JP3124789B2 - MR imaging method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an MR imaging system, and more particularly to an MR imaging system suitable for measuring a fluid velocity such as a blood flow velocity.

[0002]

2. Description of the Related Art As an MR imaging method, a technique for visualizing fluid information such as blood flow as well as morphological information is known. Conventional techniques of this type include, for example, Shimizu Kay, Mazda Tei, and Etoal: Visualization of Moving Fluid: Quantitative Analysis of Blood Flow Using Viability M Imaging. Radiology 159: 195-199, 1986 (Simi
zu K, Matuta T, et al: Visual
Ization of moving fluid: Q
positive analysis of b
load flow velocityusing M
R imaging. Radiology 159: 1
95-199, 1986), and JP-A-61-18.
No. 7850, JP-A-62-109174, JP-A-63-109174
No. 186639, JP-A-63-230157 and JP-A-1-126955.

Here, an example of a conventional blood flow imaging method using the MR method will be described with reference to FIG.

As shown in a pulse sequence in FIG. 4, a high-frequency pulse (RF) pulse 201 and a gradient magnetic field 211 for slicing in a direction parallel to a flow direction of a fluid of a subject to be measured are applied to a flow. The perpendicular plane 251 is selectively excited. Next, phase encoding is performed with a gradient magnetic field 221 orthogonal to the slice gradient magnetic field. A gradient magnetic field whose magnitude is changed by a certain amount is applied each time by this phase encoding, and this is repeated a predetermined number of times to give positional information to an echo signal described later. The number of repetitions and the amount of change in the magnitude of the gradient magnetic field are determined by the resolution of the image to be obtained.

Further, gradient magnetic fields 212 parallel to the flow are used.
213 is applied to perform frequency encoding. 212,2
13, the magnitude and the application time are determined so that the signal from the fluid part becomes large. Then, an echo signal 231 is generated, and this is measured by the timing signal 241. This measurement is repeated for the number of phase encodings as described above. When the echo signal 231 thus obtained is subjected to a two-dimensional Fourier transform, the moving distance from the selective excitation to the measurement of the echo signal and the fluid velocity are known, and the fluid velocity data is subjected to image processing to obtain a blood flow velocity image.

FIG. 5 is a schematic diagram of an SE image.

FIG. 5A is an SE image of the slice surface 251, wherein a, b, c, and d represent the fluid portion as velocity data. The image corresponding to the nature of the subject is imaged, but is omitted for convenience of drawing. A typical subject is a living body, and the fluid part is a blood vessel part (blood flow part). FIG.
The gradient magnetic fields 211, 212 and 213 used in FIG.
3A, the gradient magnetic field 221 is set in a direction perpendicular to the drawing, and the gradient magnetic field 221 is set in a horizontal direction in the drawing. And FIG.
(B) is a flow velocity image 252 obtained by using the above-described pulse sequence.
The movement of the fluid is imaged as it is when viewed from the side in the direction A in FIG.

[0008]

When imaging fluid velocities such as blood flow using conventional MR imaging,
In order to excite a cross section (slice plane) perpendicular to the flow of the fluid and perform a phase encoding operation on the excited signal to add position information, the entire slice plane was imaged. Therefore, in order to obtain a blood flow image, image data must be collected by repeating excitation and phase encoding operations many times, and it takes a lot of time until image processing, and it is not possible to perform real-time blood flow measurement and the like. It was impossible.

The present invention has been made in view of the above points, and an object of the present invention is to provide an MR capable of displaying fluid velocity data of an object and its image in near real time with one pulse sequence.
An object of the present invention is to provide an imaging method.

[0010]

In order to achieve the above object, the present invention focuses on obtaining the image information by focusing only on the fluid portion to be measured or in addition to the fluid portion. Basically, the following MR imaging method is proposed.

That is, in a MR imaging system in which a high-frequency magnetic field is applied to a subject placed in a static magnetic field and image processing is performed based on a nuclear magnetic resonance signal (echo signal) generated from the subject, a gradient magnetic field is applied. RF for selective excitation
Pulse (first pulse) and two 180 ° pulses (second,
A third pulse) is applied to excite a plane perpendicular to the flow (first plane) with the first pulse, and a plane perpendicular to the first plane (second plane) with the second pulse. The first surface with 3 pulses,
A surface (third surface) orthogonal to both surfaces of the second surface is excited, and a gradient magnetic field parallel to the flow direction (a gradient magnetic field similar to that used at the time of exciting the first surface) is applied to the echo signal generated through these processes. ) To perform frequency encoding to measure the echo signal,
Further, the moment with respect to the velocity in each gradient magnetic field direction is set to zero.

[0012]

According to the above arrangement, the selective excitation planes (first plane, first plane, and second plane) obtained by the first to third pulses for selective excitation are obtained.
Only the orthogonal portions between the second and third surfaces are localized as echo signal generation regions.

Therefore, the position of a portion of the subject to which the fluid velocity data is to be determined is checked in advance, and the gradient magnetic field (for example, the first, second, and third axes) in each direction (for example, the Z axis, the Y axis, and the X axis) is adjusted to match this position. By setting a gradient magnetic field for performing selective excitation in cooperation with each of the pulse, the second pulse, and the third pulse, only a specific fluid portion is narrowed down as an echo signal generation region.

When a gradient magnetic field parallel to the flow direction is applied to the echo signals generated by the first to third pulse excitations, the position information of the fluid flowing out of the localized region is frequency-encoded. . When the frequency-encoded echo signal is subjected to one-dimensional Fourier transform, the movement amount and velocity of the fluid from the first pulse (RF pulse) for selective excitation to signal measurement can be determined. When such a pulse sequence is used, for example, only one of the fluid parts A to D shown in FIG. 5 is selected (localized), and image processing using only the velocity data can be performed.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is an explanatory view of a pulse sequence of the MR imaging system of the present embodiment and an excitation plane obtained by the pulse sequence, and FIG. 2 is a configuration diagram of an MR imaging apparatus used in the present embodiment.

First, the MR imaging apparatus shown in FIG. 2 will be described.

A subject 102 is placed in a magnet 101 that generates a uniform static magnetic field, and an RF (high frequency) pulse necessary for generating nuclear magnetic resonance is transmitted to ¹ H in the subject in a transmission / reception system 106. The RF pulse is generated and applied to the transmission coil 104, and the coil 104 irradiates the subject 102 as a high-frequency magnetic field.

Nuclear magnetic resonance signals (echo signals) generated from ¹ H in the subject after irradiation with the RF pulse for a predetermined time.
Is detected by the reception coil 105, and the transmission / reception system 1
06. This echo signal is converted to an audible frequency by the transmission / reception system 106, and further converted to an A / D signal.
The signal is converted into a digital signal by the converter 107. This digital signal is subjected to necessary processing by a computer 109,
The obtained image is displayed on the display 110.

In the case of performing the above-described excitation by the RF pulse, the computer 109 controls the gradient magnetic field power supply 108 based on predetermined conditions to apply the gradient magnetic field coil 103 connected to the power supply 108. A gradient magnetic field for adding position information necessary for imaging to the echo signal is generated. The transmission / reception system 106 is also controlled by the computer 109.

Next, the MR imaging system of this embodiment will be described with reference to FIG.

First, an RF pulse (90 ° pulse; first pulse) 301 and a gradient magnetic field 311 (a gradient magnetic field Gz parallel to the flow direction of the fluid) are applied to a surface 361 (perpendicular to the flow direction of the fluid to be measured). (1st surface) is excited. Next, a surface 362 (second surface) orthogonal to the first surface is excited by the second pulse 302 and the gradient magnetic field 322, and then the third pulse 303
And a plane 36 perpendicular to the first and second planes with the gradient magnetic field 332
3 (third surface) is excited. Through the above series of processes, the first surface 361, the second surface 362, and the third surface 3
63 orthogonal regions P are locally set as echo signal generation locations (in the figure, hatched portions are regions where signals are generated).

When the local region P is formed, the position of the fluid portion to be measured is confirmed in advance, and the gradient magnetic fields 311, 322, and 332 are set in accordance with the position. Further, the first surface 361 and the second surface 36 are generated by the respective gradient magnetic fields.
2. The thickness of the third surface 363 can be controlled, and the size of the local area P can be arbitrarily changed.

An echo signal 341 generated after the application of the RF pulses 301 to 303 is subjected to frequency encoding with a gradient magnetic field 313 (same gradient magnetic field used at the time of the first surface excitation) parallel to the flow direction, and a timing 351 is performed. Measure the signal with. This measurement signal is obtained by frequency-encoding the position information of the fluid flowing out of the localized area. When this signal is subjected to one-dimensional Fourier transform, the RF pulse 3
The movement amount and speed of the fluid from application of 01 to measurement of the signal are known. Also, gradient magnetic fields 312, 321, 323, 3
31 and 333 are applied so that the moment with respect to the velocity in each gradient magnetic field direction becomes zero. Thereby, the phase change of the spin caused by the movement of the fluid is corrected, and a large fluid velocity signal is obtained.

The fluid velocity data subjected to the one-dimensional Fourier transform is displayed on a screen of the display 110 as a line. When this image display is performed, the latest fluid velocity data obtained by the one-dimensional Fourier transform is displayed at one end of the screen on the display as shown in FIG. If the previous data is shifted one line at a time toward the center of the image within the same screen, a series of fluid velocity data can be displayed in a graph in correspondence with the time axis.

In the display of the fluid velocity data, instead of the above method, only the latest data may be displayed by changing the image frame for each line.

According to the above-described embodiment, blood flow velocity data for MR imaging can be obtained by focusing on a fluid portion (for example, a blood vessel portion) having only a necessary minimum area. As a result, blood flow measurement can be performed in near real time (30 ms), and the result can be viewed through a display in near real time. Therefore, it is also possible to observe a sudden abnormal blood flow such as an irregular pulse requested by the user.

Displaying an electrocardiographic waveform on the same screen as the above-mentioned graph has an advantage that the relationship between the blood flow velocity of each part of the human body and the movement of the heart can be easily understood.

[0029]

According to the present invention, only the fluid portion of the subject can be locally narrowed and its fluid velocity can be measured by one pulse sequence. The time required for the image processing can be greatly reduced (in the case of using phase encoding as in the conventional MRI method, it takes about two to three minutes.
(Approximately 0 ms), and an image display of fluid velocity in near real time can be realized.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a pulse sequence of MR imaging according to one embodiment of the present invention and an excitation plane obtained by the pulse sequence.

FIG. 2 is a configuration diagram of an MR imaging apparatus used in the embodiment.

FIG. 3 is an explanatory diagram showing an example of display display of fluid velocity data obtained by the embodiment.

FIG. 4 is an explanatory view of a pulse sequence showing an example of conventional MR imaging and an excitation plane obtained by the pulse sequence.

FIG. 5 shows S obtained by the conventional pulse sequence.
FIG. 4 is a schematic diagram of an E image and an explanatory diagram of a state in which the fluid velocity is displayed as an image.

[Explanation of symbols]

301: first pulse, 302: second pulse, 303: third pulse, 311, 322, 332: gradient magnetic field, 361
... First surface, 362... Second surface, 363.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI G01N 24/08 510Y (56) References JP-A-60-146138 (JP, A) JP-A-63-117743 (JP, A) JP-A-4-303418 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) A61B 5/055 JICST file (JOIS)

Claims (4)

(57) [Claims] 1. An MR (nuclear magnetic resonance) imaging method in which a high-frequency magnetic field (RF pulse) is applied to a subject placed in a static magnetic field, and image processing is performed based on a nuclear magnetic resonance signal (echo signal) generated from the subject. In the method, an RF pulse (first pulse) for selective excitation and two pulses are applied while applying a gradient magnetic field.
80 ° RF pulse (second and third pulses)
A pulse perpendicular to the flow (first surface) is excited by the pulse, a surface perpendicular to the first surface (second surface) is excited by the second pulse, and both the first and second surfaces are excited by the third pulse. A plane (third plane) orthogonal to the above is excited, and the echo signal generated through these processes is frequency-encoded by a gradient magnetic field parallel to the flow direction (a gradient magnetic field similar to that used at the time of the first plane excitation) for echo signals generated through these processes. And an echo signal is measured, and a moment with respect to the velocity in each gradient magnetic field direction is made zero. 2. The MR according to claim 1, wherein the measured echo signal is immediately subjected to one-dimensional Fourier transform to obtain fluid velocity data, and the fluid velocity data is set to be displayed in a line on a display. Imaging method. 3. The method according to claim 1, wherein the measured echo signal is immediately subjected to one-dimensional Fourier transform to obtain fluid velocity data, and the latest one of the fluid velocity data is displayed at one end of a screen on a display. An MR imaging system characterized in that each time the latest fluid velocity is obtained, the previous data is sequentially shifted one line at a time within the same screen to display a series of fluid velocity data as an image. 4. The MR imaging according to claim 2, wherein when the fluid velocity data is a blood flow velocity, an electrocardiographic waveform is displayed on the same screen of the display. method.