannot be ignored.
- the FA of the refocus RF pulse can be adjusted so that the conventional T2 contrast can be obtained even when T1 attenuation and T2 attenuation are mixed.
- these time constants T1 and T2 are different for each imaging target tissue. For this reason, it is difficult to adjust in consideration of a combination of infinite time constants T1 and T2. For example, adjustments to normal tissue may not be effective for imaging with contrast agents.
- the present invention has been made in view of the above circumstances, and is a multi-echo imaging that reduces unnecessary contrast and enhances the intended contrast in imaging including refocus RF pulses other than 180-degree pulses.
- the purpose is to obtain quality images.
- the present invention adjusts the imaging parameters so that unnecessary contrast is reduced. Adjustment is performed with a small difference in the signal strength of the echo signal that determines the contrast, such as the center of k-space, for echo signals from multiple tissues with different relaxation times that produce the intended contrast. Do so.
- the imaging parameters to be adjusted are the repetition time, the DE pulse FA, the saturation pulse FA, the saturation pulse application timing, the gradient magnetic field application intensity during the recovery period, the application timing, and the like.
- the adjusted imaging parameters that reduce the effects of T1 attenuation and T2 attenuation are presented to the user so that the user can refer to the contrast adjustment.
- the present invention in multi-echo imaging, in which imaging is affected by both T1 relaxation and T2 attenuation, it is possible to reduce unnecessary contrast and obtain a high-quality image that emphasizes intended contrast. it can.
- Block diagram of the MRI apparatus of the first embodiment Functional block diagram of the control unit of the first embodiment Pulse sequence diagram of the FSE sequence of the first embodiment Explanatory drawing for demonstrating an example of FA change shape of 1st embodiment (a) And (b) is explanatory drawing for demonstrating the imaging parameter input screen of 1st embodiment.
- Explanatory drawing for demonstrating the adjustment process of 1st embodiment (a) and (b) are explanatory diagrams for explaining specific examples of parameter adjustment.
- Flow chart of imaging processing of the first embodiment Flow chart of parameter adjustment processing of the first embodiment
- summary of an adjustment process in case adjustment parameter is the application timing of a saturation pulse in 1st embodiment.
- summary of an adjustment process in case the adjustment parameter is a combination of a some imaging parameter in 1st embodiment.
- Flowchart of parameter adjustment processing when there are a plurality of relaxation times to consider in the first embodiment Explanatory drawing for demonstrating the specific example of parameter adjustment when there are multiple relaxation times to consider in the first embodiment Explanatory drawing for demonstrating the adjustment process of 2nd embodiment.
- (a) And (b) is explanatory drawing for demonstrating the adjustment process of 2nd embodiment.
- Explanatory drawing for demonstrating the adjustment process in case the adjustment parameter is made into the flip angle of DE pulse in 2nd embodiment.
- the flowchart of the imaging process of the modification of embodiment of this invention Explanatory drawing for demonstrating the adjustment process of the modification of embodiment of this invention
- FIG. 1 is a block diagram showing the overall configuration of the MRI apparatus 100 of the present embodiment.
- the MRI apparatus 100 of the present embodiment obtains a tomographic image of the subject 101 using the NMR phenomenon, and as shown in FIG. 1, is disposed in a static magnetic field and a static magnetic field generator 120 that generates a static magnetic field.
- the subject 101 generates a gradient magnetic field generator 130 that applies a gradient magnetic field to the subject 101, a transmitter 150 that transmits a high-frequency magnetic field pulse that excites the magnetization of the subject 101 at a predetermined flip angle, and the subject 101.
- a receiving unit 160 that receives an echo signal, and a control unit that reconstructs an image from the echo signal received by the receiving unit 160 and controls operations of the gradient magnetic field generating unit 130, the transmitting unit 150, and the receiving unit 160 according to an imaging sequence 170 and a sequencer 140.
- the static magnetic field generator 120 generates a uniform static magnetic field in the direction perpendicular to the body axis in the space around the subject 101 if the vertical magnetic field method is used, and in the body axis direction if the horizontal magnetic field method is used.
- the apparatus includes a permanent magnet type, normal conducting type or superconducting type static magnetic field generating source disposed around the subject 101.
- the gradient magnetic field generation unit 130 includes a gradient magnetic field coil 131 wound in the three-axis directions of X, Y, and Z, which is a coordinate system (device coordinate system) of the MRI apparatus 100, and a gradient magnetic field power source that drives each gradient magnetic field coil 132 and drive gradient magnetic field power supply 132 of each gradient coil 131 in accordance with a command from sequencer 140, which will be described later, to apply gradient magnetic field pulses Gx, Gy, Gz in the three axis directions of X, Y, and Z To do.
- the gradient magnetic field pulses Gx, Gy, and Gz are applied in the direction orthogonal to the slice plane (imaging cross section) at the time of imaging, respectively, and the role of setting the slice plane for the subject 101 is orthogonal to the set slice plane, In addition, there is a role of applying the information in the remaining two directions orthogonal to each other and encoding position information in two directions into the NMR signal (echo signal).
- the gradient magnetic field pulse applied to set the slice plane is called the slice direction gradient magnetic field pulse (Gs), and the gradient magnetic field pulses applied in the other two directions are respectively the phase encoding direction gradient magnetic field pulses (Gp).
- the frequency encoding direction gradient magnetic field pulse (Gf) are applied in the direction orthogonal to the slice plane at the time of imaging, respectively, and the role of setting the slice plane for the subject 101 is orthogonal to the set slice plane, In addition, there is a role of applying the information in the remaining two directions orthogonal to each other and encoding position information in two directions into the NMR
- the transmitter 150 irradiates the subject 101 with a high-frequency magnetic field pulse (hereinafter referred to as “RF pulse”) in order to cause nuclear magnetic resonance to occur in the nuclear spins of the atoms constituting the biological tissue of the subject 101.
- RF pulse high-frequency magnetic field pulse
- the high frequency oscillator 152 generates an RF pulse and outputs it at a timing according to a command from the sequencer 140.
- the modulator 153 amplitude-modulates the output RF pulse, and the high-frequency amplifier 154 amplifies the amplitude-modulated RF pulse and supplies the amplified RF pulse to the transmission coil 151 disposed close to the subject 101.
- the transmission coil 151 irradiates the subject 101 with the supplied RF pulse.
- the receiving unit 160 detects a nuclear magnetic resonance signal (echo signal, NMR signal) emitted by nuclear magnetic resonance of the nuclear spin constituting the biological tissue of the subject 101, and receives a high-frequency coil (receiving coil) on the receiving side. 161, a signal amplifier 162, a quadrature detector 163, and an A / D converter 164.
- the reception coil 161 is disposed in the vicinity of the subject 101 and detects an NMR signal in response to the subject 101 induced by the electromagnetic wave irradiated from the transmission coil 151.
- the detected NMR signal is amplified by the signal amplifier 162 and then divided into two orthogonal signals by the quadrature phase detector 163 at the timing according to the command from the sequencer 140, and each is digitally converted by the A / D converter 164. It is converted into a quantity and sent to the controller 170.
- Sequencer 140 repeatedly applies RF pulses and gradient magnetic field pulses according to a predetermined pulse sequence.
- the pulse sequence describes the high-frequency magnetic field, the gradient magnetic field, the timing and intensity of signal reception, and is stored in the control unit 170 in advance.
- the sequencer 140 operates in accordance with an instruction from the control unit 170, and transmits various commands necessary for collecting tomographic image data of the subject 101 to the transmission unit 150, the gradient magnetic field generation unit 130, and the reception unit 160.
- the control unit 170 controls the entire MRI apparatus 100, performs operations such as various data processing, displays and stores processing results, and includes a CPU 171, a storage device 172, a display device 173, and an input device 174.
- the storage device 172 includes an internal storage device such as a hard disk and an external storage device such as an external hard disk, an optical disk, and a magnetic disk.
- the display device 173 is a display device such as a CRT or a liquid crystal.
- the input device 174 is an interface for inputting various control information of the MRI apparatus 100 and control information of processing performed by the control unit 170, and includes, for example, a trackball or a mouse and a keyboard.
- the input device 174 is disposed in the vicinity of the display device 173. The operator interactively inputs instructions and data necessary for various processes of the MRI apparatus 100 through the input device 174 while looking at the display device 173.
- the CPU 171 implements each process of the control unit 170 such as control of operations of each unit of the MRI apparatus 100 and various data processing by executing a program stored in advance in the storage device 172 according to an instruction input by the operator. .
- the CPU 171 executes processing such as signal processing and image reconstruction, and displays the tomogram of the subject 101 as a result on the display device 173.
- processing such as signal processing and image reconstruction, and displays the tomogram of the subject 101 as a result on the display device 173.
- it is stored in the storage device 172.
- the transmission coil 151 and the gradient magnetic field coil 131 are opposed to the subject 101 in the static magnetic field space of the static magnetic field generation unit 120 into which the subject 101 is inserted if the vertical magnetic field method is used, and if the horizontal magnetic field method is used. It is installed so as to surround the subject 101. Further, the receiving coil 161 is installed so as to face or surround the subject 101.
- the nuclide to be imaged by the MRI apparatus which is widely used clinically, is a hydrogen nucleus (proton) which is a main constituent material of the subject 101.
- the MRI apparatus 100 by imaging information on the spatial distribution of proton density and the spatial distribution of relaxation time in the excited state, the form or function of the human head, abdomen, limbs, etc. can be expressed two-dimensionally or three-dimensionally. Take an image.
- the imaging sequence from which the CPU 171 of the control unit 170 gives a control signal to the sequencer 140 includes a pulse sequence in which application timing of the RF pulse and gradient magnetic field pulse is determined, application intensity of the RF pulse and gradient magnetic field pulse, application timing, and the like. It is determined by the designated imaging parameter.
- the pulse sequence is preset and held in the storage device 172.
- the control unit 170 receives an imaging parameter from a user, and uses the imaging parameter and a pulse sequence stored in advance to create an imaging sequence used for imaging. And an imaging unit 720 that controls each unit and executes imaging in accordance with the created imaging sequence.
- the sequence creation unit 710 is realized by the CPU 171 loading a program previously stored in the storage device 172 into the memory and executing it.
- a pulse sequence for multi-echo imaging such as FSE is used as the pulse sequence.
- FSE pulse sequence for multi-echo imaging
- a case where an FSE pulse sequence is used will be described as an example.
- Fig. 3 shows the RF pulse application timing of the FSE pulse sequence 200 and the echo signal acquisition timing. As shown in this figure, in the FSE pulse sequence 200, execution of the intra-TR sequence 200a is repeated at every repetition time TR (Repetition Time).
- N is a natural number
- refocus RF pulses 202 are applied after one excitation RF pulse 201.
- Each applied refocus RF pulse 202 is represented as a refocus RF pulse 202 n (n is a natural number satisfying 1 ⁇ n ⁇ N).
- the subscript n is given in the order of application.
- the flip angle of the refocus RF pulse 202 n to be applied n-th is expressed as FA n .
- the flip angle FA n of the refocus RF pulse 202 n to be applied n-th is called the n-th FA.
- the echo signal 203 n is measured immediately after the n-th refocus RF pulse 202 n to be applied, and the echo number is n.
- the signal strength SS of each echo signal 203 n represents a SS n. Note that the signal strength SS used here ignores changes in strength due to various encodings.
- a refocus RF pulse 202 If there is no need to distinguish between them, they are referred to as a refocus RF pulse 202, a flip angle FA, an echo signal 203, and a signal intensity SS, respectively.
- a refocus RF pulse 202 a flip angle FA, an echo signal 203, and a signal intensity SS, respectively.
- FIG. 3 as an example, a case where six refocus RF pulses 202 are applied is illustrated.
- a DE pulse (Driven Equilibrium Pulse) 204 is applied.
- the DE pulse 204 is a pulse for returning the transverse magnetization remaining after the echo train to the longitudinal magnetization.
- a VRFA sequence 200 in which each flip angle FA n of the refocus RF pulse 202 is variable is used as a pulse sequence.
- the values of the flip angles FA n of the 1st to Nth refocus RF pulses 202 n arranged in order are referred to as FA change shape FAP, and the 1st to Nth echo signals 203 n those arranged signal strength SS n in order, called the signal intensity change shape SSP. That is, the FA variation shape FAP is composed of the flip angle FA for each refocus RF pulse 202, and the signal strength variation shape SSP is composed of the signal strength SS for each echo signal obtained for each refocus RF pulse 202.
- An example of the FA changing shape FAP is shown in FIG.
- the pulse sequence used in the present embodiment is not limited to the so-called VRFA sequence 200 in which FA gradually changes. Any pulse sequence may be used as long as the refocus RF pulse 202 includes an RF pulse with FA other than 180 degrees.
- the FA of all the refocus RF pulses 202 may be 150 degrees.
- the pulse sequence used in this embodiment is not limited to the FSE pulse sequence 200. This is a pulse sequence that applies multiple refocus RF pulses within the repetition time TR after applying an excitation RF pulse (90 degree pulse), and at least one flip angle of the refocus RF pulse is other than 180 degrees Any sequence may be used.
- the longitudinal magnetization is also changed by applying the refocus RF pulse 202. . Therefore, the influence of T1 attenuation (T1 contrast) and the influence of T2 attenuation (T2 contrast) are mixed.
- the sequence creation unit 710 of the present embodiment includes a parameter adjustment unit 711 that adjusts a predetermined imaging parameter to be adjusted to reduce unnecessary contrast, as shown in FIG.
- the parameter adjustment unit 711 is configured so that the first relaxation times for causing the intended contrast are equal, and the second relaxation times for causing the unnecessary contrast are in the k-space in the echo signals from the different tissues.
- the parameter to be adjusted is adjusted so that the difference in the signal intensity of the echo signal arranged at the center is reduced.
- the parameter adjustment unit 711 of this embodiment adjusts the adjustment parameter using the signal strength of the echo signal arranged at the center of the k space among the echo signals from a plurality of tissues having different combinations of T1 and T2.
- T2 is equal, the adjustment is performed so that the difference in signal strength is small even if T1 is different.
- the parameter adjustment unit 711 of the present embodiment adjusts the parameter to be adjusted in advance so as to reduce the influence of T1 attenuation (T1 contrast) that causes unnecessary contrast.
- T1 attenuation T1 contrast
- the parameter to be adjusted is called an adjustment parameter.
- the imaging parameter used as the adjustment parameter is at least one of a high-frequency magnetic field pulse and a gradient magnetic field applied during the recovery period from the application of the last refocus RF pulse 202 of the echo train to the application of the next excitation RF pulse 201.
- the RF pulse applied during the recovery period include a DE pulse 204 and a saturation pulse described later.
- the adjustment target application parameter of the DE pulse 204 and the saturation pulse is FA.
- the application timing is also an application parameter to be adjusted.
- the application parameters of the gradient magnetic field applied during the recovery period include strength and application timing. Note that the length of the recovery period from the end of the echo train to the next TR can be adjusted by adjusting the imaging parameter TR. Details of the adjustment will be described later.
- the sequence creation unit 710 of the present embodiment receives imaging parameters from the user, and causes the parameter adjustment unit 711 to adjust the adjustment parameters using the imaging parameters.
- the adjusted adjustment parameter (optimum value) may be automatically reflected in the imaging sequence, or may be only presented to the user.
- an approval instruction is received for the adjusted optimum value from the user, it may be reflected in the imaging sequence, or the adjustment parameter is only presented and further adjustment is accepted from the user. It may be configured.
- FIG. 5A shows an imaging parameter input screen 400 that is generated and displayed on the display device 173 when the sequence creation unit 710 accepts imaging parameters from the user.
- the imaging parameter input screen 400 receives an imaging parameter input from a user and displays a set parameter.
- the imaging parameter input screen 400 captures an image using an imaging parameter input via the imaging parameter setting area 410.
- a determination button 420 for receiving an instruction to start the operation.
- the imaging parameter setting area 410 includes an adjustment parameter input area 401 that receives an input of the adjustment parameter and an adjustment parameter display area 402 that displays an adjustment result. Further, a button (reflection button) 404 for reflecting the adjustment result may be provided.
- TR transmission button
- the sequence creation unit 710 when receiving an input of imaging parameters including adjustment parameters from the user via the imaging parameter setting area 410, causes the parameter adjustment unit 711 to adjust the adjustment parameters, and displays the adjustment results in the adjustment parameter display area 402. To display.
- the user looks at the display and decides whether to perform imaging using the adjusted parameter after adjustment or to change the adjustment parameter.
- imaging is performed using the displayed adjustment parameter after adjustment
- the value in the adjustment parameter display area 402 is input to the adjustment parameter input area 401.
- the sequence creation unit 710 generates an imaging sequence using the parameters set in the adjustment parameter input area 401 and other imaging parameters.
- the sequence creation unit 710 causes the parameter adjustment unit 711 to adjust the adjustment parameter every time a value is input to the adjustment parameter input area 401.
- the sequence creation unit 710 receives input of imaging parameters from the user via the imaging parameter setting area 410 and causes the parameter adjustment unit 711 to adjust the adjustment parameters.
- an imaging sequence is generated using the adjusted adjustment parameters and other imaging parameters.
- a contrast adjustment setting area 403 for designating a contrast adjustment method may be provided in the imaging parameter setting area 410 as shown in FIG. Good.
- the user designates the adjustment method via the contrast adjustment setting area 403 that designates the contrast adjustment method.
- the contrast adjustment method designated by the user is an image type to be acquired, such as T2-weighted image acquisition or T1-weighted image acquisition. For example, if it is desired to acquire a T2-weighted image, T2 or the like is designated. If a T1-weighted image is desired, T1 or the like is designated.
- T2 the sequence creation unit 710 causes the parameter adjustment unit 711 to adjust the imaging parameters so as to reduce the influence of T1.
- T1 the sequence creation unit 710 causes the parameter adjustment unit 711 to adjust the imaging parameters so as to reduce the influence of T2.
- TR may be configured to specify whether TR is automatically set or only the optimum TR is presented via the contrast adjustment setting area 403.
- the parameter adjustment unit 711 of the present embodiment uses the signal strength of the echo signal arranged at the center of the k space, among the echo signals from a plurality of tissues having different combinations of T1 and T2, to adjust the adjustment parameter. adjust.
- T2 the adjustment is performed so that the difference in signal strength is small even if T1 is different.
- FIG. 6 shows, as an example, a change in the magnitude of magnetization of two tissues A and B having the same T2 and different T1, the application timing of the RF pulse, and the acquisition timing of the echo signal. It is not necessary that such T1 and T2 organizations actually exist. It is an example for demonstrating the influence of T1 and T2. Similarly, the organization used in the following description is an example.
- the VRFA sequence 200 shown in FIG. 3 is used as the pulse sequence. As described above, the sequence to be used is not limited to the VRFA sequence 200. It is sufficient that the FA of at least one refocusing RF pulse 202 is a sequence other than 180 degrees.
- the longitudinal relaxation time T1A of the tissue A is shorter than the longitudinal relaxation time T1B of the tissue B (T1A ⁇ T1B).
- a solid line 301 indicates a change in the magnitude of the magnetization of the tissue A
- a broken line 302 indicates a change in the magnitude of the magnetization of the tissue B.
- the magnitude of magnetization shows only what contributes to the acquired echo signal.
- the change between 1TR when the VRFA sequence 200 is repeated sufficiently and it will be in a steady state is shown.
- both tissues A and B are refocused by the refocusing RF pulse 202 until the end of the echo train.
- the magnitudes 301 and 302 of the magnetization of the magnetic field change.
- the magnetization magnitude changes 301 and 302 include T1 attenuation corresponding to longitudinal magnetization caused by the fact that the FA of the refocus RF pulse 202 is not 180 degrees. This period is called an attenuation period (Tet1).
- the magnetization contributing to the acquired echo signal becomes longitudinal magnetization, and T1 recovers until the end of TR.
- This period is called a recovery period (Trecov).
- the recovered longitudinal magnetization contributes to the echo signal acquired in the next TR. That is, in the next TR, the change starts from the magnitude of the magnetization recovered at the end of the immediately preceding TR. Therefore, the degree of magnetization recovery during the recovery period can be adjusted, and the magnitude of magnetization at the end of TR can be made the optimum magnitude of magnetization at the start of subsequent TR.
- the optimum magnitude of magnetization at the end of TR is the timing of obtaining the k-space center that determines the contrast in the next TR at the timing of obtaining the magnetization of each tissue A and B.
- the magnitude (signal strength) is substantially equal.
- the parameter adjustment unit 711 sets the variance Scvar of each signal intensity Sc to a minimum (or as a state where the signal intensity Sc at the center of the k space in the steady state is approximately equal for each of the plurality of tissues having the same T2 and different T1. Adjust the adjustment parameter so that it becomes (minimum). That is, the parameter adjustment unit 711 of the present embodiment searches for an adjustment parameter that uses the variance Scvar as an objective function and minimizes (or minimizes) the objective function, and determines the optimum value.
- the adjustment parameter is TR
- the adjustment of TR is realized by adjusting a period from the application of the DE pulse 204 to the start of the next TR (recovery period Trecov).
- TR is the sum of the decay period (Tet1) from the excitation RF pulse 201 application to the DE pulse 204 application and the recovery period Trecov.
- the decay period Tet1 is fixed. Therefore, adjusting the recovery period Trecov means adjusting the TR.
- T1 (n) (n 1,2,3, ..., N), where T1 is equal to T2 and T1 is different (N is an integer greater than or equal to 2).
- the objective function is a variance Scvar of N Sc (n).
- the parameter adjustment unit 711 of this embodiment determines an adjustment parameter TR (here, Trecov) that minimizes (or minimizes) the objective function Scvar.
- the formula required for obtaining Sc (n) is shown below.
- the magnitude MTend of transverse magnetization at the end of echo train (immediately before applying DE pulse), the magnitude MLde of longitudinal magnetization after applying DE pulse 204, the magnitude MT0 of transverse magnetization immediately after excitation, and the signal intensity Sc (n) are as follows: These are divided into four formulas (1) to (4).
- MTend MT0 ⁇ Rend (n) (1)
- MLde MTend ⁇ sin (-FAde) ⁇ ⁇ ⁇ (2)
- MT0 1 ⁇ (1 ⁇ MLde) ⁇ exp ( ⁇ Trecov / T1 (n)) (3)
- Sc (n) MT0 ⁇ Rcent (n) (4)
- Rend (n) is the ratio of the magnitude of transverse magnetization at the end of the echo train to the start of the echo train when T1 is T1 (n), and the Bloch equation from FA, T1, and T2 of the refocus RF pulse 202 Can be obtained using FAde is the FA of the second pulse of the DE pulse 204.
- the phase is the same as that of the excitation pulse (negative when flipping back).
- Trecov is the time from the application of the DE pulse 204 to the next application of the excitation RF pulse 201 as described above.
- Rcent (n) is the ratio of the transverse magnetization at the time of k-space center collection to the transverse magnetization at the start of the echo train when T1 is T1 (n). It can be calculated from T1 and T2 using the Bloch equation. Note that the timing of collecting the echo signals arranged at the center of the k space can be arbitrarily changed by echo shift or the like.
- MT0 in the steady state is represented by Rend (n), FAde, Trecov, and T1 (n). Then, the obtained MT0 is substituted into Equation (4) to obtain Sc (n).
- the FA of the DE pulse 204 is set to 0, and the end of Tet1 and the start of Trecov are not the DE pulse but the last pulse of the echo train. Further, in the above example, the magnitude of the longitudinal magnetization MLend at the end of the echo train (immediately before application of the DE pulse 204) is set to 0 for simplicity.
- the longitudinal magnetization M1end at the end of the echo train add the longitudinal magnetization plate (1-1) of equation (1), and replace the equation (2-1) with the longitudinal magnetization component of MTend using equation (2-1). Also consider.
- RLend (n) and CLend (n) are coefficients when formulas representing changes in longitudinal magnetization in the echo train when T1 is T1 (n) are arranged with respect to MT0.
- the parameter adjustment unit 711 searches for an adjustment parameter that minimizes (minimizes) the objective function (Scvar) while changing the adjustment parameter TR (here, Trecov that determines TR).
- a general optimization method can be used for this search. For example, search for an adjustment parameter that minimizes (minimizes) the objective function using the steepest descent method with the adjustment parameter set by the user as the initial value, and minimizes (minimizes) the objective function while changing it according to the bisection method, etc.
- a technique such as searching for an adjustment parameter to be used can be used.
- a general method can be used for convergence determination. For example, it is possible to use a technique such as repeating the search a predetermined number of times (M times) or repeating the search until the change in the objective function is sufficiently small.
- the parameter adjustment unit 711 searches for an adjustment parameter that minimizes (minimizes) the objective function, and outputs TR determined by the search result as an adjustment result (optimum value).
- FIGS. 7 (a) and 7 (b) are diagrams for explaining a specific example of parameter adjustment, in which the signal intensity Sc at the center of the steady state k-space for each of the three tissues having the same T2 but different T1 only. It is a graph which shows the mode of the change by TR.
- FIG. 7 (a) is a graph showing changes in signal intensity of a tissue having T2 of 50 ms, and FIG.
- FIG. 7 (b) is a graph showing changes in signal intensity of a tissue having T2 of 100 ms.
- ETL number of echo trains
- IET echo interval
- the FA of the refocus RF pulse 202 was changed according to the FA changing shape FAP shown in FIG.
- the DE pulse 204 was not applied (FA was 0 degree).
- the TR (optimum value) that minimizes the Sc dispersion Scvar is about 1.75 seconds.
- the time is 1.85 seconds.
- FIG. 8 is a processing flow of the imaging process of the present embodiment.
- the sequence creation unit 710 only adjusts the imaging parameters and presents them to the user, and finally generates an imaging sequence with the imaging parameters set by the user.
- the imaging process starts by receiving a start instruction from the user.
- the sequence creation unit 710 displays the imaging parameter input screen 400 on the display device 173 (step S1101) and waits for input by the user.
- the parameter adjustment unit 711 performs parameter adjustment processing for adjusting a predetermined adjustment parameter using the above method (step S1103). For example, when the adjustment parameter is TR and T2 enhancement is designated as the imaging parameter for setting the adjustment method, the optimum TR for reducing the T1 contrast is determined.
- the sequence creation unit 710 displays the adjustment result (optimum value) by the parameter adjustment unit 711 (step S1104).
- the image is displayed in the adjustment parameter display area 402 of the imaging parameter input screen 400.
- the sequence creation unit 710 waits for and accepts an imaging start instruction from the user via the imaging parameter input screen 400 (step S1105), and creates an imaging sequence using the imaging parameters at that time (step S1106). . Then, the imaging unit 720 performs imaging according to the imaging sequence (step S1107).
- step S1105 when receiving an input such as a change in imaging parameter from the user during standby, the sequence creation unit 710 returns to step S1102 and repeats the process. In this way, the user can change the adjustment parameter with reference to the optimum value of the displayed adjustment parameter until the user gives an instruction to start imaging.
- FIG. 9 is a processing flow of parameter adjustment processing of the present embodiment.
- the target imaging parameter is TR.
- the adjustment parameter is updated M times.
- the adjustment function updated i times is represented by TR (i) and the objective function Scvar obtained by TR (i) is represented by f (TR (i)).
- ⁇ f (TR (i)) is f (TR (i) + h) ⁇ f (TR (i)).
- h is a sufficiently small value and is determined appropriately so that it can be performed well by the steepest descent method. For example, 1/1000 of TR (0). Or you may decide according to the precision which can be set to TR.
- ⁇ is a predetermined small number.
- ⁇ is appropriately determined by a method often used in the steepest descent method. For example, 1 / ( ⁇ f (TR (0)) / h) ⁇ TR (0) / 1000 is set.
- the change of the objective function f (TR (i)) may be investigated empirically to determine convergence so as to improve convergence.
- step S1203 and S1204 are repeated M times (steps S1205 and S1206). Then, the adjustment parameter TR (M) after being repeated M times is determined as the optimum value (step S1207), and the process is terminated.
- a search range may be set when adjusting the adjustment parameter. That is, the adjustment parameter adjustment range and the range in which the adjustment parameter value is changed (change range) may be limited.
- the TR at which the variance Scvar of the signal intensity is minimum is 0.6 seconds.
- This is a TR in which the signal intensity Sc of all T1 (1), T1 (2), and T1 (3) is 0, and Trecov is 0.
- T1 recovery is not performed at all, and since no signal is generated thereafter, the setting is actually meaningless.
- a limit is set such that the change range of TR is 1 second or longer.
- TR is limited to 10 seconds or less.
- Fig. 10 shows the processing flow of the parameter adjustment process when there is a limit on the range (change range) that allows the change of the adjustment parameter value. This is basically the same as the process flow of the parameter adjustment process shown in FIG. However, the difference is that the change range of the adjustment parameter value is set at the initial setting, and the adjustment parameter value is changed within the set change range.
- step S1202a when setting the initial value for the adjustment parameter in step S1202a, the change range of the adjustment parameter value is also set. Further, after updating the adjustment parameter in step S1204, it is determined whether or not the updated adjustment parameter is within the range set in step S1202a (step S1211). If it is within the range, the process proceeds to step S1205. On the other hand, if it is out of the range, the adjustment parameter is changed to the closest value within the change range (step S1212).
- the adjustment parameter is set to TR in the adjustment at the time of T2-weighted image capturing
- the adjustment parameter to be adjusted at the time of T2-weighted image capturing is limited to this. I can't. Any imaging parameter that affects T1 recovery or T1 attenuation may be used.
- the application parameter of the RF pulse or the gradient magnetic field applied in the recovery period Trecov from the last refocus RF pulse application of the echo train to the next excitation RF pulse 201 can be used as an adjustment parameter.
- the FA of the DE pulse 204, the saturation pulse, the FA of each of one or more RFs applied during the recovery period Trecov, the intensity of the gradient magnetic field pulse applied between the Trecov, and a combination thereof are adjusted parameters. It is good.
- each FA of VRFA, echo shift, etc. may be used as adjustment parameters.
- FA and echo shift are difficult to handle because they change the effect of T2, but they can be used for adjustment because they change the effect of T1.
- FIG. 11 shows changes in the magnitudes of magnetization of two tissues A and B having the same T2 and different T1, the application timing of the RF pulse, and the acquisition timing of the echo signal.
- the pulse sequence used is, for example, the VRFA sequence 200, and the relationship between T1 (T1A and T1B) of tissues A and B is T1A ⁇ T1B.
- a solid line 301 indicates a change in the magnitude of the magnetization of the tissue A
- a broken line 302 indicates a change in the magnitude of the magnetization of the tissue B.
- the magnitude of magnetization shows only what contributes to the acquired echo signal.
- the change between 1TR when the VRFA sequence 200 is repeated sufficiently and it will be in a steady state is shown.
- the parameter adjustment unit 711 can optimize the magnitude of magnetization at the end of TR by adjusting the FA of the DE pulse 204. Also in this case, the optimum magnetization size at the end of TR is the timing at which the k-space center that determines the contrast is acquired in the next TR, and the magnetization size (signal intensity) of each tissue A and B is approximately It will be equal.
- the signal intensity Sc (n) can be obtained from Equation (1) to Equation (4), as in the case where the adjustment parameter is TR.
- the parameter adjustment unit 711 adjusts the adjustment parameter so as to minimize (minimize) the objective function (Scvar) while changing the FA (FAde) of the DE pulse 204 as in the case where the adjustment parameter is TR. The only difference is that the adjustment parameter is FAde.
- the adjustment parameter at the time of T2-weighted image capture may be the application timing of the saturation pulse.
- the saturation pulse is usually an RF pulse applied to suppress a signal from a specific component or place.
- it is used to mean an RF pulse applied between echo trains to suppress signals. It is not necessary to limit to a specific component or place.
- a gradient magnetic field is also applied to extinguish a signal.
- the gradient magnetic field only needs to be applied so as to erase the signal, so only the method of applying an RF pulse will be described here.
- FIG. 12 shows changes in the magnitudes of the magnetizations of two tissues A and B having the same T2 and different T1, the application timing of the RF pulse, and the acquisition timing of the echo signal.
- the pulse sequence used is, for example, the VRFA sequence 200, and the relationship between T1 (T1A and T1B) of tissues A and B is T1A ⁇ T1B.
- a solid line 301 indicates a change in the magnitude of the magnetization of the tissue A
- a broken line 302 indicates a change in the magnitude of the magnetization of the tissue B.
- the magnitude of magnetization shows only what contributes to the acquired echo signal.
- the change between 1TR when the VRFA sequence 200 is repeated sufficiently and it will be in a steady state is shown.
- the saturation pulse 205 when the saturation pulse 205 is applied at a predetermined timing between echo trains, that is, between Trecov, there is no magnetization contributing to the acquired echo signal, and T1 is recovered from the application of the saturation pulse 205 to the end of TR.
- the degree of magnetization recovery can be adjusted by changing the application timing of the saturation pulse 205. That is, the parameter adjustment unit 711 can optimize the magnitude of magnetization at the end of TR by adjusting the application timing of the saturation pulse 205.
- the optimum magnetization size at the end of TR is the timing at which the k-space center that determines the contrast is acquired in the next TR, and the magnetization size (signal intensity) of each tissue A and B is approximately It will be equal.
- the parameter adjustment unit 711 replaces the above equation (3) with the following equations (5) and (6), and calculates an optimum value.
- Msat 1 ⁇ (1 ⁇ MLde) ⁇ exp ( ⁇ Trecov1 / T1 (n)) (5)
- MT0 1 ⁇ (1 ⁇ Msat ⁇ cos (FAsat)) ⁇ exp ( ⁇ Trecov2 / T1 (n)) (6)
- Msat is the magnitude of magnetization just before the saturation pulse 205 application
- FAsat is the FA of the saturation pulse 205
- Trecov1 is the time from the DE pulse 204 to the saturation pulse 205 application
- Trecov2 is from the saturation pulse 205 to the start of the next echo train Is the time.
- Equation (1) By solving Equation (1), Equation (2), Equation (5) and Equation (6), MT0 in steady state is represented by Rend (n), FAde, FAsat, Trecov1, Trecov2 and T1 (n) . Then, this MT0 is substituted into the equation (4) to obtain Sc (n).
- the parameter adjustment unit 711 adjusts the adjustment parameter so as to minimize (minimize) the objective function (Scvar) while changing Trecov2 as in the case where the adjustment parameter is TR. The only difference is that the tuning parameter is Trecov2.
- the magnetization can be set to 0 at a desired timing. For this reason, the desired T1 recovery can be realized regardless of the length of TR. For example, even if TR is long, the degree of T1 recovery can be suppressed by delaying the application timing of the saturation pulse 205. Therefore, it is useful for imaging where a short TR cannot be specified, such as synchronous measurement.
- the adjustment parameter may be FAsat.
- the adjustment method has been described by taking as an example the case of adjusting one of the variables appearing in Equations (1) to (6) as an adjustment parameter.
- the adjustment parameter is not limited to one. You may adjust combining several.
- the length of the recovery period Trecov, the RF waveform applied during Trecov, and the gradient magnetic field strength applied during Trecov can be used as the adjustment parameters.
- the RF waveform applied during Trecov is determined by the FA value sequence of the RF pulse for flip back / down applied during Trecov.
- one or more imaging parameters are used as adjustment parameters.
- FIG. 13 similarly to FIG. 6, changes in the magnitudes of the magnetizations of two tissues A and B having the same T2 and different T1, the application timing of the RF pulse, the application timing of the gradient magnetic field, and the echo signal The acquisition timing is shown.
- the pulse sequence used is, for example, the VRFA sequence 200, and the relationship between T1 (T1A and T1B) of tissues A and B is T1A ⁇ T1B.
- a solid line 301 indicates a change in the magnitude of the magnetization of the tissue A
- a broken line 302 indicates a change in the magnitude of the magnetization of the tissue B.
- the magnitude of magnetization shows only what contributes to the acquired echo signal.
- the change between 1TR when the VRFA sequence 200 is repeated sufficiently and it will be in a steady state is shown.
- the magnetization contributing to the acquired echo signal becomes longitudinal magnetization, and T1 recovers until the end of TR.
- the degree of magnetization recovery is adjusted by adjusting the recovery period Trecov, applying the RF pulse waveform 206 during this period, or applying the gradient magnetic field 207.
- the optimum magnetization size at the end of TR is that the magnetization size (signal intensity) of each tissue A and B becomes substantially equal at the timing of acquiring the k-space center that determines the contrast in the next TR. is there.
- all of the sequence shapes such as the application timing, RF waveform, and gradient magnetic field strength can be adjusted as adjustment parameters.
- the examples described so far are examples in which some of them are adjusted.
- TR is the adjustment parameter
- the RF waveform and the gradient magnetic field strength are fixed, and only the last waiting time among the application timings is the adjustment parameter.
- FA of DE pulse 204 and FA of saturation pulse 205 are used as adjustment parameters
- the application timing and gradient magnetic field strength are fixed, and only the intensity of some pulses in the RF waveform are used as adjustment parameters. is there.
- the magnitude of the echo signal arranged at the center of the k space that determines the contrast is obtained using the Bloch equation shown in the following equation (7).
- a general method is used for obtaining. For example, when a gradient magnetic field is taken into account, the equations may be solved and added for each gradient magnetic field application direction. Moreover, what is necessary is just to repeat enough time to obtain a steady state. A desired variable among the variables included in this equation may be used as an adjustment parameter.
- the Trecov period, RF waveform, and gradient magnetic field strength are limited to some extent, and the imaging parameters are adjusted with simple equations. Also good.
- a change range may be set and adjustment may be performed within the range.
- the optimum adjustment parameter is determined using the signal intensity Sc at the center of k-space for tissues having different T1 for one T2.
- the objective function is the sum of the coefficient of variation (variance / average) of the signal intensity Sc for each T2 value.
- T2 is T2 1 and the coefficient of variation Sccc 1 of the signal strength at the center of k-space obtained using multiple tissues with different T1
- T2 is T2 2
- Sccv 1 + Sccv 2 which is the sum of the variance Sccv 2 of the signal intensity at the center of the k-space obtained using a plurality of tissues with different T 1 as an objective function.
- the processing flow in this case is the same as the parameter adjustment processing described with reference to FIG. 9 or FIG.
- FIG. 14 shows the flow of parameter adjustment processing when there are a plurality of relaxation times to be considered.
- the optimum value of the adjustment parameter is calculated using a plurality of tissues having the same T2 and different T1 (step S1301).
- the average of the optimum values obtained every T2 is calculated (step S1302), and the optimum value of the adjustment parameter output as the adjustment result is determined.
- the method of determining the optimum value for each T2 in step S1301 is the same as the parameter adjustment processing described with reference to FIG. 9 or FIG.
- the target for minimizing the variance may be the contrast instead of the signal intensity.
- the contrast is obtained by the ratio of the signal strengths Sc (n) of two different T2 values. Assume that the T1 values of the tissues taking the signal intensity ratio are the same. For example, in the example of FIGS. 7 (a) and 7 (b), the signal strength of each T1 value when T2 is 50 ms is Sc1 (n), and the signal strength of each T1 value when T2 is 100 ms is Sc2 ( If n), the contrast Rc (n) is expressed by Sc1 (n) / Sc2 (n).
- the parameter adjusting unit 711 uses the variance Rcvar of the contrast Rc (n) as an objective function, and searches for a value that minimizes (minimizes) the objective function.
- Fig. 15 shows an adjustment example when the FA of the DE pulse 204 is the adjustment parameter and the objective function is the contrast dispersion Rcvar.
- the two T2s are 50 ms and 100 ms, respectively.
- the FA change shape FAP of the FA of the refocus RF pulse 202 is the shape shown in FIG. 4 as in the first embodiment.
- T1 is infinite means that the above equation (3) is replaced with the following equation (8), and the influence of T1 is ignored.
- the MRI apparatus 100 of the present embodiment includes a static magnetic field generation unit 120 that generates a static magnetic field, and a gradient magnetic field generation unit 130 that applies a gradient magnetic field to a subject arranged in the static magnetic field.
- a transmitter 150 that transmits a high-frequency magnetic field pulse that excites the magnetization of the subject at a predetermined flip angle, a receiver 160 that receives an echo signal generated by the subject, and an echo signal received by the receiver
- a control unit 170 that controls operations of the gradient magnetic field generation unit 130, the transmission unit 150, and the reception unit 160 according to an imaging sequence, and an adjustment target that is predetermined to reduce unnecessary contrast.
- a parameter adjustment unit 711 that adjusts the imaging parameters of the imaging unit, the imaging parameters adjusted by the parameter adjustment unit 711, and the imaging parameters and the pulse sequence. Comprising a sequence creation unit 710 generates a sequence, the.
- the pulse sequence is a pulse sequence in which a plurality of refocusing high frequency magnetic field pulses are applied within a repetition time after application of one excitation high frequency magnetic field pulse, and at least one flip angle of the refocusing high frequency magnetic field pulse is 180 Other than degrees. Then, the parameter adjustment unit 711 adjusts the imaging parameter to be adjusted so as to reduce the T1 contrast.
- T1 contrast is suppressed by adjusting the degree of T1 recovery after acquisition of echo train. The adjustment is performed by the length of TR, the application timing of the RF pulse for flip back / down applied during the recovery period, FA, gradient magnetic field strength, and the like. In other words, the T1 contrast is canceled by attenuation and recovery that naturally have opposite effects.
- the adjusted value of the parameter adjusted to cancel the influence of T1 is presented to the user. For this reason, the user can grasp
- Second Embodiment a second embodiment to which the present invention is applied will be described.
- the adjustment parameter when obtaining a T2-weighted image, the adjustment parameter is adjusted so as to reduce the influence of T1.
- the adjustment is performed so as to reduce the T2 contrast when acquiring the T1-weighted image.
- the MRI apparatus of the present embodiment has basically the same configuration as the MRI apparatus 100 of the first embodiment.
- the functional configuration of the control unit 170 of the present embodiment is also the same.
- the parameter adjustment processing by the parameter adjustment unit 711 is different.
- the pulse sequence to be used and the flow of imaging processing are the same as in the first embodiment.
- the parameter adjustment unit 711 of the present embodiment adjusts the imaging parameters set by the user so as to reduce the influence of T2 that causes unnecessary contrast. That is, the parameter adjustment unit 711 adjusts the adjustment target imaging parameter so as to reduce the T2 contrast.
- the adjustment parameters to be adjusted are the same as those in the first embodiment.
- the parameter adjustment unit 711 of this embodiment adjusts the adjustment parameter using the signal strength of the echo signal arranged at the center of the k space among the echo signals from a plurality of tissues having different combinations of T1 and T2.
- T1 the adjustment is performed so that the difference in signal strength is small even if T2 is different.
- the difference is reduced by adjusting the adjustment parameter so that the variance of the signal intensity of the echo signal arranged at the center of the k space is minimized (minimum).
- FIG. 16 shows the relationship between the change in the magnitude of magnetization of two tissues C and D having the same longitudinal relaxation time T1 and different transverse relaxation times T2, and the pulse sequence.
- the lateral relaxation time T2C of the tissue C is shorter than the lateral relaxation time T2D of the tissue D (T2C ⁇ T2D).
- the pulse sequence used is the VRFA sequence 200 shown in FIG. In this embodiment, the sequence to be used is not limited to the VRFA sequence 200 as in the first embodiment. It is sufficient that the FA of at least one refocusing RF pulse 202 is a sequence other than 180 degrees.
- the change in the magnitude of magnetization of tissue C (solid line) 501, the change in the magnitude of magnetization of tissue D (broken line) 502, and the application timing of excitation RF pulse 201, refocus RF pulse 202, DE pulse 204 And the acquisition timing of the echo signal 203 are shown. Also in this figure, the magnitude
- both tissues C and D are refocused by the refocus RF pulse 202 until the end of the echo train.
- the magnitudes 501 and 502 of the magnetizations change. This change in the magnitudes 501 and 502 includes T1 attenuation corresponding to the longitudinal magnetization caused by the fact that the FA of the refocus RF pulse 202 is not 180 degrees.
- the magnetization contributing to the acquired echo signal becomes longitudinal magnetization, and T1 recovers until the end of TR.
- the recovered longitudinal magnetization contributes to the echo signal acquired in the next TR. That is, in the next TR, the change starts from the magnitude of the magnetization recovered at the end of the immediately preceding TR. Therefore, by adjusting the degree of magnetization recovery during this recovery period, the magnitude of magnetization at the end of TR can be made the optimum magnitude of magnetization at the start of subsequent TRs.
- the parameter adjustment unit 711 of this embodiment searches for an adjustment parameter that optimizes the magnitude of magnetization at the end of TR.
- the optimum magnetization size at the end of TR is the timing of obtaining the k-space center that determines the contrast in the next TR at the timing of acquiring the magnetization of each tissue C and D.
- the magnitude (signal strength) is substantially equal.
- the parameter adjustment unit 711 is configured so that the signal strengths Sc at the center of the k space in the steady state are substantially equal for each of the plurality of tissues having the same T1 and different T2.
- the adjustment parameter is adjusted so that the variance Scvar of the signal strength Sc is minimized (or minimized). That is, the parameter adjustment unit 711 of the present embodiment searches for an adjustment parameter that uses the variance Scvar as an objective function and minimizes (or minimizes) the objective function, and determines the optimum value.
- the parameter adjustment unit 711 of this embodiment searches for and determines an adjustment parameter that minimizes (or minimizes) the objective function Scvar.
- the formula necessary for obtaining Sc (n) of this embodiment is shown below. These formulas are basically the same as the formulas (1) to (4) of the first embodiment. That is, as in the first embodiment, the transverse magnetization magnitude MTend at the end of the echo train (immediately before the DE pulse application), the longitudinal magnetization magnitude MLde after the DE pulse 204 application, the transverse magnetization magnitude MT0 immediately after the excitation, The signal strength Sc (n) is described by being divided into the following four formulas (9) to (10).
- MTend MT0 ⁇ Rend (n) (9)
- MLde MTend ⁇ sin (-FAde) ⁇ ⁇ ⁇ (10)
- MT0 1 ⁇ (1 ⁇ MLde) ⁇ exp ( ⁇ Trecov / T1) (11)
- Sc (n) MT0 ⁇ Rcent (n) (12)
- FAde is the FA of the DE pulse 204.
- the phase is the same as that of the excitation pulse (negative when flipping back).
- Trecov is the time from the application of the DE pulse 204 to the next application of the excitation RF pulse 201 as described above.
- Rend (n) which is the ratio of the magnitude of the transverse magnetization at the end of the echo train to the start of the echo train, and the magnitude of the transverse magnetization at the center of k-space with respect to the magnitude of the transverse magnetization at the start of the echo train Rcent (n) is a value when T2 is T2 (n).
- the size of the longitudinal magnetization MLend at the end of the echo train (immediately before application of the DE pulse 204) is set to 0 for simplicity.
- the longitudinal magnetization plate (1-1) of equation (9) is added in the same way as equations (1) to (4), and equation (10) Consider MTend's longitudinal magnetization component instead of 2-1).
- the FA of the DE pulse 204 is set to 0.
- the adjustment parameter search method for minimizing (or minimizing) the objective function Scvar is the same as in the first embodiment. That is, the flow of parameter adjustment processing by the parameter adjustment unit 711 of the present embodiment is the same as the flow of parameter adjustment processing of the first embodiment described with reference to FIG. For example, when the adjustment parameter is the FA of the DE pulse 204, the parameter adjustment unit 711 searches for and determines the FAde that minimizes the objective function Scvar.
- FIGS. 17 (a) and 17 (b) Specific examples of adjustment by the parameter adjustment unit 711 of this embodiment are shown in FIGS. 17 (a) and 17 (b).
- 4 is a graph showing changes in adjustment parameters of steady-state k-space center signal strengths Sc of four tissues having the same T1 and different T2.
- the adjustment parameter is FA of the DE pulse 204.
- FIG. 17 (a) is a graph showing changes in signal intensity of a tissue having T1 of 500 ms
- FIG. 17 (b) is a graph showing changes in signal intensity of a tissue having T1 of 1000 ms.
- the FA of the refocus RF pulse 202 was changed according to the FA changing shape FAP shown in FIG.
- the FA (optimum value) of the DE pulse 204 that minimizes (or minimizes) the Sc dispersion Scvar is 40 degrees.
- the FA (optimum value) of the DE pulse 204 that minimizes (or minimizes) Scvar is 20 degrees in the case of a tissue with T1 of 1000 ms.
- the adjustment parameter uses the length of the recovery period Trecov, the RF waveform applied during Trecov, the gradient magnetic field strength applied during Trecov, and the like. Can do.
- Trecov that minimizes (or minimizes) Scvar is determined using the above equations (9) to (12).
- Msat is the magnitude of magnetization just before the saturation pulse 205 application
- FAsat is the FA of the saturation pulse 205
- Trecov1 is the time from the DE pulse 204 to the saturation pulse 205 application
- Trecov2 is from the saturation pulse 205 to the start of the next echo train Is the time.
- the FA of the saturation pulse 205 may be used as an adjustment parameter.
- the FAsat that minimizes the variance Scvar for a plurality of n of the above Sc (n) is calculated as the optimum value.
- the optimum value searching method is the same as that when the adjustment parameter is TR.
- the saturation pulse 205 When the saturation pulse 205 is used as an adjustment parameter, the magnetization can be reduced at a desired timing. Therefore, the desired T1 recovery can be realized regardless of the TR length. That is, even when TR is long, the degree of recovery of T1 can be suppressed by delaying the application timing of the saturation pulse 205. Therefore, it is useful for imaging where a short TR cannot be specified, such as synchronous measurement.
- the magnitude of magnetization is obtained using the Bloch equation shown in the above equation (7) as in the first embodiment.
- the Bloch equation may not be solved directly, but the Trecov period, the RF waveform, and the gradient magnetic field strength may be limited to some extent, and the imaging parameters may be adjusted by a simple formula.
- a limit may be provided for the change range of the value of each adjustment parameter.
- the flow of parameter adjustment processing in this case is the same as in the first embodiment.
- a plurality of T1s may be considered as in the first embodiment.
- the objective function is the sum of the variation coefficients of the signal intensity Sc for each T1 value.
- T1 is T1 1
- T2 is the coefficient of variation Sccc 1 of the signal strength at the center of k-space obtained using multiple tissues with different T2
- T1 is T1 2 .
- the above parameter adjustment processing is performed using Sccv 1 + Sccv 2 , which is the sum of the variation coefficient Sccv 2 of the signal intensity at the center of k-space obtained using a plurality of tissues having different T2 as an objective function.
- the process flow in this case is the same as the parameter adjustment process of the first embodiment described with reference to FIG. 9 or FIG.
- the above parameter adjustment processing may be performed on each T1 value, and the obtained optimum values may be averaged.
- the process flow in this case is the same as the process flow of the first embodiment described with reference to FIG.
- the contrast may be used instead of the signal intensity, and the variance may be used as the objective function. That is, the parameter adjustment unit 711 may set the value that minimizes (minimizes) the contrast dispersion as the optimum value of the adjustment parameter. Contrast is calculated as the ratio of the signal strengths of two different T1 values.
- the parameter adjustment unit 711 uses this Rc (n) as an objective function, and sets the value at which the variance Rcvar is minimum as the optimum value of the adjustment parameter.
- Fig. 18 shows a graph of contrast Rc for each T2 (n) when the adjustment parameter is the FA of the DE pulse 204. As shown in this figure, in this case, 0 degree is obtained as the optimum value. As can be seen from FIG. 17 (a) and FIG. 17 (b), even if the T1 is the same, the signal intensity changes greatly if T2 is different. That is, a T2 contrast is added to a T1-weighted image. Therefore, when the imaging target T2 is in a narrow range, the process using the contrast can be applied.
- the MRI apparatus 100 of the present embodiment includes a static magnetic field generation unit 120 that generates a static magnetic field, and a gradient magnetic field generation unit 130 that applies a gradient magnetic field to a subject arranged in the static magnetic field.
- a transmitter 150 that transmits a high-frequency magnetic field pulse that excites the magnetization of the subject at a predetermined flip angle, a receiver 160 that receives an echo signal generated by the subject, and an echo signal received by the receiver
- a control unit 170 that controls operations of the gradient magnetic field generation unit 130, the transmission unit 150, and the reception unit 160 according to an imaging sequence, and an adjustment target that is predetermined to reduce unnecessary contrast.
- a parameter adjustment unit 711 that adjusts the imaging parameters of the imaging unit, the imaging parameters adjusted by the parameter adjustment unit 711, and the imaging parameters and the pulse sequence.
- Comprising a sequence creation unit 710 generates a sequence, the.
- the pulse sequence is a pulse sequence in which a plurality of refocusing high frequency magnetic field pulses are applied within a repetition time after application of one excitation high frequency magnetic field pulse, and at least one flip angle of the refocusing high frequency magnetic field pulse is 180 Other than degrees. Then, the parameter adjustment unit 711 adjusts the imaging parameter to be adjusted so as to reduce the T2 contrast.
- the adjusted value of the parameter adjusted to cancel the influence of T2 is presented to the user. For this reason, the user can grasp
- the parameter adjustment process is executed every time the imaging parameter is set, and the optimum value of the adjustment parameter is determined.
- the optimum value of the adjustment parameter may be calculated in advance for each imaging condition and stored in the storage device 172 or the like.
- the optimum value is calculated according to, for example, the FA change shape FAP, the imaging target contrast, and the like. In this case, each time an imaging parameter is set, an optimum value that is held in association with the set imaging parameter is acquired.
- Fig. 19 shows the processing flow of the imaging process when the optimum value is calculated in advance. This process is basically the same as the imaging process described with reference to FIG. However, when the imaging condition is accepted in step S1102, the optimum value stored in association with the imaging condition is acquired (step S1103a), and the acquired optimum value is displayed on the imaging parameter input screen 400 (step S1104a).
- This method may be applied after adjusting the adjustment parameter by the method of each of the above embodiments.
- FIG. 20 is an explanatory diagram for explaining the present technique.
- the two tissues A and B under the same conditions as in FIG. 6 above, the change in magnetization magnitude 601, 602, the application timing of each RF pulse 201, 202, 204, the application timing of the gradient magnetic field, The acquisition timing of the echo signal 203 is shown.
- FIG. 20 shows an example in which the gradient magnetic field 220 is used.
- the gradient magnetic field 220 may be switched so as not to be applied during application of the RF pulse 210. Note that when the application time of the RF pulse 210 can be sufficiently shortened so as not to be substantially sliced, there is no need to switch.
- the FA of the RF pulse 210 to be applied is determined by the following equation (15).
- FAss is the FA of the RF pulse 210 that is continuously applied
- ⁇ m is the ratio of the magnitude of the magnetization that changes during the application interval ⁇ t of the RF pulse 210.
- ⁇ m (M2 ⁇ M1) / M1 when the magnetization of the magnitude M1 changes to the magnitude M2.
- ⁇ m dM / dt / M1 ⁇ ⁇ t may be used by using an instantaneous change rate.
- the variance or coefficient of variation (variance / average) of the signal strength Sc at the center of the k space in the steady state is used as the objective function, but the objective function is not limited to this.
- the distribution range (difference between the maximum value and the minimum value) may be used.
- the relaxation times for example, T2
- the relaxation times for example, T1
- the objective function may be any objective function that can realize the adjustment processing described in the first embodiment, such that adjustment is performed so that the difference in signal strength of echo signals arranged at the center of the k space is reduced.
- 100 MRI apparatus 101 subject, 120 static magnetic field generation unit, 130 gradient magnetic field generation unit, 131 gradient magnetic field coil, 132 gradient magnetic field power supply, 140 sequencer, 150 transmission unit, 151 transmission coil, 152 high frequency oscillator, 153 modulator, 154 High frequency amplifier, 160 receiver, 161 receiver coil, 162 signal amplifier, 163 quadrature detector, 164 A / D converter, 170 controller, 171 CPU, 172 storage device, 173 display device, 174 input device, 200 FSE pulse Sequence (VRFA sequence), 201 excitation RF pulse, 202 refocus RF pulse, 203 echo signal, 204 DE pulse, 205 saturation pulse, 206 RF pulse waveform, 207 gradient magnetic field, 210 RF pulse, 200a TR sequence, 220 gradient magnetic field , 301 Changes in the magnitude of the magnetization of tissue A, 302 Changes in the magnitude of the magnetization of tissue B, 400 Imaging parameter input screen, 401 Adjustment parameter input area, 402 Adjustment parameters Display area, 403 Contrast adjustment setting area
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Abstract
Description
以下、本発明を適用する第一の実施形態について説明する。以下、本発明の実施形態を説明するための全図において、同一機能を有するものは同一符号を付し、その繰り返しの説明は省略する。
なお、上述のように、用いるシーケンスはVRFAシーケンス200に限られない。少なくとも1つの再収束RFパルス202のFAが180度以外のシーケンスであればよい。
MLde=MTend×sin(-FAde)・・・(2)
MT0=1-(1-MLde)×exp(-Trecov/T1(n))・・・(3)
Sc(n)=MT0×Rcent(n)・・・(4)
MLde=MTend×sin(-FAde)+MLend×cos(FAde)・・・(2-1)
ここで、RLend(n)、CLend(n)は、T1がT1(n)のときのエコートレイン内での縦磁化の変化を表す式を、MT0に関して整理した時の係数である。
ここでは、対象の撮像パラメータをTRとする。また、調整パラメータの更新をM回行うものとする。i回更新された調整パラメータをTR(i)、TR(i)により得た目的関数Scvarを、f(TR(i))と表す。
そして、ユーザが入力した値を調整パラメータの初期値(TR(0))に設定する(ステップS1202)。
MT0=1-(1-Msat×cos(FAsat))×exp(-Trecov2/T1(n))・・・(6)
ここで、Msatは飽和パルス205印加直前の磁化の大きさ、FAsatは飽和パルス205のFA、Trecov1はDEパルス204から飽和パルス205印加までの時間、Trecov2は飽和パルス205から次のエコートレイン開始までの時間である。
この方程式に含まれる変数の中の、所望の変数を調整パラメータとすれば良い。
図15の例では、DEパルス204のFAが略0度の場合、目的関数Rcvarが最小(極小)となることがわかる。
次に、本発明を適用する第二の実施形態を説明する。第一の実施形態は、T2強調画像を取得する際、T1の影響を低減するよう調整パラメータを調整する。一方、本実施形態は、T1強調画像を取得時に、T2コントラストを低減するよう調整する。
MLde=MTend×sin(-FAde)・・・(10)
MT0=1-(1-MLde)×exp(-Trecov/T1)・・・(11)
Sc(n)=MT0×Rcent(n)・・・(12)
ここで、完全に回復後、励起した直後の磁化の大きさを1とする。FAdeは、DEパルス204のFAである。励起パルスと同位相(フリップバックする時を負とする)とする。Trecovは、上述のように、DEパルス204印加から、次の励起RFパルス201印加までの時間である。
MT0=1-(1-Msat×cos(FAsat))×exp(-Trecov2/T1)・・・(14)
ここで、Msatは飽和パルス205印加直前の磁化の大きさ、FAsatは飽和パルス205のFA、Trecov1はDEパルス204から飽和パルス205印加までの時間、Trecov2は飽和パルス205から次のエコートレイン開始までの時間である。
ここで、FAssは印加し続けるRFパルス210のFAで、ΔmはRFパルス210の印加間隔Δtの間に変化する磁化の大きさの割合である。例えば、大きさM1の磁化が大きさM2に変化したとき、Δm=(M2-M1)/M1である。または、瞬間の変化率を使って、Δm=dM/dt/M1×Δtなどとしても良い。
Claims (14)
- 静磁場を発生する静磁場発生部と、
前記静磁場中に配置された被検体に対して傾斜磁場を印加する傾斜磁場発生部と、
前記被検体の磁化を所定のフリップ角で励起する高周波磁場パルスを送信する送信部と、
前記被検体が発生するエコー信号を受信する受信部と、
不要なコントラストを低減するよう予め定めた調整対象の撮像パラメータを調整するパラメータ調整部と、
前記パラメータ調整部により調整された撮像パラメータと、繰り返し時間内に励起高周波磁場パルスと、1つ以上のフリップ角が180度以外である複数の再収束高周波磁場パルスを印加するパルスシーケンスと、を用いて撮像シーケンスを生成するシーケンス作成部と、
前記受信部が受信したエコー信号から画像を再構成するとともに、前記撮像シーケンスに従って、前記傾斜磁場発生部、前記送信部、前記受信部の動作を制御する制御部と、
を備えていることを特徴とする磁気共鳴イメージング装置。 - 請求項1記載の磁気共鳴イメージング装置であって、
前記パラメータ調整部は、T1コントラストまたはT2コントラストを低減させるよう、前記調整対象の撮像パラメータを調整すること
を特徴とする磁気共鳴イメージング装置。 - 請求項1記載の磁気共鳴イメージング装置であって、
前記調整対象の撮像パラメータは、繰り返し時間であること
を特徴とする磁気共鳴イメージング装置。 - 請求項1記載の磁気共鳴イメージング装置であって、
前記調整対象の撮像パラメータは、前記高周波磁場パルスおよび前記傾斜磁場の少なくとも一方の印加パラメータであること
を特徴とする磁気共鳴イメージング装置。 - 請求項1記載の磁気共鳴イメージング装置であって、
前記調整対象の撮像パラメータは、前記再収束高周波磁場パルス印加後から次の前記励起高周波磁場パルス印加までの回復期間に印加される、前記高周波磁場パルスおよび前記傾斜磁場の少なくとも一方の印加パラメータであること
を特徴とする磁気共鳴イメージング装置。 - 請求項5記載の磁気共鳴イメージング装置であって、
前記調整対象の撮像パラメータに前記高周波磁場パルスの印加パラメータが含まれる場合、前記印加パラメータは、当該高周波磁場パルスのフリップ角または印加タイミングであること
を特徴とする磁気共鳴イメージング装置。 - 請求項6記載の磁気共鳴イメージング装置であって、
前記高周波磁場パルスは、DEパルスまたは飽和パルスであること
を特徴とする磁気共鳴イメージング装置。 - 請求項1記載の磁気共鳴イメージング装置であって、
前記調整対象の撮像パラメータの調整範囲は予め定めた変化範囲に制限されること
を特徴とする磁気共鳴イメージング装置。 - 請求項1記載の磁気共鳴イメージング装置であって、
前記パラメータ調整部は、意図したコントラストを生じさせる第一の緩和時間が等しく、かつ、前記不要なコントラストを生じさせる第二の緩和時間が異なる複数の組織からのエコー信号の中の、k空間中心に配置されるエコー信号の信号強度の分散が極小となるよう、前記調整対象の撮像パラメータを調整すること
を特徴とする磁気共鳴イメージング装置。 - 請求項1記載の磁気共鳴イメージング装置であって、
前記パラメータ調整部は、前記不要なコントラストを生じさせる第二の緩和時間が等しく、意図したコントラストを生じさせる第一の緩和時間が異なる2つの組織間のk空間に配置されるエコー信号の信号強度の比を、複数の異なる前記第二の緩和時間について計算し、当該計算結果の分散が最小となるよう前記調整対象の撮像パラメータを調整すること
を特徴とする磁気共鳴イメージング装置。 - 請求項9記載の磁気共鳴イメージング装置であって、
前記パラメータ調整部は、前記k空間中心に配置されるエコー信号の信号強度の分散を、前記第一の緩和時間を変えて複数算出し、当該算出結果の和を極小とするよう前記調整対象の撮像パラメータを調整すること
を特徴とする磁気共鳴イメージング装置。 - 請求項9記載の磁気共鳴イメージング装置であって、
前記パラメータ調整部は、前記第一の緩和時間を変えて、前記k空間中心に配置されるエコー信号の信号強度の分散が極小となる前記調整対象の撮像パラメータを複数算出し、当該算出結果の平均値を算出し、調整結果とすること
を特徴とする磁気共鳴イメージング装置。 - 請求項1記載の磁気共鳴イメージング装置であって、
前記パラメータ調整部は、前記撮像パラメータを受け付ける撮像パラメータ入力画面を生成し、
前記撮像パラメータ入力画面は、前記調整対象の撮像パラメータの、前記調整後の値を表示する調整パラメータ表示領域、前記調整対象の撮像パラメータの、前記調整後の値を撮像パラメータに反映させる指示を受け付ける反映ボタン、および、意図するコントラストの指定を受け付けるコントラスト調整設定領域の少なくとも1つを備えること
を特徴とする磁気共鳴イメージング装置。 - 静磁場を発生する静磁場発生部と、
前記静磁場中に配置された被検体に対して傾斜磁場を印加する傾斜磁場発生部と、
前記被検体の磁化を所定のフリップ角で励起する高周波磁場パルスを送信する送信部と、
前記被検体が発生するエコー信号を受信する受信部と、
を備えた磁気共鳴イメージング装置において、制御部が、
不要なコントラストを低減するよう予め定めた調整対象の撮像パラメータを調整する処理と、
前記調整された撮像パラメータと、繰り返し時間内に励起高周波磁場パルスと、1つ以上のフリップ角が180度以外である複数の再収束高周波磁場パルスを印加するパルスシーケンスと、を用いて撮像シーケンスを生成する処理と、
前記撮像シーケンスを実行し、前記受信部が受信したエコー信号から画像を再構成する処理と、
を行うことを特徴とする不要コントラスト低減方法。
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JP2005021690A (ja) * | 2003-07-02 | 2005-01-27 | Ge Medical Systems Global Technology Co Llc | 多相型rfパルス・フリップ角を組み入れて高磁場mr撮像でのrf電力を低減する方法及び装置 |
JP2007313303A (ja) * | 2006-04-25 | 2007-12-06 | Toshiba Corp | 磁気共鳴イメージング装置および磁気共鳴イメージング装置における撮影条件設定方法 |
WO2012169350A1 (ja) * | 2011-06-09 | 2012-12-13 | 株式会社 日立メディコ | 磁気共鳴イメージング装置及びフリップ角決定方法 |
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JP7496980B2 (ja) | 2020-01-31 | 2024-06-10 | 国立研究開発法人産業技術総合研究所 | 脂肪含有率等の計測装置及び方法 |
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US20150355304A1 (en) | 2015-12-10 |
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