Method for the magnetic resonance examination of a measurement object and to a radio-frequency unit of a magnetic resonance imaging scanner

Patent metadata

Field	Value
Publication number	US-11061091-B2
Application number	US-201715829085-A
Country	US
Kind code	B2
Filing date	Dec 1, 2017
Priority date	Dec 2, 2016
Publication date	Jul 13, 2021
Grant date	Jul 13, 2021

Abstract

A method for the magnetic resonance examination of a measurement object is described, in which a measurement sequence is used in which the magnetic resonance response to the transmitted signal during transmission is measured. It is provided that a correction signal corresponding to the transmitted signal be generated and be used for correction of the response signal. To this end, the correction signal is modulated by a phase value and an amplitude value. The phase value and the amplitude value are automatically and iteratively customized for optimum correction of the response signal by an optimization method using a respective present state value of the measurement signal. Further, a radio-frequency unit (1) is described that can be used to carry out the method according to the invention.

First claim

The invention claimed is:

1. A method for the magnetic resonance examination of a measurement object, comprising:
radiating a transmitted signal into the measurement object,
picking up a response signal emitted by the measurement object in reaction to the transmitted signal, the response signal being at least intermittently picked up during a period of radiation of the transmitted signal,
generating a measurement signal by correction of the response signal and reconstructing a piece of information about the measurement object from the measurement signal,
generating a correction signal corresponding to the transmitted signal and using the correction signal for correction of the response signal and iteratively carrying out the following steps for correction of the response signal automatically:
ascertaining a present state value of the measurement signal, then ascertaining at least one of a present phase value or a present amplitude value for the correction signal using an optimization method, the optimization method using the present state value of the measurement signal as an input,
then modulating a present section of the correction signal that corresponds to a present section of the transmitted signal with the at least one of the present phase value or the present amplitude value,
then generating a present section of the measurement signal by subtraction of the present section of the correction signal from a present section of the response signal that is picked up at a same time as the present section of the transmitted signal is radiated, and
also using the respective present section of the measurement signal for reconstruction of the information about the measurement object.

2. The method as claimed in claim 1 , wherein the present state value of the measurement signal is the measure of at least one of a transmitted signal component or a signal strength in the measurement signal.

3. The method as claimed in claim 1 , wherein the optimization method further comprises using at least one further previously ascertained state value of the measurement signal as an input.

4. The method as claimed in claim 1 , wherein the optimization method further comprises ascertaining at least one of the respective present phase value or amplitude value by a gradient method.

5. The method as claimed in claim 4 , further comprising in each iteration, altering a variable on which at least one of the phase value or the amplitude value is dependent, reading a direction in which the variable has been altered in a previous iteration, choosing a step size for an alteration of the variable, comparing the present state value of the measurement signal with the present state value that was previously ascertained and altering the variable in the read direction in an event of an improvement in the present state value and altering the variable in a direction opposite to the read direction in an event of a worsening of the present state value.

6. The method as claimed in claim 1 , further comprising picking up the response signal completely during a period of radiation of the transmitted signal.

7. The method as claimed in claim 1 , wherein the information about the measurement object is reconstructed from the measurement signal by using at least 90% of a total pickup time of the response signal.

8. The method as claimed in claim 1 , wherein the modulating of the present section of the correction signal that corresponds to the present section of the transmitted signal with at least one of the present phase value or the present amplitude value is effected in voltage-controlled fashion using at least one of a phase modulator ( 13 ), an amplitude modulator ( 14 ) adjustable in voltage-controlled fashion, or a digital voltage controller.

9. The method as claimed in claim 1 , wherein the measurement signal is amplified using a signal amplifier ( 9 ), the signal amplifier ( 9 ) having a dynamic bandwidth that is outside a signal strength of an amplitude-modulated correction signal.

10. The method as claimed in claim 1 , further comprising first checking the present state value of the measurement signal and, in the event of a first limit value being exceeded, carrying out the steps for correction of the response signal until the state value of the measurement signal has reached a second limit value.

11. The method of claim 10 , wherein the second limit value is identical to the first limit value.

12. The method of claim 10 , wherein at least one of the first or the second limit value is greater than an estimate of a maximum state value of the measurement signal.

13. The method as claimed in claim 1 , wherein in the event of the present state value of the measurement signal exceeding a third limit value, generating a most recently generated section of the measurement signal again.

14. The method as claimed in claim 1 , wherein an on-resonant pulse is radiated into the measurement object in order to generate the present section of the measurement signal.

15. A radio-frequency unit ( 1 ) of a magnetic resonance imaging scanner comprising:
a generator ( 2 ) for generating a radio-frequency signal,
a signal divider ( 4 ) that has a signal input operatively connected to an output of the generator ( 2 ) and that has a first output and a second output,
a transmission coil ( 5 ) that generates a transmitted signal and that is operatively connected to the first output of the signal divider ( 4 ),
a receiving coil ( 6 ) that picks up a response signal forming a magnetic resonance signal from a measurement object,
a modulator ( 8 ) that is operatively connected to the second output of the signal divider ( 4 ), the modulator ( 8 ) comprising a phase modulator ( 13 ) and/or an amplitude modulator ( 14 ),
a signal combiner ( 7 ) that is operatively connected to the receiving coil ( 6 ) and the modulator ( 8 ) that generates a measurement signal,
a control unit ( 11 ) operatively connected to the signal combiner ( 7 ) and the modulator ( 8 ), the control unit being configured such that the radio-frequency unit ( 1 ) carries out the method as claimed in claim 1 .

Assignees

• Univ Freiburg Albert Ludwigs

Inventors

• Ozen Ali Caglar
• Bock Michael

Classifications

• G01R33/3657

  Decoupling of multiple RF coils wherein the multiple RF coils do not have the same function in MR, e.g. decoupling of a transmission coil from a receive coil · CPC title

• G01R33/4641

  Sequences for NMR spectroscopy of samples with ultrashort relaxation times such as solid samples · CPC title

• G01R33/3621 Primary

  NMR receivers or demodulators, e.g. preamplifiers, means for frequency modulation of the MR signal using a digital down converter, means for analog to digital conversion [ADC] or for filtering or processing of the MR signal such as bandpass filtering, resampling, decimation or interpolation · CPC title

• G01R33/4816

  NMR imaging of samples with ultrashort relaxation times such as solid samples, e.g. MRI using ultrashort TE [UTE], single point imaging, constant time imaging · CPC title

• G01R33/561

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