Magnetic resonance method and apparatus wherein signal contributions outside of the measurement region are reduced

Patent metadata

Field	Value
Publication number	US-9726743-B2
Application number	US-201414173176-A
Country	US
Kind code	B2
Filing date	Feb 5, 2014
Priority date	Feb 5, 2013
Publication date	Aug 8, 2017
Grant date	Aug 8, 2017

Abstract

In magnetic resonance imaging using a measurement sequence of the “free precession of transverse magnetization in the steady state”-type i.e., an SSFP measurement sequence, during the SSFP measurement sequence, the implementation of a preparation sequence takes place to reduce a signal contribution of the transverse magnetization in an outer region surrounding a measurement region in the MR imaging. The implementation of the preparation sequence includes the radiation of a multidimensional, spatially selective RF pulse that acts in a spatially selective manner on the transverse magnetization in the outer region. Saturation of the transverse magnetization and/or dephasing of the transverse magnetization in the outer region can be achieved by the multidimensional, spatially selective RF pulse.

First claim

I claim as my invention:

1. A method for acquiring magnetic resonance (MR) data from a subject, comprising:
operating an MR data acquisition unit, with an examination subject situated therein, to implement a “free precession of transverse magnetization in the steady state”-type (SSFP) data acquisition sequence;
in said SSFP data acquisition sequence, operating a radio-frequency (RF) radiator to radiate RF pulses that produce a transverse magnetization of nuclear spins in a measurement region of the examination subject and in an outer region of the examination subject that surrounds and adjoins said measurement region, said nuclear spins then emitting an MR signal;
also in said SSFP data acquisition sequence, operating said MR data acquisition unit to execute a preparation sequence that reduces a signal contribution, to said MR signal, of nuclear spins having said transverse magnetization in said outer region, by radiating, via said RF radiator, a multidimensional, spatially selective RF pulse that by itself spatially selectively acts in at least two dimensions on said transverse magnetization of said nuclear spins in said outer region; and
operating an RF detector of said MR data acquisition unit, in said SSFP data acquisition sequence, to detect said MR signals and to enter the detected MR signals into an electronic memory, organized as k-space, to produce an electronically accessible data file in said electronic memory.

2. A method as claimed in claim 1 comprising operating said MR data acquisition unit for saturate the transverse magnetization of said nuclear spins in said outer region by radiating said multidimensional, spatially selective RF pulse.

3. A method as claimed in claim 1 comprising operating said MR data acquisition unit to phase-incoherently excite said transverse magnetization of said nuclear spins in said outer region by radiating said multidimensional, spatially selective RF pulse.

4. A method as claimed in claim 1 comprising operating said MR data acquisition unit to dephase said transverse magnetization of said nuclear spins in said outer region by radiating said multidimensional, spatially selective RF pulse.

5. A method as claimed in claim 1 comprising operating said MR data acquisition unit to apply a gradient field, with a gradient system of said MR data acquisition unit, which dephases said transverse magnetization of said nuclear spins in said outer region.

6. A method as claimed in claim 1 comprising operating said MR data acquisition unit in said operation sequence to make said multidimensional, spatially selective RF pulse spatially selective by amplitude modulation of said multidimensional, spatially selective RF pulse by activating a spatially selective gradient field, during radiation of said multidimensional, spatially selective RF pulse, with a gradient system of said MR data acquisition unit.

7. A method as claimed in claim 1 wherein said RF radiator comprises a plurality of RF coils, and comprising operating said MR data acquisition unit to make said multidimensional, spatially selective RF pulse spatially selective by radiating chronologically overlapping RF energy from multiple RF coils, among said plurality of RF coils.

8. A method as claimed in claim 1 , comprising:
operating said MR data acquisition unit to radiate, at a beginning of said preparation sequence, an RF pulse that aligns said nuclear spins along a longitudinal direction of said MR data acquisition unit; and
operate said MR data acquisition unit to radiate, at an end of said preparation sequence, a further RF pulse that aligns said transverse magnetization of said nuclear spins in a transverse plane that is orthogonal to said longitudinal direction.

9. A method as claimed in claim 8 , comprising:
operating said MR data acquisition unit, in said SSFP data acquisition sequence, to radiate excitation RF pulses that are alternating positive and negative a pulses;
operating said MR data acquisition unit to radiate said RF pulse at said beginning of said preparation sequence as a positive α/2 pulse; and
operating said MR data acquisition unit to radiate said RF pulse at said end of said preparation sequence as a positive α/2 pulse.

10. A method as claimed in claim 8 , comprising:
repeating radiation of said RF excitation pulses in said SSFP data acquisition sequence with a defined repetition time;
operating said MR data acquisition unit to radiate said RF pulse at said beginning of said preparation sequence at a time interval, following a selected RF excitation pulse of said SSFP data acquisition sequence, that is half of said repetition time; and
operating said MR data acquisition unit to radiate said RF pulse at said end of said preparation sequence at a time interval following a different selected RF excitation pulse of said SSFP data acquisition sequence, which is half of said repetition time.

11. A method as claimed in claim 1 comprising:
operating said MR data acquisition unit, in said SSFP data acquisition sequence, to detect said MR signals from each of said measurement region and said outer region;
operating said MR data acquisition unit in said preparation sequence to also detect MR signals from the transverse magnetization of said nuclear spins said outer region;
in a processor, automatically calculating a signal contribution of said transverse magnetization of the nuclear spins in said outer region to said MR signals detected in said SSFP data acquisition unit sequence, based on said MR signals detected from said transverse magnetization of said nuclear spins in said outer region in said preparation sequence; and
in said processor, correcting said MR signals detected in said SSFP data acquisition sequence by removal therefrom of the calculated signal contribution of the transverse magnetization of the nuclear spins in said outer region.

12. A method as claimed in claim 11 comprising operating said MR data acquisition unit to detect said MR signal from said transverse magnetization of said nuclear spins in said outer region in said preparation sequence, and calculating said signal contribution thereof, using an MR fingerprinting technique.

13. A method as claimed in claim 11 , comprising:
operating said MR data acquisition unit to execute said preparation sequence multiple times;
operating said MR data acquisition unit, in successive repetitions of said preparation sequence, with at least one MR parameter of said MR data acquisition unit being different in the respective successive repetitions; and
selecting said at least one MR parameter from the group consisting of a time between said successively repeated preparation sequences, a flip angle of said multidimensional, spatially selective RF pulse, an echo time for detection of said MR signal in the preparation sequence, phase coding produced by a gradient field activated by a gradient system of said MR data acquisition unit in said SSFP data acquisition sequence, a phase of said multidimensional, spatially selective RF pulse, an amplitude of said multidimensional, spatially selective RF pulse, a number of gradient fields applied by a gradient system of said MR data acquisition unit during said SSFP data acquisition sequence, and a type of spatially selective gradient fields applied by a gradient coil system of said MR data acquisition unit in said SSFP data acquisition sequence.

14. A method as claimed in claim 11 , comprising:
calculating said signal contribution of the transverse magnetization of nuclear spins in said outer region by comparing a time curve of said MR signals detected in said preparation sequence for said transverse magnetization of said

Assignees

• Fautz Hans-Peter
• Siemens Ag

Inventors

• Fautz Hans-Peter

Classifications

• G01R33/561 Primary

  by reduction of the scanning time, i.e. fast acquiring systems, e.g. using echo-planar pulse sequences · CPC title

• G01R33/5613

  Generating steady state signals, e.g. low flip angle sequences [FLASH] · CPC title

• G01R33/4838 Primary

  using spatially selective suppression or saturation of MR signals · CPC title

• G01R33/4836

  using an RF pulse being spatially selective in more than one spatial dimension, e.g. a 2D pencil-beam excitation pulse · CPC title