Patent EP0144026A2 successfully refreshed from Google Patents.
EP0144026A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Apparatus and method of NMR imaging with off-center zoom scan
Assignee: General Electric Co
•
Filing: 1984-11-15
•
Granted: —
•
Expires: 2004-11-15
Abstract
Abstract In Fourier transform NMR imaging, magnified images free of aliasing artifacts are achieved by band limiting the NMR signal in the X- and Y-axes directions thereby avoiding under-sampling. Band limiting in the X-axis direction is accomplished by reducing the signal bandwidth by a low-pass filter before AD conversion. In the Y-axis direction, the signal is band limited by providing selective excitation of the spin isochromats, such that only spins in a selected Y region of the object are available to contribute to the signal. When the region of interest is not centered, offsets in the X- and Y-axes, directions are obtained by shifting the receiver frequency by an amount Af R , and causing the selective RF pulse to have a complex amplitude.
Inventors
- 👤 Gary Harold Glover
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-30 17:05
CPC Classifications
G; G01; G01R; G01R33/00; G01R33/20; G01R33/44; G01R33/48; G01R33/483; G01R33/4833; G01R33/54; G01R33/56; G01R33/5604
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
250 words
A method of producing NMR images free of aliasing artifacts, comprising the steps of: (a) positioning an object to be imaged in a homogeneous magnetic field directed along a first axis of said object; (b) exciting to resonance a plurality of nuclear spins in a predetermined region of said object; (c) applying to said predetermined region at least one phase-encoding magnetic-field gradient, having one of a plurality of programmable amplitudes, which gradient is directed along at least one additional axis of said object; (d) irradiating said object with a selective, inverting RF pulse in the presence of a first magnetic-field gradient to initiate the refocussing of nuclear spins in a portion of said predetermined region; (e) allowing said nuclear spins in said portion to refocus in the presence of a second magnetic-field gradient to produce a spin-echo signal having a frequency dependence on position in the direction of said second - gradient, said spin echo being phase limited in the direction of said first gradient; (f) filtering said spin-echo signal to band limit the frequency content thereof to frequencies corresponding to those associated with said second gradient co-extensive with said portion; (g) sampling said spin-echo signal at a sufficient rate to recover the maximum frequency in the filtered signal, prior to repeating said steps (b)-(f) for a different amplitude of said phase-encoding gradient; and (h) Fourier analyzing said sampled spin-echo signals to obtain pixel image data for reconstructing an image of said object portion which is free of aliasing artifacts.
Claim 2
Independent Claim
250 words
A method of producing NMR images free of aliasing artifacts, comprising the steps of: (a) positioning an object to be imaged in a homogeneous magnetic field directed along a first axis of said object; (b) exciting to resonance a plurality of nuclear spins in a predetermined region of said object; (c) applying to said predetermined region at least one phase-encoding magnetic-field gradient, having one of a plurality of programmable amplitudes, which gradient is directed along at least one additional axis of said object; (d) irradiating said object with a selective, inverting RF pulse in the presence of a first magnetic-field gradient to initiate the refocussing of nuclear spins in a portion of said predetermined region; (e) allowing said nuclear spins in said portion to refocus in the presence of a second magnetic-field gradient to produce a spin-echo signal having a frequency dependence on position in the direction of said second - gradient, said spin echo being phase limited in the direction of said first gradient; (f) filtering said spin-echo signal to band limit the frequency content thereof to frequencies corresponding to those associated with said second gradient co-extensive with said portion; (g) sampling said spin-echo signal at a sufficient rate to recover the maximum frequency in the filtered signal, prior to repeating said steps (b)-(f) for a different amplitude of said phase-encoding gradient; and (h) Fourier analyzing said sampled spin-echo signals to obtain pixel image data for reconstructing an image of said object portion which is free of aliasing artifacts.
Claim 3
Dependent Claim
36 words
The method of Claim 1 wherein said step of exciting comprises: irradiating said object in the presence of a third magnetic-field gradient with a selective excitation RF pulse having a component perpendicular to said first axis.
Claim 4
Dependent Claim
15 words
The method of Claim 2 wherein said selective excitation pulse comprises a 90° RF pulse.
Claim 5
Dependent Claim
15 words
The method of Claim 3 wherein said phase-encoding gradient is orthogonal to said first axis.
Claim 6
Dependent Claim
20 words
The method of Claim 4 wherein said first magnetic-field gradient is directed in the same direction as said phase-encoding gradient.
Claim 7
Dependent Claim
50 words
The method of Claim 5 wherein said second magnetic-field gradient is orthogonal to said phase-encoding and to said third magnetic-field gradients, wherein the intersection of the planes containing said second, third, and phase-encoding gradients define an isocenter which is coincident with the image center having a center frequency associated therewith.
Claim 8
Dependent Claim
15 words
The method of Claim 6 wherein said inverting RF pulse comprises a selective 180° pulse.
Claim 9
Dependent Claim
46 words
The method of Claim 7 wherein said 90° and 180° RF pulses are each modulated by a sin x/x function, the bandwidth f B of said 180° pulse being 2/T, wherein T is the temporal interval between the first two zeroes of said sin x/x function.
Claim 10
Dependent Claim
59 words
The method of Claim 7 wherein the field of view L y of said portion of said predetermined region is given by wherein Y is the gyromagnetic ratio; Gy is the amplitude of said first magnetic-field gradient; T is the temporal interval between the first two zeroes of a sin x/x function used to modulate said 180° RF pulse.
Claim 11
Dependent Claim
59 words
The method of Claim 6 wherein said image center is offset by an amount X along the direction of said second magnetic-field gradient from said isocenter, such that said spin-echo signal is received at a frequency offset from said center frequency by an amount Δ f R given by wherein G is the magnitude of said second magnetic-field gradient.
Claim 12
Dependent Claim
82 words
The method of Claim 7 or 10 wherein said image center is offset from said isocenter by an amount Y o along the direc t on of said phase-encoding magnetic-field gradient, such that the amplitude of said 180° RF pulse is caused to have a complex amplitude AM given by where t is time, and f B is the bandwidth of said 180° RF pulse, and wherein where L y is the field of view of said portion of said predetermined region.
Claim 13
Dependent Claim
77 words
The method of Claim 6, 7, or 10 further comprising the step of applying an additional phase-encoding magnetic-field gradient having a direction orthogonal to the phase-encoding gradient in step (c), said additional phase-encoding gradient having one of a plurality of programmable amplitudes; and holding the amplitude of one of said phase-encoding gradients constant, while sequencing through all of the programmable amplitudes of the other phase-encoding gradient prior to selecting a different amplitude of said one phase-encoding gradient.
Claim 14
Dependent Claim
78 words
The method of Claim 12 wherein said image center is offset from said center by an amount Y o along the directon of said phase-encoding magnetic-field gradient, such that the amplitude of said 180° RF pulse is caused to have a complex amplitude AM given by where t is time, and f B is the bandwidth of said 180° RF pulse, and wherein where L y is the field of view of said portion of said predetermined region.
References Cited (Backward Citations)
No citation records indexed.
USPTO Annuity & Maintenance Windows
Maintenance schedule is calculated for granted US utility patents.