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US5140268A
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Method and means for correcting RF amplifier distortion in magnetic resonance imaging
Assignee: Leland Stanford Junior University
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Filing: 1990-06-15
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Granted: 1992-08-18
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Expires: 2010-06-15
Abstract
Abstract In a magnetic resonance imaging system, an RF power amplifier is employed to boost an RF pulse to sufficient strength to excite the nuclear spins in a subject. The non-ideal behavior of the amplifier distorts the shape of an excitation pulse, and this distortion in turn degrades a slice profile. The distortion of the RF signal is manifested by nonlinearity in amplification and in incidental phase modulation. By determining the amount of nonlinearity and the phase modulation resulting from the power amplification, the baseband RF signal can be predistorted or prewarped to offset the distortion resulting from amplification. Improved slice selectivity results therefrom.
Inventors
- 👤 Frandics P. Chan
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-06 16:25
CPC Classifications
G; G01; G01R; G01R33/00; G01R33/20; G01R33/28; G01R33/32; G01R33/36; G01R33/3614; G01R33/3607
Claims Analysis
Total Claims: 17
Claim 1
Independent Claim
91 words
In a magnetic resonance imaging system, a method of improving slice definition in imaging comprising the steps of generating an RF signal by modulating a carrier signal with a baseband selective-excitation pulse for selectively energizing a slice of an object in accordance with the equation ω.sub.0 =B.sub.0 ·γ where ω 0 =angular frequency of said RF signal, B 0 =magnetic field through said slice, γ=magnetogyric ratio amplifying said RF signal, determining distortion of said RF signal after amplification, and predistorting said selective-excitation pulse to offset distortion by amplifying said RF signal.
Claim 2
Dependent Claim
91 words
In a magnetic resonance imaging system, a method of improving slice definition in imaging comprising the steps of generating an RF signal by modulating a carrier signal with a baseband selective-excitation pulse for selectively energizing a slice of an object in accordance with the equation ω.sub.0 =B.sub.0 ·γ where ω 0 =angular frequency of said RF signal, B 0 =magnetic field through said slice, γ=magnetogyric ratio amplifying said RF signal, determining distortion of said RF signal after amplification, and predistorting said selective-excitation pulse to offset distortion by amplifying said RF signal.
Claim 3
Dependent Claim
20 words
The method as defined by claim 1 wherein said step of determining distortion includes demodulating said RF signal after amplification.
Claim 4
Dependent Claim
19 words
The method as defined by claim 2 wherein said baseband signal includes an in-phase component and a quadrature-phase component.
Claim 5
Dependent Claim
40 words
The method as defined by claim 3 wherein said RF signal is generated by using one of the in-phase and quadrature-phase components in modulating said carrier signal and said step of determining distortion includes determining nonlinearity and incidental phase modulation.
Claim 6
Dependent Claim
24 words
The method as defined by claim 4 wherein said steps of generating an RF signal, determining distortion, and predistorting said RF signal are iterative.
Claim 7
Dependent Claim
38 words
The method as defined by claim 4 wherein said steps of generating an RF signal, determining distortion, and predistorting said RF signal utilizes a look-up table of a magnitude transfer function and phase of the baseband gain function.
Claim 8
Dependent Claim
26 words
The method as defined by claim 4 wherein said steps of generating an RF signal includes sweeping the RF signal from zero to a maximum amplitude.
Claim 9
Dependent Claim
30 words
The method as defined by claim 4 wherein said steps of generating an RF signal includes repetitive sweeping the RF signal to obtain time-dependant characteristics of the baseband gain function.
Claim 10
Dependent Claim
109 words
In a magnetic resonance imaging system including a modulator for modulating an RF carrier with a baseband input signal, an RF power amplifier, and a receiver including a demodulator for demodulating RF signals, a method of pre-warping the baseband input signal to offset RF amplifier signal distortions comprising the steps of generating an RF signal for selectively energizing an object in accordance with the equation ω.sub.0 =B.sub.0 ·γ including modulating a carrier signal with a baseband signal, amplifying said RF signal, determining distortion of said RF signal after amplification including demodulating said RF signal after amplification, and predistorting said baseband signal to offset distortion by amplifying said RF signal.
Claim 11
Dependent Claim
109 words
In a magnetic resonance imaging system including a modulator for modulating an RF carrier with a baseband input signal, an RF power amplifier, and a receiver including a demodulator for demodulating RF signals, a method of pre-warping the baseband input signal to offset RF amplifier signal distortions comprising the steps of generating an RF signal for selectively energizing an object in accordance with the equation ω.sub.0 =B.sub.0 ·γ including modulating a carrier signal with a baseband signal, amplifying said RF signal, determining distortion of said RF signal after amplification including demodulating said RF signal after amplification, and predistorting said baseband signal to offset distortion by amplifying said RF signal.
Claim 12
Dependent Claim
38 words
The method as defined by claim 9 wherein said baseband signal includes an in-phase component and a quadrature-phase component, said RF signal being generated by using one of the in-phase and quadrature-phase components in modulating said carrier signal.
Claim 13
Dependent Claim
26 words
The method as defined by claim 8 wherein said steps of generating an RF signal includes sweeping the RF signal from zero to a maximum amplitude.
Claim 14
Dependent Claim
24 words
The method as defined by claim 9 wherein said steps of generating an RF signal, determining distortion, and predistorting said RF signal are iterative.
Claim 15
Dependent Claim
38 words
The method as defined by claim 11 wherein said steps of generating an RF signal, determining distortion, and predistorting said RF signal utilizes a look-up table of a magnitude transfer function and phase of the baseband gain function.
Claim 16
Dependent Claim
30 words
The method as defined by claim 10 wherein said steps of generating an RF signal includes repetitive sweeping the RF signal to obtain time-dependant characteristics of the baseband gain function.
Claim 17
Dependent Claim
31 words
The method as defined by claim 9 wherein the output of said RF power amplifier is connected through attenuation means to said receiver before said step of generating an RF signal.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1995-08-18 | 1996-02-17 | 1996-08-18 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1999-08-18 | 2000-02-17 | 2000-08-18 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2003-08-18 | 2004-02-17 | 2004-08-18 | $7700.00 | Window Closed / Lapsed |