JP2004261619A - Magnetic resonance imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic resonance imaging apparatus which performs imaging by using the phenomenon of chemical exchange and/or crossing relaxation positively among a plurality of kinds of nuclear pools represented by an MT effect in magnetic resonance imaging using the sequence of IR series including an inversion pulse. <P>SOLUTION: Inversion sequence including the inversion pulse is performed to a subject placed in a static magnetic field. After the performance of this inversion sequence, the magnetic resonance imaging instrument which performs the imaging sequence for gathering an MR signal from the subject is provided. A flip angle of the inversion pulse is set up smaller than 180°. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to medical magnetic resonance imaging based on nuclear spin magnetic resonance phenomena, and more particularly to an IR (inversion recovery) using an inversion pulse by actively taking in a phenomenon relating to mutual interference between a plurality of types of nuclear spins. A) a magnetic resonance imaging apparatus for executing a series of pulse sequences;

  2. Description of the Related Art Conventionally, as one method of medical magnetic resonance imaging, a method of using an MT (Magnetization Transfer) effect to obtain a different contrast image depending on the presence or absence of an MT effect in a living body is known. A specific example of this imaging method is described in Patent Document 1 (US Pat. No. 5,050,609: "Magnetization Transfer Contrast and Proton Relaxation and Use Thereof In Magnetic Resonance Imaging", by Robert S. Balaban et al.). It has been disclosed.

  The MTC effect originates from the ST (Saturation Transfer) method by "Forsen & Hoffman" (for example, Non-Patent Document 1 (Forsen et al., Journal of Chemical Physics, vol. 39 (11), pp. 2892-2901). (1963))), based on chemical exchange and / or cross relaxation of protons between free water and macromolecules, for example as a pool of multiple nuclei.

The MR (Magnetic Resonance) relationship between the free water and the proton of the polymer is as follows: free water (T ₂ = about 100 msec) having a long T ₂ relaxation (lateral relaxation) time and a polymer (T ₂ = about 0 m) having a short T ₂ relaxation time. .1 to 0.2 msec) resonate at the same frequency. The left column of FIG. 24 (a) shows the relationship on the frequency spectrum between free water and a polymer, and the right column of FIG. 24 (a) shows the exchange / relaxation relationship of magnetization (see FIGS. 24 (b) and (c)). The same applies). The signal value of the free water is due to the the T ₂ relaxation time is long, the signal value of the Fourier transform shows the narrow sharp peak half width as shown. On the other hand, the signal value of a proton whose movement is restricted between macromolecules such as protein (restricted) is short due to a short T ₂ relaxation time, so that the signal value after Fourier transform has a wide half-value width and a peak on the spectrum. Does not appear.

In the conventional imaging method utilizing the MT effect, when the peak of free water is considered as the center frequency, the resonance frequency of the free water is calculated by the frequency-selective pre-pulse (MTC pulse) as shown in FIG. A frequency shifted by 500 Hz is excited (off-resonance excitation). As a result, the magnetization Hf of the free water moves to the magnetization Hr of the polymer, and the MR signal value from the proton of the polymer decreases as shown in FIG. It decreases at a higher rate. Therefore, a difference occurs in the signal value between a part where the chemical exchange and / or cross-relaxation between free water and the polymer is reflected and a part where the chemical exchange and / or cross relaxation are not reflected, so that different contrast images can be obtained. It can be used for identification with.
U.S. Pat. No. 5,050,609 Forsen et al., Journal of Chemical Physics, vol.39 (11), pp.2892-2901 (1963)

  However, since the above-described MT effect is a result of interference between spins of different kinds of nucleus pools, conventionally, even in imaging where the special effect of the MT effect was not conscious, It is affected by the MT effect.

  In particular, for example, in the FLAIR (Fluid-Attenuated Inversion-Recovery) method and the fast FLAIR (fast FLAIR) method, a large number of applied inversion pulses (for example, 180 ° RF pulse) cause an MT effect on an adjacent slice plane. , Resulting in a decrease in signal strength. However, conventionally, this MT effect is not considered, and uneven sensitivity occurs between slices due to non-uniform application intervals of the inversion pulse.

  It is also known that not only the inversion pulse performed by the fast FLAIR method but also a plurality of 180 ° refocusing pulses according to the FSE (fast SE) method generate the MT effect. Affects the contrast between. From the opposite viewpoint, the contrast between tissues to be imaged can be changed by using the MT effect. However, at present, imaging methods utilizing the MT effect have not been developed for IR sequence sequences.

  Therefore, an object of the present invention is to provide a magnetic resonance imaging system using a sequence of an IR sequence including an inversion pulse to perform chemical exchange and / or cross-relaxation between a plurality of types of nuclear pools represented by the MT effect. The purpose is to perform imaging utilizing the phenomenon positively.

  Further, another object of the present invention is to provide a multi-slice type magnetic resonance imaging based on an IR sequence using an inversion sequence and an FSE method, in which chemical exchange between a plurality of types of nucleus pools affecting a plurality of slice planes and / or Alternatively, the effect of the cross-relaxation phenomenon is reduced and averaged to reduce sensitivity unevenness between slice planes.

  Further, another object of the present invention is to provide a method for multi-slice magnetic resonance imaging using an IR sequence using an inversion sequence and an FSE method. The influence of the phenomenon of cross relaxation can be reduced and averaged to reduce the sensitivity unevenness between slice planes, the repetition time TR / reversal time TI can be easily set by the user, and a large number of slices can be secured as much as possible. It is to be.

  Furthermore, another object of the present invention is to achieve one or more of the above objects and simultaneously perform so-called fat suppression in which MR signals from fat are suppressed in imaging using a sequence of IR sequences. That is.

  According to one embodiment of the present invention, there is provided a magnetic resonance imaging apparatus comprising: performing an inversion sequence including an inversion pulse on a subject placed in a static magnetic field; In the magnetic resonance imaging apparatus configured to execute an imaging sequence for acquiring an MR signal from the subject after the execution of the above, the flip angle of the inversion pulse is set to be smaller than 180 °.

  According to another aspect of the present invention, an inversion sequence including an inversion pulse is performed on a subject placed in a static magnetic field, and after execution of the inversion pulse, an MR signal is collected from the subject. A magnetic resonance imaging apparatus configured to execute an imaging sequence for performing a first process of applying an RF excitation pulse and a first slice gradient magnetic field to the subject; After the process, a second process of applying an RF refocus pulse and a second slice gradient magnetic field to the subject, and applying the RF excitation pulse and the first and second slice gradient magnetic field pulses to the PASTA ( polarity altered spectral and spatial selective acquisition) method.

  Further, as another embodiment of the present invention, an inversion sequence including an inversion pulse executed on each of a plurality of slice planes of a subject placed in a static magnetic field, and after an inversion time has elapsed from this inversion sequence. A magnetic resonance imaging apparatus configured to repeat a sequence of an IR sequence including an imaging sequence to be executed on each of the slice planes at every repetition time; and a means for manually designating the repetition time and the reversal time; Assigning the inversion sequence to be executed to at least one of the remaining slice planes during the inversion time given to each of the plurality of slice planes according to the inversion time, and assigning the remaining slice planes On at least one slice plane of While allocating the imaging sequence, the plurality of inversion sequences and the time interval of the magnetic action on the nuclear spins of the plurality of slice planes executed by the plurality of imaging sequences are set using two types of waiting time parameters. Means for setting the sequence of the IR sequence so as to be the same within the repetition time, and means for performing a multi-slice scan on the plurality of slice planes using the sequence of the IR sequence set by the setting means. It is characterized by having.

  ADVANTAGE OF THE INVENTION According to the magnetic resonance imaging apparatus which concerns on this invention, in the magnetic resonance imaging using the sequence of IR series containing an inversion pulse, the phenomenon of the chemical exchange and / or cross relaxation between a plurality of types of nucleus pools is positively affected. It is possible to perform imaging using, for example, to improve the contrast between white matter / gray matter or the like, or to improve the S / N ratio, for example, to improve the ability to depict active nerve tissue. It is possible to obtain a high quality MR image without any.

  Also, so-called fat suppression, in which MR signals from fat are suppressed in imaging using an IR sequence sequence, can be performed simultaneously.

  Furthermore, in multi-slice magnetic resonance imaging using an IR sequence using an inversion sequence and the FSE method, the effect of the phenomenon of chemical exchange and / or cross-relaxation between a plurality of types of nuclear pools on a plurality of slice planes is reduced. In addition, the sensitivity unevenness between slice planes can be reduced by averaging, the repetition time TR / reversal time TI can be easily set on a user basis, and a large number of slices can be secured as much as possible.

  Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 shows a schematic configuration of a magnetic resonance imaging apparatus according to this embodiment. This magnetic resonance imaging apparatus includes a magnet unit for generating a static magnetic field, a gradient magnetic field unit for adding positional information to the static magnetic field, a transmitting / receiving unit for receiving an MR signal, and a control and control unit that performs system control and image reconstruction. And an operation unit.

  The magnet unit includes, for example, a superconducting magnet 1 and a static magnetic field power supply 2 for supplying a current to the magnet 1, and generates a static magnetic field H0 in the Z-axis direction of a cylindrical opening into which the subject P is inserted. Let it. The magnet unit is provided with a shim coil 14 for primary shimming necessary for performing fat suppression. By adjusting the current supplied to the shim coil 14, shimming can be performed.

The gradient magnetic field unit includes three sets of gradient magnetic field coils 3x to 3z in the X, Y, and Z axis directions incorporated in the magnet 1, a gradient magnetic field power supply 4 for supplying a current to the gradient magnetic field coils 3x to 3z, And a gradient magnetic field sequencer 5a in the sequencer 5 for controlling the sequencer 4. The gradient magnetic field sequencer 5a includes a computer, and receives a signal for instructing an acquisition pulse sequence according to the high-speed FLAIR method or the like from a controller 6 (including a computer) of the entire apparatus. Thus, the gradient sheet - sequencer. 5a, X in accordance with the command pulse sequence, Y, and controls the application and its intensity of each gradient magnetic field in the Z axis direction, superimposable their gradient magnetic field in the static magnetic field H ₀ It has become. In this embodiment, a slice gradient G _S the gradient magnetic field in the Z-axis direction of the three mutually orthogonal axes, its X-axis direction and a readout gradient field G _R, further Y-axis direction that the phase ene - a gradient magnetic field G _E for de.

  The transmitting and receiving unit includes a high-frequency coil 7 disposed near the subject P in the imaging space in the magnet 1, a transmitter 8T and a receiver 8R connected to the coil 7, and a transmitter 8T and a receiver And an RF sequencer 5b (computer mounted) in the sequencer 5 for controlling the operation of the 8R. The transmitter 8T and the receiver 8R supply an RF current pulse having a Larmor frequency for exciting nuclear magnetic resonance (NMR) to the high frequency coil 7 under the control of the RF sequencer 5b, while the high frequency coil 7 The received MR signal (high-frequency signal) is subjected to various kinds of signal processing to form a corresponding digital signal.

  The control / arithmetic unit further includes, in addition to the controller 6 described above, an arithmetic unit 10 for inputting digital data of an MR signal formed by the receiver 8R and calculating image data, and a storage unit for storing the calculated image data 11, a display 12 for displaying an image, and an input unit 13. The arithmetic unit 10 specifically performs processing such as arrangement of measured data in a two-dimensional Fourier space, which is a memory space, and Fourier transform for image reconstruction. The controller 6 controls the operation contents and operation timing of the gradient magnetic field sequencer 5a and the RF sequencer 5b while synchronizing the two. In addition, the controller 6 executes a scan plan process illustrated in FIG. 18 in an interactive manner via the input device 13.

  Here, some features related to the imaging method employed in the present embodiment will be described.

(1) Applicable Sequence The sequence applicable to the magnetic resonance imaging apparatus of the present embodiment is an IR (inversion recovery) sequence pulse sequence using an inversion pulse (IR pulse). Specifically, a sequence combining the inversion pulse and the FE method (or the fast FE method), a FLAIR method sequence combining the inversion pulse and the SE method, and a high-speed sequence combining the inversion pulse and the fast SE method. There are a FLAIR sequence, a sequence combining an inversion pulse and an EPI (echo planar imaging) method, and the like.

  As one aspect of the fast FLAIR method, there is also an IR sequence sequence in which the fast SE method is implemented by a PASTA (polarity altered spectral and spatial selective acquisition) method.

(2) Nested Structure of Sequence In this embodiment, the multi-slice scan is executed by a sequence using an inversion pulse. The inversion sequence including the inversion pulse applied to each of the plurality of slice planes, and the subsequent imaging (signal acquisition) sequence employ a nesting method in the order of application to the slice planes. Here, two modes (sequential mode and interleave mode) are prepared as the nesting method.

  2 and 3 show sequence examples of the nesting method in the sequential mode. As shown in FIG. 2, seven inversion sequences including the inversion pulse are represented by seven Inv1 to Inv7, and corresponding imaging sequences are represented by seven imaging1 to imaging7. FIG. 3A shows seven adjacent slice planes 1 to 7 which are multi-slice scanned by this sequence.

  First, the inversion sequence Inv1 is applied to the first slice plane 1, and then, after a first adjustment time TiWait, the imaging sequence Imaging6 is executed on the slice plane 6 to which the inversion sequence Inv6 has already been applied. Further, the inversion sequence Inv2 is applied to the second slice plane 2 after a second adjustment time TrWait. Thereafter, after the first adjustment time TiWait, the imaging sequence Imaging7 is executed on the slice surface 7 to which the inversion sequence Inv7 has already been applied. Further, after the second adjustment time TrWait is set, the inversion sequence Inv3 is applied to the third slice surface 3. Furthermore, after the first adjustment time TiWait, the imaging sequence Imaging1 is executed on the slice surface 1 to which the inversion sequence Inv1 has been applied. Then, after the second adjustment time TrWait again, the inversion sequence is applied to the fourth slice surface 4. Hereinafter, pulse application and MR signal acquisition are performed in the same manner, and an imaging sequence Imaging5 is executed on the fifth slice plane, thereby ending the repetition time TR.

  As described above, in the case of the sequential mode nested sequence, the imaging sequence (Imaging6, Imaging6) for the other two surfaces (slice surfaces 6,7) is performed during the inversion time TI between one inversion sequence Inv1 and its imaging sequence Imaging1. 7) and an inversion sequence (Inv2, 3) for another two surfaces (slice surfaces 2, 3) are alternately entered, and a sequence corresponding to two slice surfaces as the offset number Offset is nested. Moreover, the order of the slice planes to be collected is continuous with the slice planes 6, 7, 1 to 5. FIG. 3B schematically shows the timing between the application of the inversion sequence to the slice planes 1 to 7 and the execution of the imaging sequence.

  On the other hand, FIGS. 4 and 5 show sequence examples of the nesting method of the interleave mode. In FIG. 4, in the same manner as described above, inversion sequences Inv1 to Inv7 including IR pulses are shown, and corresponding imaging sequences are shown by Imaging1 to Imaging7. FIG. 5A shows seven adjacent slice planes 1 to 7 which are subjected to multi-slice scanning according to this sequence.

  First, the inversion sequence Inv1 is applied to the first slice plane 1, and after that, with the first adjustment time TiWait, the imaging sequence Imaging4 is executed on the fourth slice plane 4 to which the inversion sequence Inv4 has already been applied. I do. Further, the inversion sequence Inv3 is applied to the third slice surface 3 after a second adjustment time TrWait. Thereafter, the imaging sequence Imaging6 is executed again on the sixth slice plane 6 to which the inversion sequence Inv6 has already been applied after the first adjustment time TiWait. Further, after the second adjustment time TrWait is set, the inversion sequence Inv5 is applied to the fifth slice plane 5. Further, after the first adjustment time TiWait, the imaging sequence Imaging1 is executed on the first slice plane 1 to which the inversion sequence Inv1 has been applied. Then, after the second adjustment time TrWait again, the inversion sequence is applied to the seventh slice surface 7. Thereafter, pulse application and MR signal collection are performed in the same manner, and the imaging sequence Imaging2 is executed on the second slice plane, thereby ending the repetition time TR.

  In the case of the nesting method of the interleave mode, the imaging sequence (Imaging4, 6) for the other two planes (slice planes 4, 6) is different between the inversion time TI between one inversion sequence Inv1 and its imaging sequence Imaging1. The inversion sequence (Inv3, 5) for the other two planes (slice planes 3, 5) alternates, and the sequence for two slice planes as the offset number Offset is nested. Moreover, the order of the slice planes to be collected is every other slice planes 4, 6, 1, 3, 5, and 7. FIG. 5B schematically shows the timing of applying the inversion sequence to the slice planes 1 to 7 and executing the imaging sequence.

(3) Consideration of Two Adjustment Times TiWait and TrWait Regardless of whether the nesting method is the sequential mode or the interleave mode, as described above (FIGS. 2 and 4), the two adjustment times TiWait and TrWait correspond to each slice plane. Are set before and after the imaging sequence (or inversion sequence).

  This aims at maximizing the number of slices, reducing and averaging the MT effect on each of a plurality of slice planes, and further facilitating setting of the repetition time TR and the reversal time TI from the viewpoint of the user. is there. In the present embodiment, such an object is achieved by using two adjustment times TiWait and adjustment time TrWait, and the setting is based on the following equation.

  The repetition time is TR, the inversion time is TI, the number of multi-slices is NS, the number of inversion sequences Inv included in the inversion time TI for one slice plane is TIoffset, the duration of the inversion sequence Inv is InvTime, and the duration of the imaging sequence Imaging is Assuming that the time is ScanTime, the first and second adjustment times are TiWait, and the adjustment time TrWait, the following equation holds for the repetition time TR and the inversion time TI.

[Equation 1]
TR = NS (Invtime + ScanTime + TrWait + TiWait) …… (1)
[Equation 2]
TI = TIoffset (Invtime + TiWait) + (TIoffset-1) (ScanTime + TrWait) …… (2)
From these two equations, a first adjustment time TiWait and a second adjustment time TrWait are calculated and set before and after the imaging sequence (or inversion sequence).

  However, as described later, the user first specifies any values as the repetition time TR and the inversion time TI. Therefore, the two adjustment times TiWait and TrWait calculated from the above two equations can be positive, negative, or zero in calculation. However, since the physical adjustment time is set, negative values of the adjustment times TiWait and TrWait are excluded (that is, only positive values or zero are adopted).

  Taking this time value condition into account, the number of slices NS does not always match the specified value. Therefore, in the present embodiment, the specified repetition time TR, inversion time TI, the duration of the imaging sequence Imaging can be calculated from the above two equations based on ScanTime, and the duration of the inversion sequence Inv can be calculated based on InvTime. The number of slices NS, the number of offsets Offset (the number of slices nested within the inversion time TI), and the first and second adjustment times TiWait and TrWait are presented.

  Therefore, the number of slices NS is usually discrete and given as a set of the number of slices NS and the number of offsets Offset (see FIG. 19). For example, in the case of TR = 8000 ms, TI = 2000 ms, ScanTime = 240 ms, and InvTime = 15 ms, the maximum number of slices that can be scanned (the number of slices that can be ensured for the same offset number in calculation) NS = 25. In this case, it is necessary to set the number of offset sheets at that time = 7. The number of discrete slices NS is 3, 7, 10, 14, 17, 21, and 25, and the offset numbers for the slice number NS are 1,..., 7 respectively. . That is, the number of slices and the number of nests are automatically determined as a set.

  The number of slices desired by the user does not always match the automatically set number of slices NS. In order to save the memory area of the storage device that stores the collected MR data, it is desirable that the number of slices can be changed one by one. The present embodiment employs the following method in order to satisfy both the condition for changing one sheet and the condition for averaging the MT effect. In other words, when the user automatically specifies the automatically calculated number of slices (maximum number of slices) NS that satisfies (includes) the desired number of slices NSdes and includes unnecessary slice planes, This slice plane is automatically designated, and the blanking is commanded. " In the case of “blank hit”, an RF pulse or a gradient magnetic field is actually applied to an unnecessary slice plane, but the resulting echo signal is not collected, or is not stored even if collected, and image reconstruction is performed. Don't get involved, say that.

(4) MT effect and RMT (Reverse MT) effect The MT (Magnetization Transfer) effect is a phenomenon of chemical exchange and / or cross-relaxation of protons between different types of nucleus pools such as free water and polymers. It is described as. In other words, the MT effect uses, for example, a broadband inversion pulse set as shown in FIG. 6 to transfer the magnetization of the protons of free water to the magnetization of protons of a polymer, for example. It is known as a phenomenon in which the value decreases (see FIG. 24).

  On the other hand, in the case of the combination of the free water and the polymer, the MT effect of raising the signal value from the free water (hereinafter, this effect is called “RMT (Reverse MT) effect”) is known. .

  For example, as shown in FIG. 7, for an inversion pulse (for example, a 180 ° RF pulse), the side lobe of a sinc function is lengthened, the number of lobes is increased, and the overall pulse length is set long. . As shown in FIG. 8, the excitation range of the pulse length of the inversion pulse is narrow so as to almost match the bandwidth on the frequency spectrum of the nucleus pool (for example, a pool of free water protons) to be examined. Set to bandwidth.

  Now, one of the two types of nuclei in the subject in a chemical exchange and / or cross-relaxation bond relationship is a free water proton and the other is a polymer proton. The target nucleus pool. In this case, the number of lobes of the inversion pulse is (-4, +1) π, for example, and the pulse length is set to 22 msec. As a result, the excitation bandwidth of the inversion pulse becomes 227 Hz, and becomes a “narrow band” almost matching the bandwidth of the spectrum curve of the free water as shown in FIG. Further, for example, when the number of π = ± 2π and the pulse length = 15 msec, the excitation band width is 267 Hz, which is a “narrow band”.

  By applying a slice gradient magnetic field together with the inversion pulse, a region of a predetermined slice width of the subject is selected, and proton spins of free water in the plane are frequency-selectively excited, and the −z ′ axis Flip to (rotational coordinates). At this time, the inversion pulse only sufficiently excites free water only in a frequency-selective manner, and its bandwidth is narrow as shown in FIG. Limited to That is, the proton spin of the polymer is hardly excited (saturated) by the inversion pulse.

Therefore, the magnetization H _r by proton spin magnetization H _f and polymer by proton spin of free water was in equilibrium while maintaining the mutual chemical bonding relationship as before excitation shown in FIG. 9 (a) what was found in the following excitation, as shown in FIG. (b), the magnetization in the excited non (not saturated) sufficiently excited from the magnetization H _r of the polymer (saturated) magnetizable H _f of free water Movement occurs.

In other words, as much as possible upon excitation by narrow-band inversion pulse, it is possible to move the magnetization H _r by spin polymer which is preserved so as not to saturate the free water through chemical exchange and / or cross relaxation after excitation. As a result, a higher signal value can be obtained as compared with the case where the value of the MR signal (echo signal) of free water reflected in imaging is collected using the conventional “negative” MT effect.

  Sites reported to have high MT effects in the human body include brain white matter / gray matter, liver, cartilage, kidney and the like. Therefore, the signal values of these portions have been lowered due to the conventional "negative" MT effect. By using the RMT effect, the signals at these sites are increased.

(5) Inversion pulse frequency bandwidth (BW)
It is known that a conventional inversion pulse is generally used in a range of about 1.0 msec to about 0.8 msec lobe length when formed by a sync function. That is, when converted into a frequency bandwidth, it corresponds to about 1000 Hz to about 1250 Hz (normal bandwidth). The spectrum waveform is adjusted by the side lobe of the inversion pulse.

  The frequency bandwidth of the inversion pulse of interest in the present invention is about 1000 Hz or less on the narrow bandwidth side and about 1250 Hz or more on the wide bandwidth side. In particular, on the narrow bandwidth side, it is desirable to be 800 Hz or lower at which the RMT effect appears substantially remarkably. On the other hand, on the broadband side, since it is considered that there is already a certain MT effect in the normal bandwidth region, one of the features of the present invention is to actively set the MT effect beyond the normal bandwidth.

  The relationship between the frequency bandwidth of the inversion pulse used in the inversion sequence and the phenomenon of chemical conversion and / or cross-relaxation of nuclear spins (MT effect and RMT effect) will be described.

  It has been confirmed that when the frequency bandwidth of the inversion pulse is set to a wide band (1000 Hz or more in this case), the MT effect is enhanced (or the RMT effect is reduced).

  FIG. 10 shows changes in signal values (arbitrary values) of the white matter (W) and gray matter (G) of the head with respect to changes in the frequency bandwidth of the inversion pulse in the fast FLAIR method. This experiment was performed using a magnetic resonance imaging apparatus of 0.5 T and setting the parameters of the fast FLAIR method to TR = 6000 ms, TI = 1700 ms, NS = 15, and an inversion pulse (± 3π, τ length variable). Was. The frequency bandwidth BW of the inversion pulse was changed from 385 Hz to 1538 Hz.

  As is apparent from the experimental results, the signal intensity changes according to the change in the frequency bandwidth of the inversion pulse. The MT effect and the RMT effect are balanced near the frequency bandwidth = 800 Hz. When the bandwidth is wider or narrower than this, the signal value increases according to the change in the bandwidth. Increasing the frequency bandwidth of the inversion pulse (especially above 1000 Hz) causes a restricted proton emission, resulting in a higher MT effect and a shorter T1app. If T1app is shorter, the recovery is quicker, so waiting for a TI time of 1700 ms improves the signal value (S / N ratio).

  Conversely, when the frequency bandwidth is set to 800 Hz or less, the signal value increases due to the RMT effect.

(6) Frequency bandwidth of 90 ° RF pulse of the SE (FSE) method in the IR sequence sequence In the FLAIR method or the fast FLAIR method, the signal value when the frequency bandwidth of the inversion pulse is changed is qualitatively illustrated. As shown in FIG. 10, the shape changes to a substantially V shape. Further, when such a measurement is performed while changing the frequency bandwidth of the 90 ° RF pulse of the SE (or FSE) method, the substantially V-shaped curve moves and is represented in the horizontal axis direction in FIG. Therefore, the contrast of the image can be determined using the frequency bandwidths of both the inversion pulse and the 90 ° RF pulse as parameters. That is, the degree of freedom for determining the contrast is increased.

(7) Application of MT Effect By increasing the frequency bandwidth of the inversion pulse, the MT effect in which the signal value to be collected is reduced can be reflected in imaging. The principle will be described with reference to FIG. The graph shown in the figure is obtained under scan conditions of, for example, 1.5T, TR = about 7000 ms, and TI = 2000 ms.

  For example, in the case of the fast FLAIR method, the frequency bandwidth is set to a wide band of, for example, 1250 Hz or more by shortening the lobe length of the inversion pulse. Due to this broadening of the band, the MT effect is further enhanced as described above. In the case of the fast FLAIR method, the MT effect is also enhanced due to the FSE sequence. It is assumed that the scan region is the head, and the longitudinal relaxation Mz '(that is, the signal value) of the white matter (W) and the gray matter (G) in the normal band (about 1000 to 1250 Hz) in which the frequency bandwidth of the inversion pulse is not broadened. ) Are denoted by a and b, and those curves when the band is widened are denoted by a ′ and b ′. Since the degree of occurrence of the MT effect is white matter (W)> gray matter (G), by widening the band, the degree of reduction in the signal value of the white matter (W) is greater than that of the gray matter (G). For example, when observed at an inversion time TI = 2000 ms, assuming that the signal value difference between the white matter (W) and the gray matter (G) is A in FIG. (> A). Therefore, the magnitude of the signal value differences A and B can be reflected on the contrast. That is, the contrast between white matter / gray matter is improved.

(8) Application of RMT Effect In addition, by narrowing the frequency bandwidth of the inversion pulse, the RMT effect that increases the signal value to be collected can be reflected in imaging. FIG. 12 illustrates the principle. The scan conditions are set, for example, the same as in FIG.

  For example, in the case of the high-speed FLAIR method, the frequency bandwidth is set to a narrow band of 1000 Hz or less by setting a long lobe length of the inversion pulse. Due to the narrowing of the band, the RMT effect becomes more remarkable as described above. In the case of the fast FLAIR method, the RMT effect is enhanced even by the FSE sequence. It is assumed that the scan region is the head, and the longitudinal relaxation Mz '(that is, the signal) of the white matter (W) and the gray matter (G) at the time of the normal bandwidth (about 1000 to 1250 Hz) which does not broaden the frequency bandwidth of the inversion pulse. Values) are a and b, and those curves when the band is narrowed are a 'and b'. Since the degree of occurrence of the RMT effect is white matter (W)> gray matter (G), by narrowing the band, the degree of increase in the signal value of white matter (W) is greater than that of gray matter (G). For example, when the observation is performed at the inversion time TI = 2000 ms, assuming that the signal value difference between the basal ganglia and the white matter (W) in the normal bandwidth is A in FIG. B (> A). Therefore, the contrast between the basal ganglia and the white matter (W) is improved, and the degree of depiction of the nerve tissue in the white matter (W) is improved. This is considered to be because the apparent T1 of the white matter becomes longer and the signal value can be maintained longer due to the RMT effect, so that the contrast of the white matter / cerebral nerve tissue is improved.

(9) Flip Angle of Inversion Pulse In the case of head imaging using an IR sequence, the inversion pulse is usually used to reduce the MR signal from cerebrospinal fluid (CSF) to zero. Therefore, the inversion time TI (time from the inversion pulse to the FES sequence) is set to the time to a null point (Null Point) on the vertical relaxation recovery curve as shown in FIG. By setting the flip angle of the inversion pulse FA <180 °, the null point can be accelerated while the MT effect or the RMT effect is emphasized. By reducing the flip angle of the inversion pulse to 150 °, the repetition time TR can be reduced as compared with the case where the flip angle is 180 °, so that the scan time is shortened.

(10) Adjustment of Inversion Time TI When the IR sequence is performed as the “FLAIR method” or the “high-speed FLAIR method”, the inversion time TI is set to a period from the inversion pulse to a null point (Null Point) (FIG. 13). However, different parameters can be emphasized by setting the inversion time TI to be “short TI time” shorter than that. When the “short TI time” is set in the FLAIR method, a T1-weighted image in which the T1 contrast is further enhanced is obtained. Further, when the “short TI time” is set in the fast FLAIR method, a T2-weighted image in which the T2 contrast is enhanced is obtained.

  The technique of "short TI time" can also use a technique for broadening the bandwidth of the inversion pulse (promoting the MT effect) or narrowing the bandwidth (promoting the RMT effect).

(11) Fat Suppression by PASTA Method PASTA (Polarity altered spectral and spatial selective acquisition), which is one of the fat suppression methods, can be incorporated into the above-described IR sequence pulse sequence. The PASTA method is described in, for example, “SMR 1995 # 657“ A polarity Altered Spectral and Spatial Selective Acquisition Technique ””, the outline of which will be described with reference to FIGS.

  FIG. 14 shows a pulse sequence of the PASTA method having a fat suppression effect, which is performed using the SE method. FIG. 15 shows the frequency bands of the spin inversion of the 90 ° RF excitation pulse and the 180 ° RF refocus pulse. The 90 ° RF pulse is formed with a sync function waveform so as to show a rectangle in a frequency band, and is shaped left and right asymmetrically on the time axis in order to shorten the echo time TE. For example, a 90 ° RF pulse is set at τ length = 4 ms and BW = 250 Hz when the total pulse length is 16 ms at 1.5 T. The 90 ° RF pulse is also set to a narrow band ΔF90 whose frequency band excites water spins at the slice center and does not excite fat spins in the presence of the first gradient magnetic field G90 in the slice direction. On the other hand, the band ΔF180 of the 180 ° RF pulse is set wider than that of the 90 ° RF pulse ΔF90.

  In order to suppress the collection of the fat signal, the polarity of the second gradient magnetic field G180 in the slice direction is inverted with respect to the first gradient magnetic field G90, and the intensity of the second gradient magnetic field G180 is equal to that of the first gradient magnetic field G90. The intensity is set to n times (n> 2). FIG. 16 shows the relationship between the slice position and the frequency based on the intensity ratio.

  Next, the behavior of spin will be described. When the 90 ° RF excitation pulse is applied from the initial state of FIG. 17A in the presence of the first gradient magnetic field G90, the water spins at the slice position AA ′ in FIG. 16 (FIG. 17B). ), The fat spins are tilted on the X 'axis of the rotation coordinates at the slice position of CC' in FIG. 16 (FIG. 17D) due to chemical shift.

  Next, when a 180 ° RF refocusing pulse is applied in the presence of the second gradient magnetic field G180 having the opposite polarity, the water spins at the slice position HH ′ in FIG. 16 (FIG. 17C). The spin is inverted by 180 ° at the slice position of II ′ in FIG. 16 (FIG. 17E) due to the chemical shift.

  That is, as shown in FIG. 16, since the slice position HH 'is included in AA', the water spins in the range of the slice position HH 'are inverted from the X' axis to the -X 'axis, and the phase converges. To generate an echo. On the other hand, since the slice position II ′ does not overlap with the CC ′ in the slice position, fat spins in the range of the slice position II ′ are not affected by the 90 ° RF pulse, It only reverses from the Z ′ axis to the −Z ′ axis by the 180 ° RF pulse. That is, since the fat spin has no X'Y 'rotation component, it is not detected as an echo signal by the high-frequency coil 7 arranged in parallel with the XY plane. Furthermore, since the fat spins in the range of the slice position CC ′ are only affected by the 90 ° RF pulse and are not affected by the 180 ° RF pulse, after flipping on the X axis, FIG. As shown in (1), only the signal fluctuates around the X 'axis, but no echo signal is generated. As a result, most of the collected echo signals are only the water echo signals on the slice plane AA ′, and the turbidity of the echo signals from fat can be efficiently suppressed.

  In the case of the PASTA method, the frequency selective excitation of water is accurately applied without shimming the static magnetic field, and effective fat suppression can be achieved.

  Next, the overall operation of the present embodiment will be described with reference to FIGS.

  The controller 6 performs the processing of FIG. 18 relating to the multi-slice scan. First, in step 101 of the figure, scan conditions instructed by the operator via the input device 13 are input. The scan conditions include a pulse sequence of an IR sequence, a frequency bandwidth (wide, normal, narrow) and a flip angle of an inversion pulse used in the sequence, and whether or not the PASTA method is performed. When the designated sequence is the FLAIR method or the fast FLAIR method, the value of the frequency bandwidth of the 90 ° RF pulse in the SE method or the FSE method is also specified to be a wide, normal, or narrow value. The effects of the frequency bandwidth, the magnitude of the flip angle, and the presence / absence of the PASTA method on the MR image are as described above. Therefore, these parameters are designated by the operator according to the characteristics of the MR image to be obtained.

  Next, the process proceeds to step 102, where the controller inputs, via the input device 13, the designation information of the nesting method regarding the multi-slice scan. As described above, as the nesting method, a “sequential mode” (see FIGS. 2 and 3) and an “interleave mode” (see FIGS. 4 and 5) are prepared. By this information input, one of the nesting methods is determined.

  Further, in step 103, parameters relating to the designated IR sequence pulse sequence are input from the input device 13. These parameters include, for example, a repetition time TR, a reversal time TI, a reversal sequence time InvTime, and a time of an imaging sequence (for example, FSE method) as shown in FIG. 19 (which illustrates the fast FLAIR method). ScanTime is included.

  Regarding the repetition time TR and the reversal time TI, the operator can specify any time. For this reason, in many cases, it is possible to specify a time value that is sharp and crisp, such as TR = 8000 ms and TI = 2000 ms.

  When the input processing of steps 101 to 103 is completed, the controller 6 sequentially shifts the processing to steps 104 and 105. In step 104, using the input data TR, TI, InvTime, and ScanTime, the number of slices NS, the number of offsets Offset that forms a pair with the number of slices NS, the adjustment times TrWait, and TiWait based on the equations (1) and (2). The recommended list data is calculated. In step 105, the list data is displayed via the display unit 12 as a recommended value list from the apparatus side to the operator. This display example is shown in FIG.

  Next, the controller waits for a response from the operator in step 106. If the operator does not find the set of the desired number (slice number, offset number) in the recommended value list, and wants to perform the calculation again by changing the parameter (NO in step 106), the process returns to step 103. It is. On the other hand, if the recommended number list includes the desired number of sets (YES in step 106), the process proceeds to step 107.

  In step 107, the desired number of slices NSdes specified by the operator is input. Thereafter, in step 108, the minimum number of slices NSsel including the desired number of slices NSdes (the maximum number of slices for the offset number specified in the same group) is selected from the data group of the recommended value list. .

  Then, in a step 109, it is determined whether or not NSdes <NSsel. When this determination is NO, NSdes = NSsel. That is, this is a case where the number of slices NSdes desired by the operator directly matches the number of slices in the recommended value list. In this case, the processing of the subsequent step 110 is skipped.

  On the other hand, if the answer is YES in step 109, the recommended number of slices NSsel automatically determined by the apparatus is larger than the number of slices NSdes desired by the operator. For example, there is a case where the operator specifies NSdes = 15 sheets, but NSsel = 17 sheets is specified automatically by the apparatus.

  In this case, the controller 6 performs the process of step 110. Now, if NSdes = 15 and NSsel = 17, there are two more. Therefore, the two slice planes corresponding to the larger number are designated as idle shot planes. The number and position of the slice planes for the blank shot are automatically determined by the controller 6 based on the setting mode stored in advance. In this setting mode, the blanking slice plane is set at i) both ends in the slice direction, ii) set at one end in the slice direction, and iii) the slice direction when the number of blank shots is one. Is set at a predetermined one-side end. It should be noted that the setting mode can be designated by the operator each time.

  When the scan preparation is completed in this way, in step 111, a multi-slice scan of the designated IR sequence is performed. In this scan, the scan conditions, the nesting method, the sequence parameters, and the blank shot (only when necessary) specified in the above-described processing are fetched.

  Now, assuming that the "high-speed FLAIR method" is specified based on the "sequential" nesting method, a specific sequence example will be described with reference to FIGS. In this sequence, the gradient magnetic field sequencer 5a and the RF sequencer 5b work in cooperation.

  First, an inversion sequence Inv1 for the slice plane 1 is performed. The inversion sequence Inv1 includes, for example, an inversion pulse IP composed of a 180 ° RF pulse and a slice gradient magnetic field Gs, and both are applied in parallel. The inversion pulse Inv1 is applied from the transmitter 8T via the high frequency coil 7, and the slicing gradient magnetic field Gs is applied from the gradient magnetic field power supply 4 via the gradient magnetic field coils 3z, 3z.

  The inversion pulse IP has its frequency bandwidth broadened or narrowed, and / or its flip angle is automatically set to 180 ° or a value smaller than 180 ° according to input information from an operator. ing. The same applies to other inversion pulses. The waveform area of the slice gradient magnetic field Gs is set so that the slice plane 1 can be selectively excited.

  When the inversion sequence Inv1 ends, the process waits for the first adjustment time TiWait automatically calculated. After this standby, the imaging sequence Imaging6 of the slice plane 6 that has been inverted and excited during the previous repetition time TR is performed by the FSE method.

  That is, first, a 90 ° RF pulse is applied together with the slice gradient magnetic field Gs. As a result, the slice plane 6 of the subject is selected, and proton spins in the plane are excited, and flip to the y 'axis (rotational coordinate). Next, in the sequence, the slice gradient magnetic field Gs is reversed. Thereafter, the readout gradient magnetic field Gr is applied via the gradient magnetic field coils 3x, 3x. This is an application for ensuring that the phases of the spins arranged in the Gr direction in the slice plane are aligned at the center time of each echo.

  Next, the first 180 ° RF pulse is applied together with the slice gradient magnetic field Gs. This causes the proton spin to rotate 180 degrees about the y 'axis. Further, after the first gradient magnetic field Ge = A for phase encoding is applied from the gradient magnetic field power supply 4 to the subject P through the gradient magnetic field coils 3y and 3y, the readout is applied through the gradient magnetic field coils 3x and 3x. The first spin echo signal R1 is collected via the high-frequency coil 7 together with the gradient magnetic field Gr.

  Thereafter, an inverted phase encoding gradient magnetic field Ge = -A is applied. This is to return the encode position to the center position (ke = 0) in the phase encode direction on the k-space when a 180 ° RF pulse is applied in order to avoid image quality deterioration due to a simulated echo.

  Next, after the second 180 ° RF pulse is applied together with the slice gradient magnetic field Gs, the second phase encoding gradient magnetic field Ge = B is applied. Then, the second spin echo signal R2 is collected via the high-frequency coil 7 together with the application of the readout gradient magnetic field Gr.

  Similarly, the third and fourth spin echo signals R3 and R4 are collected.

  In this imaging sequence, when the PASTA method for fat suppression is commanded in the processing of FIG. 18 described above, although not shown in FIG. 19, the 90 ° RF excitation pulse is set to a narrow band, and The magnitude and polarity of the slice gradient magnetic fields Gs90 and Gs180 applied in parallel with the 90 ° RF excitation pulse and the 180 ° RF refocus pulse are adjusted to those described above.

  After the imaging sequence 6 is performed on the slice surface 6 in this manner, the process waits for the second adjustment time TrWait. When the standby is completed, an inversion pulse IP for the slice surface 2 is applied together with the slice gradient magnetic field Gs. The magnitude of the magnetic field waveform of the magnetic field Gs is set so as to selectively excite the slice plane 2 adjacent to the slice plane 1.

  After the reversal sequence Inv2, the process waits again for the first adjustment time TiWait. Then, the imaging sequence Imaging7 of the slice plane 7 that has been inverted and excited at the previous repetition time TR is executed.

  Hereinafter, since the same repetition is performed, the protons on the seven slice planes 1 to 7 shown in FIG. 3A are inverted in the adjacent order and at regular intervals ta as shown in FIG. The imaging process is also performed in the order of adjacency and at regular intervals tb.

  These processes are further repeated for each of the seven slice planes 1 to 7 at a predetermined repetition time TR.

  The echo signals of the multi-slice scan collected in this manner are sequentially sent to the receiver 8R, where they are subjected to processing such as amplification, intermediate frequency conversion, phase detection, and low frequency amplification, and then A / D converted and echoed. Generated to data. In the arithmetic unit 10, the data of the echo data is arranged in a memory area capable of Fourier transform and corresponding to the k-space. Then, the image is reconstructed into a real space image by the two-dimensional Fourier transform. This image is stored in the storage unit 13 and displayed on the display 14.

  When the nesting method of the “interleave” mode is designated, the protons of the seven slice planes 1 to 7 shown in FIG. 5A are inverted every other slice as shown in FIG. The imaging process is also performed every other sheet. Unlike the “sequential” mode, since the inversion is performed every other slice and the signal is collected, the vacant time until the inversion between adjacent slices is a constant interval ta ′ (> ta: FIG. 3B), and its imaging is performed. The idle time until the processing is a constant interval tb '(> tb: FIG. 3B). That is, those times are longer than in the “sequential” mode.

  At the time of diagnosis, imaging is performed for both the case where the frequency bandwidth of the inversion pulse is shifted from the normal width to emphasize the MT effect or the RMT effect, and the case where the frequency bandwidth is set to the normal width. . A plurality of types of images having different contrasts obtained thereby are used for image interpretation.

  According to the present embodiment, there are the following advantages.

  First, advantages of the above-described nesting method will be described in comparison with a conventional multi-slice scan of an IR sequence. FIG. 22 shows a conventional normal (not nested) method, in which a pair of an inversion sequence and an imaging sequence is repeated in sequence during a certain repetition time TR while setting one adjustment time TrWait. FIG. 23 shows a conventional example of the nesting method. However, in the example of FIG. 22, the number of multi-slices is small, and in the example of FIG. 23, the sequence applied between adjacent slices is irregular, so that sensitivity unevenness between slices occurs.

  However, according to the present embodiment, in both the sequential mode and the interleave mode, the period ta, ta ′ of the inversion pulse applied to the adjacent slice plane is set to be as long as possible. Can minimize the effect of the MT effect (or RMT effect) on the adjacent slice planes by the inversion pulse applied to the slice plane. The effect is particularly remarkable in the interleave mode. In addition, since the effect of the MT effect (or RMT effect) is uniform on all slice planes, there is almost no sensitivity unevenness between slice planes due to such effects, and stable image quality can be provided.

  By the way, as a nesting method in the high-speed FLAIR method, J. One proposal was made by Listerud et al. (# 643 SMR '95, abstract "Optimized Inter-Leaved Fluid Attenuation with Inversion Recovery (OIL FLAIR)"). However, this conventional method does not adopt a method in which an operator can arbitrarily set the repetition time TR. Since the repetition time TR is a system obtained as a result of how the sequence is assembled, the value of the repetition time TR is odd, the degree of freedom in setting the repetition time TR is very low, and there are many restrictions on use. Further, no consideration is given to the MT effect and the RMT effect described above, and the sequence is determined while ignoring them.

  On the other hand, in the nesting method in the present embodiment, the operator can first set the repetition time TR and the reversal time TI. Therefore, in many cases, a sharp and precise time such as TR = 8000 ms and TI = 2000 ms can be set, and the setting flexibility is high. In addition, as described above, the MT effect and the RMT effect are made uniform between the slice planes at the lowest level, thereby eliminating sensitivity unevenness.

  Furthermore, the maximum number of slices can be set in a state in which a high degree of freedom in setting time and an improvement in sensitivity between slices and uniformity are maintained under given conditions. If the operator desires the maximum number of slices, that number of slice planes are scanned. However, when the number of slices desired by the operator is smaller than the maximum number of slices, the position of the surplus slice plane is automatically determined, and the blanking is designated. For example, in FIG. 3A or FIG. 5A described above, it is assumed that the operator has scanned five slice planes 1 to 7 at maximum (offset number Offset = 2). In this case, for example, the blanking is instructed to the slice surfaces 1 and 7 at both ends. When the blank shot is performed, it becomes irrelevant to the image reconstruction, but an actual MT effect or RMT effect occurs in slice planes 1 and 7. As a result, the effect of chemical exchange of spin levels and / or cross-relaxation on adjacent slice planes 2 and 6 becomes almost the same as the other slice planes 3 to 5. Therefore, the sensitivity unevenness between slice planes can be kept constant while being kept as low as possible.

  Further, according to the present embodiment, the MT effect and the RMT effect are positively used as needed, whereby, for example, the contrast between white matter / gray matter in the head, the parenchyma and the deep part of the brain are obtained. The contrast with the basal ganglia can be improved, and a diagnostically effective MR image which has never existed can be provided. Further, if necessary, by making the flip angle of the inversion pulse smaller than 180 °, the null point of the CSF signal can be increased, the TI time can be shortened, and the repetition time TR can be shortened. Further, if necessary, by setting the frequency bandwidth of the inversion pulse to a wide band or a narrow band, the "short TI time" state can be positively obtained and a T1-weighted image can be obtained. Furthermore, if necessary, the PASTA method can be applied to the SE sequence or the FSE sequence of the IR sequence, and the effect of fat suppression can be obtained together with the various effects described above.

  Note that the nested sequence according to the present invention, the width of the frequency band of the inversion pulse, the setting of the flip angle of the inversion pulse (<180 °), and the presence or absence of the PASTA method are performed independently of each other. Or may be implemented by combining appropriate items. Further, a single slice scan may be performed instead of the multi slice scan. Furthermore, an EPI method (FE system, SE system) may be adopted as the imaging sequence.

FIG. 1 is a schematic block diagram of a magnetic resonance imaging apparatus according to one embodiment of the present invention. 9 is a pulse sequence illustrating an example of a high-speed FLAIR method according to a nesting method (sequential mode). FIG. 7 is a diagram for explaining the relationship between a plurality of slice planes and slice positions and time in the sequential mode. 9 is a pulse sequence illustrating an example of a high-speed FLAIR method according to a nesting method (interleave mode). FIG. 4 is a diagram for explaining a relationship between a plurality of slice planes and slice positions and time in an interleave mode. The figure which shows an example of the frequency characteristic of the inversion pulse of a wide bandwidth. Waveform diagram showing an example of an inversion pulse The figure which shows the excitation range of a narrow band inversion pulse. FIG. 7 is a diagram for explaining a magnetization state before and after excitation according to the “Reverse MTC effect”. 9 is an experimental graph showing an example of a relationship between a change in the frequency bandwidth of an inversion pulse and an MR signal value. FIG. 4 is a diagram for explaining an MT effect when an inversion pulse is set to a wide band. The figure explaining the RMT effect when an inversion pulse is set to a narrow band. The figure explaining the change of the flip angle of an inversion pulse, and the change of TI time. A pulse sequence illustrating the PASTA method. The figure explaining the band of the narrow band 90 degree RF excitation pulse concerning the PASTA method. The figure explaining the difference of the slice position of water and fat in the PASTA method. The figure explaining the behavior of the proton spin of water and fat in the PASTA method. 4 is a schematic flowchart illustrating scan preparation according to the embodiment. 5 is a flowchart partially showing a detailed example of the fast FLAIR method. The figure which shows the example of a display of the recommendation data on a display. FIG. 4 is an explanatory diagram illustrating an example of a slice position of an empty shot. FIG. 9 is a diagram showing an example of a conventional IR sequence sequence in comparison with the present embodiment. FIG. 9 is a diagram showing another example of a conventional IR sequence sequence in comparison with the present embodiment. The figure explaining MT effect from spin behavior and spectrum distribution.

Explanation of reference numerals

Reference Signs List 1 magnet 2 static magnetic field power supply 3x to 3y gradient magnetic field coil 4 gradient magnetic field power supply 5 sequencer 6 controller 7 high frequency coil 8T transmitter 8R receiver 10 arithmetic unit 11 storage unit 13 input device

Claims (6)

An inversion sequence including an inversion pulse is performed on a subject placed in a static magnetic field, and after the inversion sequence is performed, an imaging sequence for acquiring an MR signal from the subject is performed. In a resonance imaging apparatus,
A magnetic resonance imaging apparatus, wherein a flip angle of the inversion pulse is set smaller than 180 °. An inversion sequence including an inversion pulse is performed on a subject placed in a static magnetic field, and after the execution of the inversion pulse, an imaging sequence for acquiring an MR signal from the subject is performed. In a resonance imaging apparatus,
The imaging sequence includes a first process of applying an RF excitation pulse and a first slice gradient magnetic field to the subject, and, after the first process, an RF refocusing pulse and a second slice And applying a PASTA (polarity altered spectral and spatial selective acquisition) method to the RF excitation pulse and the first and second slice gradient magnetic field pulses. Magnetic resonance imaging device. An inversion sequence including an inversion pulse to be performed on each of the plurality of slice planes of the subject placed in the static magnetic field, and an imaging sequence to be performed on each of the slice planes after an inversion time has elapsed from this inversion sequence. In a magnetic resonance imaging apparatus in which a sequence of an IR sequence including
Means for manually specifying the repetition time and the reversal time;
In accordance with the repetition time and the inversion time, during the inversion time given to each of the plurality of slice planes, the inversion sequence to be executed is assigned to at least one of the remaining slice planes and executed. Assigning the imaging sequence to be performed to at least one of the remaining slice planes, and magnetically applying nuclear spins of the plurality of slice planes performed by the plurality of inversion sequences and the plurality of imaging sequences. Means for setting the sequence of the IR sequence so that the time intervals of action are the same within the repetition time using two types of standby time parameters;
Means for performing a multi-slice scan on the plurality of slice planes using the sequence of the IR sequence set by the setting means. The magnetic resonance imaging apparatus according to claim 3, wherein the two types of standby time parameters are parameters set before and after each of the plurality of imaging sequences. Means for displaying a set of data of the number of offset slice planes corresponding to at least one of the remaining slice planes and the maximum number of slices corresponding to the number of offset slice planes; Means for designating the number of slices, means for designating the minimum maximum number of slices including the desired number of slices, and determining whether the minimum maximum number of slices and the desired number of slices match. Means for determining, and, when it is determined that the minimum maximum number of slices is greater than the desired number of slices by this determination, means for designating the larger number of slice planes as blank shot slice planes. The magnetic resonance imaging apparatus according to claim 4. The magnetic resonance imaging apparatus according to claim 5, wherein a frequency bandwidth of the inversion pulse is set to be wider or narrower than a bandwidth of 1000 to 1250 Hz.

Images