Magnetic resonance using quazi-continuous RF irradiation

Patent metadata

Field	Value
Publication number	US-9547060-B2
Application number	US-201214002549-A
Country	US
Kind code	B2
Filing date	Feb 28, 2012
Priority date	Mar 3, 2011
Publication date	Jan 17, 2017
Grant date	Jan 17, 2017

Abstract

The invention relates to a method of MR imaging of at least a portion of a body ( 110 ) of a patient placed in an examination volume of a MR device, the method comprising the steps of:—subjecting the portion of the body ( 110 ) to an imaging sequence comprising at least one RF pulse, the RF pulse being transmitted toward the portion of the body ( 110 ) via a RF coil arrangement ( 109 ) to which RF signals are supplied by two or more RF power amplifiers the RF power amplifiers being activated alternately during the imaging sequence in a time-multiplexed fashion, wherein the imaging sequence requires a RF duty cycle and/or a RF pulse duration exceeding the specification of at least one of the RF power amplifiers;—acquiring MR signals from the portion of the body ( 110 ); and—reconstructing a MR image from the acquired MR signals. Moreover, the invention relates to a method of MR spectroscopy involving the alternating use of RF power amplifiers in a time-multiplexed fashion.

First claim

The invention claimed is:

1. A method of magnetic resonance (MR) imaging of at least a portion of a body, the method comprising:
subjecting the portion of the body to an imaging sequence comprising at least one radiofrequency (RF) pulse, the RF pulse being transmitted toward the portion of the body via an RF coil arrangement to which RF signals are supplied by two or more RF power amplifiers, the RF power amplifiers being activated alternately during the imaging sequence in a time-multiplexed fashion, wherein the RF power amplifiers associated with different groups of coil elements are activated during non-overlapping or partly overlapping time slots and in the case of a non-overlapping activation of the different RF power amplifiers, an incoherent sum of the RF signals is generated during the different activation periods and in the case of a partly overlapping activation of the individual RF power amplifiers, a coherent superposition of the RF signals is generated and wherein the imaging sequence requires an RF duty cycle and/or an RF pulse duration exceeding a specification of at least one of the RF power amplifiers;
acquiring MR signals from the portion of the body; and
reconstructing an MR image from the acquired MR signals.

2. The method of claim 1 , wherein the at least one RF pulse is generated by alternately activating the RF power amplifiers , wherein the at least one RF pulse is subdivided into sets of RF pulse segments, each set of RF pulse segments being generated by a different RF power amplifier or set of RF power amplifiers.

3. The method of claim 2 , wherein the frequency of the RF pulse is substantially the same for all RF pulse segments.

4. The method of claim 1 , wherein the at least one RF pulse is
a saturation RF pulse for saturating nuclear magnetization, or
a spin locking RF pulse, or
a polarization transfer RF pulse for transferring magnetization between different nuclear spins, or
a proton decoupling RF pulse.

5. The, method of claim 4 , wherein the at least one RF pulse is a frequency-selective saturation RF pulse for saturating nuclear magnetization of protons of an exchangeable endogenous proton pool or of a CEST contrast agent.

6. The method of claim 1 , wherein the RF coil arrangement comprises two or more coil elements each coil element being assigned to a group of coil elements, wherein each group of coil elements is associated with at least one RF power amplifier supplying RF signals to the coil elements of the respective group of coil elements.

7. A magnetic resonance (MR) device configured to perform the method of claim 1 , the MR device comprising:
a main magnet for generating a uniform, steady magnetic field within an examination volume,
at least one RF coil arrangement for generating RF pulses within the examination volume and/or for receiving MR signals from an object positioned in the examination volume,
a transmission unit, which includes two or more RF power amplifiers supplying RF signals to the RF coil arrangement,
a control unit controlling the temporal succession of RF pulses, which control unit is adapted to activate the RF power amplifiers alternately in a time-multiplexed fashion, wherein the RF power amplifiers associated with different groups (I, II) of coil elements are activated during non-overlapping or partly overlapping time slots and in the case of a non-overlapping activation of the different RF power amplifiers, an incoherent sum of the RF signals is generated during the different activation periods and in the case of a partly overlapping activation of the individual RF power amplifiers, a coherent superposition of the RF signals is generated, thereby generating a sequence of RF pulses requiring a RF duty cycle and/or a RF pulse duration exceeding the specification of at least one of the RF power amplifiers.

8. The MR device of claim 7 , wherein the transmission unit comprises attenuators and/or phase shifters operated by the control unit for controlling the amplitudes and/or phases of the RF signals supplied to the RF coil arrangement.

9. The MR device of claim 7 , wherein all RF power amplifiers are high-power/low-duty-cycle amplifiers.

10. The MR device of claim 7 , wherein at least one RF power amplifier is a high-power/low-duty-cycle amplifier while at least one other RF power amplifier is a low-power/high-duty-cycle amplifier.

11. The MR device of claim 7 , wherein all RF power amplifiers are configured to generate the RF signals at substantially the same frequency throughout the sequence of RF pulses.

12. The MR device of claim 7 wherein the control unit is configured to control the amplitudes and/or the phases of the RF signals supplied to the RF coil arrangement via the individual RF power amplifiers in such a manner that the instantaneous and/or the time-integrated homogeneity of the RF magnetic field distribution of the at least one RF pulse is optimized and/or the heat deposition induced by the at least one RF pulse within the portion of the body is minimized.

13. The method of claim 1 , wherein the amplitudes and/or the phases of the RF signals supplied to the RF coil arrangement via the individual RF power amplifiers are controlled in such a manner that the instantaneous and/or the time-integrated homogeneity of the RF magnetic field distribution of the at least one RF pulse is optimized and/or the heat deposition induced by the at least one RF pulse within the portion of the body is minimized.

14. A method of magnetic resonance (MR) spectroscopy of an object, the method comprising the steps of:
subjecting the object to a spectroscopy sequence comprising at least one radiofrequency (RF) pulse, the RF pulse being transmitted toward the object via an RF coil arrangement to which RF signals are supplied by two or more RF power amplifiers , the RF power amplifiers being activated alternately during the spectroscopy sequence in a time-multiplexed fashion, wherein the RF power amplifiers associated with different groups (I, II) of coil elements are activated during non-overlapping or partly overlapping time slots and in the case of a non-overlapping activation of the different RF power amplifiers, an incoherent sum of the RF signals is generated during the different activation periods and in the case of a partly overlapping activation of the individual RF power amplifiers, a coherent superposition of the RF signals is generated, wherein the spectroscopy sequence requires an RF duty cycle and/or an RF pulse duration exceeding a specification of at least one of the RF power amplifiers;
acquiring MR signals from the object; and
deriving an MR spectrum from the acquired MR signals.

15. The method of claim 14 , wherein the at least one RF pulse is generated by alternately activating the RF power amplifiers, wherein the at least one RF pulse is subdivided into sets of RF pulse segments, each set of RF pulse segments being generated by a different RF power amplifier or set of RF power amplifiers.

16. The method of claim 15 , wherein the frequency of the RF pulse is substantially the same for all RF pulse segments.

17. The method of claim 14 , wherein the at least one RF pulse is
a saturation RF pulse for saturating nuclear magnetization, or
a spin locking RF pulse, or
a polarization transfer RF pulse for transferring magnetization between different nuclear spins, or
a proton decoupling RF pulse.

18. The method of claim 17 , wherein the at least one RF pulse is a frequency-selective saturation RF pulse for saturating nuclear magnetization of protons of an exchangeable endogenous proton

Assignees

• Keupp Jochen
• Van Den Brink Johan Samuel
• Harvey Paul Royston
• Koninklijke Philips Nv

Inventors

• Keupp Jochen
• Van Den Brink Johan Samuel
• Harvey Paul Royston

Classifications

• G01R33/5612

  Parallel RF transmission, i.e. RF pulse transmission using a plurality of independent transmission channels · CPC title

• G01R33/54 Primary

  Signal processing systems, e.g. using pulse sequences {; Generation or control of pulse sequences; Operator console} · CPC title

• G01R33/5659

  caused by a distortion of the RF magnetic field, e.g. spatial inhomogeneities of the RF magnetic field (G01R33/56509, G01R33/56518, G01R33/56536 take precedence) · CPC title

• G01R33/5605

  by transferring coherence or polarization from a spin species to another, e.g. creating magnetization transfer contrast [MTC], polarization transfer using nuclear Overhauser enhancement [NOE] · CPC title

• G01R33/34076

  Birdcage coils · CPC title