MRI probe for external imaging

• US 5,572,132 A
• Filed: 08/15/1995
• Issued: 11/05/1996
• Est. Priority Date: 08/15/1995
• Status: Expired due to Term

• Current Assignee: Brigham and Women's Hospital Incorporated
• Original Assignee: Brigham and Women's Hospital Incorporated
• Inventors: Patz, Samuel, Pulyer, Yuly M.
• Primary Examiner(s): TOKAR, MICHAEL J
• Application Number:
  US08/515,483
• Time in Patent Office: 448 Days
• Field of Search: 324/300, 324/307, 324/309, 324/310, 324/311, 324/312, 324/313, 324/314, 324/318, 324/319, 324/320, 324/322, 128/653.1, 128/653.2, 128/653.3
• US Class Current: 324/318
• CPC Class Codes: G01R 33/34061 Helmholtz coils
• CPC Class Codes: G01R 33/34069 Saddle coils
• CPC Class Codes: G01R 33/3678 involving quadrature drive or detection, e.g. a circularly polarized RF magnetic field
• CPC Class Codes: G01R 33/3808 Magnet assemblies for single-sided MR wherein the magnet assembly is located on one side of a subject only; Magnet assemblies for inside-out MR, e.g. for MR in a borehole or in a blood vessel, or magnet assemblies for fringe-field MR
• CPC Class Codes: G01R 33/383 using permanent magnets
• CPC Class Codes: G01R 33/385 using gradient magnetic field coils

Abstract

A magnetic resonance imaging (MRI) probe having an external background magnetic field B_o is described. The probe has a primary magnet having a longitudinal axis and an external surface extending in the axial direction and a rf coil surrounding and proximal to the surface. The magnet provides a B_o field having an external region of substantial homogeneity proximal to the surface. Preferably, the B_o field is provided by two magnets spaced axially and in axial alignment and wherein said region of homogeneity intersects a plane located between the magnets and perpendicular to the axis. For MR imaging, surrounding the primary magnet are r-, z- and .o slashed.-gradient coils to provide spatial encoding fields.

Claims

1. A magnetic resonance imaging (MRI) probe having an external background magnetic field B_o, said probe comprising:

a primary magnet having a longitudinal axis and an external surface extending in the axial direction, and

a rf coil surrounding and proximal to said surface,

wherein the B_o field provides an imaging volume having a region of substantial homogeneity of axial directed field component along said surface and proximal to said surface.

2. The MRI probe of claim 1 wherein said primary magnet is a permanent magnet.

3. The MRI probe of claim 1 wherein said primary magnet has soft ferromagnetic end caps.

4. The MRI probe of claim 2 wherein said primary magnet has soft ferromagnetic end caps.

5. The MRI probe of claim 1 wherein said B_o field is provided by two magnets spaced axially and in axial alignment, the magnetic moment vector of each magnet being oriented in the same direction.

6. The MRI probe of claim 1 wherein said primary magnet is a cylindrical permanent magnet and surrounding said primary magnet are r-, z- and .o slashed.-gradient coils.

7. The MRI probe of claim 1 wherein said rf receiver coil also provides an excitation pulse to excite nuclei in an imaging region.

8. The MRI probe of claim 1 wherein said rf coil comprises a quadrature (two phase) coil to produce a circularly polarized, synchronous rotation excitation field orthogonal at each angular position to the z-oriented B_o field.

9. An angular gradient coil for use in magnetic resonance imaging in a cylindrical coordinate system having axial (z-), radial (r-) and angular (.o slashed.-) coordinates, said coil comprising two mirror image subcoils on a cylindrical surface, the subcoils being spaced in the z-direction, each subcoil having a plurality of parallel segments of electrical conductors, the length and direction of current in each segment being arranged and constructed to provide a magnetic field B_z component in the direction that varies with angular position .o slashed. in a periodic manner over a selected range of angular position and is constant over z between the mirror image subcoils.

10. A magnetic resonance imaging (MRI) probe having an external background magnetic field B_o, said probe comprising:

a primary magnet having a longitudinal axis and an external surface extending in the axial direction, and

surrounding said primary magnet are r-, z- and .o slashed.-gradient coils;

wherein the B_o field provides an imaging volume having a region of substantial homogeneity of axial directed field component along said surface and proximal to said surface.

11. The MRI probe of claim 10 further comprising a rf coil surrounding and proximal to said surface.

12. The MRI probe of claim 10 wherein said primary magnet is a cylindrical permanent magnet and a rf coil surrounds and is proximal to said surface.