JPH05200012A - Magnetic resonance diagnosing apparatus - Google Patents

Abstract

PURPOSE:To provide a magnetic resonance diagnosing apparatus capable of detecting accurately a fine compound (metabolic substance) contained in a living body. CONSTITUTION:While a gradient magnetic field pulse for spoiling a high frequency exciting pulse and excited magnetized component is applied to restrain an unnecessary water signal, a (proton) compound in a region previously saturated with signals to be observed except for regions to be observed is selectively excited and the following multiple dimensional MRSI pulse sequence (MRSI) utilize a magnetic resonance phenomenon to observe a fine metabolic product in a living body including nuclides such as 1H, 31P, etc. The distribution of (proton) metabolic substance is obtained by the use of these processes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance diagnostic apparatus for obtaining anatomical information and biochemical information of a subject by utilizing a magnetic resonance phenomenon, and in particular, for obtaining information from a desired local region in a short time. The present invention relates to a magnetic resonance diagnostic apparatus.

[0002]

2. Description of the Related Art In recent years, MRSI (Magnetic Resonam) has been used as an effective method for early diagnosis of diseases and judgment of cancer treatment effect.
ce Spectraoscoopic Imaging) is attracting attention. MR
SI is a method for observing minute metabolites in a living body including nuclides such as 1H and 31P by utilizing a magnetic resonance phenomenon. For example, in 1H-MRSI, NAA (N-acetylaspartic acid), Cho (choline), PCr / Cr
(Creatine phosphate / creatinine), Glx (glutamine and glutamic acid), Lac (lactic acid), etc. can be observed. In 31P-MRSI, ATP (adenosine triphosphate), PCr (creatine phosphate), Pi (inorganic) Phosphoric acid), PME (phosphomonoester), PD
A three-dimensional distribution of metabolites such as E (phosphodiester) can be observed.

In such MRSI, since proton compounds such as NAA existing in the living body are smaller than the concentration of living body water by about four orders of magnitude, signals from metabolites are generated at the usual A / D converter bit number. Was not sufficiently detected, and the proton compound could not be observed unless the water signal was selectively suppressed.

As a method of suppressing this water signal, various methods utilizing the difference in chemical properties between water and a desired proton compound have been proposed, which are roughly classified into (1) the difference in chemical shift. Method (2) longitudinal relaxation time (T
The method of using the difference of 1), the method of using the difference of the transverse relaxation time (T2), the method of using the presence or absence (difference) of spin-spin coupling, and the difference of the diffusion constant of (5) The method of use, etc. are devised.

Of these methods, two methods (1) utilizing the difference in chemical shift are further known: (a) selective excitation method and (b) selective saturation method. In combination, the selective saturation method (b) is frequently used. In this selective saturation method, CHESS (CHEmical Shi
ft Selective) pulse (A.Haase, et al., Phys.Med.Bio
L.30,341 (1968)), the magnetization of the water signal alone is shunted to the horizontal plane by the selective excitation pulse, and then the horizontal signal magnetization is spoiled by the gradient magnetic field pulse to suppress the water signal. Then, it becomes possible to observe signals of minute metabolites by such a water signal suppression technique.

[0006] Further, for example, when observing a proton compound in the brain, the adipose tissue existing in the peripheral region of the brain is also
Since the abundance ratio is much higher than that of the proton compound, mixing of fat signals becomes a big problem when performing MRSI. This is because the matrix size in MRSI is relatively coarse, and thus signal mixing between voxels occurs.

Further, the magnetic field homogeneity in the peripheral region of the brain is usually higher than that in the central region of the brain, which is generally occupied by uniform tissue.
It is known that it becomes worse under the influence of magnetic susceptibility. Due to the inhomogeneity of the magnetic field, the resonance signal of water is several pp
CHE for suppressing the water signal mentioned earlier
Due to the deviation from the excitation band of the SS pulse, the water signal cannot be suppressed and the NAA, C to be observed
There is a possibility of overlapping with the chemical shift region where compounds such as ho and Cr exist.

Even in such a case, since signals are mixed between voxels when MRSI is performed, it is difficult to identify the spectrum of the original proton compound and the spectrum of the residual water signal.

Therefore, conventionally, the proton MRS of the head has been conventionally used.
When I is performed, the metabolic image of the whole head is not obtained, but in order to remove the influence of signals such as fat, as shown in FIG. 13, the central part of the brain is locally excited and the excitation is performed. A method of collecting a signal from only a part, that is, a local excitation method is used.

However, since the high-frequency excitation pulse applied for performing local excitation is usually a pulse having a shape based on the sampling function (or a function waveform obtained by filtering this), its excitation characteristic is As shown in FIG. 14, it has a shape having side lobes 141 and 142 at both ends.

For this reason, when the exciting region is large, fat and the like in the peripheral region of the brain are mixed in, and the size of the region that can be locally excited (region in which metabolic imaging is possible) is of course limited and unnecessary. Since a signal component is mixed, a correct metabolite image could not be obtained.

On the other hand, in the quantification of metabolites, since the relaxation time of the nuclide of each metabolite is different, unless the data is collected with a sufficiently long excitation pulse repetition time (TR), the relative amount of each metabolite is Even there was a problem that they could not be simply compared. In 1H-MRSI, usually Lac
Since the relaxation time of 1H is the longest and is about 1 second, it is preferable to set TR as 5 seconds or more. 31P-MRS
In I, the relaxation time of 31P of PCr is 2-3 seconds, so T
R is preferably set to about 15 seconds.

However, in this TR, the spatial three-dimensional M
In order to obtain RSI data, for example, in the case of 1H-MRSI with a resolution of 1.5 cm and a 16 × 16 × 16 matrix, a measurement time of less than 6 hours is required, and 31P-MRS is required.
In the case of I with a resolution of 3 cm and an 8 × 8 × 8 matrix, measurement time of about 2 hours was required, which was not practical.

[0014]

As described above, in the case of performing the localized MRSI using the conventional magnetic resonance diagnostic apparatus, the excitation characteristic of the high frequency excitation pulse applied for the local excitation is as shown in FIG. Side lobes 141,
Since it has 142, there is a drawback that an unnecessary metabolite image cannot be obtained because an unnecessary signal is mixed in the observation target region.

The present invention has been made in order to solve such a conventional problem, and provides a magnetic resonance diagnostic apparatus capable of suppressing unnecessary magnetic resonance signals mixed in an observation target region, and further, It is an object of the present invention to provide a magnetic resonance diagnostic apparatus capable of efficiently collecting a magnetic resonance signal from a local spatial three-dimensional region in a short time by applying the multi-slice method in combination with the local excitation means.

[0016]

In order to solve the above-mentioned conventional problems, the present invention applies a high-frequency pulse and a gradient magnetic field pulse to a subject placed in a static magnetic field, and In a magnetic resonance diagnostic apparatus that collects the magnetic resonance signals of the above and performs image processing based on the magnetic signals, a high frequency excitation pulse is applied to selectively saturate the magnetic resonance signals generated from outside the target region of diagnosis. A pulse applying means, a gradient magnetic pulse applying means for applying a gradient magnetic field pulse for phase compensation of a magnetic resonance signal excited by the high frequency excitation pulse, and a magnetic resonance by a local excitation sequence for locally exciting the target region. And a magnetic resonance signal collecting means for collecting the signal. Another is to apply a 90-degree pulse having a predetermined frequency and a gradient magnetic field to a subject placed in a uniform static magnetic field, and A first step of selective excitation, and after a lapse of a predetermined time from this first step, a 180-degree pulse and a gradient magnetic field which are selectively excited in two directions orthogonal to one imaging tomographic plane of the subject are applied. And a third step of observing a magnetic resonance signal generated from the subject by the second step. The steps from the first step to the third step are performed at predetermined time intervals. A magnetic resonance diagnostic apparatus using a multi-slice method for collecting magnetic resonance signals from a desired metabolite by repeating a plurality of times and performing image processing based on the magnetic resonance signals. Up to the first process of In addition, another 90-degree pulse having a frequency different from the one 90-degree pulse and a gradient magnetic field are applied to selectively excite another imaging tomographic plane of the subject to perform another imaging of the subject. 2 orthogonal to the fault plane
A 180-degree pulse that selectively excites each direction is applied, and another magnetic resonance signal generated from the subject is observed.

[0017]

As described above, the selective saturation pulse is applied to the peripheral region of the target region to suppress the magnetic resonance signal generated from this region, and thereafter, the water signal is suppressed by the pulse for suppressing the water signal. Apply a selective excitation pulse to the region,
If the proton compounds in this region are excited, the proton compounds can be excited with good selectivity, and the contamination of fat signals and residual water signals from the surrounding tissues can be suppressed, enabling metabolic imaging of a wide area of the brain. In addition to the above, it is possible to eliminate a false diagnosis due to a false image of a metabolic image due to an unnecessary signal.

Further, after a desired imaging tomographic plane of the subject is selectively excited to observe a magnetic resonance signal, another imaging tomographic plane parallel to this imaging tomographic plane is selectively excited to observe a magnetic resonance signal. Therefore, it is possible to obtain a magnetic resonance image from a desired local three-dimensional region in a short time.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

The first is a block diagram showing the configuration of a magnetic resonance diagnostic apparatus according to an embodiment of the present invention. The magnetic resonance diagnostic apparatus shown in FIG. 1 includes a static magnetic field magnet 1 for generating a static magnetic field.
0, the magnet power supply 11, the shim coil system 12 including a plurality of shim coils, and the shim coil power supply 13 are orthogonal to each other,
Gradient coil system 14 and gradient coil power supply 15 for generating gradient magnetic fields each having a linear magnetic field distribution in the three Z directions.
A high frequency probe 16 for applying a high frequency magnetic field and detecting a magnetic resonance signal; a transmitter 17 for supplying a high frequency pulse to the probe 16; and a magnetic resonance signal detected by the probe 16 for receiving, amplifying and detecting. Receiver 18,
It is composed of a sequence controller 19 and a computer 20. The sequence controller 19 is a computer 20.
Transmitter 1 according to the sequence program sent from
7. A control signal is sent to the gradient coil power supply 13 and the like to apply a high frequency pulse and a gradient magnetic field pulse. Calculator 20
Controls the sequence controller 19 and shim coil power supply output, and collects and processes signals from the receiver.

FIG. 2 shows MRSI for observing proton compounds (metabolites) using the above-mentioned magnetic resonance diagnostic apparatus.
It is a pulse sequence diagram, and the operation of the present embodiment will be described below with reference to the same figure.

First, in the pulse sequence shown in the section t ₁ shown in FIG. 2, a high frequency pulse P ₁ having a frequency band ΔF is applied in order to suppress a magnetic resonance signal outside the target area. Simultaneously with the high frequency pulse P ₁ , gradient magnetic fields S ₁ , S ₂ , S corresponding to the regions to be selectively saturated are also provided.
Apply ₃ . As a result, the magnetization outside the target region can be saturated, and the magnetic resonance signal from this region can be suppressed. At this time, the gradient magnetic field pulse S ₁ ,
S ₂ and S ₃ also include the effect of spoiling the excited magnetic resonance signal. Further, the relationship between the frequency band ΔF, the gradient magnetic field strength G, and the size (width) ΔX of the saturation region is expressed by the following equation (1). G = ΔF / ΔX (1) Therefore, by appropriately selecting the center frequency of the high-frequency excitation pulse P ₁ , the position of the saturated region can be set arbitrarily.

FIG. 3 shows the profile of the excitation region (one-dimensional)
FIG. 4 is an explanatory view showing the local saturation characteristic S ₁₂ due to the high frequency pulse P ₁ and the high frequency excitation pulse P ₃ , P ₄ or P ₅
3 shows the local excitation characteristic S _{11 according} to FIG. As is clear from the figure, the center frequency of the high frequency pulse P ₁ for selective saturation and the size of the region are such that the characteristics of the high frequency excitation pulse P ₃ , P ₄ or P ₅ applied later are supplemented. Is set to. That is, the local excitation characteristic S ₁₁ shown in FIG.
The side lobe 31 possessed by is canceled by the local saturation characteristic S ₁₂ . As a result, it is possible to prevent unwanted signals from being mixed due to side lobes.

FIG. 4 is a sectional view of the human brain, showing an image of the fat component 41. However, in reality, a positional shift occurs due to the difference in the chemical shift components, so that an image deviated from the actual fat component 41 is obtained as indicated by reference numeral 42. Therefore, when setting the center frequency of the high-frequency pulse P _1, the position shift due to this chemical shift component may be taken into consideration for selection.

On the other hand, by utilizing the displacement of the chemical shift, for example, when saturating the brain right, fat components in FIG. 4 (+) for high frequency pulse P ₁ at the same time as applying region limited so as to shift in the direction Gradient magnetic fields S ₁ , S ₂ , S
_When setting the polarity of ₃ and conversely saturating the left side of the brain, by inverting the polarity of the gradient magnetic field and shifting the adipose tissue to the (-) side, the fat signal can be saturated more effectively. ..

Further, the high-frequency pulse P ₁ is not limited to being applied once, and the same region or a plurality of regions to be excited are moved so that the selective excitation characteristic of the target region is improved. A high frequency pulse may be applied. At this time, it is desirable to adjust the RF power of each high-frequency pulse P ₁ so that the longitudinal magnetization is minimized at the time of exciting the target region, that is, at the time of applying the high-frequency pulse P ₃ in FIG.

In particular, when the target area is made into a rectangular parallelepiped shape and its peripheral area is saturated, the number of times N the high frequency pulse P ₁ is applied is 6 times. Further, as shown in FIGS. 5A to 5E, since the positional relationship between the excitation region 51 and the saturation region 52 can be set arbitrarily, the shape of the imaging target region, the composition of the tissue, etc. are considered. It becomes possible to set it optimally.

Then, in a section t ₂ shown in FIG. 2, a pulse sequence (M times) for suppressing a water signal is applied, and thereafter, in a section t ₃ , a multidimensional MRSI (Fig. Represents a 3D-MRSI) pulse sequence is performed to obtain a distribution of proton metabolites.

As described above, in this embodiment, the high frequency pulse for saturating the peripheral region of the target region to be locally excited is applied before the local excitation pulse sequence is executed. Therefore, unnecessary signals from other regions are not mixed in the magnetic resonance signal obtained from the target region,
An accurate metabolite image can be obtained.

Further, if the area to be saturated is set in consideration of the displacement of the metabolite image due to the chemical shift, unnecessary signals from the surroundings can be suppressed more effectively. In this embodiment, the spin echo sequence is shown as an example of the local excitation method, but the present invention is not limited to this, and another local excitation sequence may be used.

FIG. 6 is a diagram showing a pulse sequence used in the magnetic resonance imaging apparatus according to the second embodiment of the present invention, and shows timings of application of a high frequency pulse, a magnetic field gradient pulse and signal observation. .. Two-dimensional spatial MRSI at slice plane 1 in a particular direction of space
Pulse train for obtaining the
It is repeated at intervals of repeating time TR while changing ₂ or GS ₃ . Two-dimensional spatial MRS in slice plane 2
The pulse train for obtaining I is applied during the repetition time TR after observing the signal from the slice plane 1. If necessary, and as long as the repetition time TR is entered, a similar pulse train can be applied n times in order to obtain a signal from another slice plane.

Next, a pulse train for obtaining spatial two-dimensional MRSI on one slice plane will be described. 9
After the magnetic field gradient pulse GS ₁ for the slice direction of the 0 degree pulse (π / 2) is applied, the two 180 degree pulse (π) magnetic field gradient pulses GS ₂ and GS in the directions orthogonal to each other in the slice plane. Sequentially applied with ₃ .
τ is 180 from the center of 90 degree pulse (π / 2)
Represents the time to the center of the degree pulse (π), and τ + τ ′ represents the time from the center of the first 180 degree pulse (π) to the center of the second 180 degree pulse (π). This τ and τ ′ may be equal. The above pulse sequence is changed to the time TR while changing the intensities of the magnetic field gradient pulses GS ₂ and GS ₃ , respectively.
Repeat to collect data. In order to obtain a desired slice plane, the magnetic resonance frequency f ₀ determined by the static magnetic field
Is performed by modulating a 90-degree pulse with a frequency obtained by adding an offset frequency determined by the gradient magnetic field strength at a desired slice position. In FIG. 6, offset frequencies f ₁ and f ₂ are used to select slice plane 1 and slice plane 2. If a 90-degree pulse is used to select the slice plane as in this embodiment, the slice planes other than that are excited by the next two 180-degree pulses, but are rotated by 360 degrees and return to the state before the excitation. Even after observing the signal from the first slice plane, other planes can be excited. At this time, τ + τ ′ should be as short as possible so that the magnetization does not relax in the time of τ + τ ′.

In 1H-MRSI, as shown in FIG. 7, a frequency selective saturation pulse 21 for suppressing a water signal is added before applying a 90-degree pulse. As shown in FIG. 8, the frequency selective saturation pulse 21 is applied as necessary in order to disperse and apparently eliminate the phase of the narrow band pulse P21 for exciting only the water signal and the transverse magnetization generated by the excitation. It is composed of magnetic field gradient pulses GS ₁ , GS ₂ and GS ₃ . The narrow band pulse P21 is usually set to have a narrow band of 1 to 2 ppm, and uses a sinc function, a Gaussian distribution function, or a function optimized so that the final excitation characteristic becomes rectangular. This describes the motion of magnetization B
In this method, the high-frequency pulse waveform input as an initial value is modified using an optimization method so that the solution of the loch equation has a rectangular excitation characteristic. If saturation is insufficient with one frequency selective saturation pulse, the magnetic field gradient is changed several times while changing the direction.

A space selective saturation pulse 22 may be added to pre-saturate a signal in an uninteresting area in 1H, 31P MRSI. FIG. 9 is a diagram showing a pulse sequence when the space selective saturation pulse 22 is used, and the frequency selective saturation pulse 21 is applied after the space selective saturation pulse 22 is applied. As shown in FIG. 10, the space selective saturation pulse 22 is composed of a high frequency pulse P ₂₂ of a desired band and a magnetic field gradient pulse GS ₁ , GS ₂ , GS ₃ applied at the same time as used for local excitation. .. When there is residual transverse magnetization, a magnetic field gradient pulse is applied if necessary. The space selective saturation pulse 22 is
For example, it is used to saturate the signal on the selective saturation plane 24 outside the imaging region 23 as shown in FIG. The direction of selective saturation in this case can be determined by applying a magnetic field gradient pulse in a direction orthogonal to the selective saturation plane 24. Also,
The position of the selective saturation surface 24 can be controlled by changing the offset frequency f _x (x = 1, 2, ...) Of the high frequency pulse, and the width of the selective saturation surface 24 depends on the magnitude of the magnetic field gradient and the high frequency pulse. It can be controlled by changing the bandwidth. Furthermore, the front / rear / left / right /
If you want to selectively saturate the upper and lower parts, the space selective saturation pulse 22
May be applied repeatedly.

FIG. 12 is a diagram showing a pulse sequence for obtaining a local high resolution image. In FIG. 12, G
S ₁ , GS ₂ and GS ₃ indicate the slice direction, the read direction and the encode direction, respectively. The local excitation pulse sequence 25 that performs this multi-slice can also be used to obtain a local water distribution image with high resolution. The same matrix because the imaging area is localized,
That is, a high-resolution image can be obtained even with the same number of encodings. The magnetic field gradient pulse applied after the observation time is applied as necessary to disperse the phase of the residual transverse magnetization.

[0036]

As described above, according to the first invention, prior to selective excitation of a target region for observing a compound when performing MRSI, magnetic resonance signals other than the target region are selectively saturated. By doing so, unnecessary signals can be suppressed. Therefore, the MRS over a wide area that is not affected by the fat signal and the residual water signal in the peripheral area.
I can be obtained.

According to the second aspect of the invention, unwanted signals are prevented from being mixed from the periphery of the target area, and the desired local area 3
It is possible to obtain a magnetic resonance signal from the dimensional region in a short time.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a magnetic resonance diagnostic apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a pulse sequence used in a magnetic resonance diagnostic apparatus according to an embodiment of the present invention.

FIG. 3 is a diagram showing profiles of a local excitation region and a local saturation region.

FIG. 4 is an explanatory diagram showing a positional shift due to a chemical shift component.

FIG. 5 is an explanatory diagram showing a target region of local excitation and a saturation region around the target region.

FIG. 6 is a diagram showing a pulse sequence used in the magnetic resonance diagnostic apparatus according to the embodiment of the present invention.

FIG. 7 is a diagram showing a pulse sequence used in the magnetic resonance diagnostic apparatus according to one embodiment of the present invention.

8 is a diagram showing an example of a frequency selective saturation pulse in FIG.

FIG. 9 is a diagram showing a pulse sequence used in the magnetic resonance diagnostic apparatus according to the embodiment of the present invention.

FIG. 10 is a diagram showing an example of a space selective saturation pulse in FIG.

FIG. 11 is a diagram for explaining the function of the space selective saturation pulse in FIG.

FIG. 12 is a diagram showing a pulse sequence used in the magnetic resonance diagnostic apparatus according to the embodiment of the present invention.

FIG. 13 is a diagram showing a pulse sequence for performing conventional spatial two-dimensional local MRSI.

FIG. 14 is an explanatory diagram showing a local excitation method.

[Explanation of symbols]

 10 Static magnetic field magnet 11 Magnet power supply 12 Shim coil system 13 Shim coil power supply 14 Gradient coil system 15 Gradient coil power supply 16 High frequency probe 17 Transmitter 18 Receiver 19 Sequence controller 20 Computer 21 Frequency selection saturation pulse 22 Space selection saturation pulse 23 Imaging area 24 selection Saturation surface 25 Local excitation pulse

Claims (8)

[Claims] 1. A magnetic resonance signal from a desired metabolite is collected by applying a high-frequency pulse and a gradient magnetic field pulse to a subject placed in a static magnetic field, and image processing is performed based on this magnetic resonance signal. In the magnetic resonance diagnostic apparatus for performing, a high-frequency excitation pulse applying means for applying a high-frequency excitation pulse to saturate a magnetic resonance signal generated from outside the region to be diagnosed in the subject, and excitation by the high-frequency excitation pulse Gradient magnetic field pulse applying means for applying a gradient magnetic field pulse to phase-disperse the generated magnetic resonance signal, and means for collecting the magnetic resonance signal by a local excitation sequence for locally exciting the target region, Magnetic resonance diagnostic device. 2. The metabolite is a proton compound,
The magnetic resonance diagnostic apparatus according to claim 1, wherein the local excitation sequence includes a high frequency pulse for water signal saturation. 3. The magnetic resonance diagnostic apparatus according to claim 1, wherein the sign of the gradient magnetic field applied at the same time as the high frequency pulse for saturating the outside of the target region is reversed. 4. A center frequency of the high-frequency excitation pulse according to a positional shift due to a chemical shift in the target region,
The magnetic resonance diagnostic apparatus according to claim 1, wherein the gradient magnetic field strength applied at the same time is set. 5. A selective excitation of one imaging tomographic plane of the subject by applying a 90-degree pulse having a predetermined frequency and a gradient magnetic field to the subject placed in a uniform static magnetic field. And a step of applying a 180 degree pulse and a gradient magnetic field which are selectively excited in two directions orthogonal to one imaging tomographic plane of the subject after a predetermined time has elapsed from the first step. 2 and a third step of observing a magnetic resonance signal generated from the subject by the second step. The first step to the third step are repeated a plurality of times at predetermined time intervals. A multi-slice magnetic resonance diagnostic apparatus that repeatedly collects a magnetic resonance signal from a desired metabolite and performs image processing based on the magnetic resonance signal. Until the process of 1 , Another 90-degree pulse having a frequency different from that of the one 90-degree pulse and a gradient magnetic field are applied to selectively excite another imaging tomographic plane of the subject and orthogonal to the other imaging tomographic plane. A magnetic resonance diagnostic apparatus is characterized in that a 180-degree pulse for selective excitation is applied to each of the two directions, and another magnetic resonance signal generated from the subject is observed. 6. Before applying the one 90 degree pulse,
The magnetic resonance diagnostic apparatus according to claim 5, wherein a frequency selective saturation pulse for suppressing a water signal is applied. 7. Before applying the one 90 degree pulse,
The magnetic resonance diagnostic apparatus according to claim 5, wherein a space-selective saturation pulse that selectively excites and saturates at least a part of a region other than a desired local region is applied. 8. After the observation of the magnetic resonance signal in the third step, a gradient magnetic field pulse for dispersing the phase of transverse magnetization is applied before the next 90 ° pulse is applied. Item 5. A magnetic resonance diagnostic apparatus according to item 5.