CN1899216A

CN1899216A - Radio frequency transmitting coil for vertical field magnetic resonant imaging system

Info

Publication number: CN1899216A
Application number: CN 200510084052
Authority: CN
Inventors: 包尚联; 张宏杰
Original assignee: HAISIWEI SCIENCE AND TECHNOLOGY Co Ltd BEIJING
Current assignee: HAISIWEI SCIENCE AND TECHNOLOGY Co Ltd BEIJING
Priority date: 2005-07-18
Filing date: 2005-07-18
Publication date: 2007-01-24
Anticipated expiration: 2025-07-18
Also published as: CN1899216B

Abstract

The RF transmitting coil for vertical field magnetic resonant imaging system includes two parallel trapezoidal coils set separately near two pole plates of the magnet and two capacitors with the same capacitance. Each of the trapezoidal coils includes two bevel sides of conductor and two connecting crosspieces, and the capacitor may be set in the crosspiece or the bevel side. By means of regulating the inductance or the capacitance, required resonant mode may be reached. The present invention has regular coil structure, precise mutual inductance calculation and high coil efficiency.

Description

Radio frequency transmitting coil for vertical field magnetic resonant imaging system

Technical field

The present invention relates to a kind of MR imaging apparatus, particularly about a kind of magnetic resonance imaging radiofrequency coil.

Background technology

Nuclear magnetic resonance (MRI) utilizes the space encoding technology to realize, is the NMR signal that reflects object inner material space-time is realized visual technology.Human body is placed in the stable magnetic field, add a gradient magnetic then, suitable radio frequency (RF) field action of reuse is in by the imaging human body, the electromagnetic wave that has carried human body information after detection and human body interact just can show anatomy, physiology and the psychologic information of interior of articles, mode with image shows, is used for body science's research and people's disease treatment.

The effect of radio-frequency coil in the MRI system is the RF electromagnetic field that is used for producing the excitation object to be imaged (hereinafter to be referred as sample), and receives sample magnetic resonance signal emission, that carry the sample customizing messages.Therefore, the RF coil has and transmits and receives two kinds of functions.For fear of not only doing transmitting coil but also do the interference that receiving coil causes, usually independent in the modern MRI system transmitting coil and receiving coil, middlely the RF signal that transmits and receives is separated by an isolating switch.Therefore, radio-frequency coil can be divided into transmitting coil and receiving coil.

The structure that produces the magnet of main field in the MRI system mainly is divided into superconducting magnet that produces the horizontal direction field and the permanent magnet that produces the vertical direction field at present.Main field is in the MRI system of vertical direction, and main transmitting coil commonly used is plate coil, places a plurality of conductor groups in the position near pole plate exactly, realizes the RF field perpendicular to main field.

Relevant patent comprises United States Patent (USP) 5467017, Chinese patent application number 02156429.9, Chinese patent application number 00120084.4.The shortcoming of their structures is: the CURRENT DISTRIBUTION that need regulate each coil groups respectively is to reach the required RF field perpendicular to main field; Also need simultaneously each coil groups is carried out frequency adjustment; The 3rd states on the implementation that coil groups can influence each other when regulating; If the 4th solves the loop problem of electric current with screen layer, can cause the efficient of coil to reduce.

Summary of the invention

At the problems referred to above, the plane radio-frequency sending coil that the MRI system that to the purpose of this invention is to provide a kind of suitable main field be vertical magnetic field uses, its electric current with structure rule distribute, uniformity on the scene, there is bigger advantage tuning and efficient aspect.

For achieving the above object, the present invention takes following technical scheme: a kind of MRI RF transmitting coil, its feature comprises: the trapezium structure unit that plain conductor and electric capacity are formed, as shown in Figure 1, two parallel parts are called the limit up and down, a plurality of structures following in the connection are called crosspiece (generally greater than 4), and the equivalent capacitance element can be by the form arrangement of Fig. 1.

To structure shown in Figure 1 utilization Kirchhoff theorem, the structure that can calculate grid number and be N has N frequency (pattern), and the expression formula of frequency is:

ω=[C (L _Crosspiece+ L _{The limit}/ 2sin ²(n _Modeπ/N))] ^-1/2

Wherein ω is an angular frequency, and C is a capacitance, L _CrosspieceSelf-induction for trapezium structure unit crosspiece.L _{The limit}For the limit by the self-induction of sections that crosspiece is cut apart, N is the unitary grid number of trapezium structure, n _ModeBe N pattern.

Use the Biot-Savart theorem, can prove, pattern 1 has radio-frequency field as shown in Figure 2.

In order to produce uniform radio-frequency (RF) magnetic field, as shown in Figure 3, the bottom crown installing structure is identical on magnet, and signal phase differs the above-mentioned trapezium structure unit of 180 degree, forms transmitting winding group, just can produce the uniform radio-frequency (RF) magnetic field perpendicular to main field between pole plate.Can also turn 90 degrees by the coil groups of above-mentioned phase phase difference 180 degree is revolved around two pole plate lines of centres of main magnet, form another transmitting winding group, two coil groups are combined, form crossed coil, between pole plate, form the radio-frequency field of omnidirectional distribution, make the emission effciency of radio frequency improve 1.4 times.

The present invention is owing to take above design, it has the following advantages: 1, this trapezium structure unit is under pattern 1 situation, and electric current exists with the form of a standing wave in the limit, so each crosspiece electric current is to the standing wave current sample, be the Sine distribution of rule, do not need to regulate respectively; 2, the electric capacity of composition coil is identical with inductance value, so the coil resonates frequency is tuning simple and convenient; 3, owing to the loop construction rule, mutual inductance is calculated more accurate, can better solve the interstructural problem that influences each other; 4, self current loop does not need to solve the current loop problem by screen layer, so the corresponding raising of the efficient of coil.

Description of drawings

Fig. 1 is a trapezium structure sketch map used in the present invention

Structure shown in Fig. 2 Fig. 1 produces the sketch map of radio-frequency (RF) magnetic field

Fig. 3 is a radio frequency coil sketch map of the present invention

Fig. 4 is the unitary second kind of form sketch map of trapezium structure used in the present invention

Fig. 5 is unitary the third form sketch map of trapezium structure used in the present invention

The specific embodiment

As shown in Figure 3, the present invention includes as shown in Figure 1 construction unit 1, construction unit 2, coaxial cable 3 and 4, power splitter 5 and radio frequency amplifier 6.Construction unit 1 and 2, electric capacity are spacedly distributed substantially on two limits, and six crosspieces substantially evenly are connected on two limits, and coaxial cable 3 and 4 is connected to power splitter 5 to trapezium structure by Capacitance Coupled, and power splitter is connected to radio frequency amplification apparatus by cable 6.

In order to improve the efficient of radio-frequency transmissions, can also turn 90 degrees by coil groups shown in Figure 3 is revolved around two pole plate lines of centres, form another coil groups, two coil groups are combined, between pole plate, form the radio-frequency field of omnidirectional distribution, make the emission effciency of radio frequency improve 1.4 times.

Trapezium structure unit further of the present invention is a form as shown in Figure 4 and Figure 5.Wherein,, can replace with several polyphone electric capacity of equivalence in order to increase the uniformity of radio-frequency field for the electric capacity in Fig. 4 and Fig. 5 crosspiece.

Trapezium structure of the present invention unit crosspiece can be optimized to other quantity as required generally greater than 4.

In sum, radio-frequency coil of the present invention is to be fit to the plane radio-frequency sending coil that vertical magnetic field uses, and its electric current is regular distribution with structure, and there is bigger advantage uniformity on the scene, tuning and efficient aspect.

Claims

1, a kind of radio-frequency sending coil that is used for the vertical magnetic field magnetic resonance imaging system is characterized in that it comprises:

By applying the trapezium structure of electric current generation perpendicular to the radio-frequency field of main field, trapezium structure comprises two limits that are made of a conductor, and a plurality of crosspieces that connect two limits, equivalent electric capacity can be distributed on the crosspiece, also can be distributed on two positions between the top rail of limit, regulate conductor inductance and electric capacity like this and can reach the resonance mode corresponding with the trapezium structure grid number, wherein the CURRENT DISTRIBUTION of pattern 1 correspondence can form more uniformly perpendicular to the planar radio-frequency field in trapezium structure place.

2, trapezium structure as claimed in claim 1, it is characterized in that: by the trapezium structure that two substantially parallel current phases differ 180 degree is set near two magnetic pole strengths that produce vertical magnetic field, form radio frequency coil, so just can between magnet pole, produce radio-frequency (RF) magnetic field zone uniformly.

3, magnetic resonance imaging radiofrequency coil group as claimed in claim 2, it is characterized in that: can also turn 90 degrees by coil groups is revolved around two pole plate lines of centres, form another coil groups, two coil groups are combined, between pole plate, form the radio-frequency field of omnidirectional distribution, make the emission effciency of radio frequency improve 1.4 times.

4, as claim 1 or 2 or 3 described magnetic resonance imaging radiofrequency coil, it is characterized in that: the electric capacity that is positioned at crosspiece can distribute by equivalent polyphone, makes that the field is more even.