# US 10,502,802 B1 · System and method for noise reduction in magnetic resonance imaging

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- Number: US 10,502,802 B1
- Document ID: US10502802B1
- Status: Granted
- Kind: B1
- Application number: 14/636,713
- Filed: 2015-03-03
- Granted: 2019-12-10
- Earliest claimed: 2010-04-14
- Assignees: Hypres, Inc.
- Applicants: Hypres, Inc.
- Inventors: Alan Kadin
- Web page: https://patentgrep.com/patent/US10502802B1

## CPC

- G01R 33/56: Image enhancement or correction, e.g. subtraction or averaging techniques {, e.g. improvement of signal-to-noise ratio and resolution}
- G01R 33/3621: {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}
- G01R 33/3678: {involving quadrature drive or detection, e.g. a circularly polarized RF magnetic field}
- G01R 33/543: {Control of the operation of the MR system, e.g. setting of acquisition parameters prior to or during MR data acquisition, dynamic shimming, use of one or more scout images for scan plane prescription (G01R33/546 takes precedence)}
- G01R 33/546: {Interface between the MR system and the user, e.g. for controlling the operation of the MR system or for the design of pulse sequences}
- 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 33/56518: {due to eddy currents, e.g. caused by switching of the gradient magnetic field}
- G01R 33/56563: {caused by a distortion of the main magnetic field B0, e.g. temporal variation of the magnitude or spatial inhomogeneity of B0 (G01R33/56509, G01R33/56518, G01R33/56536 take precedence)}
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)

## Abstract

Signals of interest in magnetic resonance imaging (MRI) systems comprise narrowband, circularly polarized (CP) radio-frequency magnetic fields from rotating atomic nuclei. Background “body noise” may comprise broadband, linearly polarized (LP) magnetic fields from thermally-activated eddy currents, and may exceed the signal in a band of interest, limiting the imaging resolution and requiring excessive averaging times. Noise may be selectively detected and substantially suppressed, while enhancing the signal of interest, using appropriate digital time-domain algorithms. At least two quadrature receiving antennas may be employed to distinguish and separate the LP noise from the CP signal. At least one broadband receiver may be used to identify and localize fast noise sources and to digitally filter the representation of their radio-frequency magnetic fields in the signal. Selective body noise reduction may allow enhanced signal-to-noise ratio of the system, leading to improved imaging resolution and shorter scan time.

## Claims

### Claim 1

A magnetic resonance imaging processing system, comprising:
at least one automated digital processor, configured to:
process magnetic resonance data derived from at least two antennas having different orientations with respect to a radio frequency magnetic field from an imaging region, representing each of a phase coherent narrowband oscillating signal of interest, and a broadband interfering signal from a current dipole having at least one component within the narrow band of the signal of interest, based on at least a time-correlated model of the broadband interfering signal from the current dipole, correlating portions of the broadband interfering signal from the current dipole outside the narrow band of the signal of interest with the at least one component within the narrow band of the signal of interest, and
generate a reduced interference signal having a reduced interference of the broadband interfering signal from the current dipole with the signal of interest; and
a memory, configured to store the reduced interference signal,
wherein the signal of interest is substantially circularly polarized, the broadband interfering signal from the current dipole is substantially linearly polarized, and the at least two antennas have a differential response pattern to circularly polarized and linearly polarized radio frequency magnetic fields within the narrow band from the imaging region.

### Claim 2 (depends on 1)

The system according to claim 1, wherein the at least two antennas are configured to distinguish a spatial characteristic of a radio frequency magnetic field from the imaging region.

### Claim 3 (depends on 1)

The system according to claim 1, wherein the at least two antennas are configured in a two dimensional array, each element of the array having a different respective spatial sensitivity.

### Claim 4 (depends on 1)

The system according to claim 1, wherein the broadband interfering signal from the current dipole comprises at least one pulse, and wherein the at least one automated processor is configured to perform a time domain analysis of the magnetic resonance data.

### Claim 5 (depends on 1)

The system according to claim 1, wherein the at least one automated processor is configured to perform a frequency domain analysis of the magnetic resonance data.

### Claim 6 (depends on 1)

The system according to claim 1, wherein the at least one automated processor is configured to perform a correlation analysis of the broadband interfering broadband signal from the current dipole within the narrow band with components of the broadband signal from the current dipole outside of the narrow band.

### Claim 7 (depends on 1)

The system according to claim 1, wherein the at least one automated processor is configured to process sequential time samples representing the radio frequency magnetic field, to estimate a time domain waveform of the broadband interfering signal from the current dipole, and to selectively digitally remove the estimated waveform of the broadband interfering signal from the current dipole, from the magnetic resonance data to produce the reduced interference signal.

### Claim 8 (depends on 1)

The system according to claim 1, further comprising an automated output processor configured to process the reduced interference signal receive and to generate a spatial map corresponding to the reduced interference signal.

### Claim 9 (depends on 1)

The system according to claim 1, where the at least two antennas are together configured to generate at least two quadrature-related radio frequency magnetic resonance signals from the radio frequency magnetic field.

### Claim 10 (depends on 1)

The system according to claim 1, wherein the at least one automated processor is configured to produce the signal having the reduced interference of the broadband interfering signal from the current dipole with the signal of interest within the narrowband by greater than 3 dB.

### Claim 11 (depends on 1)

The system according to claim 1, further comprising at least one analog-to-digital converter configured to directly oversample a signal from a respective antenna representing the radio frequency magnetic field without frequency translation.

### Claim 12 (depends on 11)

The system according to claim 11, wherein the analog-to-digital converter samples at a multi-GHz rate.

### Claim 13 (depends on 1)

The system according to claim 1, wherein the at least one automated processor is configured to perform a nonlinear transformation on a representation of the radio frequency field.

### Claim 14

A magnetic resonance imaging processing method, comprising:
receiving magnetic resonance data as at least two signals, derived from at least two antennas having different orientations with respect to a radio frequency magnetic field from an imaging region, representing a vector sum of a phase coherent narrowband oscillating signal of interest which is predominantly circularly polarized, and a broadband interfering signal from a current dipole which comprises at least one linearly polarized component having at least one component within the narrow band of the signal of interest, projected in at least two directions;
digitally correlating portions of the broadband interfering signal from the current dipole outside the narrow band of the signal of interest with the at least one component within the narrow band of the signal of interest to generate a time-correlated model of the broadband interfering signal from the current dipole;
processing the received magnetic resonance data as the at least two signals based on at least the time-correlated model of the broadband interfering signal from the current dipole, to separate the signal of interest, from the broadband interfering signal from the current dipole, based on a spatial difference therebetween, to produce a reduced interference signal having a reduced interference of the broadband interfering signal from the current dipole with the signal of interest; and
storing the reduced interference signal in a memory,
wherein the signal of interest is predominantly circularly polarized, and the broadband interfering signal from the current dipole comprises at least one linearly polarized component, further comprising:
receiving from the at least two antennas at least two signals representing a respective vector sum of the signal of interest and the broadband interfering signal from the current dipole, projected in at least two directions; and
analyzing the at least two received signals, to separate out the signal of interest from the broadband interfering signal from the current dipole based on a spatial difference therebetween.

### Claim 15 (depends on 14)

The method according to claim 14, wherein the at least two antennas comprise a plurality of antenna elements configured in a two dimensional array, each element of the array having a different respective spatial sensitivity.

### Claim 16 (depends on 14)

The method according to claim 14, wherein the broadband interfering signal from the current dipole comprises at least one pulse, and wherein the processing comprises time domain processing of a time sequence of digital data representing the sensed radio frequency field at a sample rate in excess of 2.5 gigasamples per second.

### Claim 17 (depends on 14)

The method according to claim 14, wherein:
the at least two antennas are oriented to sense a radio frequency field with different electromagnetic vector components;
the at least two antenna elements are configured to have a differential response pattern to circularly polarized and linearly polarized radio frequency fields within the narrow band; and
the processing comprises processing a time series representing a radio frequency field sensed by the at least two antennas, and generating a digital output signal that increases a ratio of the signal of interest and noise comprising the broadband interfering signal from the current dipole;
further comprising generating a spatial map corresponding to the reduced interference signal.

### Claim 18

A method of enhancing detection of a signal of interest in a magnetic resonance imaging system, comprising:
receiving magnetic resonance vector information from at least two antennas having different orientations with respect to a radio frequency magnetic field from an imaging region, representing a phase coherent signal of interest within a band, and an interference signal overlapping the band from a current dipole;
digitally correlating portions of the interference signal within the band with at least one component of the interference signal outside the band;
selectively estimating a vector direction of the interference signal; and
digitally subtracting the interference signal within the band based on at least the estimated vector direction and the correlation of the portions of the interference signal within the band with at least one component of the interference signal outside the band, from the received magnetic resonance vector information, to generate a filtered signal,
wherein the signal of interest is substantially circularly polarized, the interfering signal overlapping the band from the current dipole is substantially linearly polarized, and the at least two antennas have a differential response pattern to circularly polarized and linearly polarized radio frequency magnetic fields within the band from the imaging region.