JPH11313810A - Mri device and mr image pickup method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a blood flow image and a substantial part image of high depicting capacity by greatly improving contrast between blood flow and a substantial part by an MT effect in comparison to a conventional method. SOLUTION: An MRI device comprises a means for applying MT pulse of different frequency from frequency specifying an image pickup area; a means for applying gradient magnetic field spoiler pulse; and a means for executing scan based on a data collecting sequence. The applied MT pulse comprises a plurality of divided MT pulses. Each of these divided MT pulses is an RF pulse that excites spin in a sliced area determined by the frequency of this MT pulse. The MRI device is also provided with a means for applying gradient magnetic field pulse applied abreast with the RF pulse to select the sliced area. The applied time of each RF pulse is short, and a flip angle of the spin excited by each RF pulse is set to a small value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an MRI apparatus and an MR imaging method for obtaining a blood flow image or an image of a substantial part inside a subject based on a magnetic resonance phenomenon of nuclear spin of the subject. In particular, MT (magnetization transfer)
The present invention relates to an MRI apparatus and an MR imaging method for obtaining an image with improved contrast between blood (or blood flow) and a substantial part using a pulse.

[0002] As used herein, "blood (or blood flow)" is used to mean "fluid" representing cerebrospinal fluid, blood (blood flow), and the like flowing in a subject.

[0003]

2. Description of the Related Art In magnetic resonance imaging (MRI), a nuclear spin of a subject placed in a static magnetic field is magnetically excited by a high frequency signal of a Larmor frequency, and an image is generated based on an MR signal generated by the excitation. This is an imaging method for obtaining.

[0004] One field of this magnetic resonance imaging is MR angiography (MR angiography).
As one of the conventional methods of the MR angiography, a phase method using a pulse called a flow encode pulse is known. As another approach to MR angiography, the MT effect (MTC (magnetizationtr.
In recent years, techniques for obtaining a blood flow image with a contrast between blood (blood flow) and a substantial part using the ansfer contrast (effect) have been actively used in recent years. One example is described in US Patent Publication No. 5,050,609.
(Magnetization Transfer Contrast and Proton Rel
axation and Use there in MagneticResonance Imagi
ng).

[0005] The study of the MT effect is described in Forsen & Hoffman.
ST (saturation transfer) method based on
et al., Journal of Chemical Physics, Vol. 39 (11), p.
p.2892-2901 (1963)), and as a plurality of nuclear pools, for example, chemical exchange and / or cross relaxation of protons between free water and a polymer. relaxation).

Several methods have been proposed for the conventional MR angiography utilizing the MT effect as follows.

FIGS. 17A and 17B show the frequency spectrum of free water and a polymer on the left side, and the exchange / relaxation relation of magnetization H on the right side. Looking at the spectra of free water and protons of the polymer, as shown in the figure, T2 relaxation (lateral relaxation)
There is a region where free water having a long time (T2 is about 100 msec) and a polymer having a short T2 relaxation time (T2 is about 0.1 to 0.2 msec) resonate at the same frequency. Since the T2 relaxation time of the signal value of the free water is long, the signal value after the Fourier transform shows a peak having a narrow half width as shown in the figure. On the other hand, the signal values of protons whose movements are restricted between macromolecules, such as proteins, are short because the T2 relaxation time is short, so that the signal values after Fourier transform have a wide half-value width and a peak on the spectrum. It hardly appears as a value.

[0008] Therefore, when a center frequency resonance peak frequency f ₀ of free water, as shown in FIG. (B) the left column, a frequency-selective pulse as the MT pulse, a center frequency f ₀ of, for example 500Hz of free water Exclude the shifted frequency band (off-resonance excitation). Thereby, between the magnetization Hf of the free water and the magnetization Hr of the polymer in the equilibrium state as shown in the right column of FIG. Hf moves to the magnetization Hr of the polymer. As a result, the MR signal value of protons of free water decreases as shown in the left column of FIG. Therefore, there is a difference in the signal value between the site where the chemical exchange and / or cross-relaxation between free water and the macromolecule is reflected and the site where the cross-relaxation is not reflected. There is a contrast difference between the two parts, and a blood flow image can be obtained.

At present, the MR angiography method based on the MT effect is largely spatially non-selective (sp
It can be classified into an atially non-selective imaging method and a slice-selective imaging method.

As the former, for example, “GBPike, MRM 25,
327-379, 1992 ", a frequency-selective binomial pulse is used as the MT pulse.
alpulse) is applied spatially and non-selectively, and the
Effect> MT effect of blood flow "to obtain contrast between the parenchyma and blood flow.

An example of the latter is "M. Miyazaki, M.
RM 32, 52-59, 1994 ". A slice-selective MT pulse is formed from an RF excitation pulse with a long application time and a gradient spoiler pulse, and imaging is performed by applying this pulse. The signal from the substantial part (stationary part) of the surface is significantly reduced by the MT effect from the blood flow, and the MT effect of the blood flow flowing into the imaging surface is reduced (the signal from the blood flow decreases more than the substantial part). This is a technique for extracting contrast between blood flow and parenchyma.

[0012]

However, in the case of MR angiography using the slice-selective MT pulse described above, "MT effect of parenchyma> MT effect of blood flow"
, The spin flip angle associated with the application of the MT pulse is large (for example, 500 ° to 1000 °).
Therefore, the MT effect on the blood flow flowing into the imaging surface is considerably large. As a result, the MR signal value from the blood flow on the imaging surface is considerably reduced. Therefore, it is not always possible to obtain a sufficiently satisfactory contrast difference between the blood flow / substantial part to meet the recent demand for higher resolution. I couldn't say it.

The present invention relates to the slice selective MT described above.
The purpose of the present invention is to overcome the current state of MR imaging using a pulse, and to obtain an image obtained by differentiating a moving blood flow from a stationary blood flow or a parenchyma with an MT pulse, and receiving an MT pulse from the MT. An object of the present invention is to provide a blood flow image and an image of a parenchyma with high imaging performance by reducing the effect of the effect and significantly improving the contrast between the blood flow and the parenchyma compared with the conventional method.

[0014]

In order to achieve the above object, an MRI apparatus according to the present invention is an MRI apparatus for obtaining an MR image of an imaging region of a subject, and has a frequency different from a frequency defining the imaging region. An MT pulse applying means for applying an MT pulse, and a spoiler applying means for applying a gradient magnetic field spoiler pulse after applying the MT pulse are provided.

[0015] As an example, it is desirable to have an imaging means for executing a scan based on a data acquisition sequence after applying the gradient magnetic field spoiler pulse to acquire an MR signal from the imaging region.

Preferably, the MT pulse applied by the MT pulse applying means comprises a plurality of divided MT pulses.

Further, preferably, each of the plurality of divided MT pulses is an RF pulse for exciting a spin in a slice region determined by the frequency of the MT pulse, and is applied in parallel with the RF pulse; A gradient magnetic field applying unit for applying a gradient magnetic field pulse for selecting the slice region; In this case, the application time of the RF pulse is short, and the flip angle of the spin excited by the RF pulse is set small.

Preferably, the gradient magnetic field spoiler includes:
In this configuration, the voltage is applied in any one of the slice direction, the readout direction, and the phase encode direction, any two directions, or all three directions.

On the other hand, the MR imaging method of the present invention is, as one aspect, an MR imaging method for obtaining an MR image of an imaging region of a specimen, wherein a plurality of slice regions different from the frequency defining the imaging region are selected. And applying a gradient magnetic field spoiler pulse to the subject,
Thereafter, a scan based on a data collection sequence is executed to collect MR signals from the imaging region.

Further, another aspect of the MR imaging method according to the present invention provides a method for imaging at least two of the subjects in a binding relationship based on at least one of a chemical conversion phenomenon and a cross relaxation phenomenon.
An MR imaging method for acquiring MR signals based on magnetic resonance phenomena of at least two types of nucleus pools, wherein a plurality of divided MT pulses are sequentially applied to a selected slice region in the subject, and the at least two types of nucleus pools are collected. Is decoupled, a gradient magnetic field spoiler pulse is applied to the decoupled nucleus pool, and thereafter, MR signals in an imaging region different from the slice region are collected.

Typically, the two nuclear pools are a free water nuclear pool and a polymeric nuclear pool.

As described above, a plurality of divided MT pulses, each of which has a short application time and a small flip angle, are applied to a slice area different from the imaging area, and the imaging area is off-resonance (off). -resonance). This divided MT pulse reduces the apparent T1 time of the flowing blood flow. That is, by turning on and off each MT pulse, the longitudinal relaxation (T1) of the spin of the moving blood flow is promoted, and the return to the steady state is accelerated. In other words, the MT effect on the free water of the blood flow until the final divided MT pulse application is reduced, and the total MT effect is reduced. Therefore, the signal value of the blood flow flowing from the slice region to which the MT pulse has been applied to the imaging region is higher than when the conventional MT pulse is applied.

On the other hand, since the substantial part is usually not moving, or even if it is moving, the moving amount is small, a plurality of divided MT pulses are effective as a sum of the divided MT pulses, and a desired MT effect is obtained. , The signal value from the substantial part decreases.

As a result, the contrast of the blood flow / substantial portion of the MRA image in the imaging region is smaller than that of the conventional slice-selective MT pulse applying method by the effect of shortening the T1 time for the moving blood flow. , Improved and excellent blood flow visualization ability.

One mode of the MRI apparatus for performing imaging based on the above principle is as follows.

That is, this MRI apparatus includes, in addition to the MT pulse applying means and the spoiler pulse applying means,
A second imaging unit that executes a scan based on a first pulse sequence in a state where the MT pulse and the gradient magnetic field spoiler pulse are not applied to collect a first MR signal from the imaging region; and After each application of the gradient magnetic field spoiler pulse, the second
A second imaging means for executing a scan based on the pulse sequence to collect a second MR signal from the imaging region; and an image generating means for generating the MR image from the first and second echo signals. It is characterized by having.

For example, the MT pulse applied by the MT pulse applying means includes a plurality of divided MT pulses. For example, each of the plurality of divided MT pulses is an RF pulse that excites a spin in a slice region determined by the frequency of the MT pulse.
And a gradient magnetic field applying means for applying a gradient magnetic field pulse applied in parallel with the F pulse and for selecting the slice area.

Specifically, the application time of each of the RF pulses is short, and the flip angle of the spin excited by each of the RF pulses is set to a small value. For example, the plurality of RF pulses are arranged adjacently on a time axis. In this case, the gradient magnetic field applying unit may be a unit that causes the gradient magnetic field pulse to rise and fall one by one corresponding to the rise and fall of each of the plurality of RF pulses. Further, the gradient magnetic field applying means may be means for raising and lowering the gradient magnetic field pulse corresponding to the first rising and falling of the plurality of RF pulses as a whole.

Preferably, the gradient magnetic field spoiler comprises:
In this configuration, the voltage is applied in any one of the slice direction, the readout direction, and the phase encode direction, any two directions, or all three directions.

[0030] More preferably, said image generating means is means for performing a difference calculation between image data based on said first and second echo signals.

Still another preferred configuration is provided with breath-hold command means for commanding the subject to hold his / her breath during the imaging by the first and second imaging means. On the other hand, the first and second imaging means are detection means for detecting a signal representing a cardiac phase of the subject, and synchronization means for executing the first and second pulse sequences in synchronization with the signal. May be provided.

More preferably, the first and second pulse sequences are the same two-dimensional scan or three-dimensional scan pulse sequence, and the pulse sequence is an SE method, an FSE method, a FASE method, an FE method, FFE
Method, segmented FFE method, and EPI method
It is a configuration that assumes one.

Further, for example, the imaging region of the subject including the imaging region is a lung field.

[0034]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

[First Embodiment] The first embodiment is shown in FIG.
This will be described with reference to FIG.

FIG. 1 shows a schematic configuration of an MRI (magnetic resonance imaging) apparatus according to this embodiment.

This MRI apparatus comprises a bed on which a subject P is placed, a static magnetic field generator for generating a static magnetic field, a gradient magnetic field generator for adding positional information to the static magnetic field, and a transceiver for transmitting and receiving high-frequency signals. Unit, a control / arithmetic unit for controlling the whole system and image reconstruction, an electrocardiographic measuring unit for measuring an ECG signal as a signal representing the cardiac phase of the subject P, and breathing the subject (patient). A breath-holding designating unit for giving a command to temporarily stop for diagnosis.

The static magnetic field generating section includes, for example, a superconducting magnet 1 and a static magnetic field power supply 2 for supplying a current to the magnet 1, and a cylindrical opening (diagnostic space) into which the subject P is loosely inserted. the axial direction (Z axis direction) to generate a static magnetic field H _0.
Note that a shim coil 14 is provided in this magnet portion. The shim coil 14 is supplied with a current for homogenizing a static magnetic field from a shim coil power supply 15 under the control of a host computer described later. The couch part can retreatably insert the top plate on which the subject P is placed into the opening of the magnet 1.

The gradient magnetic field generator has a gradient coil unit 3 incorporated in the magnet 1. The gradient magnetic field coil unit 3 includes three sets (types) of x, y, and z coils 3x to 3z for generating gradient magnetic fields in the X, Y, and Z-axis directions as physical axes of the gantry, which are orthogonal to each other. .
The gradient magnetic field unit further includes a gradient magnetic field power supply 4 for supplying a current to the x, y, z coils 3x to 3z. The gradient power supply 4 controls x, y, and x under the control of a sequencer 5 described later.
A pulse current for generating a gradient magnetic field is supplied to the z coils 3x to 3z.

The x, y, z coils 3x from the gradient magnetic field power supply 4
By controlling the pulse current supplied to ~ 3z,
A physical axis X, Y, by combining the gradient magnetic field in the Z direction, slice direction gradient magnetic field G _S, the phase encode direction gradient magnetic field G _E, and readout direction (frequency encode direction) arbitrarily gradient G _R set and Can be changed. Slice direction, phase encoding direction and readout direction are logic-axis directions perpendicular to each other, the gradient of each direction are superimposed on the static magnetic field H _0.

The transmitting and receiving unit includes an RF coil 7 disposed near the subject P in the imaging space in the magnet 1,
And a transmitter 8T and a receiver 8R, which are connected to each other. The transmitter 8T and the receiver 8R are connected to a sequencer 5 described later.
It operates under the control of. The transmitter 8T uses the magnetic resonance (M
An RF current pulse having a Larmor frequency for causing R) is supplied to the RF coil 7. The receiver 8R captures the MR signal (high-frequency signal) received by the RF coil 7 and performs various signal processing on the MR signal to generate digital data (original data).

The control / arithmetic unit includes a sequencer (also called a sequence controller) 5, a host computer 6, an arithmetic unit 10, a storage unit 11, and a display unit 1.
2, an input device 13 and a sound generator 16 are provided.

Among them, the host computer 6 has a function of instructing the sequencer 5 on pulse sequence information and controlling the operation of the entire apparatus by the stored software procedure.

The sequencer 5 has a CPU and a memory, stores the pulse sequence information sent from the host computer 6, and controls the operation of the gradient magnetic field power supply 4, the transmitter 8T, and the receiver 8R according to this information. At the same time, the receiver 8R is configured to temporarily receive the decibel data of the MR signal output from the receiver 8R and transfer the same to the arithmetic unit 10.

Here, the pulse sequence information is all information necessary for operating the gradient magnetic field power supply 4, the transmitter 8T, and the receiver 8R in accordance with a series of pulse sequences, for example, x, y, z coils. Information about the intensity of the pulse current applied to 3x to 3z, the application time, the application timing, and the like are included.

The pulse sequence may be a two-dimensional scan or a three-dimensional scan,
The form of the pulse train includes an SE (spin echo) method, an FE (field gradient echo) method,
FSE (fast SE) method, FASE (fast Asymmetric
Any pulse train such as the SE) method may be used.

In this MRI apparatus, as will be described later, under the control of the host computer 6, by driving the sequencer 5, the RF pulse as the MT pulse and the logical axis direction (arbitrary one among the slice direction, the phase encode direction, and the read direction) are read. A pre-sequence including a gradient spoiler to be applied in the (direction) is applied prior to the data acquisition sequence (also called the present sequence).

This MT pulse is set so as to be applied by slice selection. That is, the MT pulse is
As shown in FIG. 2, for example, a plurality of RF pulses for excitation formed by a sinc function are set, and in parallel with the application of each MT pulse, a slice gradient magnetic field G _{S is applied.} Is applied. The number of application of this MT pulse is plural n (for example, 10
The flip angle is set to a smaller divided value (for example, about 90 ° to 100 °) than a large value (500 ° to 1000 °) by the conventional MT pulse. The MT pulse is formed, for example, by modulating an RF signal having a desired frequency offset value with a sinc function. By the application of the MT pulse, the substantial part of the imaging site and the moisture receive the MT effect, and the signal value of the substantial part is reduced more than the moisture, thereby increasing the contrast between the two.

[0049] The after sequentially applied to n sets of MT pulse and slice gradient G _S, the slice direction, phase encoding direction, and gradient magnetic field spoiler pulse for spin phase dephased in readout direction is applied simultaneously.

The arithmetic unit 10 receives the digital data of the MR signal from the receiver 8R and inputs the raw data (raw data) to the Fourier space (also called k-space or frequency space) of the image formed in the built-in memory. ) And two-dimensional or three-dimensional Fourier transform processing for reconstructing original data into a real space image.

The storage unit 11 can store image data to which original data and reconstructed image data have been applied. The display 12 displays an image. Information such as scan conditions and pulse sequences can be input to the host computer 6 via the input device 13.

The voice generator 14 is an element functioning as a part of the breath-hold designating section, and can issue a breath-hold start and a breath-hold end message as voice when instructed by the host computer 6. .

Further, the electrocardiogram measuring section is provided with an ECG sensor 17 which is attached to the body surface of the subject to detect an ECG signal as an electric signal, and performs various processes including digitizing process on the sensor signal to perform host computer processing. 6 and an ECG unit 18 for outputting to the sequencer 5. The measurement signal from the electrocardiograph is used by the host computer 6 as a timing signal when the scan sequence is executed. As a result, the synchronization timing for ECG synchronization can be appropriately set, and an ECG-gated scan based on the set synchronization timing can be performed to collect MR original (raw) data.

Next, the operation of the MRI apparatus of this embodiment will be described with reference to FIGS.

In the MRI apparatus of this embodiment, the pulse sequence for MR angiography shown in FIG. 2 is executed based on a command from the sequencer 5.

As shown in the figure, this pulse sequence includes a pre-sequence SQ _pre executed first in each RF excitation, and a data acquisition sequence SQ _acq executed subsequently.

The pre-sequence SQ _pre is composed of an MT pulse train P _MT for producing an MT effect and the MT pulse train P
Gradient magnetic field spoiler pulse SP applied after application of _MT
S, SP _R, and a SP _E. The MT pulse train P _MT is M
RF pulse for a plurality of excitation sequentially applied as T pulse _{P 1, P 2, P 3} , ..., consisting of a P _n, inclined magnetic field pulse G _S slice to be applied in parallel with these MT pulse.

Slice gradient magnetic field pulse G _S The applied strength = G _S1 is a slice selective side due to the magnetic field, FIG. 3
As illustrated in (a) or (b), the gap is set to be a gapless or gap-free position different from the imaging surface _Sima .

Each MT pulse P ₁ (P ₂ , P ₃ ,...,
P _n ) is formed, for example, by a SINC function, and the flip angle of the spin FA accompanying this pulse application is, for example, 90 °.
The strength is set so that MT pulse P ₁ , P
_{2, P 3, ..., P} n Is set to 10 as an example.

That is, in the present embodiment, instead of the conventional configuration in which one MT pulse with a large flip angle FA (for example, 500 ° to 1000 °) is applied by slice selection,
This MT pulse is divided into a plurality of MT pulses to be sequentially applied.
A pulse train configuration is adopted.

Each MT pulse P ₁ (P ₂ , P ₃ ,...,
The flip angle FA given to P _n ) is a value (preferably 90 ° to 100 °) divided so as to cause a desired MT effect in the entire MT pulse train, and the number of the flip angles FA is also equal to the entire MT pulse train. An appropriate number (5 to 10) is determined depending on the balance between the MT effect and the imaging time. The application time of each divided MT pulse is about 1300 μsec, which is a conventional slice selection MT pulse.
It is shorter than the pulse by the division.

Further, the divided MT in the MT pulse train
The time interval Δt between the pulses is set to a value that can optimize the MT effect of water / fat in a substantial part of the MT pulse application surface (see FIG. 3). The time interval Δt differs depending on the measurement site, and may be set to Δt = 0 in some cases.

[0063] On the other hand, the slice direction, the read direction, and gradient magnetic field spoiler pulses SP _S were placed in three directions of the phase encoding direction, SP _R, SP _E is pre-sequence S
It is used as an end spoiler in Q _{p re.} For this reason, the gradient magnetic field spoiler pulses SP _S , SP _R , S
Each P _E, dispersed in every direction spin phase after a plurality of partitioning MT pulse application, without interference of the spin phase between the pre-sequence and the data acquisition sequence, preventing the occurrence of pseudo-echo I am trying to do it.
The spoiler pulse may be applied in any one or two directions.

[0064] Data acquisition sequence _{SQ acq} employs gradient for slice of each logical axis _{G S,} reading gradient field _{G R,} and the phase encoding gradient field _{G E,} for example, FSE method.

The host computer 6 executes a predetermined main program, and applies each pulse of the pulse sequence shown in FIG. This pulse application is performed via the x, y, z coils 3x to 3z and the RF coil 7 under the control of the sequencer 5.

First, in the pre-sequence SQ _pre , n flip-flops with a flip angle FA = α ° (eg, 90 °) (n
≧ 2: For example, n = 10) MT pulses P _{1 to} P _n are sequentially applied together with the slice gradient magnetic field G _S (= strength G _S1 ). Each of the MT pulses P _{1 to} P _n is formed by, for example, a sink function.

For example, the diagnostic site is set as shown in FIG.
If it is a limb, the slice gradient magnetic field G _S= G_S1For example
By appropriately setting the intensity, the desired imaging surface S_ima 
Pre-excitation of predetermined thickness approximately adjacent to the arterial inflow side of the rat
Surface S_mtIs set. As a result, the pre-excitation surface S_mtTo
MT pulses divided into n pieces are sequentially printed at regular time intervals Δt.
Will be added.

The slice gradient magnetic field G_SFor example strong
By adjusting the degree, the pre-excitation surface S _mtThe shooting surface S
_imaTo the outflow side of the artery, that is, the inflow side of the vein.
Can be. Also, the shooting surface S_imaAnd pre-excitation surface S_mt
A gap may be provided between the
It may be set to a state of topless.

Further, in the pre-sequence SQ _pre , immediately after the application of the divided MT pulse, the gradient magnetic field spoiler pulse SP _S is applied in each of the slice direction, the readout direction, and the phase encode direction. , SP _R And SP _E respectively applied.

Thus, first, the pre-excitation surface S
_mt is selectively excited a plurality of times sequentially by a plurality of divided MT pulses, that is, MT pulses having a smaller flip angle and shorter application time than the MT pulse according to the conventional method. With spins in the pre-excitation surface S _{m t} is excited by this, the excitation for the imaging surface S _ima off-
Because of resonance, M unique to the present invention as described later
The T effect is brought to the imaging surface S _ima . Spins remaining in the transverse magnetization due to the excitation of the plurality of divided MT pulses are generated by the subsequent spoiler pulse SP _S , SP _R , and SP _E.

Thereafter, the data collection sequence SQ _acq
Then, the sequencer 5 instructs the scan based on the FSE method as an example to the imaging surface _Sima . With this sequence, the slice gradient magnetic field G _S = G
_{Since S2} (≠ G _S1 ) is set, the imaging surface S
_ima is set to a desired slice position. Imaging surface S
A plurality of echo signals in response to a plurality of refocusing RF pulses are collected from the _ima via the RF coil 7 and sent to the receiver 8R. This series of imaging processing is executed for each excitation.

The echo data collected from the subject P is processed into digital data by the receiver 8R, and is sequentially stored in the arithmetic unit 10. The arithmetic unit 10 responds to a reconstruction command from the host computer 6 to perform a two-dimensional Fourier transform on a set of echo data arranged in the two-dimensional Fourier space, thereby reconstructing an MRA image of the imaging plane _Sima .

This MRA image has few artifacts, and the image contrast between the inflowing blood flow and the parenchyma is significantly improved as compared with the case where the conventional MT pulse is used. This is because, by using a plurality of divided MT pulses according to the present invention, the echo signal from the substantial part (stationary part) of the imaging surface S _ima is reduced by the MT effect, and the imaging surface S _ima blood flowing into the _ima (arteries and / or
Or vein) MT effect is reduced (reduced). That is, the apparent longitudinal relaxation T1 time of the flowing or tumbling blood flow is shortened due to the short MT pulse divided into a plurality, and the MT pulse is reduced.
While the effect is reduced, the substantial part (stationary part) has a signal value reducing effect that works as the sum of the plurality of divided MT pulses, and therefore, the blood flow (blood) flowing into the imaging surface _Sima . The image contrast between the image and the substantial part is significantly improved over the conventional MT effect using one MT pulse.

This feature will be described in detail below in terms of its principle.

First, an RF pulse with a long application time is applied once as an MT pulse, and an RF pulse with a short application time is applied.
M applied to a flowing or tumbling blood flow when a pulse is continuously applied a plurality of times.
Consider the T effect.

First, general factors that contribute to the time T1 will be described. The longitudinal relaxation time T1 depends on temperature and paramagnetism (para
It is known that the composition varies depending on the component, the size of the molecule, its environment, viscousness, and the like, and that between the molecules constituting the component is represented by the sum of the following factors.

[0077]

(Equation 1)

In the formula, T1 (DD) of the first item is “internuc
lear dipole-dipole interaction ". As shown schematically in FIG. 4, this interaction transfers its energy to a lattice based on RF excitation, thereby decoupling between the spins A and B of the coupled molecules. And increase the signal value.

The second item T 1 (SR) is “spin rota
tional ". The bound molecules make a rotational movement.
When a molecule rotates, depending on the magnitude of the motion, a partial “local magnetic field” is generated and T1
Contribute to shortening.

The third item, T 1 (SC), is “scaler coupling
". In this coupling, one of the coupling atoms is a quadrupole (quadrupole, spin quantum number I).
≧ 1 atom, for example, O ¹⁷ = 5/2, _mn ⁵⁵ = 5/2, and H ¹ == 1/2), the quadrupole has a unique short relaxation time called Quadrupole relation, and also shortens the relaxation time of the spin coupled to the quadrupole.

The fourth item, T 1 (CSA), is “chemical shift a
nizotoropy ”, which represents the change in the local field due to the change in the electron shielding effect. This change also affects T1.

As described above, the time T1 varies depending on various factors. There are other factors that affect T1 in addition to the factors described above, but those that have a large effect are the factors described above.

Even in stationary blood, oxyhemogro
bin and deoxyhemogrobin (oxidized and non-oxidized hemoglobin)
Also, since it has paramagnetic ions (mainly iron I and iron II), a local magnetic field is created and the T1 time is reduced.
Also, depending on the presence or absence of O ₂ , spin-spin relaxation
(T2), vein (w oxygen, T2 = 120 msec) and artery (less oxygen, T2 = 220 msec) are different.

FIG. 5 shows the dependence of T1, T2, and T1P on the effective correlation: Tc. In the figure, A is a hard solid, B is a soft solid, C is a high-clay liquid, and D is a normal liquid (TCFarrar and
EDBecker, Pulse and Fourier Transform NMR, P.98,
Academic Press (1971)).

Effective correlation: Tc is a factor representing the movement of a molecule, and indicates the degree of tumbling (rotation, vibration) of a fast-moving molecule. The further to the right on the abscissa in the figure, the higher the degree of solids and the slower the movement of molecules. From this relationship, it can be seen that the T1 time value differs between fast flowing blood and almost stationary blood.

Further, the apparent longitudinal relaxation time T of flowing blood is obtained by dividing and applying a plurality of MT pulses.
1 is shortened.

As described above, the MT (magnetization transfer) effect means that the equilibrium state of the free water Hf near the polymer Hr in a dipole-dipole interaction relationship is RF-excited from the free water to an off-resonance frequency with an RF pulse. This excites the protons of the polymer, thereby affecting the signal strength of free water interacting with the protons. That is, the magnetization of the free water is Hf, the magnetization of the polymer is Hr, and the constant of the reaction time is k ₁
And k− ₁ ,

(Equation 2) It is expressed as [] Is the concentration and K is the reaction constant.

Then, if T1 time of free water is T1f and T1 time of polymer is T1r,

(Equation 3) M _{f (t)} : magnetization of free water at time = t, M _{f (0)} : magnetization of free water at time = 0, M _{r (t)} : high at time = t Molecule magnetization and M _{r (0)} : Assuming the magnetization of the polymer at time = 0,

(Equation 4) Becomes

The magnetization M _fSAT when the MT pulse is applied is

(Equation 5) And the longitudinal relaxation time T _{1SAT at} that time is

(Equation 6) Becomes Thus, reaction constant _{k 1} is

(Equation 7) Becomes Here, T _1SAT is the apparent T1 (“Bala
ban, Magn. Reson. Quarterly Vol. 8, No. 2, 1992).

Therefore, the magnetization HfA of the protons of the free water in the moving blood, the magnetization of the protons of the macromolecules in the blood is HrA, the magnetization of the protons of the free water in the stationary substantial part is HfB, and FIG. 6 schematically shows the behavior of the magnetization of the present invention accompanying the application of the MT, where HrB is the magnetization of the protons of the macromolecules in the substantial part at rest.

The first divided MT pulse P ₁ (with a flip angle of, for example, 100 °) is applied to the magnetization HfA of free water protons and the polymer protons (see FIG. 10A) in equilibrium in the moving blood. When applied, the magnetization HrA of the polymer
The magnetization spin moves from the (nuclear pool) to the free water magnetization HfA (nuclear pool) (magnetization transfe
r) Conversely, energy is transferred from the magnetization HfA of free water to the magnetization HrA of the polymer (see FIG. 3B). Since they are divided MT pulses, their movement amounts are both small. That is, the MT effect is small.

The magnetization HrA of the polymer returns to the initial equilibrium state due to the longitudinal relaxation. At this time, as described above,
Due to factors such as dipole-dipole interaction and paramagnetic effect, T1 time is apparently reduced, and the return speed of the magnetization spin HrA is increased.

The divided MT pulse P
_{2, P} 3, ..., although _{P n} is sequentially applied, the total of the MT effect, apparently, decreased by the shortened time T1 (see FIG. 6 (c) (d)) . Thus, the MT effect on flowing (moving) blood is higher than that of stationary or hardly moving blood or parenchyma.
The effect is small, and the intensity of the echo signal collected from the imaging surface _Sima is high.

On the other hand, the MT effect generated between the proton magnetization HfB of the free water of the substantial part that is stationary or has little movement and the proton magnetization HrB of the polymer is described with reference to FIG.
Is the same as That is, in this case, it works as the sum of the individual divided MT pulses. For this reason, the MT effect is exerted on the substantial part of such an imaging surface _Sima as in the conventional case, and the collected echo signal is reduced as in the conventional case.

Therefore, the MRI apparatus according to the present embodiment can differentiate and image a stationary or hardly moving object and a moving object by using the slice-selective MT effect. In the obtained MRA image, the contrast of blood (blood flow) / substantial portion on the imaging surface can be remarkably improved as compared with the conventional method in which an MT pulse having a long application time and a large flip angle is applied once. . As a result, it is possible to provide a higher quality MRA image with a high ability to depict the blood flow on the imaging surface.

Further, the MRA image according to this embodiment is M
Since no R contrast agent is used, the non-invasive characteristics of normal MR imaging are utilized. For this reason, the mental and physical burden on the patient can be significantly reduced as compared with the case of taking an MRA image using a contrast agent.

[0097] In the example of the pulse sequence shown in FIG. 2, although the pulses are also multiple application configuration of a plurality of partitioning MT pulse slice gradient G _S upon application of, instead of this configuration As shown in FIG. 7, during the application of the plurality of divided MT pulses, the slice gradient magnetic field G _{S is} continuously obtained. Can be set to apply one pulse. Thereby, the MT pulse train P
_The time required for applying the _MT is short, and the entire imaging time can be shortened.

As another example of applying a plurality of divided MT pulses, there is a method shown in FIG. This technique is
The divided MT pulse is applied alone without applying a gradient magnetic field pulse in any of the slice direction, the readout direction, and the phase encode direction, and then any of the slice direction, the readout direction, and the phase encode direction is applied. The gradient magnetic field spoiler pulse is applied in one or more directions. That is, the divided MT pulse is applied in a slice non-selective manner. Thus, the divided MT pulse is effectively applied to a wide area, and is not limited to a slice or a slab. 7 and 8, the illustration of the gradient magnetic field (including the spoiler pulse) in the reading direction and the phase encoding direction is omitted.

The data collection sequence that can be used in the MRI apparatus according to the present embodiment is the normal F
Not limited to SE law, FE law, SE law, EPI
, FLAIR, FASE, and other imaging methods.

[Second Embodiment] FIG. 9 shows a second embodiment.
This will be described with reference to FIG.

This embodiment relates to an MRI apparatus capable of imaging a substantial part of a lung field using a plurality of divided MT pulses, the basic principle of which has been described above.

In the field of MRI, regarding the lung field,
Three methods have been proposed as the main imaging methods. They are based on a method using a hyper-polarized (xenon or helium) gas, a perfusion method using a contrast agent Gd-DTPA (for example, the literature "Hatabu H, et al., MRM 3").
6: 503-508, 1996), and a method by oxygen inhalation using molecular oxygen (see, for example, the document "Edelman RR, et al., Na
Nature Medicine, 2, 11, 1236-1239, 1996).

Among these, the first method using a hyper-polarized (xenon or helium) gas is a method in which the gas is inhaled into the lung field and an image is formed using, for example, the MR frequency of xenon (Xe) gas. In addition, the second contrast agent Gd-D
Perfusion using TPA is based on Gd-DTP in blood.
This is a method for observing the state where A is perfused. The third method of inhaling molecular oxygen is based on the report that although molecular oxygen is weakly paramagnetic, it exerts a sufficient signal change on the water signal observable by MRI on the surface of the alveoli.

However, the above-described imaging method has the following problems. The first method using a hyper-polarized (xenon or helium) gas has a problem that the cost is high because normal xenon gas needs to be hyper-polarized. Also, the second contrast agent G
Perfusion using d-DTPA requires the administration of a contrast agent, which requires invasive treatment, and above all, imposes a heavy mental and physical burden on the patient. In addition, inspection costs are high. Further, depending on the patient's constitution, the contrast agent may not be administered in some cases. Further, even with the third method of inhaling oxygen molecules, the change in signal is not sufficient on an image, and a satisfactory image that can be used for clinical practice or research, or even its form, cannot be captured.

The structure of the lung field is such that spongy alveoli, bronchi, pulmonary arteries, and pulmonary veins occupy most of their surface area,
There is air around it. Although the surface area of spongy alveoli is enormous, it does not have as much free water inside and outside cells as other organs (liver, kidney, etc.). Therefore, in the case of the lung field, the water signal to be detected by MRI is only detected from the vascular system, and the water signal value in the substantial lung field is insufficient. It is estimated that the area around the alveoli is not reflected as an MR signal because the water molecules are smaller than the surface area. Therefore, lung field T2
Value = 80 ms (Document "JMRI, 2 (S): 13-17,199
2)), it is presumed that conventional MR imaging cannot render the parenchyma of the lung field unless a contrast agent or the like is used, though it is comparable to other organs.

Therefore, in the present embodiment, the present invention
The advantages of the plurality of divided MT pulses are fully exhibited, and the parenchyma of the lung field, which has been conventionally difficult, can be imaged without using a contrast agent or the like.

The MRI apparatus according to this embodiment has the same hardware configuration as that of the first embodiment, but differs in the scanning procedure as follows.

The host computer 6 carries out at least two first and second imagings, as shown in FIG. 9, following the preparation work such as a positioning scan (not shown) and inputting of imaging conditions. . Each of these two imagings
This is a two-dimensional or three-dimensional MR scan for acquiring a set of echo data necessary for image reconstruction. It is desirable that each of these imagings be performed in combination with a breath holding method in which the patient consciously temporarily holds the image while holding his / her breath, and an ECG gating method based on an ECG signal.

The pulse sequence that can be used for this imaging may be a two-dimensional (2D) scan or a three-dimensional (3D) scan as long as it is a pulse sequence to which the Fourier transform method is applied. As a form,
SE method, FSE (high-speed SE) method, FASE (high-speed Asymm
etric SE) method (ie, an imaging method combining the fast Fourier method with the fast SE method), the FE method, and the fast F method.
E method, segmented high-speed FE method, EPI (echo planar imaging) method, and the like can be used.

The arithmetic unit 10 converts the digital data (original data) output from the receiver 8R into the sequencer 5
, And places the original data (also called raw data) in the Fourier space (also called k-space or frequency space) of the image on its internal memory, and divides the original data into two-dimensional or three-dimensional Fourier After conversion, the image data is reconstructed into real space image data. The operation unit 10
It is also possible to perform data synthesis processing and difference calculation processing on images.

The synthesizing process includes a process of adding image data of a plurality of frames for each corresponding pixel, a maximum value projection (MIP) process of selecting a maximum value for each corresponding pixel among the image data of a plurality of frames, and the like. . As another example of the combining process, the axes of a plurality of frames may be matched in Fourier space to combine the original data with the original data of one frame. Note that the addition processing includes simple addition processing, averaging processing, weighted addition processing, and the like.

The storage unit 11 can store not only reconstructed image data but also image data that has been subjected to the above-described synthesizing processing and difference processing. The display 12 displays an image. Further, through the input device 13, information on an imaging condition, a pulse sequence, image synthesis, and difference calculation desired by the operator can be input to the host computer 6.

The voice generator 16 is provided as an element of the breath-hold command unit. The voice generator 16 can emit a breath-hold start and a breath-hold end message as voice when instructed by the host computer 6.

Further, the electrocardiogram measuring section is provided with an ECG sensor 17 which is attached to the body surface of the subject to detect an ECG signal as an electric signal, and performs various processings including digitization processing on the sensor signal to execute the processing on the host computer. 6 and an ECG unit 18 for outputting to the sequencer 5. The measurement signal from the electrocardiogram measurement unit is used by the sequencer 5 when performing imaging. As a result, the synchronization timing by the ECG gating method (cardiac synchronization method) can be appropriately set, and data can be collected by performing imaging using the ECG gating method based on the synchronization timing.

Next, the operation of imaging by the MRI apparatus of this embodiment will be described with reference to FIGS.

By executing a predetermined main program (not shown), the host computer 6 executes, as shown in FIG.
Two images are taken as a three-dimensional FASE (High-speed As
ymmetric SE) method. The first imaging is performed in a state in which the breath holding method and the ECG gating method are used together and the MT pulse is not applied (off) as described later. At an appropriate timing after the end of the first imaging, the second imaging is performed by using both the breath hold method and the ECG gate method as in the first imaging. However, the second imaging is performed by applying the MT pulse (on).

FIG. 12 shows an example of the pulse sequence of the first and second imagings. This pulse sequence is based on a pulse sequence of a high-speed Asymmetric SE method of a three-dimensional scan (a scanning method in which the half-Fourier method is combined with the high-speed SE method). FIG.
Here, illustration of a gradient magnetic field (including a spoiler pulse) in the phase encoding direction is omitted.

In the case of the first imaging, only the data acquisition sequence SQ _acq in FIG. 12 is used, and the pre-sequence SQ _pre is not used. That is, the MT pulse train P _MT and the gradient magnetic field spoiler pulses SP _S , SP _R , and SP _E forming the pre-sequence SQ _pre are the first pulses.
It is not applied at the time of the second time. Therefore, the first time is M
Scanning is performed with the T pulse = off. This MT pulse train is composed of divided MT pulses as in the first embodiment.

On the other hand, in the case of the second imaging, FIG.
Prior to the data collection sequence SQ _acq in 2,
A pre-sequence SQ _pre is applied. That is, MT
Scanning is performed with pulse = on.

Although not shown in FIG. 12, in the pulse sequence used in the second imaging, the slice selection of the RF pulse in the data acquisition sequence SQ _acq (main scan) is not changed, and the division is performed. A configuration may be employed in which a gradient magnetic field is applied so that the selection region to which the MT pulse is applied is set not only in the slice direction but also in the phase encoding direction or the reading direction.

As an example, the three-dimensional FA shown in FIG.
In the pulse sequence of the SE method, the effective echo time TEef
f = 100 ms and the echo interval ETS = 5 ms. The MT pulse has a frequency offset = 13.
00 Hz, the number of divided MT pulses = 5 (total flip angle of all five MT pulses = 800 °). Further, the repetition time TR = 3247 ms, flip angle of flip pulse / flop pulse = 90 ° /
140 °, matrix size = 256 × 256, FOV
= 37 × 37 cm. In addition, when taking into account the running directions of the blood flow in the lung field in all directions, the average value of data obtained by scanning a plurality of times while changing the phase encoding direction (for example, changing the phase encoding direction by 90 °) is used as image data for each imaging. It is preferable to use a technique that employs an average added value of two scans of image data. This method is described in, for example, “J. of Magn. Reson. Imaging (JMR
I) 8: 503-507, 1998 ".

First, the first imaging is executed as follows. The host computer 6 executes a process shown in FIG. 10 in response to operation information from the input device 13 while executing a predetermined main program (not shown).

More specifically, the host computer 6 firstly inputs the delay time _TDL for the ECG gating method appropriately determined through, for example, the input device 13 (step S2).
0). Next, the host computer 6 determines the scanning conditions (the direction of phase encoding, the image size, the number of scans, the pulse sequence, the delay time of the ECG gate method, etc.) specified by the operator from the input device 13 and the information of the image processing method (addition processing or not). A maximum value projection (MIP) process or the like is input, the information is processed into control data, and the control data is output to the sequencer 5 and the arithmetic unit 10 (step S21).

Next, if it can be determined that the preparation completion notification before the scan has been received (step S22), step S2 is performed.
In step 3, a command to start breath holding is output to the voice generator 14 (step S23). As a result, the voice generator 14 emits a voice message such as "Please hold your breath after inhaling enough", and the patient who hears this will stop breathing with sufficient inhalation. Become.

After that, the host computer 6 instructs the sequencer 5 to start imaging (see step S24 and FIG. 11).

As shown in FIG. 11, when the sequencer 5 receives a command to start imaging (step S24-1), the sequencer 5
Signal reading is started (step S24-2), and EC is read.
The n-th occurrence of the peak value of the R wave (reference waveform) in the G signal is determined from the ECG trigger signal synchronized with the peak value (step S24-3). Here, the reason for waiting for the appearance of the R wave n times (for example, two times) is to surely estimate the time when the state has shifted to the breath holding state. This allows
An adjustment time T _sp for waiting for the appearance of the n-th R wave is set (see FIG. 12).

When the predetermined n-th R wave appears, a process of waiting for a delay time T _DL appropriately set in advance is performed (step S24-4). As described above, the delay time T _DL has the highest intensity of the echo signal when imaging the target lung field tissue, and is optimized to a value excellent in the rendering ability of the entity.

It is assumed that the time point at which the optimal delay time T _DL has elapsed is the optimal ECG-synchronized timing, and the sequencer 5
Executes imaging (step S24-5). Specifically, the transmitter 8T and the gradient magnetic field power supply 4 are driven according to the pulse sequence information already stored, and the three-dimensional FAS
The first scan based on the pulse sequence of the E method is executed by the ECG gate method (electrocardiographic synchronization method) as shown in FIG. However, the MT pulse train P _MT related to the pre-sequence SQ _pre is not applied (MT pulse = off).
As a result, under the initial slice encoding amount SE1, the scan time of about 600 ms is obtained as shown in FIG.
As shown in the figure, the three-dimensional imaging region R set including the lung field
_An echo signal is collected from _ima .

When the first scan based on the one slice encode amount SE1 ends, the sequencer 5 determines whether the scan based on the final slice encode amount SEn has been completed (step S4-6). In the case of NO (final scan has not been completed), while monitoring the ECG signal, the apparatus waits until, for example, two heart beats (2R-R) from the R wave used for imaging, for example, a shorter set period elapses, and stops. The recovery of the longitudinal magnetization of the spin of the substantial part is actively suppressed (step S24-7). That is, this waiting period is the repetition time TR.

Thus, after waiting for a period corresponding to, for example, 2R-R, for example, when the third R wave appears (step S24-7, YES), the sequencer 5 executes the processing in step S24-4 described above. return. Thereby, at the time when the designated delay time T _DL has elapsed from the ECG trigger signal synchronized with the third R-wave peak value, the second scan based on the slice encode amount SE2 is executed in the same manner as described above,
Echo signals are acquired from the three-dimensional imaging region _{R im a} (step S24-4,5). Similarly, scanning is repeated until the final slice encoding amount SEn (for example, n = 8) to collect echo signals.

When the last scan based on the slice encoding amount SEn is completed, the determination in step S24-6 is YES, and the sequencer 5 outputs a notice of completion of imaging to the host computer 6 (step S24-8).
Thereby, the processing is returned to the host computer 6.

Upon receiving the scan completion notification from the sequencer 5, the host computer 6 (FIG. 10, step S2)
5) A command to release breath holding is output to the sound generator 16 (step S26). For this reason, the voice generator 16 issues a voice message, for example, "You can breathe" to the patient, and the breath holding period ends.

Therefore, as described in the sequence of FIG. 12, scanning for each slice encoding amount is performed n times (for example, 8 times) based on the ECG gating method every 2R-R. The time required for the n scans, that is, the time for the patient to continue holding his / her breath, differs depending on the imaging conditions, but is, for example, about 20 to 25 seconds.

The eco signal generated from the patient P is received by the RF coil 7 for each scan and sent to the receiver 8R. The receiver 8R performs various pre-processing on the echo signal and converts it into a digital amount. This digital amount of echo data is sent to the arithmetic unit 10 through the sequencer 5, and is arranged in a three-dimensional k-space of an image formed in the memory. Since the half Fourier method is adopted, the data of the k-space that has not been collected is obtained by calculation and filled. Thus, the echo data is arranged in the entire k space.

Thereafter, when a predetermined standby time elapses, the second imaging is performed in the same manner as described with reference to FIGS. However, in step S21 of FIG. 10, the MT pulse train P related to the _pre- sequence SQ _pre
Information for applying _MT (MT pulse = on) is provided to the host computer 6, and control data such as scan conditions and an image processing method including the information is provided to the sequencer 5.
Other scan states are the same as those in the first scan. Therefore, the pulse sequence based on the three-dimensional FASE method executed in step S24-5 in FIG.
As shown in FIG. 2, a pre-sequence SQ _pre and a data collection sequence SQ _acq are included. That is, the second imaging is performed with the plurality of divided MT pulses applied to the beginning of each scan in the first imaging.

As a result, the echo data (original data) collected by the second imaging is also arranged in the k-space of the image as in the first imaging.

When the collection of the echo data by the two imagings is completed, the host computer 6 sends the data to the arithmetic unit 10
To process and display image data. This series of processing is shown in FIG.

First, the arithmetic unit 10 adds the echo data on the k space collected and arranged by the first imaging to 3
A dimensional Fourier transform is performed to reconstruct the absolute value image data IM1 in the real space (FIG. 14, step 31). Similarly, for the second imaging scan, similar reconstruction is executed to reconstruct the absolute value image data IM2 in the real space (step S32).

The signal value levels of the image data of the lung field axial image thus generated are schematically shown in FIGS. 15A and 15B (both are shown as two-dimensional images for convenience). FIG. 2A shows an image IM1 when the MT pulse is off, and FIG. 2B shows an image IM2 when the MT pulse is on. In FIG. 6B, the signal value is reduced due to the MT effect caused by the application of the divided MT pulse. When the decrease is compared between the substantial part and the blood flow, the percentage of the decrease in the substantial part is determined by the blood rate. Greater than that of the flow. Therefore, in FIG. 2B, only the substantial part where the rate of decrease is large is hatched and schematically shown.

FIG. 1 shows a comparison of the reduction rate of the signal value level.
6 (a) and 6 (b). Since the first image data IM1 has the MT pulse = off, the lung field LG
The signal value level of the substantial part and the blood flow becomes a level determined by the imaging state, as schematically shown in FIG. On the other hand, the second image data IM2 is data to which a plurality of divided MT pulses are applied. Therefore, the lung field L
The parenchyma part of G is more affected by the MT effect than the blood flow.
As shown schematically in FIG. 6 (b), the rate of decrease of the signal value Δ
T is large and is larger than the blood flow reduction rate ΔB. The difference of the reduction rate = “ΔT−ΔB” becomes the image data of the substantial part of the lung field LG.

Therefore, the arithmetic unit 10 uses the appropriate coefficient α (0 <α ≦ 1) to calculate both image data IM1, I2
For M2 (absolute value data),

## EQU8 ## Difference processing of IM1-α.IM2 is performed (FIG. 14, step S33). As a result, as schematically shown in the image data IM3 in FIG. 15C (shown as a two-dimensional image for convenience), the signal value of the blood flow in the lung field LG is almost canceled by the difference, and a substantial part remains.

The maximum intensity projection (MIP) process is performed on the thus generated three-dimensional image data IM3 in the real space to create two-dimensional image data (FIG. 14, step S34). This image data is stored in the storage unit 11 while being displayed as an image on the display 12. Also, the three-dimensional image data IM3 is stored in the same manner (step S35).

As described above, according to the MRI apparatus of the present embodiment, a plurality of divided MT pulses are used at the time of one of the imaging operations. , And a large MT effect can be provided. The reduction rate of the signal value due to the MT effect is surely larger than that of the pulmonary blood flow. Therefore, by performing a difference process (either a simple difference process or a weighted difference process) with the captured image when the MT pulse is off, the lung field substantial part can be imaged. That is, it is possible to satisfactorily image a substantial part of a lung field, which has conventionally been impossible to image without using gas, a contrast agent, oxygen, or the like.

As a result, it is not necessary to administer a contrast agent or the like, so that non-invasive imaging can be performed, and the mental and physical burden on the patient is significantly reduced. At the same time, the inconvenience inherent in the contrast method, such as the need to measure the timing of the contrast effect, is released, and unlike the contrast agent method, repeated imaging can be easily performed as necessary. Further, since no contrast agent or gas is used, it is advantageous in terms of inspection costs required for imaging.

In the present embodiment, the gradient magnetic field spoiler pulse is applied only once to the final stage of the plurality of divided MT pulses, and only the plurality of MT pulses are sequentially applied before that. For this reason, the standby time between MT pulses can be reduced (or almost zero), and the recovery of longitudinal relaxation of magnetization spin between MT pulses also decreases. Thereby, a larger signal value can be obtained.

Furthermore, the repetition time TR and the echo interval can be set short, and the slice direction can be set, for example, in the direction of the front and back of the patient (ie, in the direction from the front to the back). This reduces the overall scan time, and
Since the imaging length in the slice direction is shortened and the number of slice encodings can be reduced, the entire imaging time is shorter than the conventional T
It is greatly reduced compared to the OF method and the phase encoding method.
This reduces the burden on the patient and increases the patient throughput.

Along with this, each of the two scans (i.e., the scan for acquiring the target echo data group) can be completed within one breath-holding period, thereby reducing the burden on the patient. Significantly reduced.

Further, in the case of the above-described embodiment, the whole imaging for collecting the target echo data group is completed in each breath holding period. For this reason, the occurrence of body motion artifacts due to the periodic movement of the lungs and the like can be suppressed, and the occurrence of body motion artifacts due to positional displacement of the patient's body itself when performing breath-holding imaging multiple times can also be reduced. . Thereby, a high-quality image with less artifacts can be provided.

Further, since the ECG gating method is also used, it is possible to obtain image data from which body motion artifacts due to the movement of the heart are almost eliminated.

In the ECG gating method according to this embodiment, the scan is started at a time phase delayed from the R group by the delay time T _DL, but this scan start time is set according to individual clinical requirements. , May be set at other timings.

The contents described in the above embodiment are as follows.
It is only an exemplary mode for carrying out the invention described in the claims, and it is needless to say that those skilled in the art can change and modify various modes without departing from the spirit of the present invention.

[0152]

As described above, according to one embodiment of the MRI apparatus and the MR imaging method of the present invention, the MT pulse set to a slice-selective, long application time and a large flip angle, which has been conventionally used, is used. Instead of using a plurality of divided MT pulses with a short application time and a small flip angle, a blood flow (blood) flowing while applying the plurality of divided MT pulses is used. Means that the apparent T1 time is reduced, the MT effect is reduced, and the signal value is increased, while for stationary or almost stationary blood flow or parenchyma, the individual divided MT Since the MT effect as a sum of the effects is effective, the differentiation between a stationary or almost stationary object and a moving object becomes remarkable,
Compared with the conventional method, the cotton trust between the blood flow (blood) flowing into the imaging surface and the substantial part of the imaging surface is remarkably improved, and an MRA image with high blood flow rendering ability can be provided.

Further, according to another aspect of the MRI apparatus of the present invention, the MT pulse and the gradient magnetic field spoiler pulse are respectively applied to the image data by the MR signal imaged without applying the MT pulse and the gradient magnetic field spoiler pulse. From the image data by the MR signal
For example, by calculating the difference between pixels between data,
R image data is generated. For this reason, the phenomenon that the MT effect by the plurality of divided MT pulses has a greater effect on the substantial part than the blood flow is fully exhibited, thereby making it impossible, for example, conventionally to administer a contrast agent or the like. It is possible to provide the MR image of the parenchyma of the lung field without performing a highly invasive treatment such as a contrast agent. That is, imaging can be performed easily and non-invasively.

Further, by using the breath-holding method and the ECG gating method together with this imaging, it is possible to provide a high-quality MR image with less body motion artifacts.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing a configuration example of an MRI apparatus according to an embodiment of the present invention.

FIG. 2 is a timing chart illustrating an example of a pulse sequence according to the first embodiment.

FIGS. 3A and 3B are diagrams showing a positional relationship between an imaging plane and a pre-excitation plane for each diagnostic site.

FIG. 4 is a diagram illustrating decoupling between spins.

FIG. 5 is a view for explaining Tc dependence such as T1 relaxation time.

FIG. 6 is a view for explaining an MT effect based on a divided MT pulse with respect to free water and a polymer spin of a moving object.

FIG. 7 is a partial pulse sequence showing another example of application of divided MT pulses.

FIG. 8 is a partial pulse sequence showing still another example related to application of a divided MT pulse.

FIG. 9 is a view for explaining the temporal order of two imagings according to the second embodiment and a method performed in parallel with each imaging.

FIG. 10 is a schematic flowchart illustrating the procedure of the first imaging performed by the host computer.

FIG. 11 is a timing chart showing a flow of imaging using the ECG gate method.

FIG. 12 is a schematic diagram showing a pulse sequence of two imagings based on the ECG gating method.

FIG. 13 is a diagram illustrating a relationship between a three-dimensional imaging region and a logical axis direction.

FIG. 14 is a schematic flowchart illustrating an example of image processing after echo collection.

FIG. 15 is a diagram illustrating a weighted difference process, which is one process of image processing.

FIG. 16 is a schematic diagram for explaining a difference in the effect of the MT effect on the parenchyma and blood flow.

FIG. 17 is a view for explaining an MT effect based on a conventional MT pulse.

[Explanation of symbols]

 Reference Signs List 1 magnet 2 static magnetic field power supply 3 gradient magnetic field coil unit 4 gradient magnetic field power supply 5 sequencer 6 host computer 7 RF coil 8T transmitter 8R receiver 10 operation unit 11 storage unit 12 display 13 input device 16 sound generator 17 ECG sensor 18 ECG unit

Claims (23)

[Claims] An MRI for obtaining an MR image of an imaging region of a subject
In the apparatus, an MT having a frequency different from a frequency defining the imaging region may be used.
An MRI apparatus comprising: MT pulse applying means for applying a pulse; and spoiler applying means for applying a gradient magnetic field spoiler pulse after applying the MT pulse. 2. The imaging device according to claim 1, further comprising: an imaging unit configured to execute a scan based on a data acquisition sequence after applying the gradient magnetic field spoiler pulse to acquire an MR signal from the imaging region. MRI apparatus. 3. The MRI apparatus according to claim 1, wherein the MT pulse applied by the MT pulse applying unit includes a plurality of divided MT pulses. 4. The MRI apparatus according to claim 3, wherein the plurality of divided MT pulses applied by the MT pulse applying unit are composed of RF pulses applied in a non-slice manner. 5. The invention according to claim 3, wherein each of the plurality of divided MT pulses is M
An MRI comprising a gradient magnetic field applying means for applying a gradient magnetic field pulse for exciting a spin in a slice region determined by the frequency of the T pulse and applied in parallel with the RF pulse and for selecting the slice region
apparatus. 6. The MRI apparatus according to claim 5, wherein the application time of each of the RF pulses is short, and the flip angle of the spin excited by each of the RF pulses is set to a small value. 7. The invention according to claim 6, wherein the gradient magnetic field spoiler has a slice direction, a read direction,
And MRI configured to apply in any one of the phase encoding directions, any two directions, or all three directions
apparatus. 8. The apparatus according to claim 1, wherein a scan based on a first pulse sequence is executed without applying the MT pulse and the gradient magnetic field spoiler pulse to generate a first MR signal from the imaging region. A second imaging unit for collecting, and a second imaging unit after applying the MT pulse and the gradient magnetic field spoiler pulse, respectively.
A second imaging means for executing a scan based on the pulse sequence to collect a second MR signal from the imaging region; and an image generating means for generating the MR image from the first and second echo signals. MR characterized by comprising:
I device. 9. The MRI apparatus according to claim 1, wherein the MT pulse applied by the MT pulse applying means includes a plurality of divided MT pulses. 10. The invention according to claim 9, wherein each of said plurality of divided MT pulses is
An MRI comprising a gradient magnetic field applying means for applying a gradient magnetic field pulse for exciting a spin in a slice region determined by the frequency of the T pulse and applied in parallel with the RF pulse and for selecting the slice region
apparatus. 11. The MRI apparatus according to claim 10, wherein the application time of each of the RF pulses is short, and the flip angle of the spin excited by each of the RF pulses is set to a small value. 12. The MRI apparatus according to claim 11, wherein the plurality of RF pulses are arranged adjacently on a time axis. 13. The MRI according to claim 12, wherein the gradient magnetic field applying unit is a unit that causes the gradient magnetic field pulse to rise and fall one by one corresponding to the rise and fall of each of the plurality of RF pulses. apparatus. 14. The invention according to claim 12, wherein said gradient magnetic field applying means is means for raising and lowering said gradient magnetic field pulse corresponding to the first rise and fall of said plurality of RF pulses as a whole. MRI equipment. 15. The invention according to claim 11, wherein the gradient magnetic field spoiler includes a slice direction, a read direction,
And MRI configured to apply in any one of the phase encoding directions, any two directions, or all three directions
apparatus. 16. The apparatus according to claim 12, wherein said image generating means is means for performing a difference operation between image data based on said first and second echo signals.
RI equipment. 17. The MRI apparatus according to claim 7, further comprising: a breath-hold instruction unit that instructs the subject to hold his / her breath during imaging by the first and second imaging units. 18. The apparatus according to claim 7, wherein the first and second imaging means detect a signal representing a cardiac phase of the subject, and the first and second imaging means synchronize with the signal to detect the first cardiac phase. And an MRI apparatus having synchronization means for executing a second pulse sequence. 19. The invention according to claim 7, wherein the first and second pulse sequences are the same two-dimensional scan or three-dimensional scan pulse sequence, and the pulse sequence is SE Law, FSE Law, FAS
An MRI apparatus which is one of E method, FE method, FFE method, segmented FFE method, and EPI method. 20. The MRI apparatus according to claim 7, wherein the imaging region of the subject including the imaging region is a lung field. 21. An MR for obtaining an MR image of an imaging region of a subject
In the imaging method, an MT having a frequency different from a frequency defining the imaging region may be used.
An MR imaging method, comprising: applying a pulse, applying a gradient magnetic field spoiler pulse to the subject, and thereafter executing a scan based on a data acquisition sequence to acquire an MR signal from the imaging region. 22. An MR imaging method for acquiring an MR signal based on a magnetic resonance phenomenon of at least two kinds of nucleus pools in a subject having a binding relationship based on at least one of a chemical conversion phenomenon and a cross relaxation phenomenon, A plurality of divided MT pulses are sequentially applied to a selected slice region in the subject to decouple a coupling relationship between the at least two types of nucleus pools, and a gradient magnetic field spoiler pulse is applied to the decoupled nucleus pools. Applying an MR signal, and thereafter collecting an MR signal of an imaging region different from the slice region. 23. The MR imaging method according to claim 22, wherein the two types of nuclear pools are a free water nuclear pool and a polymer nuclear pool.