US5233991A
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Method and apparatus for estimating oxygen saturation of blood using magnetic resonance
Assignee: Leland Stanford Junior University
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Filing: 1991-08-08
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Granted: 1993-08-10
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Expires: 2011-08-08
Abstract
Abstract The oxygen saturation of blood is determined by obtaining spin-spin relaxation time (T2b) of the fluid using magnetic resonance imaging techniques. A simplified model relates oxygen saturation of blood to measured spin-spin relaxation time. A pulse sequence is given for in vivo estimation of T2b including a plurality of 180 DEG refocusing RF signals which are equally spaced in time. The last refocusing pulse is slice selective. Fat signal is suppressed by initially using a short inversion recovery sequence followed by a frequency selective 90 DEG pulse that excites only water protons.
Inventors
- 👤 Graham A. Wright
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-31 21:21
CPC Classifications
A; A61; A61B; A61B5/00; A61B5/145; A61B5/05; A61B5/055; G; G01; G01R; G01R33/00; G01R33/20; G01R33/44; G01R33/46; G01R33/465
Claims Analysis
Total Claims: 17
Claim 1
Independent Claim
149 words
A method of determining a characteristic of a moving fluid based on measurements of spin-spin relaxation time of the fluid comprising the steps of a) placing said moving fluid in a static magnetic field (B 0 ) along a first axis (z), b) applying an excitation RF signal to said moving fluid thereby establishing transverse nuclei spins, c) applying a plurality (0,1,2, . . . N) of 180° refocusing pulses to said moving fluid with said pulses being equally spaced, the number and spacing of said pulses determining echo time, d) applying after said plurality of 180° refocusing pulses a slice selective pulse (that is slice selective), the time between said slice selective pulse and an echo being constant, e) detecting signals from said nuclei spins, f) determining the spin-spin relaxation time of said nuclei spins from said signals, and g) determining said characteristic from said spin-spin relaxation time.
Claim 2
Independent Claim
149 words
A method of determining a characteristic of a moving fluid based on measurements of spin-spin relaxation time of the fluid comprising the steps of a) placing said moving fluid in a static magnetic field (B 0 ) along a first axis (z), b) applying an excitation RF signal to said moving fluid thereby establishing transverse nuclei spins, c) applying a plurality (0,1,2, . . . N) of 180° refocusing pulses to said moving fluid with said pulses being equally spaced, the number and spacing of said pulses determining echo time, d) applying after said plurality of 180° refocusing pulses a slice selective pulse (that is slice selective), the time between said slice selective pulse and an echo being constant, e) detecting signals from said nuclei spins, f) determining the spin-spin relaxation time of said nuclei spins from said signals, and g) determining said characteristic from said spin-spin relaxation time.
Claim 3
Dependent Claim
22 words
The method as defined in claim 1 wherein said moving fluid is blood and said characteristic is oxygen saturation of the blood.
Claim 4
Dependent Claim
69 words
The method as defined in claim 2 wherein the relationship of measured spin-spin relaxation time, T2 b , to calculated oxygen saturation of blood, %HbO 2 , is given by: ##EQU3## where T2 0 is the spin-spin relaxation time of fully oxygenated blood, τ 180 is time between successive pulses in said plurality of 180° refocusing pulses, ω 0 is the resonant nuclei frequency, and K is a constant.
Claim 5
Dependent Claim
47 words
The method as defined by claim 3 wherein step b) includes at least one of i) applying an inversion pulse, then applying a magnetic gradient (Gz) along said first axis, and ii) applying a frequency selective 90° pulse that excites water protons, thereby suppressing signals from fat.
Claim 6
Dependent Claim
28 words
The method as defined by claim 3 wherein step c) includes applying a pair of spoiling gradients with said last pulse to dephase any out of section signal.
Claim 7
Dependent Claim
20 words
The method as defined by claim 3 wherein step d) includes spatially encoding the signals using two-dimensional Fourier transform encoding.
Claim 8
Dependent Claim
24 words
The method as defined by claim 3 wherein step d) includes spatially encoding the signals using spiral gradients in k space during data acquisition.
Claim 9
Dependent Claim
42 words
The method as defined by claim 1 wherein step b) includes applying an inversion pulse, then applying a magnetic gradient (Gz) along said first axis, and then applying a frequency selective 90° pulse that excites water protons, thereby suppressing signals from fat.
Claim 10
Dependent Claim
28 words
The method as defined in claim 1 wherein step c) includes applying a pair of spoiling gradients with said last pulse to dephase any out of section signal.
Claim 11
Dependent Claim
20 words
The method as defined in claim 1 wherein step d) includes spatially encoding the signals using two-dimensional Fourier transform encoding.
Claim 12
Dependent Claim
23 words
The method as defined in claim 1 wherein step d) includes spatially encoding signals using spiral gradients in k space durnig data acquisition.
Claim 13
Dependent Claim
141 words
Apparatus for determining a characteristic of a moving fluid based on measurements of spin-spin relaxation time of the fluid comprising a) means for establishing a static magnetic field (B 0 ) through said fluid along a first axis (z), b) means for applying an inversion RF signal to said moving fluid thereby establishing transverse nuclei spins, c) means for applying a plurality of 180° refocusing pulses to said moving fluid with said pulses being equally spaced, d) means for applying a slice selective pulse after said plurality of 180° pulses, the time between said slice selective pulse and an echo being constant, e) means for detecting free induction decay signals from said nuclei spins, f) means for determining the spin-spin relaxation times of said nuclei spins from said signals, and g) means for determining said characteristic from said spin-spin relaxation time.
Claim 14
Dependent Claim
141 words
Apparatus for determining a characteristic of a moving fluid based on measurements of spin-spin relaxation time of the fluid comprising a) means for establishing a static magnetic field (B 0 ) through said fluid along a first axis (z), b) means for applying an inversion RF signal to said moving fluid thereby establishing transverse nuclei spins, c) means for applying a plurality of 180° refocusing pulses to said moving fluid with said pulses being equally spaced, d) means for applying a slice selective pulse after said plurality of 180° pulses, the time between said slice selective pulse and an echo being constant, e) means for detecting free induction decay signals from said nuclei spins, f) means for determining the spin-spin relaxation times of said nuclei spins from said signals, and g) means for determining said characteristic from said spin-spin relaxation time.
Claim 15
Dependent Claim
81 words
Apparatus as defined by claim 12 wherein said moving fluid is blood and said characteristic is oxygen saturation of blood, the relationship of measured spin-spin relaxation time, T2 b , to calculated oxygen saturation of blood, %HbO 2 , is given by: ##EQU4## where T2 0 is the spin-spin relaxation time of fully oxygenated blood, τ 180 is time between successive pulses in said plurality of 180° refocusing pulses, ω 0 is the resonant nuclei frequency, and K is a constant.
Claim 16
Dependent Claim
27 words
Apparatus as defined by claim 13 wherein said means for detecting free induction decay signals includes means for spatially encoding the signals using two-dimensional Fourier transform encoding.
Claim 17
Dependent Claim
27 words
Apparatus as defined by claim 14 wherein said means for detecting free induction decay signals includes means for applying spiral gradients in k space during data acquisition.
References Cited (Backward Citations)
US4775522A
Cited
US4984574A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
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| 3.5 Years (Year 4) | 1996-08-09 | 1997-02-08 | 1997-08-10 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2000-08-09 | 2001-02-08 | 2001-08-10 | $3760.00 | Window Closed / Lapsed |
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