US5280245A
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Magnetic resonance apparatus employing delayed self-refocusing RF excitation
Assignee: Leland Stanford Junior University
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Filing: 1992-07-27
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Granted: 1994-01-18
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Expires: 2012-07-27
Abstract
Abstract MRI Apparatus for obtaining a spin-echo signal applies a self-refocusing RF pulse with variable delay in the spin-echo signals following application of the RF pulse. The RF pulse is designed using the Shinnar-LeRoux algorithm B 1 (t)=SLR -1 {A n (z), B n (z) } with A n '(z) substituted for A n (z). A n '(z) is slightly non-minimum phase and equals P(z) A n (z) where P(z) is a unit amplitude phase function chosen to compensate the phase of B n (z). The RF pulse can be designed for a specific delay, a specific power constraint, and small tip angle.
Inventors
- 👤 John M. Pauly
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-07 10:50
CPC Classifications
G; G01; G01R; G01R33/00; G01R33/20; G01R33/44; G01R33/446
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
108 words
A method of exciting a body with RF excitation in MRI apparatus with a self-refocusing spin echo and variable delay following the RF excitation comprising the steps of: (a) placing said body in a magnetic field (B O ), (b) applying an RF excitation pulse, B 1 (t), to said body, said excitation pulse being defined as B.sub.1 (t)=SLR.sup.-1 {P(z) A.sub.n (z), B.sub.n (z)} where SLR is the Shinnar-LeRoux algorithm B n (z) is a polynomial defining an FIR filter A n (z) is a minimum phase polynomial consistent with B n (z) P(z) is a unit amplitude phase function which compensates the phase of B n (z).
Claim 2
Independent Claim
108 words
A method of exciting a body with RF excitation in MRI apparatus with a self-refocusing spin echo and variable delay following the RF excitation comprising the steps of: (a) placing said body in a magnetic field (B O ), (b) applying an RF excitation pulse, B 1 (t), to said body, said excitation pulse being defined as B.sub.1 (t)=SLR.sup.-1 {P(z) A.sub.n (z), B.sub.n (z)} where SLR is the Shinnar-LeRoux algorithm B n (z) is a polynomial defining an FIR filter A n (z) is a minimum phase polynomial consistent with B n (z) P(z) is a unit amplitude phase function which compensates the phase of B n (z).
Claim 3
Dependent Claim
35 words
The method as defined by claim 1 wherein ##EQU3## where Z o =re i φ, and r,Φ are parameters that define locations of poles and zeros of the all-pass filter stage defined by the equation.
Claim 4
Dependent Claim
36 words
The method as defined by claim 1 wherein said excitation pulse has minimum SAR, where SAR is proportional to (1-a o ) and a o is the zero order coefficient of the A n (z) polynomial.
Claim 5
Dependent Claim
20 words
The method as defined by claim 1 wherein B n (z) is a polynomial defining a minimum phase FIR filter.
Claim 6
Dependent Claim
22 words
The method as defined by claim 1 wherein B n (z) is scaled to produce a tip angle of less than 90°.
Claim 7
Dependent Claim
22 words
The method as defined by claim 1 wherein B n (z) is scaled to produce a tip angle of greater than 90°.
Claim 8
Dependent Claim
108 words
Apparatus for obtaining MRI signals from a body comprising: (a) means for establishing a magnetic field (B O ) through said body, (b) means for exciting said body with an RF excitation pulse, B 1 (t), as follows: B.sub.1 (t)=SLR.sup.-1 {P(z) A.sub.n (z), B.sub.n (z)} where SLR is the Shinnar-LeRoux algorithm B n (z) is a polynomial defining an FIR filter A n (z) is a minimum phase polynomial consistent with B n (z) P(z) is a unit amplitude phase function which compensates the phase of B n (z); and (c) means for detecting a spin echo signal from said body following application of said RF excitation pulses.
Claim 9
Dependent Claim
108 words
Apparatus for obtaining MRI signals from a body comprising: (a) means for establishing a magnetic field (B O ) through said body, (b) means for exciting said body with an RF excitation pulse, B 1 (t), as follows: B.sub.1 (t)=SLR.sup.-1 {P(z) A.sub.n (z), B.sub.n (z)} where SLR is the Shinnar-LeRoux algorithm B n (z) is a polynomial defining an FIR filter A n (z) is a minimum phase polynomial consistent with B n (z) P(z) is a unit amplitude phase function which compensates the phase of B n (z); and (c) means for detecting a spin echo signal from said body following application of said RF excitation pulses.
Claim 10
Dependent Claim
34 words
Apparatus as defined by claim 7 wherein ##EQU4## where Z o =re i φ, and r,Φ are parameters that define locations of poles and zeros of the all-pass filter stage defined by the equation.
Claim 11
Dependent Claim
35 words
Apparatus as defined by claim 7 wherein said excitation pulse has minimum SAR, where SAR is proportional to (1-a o ) and a o is the zero order coefficient of the A n (z) polynomial.
Claim 12
Dependent Claim
19 words
Apparatus as defined by claim 7 wherein B n (z) is a polynomial defining a minimum phase FIR filter.
Claim 13
Dependent Claim
21 words
Apparatus as defined by claim 7 wherein B n (z) is scaled to produce a tip angle of less than 90°.
Claim 14
Dependent Claim
21 words
Apparatus as defined by claim 7 wherein B n (z) is scaled to produce a tip angle of greater than 90°.
References Cited (Backward Citations)
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| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
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| 3.5 Years (Year 4) | 1997-01-17 | 1997-07-19 | 1998-01-18 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2001-01-17 | 2001-07-19 | 2002-01-18 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2005-01-17 | 2005-07-19 | 2006-01-18 | $7700.00 | Window Closed / Lapsed |