CN108418406A - A kind of gradient amplifier and magnetic resonance imaging device - Google Patents
A kind of gradient amplifier and magnetic resonance imaging device Download PDFInfo
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- CN108418406A CN108418406A CN201810205331.7A CN201810205331A CN108418406A CN 108418406 A CN108418406 A CN 108418406A CN 201810205331 A CN201810205331 A CN 201810205331A CN 108418406 A CN108418406 A CN 108418406A
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/14—Arrangements for reducing ripples from dc input or output
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves
- A61B5/055—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
- G01R33/385—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using gradient magnetic field coils
- G01R33/3852—Gradient amplifiers; means for controlling the application of a gradient magnetic field to the sample, e.g. a gradient signal synthesizer
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
- H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
- H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/21—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/217—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M7/219—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only in a bridge configuration
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
- H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
- H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/21—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/217—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M7/219—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only in a bridge configuration
- H02M7/2195—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only in a bridge configuration the switches being synchronously commutated at the same frequency of the AC input voltage
Abstract
The present invention discloses a kind of gradient amplifier and magnetic resonance imaging device, wherein and gradient amplifier is applied to magnetic resonance imaging device, for providing electric current for the gradient coil in magnetic resonance imaging device, including：Rectifier, H bridges, filter circuit and control circuit；Rectifier connects AC power, and the AC rectification for providing AC power is direct current；The output end of the input terminal connection rectifier of H bridges, the output end of H bridges connect filter circuit；Filter circuit, for filtering out the harmonic wave in the H bridges output current；The output end of filter circuit connects the gradient coil；Filter circuit includes concatenated filter inductance and variable filtering impedance；Control circuit, for when gradient coil is greater than or equal to gradient coil saturation current reference value to constant current, increase the impedance value that can be changed filtering impedance, the gradient coil current caused by filter inductance magnetic saturation can be avoided to shake, and then image quality is improved, and cost of goods manufactured can be reduced.
Description
Technical field
The present invention relates to technical field of medical equipment more particularly to a kind of gradient amplifiers and magnetic resonance imaging device.
Background technology
The main function of gradient amplifier be provide driving current for the gradient coil in magnetic resonance imaging device, and
The electric current of gradient coil can be accurately controlled, gradient coil equivalent can be interpreted as an inductance, so working as gradient coil current
Quickly when variation, gradient amplifier needs moment to export high pressure；When gradient coil current is direct current, gradient amplifier needs fast
Speed switchs to a low pressure from high pressure.
Currently, gradient amplifier meets the requirement of Magnetic resonance imaging using cascaded H bridge topology.Specifically it may refer to Fig. 1
And Fig. 2, for the gradient amplifier schematic diagram of the cascaded H bridge-type provided in the prior art.
Fig. 1 is the schematic diagram of a H bridge, and Fig. 2 is the schematic diagram that three H bridges are cascaded.The switching tube of H bridges is by controlling
The pulse signal of circuit output controls its on off operating mode.
The phase of three H bridge output voltages misphase each other, so as to realize that gradient coil both ends equivalent switching frequency increases
Add, current ripples can be reduced in this way, realizes the purpose for accurately controlling electric current.
In order to ensure that gradient coil current does not contain high-frequency harmonic, H bridge output ends are connected into electromagnetic interference
(Electromagnetic Interference, EMI) filter, the electromagnetic interface filter include filter inductance and filter capacitor.Its
In, filter inductance is magnetic material, and when the electric current of gradient coil constantly increases, the inductance value of filter inductance can increase with electric current
Reduce greatly, when the electric current of gradient coil exceeds filter inductance load current value, filter inductance can be caused magnetic saturation occur, from
And the electric current of gradient coil is caused to generate concussion, influence the image quality of final magnetic resonance imaging device.
It is to solve the problems, such as that filter inductance magnetic saturation leads to current oscillation in the prior art, anti-saturation characteristic can be selected preferable
Magnetic material filter inductance, but product design costs will be increased in this way.
Invention content
In order to solve the above technical problem existing in the prior art, the embodiment of the present invention provide a kind of gradient amplifier with
And magnetic resonance imaging device, the gradient coil current caused by filter inductance magnetic saturation can be avoided to shake, and then from improving
Image quality, and cost of goods manufactured can be reduced.
For this purpose, the embodiment of the present invention provides the following technical solutions：
In a first aspect, the embodiment of the present invention provides a kind of gradient amplifier, the gradient amplifier be applied to nuclear magnetic resonance at
As equipment, for providing electric current for the gradient coil in magnetic resonance imaging device, including：Rectifier, H bridges, filter circuit and
Control circuit；
The rectifier connects AC power, and the AC rectification for providing AC power is direct current；
The input terminal of the H bridges connects the output end of the rectifier, and the output end of the H bridges connects the filtered electrical
Road；
The filter circuit, for filtering out the harmonic wave in the H bridges output current；The output end of the filter circuit connects
The gradient coil；
The filter circuit includes concatenated filter inductance and variable filtering impedance；
The control circuit, for being greater than or equal to gradient coil saturation current reference value to constant current when gradient coil
When, increase the impedance value of the variable filtering impedance.
Optionally, the variable filtering impedance includes at least following two parallel branches：The first branch and the second branch；
The first branch includes the first filter capacitor；
The second branch includes concatenated first impedance and switch；
First impedance include at least it is following in one kind：Capacitance and inductance；
The control circuit, for when gradient coil is greater than or equal to gradient coil saturation current reference value to constant current
Increase the impedance value of the variable filtering impedance by being closed the switch.
Optionally, when first impedance includes the first capacitance, the second branch includes concatenated first electricity
Hold and the switch.
Optionally, when first impedance includes the first inductance, the second branch includes concatenated first electricity
Sense and the switch.
Optionally, when first impedance includes the second inductance and the second capacitance, the second branch includes concatenated
Second inductance, the second capacitance and the switch.
Optionally, the variable filtering impedance further includes third branch；
The third branch includes concatenated second impedance and switch；
Second impedance include at least it is following in one kind：Capacitance and inductive resistance；
The control circuit, for when gradient coil is greater than or equal to gradient coil saturation current reference value to constant current
Increase the impedance value of the variable filtering impedance by being closed the switch.
Optionally, the control circuit includes：Comparator and driving circuit；
The first input end of the comparator connects the gradient coil to constant current, the second output terminal of the comparator
The filter inductance saturation current reference value is connected, the output end of the comparator connects the driving circuit；
The driving circuit, for determining that the gradient coil is greater than or equal to filtered electrical to constant current in the comparator
The switch is driven to be closed when feeling saturation current reference value.
Optionally, the comparator is digital comparator or analog comparator.
Optionally, the control circuit further includes：Controller；
The controller, the given electricity of the gradient coil for receiving the transmission of magnetic resonance imaging device control computer
Stream, and the gradient coil is compared to constant current with gradient coil current value, it is adjusted to the H bridges according to comparison result
Drive pulse signal.
Second aspect, the embodiment of the present invention provide a kind of magnetic resonance imaging device, including the gradient described in first aspect
Amplifier further includes：Gradient coil；
The gradient amplifier, for providing electric current for gradient coil.
Compared with prior art, the present invention has at least the following advantages：
The gradient amplifier includes filter circuit, for filtering out the harmonic wave in the H bridges output current；The filter circuit
Output end connect the gradient coil；The filter circuit includes concatenated filter inductance and variable filtering impedance；The control
Circuit processed, it is described variable for when gradient coil is greater than or equal to gradient coil saturation current reference value to constant current, increasing
The impedance value of filtering impedance.
When gradient coil is greater than or equal to filter inductance saturation current reference value to constant current, the induction reactance value of filter inductance
It can decline, therefore in order to make total resistance remain unchanged, the impedance with the concatenated variable filtering impedance of filter inductance can be increased
Value, and then ensure that the electric current of gradient coil not will produce concussion, it is seen then that the scheme provided through the embodiment of the present invention, without making
Filter inductance is formed with the preferable magnetic material of expensive anti-saturation, also can avoid causing due to filter inductance magnetic saturation
Gradient coil current concussion, and then improve image quality, and reduce the manufacturing cost of product.
Description of the drawings
In order to illustrate the technical solutions in the embodiments of the present application or in the prior art more clearly, to embodiment or will show below
There is attached drawing needed in technology description to be briefly described, it should be apparent that, the accompanying drawings in the following description is only this
Some embodiments described in application, for those of ordinary skill in the art, without creative efforts,
It can also be obtained according to these attached drawings other attached drawings.
Fig. 1 is the schematic diagram of a H bridge；
Fig. 2 is the schematic diagram that three H bridges are cascaded；
Fig. 3 is the relation schematic diagram of the inductance value and electric current of filter inductance；
Fig. 4 is that gradient coil current generates concussion schematic diagram；
Fig. 5 is a kind of gradient amplifier structural schematic diagram provided in an embodiment of the present invention；
Fig. 6 is another gradient amplifier structural schematic diagram provided in an embodiment of the present invention；
Fig. 7 A are the first filter capacitor provided in an embodiment of the present invention and the first capacitance connection schematic diagram；
Fig. 7 B are the first filter capacitor provided in an embodiment of the present invention and the first inductance connection schematic diagram；
Fig. 7 C are the first filter capacitor provided in an embodiment of the present invention and the second inductance, the second capacitance connection schematic diagram；
Fig. 8 is comparing result schematic diagram provided in an embodiment of the present invention before and after increasing the impedance value that can be changed filtering impedance；
Fig. 9 is a kind of magnetic resonance imaging device structural schematic diagram provided in an embodiment of the present invention.
Specific implementation mode
In order to enable those skilled in the art to better understand the solution of the present invention, below in conjunction in the embodiment of the present invention
Attached drawing, technical scheme in the embodiment of the invention is clearly and completely described, it is clear that described embodiment is only this
Invention a part of the embodiment, instead of all the embodiments.Based on the embodiments of the present invention, those of ordinary skill in the art exist
The every other embodiment obtained under the premise of creative work is not made, shall fall within the protection scope of the present invention.
The technical solution provided to facilitate the understanding of the present invention below first carries out the background technology of technical solution of the present invention
Simple declaration.
Inventor has found that the inductance value of filter inductance reduces with the increase of electric current under study for action, filters as shown in Figure 3
The inductance value of inductance and the relation schematic diagram of electric current can lead to filter inductance if electric current exceeds the rated value of filter inductance
Saturation in turn results in gradient coil current and generates concussion, and when filter inductance as shown in Figure 4 is saturated, gradient coil current generates shake
Swing schematic diagram.Reduce in the prior art with electric current increase to solve filter inductance, when filter inductance current saturation, causes
Gradient coil current leads to the problem of concussion, and the preferable magnetic material of anti-saturation is selected to form filter inductance, and generally anti-full
It is higher by a lot of times than common magnetic material with the preferable magnetic material price of property, manufacturing cost can be caused very high in this way；
On the other hand, gradient amplifier range of tolerable variance relative narrower is higher to filter inductance tolerances itself so that gradient amplifier
Robustness is not strong.
Based on this, an embodiment of the present invention provides a kind of gradient amplifier, which includes rectifier, H bridges, filter
Wave circuit and control circuit, wherein filter circuit includes concatenated filter inductance and variable filtering impedance, when gradient coil is given
When electric current is greater than or equal to filter inductance saturation current reference value, control circuit control can be changed filtering impedance, increase variable filtering
The resistance value of impedance.
As it can be seen that when gradient coil is greater than or equal to filter inductance to constant current and is saturated electric reference value, filter inductance
Inductance value can reduce, to avoid causing the electric current of gradient coil to shake because the inductance value of filter inductance reduces, control electricity
The impedance value that road control can be changed filtering impedance increases, and ensures that the total resistance of filter circuit remains unchanged, and avoids gradient coil electric
Stream shakes, i.e., the gradient amplifier provided through the embodiment of the present invention, and filter inductance is formed using common magnetic material, when
When gradient coil causes filter inductance to be saturated to constant current is larger, the impedance value that filtering impedance can be can be changed by increase avoids gradient
Coil current generates concussion, reduces manufacturing cost；Moreover, because control circuit can adjust the resistance value of variable filtering impedance, because
This so that gradient amplifier reduces the range of tolerable variance requirement to filter inductance, improves the robustness of gradient amplifier.
Embodiment one
It describes in detail below in conjunction with the accompanying drawings to a kind of gradient amplifier of the exemplary offer of the present invention.
Referring to Fig. 5, which is a kind of gradient amplifier structural schematic diagram that inventive embodiments are provided.
Gradient amplifier provided in this embodiment is applied to magnetic resonance imaging device, for being magnetic resonance imaging device
In gradient coil provide electric current.
Gradient amplifier provided in this embodiment includes：Rectifier 501, H bridges 502, filter circuit 503 and control circuit
504。
The rectifier 501 connects AC power, and the AC rectification for providing AC power is direct current.
501 input terminal of rectifier is connect with AC power, and output end is connect with H bridges 502, thus by the direct current after rectification
It exports to H bridges 502.
In the present embodiment, the quantity of rectifier (AC/DC) 501 can be consistent with the quantity of H bridges, as shown in figure 5,
The figure includes 3 AC/DC, and the input terminal of each AC/DC is connect with AC power (not shown), the input of output end and H bridges
End connection.
The input terminal of the H bridges 502 connects the output end of the rectifier 501, and the output end of the H bridges 502 connects institute
State filter circuit 503.
Gradient amplifier can utilize different circuit topology realizations to accurately control gradient coil current, different electricity
Road topology includes that the quantity of H bridges is also different, can be a H bridge, or and multiple H bridges, the present embodiment do not limit herein,
For ease of description and understand, is introduced by taking three H bridges as an example below.
As shown in figure 5, the figure includes three H bridges, respectively H1, H2, H3, the output end series connection of three H bridges.Wherein,
The input terminal of H1, H2 and H3 are connect with the output end of AC/DC1, AC/DC2, AC/DC3 respectively, the first output end and the filtering of H1
The first input end of circuit 503 connects；The second output terminal of H1 and the first output end of H2 connect, the second output terminal and H3 of H2
The connection of the first output end, the second output terminal of H3 connect with the second input terminal of filter circuit 503.
The filter circuit 503, for filtering out the harmonic wave in 502 output current of H bridges；The filter circuit 503
Output end connects the gradient coil 305.
The output end of the input terminal connection H bridges 502 of filter circuit 503, the output end of filter circuit 503 connect gradient coil
505 input terminal will filter out the electric current after harmonic wave and export to gradient coil 505, reduces the height flowed through in 505 electric current of gradient coil
Frequency harmonic wave improves image quality.
The filter circuit 503 may include concatenated filter inductance 506 and variable filtering impedance 507.
In the present embodiment, the positive output end and negative output terminal one filter inductance 506 of each series connection of connection H bridges 502, H bridges 502
Positive output end and two filter inductance Lfdm being separately connected of negative output terminal it is symmetrical, as shown in figure 5, the company of two filter inductances
It connects that relationship is identical, the connection relation of filter inductance is described in detail below.
As shown in figure 5, the input terminal of filter inductance 506 and the first output end of H1 connect, the output end of filter inductance 506
It is connect with the input terminal of variable filtering impedance 507, can be changed the output end ground connection of filtering impedance 507.Wherein, Rfdm is filter in Fig. 5
The equivalent resistance of wave inductance.
Gradient coil 505 is equivalent to resistance Rgc shown in Fig. 5, capacitance Cgc and inductance Lgc in the present embodiment.Wherein, Igc
The electric current of gradient coil is flowed through in expression.
The control circuit 504, for being referred to more than or equal to filter inductance saturation current to constant current when gradient coil
When value, increase the impedance value of the variable filtering impedance.
Wherein, filter inductance saturation current reference value is corresponding current threshold when filter inductance is saturated, due to filtered electrical
The inductance value of sense can reduce with the increase of electric current, and the total resistance of filter circuit is caused to reduce, when the given electricity of gradient coil
When stream is greater than or equal to filter inductance saturation current reference value, filter inductance can be caused to be saturated, in turn result in gradient coil current
Concussion is generated, image quality is influenced.
In the present embodiment, filter inductance 506 can utilize lower-cost general magnetic material manufacture, by with variable filter
Wave impedance 507 is connected, and when gradient coil causes filter inductance to be saturated to constant current is larger, can be changed filtering impedance by increase
507 impedance value ensures that the total resistance of filter circuit is not reduced because the inductance of filter inductance reduces, and avoids gradient coil electric
The raw concussion of miscarriage influences image quality, i.e., while reducing manufacturing cost, also can guarantee that the performance of gradient amplifier is not damaged
It loses.
When gradient coil to constant current be greater than or equal to filter inductance saturation current reference value when, for make up filter inductance because
Filter circuit total resistance caused by the increase inductance value of electric current is smaller reduces defect, and control circuit control can be changed filtering impedance
Impedance value increase, increase the stability of filter circuit, to avoid the reduction of filter circuit total resistance, and then ensure gradient
Coil current, which not will produce concussion, influences image quality.The gradient amplifier provided through the embodiment of the present invention, even with
Common magnetic material forms filter inductance, can also eliminate the concussion of gradient coil current generation.
It is understood that since control circuit 504 can adjust the impedance value of variable filtering impedance, even if filter inductance
Inductance value exceed range of tolerable variance, the impedance value that filtering impedance can also be can be changed by increase ensure the total impedance of filter circuit
Value will not be reduced because the inductance value of filter inductance reduces, it is seen then that the gradient amplifier provided through this embodiment can relax
To filter inductance range of tolerable variance, the requirement to filter inductance range of tolerable variance is reduced, the robustness of gradient amplifier is improved.
The gradient amplifier provided through this embodiment, when gradient coil is saturated to constant current more than or equal to gradient coil
When current reference value, the induction reactance value of filter inductance can decline, therefore in order to make total resistance remain unchanged, and can increase and filter
The impedance value of the concatenated variable filtering impedance of inductance, and then ensure that the electric current of gradient coil not will produce concussion, it is seen then that pass through this
The scheme that inventive embodiments provide can pass through increasing using general magnetic material manufacture filter inductance when filter inductance is saturated
The impedance value of big variable filtering impedance ensures that the electric current of gradient coil is stablized, and improves image quality, while also reducing and being manufactured into
This.
Above-described embodiment describes gradient amplifier composition and function is realized, below in conjunction with the accompanying drawings to the tool of gradient amplifier
Body composition describes in detail.
Embodiment two
Referring to Fig. 6, which is another gradient amplifier structural schematic diagram provided in an embodiment of the present invention.
It can be changed filtering impedance in gradient amplifier provided in this embodiment and include at least following two parallel branches：First
Road 600 and the second branch 700.
Wherein, the first branch includes the first filter capacitor 601；The second branch include concatenated first impedance and
Switch；First impedance include at least it is following in one kind：Capacitance and inductance.
The control circuit 602, for being referred to more than or equal to filter inductance saturation current to constant current when gradient coil
Increase the impedance value of the variable filtering impedance when value by being closed the switch.
In the present embodiment, the first impedance may include the various combination of capacitance and/or inductance, below will to various combination into
Row is introduced.
In some embodiments, when first impedance includes the first capacitance 701, the second branch includes series connection
First capacitance 701 and the switch 702.
When the second branch is concatenated first capacitance 701 and switch 702, then can be changed filtering impedance is the first filter capacitor
601 the second branches in parallel.Referring to Fig. 7 A, which is the first filter capacitor and the first inductance connection schematic diagram.
In some embodiments, when first impedance includes the first inductance 703, the second branch includes series connection
First inductance 703 and the switch 704.
When the second branch is concatenated first inductance 703 and switch 704, then can be changed filtering impedance is the first filter capacitor
601 the second branches in parallel.Referring to Fig. 7 B, which is the first filter capacitor and the first inductance connection schematic diagram.
In some embodiments, when first impedance includes the second inductance 705 and the second capacitance 706, described the
Two branches include concatenated second inductance 705, the second capacitance 706 and the switch 707.
When the second branch is concatenated second inductance 705, the second capacitance 706 and switch 707, then can be changed filtering impedance is
The second branch in parallel of first filter capacitor 601.Referring to Fig. 7 C, which is the first filter capacitor and the second inductance, the second capacitance
Connection diagram.
By above-mentioned it is found that combining form, for ease of understanding gradient amplification provided in this embodiment there are many second branches
The function of device is illustrated so that the second branch includes concatenated first capacitance 701 and switch 702 as an example.
Filtering impedance, which is can be changed, referring to Fig. 6, in Fig. 6 includes the first filter capacitor 601, the first capacitance 701 and switch 702,
In, 601 the first capacitance of parallel connection 701 of the first filter capacitor and switch 702.When gradient coil is greater than or equal to filtered electrical to constant current
When feeling saturation current reference value, control circuit controls switch 702 and is closed so that the first capacitance 701 and the first filter capacitor 601 are simultaneously
Connection increases capacitive reactance, ensures that the total resistance of filter circuit will not reduce, and then ensures that the electric current of gradient coil not will produce concussion
Influence image quality.
In some embodiments, the variable filtering impedance can also include third branch；The third branch includes
Concatenated second impedance and switch；Second impedance include at least it is following in one kind：Capacitance and inductance.
The control circuit, for when gradient coil is greater than or equal to gradient coil saturation current reference value to constant current
Increase the impedance value of the variable filtering impedance by being closed the switch.
In the present embodiment, the second impedance can also include the various combination of capacitance and/or inductance.
When the second impedance includes third capacitance, the third branch includes the concatenated third capacitance and described opens
It closes, then can be changed filtering impedance is the first filter capacitor parallel connection third branch.
When the second impedance includes third inductance, the third branch includes the concatenated third inductance and described opens
It closes, then can be changed filtering impedance is the first filter capacitor parallel connection third branch.
When the second impedance includes the 4th inductance and four capacitances, the third branch includes concatenated 4th electricity
Sense, the 4th capacitance and the switch, then can be changed filtering impedance is the first filter capacitor third branch in parallel.
To realize to gradient coil to the comparison of constant current and filter inductance saturation current reference value size, may be used more
Kind of mode realizes, the present embodiment provides a kind of optional realization method, comparator is utilized both to judge the size cases of electric current.
In some embodiments, control circuit 602 includes：Comparator 603 and driving circuit 604.
The first input end of the comparator 603 connects the gradient coil to constant current, and the second of the comparator 603
Output end connects the filter inductance saturation current reference value, and the output end of the comparator 603 connects the driving circuit
604。
The size to constant current and filter inductance saturation current reference value of gradient coil is compared using comparator 603
Compared with exporting different signals according to comparison result.For example, when gradient coil is saturated to constant current more than or equal to filter inductance
When current reference value, the output of comparator 603 1；When gradient coil is less than filtering model's saturation current reference value to constant current,
The output of comparator 603 0.
It is understood that there are many types of comparator, the type of comparator can be selected according to actual use situation,
Comparator 603 can be digital comparator or analog comparator in the present embodiment.
In the present embodiment, the signal power that may be exported due to comparator is smaller, can not directly drive variable filtering impedance
The output end of comparator can be connected to driving circuit, through driving by the closure of middle switch to ensure that switch can be driven in time
After dynamic circuit amplification, the closure that can be changed and switched in filtering impedance is driven by driving circuit, to increase the resistance that can be changed filtering impedance
Anti- value.
The driving circuit 604, for determining that the gradient coil is greater than or equal to constant current in the comparator 603
The switch is driven to be closed when filter inductance saturation current reference value.
Driving circuit 604 carries out drive control according to the comparison result that comparator 603 exports, when gradient coil is to constant current
When more than or equal to filter inductance saturation current reference value, driving circuit 604 generates drive signal, and driving switch is closed so that
The first branch and the second branch are in parallel, increase the total resistance of filter circuit, and the electric current of gradient coil is avoided to generate concussion.
In some embodiments, the control circuit 602 further includes：Controller 605.
The controller 605, for receive magnetic resonance imaging device control computer transmission the gradient coil to
Constant current, and the gradient coil is compared to constant current with gradient coil current value, it is adjusted to institute according to comparison result
State the drive pulse signal of H bridges.
In the present embodiment, controller can make the difference the gradient coil of reception to constant current and gradient coil current value, profit
The drive pulse signal of H bridges is controlled with difference, is realized that gradient coil current follows gradient coil to the accurate of constant current, is ensured
Gradient coil current can be maintained to constant current in rational difference range with gradient coil.
To embody the realization effect of gradient amplifier provided in this embodiment, shown in Figure 8 increase can be changed filtering impedance
Impedance value before and after comparing result schematic diagram, in Fig. 8, reference current value is saturated when gradient coil is more than filter inductance to constant current
When, if not increasing the impedance value of variable filtering impedance, cause the electric current of gradient coil unstable, generates concussion；Work as increase
After the impedance value of variable filtering impedance, the electric current of gradient coil tends towards stability state, it is seen then that is carried by using the embodiment of the present invention
The gradient amplifier of confession, it is also ensured that the performance of gradient amplifier is unaffected while reducing manufacturing cost.
The variable filtering impedance provided through the embodiment of the present invention, when gradient coil is greater than or equal to filtered electrical to constant current
When feeling saturation current reference value, the induction reactance value of filter inductance can decline, can be by control electricity in order to make total resistance remain unchanged
Road controls the closure switched in the second branch and/or third branch so that the first branch and the second branch and/or third branch are simultaneously
Connection increases the impedance value that can be changed filtering impedance, and then ensures that the electric current of gradient coil not will produce concussion.As it can be seen that passing through this hair
The scheme that bright embodiment provides, the filter inductance formed using general magnetic material can pass through increasing when filter inductance is saturated
The impedance value of big variable filtering impedance ensures that the electric current of gradient coil is stablized, and while improving image quality, also reduces system
Cause this.
Based on the gradient amplifier that above-described embodiment provides, the embodiment of the present invention also provides a kind of Magnetic resonance imaging and sets
It is standby, it is introduced below in conjunction with the accompanying drawings.
Embodiment three
Referring to Fig. 9, which is a kind of magnetic resonance imaging device structural schematic diagram provided in an embodiment of the present invention.
The present embodiment magnetic resonance imaging device includes the gradient amplifier in embodiment one or embodiment two, further includes：
Gradient coil.
The gradient amplifier, for providing electric current for gradient coil.
It should be noted that the setting and realization of gradient amplifier may refer to implement described in Fig. 1 to Fig. 2 in the present embodiment
Example, details are not described herein.
The magnetic resonance imaging device provided through the embodiment of the present invention, when gradient coil is greater than or equal to ladder to constant current
When spending filter inductance saturation current reference value in amplifier, the induction reactance value of filter inductance can decline, in order to make total resistance keep
Constant, the impedance value that the control circuit in gradient amplifier can control variable filtering impedance increases, and avoids due to filtering
Inductance is saturated and gradient coil current is caused to generate concussion, and then the problem of influence image quality.As it can be seen that carrying through this embodiment
The magnetic resonance imaging device of confession is avoiding the gradient coil current caused by filter inductance magnetic saturation from shaking, and then is improving
Image quality, and cost of goods manufactured can be reduced.
It should be appreciated that in this application, " at least one (item) " refers to one or more, and " multiple " refer to two or two
More than a."and/or", the incidence relation for describing affiliated partner indicate may exist three kinds of relationships, for example, " A and/or B "
It can indicate：A is only existed, B is only existed and exists simultaneously tri- kinds of situations of A and B, wherein A, B can be odd number or plural number.Word
It is a kind of relationship of "or" that symbol "/", which typicallys represent forward-backward correlation object,.At least one of " following (a) " or its similar expression refers to
Arbitrary combination in these, including individual event (a) or the arbitrary combination of complex item (a).At least one of for example, in a, b or c
(a) can indicate：A, b, c, " a and b ", " a and c ", " b and c ", or " a and b and c ", wherein a, b, c can be single, also may be used
To be multiple.
The above described is only a preferred embodiment of the present invention, being not intended to limit the present invention in any form.Though
So the present invention has been disclosed as a preferred embodiment, and however, it is not intended to limit the invention.It is any to be familiar with those skilled in the art
Member, without departing from the scope of the technical proposal of the invention, all using the methods and technical content of the disclosure above to the present invention
Technical solution makes many possible changes and modifications, or is revised as the equivalent embodiment of equivalent variations.Therefore, it is every without departing from
The content of technical solution of the present invention, according to the technical essence of the invention any simple modification made to the above embodiment, equivalent
Variation and modification, still fall within technical solution of the present invention protection in the range of.
Claims (10)
1. a kind of gradient amplifier, which is characterized in that be applied to magnetic resonance imaging device, for being magnetic resonance imaging device
In gradient coil provide electric current, including：Rectifier, H bridges, filter circuit and control circuit；
The rectifier connects AC power, and the AC rectification for providing AC power is direct current；
The input terminal of the H bridges connects the output end of the rectifier, and the output end of the H bridges connects the filter circuit；
The filter circuit, for filtering out the harmonic wave in the H bridges output current；Described in the output end connection of the filter circuit
Gradient coil；
The filter circuit includes concatenated filter inductance and variable filtering impedance；
The control circuit, for when gradient coil is greater than or equal to gradient coil saturation current reference value to constant current, increasing
The impedance value of the big variable filtering impedance.
2. gradient amplifier according to claim 1, which is characterized in that the variable filtering impedance includes at least following two
A parallel branch：The first branch and the second branch；
The first branch includes the first filter capacitor；
The second branch includes concatenated first impedance and switch；
First impedance include at least it is following in one kind：Capacitance and inductance；
The control circuit, for passing through when gradient coil is greater than or equal to gradient coil saturation current reference value to constant current
It is closed the impedance value that the switch increases the variable filtering impedance.
3. gradient amplifier according to claim 2, which is characterized in that when first impedance includes the first capacitance,
The second branch includes concatenated first capacitance and the switch.
4. gradient amplifier according to claim 2, which is characterized in that when first impedance includes the first inductance,
The second branch includes concatenated first inductance and the switch.
5. gradient amplifier according to claim 2, which is characterized in that when first impedance includes the second inductance and the
When two capacitances, the second branch includes concatenated second inductance, the second capacitance and the switch.
6. gradient amplifier according to claim 2, which is characterized in that the variable filtering impedance further includes third branch
Road；
The third branch includes concatenated second impedance and switch；
Second impedance include at least it is following in one kind：Capacitance and inductive resistance；
The control circuit, for passing through when gradient coil is greater than or equal to gradient coil saturation current reference value to constant current
It is closed the impedance value that the switch increases the variable filtering impedance.
7. according to claim 2-6 any one of them gradient amplifiers, which is characterized in that the control circuit includes：Compare
Device and driving circuit；
The first input end of the comparator connects the gradient coil to constant current, and the second output terminal of the comparator connects
The output end of the filter inductance saturation current reference value, the comparator connects the driving circuit；
The driving circuit, for determining that the gradient coil is full more than or equal to filter inductance to constant current in the comparator
The switch is driven to be closed when with current reference value.
8. gradient amplifier according to claim 7, which is characterized in that the comparator is digital comparator or simulation ratio
Compared with device.
9. according to claim 1-6 any one of them gradient amplifiers, which is characterized in that the control circuit further includes：Control
Device processed；
The controller, for receiving the gradient coil of magnetic resonance imaging device control computer transmission to constant current,
And be compared the gradient coil with gradient coil current value to constant current, it is adjusted to the H bridges according to comparison result
Drive pulse signal.
10. a kind of magnetic resonance imaging device, which is characterized in that including claim 1-9 any one of them gradient amplifiers,
Further include：Gradient coil；
The gradient amplifier, for providing electric current for gradient coil.
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| CN110441721A (en) * | 2019-09-06 | 2019-11-12 | 上海联影医疗科技有限公司 | Feed-through filter and magnetic resonance system applied to magnetic resonance system |
| CN110784099A (en) * | 2019-11-05 | 2020-02-11 | 上海联影医疗科技有限公司 | Gradient power amplifier, control method thereof, and computer-readable storage medium |
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| CN108418406B (en) | 2019-08-13 |
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