Magnetic resonance apparatus with a coil system optimized for noise reduction and method for designing the coil system

• US 6,618,611 B2
• Filed: 03/05/2001
• Issued: 09/09/2003
• Est. Priority Date: 03/07/2000
• Status: Active Grant

• Current Assignee: Siemens Healthcare GMBH (Siemens AG)
• Original Assignee: Siemens AG
• Inventors: Gebhardt, Matthias
• Primary Examiner(s): Van, Quang T.
• Application Number:
  US09/799,262
• Publication Number:
  US 20010027264A1
• Time in Patent Office: 918 Days
• Field of Search: 600/422, 600/421, 600/425, 324/318, 324/319, 324/322, 324/307, 324/309
• US Class Current: 600/422
• CPC Class Codes: G01R 33/3854 means for active and/or passive vibration damping or acoustical noise suppression in gradient magnet coil systems

Abstract

A magnetic resonance apparatus has a basic field magnet system for generating a basic magnetic field and a coil system with a coil arrangement, wherein a course of a current-carrying conductor of the coil arrangement for generating a predetermined target magnetic field is determined according to a method that allows for linear secondary conditions. A noise-causing mechanical oscillation of the coil system as a result of Lorentz forces that act on the current-carrying conductor in the basic magnetic field is thereby taken into consideration by one of the linear secondary conditions, and the course of the conductor is additionally determined by the method so that the noise-causing oscillation is diminished.

Claims

1. A magnetic resonance apparatus comprising:

a basic field magnet system for generating a basic magnetic field;

a coil system having a coil arrangement with at least one current-carrying conductor said coil system being subject to mechanical oscillations resulting from Lorentz forces acting on said current-carrying conductor in said basic magnetic field; and

said at least one current-carrying conductor following a path for simultaneously generating a predetermined target magnetic field and for reducing at least one of said mechanical oscillations which is a mechanical oscillation which contributes to said noise.

2. A magnetic resonance apparatus as claimed in claim 1 wherein said coil system has a natural resonant mode which is one of said mechanical oscillations, and wherein said at least one current-carrying conductor has a path for simultaneously generating said predetermined target magnetic field and for reducing excitation of said natural resonant mode.

3. A magnetic resonance apparatus as claimed in claim 1 wherein said coil system is a hollow-cylindrical coil system, and wherein said at least current-carrying conductor has a path for simultaneously generating said predetermined target magnetic field and for reducing one of said mechanical oscillations having a component directed radially relative to a principal axis of said hollow-cylindrical coil system.

4. A method for designing a gradient coil system for a magnetic resonance apparatus, said magnetic resonance apparatus having a basic field magnet system for generating a basic magnetic field and said coil system having a coil arrangement with a layer in which a current-carrying conductor, following a path in said layer, is disposed, and wherein said coil system is subject to mechanical oscillations resulting from Lorentz forces acting on said current-carrying conductor in said basic magnetic field, said method comprising the steps of:

determining said path of said current-carrying conductor in said layer for generating a predetermined target magnetic field using a calculation procedure which encompasses linear secondary conditions;

identifying at least one of said mechanical oscillations which is a noise-causing mechanical oscillation and representing said noise-causing mechanical oscillation as one of said linear secondary conditions which is encompassed in said calculation procedure; and

determining said path of said current-carrying conductor in said layer using said calculation procedure to simultaneously generate said predetermined target magnetic field and to reduce said noise-causing mechanical oscillation.

5. A method as claimed in claim 4 comprising employing a quadratic optimization procedure as said calculation procedure, containing a quadratic target function.

6. A method as claimed in claim 5 wherein said calculation procedure comprises the steps of:

dividing said layer of said coil arrangement into a network of meshes;

occupying each mesh in said network with an elementary coil formed by a closed winding carrying a mesh current;

identifying a magnetic field contribution to said target magnetic field generated by each mesh current, said quadratic target function comprising said mesh currents in said network, the respective magnetic field contributions of said mesh currents, and said target magnetic field;

minimizing said quadratic target function relative to said target magnetic field; and

determining said path of said current-carrying conductor dependent on the mesh currents which minimize said quadratic target function.

7. A method as claimed in claim 6 wherein said noise-causing mechanical oscillation is a natural resonant mode of said coil system, and wherein said method further comprises the steps of:

for each mesh, identifying a location dependency relative to one of said meshes subjected to said natural resonant mode;

for each mesh, identifying a Lorentz force acting on one of said meshes;

for each mesh, forming a scalar product of said location dependency and said Lorentz force;

summing the respective scalar products for all of said meshes to form a summation result; and

forming said one of said linear secondary conditions by setting said summation result to be less than a predetermined value.

8. A method as claimed in claim 7 wherein the step of determining the Lorentz force for each of said meshes comprises identifying mesh currents of neighboring meshes and values of said basic magnetic field for each of said neighboring meshes, and calculating said Lorentz force from said mesh currents of said neighboring meshes and said values of said basic magnetic field in said neighboring meshes.

9. A method as claimed in claim 7 wherein the step of determining the Lorentz force in each of said meshes includes identifying an edge length of each of said meshes, and employing said edge length for calculating said Lorentz force.