Method and apparatus for non-invasive assessment of ripple cancellation filter

Patent metadata

Field	Value
Publication number	US-10247795-B2
Application number	US-201414585554-A
Country	US
Kind code	B2
Filing date	Dec 30, 2014
Priority date	Dec 30, 2014
Publication date	Apr 2, 2019
Grant date	Apr 2, 2019

Abstract

A method that includes deriving a first power spectral density function of a signal input to a ripple cancellation filter; deriving a second power spectral density function of a signal concurrently output from the ripple cancellation filter; frequency shaping the first power spectral density according to a spectral rejection image of the ripple cancellation filter to obtain a test power spectral density; and indicating a degraded performance of the ripple cancellation filter in the event that the test and second power spectral density functions fail to match within pre-determined criteria.

First claim

What is claimed is:

1. A method comprising:
non-invasively sampling an input voltage to a ripple cancellation filter of a magnetic resonance imaging system via a filter assessment module of the magnetic resonance imaging system, the filter assessment module electrically connected to both an input and an output of the ripple cancellation filter;
transforming, via the filter assessment module, the sampled input voltage into a first power spectral density;
non-invasively sampling an output voltage of the ripple cancellation filter via the filter assessment module;
transforming, via the filter assessment module, the sampled output voltage into a second power spectral density;
frequency shaping, via the filter assessment module, the first power spectral density according to a spectral rejection image of the ripple cancellation filter to obtain a test power spectral density; and
indicating, via the filter assessment module, a degraded performance of the ripple cancellation filter in the event that the test and second power spectral densities fail to match within pre-determined criteria.

2. The method of claim 1 wherein the pre-determined criteria include a difference of less than 5% between power integrals across a sample bandwidth surrounding a fundamental noise frequency.

3. The method of claim 2 wherein the sample bandwidth is not less than +/−1% of the fundamental noise frequency.

4. The method of claim 3 wherein the sample bandwidth is not more than +/−10% of the fundamental noise frequency.

5. The method of claim 2 wherein the fundamental noise frequency is established as a multiple of a pulse width modulator switching frequency.

6. The method of claim 2 wherein the fundamental noise frequency is established as a frequency corresponding to a maximum of the first power spectral density function.

7. A method comprising:
non-invasively sampling, via a filter assessment module electrically connected to both an input and an output of a ripple cancellation filter of a magnetic resonance imaging system, a signal produced by operation of a pulse width modulator of the magnetic resonance imaging system;
transforming, via the filter assessment module, the sampled signal into a first power spectral density;
non-invasively sampling, via the filter assessment module, an output voltage of the ripple cancellation filter;
transforming, via the filter assessment module, the sampled output voltage into a second power spectral density;
frequency shaping, via the filter assessment module, the first power spectral density according to a design spectral rejection image of the ripple cancellation filter to obtain a test power spectral density; and
indicating, via the filter assessment module, a degraded performance of the ripple cancellation filter in the event that the test and second power spectral densities fail to match within pre-determined criteria.

8. The method of claim 7 wherein the pre-determined criteria include a difference of less than 5% between power integrals across a sample bandwidth surrounding a fundamental noise frequency.

9. The method of claim 8 wherein the sample bandwidth is not less than +/−1% of the fundamental noise frequency.

10. The method of claim 9 wherein the sample bandwidth is not more than +/−10% of the fundamental noise frequency.

11. The method of claim 8 wherein the fundamental noise frequency is established as a multiple of a pulse width modulator switching frequency.

12. The method of claim 8 wherein the fundamental noise frequency is established as a frequency corresponding to a maximum of the first power spectral density function.

13. An apparatus comprising:
a first sensor that non-invasively samples an input voltage to a ripple cancellation filter connected across output terminals of h-bridges of a gradient amplifier of a magnetic resonance imaging system;
a second sensor that non-invasively samples an output voltage of the ripple cancellation filter;
a filter assessment module that transforms the sampled input voltage into a first power spectral density,
transforms the sampled output voltage into a second power spectral density, obtains a design spectral rejection image of the ripple cancellation filter based on a concurrent pulse width modulator output, multiplies the first power spectral density by the design spectral rejection image to obtain a test spectral power density, and indicates a degraded performance of the ripple cancellation filter in the event that the test and second power spectral densities fail to match within pre-determined criteria.

14. The apparatus of claim 13 wherein the pre-determined criteria include a difference of less than 5% between power integrals across a sample bandwidth surrounding a fundamental noise frequency.

15. The apparatus of claim 14 wherein the sample bandwidth is not less than +/−1% of the fundamental noise frequency.

16. The apparatus of claim 15 wherein the sample bandwidth is not more than +/−10% of the fundamental noise frequency.

17. The apparatus of claim 14 wherein the fundamental noise frequency is established as a multiple of a pulse width modulator switching frequency.

18. The apparatus of claim 14 wherein the fundamental noise frequency is established as a frequency corresponding to a maximum of the first power spectral density function.

19. An apparatus comprising:
a pulse width modulator;
an image processing module that receives an input signal including switching noise produced by the pulse width modulator;
a ripple cancellation filter that samples the pulse width modulator output voltage to produce a rejection image for removing the switching noise from the input signal to the image processing module; and
a filter assessment module, electrically connected to both an input and an output of the ripple cancellation filter, that transforms the pulse width modulator output voltage into a first power spectral density, transforms an output voltage non-invasively sampled from the ripple cancellation filter into a second power spectral, multiplies the first power spectral density by the rejection image to produce a test power spectral density, and indicates to the image processing module a degraded performance of the ripple cancellation filter in the event that the test and second power spectral densities fail to match within pre-determined criteria.

20. The apparatus of claim 19 wherein the pre-determined criteria include a difference of less than 5% between power integrals across a sample bandwidth surrounding a fundamental noise frequency.

Assignees

• Gen Electric

Inventors

• Frigo Louis Martin
• Freeman Melissa Jean
• Wiza Margaret Ann
• Link Douglas
• Rose Michael Thomas
• Weber Scott Richard
• Panos Andrew John

Classifications

• G01R33/3852 Primary

  Gradient amplifiers; means for controlling the application of a gradient magnetic field to the sample, e.g. a gradient signal synthesizer · CPC title

• G01R33/38

  Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field · CPC title