Magnetic reasonance tomography apparatus and method in the form of a pulse sequence for operating same

• US 6,310,478 B1
• Filed: 01/18/2000
• Issued: 10/30/2001
• Est. Priority Date: 01/18/1999
• Status: Active Grant

• Current Assignee: Siemens AG
• Original Assignee: Siemens AG
• Inventors: Heid, Oliver
• Primary Examiner(s): Arana, Louis
• Assistant Examiner(s): Shrivastav, Brij B.
• Application Number:
  US09/484,557
• Time in Patent Office: 651 Days
• Field of Search: 324/309, 324/307, 324/312, 324/314, 324/322
• US Class Current: 324/309
• CPC Class Codes: G01R 33/5613 Generating steady state signals, e.g. low flip angle sequences [FLASH]

Abstract

In a method in the form of a pulse sequence for ultra-rapid nuclear magnetic resonance tomography and a magnetic resonance tomography apparatus operating according to the method, image data are obtained in a pulse sequence wherein the magnetization vector oscillates by an angle ±α in the steady stage, with a being smaller then 90°. This is the case, for example, given a SSFP sequence. RF pulse train composed of a number of RF pulses is respectively emitted during one-half of a readout gradient. A bipolar readout gradient pulse train can be employed, with an RF pulse train being emitted during a negative half of the readout gradient pulse train.

Claims

1. A method for rapidly obtaining image data in magnetic resonance tomography comprising the steps of:

subjecting an examination subject to a pulse sequence which causes a nuclear magnetization vector within said examination subject to oscillate between angles ±

α

in a steady state, wherein α

is less than 90°

;

in said pulse sequence, emitting a bipolar readout gradient, including a positive half and a negative half, and reading out nuclear magnetic resonance signals from said examination subject during said bipolar readout gradient; and

in said pulse sequence, emitting at least one RF excitation pulse during each negative half of said bipolar readout gradient.

2. A method as claimed in claim 1 comprising emitting a plurality of RF excitation pulses during each negative half of said bipolar readout gradient.

3. A method as claimed in claim 1 comprising amplitude modulating said at least one RF excitation pulse.

4. A method as claimed in claim 1 comprising phase modulating said at least one RF excitation pulse.

5. A method as claimed in claim 1 comprising amplitude modulating and phase modulating said at least one RF excitation pulse.

6. A method as claimed in claim 1 comprising emitting a plurality of switched gradients in said pulse sequence with gradient switching of said plurality of gradients being completely rephasing in all spatial directions between each emission of said at least one RF excitation pulse.

7. A method as claimed in claim 1 comprising, during each negative half of said bipolar readout gradient, emitting a first RF excitation pulse train comprised of a plurality of RF pulses and emitting a second RF excitation pulse train comprised of a plurality of RF pulses, said first RF excitation pulse train causing magnetization in a z-direction of an x, y, z coordinate system, arising from a preceding RF excitation pulse train, to be deflected into an x, y plane, and said second RF excitation pulse train rotating said magnetization back into said z-direction.

8. A magnetic resonance tomography apparatus comprising:

a scanner having an RF coil and at least one gradient coil for subjecting an examination subject to a pulse sequence which causes a nuclear magnetization vector within said examination subject to oscillate between angles ±

α

in a steady state, wherein α

is less than 90°

;

a controller connected to said at least one gradient coil for producing, in said pulse sequence, a bipolar readout gradient, including a positive half and a negative half, for reading out nuclear magnetic resonance signals from said examination subject during said bipolar readout gradient; and

said controller being connected to said RF coil for producing, in said pulse sequence, emitting at least one RF excitation pulse during each negative half of said bipolar readout gradient.

9. A magnetic resonance tomography apparatus as claimed in claim 8 wherein said controller caused said RF coil to emit a plurality of RF excitation pulses during each negative half of said bipolar readout gradient.

10. A magnetic resonance tomography apparatus as claimed in claim 8 comprising means for amplitude modulating said at least one RF excitation pulse.

11. A magnetic resonance tomography apparatus as claimed in claim 8 comprising means for phase modulating said at least one RF excitation pulse.

12. A magnetic resonance tomography apparatus as claimed in claim 8 comprising means for amplitude modulating and phase modulating said at least one RF excitation pulse.

13. A magnetic resonance tomography apparatus as claimed in claim 8 wherein said controller causes said at least one gradient coil to emit a plurality of switched gradients in said pulse sequence with gradient switching of said plurality of gradients being completely rephasing in all spatial directions between each emission of said at least one RF excitation pulse.

14. A magnetic resonance tomography apparatus as claimed in claim 8 wherein said controller caused said RF coil, during each negative half of said bipolar readout gradient, to emit a first RF excitation pulse train comprised of a plurality of RF pulses and to emit a second RF excitation pulse train comprised of a plurality of RF pulses, said first RF excitation pulse train causing magnetization in a z-direction of an x, y, z coordinate system, arising from a preceding RF excitation pulse train, to be deflected into an x, y plane, and said second RF excitation pulse train rotating said magnetization back into said z-direction.