Patent EP0132337A2 successfully refreshed from Google Patents.
EP0132337A2
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Apparatus and method for reducing aliasing in sagittal or coronal NMR imaging
Assignee: University of California Berkeley
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Filing: 1984-07-06
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Granted: —
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Expires: 2004-07-06
Abstract
Abstract An analog-to-digital sampling rate substantially higher than the Nyquist frequency 2f c usually associated with the cut-off frequency f c of a low pass NMR response signal filter (21) is employed to reduce NMR image artifact caused by aliasing effects in the digital signal image reconstruction process. In effect, the outer limits of the displayed NMR image field-of-view (in at least one dimension) are defined by the cut-off frequency f c of the low pass filter (21) rather than by the sampling rate which is, in the preferred exemplary embodiment approximately as great as 4f c .
Inventors
- 👤 Lawrence E. Crooks
- 👤 John C. Hoenninger, Iii
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-07 15:33
CPC Classifications
G; G01; G01R; G01R33/00; G01R33/20; G01R33/44; G01R33/48; G01R33/4818; G01R33/482; G01R33/54; G01R33/56; G01R33/565; G01R33/56545; G01R33/28; G01R33/32; G01R33/36; G01R33/3621
Claims Analysis
Total Claims: 16
Claim 1
Independent Claim
114 words
A method of NMR imaging a region of interest in an extended object which reduces aliasing effects, said method comprising the steps of: obtaining an NMR response signal from said region of interest and passing it through a low pass electrical filter having a cut-off frequency f c; successively sampling said filtered NMR response signal at a rate SR and measuring the value of the signal at each sample time interval, said sampling rate SR being substantially greater than 2f c ; and reconstructing from said measured signal values an NMR image of said region of interest with an effective field of view limited by said low pass filter cut-off frequency f c .
Claim 2
Independent Claim
114 words
A method of NMR imaging a region of interest in an extended object which reduces aliasing effects, said method comprising the steps of: obtaining an NMR response signal from said region of interest and passing it through a low pass electrical filter having a cut-off frequency f c; successively sampling said filtered NMR response signal at a rate SR and measuring the value of the signal at each sample time interval, said sampling rate SR being substantially greater than 2f c ; and reconstructing from said measured signal values an NMR image of said region of interest with an effective field of view limited by said low pass filter cut-off frequency f c .
Claim 3
Dependent Claim
23 words
A method of NMR imaging as in claim 1 wherein said sampling rate SR is at least as great as 4 f c.
Claim 4
Dependent Claim
74 words
A method of NMR imaging as in claim 1 wherein said obtaining step comprises the steps of: selectively exciting a first portion of the object with a 90° r.f. nutation pulse; and thereafter selectively exciting a second portion of the object with a 180° r.f. nutation pulse so as to elicit a spin echo NMR response signal from a region of interest defined by the common intersecting region of said first and second portions.
Claim 5
Dependent Claim
43 words
A method of NMR imaging as in claim 1, 2 or 3, wherein said obtaining and sampling steps are repeated with the corresponding sampled signal values of each repetition being accumulated and the thus accumulated signal values being used in said reconstructing step.
Claim 6
Independent Claim
23 words
A method of NMR imaging as in any preceding claim, wherein said reconstructing step includes two-dimensional Fourier transformation of said accumulated signal values.
Claim 7
Independent Claim
32 words
A method of NMR imaging as in any preceding claim, wherein said passage through a low pass filter occurs after detection of the NMR response signal while it is in analog form.
Claim 8
Independent Claim
65 words
A method of NMR imaging as in any preceding claim, wherein said region of interest is a sagittal planar volume through a human body, and wherein a magnetic gradient is applied along the long axis of the body during the NMR spin echo occurrence such that the low pass filtering reduces aliasing artifacts along the long axis of the body in the reconstructed NMR image.
Claim 9
Independent Claim
69 words
A method of NMR imaging as in any one of claims 1 to 6, wherein said region of interest is a coronal planar volume through a human body, and wherein a magnetic gradient is applied along the long axis of the body during the NMR spin echo occurrence such that the low pass filtering reduces aliasing artifacts along the long axis of the body in the reconstructed NMR image.
Claim 10
Dependent Claim
115 words
Apparatus for NMR imaging a region of interest in an extended object which reduces aliasing effects, said apparatus comprising: means for obtaining an NMR response signal from said region of interest and passing it through a low pass electrical filter having a cut-off frequency f c ; means for successively sampling said filtered NMR response signal at a rate SR and measuring the value of the signal at each sample time interval, said sampling rate SR being substantially greater than 2t ; and means for reconstructing from said measured signal values an NMR image of said region of interest with an effective field of view limited by said low pass filter cut-off frequency f c
Claim 11
Dependent Claim
115 words
Apparatus for NMR imaging a region of interest in an extended object which reduces aliasing effects, said apparatus comprising: means for obtaining an NMR response signal from said region of interest and passing it through a low pass electrical filter having a cut-off frequency f c ; means for successively sampling said filtered NMR response signal at a rate SR and measuring the value of the signal at each sample time interval, said sampling rate SR being substantially greater than 2t ; and means for reconstructing from said measured signal values an NMR image of said region of interest with an effective field of view limited by said low pass filter cut-off frequency f c
Claim 12
Dependent Claim
19 words
Apparatus as in claim 9, wherein said sampling rate SR is at least as great as 4f c .
Claim 13
Dependent Claim
72 words
Apparatus as in claim 9, wherein said means for obtaining comprises: means for selectively exciting a first portion of the object with a 90° r.f. nutation pulse; and means for thereafter selectively exciting a second portion of the object with a 180° r.f. nutation pulse so as to elicit a spin echo NMR response signal from a region of interest defined by the common intersecting region of said first and second portions.
Claim 14
Dependent Claim
48 words
Apparatus as in any one of claims 9 to 11, wherein said means for obtaining and means for sampling includes means for accumulating corresponding sampling signal values obtained by repeated NMR signal measurements and wherein said means for reconstruction uses the thus accumulated signal values in said reconstructing.
Claim 15
Dependent Claim
27 words
Apparatus as in any one of claims 9 to 12, wherein said means for reconstructing includes means for effecting two-dimensional Fourier transformation of said accumulated signal values.
Claim 16
Dependent Claim
32 words
Apparatus as in any one of claims 9 to 11 wherein said low pass filter is located to intercept said NMR response signal thereof after detection while it is in analog form.
References Cited (Backward Citations)
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