CN113640723A - System and method for improving signal-to-noise ratio of real-time monitoring type magnetic resonance imaging - Google Patents
System and method for improving signal-to-noise ratio of real-time monitoring type magnetic resonance imaging Download PDFInfo
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Abstract
The invention relates to a system and a method for improving the signal-to-noise ratio of real-time monitoring type magnetic resonance imaging, comprising the following steps: the whole magnetic resonance imaging system is arranged on a movable base, the lower part of the base is provided with a cabinet, and a driving power supply, a gradient and a radio frequency power amplifier of a spectrometer system signal enhancement device are arranged in the cabinet; an imaging magnet is arranged above the base, the positioning system is arranged in the imaging magnet, a signal enhancement device is also arranged in the imaging magnet and can move freely, and the specific position of the imaging magnet is determined by the indication of the positioning system; the signal enhancement device comprises a signal enhancement coil and an active shielding coil; the signal enhancement coil generates a magnetic field in the same direction as the main magnetic field, and the active shielding coil generates a magnetic field in the opposite direction to the main magnetic field, so that the magnetic fields of the signal enhancement coil on the upper polar plate and the lower polar plate of the main magnet are counteracted, and the influence of the signal enhancement coil on the main magnet is avoided; the two act together to generate a signal enhancement magnetic field with the same main magnetic field direction.
Description
Technical Field
The invention relates to the technical field of medical imaging, in particular to a system and a method for improving the signal-to-noise ratio of an instant monitoring type magnetic resonance imaging technology.
Background
Magnetic Resonance Imaging (MRI) is one of the best medical imaging diagnostic methods at present, and has become a necessary device for all hospitals. Generally, the following problems exist in the application of the conventional whole body magnetic resonance imaging apparatus: 1) only in the radiology department. Because the traditional equipment has huge volume, complex operation and high requirement on environment, the traditional equipment is only equipped in a radiology department at present, the configuration amount is seriously insufficient, the total detection amount is small, and the pertinence of the diagnosis test on patients is insufficient; 2) the traditional MRI equipment can not meet the actual demands of departments such as neurology department, stomatology department, obstetrical department, orthopedics department, ICU and the like; 3) the special patients such as the NICU infants can not be diagnosed in time, etc.
In recent years, a Point of care Magnetic Resonance Imaging (POC-MRI) technology is an important direction for development of the POC-MRI technology. As an important supplement to the whole-body MRI apparatus, the POC-MRI technology makes the MRI equipment no longer limited to radiology department applications, but enters professional departments or even clinics to realize real-time monitoring imaging, such as neonatal MRI equipment specially used in obstetrics and pediatrics, joint examination equipment in orthopedics department, oral outpatient examinations, brain monitoring imaging equipment in intensive care units, etc., which are small in size and flexible to use, and can be moved even among departments after rollers are installed at the bottom. The magnetic resonance imaging system is particularly suitable for department-oriented monitoring imaging application, emergency treatment application, health and physical examination, emergency application and basic medical and health institutions, forms complementation with large-scale magnetic resonance imaging equipment of radiology departments, and plays an important role in intensive care, graded diagnosis and treatment, field rescue, emergency rescue and disaster relief and the like.
In order to achieve portable mobility of a magnetic resonance imaging system, the system must be lightweight. The cost of system weight reduction is a reduction in the main magnetic field strength of the magnetic resonance imaging magnet. The central magnetic field intensity of an imaging magnet for POC-MRI is usually below 2000Gs, some magnetic fields are even hundreds of gausses, and the signal intensity in the magnetic resonance imaging process is in direct proportion to the square of the main magnetic field intensity, so that the signal-to-noise ratio of the POC-MRI equipment is greatly reduced, and the imaging quality is influenced.
In order to solve the problem of low signal-to-noise ratio in the portable magnetic resonance imaging technology, a common method is to increase the number of signal acquisitions for averaging, so as to enhance the signal-to-noise ratio, however, increasing the number of signal acquisitions means increasing the imaging time, and some imaging processes even need to last for tens of minutes, which is obviously not favorable for the application of the POC-MRI technology.
Disclosure of Invention
Aiming at the problem of low signal-to-noise ratio in the real-time monitoring type magnetic resonance imaging technology, the invention provides a system and a method for improving the signal-to-noise ratio of the real-time monitoring type magnetic resonance imaging. The basic principle is to apply a static magnetic field in the same direction as the main magnetic field at the imaging position, wherein the static magnetic field does not participate in the spatial encoding in the magnetic resonance imaging process (i.e. the static magnetic field is removed before the spatial encoding is carried out), and is not used for improving the magnetic field uniformity of the original static magnetic field (i.e. the static magnetic field has no special requirement on the uniformity), but is used for increasing the net magnetization vector in the magnetic resonance imaging process, thereby achieving the purpose of improving the signal-to-noise ratio.
The technical scheme of the invention is as follows: a system for improving signal-to-noise ratio in point-of-care magnetic resonance imaging, comprising:
the whole magnetic resonance imaging system is arranged on a movable system base, the lower part of the base is provided with a cabinet, and a driving power supply, a gradient and a radio frequency power amplifier of a spectrometer system signal enhancement device are arranged in the cabinet;
an imaging magnet is arranged above the base, the positioning system is arranged in the imaging magnet, a signal enhancement device is also arranged in the imaging magnet and can move freely, and the specific position of the imaging magnet is determined by the indication of the positioning system; the signal enhancement device comprises a signal enhancement coil and an active shielding coil; wherein the content of the first and second substances,
the signal enhancement coil and the active shielding coil are coaxially arranged, the signal enhancement coil generates a magnetic field in the same direction as the main magnetic field, and the active shielding coil generates a magnetic field in the direction opposite to the main magnetic field and is used for offsetting the magnetic fields of the signal enhancement coil on the upper polar plate and the lower polar plate of the main magnet and avoiding the influence of the signal enhancement coil on the main magnet; the signal enhancement coil and the active shielding coil have different acting distances and exciting currents, and after the signal enhancement coil and the active shielding coil act together, a signal enhancement magnetic field with the same main magnetic field direction is generated in a signal enhancement area.
Furthermore, the signal enhancement coil and the active shielding coil in the signal enhancement device are two pairs of identical circular conductor coils which are arranged coaxially in the longitudinal direction, the axes of the two pairs of circular conductor coils are parallel to the main magnetic field direction of the magnetic resonance imaging magnet, the magnetic field generated by the inner coaxial coil pair is the same as the main magnetic field direction of the magnetic resonance imaging magnet, the signal enhancement coil is used as the signal enhancement coil, the magnetic field generated by the outer coaxial coil pair is opposite to the magnetic field generated by the inner coaxial coil pair in the direction, and the active shielding coil is used for offsetting the magnetic fields generated by the inner coil pair on the upper polar plate and the lower polar plate of the magnetic resonance imaging magnet.
Further, the electromagnetic coil for signal enhancement is separate from the main magnet, and the electromagnetic coil can move freely in the main magnet and can also move out of the main magnet when not needed.
Further, the magnetic field generated by the electromagnetic coil for signal enhancement only generates a magnetic field locally, and only acts on a part needing imaging, and does not cover the whole main magnetic field area.
According to another aspect of the present invention, a method for improving the signal-to-noise ratio of magnetic resonance imaging by using the aforementioned system is provided, which includes the following steps:
step 1, positioning and pre-scanning an imaging target, and determining the position of a part to be imaged;
step 2, moving the signal enhancement device to the position of the part to be imaged by using a positioning system according to the determined position of the imaging part, so that the field center position of the signal enhancement device is superposed with the center coordinate of the scanning part;
step 3, exciting current to the signal enhancement device to generate a magnetic field with the same direction as the main magnetic field, and polarizing the imaging part by the two magnetic fields together so as to increase the net magnetization vector of the imaging part;
and 4, canceling the exciting current of the signal enhancement device, and imaging the imaging part according to the imaging sequence.
Further, the step of determining the imaging position through positioning pre-scanning means that rapid imaging is performed on an imaging target in three directions of vector, crown and axis before formal imaging, a specific position of a part needing imaging is found, and coordinates of the imaging part in a magnetic resonance imaging system coordinate system are given.
Furthermore, moving the signal enhancement device to the position of the portion to be imaged means moving the signal enhancement device to the position of the portion to be imaged by manual movement or automatic movement.
Furthermore, the excitation current of the signal enhancement device is removed, and the imaging part is imaged according to the imaging sequence, which means that the signal enhancement magnetic field only lasts for a preset time and does not participate in space-time coding in the magnetic resonance imaging process.
Further, the excitation current of the signal enhancement device is cancelled, the cancellation time of the excitation current is far shorter than the longitudinal relaxation time (T1) of the imaging part, and otherwise the signal enhancement effect is influenced; said much smaller is for example less than 10%.
In the step 3, the spectrometer system controls a driving power supply, a gradient and a radio frequency power amplifier of the signal enhancement device to complete an imaging pulse sequence; the sequence is started by first applying a predetermined duration GBPulse, GBThe pulse control signal intensifier has its drive power supply generating pulse drive current, and the signal intensifier generates a magnetic field in the same direction as the imaging magnet, which are superposed to form net magnetizing vector M of imaging part0Is enhanced.
Further, the control of the signal enhancement device may be incorporated into the magnetic resonance imaging sequence, with the spectrometer system of the magnetic resonance imaging system controlling the strength and duration of the signal enhancement magnetic field as desired.
Has the advantages that:
the signal enhancement method of the invention utilizes the electromagnetic coil to increase the polarized magnetic field of the imaging part and increase the net magnetization vector of the imaging part, thereby achieving the signal enhancement effect, the signal enhancement effect is related to the magnetic field intensity generated by the signal enhancement coil, and if the magnetic field intensity generated by the signal enhancement coil is 800Gs and the magnetic field intensity of the magnetic resonance imaging magnet is 1000Gs, the signal intensity is improved by about 80 percent (800/1000), thereby effectively improving the image quality of the monitoring type magnetic resonance imaging. And the electromagnetic coil adopted for signal enhancement is an independent part, can move out of or into the magnetic resonance imaging magnet as required, and can also freely move in the magnetic resonance imaging magnet when in use, so that the structure is simple, the use is convenient, and the realization is convenient.
Drawings
Fig. 1 is a schematic diagram of an embodiment of the method of the present invention, in which 101 is a magnetic resonance imaging magnet, 102 is an imaging target, 103 is a signal enhancing device, 104 is a spatial positioning device, 105 is a magnetic resonance imaging spectrometer, 106 is a driving power supply, 107 is a gradient and rf power amplifier, and 108 is a system base.
Fig. 2 is a structural diagram of a signal enhancement device according to an embodiment, where 201 is a signal enhancement coil, 202 is an active shield coil, 203 is an upper plate, 204 is a lower plate, and 205 is a signal enhancement region.
Fig. 3 is a control pulse sequence according to an embodiment.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments, and all other embodiments obtained by a person skilled in the art based on the embodiments of the present invention belong to the protection scope of the present invention without creative efforts.
As shown in fig. 1, the whole mri system is mounted on a movable system base 108, and the system base 108 is provided with wheels to facilitate movement. The magnetic resonance imaging spectrometer 105, a driving power supply 106 of the signal enhancement device 103, a gradient and radio frequency power amplifier 107 are arranged in a cabinet at the lower part of a system base 108, the magnetic resonance imaging magnet 101 is arranged above the base, the space positioning device 104 is arranged in the magnetic resonance imaging magnet 101, the signal enhancement device 103 is arranged in the magnetic resonance imaging magnet 101 and can move freely, and the specific position of the signal enhancement device is determined by the indication of the space positioning device 104.
Signal booster coil as shown in fig. 2, in use, the signal booster coil 201 and the active shielding coil 202 are coaxially disposed, the signal booster coil 201 generates a magnetic field in the same direction as the main magnetic field, and the active shielding coil 202 generates a magnetic field in the opposite direction to the main magnetic field, so as to cancel the magnetic field of the signal booster coil 201 on the upper plate 203 and the lower plate 204 of the magnetic resonance imaging magnet, and avoid the influence of the signal booster coil 201 on the main magnet. Due to the difference of the acting distance and the exciting current, a signal enhancement magnetic field with the same main magnetic field direction is generated in the signal enhancement region 205 of the signal enhancement coil after the two act together.
According to the method of the present invention, the signal enhancement means refers to an electromagnetic coil that can generate a static magnetic field. In order to avoid adverse effects of the electromagnetic coil on the magnetic resonance system, the electromagnetic coil is also provided with an active shielding function. The signal enhancement device consists of two coaxial pairs (four) of completely same circular conductor coils, the axes of the two coaxial coils are parallel to the direction of a main magnetic field of the magnetic resonance imaging magnet, the direction of a magnetic field generated by the inner coaxial coil pair (two) is the same as the direction of the main magnetic field of the magnetic resonance imaging magnet, the signal enhancement coil is used as a signal enhancement coil, and the direction of a magnetic field generated by the outer coaxial coil pair (two) is opposite to the direction of a magnetic field generated by the inner coaxial coil pair (two) so as to offset the magnetic fields generated by the inner coil on the upper polar plate and the lower polar plate of the magnetic resonance imaging magnet. To improve the efficiency of the signal enhancement device, the inner pair of coaxial coils should be as far away as possible from the outer pair of coaxial coils.
According to one embodiment of the invention, the electromagnetic coil for signal enhancement is separate from the main magnet, i.e. the signal enhancement device is a separate component that can be freely moved out of/into the magnetic resonance imaging magnet as desired.
According to an embodiment of the present invention, moving the signal enhancing coil to the position of the portion to be imaged means moving the signal enhancing coil to the position coordinates of the portion to be imaged by manual movement or automatic movement. Since the zero point of the spatial gradient code is located at the center of the magnetic resonance imaging magnet, the relative position of the imaging part determined by the pre-scanning and the zero point of the spatial gradient code is actually the relative position of the imaging part and the center of the magnetic resonance imaging magnet, wherein the center of the magnetic resonance imaging magnet is set as the origin of the imaging positioning coordinate system, the main magnetic field direction of the magnetic resonance imaging magnet is the Z-axis of the imaging positioning coordinate system, and the imaging positioning coordinate system (cartesian coordinate system) is established according to the right-hand rule. The coordinates of the imaging part can be measured by the pre-scanning image, and assuming that the coordinates of the imaging part in the imaging positioning coordinate system are (1mm, 2mm, 3mm), the axis of the signal enhancement coil is kept parallel to the Z axis, the axis position is placed at (1mm, 2mm), the axis center is positioned at the zero point of the Z axis of the imaging positioning coordinate system, namely the center of the signal enhancement coil is positioned at the coordinates (1mm, 2mm, 0 mm).
According to one embodiment of the invention, the magnetic field generated by the electromagnetic coil for signal enhancement only locally generates a magnetic field, and only acts on a part needing to be imaged, and does not cover the whole main magnetic field area.
According to the method, polarizing the imaging area means that an excitation current is applied to a signal intensifier, a solenoid, which produces an excitation magnetic field BpThe magnetic field and the main magnetic field B of the imaging system0The same direction, so that there is a B at a local position of the imaging site0+BpThe superimposed magnetic field of (a). From the principle of magnetic resonance, it can be seen that the net magnetization vector M is constant at absolute temperature0The magnitude depends on the strength of the applied magnetic field, the higher the field, M0The larger. The net magnetization vector M formed by the imaged part at this time0With superimposed magnetic field B0+BpRelated, net magnetization vector M0The signal to noise ratio of the image is increased.
According to an embodiment of the present invention, removing the excitation current of the signal enhancement means and imaging the imaging region according to the imaging sequence means that the signal enhancement magnetic field lasts only for a period of time (seconds or tens of seconds, etc. depending on the relaxation time of the imaging region) and does not participate in the space-time encoding during the magnetic resonance imaging, so that theoretically the ratio between the MRI signal in the presence of the enhanced magnetic field and the MRI signal in the absence of the enhanced magnetic field is (B)0+Bp)/B0I.e. the magnitude of the signal increase is proportional to the ratio between the enhancing magnetic field and the main magnetic field.
According to one embodiment of the invention, the excitation current of the signal enhancement device is withdrawn, the withdrawal time cannot be too long and is much shorter than the longitudinal relaxation time (T1) of the imaging part, otherwise the signal enhancement effect is affected.
According to one embodiment of the invention, the control of the signal enhancing means may be incorporated into the magnetic resonance imaging sequence, the strength and duration of the signal enhancing magnetic field being controlled as desired by the spectrometer system of the magnetic resonance imaging system.
According to an embodiment of the present invention, in a specific imaging process, an imaging target is first placed in an imaging region of the magnetic resonance imaging magnet 101, a magnetic resonance imaging spectrometer 105 controls a gradient and a radio frequency power amplifier 107 to perform rapid imaging in three directions of vector, crown and axis, a part to be scanned is found, specific coordinates of the center of the imaging part in a coordinate system of an imaging system are given by imaging software, and the spatial positioning device 104 guides the signal enhancement device 103 to move to a corresponding position according to the coordinates, so that a magnetic field generated by the signal enhancement device 103 acts on the imaging part. The magnetic resonance imaging spectrometer 105 controls the driving power supply 106 of the signal enhancement device, the gradient and the radio frequency power amplifier 107 to complete the imaging pulse sequence shown in fig. 3.
The imaging pulse sequence shown in figure 3 is a combination of a polarisation pulse and a spin echo sequence, the sequence being started by first applying a G of duration 100msBPulse, GBThe pulse control signal intensifier drive power supply 106 generates pulse drive current, generates a magnetic field in the same direction as the magnetic resonance imaging magnet 101 in the signal intensifier, and the magnetic fields are superposed to obtain the net magnetization vector M of the imaging part0And enhancing, then operating according to a normal spin echo sequence, and finally obtaining a spin echo image with improved signal-to-noise ratio.
Although illustrative embodiments of the present invention have been described above to facilitate the understanding of the present invention by those skilled in the art, it should be understood that the present invention is not limited to the scope of the embodiments, but various changes may be apparent to those skilled in the art, and it is intended that all inventive concepts utilizing the inventive concepts set forth herein be protected without departing from the spirit and scope of the present invention as defined and limited by the appended claims.
Claims (10)
1. A system for improving signal-to-noise ratio in point-of-care magnetic resonance imaging, comprising:
the whole magnetic resonance imaging system is arranged on a movable system base, the lower part of the base is provided with a cabinet, and a driving power supply, a gradient and a radio frequency power amplifier of a spectrometer system signal enhancement device are arranged in the cabinet;
an imaging magnet is arranged above the base, the positioning system is arranged in the imaging magnet, a signal enhancement device is also arranged in the imaging magnet and can move freely, and the specific position of the imaging magnet is determined by the indication of the positioning system; the signal enhancement device comprises a signal enhancement coil and an active shielding coil; wherein the content of the first and second substances,
the signal enhancement coil and the active shielding coil are coaxially arranged, the signal enhancement coil generates a magnetic field in the same direction as the main magnetic field, and the active shielding coil generates a magnetic field in the direction opposite to the main magnetic field and is used for offsetting the magnetic fields of the signal enhancement coil on the upper polar plate and the lower polar plate of the main magnet and avoiding the influence of the signal enhancement coil on the main magnet; the signal enhancement coil and the active shielding coil have different acting distances and exciting currents, and after the signal enhancement coil and the active shielding coil act together, a signal enhancement magnetic field with the same main magnetic field direction is generated in a signal enhancement area.
2. The system of claim 1, wherein the signal enhancing coil and the active shielding coil of the signal enhancing device are two pairs of identical circular conductor coils disposed coaxially in a longitudinal direction and having an axis parallel to a main magnetic field direction of the magnetic resonance imaging magnet, wherein the inner pair of coaxial coils generate a magnetic field in a direction same as the main magnetic field direction of the magnetic resonance imaging magnet, and the outer pair of coaxial coils generate a magnetic field in a direction opposite to the direction of the magnetic field generated by the inner coaxial coil and are active shielding coils for canceling the magnetic field generated by the inner coil on the upper and lower plates of the magnetic resonance imaging magnet.
3. The system of claim 1, wherein the electromagnetic coil for signal enhancement is separate from the main magnet, the electromagnetic coil being freely movable within the main magnet and also movable out of the main magnet when not needed.
4. The system of claim 1, wherein the electromagnetic coil for signal enhancement generates a magnetic field only locally, and only acts on the region to be imaged, rather than covering the entire main magnetic field.
5. A method for improving the signal-to-noise ratio of magnetic resonance imaging using the system of any one of claims 1 to 4, comprising the steps of:
step 1, positioning and pre-scanning an imaging target, and determining the position of a part to be imaged;
step 2, moving the signal enhancement device to the position of the part to be imaged by using a positioning system according to the determined position of the imaging part, so that the field center position of the signal enhancement device is superposed with the center coordinate of the scanning part;
step 3, exciting current to the signal enhancement device to generate a magnetic field with the same direction as the main magnetic field, and polarizing the imaging part by the two magnetic fields together so as to increase the net magnetization vector of the imaging part;
step 4, canceling the exciting current of the signal enhancement device, and imaging the imaging part according to the imaging sequence;
the magnetic resonance imaging spectrometer controls a driving power supply, a gradient and a radio frequency power amplifier of the signal enhancement device to complete an imaging pulse sequence; the sequence is first applied for a duration GBPulse, GBPulse control signal increaseThe drive power supply of the strong device generates pulse drive current, a magnetic field with the same direction as the magnetic resonance imaging magnet is generated in the signal enhancement device, the magnetic fields of the pulse drive current and the magnetic field are superposed, and the net magnetization vector M of the imaging part0Enhanced and then operated according to the required imaging sequence, and finally the magnetic resonance image with the improved signal-to-noise ratio is obtained.
6. The method of claim 5, wherein the determining the imaging position by positioning the pre-scan is to perform fast imaging on the imaging target in three directions of vector, coronal, and axial to find the specific position of the imaging region before formal imaging, and to provide the coordinates of the imaging region in the coordinate system of the magnetic resonance imaging system.
7. The method of claim 5, wherein moving the signal enhancement device to the location of the region to be imaged is moving the signal enhancement device to the location of the region to be imaged by manual movement or automatic movement.
8. The method of claim 5, wherein the exciting current of the signal enhancing device is removed, and the imaging region is imaged according to the imaging sequence, that is, the signal enhancing magnetic field only lasts for a predetermined time and does not participate in space-time encoding in the magnetic resonance imaging process; the excitation current of the signal enhancement device is withdrawn, and the withdrawal time is far shorter than the longitudinal relaxation time T1 of the imaging part.
9. The method according to claim 5, wherein in step 3, the spectrometer system controls the driving power supply, the gradient and the radio frequency power amplifier of the signal enhancement device to complete the imaging pulse sequence; the sequence is started by first applying a predetermined duration GBPulse, GBThe pulse control signal intensifier has its drive power supply generating pulse drive current, and the signal intensifier generates a magnetic field in the same direction as the imaging magnet, which are superposed to form net magnetizing vector M of imaging part0Is enhanced.
10. The method of claim 5, wherein the control of the signal enhancement device is incorporated into the magnetic resonance imaging sequence, and wherein the signal enhancement magnetic field is controlled by a spectrometer system of the magnetic resonance imaging system as needed for the intensity and duration of the signal enhancement magnetic field.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN114229245A (en) * | 2021-12-30 | 2022-03-25 | 中科微影(浙江)医疗科技有限公司 | Damping system for magnetic resonance equipment transportation |
| WO2023104948A1 (en) * | 2021-12-10 | 2023-06-15 | Multiwave Imaging | Magnetic resonance imaging apparatus provided with a magnetic assembly |
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| JPH05337101A (en) * | 1992-06-09 | 1993-12-21 | Toshiba Corp | Magnetic resonance imaging apparatus |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| WO2023104948A1 (en) * | 2021-12-10 | 2023-06-15 | Multiwave Imaging | Magnetic resonance imaging apparatus provided with a magnetic assembly |
| FR3130391A1 (en) * | 2021-12-10 | 2023-06-16 | Multiwave Imaging | Magnetic resonance imaging device with magnetic assembly |
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