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US5105152A
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Magnetic resonance imaging and spectroscopy using a linear class of large tip-angle selective excitation pulses
Assignee: Leland Stanford Junior University
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Filing: 1990-03-22
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Granted: 1992-04-14
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Expires: 2010-03-22
Abstract
Abstract Disclosed is a method of generating a linear large tip-angle selective excitation pulse for magnetic resonance imaging using a linear Fourier transform analysis. An inherently refocused small tip-angle excitation pulse which produces a rotation about an axis is first defined. Then a sequence of the small tip-angle excitation pulses is produced and concatenated whereby the sum of the tip angles produced by the sequence of pulses results in a desired net large tip-angle. The small tip-angle pulses have a Hermitian RF weighted k-space trajectory. The tip angle is the Fourier transform of the weighted k-space trajectory.
Inventors
- 👤 John M. Pauly
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-07 14:26
CPC Classifications
G; G01; G01R; G01R33/00; G01R33/20; G01R33/44; G01R33/446
Claims Analysis
Total Claims: 5
Claim 1
Independent Claim
73 words
A method of generating a linear large tip-angle selective excitation pulse for magnetic resonance imaging comprising the steps of defining a small tip-angle excitation pulse which produces a rotation of nuclear spins about an axis, producing a sequence of said small tip-angle excitation pulses, and concatenating said sequence of small tip angle excitation pulses whereby the sum of the tip angles produced by said sequence of pulses produces a desired net large tip-angle.
Claim 2
Independent Claim
73 words
A method of generating a linear large tip-angle selective excitation pulse for magnetic resonance imaging comprising the steps of defining a small tip-angle excitation pulse which produces a rotation of nuclear spins about an axis, producing a sequence of said small tip-angle excitation pulses, and concatenating said sequence of small tip angle excitation pulses whereby the sum of the tip angles produced by said sequence of pulses produces a desired net large tip-angle.
Claim 3
Dependent Claim
95 words
The method as defined by claim 1 where the rotation produced by the j th small tip-angle pulse is ##EQU37## where γ is the gyromagnetic ratio, B* is the conjugate of RF field produced by said pulses, T is the duration of said pulses, the j th pulse starts at the time T j-1 and ends at time T j , and where k j ,(t) is defined as ##EQU38## where G(s) is a magnetic gradient as a function of the variable s, and the tip angle resulting from the concentration of pulses is ##EQU39##
Claim 4
Dependent Claim
73 words
The method as defined by claim 2 wherein said large tip-angle pulse is a two-dimensional spin-echo pi pulse in which the k-space trajectory and k-space weighting are ##EQU40## where A determines the area of k-space covered, n is the number of cycles in a spiral of the k-space trajectory, T is the duration of the pulse, a scales the tip angle, and b determines a slice width which is selectively excited or refocused.
Claim 5
Dependent Claim
23 words
The method as defined by claim 3 wherein the gradient and RF waveforms to produce said k-space trajectory and k-space weighting are ##EQU41##
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) | 1995-04-14 | 1995-10-14 | 1996-04-14 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1999-04-14 | 1999-10-14 | 2000-04-14 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2003-04-14 | 2003-10-14 | 2004-04-14 | $7700.00 | Window Closed / Lapsed |