WO2019169671A1

WO2019169671A1 - Fat-suppressed black-blood magnetic resonance imaging method

Info

Publication number: WO2019169671A1
Application number: PCT/CN2018/080007
Authority: WO
Inventors: 王超; 罗海; 吴子岳; 朱高杰; 周翔; 陈梅泞; 刘霞
Original assignee: 奥泰医疗系统有限责任公司
Priority date: 2018-03-05
Filing date: 2018-03-22
Publication date: 2019-09-12
Also published as: CN108363026A

Abstract

A fat-suppressed black-blood magnetic resonance imaging method, comprising: emitting a excitation signal, the excitation signal comprising: a sequence of 90°_x, 180°_y, and 90°_x radio frequency pulses, two motion-sensitive gradient magnetic fields (1) that are the same, and a de-noising gradient magnetic field (2); applying one motion-sensitive gradient magnetic field between a first 90°_x pulse and the 180°_y pulse, and applying the other motion-sensitive gradient magnetic field between the 180°_y pulse and a second 90°_x pulse; applying the two motion-sensitive gradient magnetic fields symmetrically with the 180°_y pulse; applying the de-noising gradient magnetic field after the sequence of the 90°_x, 180°_y, and 90°_x radio frequency pulses; setting, to a signal zero point of adipose tissue, a delay after the sequence of the 90°_x, 180°_y, and 90°_x radio frequency pulses; and collecting electromagnetic wave signals. The described method may reduce sensitivity to the magnetic field non-uniformity, thereby improving the fat suppression effect; and at the same time, a specific absorption rate of an MSDE pulse sequence may be reduced.

Description

Fat-pressed black blood magnetic resonance imaging method

Technical field

The present invention relates to the field of magnetic resonance imaging technology, and in particular, to a fat-pressed black blood magnetic resonance imaging method.

Background technique

Magnetic resonance fat-suppressed black blood angiography has important applications in the clinical diagnosis of some important diseases, such as carotid atherosclerotic plaque, because of its safety, non-invasiveness, high resolution and multiple imaging angles. According to the suppression mechanism of blood signals, the current magnetic resonance imaging methods can be divided into: 1) In-flow Saturation (IS) based on influx saturation effect; 2) Black blood imaging based on double inversion recovery (Double Inversion Recovery, DIR). IS technology usually does not completely suppress blood signals, especially for tissues with more complicated flow patterns. In theory, DIR technology can completely suppress the blood flow signal as long as the layer thickness is thin enough, but it is essentially a single-layer scanning technology with a long imaging time. The method of improving the scanning speed of DIR technology has sacrificed the effectiveness of blood flow suppression to some extent. In recent years, a motion-sensitized driven-equilibrium (MSDE) method has been applied to vascular wall imaging and has achieved good results. In practical applications, MSDE often needs to suppress fat signals. Therefore, it is generally necessary to introduce a fat signal saturation module after the MSDE pre-pulse module.

The existing MSDE sequence diagram is shown in Figure 1. It consists of three parts: 1) MSDE pre-pulse module, 2) fat saturation module, and 3) Fast spin echo (FSE) sampling module. In the MSDE pre-pulse module, an identical motion-sensitive gradient is introduced between the 180-degree pulse and the two 90-degree pulses, respectively. For static tissue, the phase accumulation of the signal caused by the gradient can be completely condensed by the 180-degree pulse, and for the flow tissue (such as blood), the phase accumulation cannot be completely re-aggregated, which will eventually cause the signal phase loss to decay. On this basis, the suppression of the flow signal (blood) is achieved. The second 90-degree pulse in the MSDE pre-pulse module converts the magnetization vector after the flow signal is removed back to the longitudinal axis of the thermal equilibrium steady state. Thereafter, the fat saturation module saturates the adipose tissue using a selective excitation pulse, and the FSE sampling module performs a rapid acquisition of the magnetic resonance signal.

MSDE can effectively suppress blood flow signals. In theory, as long as the applied motion sensitive gradient area is large enough, the blood flow signal can be completely eliminated. However, frequency-selective fat saturation techniques are very sensitive to static magnetic field inhomogeneities. In practice, many parts are often difficult to achieve sufficient magnetic field uniformity due to the complexity of their geometry (such as the carotid artery). The pressure-lowering effect is not ideal. In addition, the introduction of additional frequency selective RF pulses also keeps the Specific Absorption Rate (SAR) of the MSDE pulse sequence high.

Summary of the invention

The present invention aims to provide a fat-suppressed black blood magnetic resonance imaging method capable of reducing the sensitivity to magnetic field inhomogeneity, thereby improving the liposuction effect, and at the same time, reducing the specific absorption rate of the MSDE pulse sequence.

In order to achieve the above object, the technical solution adopted by the present invention is as follows:

A fat-suppressed black blood magnetic resonance imaging method comprising:

Transmitting an excitation signal comprising: a 90° _x , 180° _y , 90° _x RF pulse sequence, two identical motion-sensitive gradient magnetic fields, a de-noising gradient magnetic field; and one of the motion-sensitive gradient magnetic fields is first loaded Between a 90° _x pulse and a 180° _y pulse, another of the motion sensitive gradient magnetic fields is applied between a 180° _y pulse and a second 90° _x pulse; two of the motion sensitive gradient magnetic fields are 180° _y Pulse-symmetrically loading; the de-noising gradient magnetic field is applied after the 90° _x , 180° _y , 90° _x RF pulse sequence; after the 90° _x , 180° _y , 90° _x RF pulse sequence The delay is set to the zero point of the signal of the fat tissue; the electromagnetic wave signal is collected.

Preferably, the excitation signal has three groups.

Preferably, the electromagnetic wave signal is acquired by using a fast spin echo sampling module.

The fat-pressed black blood magnetic resonance imaging method provided by the embodiment of the present invention, because the second 90° pulse phase of the existing radio frequency pulse sequence is inverted, so as to be in phase with the first 90° pulse, thus, Motion-sensitive gradient magnetic fields can also suppress the suppression of flow signals such as blood. At the same time, after undergoing the second 90° pulse, the magnetization vector is no longer flipped back to the forward axis of the equilibrium state, and conversely, will be oriented in the opposite direction along the longitudinal axis. In other words, the overall effect of the 90° _x , 180° _y , 90° _x RF pulse sequence is equivalent to a 180° _x pulse. As long as the delay after the 90° _x , 180° _y , and 90° _x RF pulse sequences is set to the zero point of the adipose tissue, the purpose of suppressing fat can be achieved without the need for additional fat-saturated RF pulses, and RF The reduction in the pulse causes the specific absorption rate SAR of the MSDE pulse sequence to also decrease accordingly. At the same time, since the method performs fat pressing based on the inversion recovery theory, the sensitivity to magnetic field inhomogeneity is reduced and the robustness is improved compared with the existing frequency selective saturation technique, thereby improving the pressure-lowering effect.

DRAWINGS

Figure 1 is a schematic diagram of a prior art MSDE sequence;

2 is a schematic structural view of an embodiment of the present invention;

In the figure, 1 is a motion-sensitive gradient magnetic field, and 2 is a noise-removing gradient magnetic field.

Detailed ways

In order to make the objects, technical solutions and advantages of the present invention more comprehensible, the present invention will be further described in detail with reference to the accompanying drawings.

Step 101: transmitting an excitation signal, the excitation signal comprising: a 90° _x , 180° _y , 90° _x RF pulse sequence, two identical motion-sensitive gradient magnetic fields, a de-noising gradient magnetic field; and one of the motion-sensitive gradient magnetic field loading Between the first 90° _x pulse and the 180° _y pulse, another of the motion sensitive gradient magnetic fields is applied between the 180° _y pulse and the second 90° _x pulse; two of the motion sensitive gradient magnetic fields are The 180° _y pulse is symmetrically loaded; the denoising gradient magnetic field is loaded after the 90° _x , 180° _y , 90° _x RF pulse sequence; in this embodiment, the excitation signal has three groups.

Step 102, setting a delay after the 90° _x , 180° _y , and 90° _x RF pulse sequences as a signal zero point of the adipose tissue;

In step 103, an electromagnetic wave signal is collected. Preferably, the electromagnetic wave signal is acquired by using a fast spin echo sampling module, that is, an FSE sampling module.

Another possible method is to keep the phase relationship of the 90° _x , 180° _y , and 90 _- ° _x RF pulse sequences in the MSDE pre-pulse module unchanged, and replace the 180° _y pulse with the frequency-selected water excitation pulse. And control the time interval between the two 90° pulses so that the phase evolution of the fat during this period is exactly 180°, then the MSDE pre-pulse module is equivalent to a 0 degree pulse for the water signal and quite equivalent for the fat signal. In a reverse pulse. This method may also achieve the effects of the embodiments of the present invention.

The above is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily think of changes or substitutions within the technical scope of the present invention. It should be covered by the scope of the present invention.

Claims

A fat-pressed black blood magnetic resonance imaging method, comprising:

Transmitting an excitation signal comprising: a 90° x , 180° y , 90° x RF pulse sequence, two identical motion-sensitive gradient magnetic fields, a de-noising gradient magnetic field; and one of the motion-sensitive gradient magnetic fields is first loaded Between a 90° x pulse and a 180° y pulse, another of the motion sensitive gradient magnetic fields is applied between a 180° y pulse and a second 90° x pulse; two of the motion sensitive gradient magnetic fields are 180° y Pulse-symmetrically loading; the de-noising gradient magnetic field is loaded after the 90° x , 180° y , 90° x RF pulse sequence;

Setting the delay after the 90° x , 180° y , 90° x RF pulse sequence to the signal zero point of the adipose tissue;

Collect electromagnetic wave signals.
The method of claim 1, wherein the excitation signal has three groups.
The fat-pressed black blood magnetic resonance imaging method according to claim 2, wherein the electromagnetic wave signal is acquired by a fast spin echo sampling module.