WO2011148783A1 - 磁気共鳴イメージング装置及び高周波磁場パルスの変調方法 - Google Patents
磁気共鳴イメージング装置及び高周波磁場パルスの変調方法 Download PDFInfo
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- 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
- G01R33/565—Correction of image distortions, e.g. due to magnetic field inhomogeneities
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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
- G01R33/34—Constructional details, e.g. resonators, specially adapted to MR
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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
- G01R33/4816—NMR imaging of samples with ultrashort relaxation times such as solid samples, e.g. MRI using ultrashort TE [UTE], single point imaging, constant time imaging
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- G—PHYSICS
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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
- G01R33/483—NMR imaging systems with selection of signals or spectra from particular regions of the volume, e.g. in vivo spectroscopy
- G01R33/4833—NMR imaging systems with selection of signals or spectra from particular regions of the volume, e.g. in vivo spectroscopy using spatially selective excitation of the volume of interest, e.g. selecting non-orthogonal or inclined slices
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- the present invention relates to a magnetic resonance imaging apparatus (hereinafter referred to as an MRI apparatus), and in particular, an MRI apparatus suitable for UTE imaging in which a slice is selectively excited using a half-wave high-frequency pulse and a signal is measured with an ultrashort echo time (UTE).
- an MRI apparatus suitable for UTE imaging in which a slice is selectively excited using a half-wave high-frequency pulse and a signal is measured with an ultrashort echo time (UTE).
- UTE ultrashort echo time
- a slice selective gradient magnetic field is applied together with a high-frequency magnetic field pulse in order to select and excite a specific region.
- a high frequency magnetic field pulse a high frequency modulated by an envelope such as a symmetric sinc function is usually used.
- the profile obtained by Fourier transforming the high-frequency magnetic field modulated by the sinc function in the frequency direction is rectangular, and a predetermined rectangular region determined by the slice gradient magnetic field is excited.
- the slice refocus pulse is applied to refocus the phase of magnetization dispersed by the slice gradient magnetic field, but in UTE imaging, by applying the RF pulse including the fall time of the slice gradient magnetic field, The slice refocus pulse can be omitted.
- the high-frequency magnetic field pulse is changed in accordance with the change of the slice gradient magnetic field. It is necessary to make it.
- the response (slew rate) of the ideal (eg trapezoidal) slice gradient magnetic field pulse is usually used, but the slice actually applied
- the gradient response is not necessarily an ideal slice gradient response.
- a technique has been proposed in which the gradient magnetic field response that is output in hardware is calibrated based on the gradient magnetic field response measured in advance and the gradient magnetic field is output in a more ideal response (Non-patent Document 3). .
- the gradient magnetic field response measured in advance is a gradient magnetic field response measured based on the reference gradient magnetic field pulse, and strictly speaking, is different from the gradient magnetic field response used in actual imaging.
- the gradient magnetic field changes at the high output time (near the peak output) of the RF pulse (the gradient magnetic field fall time). Resulting in significant image quality degradation. Specifically, it leads to deterioration of the excitation characteristics of the slice, deviation of the slice thickness, blur in the slice direction, and the like. In UTE imaging, artifacts from the outside occur.
- An object of the present invention is to enable modulation of a high-frequency magnetic field pulse based on a gradient magnetic field response that is actually used, thereby improving deterioration of slice excitation characteristics, and in particular, improving image quality in UTE imaging.
- the present invention provides a method of simply measuring a slice gradient magnetic field response for each actual measurement and modulating a high-frequency magnetic field pulse using the actual gradient magnetic field response.
- the MRI apparatus of the present invention calculates a slice gradient magnetic field response from a magnetic resonance signal measured by a pulse sequence using the same slice gradient magnetic field as the imaging sequence.
- the pulse sequence for obtaining the slice gradient magnetic field response measures the magnetic resonance signal by applying a read gradient magnetic field in the same direction as the slice gradient magnetic field.
- the MRI apparatus of the present invention includes a gradient magnetic field generation unit, a transmission unit that generates a high-frequency magnetic field pulse, a reception unit that receives a magnetic resonance signal from a subject, and the gradient based on an imaging pulse sequence.
- a control unit that controls a magnetic field generation unit, a transmission unit, and a reception unit, and the imaging pulse sequence includes a first measurement sequence and a second measurement sequence, and the first measurement sequence is the first measurement sequence.
- the slice selection gradient magnetic field pulse is the same as the slice selection gradient magnetic field pulse used in the second measurement sequence, and the control unit generates the transmission unit using the magnetic resonance signal measured in the first measurement sequence.
- a high-frequency magnetic field pulse calculating unit for calculating a waveform of the high-frequency magnetic field pulse; and in the second measurement sequence, a high frequency of the waveform calculated by the high-frequency magnetic field pulse calculating unit Controls the transmission unit to a magnetic field pulse is applied in conjunction with the slice selection gradient magnetic field pulses.
- the first measurement sequence is a sequence in which an echo signal is collected by applying a readout gradient magnetic field pulse to the same axis as the slice selection gradient magnetic field
- the control unit includes the first measurement sequence.
- the phase profile of the magnetic resonance signal measured in the measurement sequence is calculated, the phase profile is differentiated in the time direction, and the high frequency magnetic field pulse is modulated using the differentiated profile.
- the MRI apparatus of the present invention is an imaging pulse sequence in which the high-frequency magnetic field pulse is asymmetrical in the time axis direction, for example, a pulse that is halved from the symmetrical pulse in the time-axis direction, or the intensity of the gradient magnetic field pulse during application of the high-frequency magnetic field pulse.
- This can be applied to an MRI apparatus provided with an imaging pulse sequence in which a high-frequency magnetic field pulse is applied even at the fall or rise time of a gradient magnetic field pulse.
- the modulation method of the high-frequency magnetic field pulse of the present invention is a method of modulating the high-frequency magnetic field pulse for excitation of the MRI apparatus, applying the first high-frequency magnetic field pulse and the first slice gradient magnetic field pulse, A step of calculating a phase profile from an echo signal generated by applying a readout gradient magnetic field having the same axis as the gradient magnetic field, a step of differentiating the calculated phase profile in a time axis direction, and the first slice gradient magnetic field pulse, Modulating the second high-frequency magnetic field pulse applied together with the same second slice gradient magnetic field pulse using the profile after differentiation.
- the actual gradient magnetic field response is measured immediately before imaging, and the high-frequency magnetic field pulse is modulated using the measurement data, so that the slice excitation characteristics are deteriorated due to the estimation error of the gradient magnetic field response. No image can be obtained.
- UTE imaging using a half RF pulse it is possible to obtain a good image quality without artifacts.
- summary of the MRI apparatus with which this invention is applied The figure which shows the imaging procedure by the 1st Embodiment of this invention
- the figure which shows an example of the pulse sequence with which the MRI apparatus of this invention is provided Diagram showing calculation procedure of gradient magnetic field response
- the figure which shows the calculation procedure of the high frequency magnetic field pulse shape (a)-(c) is a figure explaining the concept of rescaling among the procedures of FIG.
- (a) is a figure which shows the shape of the gradient magnetic field calculated from the data of prior measurement
- (b) is a figure which shows the modulation result of the calculated high frequency magnetic field pulse.
- FIG. 1 shows an overall configuration diagram of an MRI apparatus to which the present invention is applied.
- the MRI apparatus mainly includes a static magnetic field generation system 11 that generates a uniform static magnetic field around the subject 10, and magnetic fields in three axial directions (x, y, z) orthogonal to the static magnetic field.
- Gradient magnetic field generating system 12 for providing a gradient, high-frequency magnetic field generating system 13 for applying an RF pulse to subject 10, receiving system 14 for detecting a magnetic resonance signal (MR signal) generated from subject 10, and receiving system 14
- a reconstruction calculation unit 15 that reconstructs a tomographic image, a spectrum, and the like of an object using the MR signal received by the control unit 16 and a control system 16 that controls operations of the gradient magnetic field generation system 12, the high-frequency magnetic field generation system 13, and the reception system 14. It has.
- the static magnetic field generation system 11 is provided with a magnet such as a permanent magnet or a superconducting magnet, and the subject is placed in the bore of the magnet.
- the gradient magnetic field generation system 12 includes a gradient magnetic field coil 121 in three axial directions and a gradient magnetic field power source 122 that drives these gradient magnetic field coils 121.
- the high-frequency magnetic field generating system 13 receives a high-frequency oscillator 131, a modulator 132 that modulates a high-frequency signal generated by the high-frequency oscillator 131, a high-frequency amplifier 133 that amplifies the modulated high-frequency signal, and a high-frequency signal from the high-frequency amplifier 133.
- an irradiation coil 134 for irradiating the subject 10 with a high-frequency magnetic field pulse.
- the receiving system 14 includes a receiving coil 141 that detects an MR signal from the subject 10, a receiving circuit 142 that receives a signal detected by the receiving coil 141, and an analog signal received by the receiving circuit 142 at a predetermined sampling frequency. And an A / D converter 143 for converting the signal.
- the digital signal output from the A / D converter 143 is subjected to calculations such as correction calculation and Fourier transform in the reconstruction calculation unit 15 to reconstruct an image.
- the processing result in the reconstruction calculation unit 15 is displayed on the display 17.
- the control system 16 controls the operation of the entire apparatus described above, and in particular, a sequencer for controlling the operations of the gradient magnetic field generation system 12, the high-frequency magnetic field generation system 13 and the reception system 14 at a predetermined timing determined by the imaging method. 18 and a storage unit (not shown) for storing parameters necessary for control.
- the control system 16 performs calculations and pulse sequence creation to determine the waveform of an RF pulse, which will be described later, and passes the result to the transmission system 13 such as the modulator 132 and the gradient magnetic field generation system 12 via the sequencer 18.
- the timing of each magnetic field pulse generation controlled by the sequencer 18 is called a pulse sequence.
- Various pulse sequences are stored in advance in the storage unit, and imaging is performed by reading out and executing a desired pulse sequence. In the MRI apparatus of the present invention, a pulse sequence for UTE imaging described later is provided as a pulse sequence.
- the control system 16 and the reconstruction calculation unit 15 are provided with a user interface for the user to set conditions necessary for the internal processing. Through this user interface, parameters necessary for selecting an imaging method and executing a pulse sequence are set.
- the MRI apparatus of the present invention is characterized in that an RF pulse applied during slice gradient magnetic field pulses such as UTE imaging is controlled corresponding to the slice gradient magnetic field pulses.
- an RF pulse applied during slice gradient magnetic field pulses such as UTE imaging is controlled corresponding to the slice gradient magnetic field pulses.
- FIG. 2 shows an operation procedure of the present embodiment
- FIG. 3 shows a pulse sequence diagram according to the present embodiment.
- the imaging according to the present embodiment is configured with a preliminary measurement 100 for measuring a gradient magnetic field pulse and a main measurement 200 using an RF pulse shape determined from the result of the preliminary measurement. .
- the above measurement 326 is repeated by changing the polarity of the slice gradient magnetic field pulse 323 applied simultaneously with the half RF pulse 321 to obtain a pair of signals.
- the echo obtained by excitation with a half RF pulse is the measurement data from one side from the origin when considering the slice axis of k-space, but the signal obtained by two measurements with different polarity of the slice gradient magnetic field By performing complex addition, it is possible to obtain a signal equivalent to that obtained when a full RF pulse is used.
- Step 110 The pre-measurement pulse sequence 310 is executed.
- the pre-measurement pulse sequence 310 as shown on the left side of FIG. 3, while applying the same slice gradient magnetic field 312 as the slice gradient magnetic field 322 of the main imaging pulse sequence 320, the half RF pulse 311 is applied, and then the readout gradient magnetic field is applied.
- the echo signals are measured 317 by applying 314 and 315 to the same axis as the slice gradient magnetic field. Subsequently, the same measurement 319 is performed while applying the same slice gradient magnetic field 313 as the slice gradient magnetic field 323 of the main imaging pulse sequence 320 to obtain an echo signal.
- Step 120 Using the pair of echo signals obtained in step 110, gradient magnetic field pulses 312 and 313 are calculated. Details of step 120 are shown in FIG.
- phase profile of the signal is obtained (step 121).
- the phase can be calculated by calculating the arc tangent of the real part and the imaginary part of the complex signal, and is proportional to the integral value of the actually applied slice gradient magnetic field, as will be described below.
- the entire phase calculated for all sample points is called a phase profile.
- the transverse magnetization of the signal measured by applying the readout gradient magnetic field to the axis of the slice gradient magnetic field can be expressed by the following equation (1).
- x is the position in the slice direction
- M 0 is the initial magnetization
- rf (t) is the high-frequency magnetic field pulse
- G (s) is the gradient magnetic field pulse in the slice direction, and represents the gradient magnetic field strength in the time axis s direction.
- the echo signal m (t) calculated by the pre-measurement is expressed by the expression in the integral symbol of Expression (1) as shown in Expression (2).
- step 121 the left side of equation (3) is determined, which is proportional to the integral of G (s).
- Equation (4) G (s) is expressed as G (t) in accordance with the phase time axis t.
- Step 210 Based on the gradient magnetic field pulse output G (t) obtained in step 120, the shape of the half RF pulse used in the main imaging is calculated. That is, the half RF pulse designed as the main imaging pulse sequence is modulated by the gradient magnetic field output G (t) obtained in step 120. Details of this step 210 are shown in FIG.
- rescaling of the sample time of the half RF pulse (hereinafter referred to as the original RF pulse) rf designed as the high-frequency magnetic field pulse of this measurement pulse sequence is performed (steps 211 and 212).
- the sample interval k (t) in the slice direction (kz direction) of the k space also changes and is not equal.
- the RF pulse is hard-controlled, it is controlled at equal sample intervals. Rescaling is a process of changing the time interval of the RF pulse corresponding to the changing sample interval in the kz direction.
- the sample interval in the kz direction is narrower than the regions 701 and 703 in the central region 702, as indicated by the upper kz axis in (c).
- this is a rescale process, which means that the RF pulse waveform shown in (a) is sampled in the gradient magnetic field strength change, that is, in the kz space. It means to extend in the time axis direction according to the interval.
- Equation (6) a cumulative sum Gsum (t) of the gradient magnetic field pulses G (s) obtained in Step 120 is created (Step 211), and the maximum value Max (Gsum ( Normalize at t)) and rescale the sample interval t in the time direction at that rate (step 212).
- k (t) is equivalent to a sample point in the slice direction of the k space.
- rf (t ') is created by interpolating the values of equally spaced sample points in the time direction (t 'Is an equally spaced sample point ranging from 0 to T) (step 213).
- G (t) _max is the maximum value of G (t). That is, RF (t ′) is obtained by multiplying rf (t ′) by G (t) normalized by the maximum value.
- Step 220 Using the RF pulse RF (t ′) calculated in step 210, an imaging pulse sequence for the main measurement is created.
- Step 230 The imaging pulse sequence created in step 210 is executed. This pulse sequence is based on the pulse sequence 320 shown in FIG. 3 and the half RF pulse shape is modulated, and the other pulses are as described above.
- the measurement is repeated with different readout gradient magnetic fields, and the obtained MR signal (2D data) is sent to the reconstruction calculation unit 15.
- the reconstruction calculation unit 15 reconstructs an image using this MR signal, displays it on the display 17, and stores it in a storage medium (not shown) or transfers it to another modality as necessary.
- the means for measuring the actual gradient magnetic field response immediately before imaging and the means for modulating the high-frequency magnetic field pulse using the measurement data are provided. Therefore, it is possible to obtain a good image quality without artifacts.
- Fig. 9 shows the imaging procedure of this embodiment.
- the prior measurement of the response of the gradient magnetic field pulse is the same as in the first embodiment. That is, also in the present embodiment, the pre-measurement pulse sequence 310 shown in FIG. 3 is executed using the same slice gradient magnetic field as the slice gradient magnetic field used in the imaging pulse sequence of the main measurement to obtain an echo signal (step 901). ). The response of the slice gradient magnetic field is calculated by obtaining the phase of the obtained echo signal and differentiating it.
- the waveform of the RF pulse used in the main measurement is calculated, and in the subsequent main imaging, an imaging pulse sequence is executed using the calculated RF pulse (step 902).
- the RF pulse waveform calculation is performed according to the procedure shown in FIGS. 4 and 6 as in the first embodiment.
- step 904 If the slice thickness and / or slice cross-section is changed after this measurement (step 904), return to the pre-measurement step 901, measure the slice gradient magnetic field response, calculate the RF pulse waveform, and change the slice conditions This measurement is performed with. If the slice condition is not changed, the main measurement is repeated until the imaging is completed (step 903).
- the RF pulse can be changed in real time in conjunction with the change of the slice condition, and a good image can be obtained even in imaging in which the response of the slice gradient magnetic field changes during imaging. .
- the present invention is not limited to UTE imaging but also a pulse sequence in which the slice gradient magnetic field strength changes during excitation by RF pulses. If there is, it can be applied.
- imaging include two-dimensional cylinder excitation (Magn. Reson. Med., 17 (2): 390-401, 1991, J. Magn. Reson., 87: 639-645, 1990).
- the slice gradient magnetic field response is obtained by calculation from the measured signal. be able to.
- 11 static magnetic field generation system 12 gradient magnetic field generation system, 13 high frequency magnetic field generation system, 14 reception system, 15 reconstruction calculation unit, 16 control system, 17 display, 18 sequencer
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Abstract
Description
図1に本発明が適用されるMRI装置の全体構成図を示す。MRI装置は、図1に示すように、主として、被検体10の周囲に均一な静磁場を発生する静磁場発生系11と、静磁場に直交する3軸方向(x、y、z)の磁場勾配を与える傾斜磁場発生系12と、被検体10にRFパルスを印加する高周波磁場発生系13と、被検体10から発生する磁気共鳴信号(MR信号)を検出する受信系14と、受信系14が受信したMR信号を用いて被検体の断層画像やスペクトルなどを再構成する再構成演算部15と、傾斜磁場発生系12、高周波磁場発生系13および受信系14の動作を制御する制御系16を備えている。
図2に本実施の形態の動作手順を、図3に本実施の形態によるパルスシーケンス図を示す。
図2に示すように、本実施の形態の撮像は、傾斜磁場パルスを測定するための事前計測100と、事前計測の結果から決定されるRFパルス形状を用いた本計測200とで構成される。
このような本撮像パルスシーケンスを踏まえて、以下、図2に示す各ステップの詳細を説明する。
事前計測パルスシーケンス310を実行する。事前計測パルスシーケンス310では、図3の左側に示したように、本撮像パルスシーケンス320のスライス傾斜磁場322と同じスライス傾斜磁場312を印加しながら、ハーフRFパルス311を印加した後、読み出し傾斜磁場314、315をスライス傾斜磁場と同じ軸に印加してエコー信号を計測317する。続けて、本撮像パルスシーケンス320のスライス傾斜磁場323と同じスライス傾斜磁場313を印加しながら同様の計測319を行い、エコー信号を得る。
ステップ110で得た一対のエコー信号を用いて、傾斜磁場パルス312、313を算出する。本ステップ120の詳細を図4に示す。
ステップ120で得られた傾斜磁場パルス出力G(t)をもとに、本撮像で用いるハーフRFパルスの形状を算出する。すなわち、本撮像パルスシーケンスとして設計されたハーフRFパルスを、ステップ120で得られた傾斜磁場出力G(t)で変調する。本ステップ210の詳細を図6に示す。
ステップ210で算出されたRFパルスRF(t’)を用いて、本計測の撮像パルスシーケンスを作成する。
ステップ210で作成された撮像パルスシーケンスを実行する。このパルスシーケンスは、図3に示すパルスシーケンス320を基本として、ハーフRFパルス形状が変調されたものであり、それ以外のパルスは前述したとおりである。読み出し傾斜磁場を異ならせて繰り返し計測を行い、得られたMR信号(2Dデータ)を再構成演算部15に送る。再構成演算部15は、このMR信号を用いて画像を再構成し、ディスプレイ17に表示するとともに、必要に応じて、図示しない記憶媒体に記憶したり、他のモダリティに転送する。
次に、本発明を、スライス選択の条件を変更しながら連続して撮像するMRI装置に適用した実施の形態を説明する。本実施の形態が対象とする連続撮像として、例えば、関節の屈折動作等の被検体動作に応じてスライス断面や撮像条件をインタラクティブに変更しながら撮像する動態撮像や、3D撮像から2D撮像に切り替える撮像などがある。
Claims (13)
- 傾斜磁場発生部と、高周波磁場パルスを発生する送信部と、被検体からの磁気共鳴信号を受信する受信部と、撮像パルスシーケンスに基づいて前記傾斜磁場発生部、送信部および受信部を制御する制御部と、を備え、
前記撮像パルスシーケンスは、第1の計測シーケンスと、第2の計測シーケンスとを含み、前記第1の計測シーケンスは前記第2の計測シーケンスで用いるスライス選択傾斜磁場パルスと同じスライス選択傾斜磁場パルスを用いるものであり、
前記制御部は、前記第1の計測シーケンスで計測した磁気共鳴信号を用いて前記送信部が発生する高周波磁場パルスの波形を算出する高周波磁場パルス算出部を備え、前記第2の計測シーケンスにおいて、前記高周波磁場パルス算出部が算出した波形の高周波磁場パルスを前記スライス選択傾斜磁場パルスとともに印加するように前記送信部を制御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に記載の磁気共鳴イメージング装置であって、
前記第1の計測シーケンスは、読み出し傾斜磁場パルスを前記スライス選択傾斜磁場と同じ軸に印加してエコー信号を収集するシーケン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2に記載の磁気共鳴イメージング装置であって、
前記制御部は、前記第1の計測シーケンスで計測した磁気共鳴信号の位相プロファイルを算出し、当該位相プロファイルを時間方向に微分し、微分後のプロファイルを用いて高周波磁場パルスを変調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に記載の磁気共鳴イメージング装置であって、
前記第1及び第2の計測シーケンスで用いるスライス選択傾斜磁場は、前記高周波磁場パルスの印加中に強度の変化するスライス選択傾斜磁場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4に記載の磁気共鳴イメージング装置であって、
前記第1及び第2の計測シーケンスで用いるスライス選択傾斜磁場は、立ち上り時間及び立下り時間を有する略台形のプロファイルを有し、
前記制御部は、前記高周波磁場パルスを、当該スライス選択傾斜磁場の立ち上り時間及び/又は立下り時間を含むスライス選択傾斜磁場印加中に印加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に記載の磁気共鳴イメージング装置であって、
前記第1及び第2の計測シーケンスの高周波磁場パルスは、時間軸方向の形状が非対称形な高周波磁場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6に記載の磁気共鳴イメージング装置であって、
前記第1及び第2の計測シーケンスの高周波磁場パルスは、時間軸方向の一点について対称な高周波磁場パルスを半分にした非対称高周波磁場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に記載の磁気共鳴イメージング装置であって、
前記撮像パルスシーケンスは、スライス選択傾斜磁場の印加条件が異なる複数の第2の計測シーケンスを含み、
前記制御部は、前記第2の計測シーケンスのスライス選択傾斜磁場の印加条件が変更される毎に、変更に先立って、前記第1の計測シーケンスの実行と高周波磁場パルスの波形の算出を行うことを特徴とする磁気共鳴イメージング装置。 - 請求項3に記載の磁気共鳴イメージング装置であって、
前記制御部は、基本となる高周波磁場パルスを前記位相プロファイルの時間軸に合わせてリスケールすることを特徴とする磁気共鳴イメージング装置。 - 磁気共鳴イメージング装置の励起用高周波磁場パルスを変調する方法であって、
第1の高周波磁場パルスと第1のスライス傾斜磁場パルスを印加し、前記第1のスライス傾斜磁場パルスと同じ軸の読み出し傾斜磁場を印加して発生させたエコー信号から位相プロファイルを算出するステップと、
算出した位相プロファイルを時間軸方向に微分するステップと、
前記第1のスライス傾斜磁場パルスと同じ第2のスライス傾斜磁場パルスとともに印加される第2の高周波磁場パルスを、微分後のプロファイルを用いて変調するステップとを含む高周波磁場パルスの変調方法。 - 請求項10に記載の高周波磁場パルスの変調方法であって、
前記変調するステップは、基本となる高周波磁場パルスを前記位相プロファイルの時間軸に合わせてリスケールするステップを含むことを特徴とする高周波磁場パルスの変調方法。 - 請求項10に記載の高周波磁場パルスの変調方法であって、
前記第1および第2のスライス傾斜磁場パルスは、高周波磁場パルス印加中に強度の変化するパルスであることを特徴とする高周波磁場パルスの変調方法。 - 請求項10に記載の高周波磁場パルスの変調方法であって、
前記第1および第2の高周波磁場パルスは、時間軸方向の一点について対称な高周波磁場パルスを半分にした非対称高周波磁場パルスであることを特徴とする高周波磁場パルスの変調方法。
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