# US 2021/0239778 A1 · Method for evaluating a pilot tone signal in a magnetic resonance facility, magnetic resonance facility, computer program and electronically readable data medium

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- Number: US 2021/0239778 A1
- Document ID: US20210239778A1
- Status: Published application
- Kind: A1
- Application number: 17/152,911
- Filed: 2021-01-20
- Published: 2021-08-05
- Earliest claimed: 2020-01-30
- Assignees: Siemens Healthcare GmbH
- Applicants: Siemens Healthcare GmbH
- Inventors: Mario Bacher; Matthias Fenchel; Peter Speier
- Web page: https://patentgrep.com/patent/US20210239778A1

## CPC

- G01R 33/36: Electrical details, e.g. matching or coupling of the coil to the receiver
- G01R 33/4818: {MR characterised by data acquisition along a specific k-space trajectory or by the temporal order of k-space coverage, e.g. centric or segmented coverage of k-space}
- G01R 33/5602: {by filtering or weighting based on different relaxation times within the sample, e.g. T1 weighting using an inversion pulse}
- G01R 33/5608: {Data processing and visualization specially adapted for MR, e.g. for feature analysis and pattern recognition on the basis of measured MR data, segmentation of measured MR data, edge contour detection on the basis of measured MR data, for enhancing measured MR data in terms of signal-to-noise ratio by means of noise filtering or apodization, for enhancing measured MR data in terms of resolution by means for deblurring, windowing, zero filling, or generation of gray-scaled images, colour-coded images or images displaying vectors instead of pixels (image data processing or generation, in general G06T)}
- G01R 33/567: gated by physiological signals {, i.e. synchronization of acquired MR data with periodical motion of an object of interest, e.g. monitoring or triggering system for cardiac or respiratory gating}
- G06F 18/2133: based on naturality criteria, e.g. with non-negative factorisation or negative correlation
- G01R 33/56509: {due to motion, displacement or flow, e.g. gradient moment nulling (G01R33/567 takes precedence)}
- G01R 33/5673: {Gating or triggering based on a physiological signal other than an MR signal, e.g. ECG gating or motion monitoring using optical systems for monitoring the motion of a fiducial marker}
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)
- G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N)

## Abstract

A computer-implemented method is provided for evaluating a pilot tone signal. In the method, the pilot tone signal is recorded using a high-frequency coil arrangement of a magnetic resonance facility and describes a movement of a patient. The method also includes extracting movement information assigned to a movement component, (e.g., a respiratory movement). A breakdown or decomposition of the pilot tone signal is effected on a basis of signal components having assigned weightings and for the purpose of determining the movement information, a part of a base which is assigned to the movement component is selected by a selection criterion. For the purpose of determining the base and the weightings, a non-negative matrix factorization is performed, in the context of which a signal matrix, which is formed from the pilot tone signal and is in particular non-negative, is formulated as a product of a non-negative signal component matrix that describes the base and a non-negative weighting matrix that describes the weightings.

## Claims

### Claim 1

A computer-implemented method for evaluating a pilot tone signal, the method comprising:
recording the pilot tone signal using a high-frequency coil arrangement of a magnetic resonance facility, wherein the pilot tone signal describes a movement of a patient; and
extracting movement information via a breakdown of the pilot tone signal, wherein the movement information is assigned to a movement component,
wherein the breakdown of the pilot tone signal is effected on a basis of signal components having assigned weightings,
wherein, for the purpose of extracting the movement information, a part of a base assigned to the movement component is selected by a selection criterion, and
wherein, for the purpose of determining the base and the weightings, a non-negative matrix factorization is performed, in the context of which a signal matrix, which is formed from the pilot tone signal, is formulated as a product of a non-negative signal component matrix that describes the base and a non-negative weighting matrix that describes the weightings.

### Claim 2 (depends on 1)

The method of claim 1, wherein the movement of the patient is a respiratory movement of the patient.

### Claim 3 (depends on 1)

The method of claim 1, wherein the signal matrix is non-negative.

### Claim 4 (depends on 1)

The method of claim 1, wherein the non-negative signal component matrix and the non-negative weighting matrix are determined in an optimization process using a target function, and
wherein the target function comprises a term which minimizes at least a norm of the difference between the signal matrix and the product of the non-negative signal component matrix and the non-negative weighting matrix.

### Claim 5 (depends on 4)

The method of claim 4, wherein a further term of the target function adds a sparsely populated weighting matrix and/or a sparsely populated signal component matrix as an optimization target.

### Claim 6 (depends on 1)

The method of claim 1, wherein a magnitude power spectrum in the frequency space is determined as the signal matrix, for which purpose the pilot tone signal is Fourier-transformed and multiplied by its complex conjugate for each matrix entry.

### Claim 7 (depends on 6)

The method of claim 6, wherein the signal matrix is formulated as a row vector containing all receive channels.

### Claim 8 (depends on 1)

The method of claim 1, wherein for the purpose of determining movement information which describes a periodic movement component, the selection criterion comprises: a bandpass filter which selects a frequency range of the periodic movement component, a determination of a ratio of the signal energy within the frequency range to the signal energy outside the frequency range, a noise analysis, an entropy analysis, or a combination thereof.

### Claim 9 (depends on 1)

The method of claim 1, wherein the movement information describing the signal components assigned to the movement component is specified for a calibration time period and is applied to subsequently recorded pilot tone signals for the extracting of the movement component.

### Claim 10 (depends on 9)

The method of claim 9, wherein the movement information is applied to subsequently recorded pilot tone signals for determining a weighting matrix of the subsequently recorded pilot tone signal.

### Claim 11 (depends on 9)

The method of claim 9, wherein when a re-learning criterion is met which indicates that long-term suitability of a currently used base no longer applies, a new determination of the movement information is effected, taking a previous movement information as a starting point.

### Claim 12 (depends on 11)

The method of claim 11, wherein the re-learning criterion checks: (1) whether a divergence value which describes the divergence of the product of the signal component matrix that is stored as part of the movement information and the determined weighting matrix of the subsequently recorded pilot tone signal from the signal matrix of the subsequently recorded pilot tone signal exceeds a first threshold value, and/or (2) whether a second threshold value is exceeded for at least one weighting of the determined weighting matrix of the subsequently recorded pilot tone signal.

### Claim 13 (depends on 11)

The method of claim 11, wherein, for the new determination of the movement information, a tracking algorithm is applied which uses the previous movement information and the subsequently recorded pilot tone signal.

### Claim 14 (depends on 13)

The method of claim 13, wherein the tracking algorithm is applied for the new determination of the signal component matrix of the movement information.

### Claim 15 (depends on 1)

The method of claim 1, wherein, when a warning criterion is met which evaluates one or more of the weighting matrix, results of a re-learning criterion, or a presence of an undesired movement for the imaging, a warning is output to a user, the recording of magnetic resonance data is interrupted, magnetic resonance data recorded during the undesired movement is discarded, or a combination thereof.

### Claim 16 (depends on 1)

The method of claim 1, wherein in the case of a parallel recording of magnetic resonance data by the magnetic resonance facility along a recording trajectory in the k-space, the sampling time window for the pilot tone signal is synchronized with the recording trajectory.

### Claim 17 (depends on 16)

The method of claim 16, wherein trajectory sections are recorded in individual repetitions and are assigned to the sampling time window, and
wherein, when a re-recording criterion indicating the presence of an undesired movement is met for a trajectory section of the trajectory sections, the recording for the trajectory section is repeated.

### Claim 18

A magnetic resonance facility comprising:
at least one transmit coil configured to emit an excitation signal;
a high-frequency coil arrangement configured to measure a pilot tone signal generated by the excitation signal, wherein the pilot tone signal describes a movement of a patient; and
a control facility configured to extract movement information via a breakdown of the pilot tone signal, wherein the movement information is assigned to a movement component,
wherein the breakdown of the pilot tone signal is effected on a basis of signal components having assigned weightings,
wherein, for the purpose of extracting the movement information, a part of a base assigned to the movement component is selected by a selection criterion, and
wherein, for the purpose of determining the base and the weightings, a non-negative matrix factorization is performed, in the context of which a signal matrix, which is formed from the pilot tone signal, is formulated as a product of a non-negative signal component matrix that describes the base and a non-negative weighting matrix that describes the weightings.

### Claim 19

A computer program, which, when executed on a control facility of a magnetic resonance facility, causes the magnetic resonance facility to:
record a pilot tone signal using a high-frequency coil arrangement of the magnetic resonance facility, wherein the pilot tone signal describes a movement of a patient; and
extract movement information via a breakdown of the pilot tone signal, wherein the movement information is assigned to a movement component,
wherein the breakdown of the pilot tone signal is effected on a basis of signal components having assigned weightings,
wherein, for the purpose of extracting the movement information, a part of a base assigned to the movement component is selected by a selection criterion, and
wherein, for the purpose of determining the base and the weightings, a non-negative matrix factorization is performed, in the context of which a signal matrix, which is formed from the pilot tone signal, is formulated as a product of a non-negative signal component matrix that describes the base and a non-negative weighting matrix that describes the weightings.