Imaging technique and magnetic resonance tomograph

• US 20020022778A1
• Filed: 06/27/2001
• Published: 02/21/2002
• Est. Priority Date: 12/24/1999
• Status: Abandoned Application

• Current Assignee: Nadim Joni Shah, Stefan Wiese
• Original Assignee: Nadim Joni Shah, Stefan Wiese
• Inventors: Shah, Nadim Joni, Wiese, Stefan
• Application Number:
  US09/742,842
• Publication Number:
  US 20020022778A1
• Time in Patent Office: Days
• US Class Current: 600/410
• CPC Class Codes: G01R 33/4828 Resolving the MR signals of different chemical species, e.g. water-fat imaging
• CPC Class Codes: G01R 33/5615 Echo train techniques involving acquiring plural, differently encoded, echo signals after one RF excitation, e.g. using gradient refocusing in echo planar imaging [EPI], RF refocusing in rapid acquisition with relaxation enhancement [RARE] or using both RF and gradient refocusing in gradient and spin echo imaging [GRASE]
• CPC Class Codes: G01R 33/5617 using RF refocusing, e.g. RARE

Abstract

The invention relates to a method to operate a nuclear resonance tomograph involving the suppression of image artifacts that are brought about by interfering nuclear spins, a transverse magnetization being generated in a volume of interest by applying a slice-selective HF excitation pulse to nuclear spins in the presence of a first magnetic field gradient and a polarizing magnetic field, and a spin echo being subsequently generated by means of at least a second slice-selective HF pulse in conjunction with a magnetic field gradient.

The method is carried out according to the invention in such a way that, outside of at least one target volume to be examined, the transversal magnetization after the application of the HF excitation pulse is disturbed by at least one additional magnetic field gradient.

Claims

1. An imaging method in which high-frequency pulses are emitted and at least one magnetic gradient field is applied in order to select at least one slice or volume of interest in which a nuclear magnetic resonance is excited and a measuring signal is ascertained, characterized in that a time sequence of the measuring signal is detected as the relaxation signal and in that at least one image signal is encoded during the detection of the relaxation signal.

2. The method of claim 1, characterized in that the gradient fields are selected during a spatial encoding in such a manner that at least one time derivative of at least one k vector in a k space is essentially constant.

3. The method of one or both of claims 1 and 2, characterized in that, during a spatial encoding, one gradient field is kept essentially constant.

4. The method of claim 3, characterized in that, during a spatial encoding, all of the gradient fields are kept essentially constant.

5. The method of one or both of claims 1 and 2, characterized in that at least one gradient field is varied over the course of time and in that detection intervals occurring at different times have lengths that differ from each other.

6. The method of claim 5, characterized in that the detection intervals are selected in such a way that they fulfill the condition k_maxΔ

x<

π

.

7. The method of one or more of claims 1 through 6, characterized in that a dephasing of the signal takes place outside of a volume of interest.

8. The method of claim 7, characterized in that the dephasing is carried out with essentially orthogonal gradients.

9. The method of one or more of claims 1 through 8, characterized in that a multiple spin-echo signal is generated in a volume of interest.

10. The method of claim 9, characterized in that a double spin echo is generated in a volume of interest.

11. The method of one or more of claims 1 through 10, characterized in that at least one signal excitation is read out by means of spatial-spectral encoding.

12. The method of claim 11, characterized in that the spatial-spectral encoding is performed in such a way that a defined (k_x, t) area is acquired in a (k, t) diagram for an excitation.

13. The method of claim 12, characterized in that, in the (k, t) diagram, a (k_x, t) slice is acquired for the excitation.

14. The method of claim 13, characterized in that the (k_x, t) slice is excited by a phaseencoding gradient in the k_y direction.

15. The method of claim 14, characterized in that the (k_x, t) slice is selected immediately after the excitation by the phase-encoding gradient in the k_y direction.

16. The method of one or more of claims 1 through 15, characterized in that a PRESS sequence with a 90°

pulse, an 180°

pulse and another 180°

pulse is employed.

17. A magnetic resonance tomograph with a means to emit high-frequency pulses, a means to apply at least one magnetic gradient field and a means to detect a measuring signal, characterized in that the magnetic resonance tomograph has a means to detect a measuring signal as the relaxation signal and a means to encode at least one image signal, whereby the encoding means is designed in such a way that it encodes the image signal during the detection of the relaxation signal.