Noise suppression methods and apparatus
According to some aspects, a method of suppressing noise in an environment of a magnetic resonance imaging system is provided. The method comprising estimating a transfer function based on multiple calibration measurements obtained from the environment by at least one primary coil and at least one auxiliary sensor, respectively, estimating noise present in a magnetic resonance signal received by the at least one primary coil based at least in part on the transfer function, and suppressing noise in the magnetic resonance signal using the noise estimate.
1. A method of suppressing noise in an environment of a magnetic resonance imaging system, the method comprising:
obtaining, using at least one primary coil and at least one auxiliary sensor different from the at least one primary coil, multiple calibration signals comprising a first plurality of calibration signals obtained by a first auxiliary sensor of the at least one auxiliary sensor and a corresponding second plurality of calibration signals obtained by a first primary coil of the at least one primary coil by:
obtaining the first plurality of calibration signals using the first auxiliary sensor, wherein each of the first plurality of calibration signals comprises multiple values; and
obtaining the second plurality of calibration signals using the first primary coil, wherein each of the second plurality of calibration signals comprises multiple values;
estimating, based on the first plurality of calibration signals and second plurality of calibration signals, a transform that, when applied to noise received by the first auxiliary sensor, provides an estimate of noise received by the first primary coil, wherein estimating the transform comprises estimating, based on the first plurality of calibration signals and the second plurality of calibration signals, a respective amplitude and phase of the transform for each of a plurality of frequency bins; and
after estimating the transform:
receiving a magnetic resonance signal using the first primary coil;
receiving a noise signal using the first auxiliary sensor;
estimating noise present in the magnetic resonance signal received by the first primary coil by applying the transform to the noise signal received by the first auxiliary sensor to obtain a noise estimate; and
suppressing noise in the magnetic resonance signal using the noise estimate.
2. The method of claim 1 , wherein the first plurality of calibration signals is indicative of multiple values for each of the plurality of frequency bins.
3. The method of claim 1 , wherein a discrete Fourier transform of the first plurality of calibration signals provides multiple values for each of the plurality of frequency bins.
4. The method of claim 1 , wherein the first plurality of calibration signals comprises a first calibration signal comprising a first plurality values obtained at a respective plurality of times.
5. The method of claim 1 , wherein obtaining the first plurality of calibration signals comprises obtaining at least ten calibration signals using the first auxiliary sensor.
6. The method of claim 1 , wherein obtaining the first plurality of calibration signals comprises obtaining at least one hundred calibration signals using the first auxiliary sensor.
7. The method of claim 1 , wherein the at least one primary coil is arranged within a field of view of the magnetic resonance imaging system to detect magnetic resonance signals produced by a sample when positioned within the field of view, and wherein the at least one auxiliary sensor comprises at least one auxiliary coil arranged outside the field of view.
8. The method of claim 7 , wherein the at least one auxiliary coil comprises a plurality of auxiliary coils, and wherein the multiple calibration signals are obtained from the environment using the plurality of auxiliary coils, wherein each auxiliary coil of the plurality of auxiliary coils obtains a respective plurality of calibration signals in the multiple calibration signals, and wherein each of the calibration signals obtained using the plurality of auxiliary coils comprises multiple values.
9. The method of claim 8 , wherein at least one of the plurality of auxiliary coils is of a different type than at least one other auxiliary coil of the plurality of auxiliary coils.
10. The method of claim 8 , wherein estimating the transform comprises estimating the transform based on the multiple calibration measurements and estimating the noise present in the magnetic resonance signal comprises applying the transform to noise signals received by each of the plurality of auxiliary coils and obtained substantially at a same time as the at least one primary coil receives the magnetic resonance signal.
11. The method of claim 1 , wherein the noise signal is received by the first auxiliary coil substantially at a same time as the first primary coil receiving the magnetic resonance signal.
12. The method of claim 1 , wherein each of the first plurality of calibration signals is obtained substantially at a same set of times as a respective one of the second plurality of calibration signals.
13. The method of claim 1 , wherein estimating the transform includes estimating the respective amplitude and phase of the transform for each frequency bin across a spectrum of interest for which the transform is defined.
14. The method of claim 1 , wherein the magnetic resonance system is a low-field magnetic resonance imaging system configured to generate a B0 field of 0.2 T or less.
15. The method of claim 14 , wherein the low-field magnetic resonance imaging system is configured to generate a B0 field of 0.1 T or less.
16. A magnetic resonance imaging (MRI) system comprising:
at least one primary coil, the at least one primary coil comprising a first primary coil;
at least one auxiliary sensor different from the at least one primary coil, the at least one auxiliary sensor comprising a first auxiliary sensor; and
at least one controller configured to:
cause the first auxiliary sensor and the first primary coil to obtain multiple calibration signals, the multiple calibration signals comprising a first plurality of calibration signals and a second plurality of calibration signals obtained by the first auxiliary sensor and the first primary coil, respectively, from an environment of the magnetic resonance imaging system, wherein each of the first plurality of calibration signals includes multiple values and each of the second plurality of calibration signals includes multiple values;
estimate, based on the first plurality of calibration signals and the second plurality of calibration signals, a transform that, when applied to noise received by the first auxiliary sensor, provides an estimate of noise received by the first primary coil wherein the at least one controller is configured to estimate the transform at least in part by estimating, based on the first plurality of calibration signals and the second plurality of calibration signals, a respective amplitude and phase of the transform for each of a plurality of frequency bins; and
after estimating the transform:
cause the first primary coil to receive a magnetic resonance signal;
cause the first auxiliary sensor to receive a noise signal;
estimate noise present in the magnetic resonance signal received by the first primary coil by applying the transform to the noise signal received by the first auxiliary sensor to obtain a noise estimate; and
suppress noise in the magnetic resonance signal using the noise estimate.
17. The MRI system of claim 16 , wherein the first plurality of calibration signals is indicative of multiple values for each of the plurality of frequency bins.
18. The MRI system of claim 16 , wherein a discrete Fourier transform of the first plurality of calibration signals provides multiple values for each of the plurality of frequency bins.
19. The MRI system of claim 16 , wherein causing the first auxiliary sensor to obtain the first plurality of calibration signals comprises causing the first auxiliary sensor to obtain at least ten calibration signals.
20. The MRI system of claim 16 , wherein causing the first auxiliary sensor to obtain the first plurality of calibration signals comprises causing the first auxiliary sensor to obtain at least one hundred calibration signals.
21. The MRI system of claim 16 , wherein the at least one primary coil is arranged within a field of view of the MRI system to detect magnetic resonance signals produced by a sample when positioned within the field of view, and wherein the at least one auxiliary sensor comprises at least one auxiliary coil arranged outside the field of view.
22. The MRI system of claim 16 , wherein each of the first plurality of calibration signals is caused to be obtained substantially at a same time as a respective one of the second plurality of calibration signals.
23. The MRI system of claim 16 , wherein the at least one controller causes the first auxiliary sensor to receive the noise signal and the first primary coil to receive the magnetic resonance signal at substantially a same time.
24. The MRI system of claim 16 , wherein the at least one auxiliary sensor comprises a plurality of auxiliary coils positioned at different respective locations, and wherein the multiple calibration signals are obtained from the environment by using the plurality of auxiliary coils, each auxiliary coil of the plurality of auxiliary coils obtains a respective plurality of calibration signals of the multiple calibration signal and each of the calibration signals obtained using the plurality of auxiliary coils comprise multiple values.
25. The MRI system of claim 24 , wherein estimating the noise present in the magnetic resonance signal comprises applying the transform to noise signals obtained from the plurality of auxiliary coils substantially at a same time as the at least one primary coil receives the magnetic resonance signal.
26. The MRI system of claim 16 , wherein the at least one controller is configured to estimate the respective amplitude and phase of the transform for each of a plurality of frequency bins across a spectrum for which the transform is defined.
27. The MRI system of claim 16 , wherein the at least one auxiliary sensor includes at least one auxiliary radio frequency coil.