JPH0622934A - Magnetic resonance imaging device and method - Google Patents

Abstract

PURPOSE:To provide an MRI device and method for measuring the flow speed of a flowing object correctly, even in case of a high flow speed. CONSTITUTION:A sequencer 2 executes the single slice multiphase pulse sequence for carrying out the execution of the photograph pulse sequence, scceeding to the application of the presaturation pulse for each phase under the control of a computer system 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nuclear magnetic resonance imaging apparatus (MRI apparatus), which obtains morphological information such as a slice image of a subject and qualitative information such as spectroscopy by utilizing a nuclear magnetic resonance phenomenon, and more particularly, The present invention relates to an MRI apparatus capable of measuring the flow velocity of a flowable object such as blood.

[0002]

2. Description of the Related Art The nuclear magnetic resonance phenomenon is a phenomenon in which an atomic nucleus having a non-zero spin and magnetic moment placed in a static magnetic field resonantly absorbs and emits only an electromagnetic wave of a specific frequency. Angular frequency ω ₀ (ω ₀ =
2πν ₀ , ν ₀ : Larmor frequency).

Ω ₀ = γH ₀ where γ is the gyromagnetic ratio peculiar to the type of nucleus,
H ₀ is the static magnetic field strength.

MR for performing biopsy using the above principle
The device I processes an electromagnetic wave of the same frequency as that induced after the above-mentioned resonance absorption to reflect information such as nuclear density, longitudinal relaxation time T ₁ , lateral relaxation time T ₂ , flow, and chemical shift. Further, it is possible to non-invasively obtain diagnostic information such as a slice image of the subject.

[0005] Such collection of diagnostic information by nuclear magnetic resonance is capable of exciting all parts of a subject placed in a static magnetic field and collecting signals, but there are restrictions on the apparatus structure and imaging. From the clinical request of the image, the actual M
The RI apparatus is designed to excite a specific site and collect its signal.

There is known a method of measuring a flow velocity by using a flow-like object such as blood as an imaging object of the nuclear magnetic resonance imaging.

In this method, first, the blood vessel to be imaged is Z
When placed along the axis, a pre-saturation pulse is applied to the saturation plane in the direction (X-axis direction) orthogonal to the blood vessel on the Z-axis, and the blood vessel located in this saturation plane is applied. Only the spin component of the blood inside is selectively saturated. Here, a 90 degree pulse is usually used as the presaturation pulse.

Next, the spin echo (SE) method or the field echo (F
E) Appropriate RF based on imaging pulse sequence such as method
By applying a pulse and a gradient magnetic field, collecting a nuclear magnetic resonance signal after the echo time T _E , and reconstructing an image based on this, a slice plane including this blood vessel (in the Y-axis direction)
To obtain a nuclear magnetic resonance image. In this nuclear magnetic resonance image,
The spin component saturated by the presaturation pulse appears as a dark region called the Tag part.

Since the Tag portion has flowed a distance d from the position of the saturation plane during the echo time T _E , the Tag portion appears by this amount. Therefore, by obtaining this distance d from the reconstructed image, the flow velocity of the blood in the blood vessel is V = d.
It becomes possible to determine as / T _E. Normally, such measurement is repeated a plurality of times and the average of all measurement results is obtained to eliminate the effect of temporary flow velocity fluctuation.

[0010]

However, in the case of measuring the flow velocity of a flow object by the above method, if the blood flow velocity is higher than a predetermined value, the Tag portion is disturbed by the turbulent flow of blood. Therefore, it becomes impossible to accurately measure the moving distance d of the Tag portion, and it becomes difficult to determine the flow velocity. Therefore, it is difficult for the conventional method to accurately measure the flow velocity of fast blood flow such as a main blood vessel.

Therefore, an object of the present invention is to enable accurate measurement of the flow velocity even when the flow velocity of the flow object is high.
It is to provide an RI device.

[0012]

In order to achieve the above-mentioned object, the present invention irradiates a desired saturation plane orthogonal to the flow direction of a flow target object with a presaturation pulse, and A presaturation means for generating a saturated portion in the image capturing means, an imaging means for collecting a nuclear magnetic resonance signal from a desired imaging region including the saturation surface and the saturated portion by executing a desired imaging pulse sequence, and the presaturation Means and the imaging means to control the means and the imaging means so that in each phase, the application of the presaturation pulse by the presaturation means is followed by the execution of the desired imaging pulse sequence by the imaging means To the control means for realizing By reconstructing the nuclear magnetic resonance image of the desired imaging region from the nuclear magnetic resonance signals acquired in each phase of the single slice multiphase pulse sequence, and the saturation plane in each reconstructed nuclear magnetic resonance image And the distance between the saturated part and
The measured distance is single-slice, multi-phase,
Means for determining the flow velocity of the flow object by dividing by the time interval between the application of the presaturation pulse in the pulse sequence and the detection of the nuclear magnetic resonance signal. And a nuclear magnetic resonance imaging apparatus for use in

Further, in order to achieve the above object, the present invention irradiates a desired saturation plane orthogonal to the flow direction of a flow object with a pre-saturation pulse so that a saturated portion is formed in the flow object. Generating, and performing a desired imaging pulse sequence to collect nuclear magnetic resonance signals from a desired imaging region including the saturation plane and the saturated portion; the presaturation irradiation step and the imaging pulse sequence. A single-slice multi-phase pulse that controls the execution stage so that the desired imaging pulse sequence is performed in the imaging pulse sequence execution stage following the application of the presaturation pulse in the presaturation irradiation stage in each phase. With the control stage that realizes the sequence From the step of executing the imaging pulse sequence, a nuclear magnetic resonance image of the desired imaging region is reconstructed from the nuclear magnetic resonance signals acquired in each phase of the single slice multiphase pulse sequence, and each reconstructed nuclear magnetic field is reconstructed. The distance between the saturation plane and the saturated part in the resonance image is measured, and the measured distance is the time interval between the application of the presaturation pulse and the detection of the nuclear magnetic resonance signal in the single-slice multiphase pulse sequence. A step of determining the flow velocity of the flow-like object by dividing by the method described above, and a nuclear magnetic resonance imaging method for measuring the flow velocity of the flow-like object.

[0014]

With the configuration of the MRI apparatus according to the present invention, the imaging pulse sequence is applied to the subject placed in the static magnetic field space for each phase in the single slice / multi-phase, following the application of the presaturation pulse. Therefore, the repetition time for applying the presaturation pulse is significantly shortened as compared with the conventional case, and the photographing operation is performed within the greatly shortened repetition time. Therefore, when measuring the flow velocity of a flow object,
Even if the flow velocity is high, it is less likely to be affected by the influence, so that the measurement can be performed accurately.

[0015]

1 is a system configuration diagram showing a schematic configuration of an embodiment of an MRI apparatus to which the present invention is applied.

The MRI apparatus of this embodiment includes a computer system 1 as a control center of the entire system, and under the control of the computer system 1, a sequencer 2 executes a desired imaging pulse sequence and a transmitter 3 and The gradient magnetic field power supply 4 is driven to generate an RF pulse from the RF coil 6 arranged in the static magnetic field space of the main magnet 5,
Gradient magnetic fields G _E , G _R , and G _S for encoding, reading, and slicing are generated from the gradient magnetic field coil 7 and applied to the subject P. Thus, the MR signal generated in the subject P is detected by the probe 8, the detected MR signal is collected by the receiver 9, and then sent to the computer system 1. Then, an image reflecting the morphological information and the qualitative information is reconstructed based on the MR signals collected by the computer system 1 and displayed on the monitor 10.

Further, in each of the above-mentioned units, the sequencer 2 applies a presaturation pulse for saturating blood (selected spin component) in a specific slice region of the subject P under the control of the computer system 1 and then an imaging pulse sequence. It stores a single-slice, multi-phase pulse sequence in which each phase is a pulse sequence for executing. The presaturation pulse is generated as a gradient magnetic field pulse.

On the other hand, the computer system 1 executes the above-mentioned pulse sequence stored in the sequencer 2 in electrocardiographically synchronized (ECG synchronized) or fingertip pulse wave synchronized (PPG synchronized), based on the acquired data. It functions as a measuring means for measuring the blood flow velocity for each phase in the single slice multi-phase.

For example, a pulse sequence for executing the imaging pulse sequence after the application of the presaturation pulse is performed for each phase of the single slice pulse phase for the subject P arranged in the static magnetic field space by the main magnet 1. When executed in ECG synchronization, the signals have the relationship shown in the timing chart of FIG.

That is, the first presaturation pulse is synchronized with the R wave which is the peak value of the ECG waveform, and the application of the second and subsequent presaturation pulses is sequentially repeated at the beginning of each phase. Echo signals (MR signals) are collected for each phase by repeatedly executing the imaging pulse sequence immediately after the application of the presaturation pulse for each phase.

Here, the time intervals ΔT1 and ΔT2 between each presaturation pulse and the corresponding echo signal.
, ΔT3, etc. are all the same.

Next, based on the MR signals acquired in each phase, an image of the blood flow in each phase is shown in FIG.
Reconstruct as shown in (A) (B) (C). here,
The saturate surface including the spin component saturated by the presaturation pulse and the Tag portion appear as dark areas, which are shown by the shaded areas in FIGS. 3A, 3B, and 3C.

In the first phase shown in FIG. 3A, the first phase
The Tag portion is in a state of flowing out the distance d1 from the saturation surface during the time interval ΔT1.

In the second phase shown in FIG. 3B, the second phase
During the time interval .DELTA.T2, the Tag portion has flowed out a distance d2 from the saturation plane, and the first Tag portion has flowed further.

In the third phase shown in FIG. 3C, the third phase
The Tag portion has flowed out a distance d3 from the saturation surface during the time interval ΔT3, and the second Tag portion has flowed further. The shape of the first Tag portion is irregularly disturbed by the turbulent flow in the bloodstream.

The blood flow velocity is V = d by measuring the distance d between the saturation surface and the Tag portion from each blood flow image and dividing this by the corresponding time interval ΔT.
Calculate as / ΔT. Here, since the blood flow velocity has different values in different phases during the heartbeat, the distances d1, d2, d3, etc. measured in each phase are generally different from each other. Therefore, by averaging multiple blood flow velocities obtained in different heartbeat phases, the effects of temporary fluctuations are eliminated,
This is the final flow velocity measurement result.

In this embodiment, it is desirable to use a 180-degree pulse as the presaturation pulse instead of the conventional 90-degree pulse. This depends on the longitudinal relaxation time T1 of the spin component whose density is saturated on the reconstructed image of the saturation surface or the Tag part, so that the density of these regions can be increased and identified easily by using a 180-degree pulse. This is because

Further, by using the 180-degree pulse, irregular turbulence of the Tag boundary due to turbulent flow in the bloodstream can be suppressed, so that the conventional 90-degree pulse makes the Tag boundary unclear. Even in the case of flow, the blood flow velocity can be measured accurately.

In the above embodiment, the single slice
ECG synchronization or P for multi-phase pulse sequence
Although the measurement accuracy is further improved by performing the PG synchronization, the present invention can be effectively implemented without using such synchronization.

Further, in the above embodiment, the case of measuring the flow velocity of blood is described, but the present invention can be similarly applied to other flow-shaped objects such as cerebrospinal fluid.

[0031]

As described above, according to the present invention, since the application of the presaturation pulse and the execution of the imaging pulse sequence are repeated for each phase in the single slice multi-phase, data acquisition is performed. It becomes possible to accurately measure the flow velocity of a flow object such as a blood flow without being affected by the turbulent flow generated in the blood flow.

[Brief description of drawings]

FIG. 1 is a system configuration diagram showing a schematic configuration of an embodiment of an MRI apparatus to which the present invention is applied.

FIG. 2 is a timing chart showing a single slice multiphase pulse sequence according to an embodiment of the present invention.

3 is a diagram showing a reconstructed image obtained in each phase of the sequence of FIG. 2 by the apparatus of FIG.

[Explanation of symbols]

 1 Computer System 2 Sequencer 3 Transmitter 4 Gradient Magnetic Field Power Supply 5 Main Magnet 6 RF Coil 7 Gradient Magnetic Field Coil 8 Probe 9 Receiver 10 Monitor

Claims (2)

[Claims] 1. A presaturation means for irradiating a desired saturation plane orthogonal to the flow direction of a stream-like object with a presaturation pulse to generate a saturated portion in the stream-like object, and a desired imaging pulse sequence. By executing an imaging means for collecting a nuclear magnetic resonance signal from a desired imaging area including the saturation surface and the saturated portion, and controlling the presaturation means and the imaging means to perform the presaturation in each phase. Control means for realizing a single-slice multi-phase pulse sequence in which the desired imaging pulse sequence is executed by the imaging means following the application of the presaturation pulse by the means, and the imaging means performs the single-slice multi-pulse pulse sequence. Phase pulse sea Reconstructing the nuclear magnetic resonance image of the desired imaging region from the nuclear magnetic resonance signals collected in each phase of the can, the distance between the saturation plane and the saturated portion in each reconstructed nuclear magnetic resonance image Determine the flow velocity of the stream-like object by measuring and dividing the measured distance by the time interval between the application of the presaturation pulse and the detection of the nuclear magnetic resonance signal in a single-slice multiphase pulse sequence. A magnetic resonance imaging apparatus for measuring the flow velocity of a flow-like object, which comprises: 2. A step of irradiating a desired saturation plane orthogonal to the flow direction of the stream-like object with a presaturation pulse to generate a saturated portion in the stream-like object, and executing a desired imaging pulse sequence. By controlling the pre-saturation irradiation step and the imaging pulse sequence execution step by collecting a nuclear magnetic resonance signal from a desired imaging region including the saturation surface and the saturated portion, the pre-saturation step is performed in each phase. Single-slice, multi-phase, such that the desired imaging pulse sequence is executed in the imaging pulse sequence execution step following the application of the pre-saturation pulse in the saturation irradiation step
From the control step of realizing a pulse sequence and the step of executing the imaging pulse sequence, the nuclear magnetic resonance image of the desired imaging region is reconstructed from the nuclear magnetic resonance signals acquired in each phase of the single slice multiphase pulse sequence. Then, the distance between the saturation plane and the saturated portion in each reconstructed nuclear magnetic resonance image is measured, and the measured distance is applied to the presaturation pulse and the nuclear magnetic resonance in the single-slice multiphase pulse sequence. Determining the flow velocity of the flow object by dividing it by the time interval between the detection of the signal and the method.