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US6307368B1
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Linear combination steady-state free precession MRI
Assignee: Leland Stanford Junior University
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Filing: 1999-05-14
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Granted: 2001-10-23
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Expires: 2019-05-14
Abstract
Abstract A fast, spectrally-selective steady-state free precession (SSFP) imaging method is presented. Combining k-space data from SSFP sequences with certain phase schedules of radiofrequency excitation pulses permits manipulation of the spectral selectivity of the image. For example, lipid and water can be rapidly resolved. The contrast of each image depends on both T1 and T2, and the relative contribution of the two relaxation mechanisms to image contrast can be controlled by adjusting the flip angle. Several applications of the technique are presented, including fast musculoskeletal imaging, brain imaging, and angiography. The technique is referred to herein as linear combination steady-state free precession (LCSSFP) and fluctuating equilibrium magnetic resonance (FEMR).
Inventors
- 👤 Shreyas S. Vasanawala
- 👤 John M. Pauly
- 👤 Dwight G. Nishimura
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-07 23:15
CPC Classifications
G; G01; G01R; G01R33/00; G01R33/20; G01R33/44; G01R33/48; G01R33/54; G01R33/56; G01R33/561; G01R33/5613; G01R33/446
Claims Analysis
Total Claims: 45
Claim 1
Independent Claim
153 words
A method of collecting image data with selective spectral suppression comprising the steps of: a) placing an object in a magnetic field b) acquiring two or more images by: i) applying a plurality of RF excitation pulses to the object at a sequence repetition rate, the phase of said RF pulses related by a fixed phase increment, ii) applying magnetic gradients between said RF excitation pulses; iii) acquiring NMR signals during the time said magnetic gradients are applied, iv) combining the NMR signals to produce an image where said phase increment is 360*(k−1)/N for the kth image out of a set of N images, c) computing the N point discrete Fourier transform for each pixel in the set of images to form Fourier transformed images, d) applying complex weighting to said Fourier transformed images, e) combining at least two of said weighted Fourier transformed images to produce an image with selective spectral suppression.
Claim 2
Independent Claim
153 words
A method of collecting image data with selective spectral suppression comprising the steps of: a) placing an object in a magnetic field b) acquiring two or more images by: i) applying a plurality of RF excitation pulses to the object at a sequence repetition rate, the phase of said RF pulses related by a fixed phase increment, ii) applying magnetic gradients between said RF excitation pulses; iii) acquiring NMR signals during the time said magnetic gradients are applied, iv) combining the NMR signals to produce an image where said phase increment is 360*(k−1)/N for the kth image out of a set of N images, c) computing the N point discrete Fourier transform for each pixel in the set of images to form Fourier transformed images, d) applying complex weighting to said Fourier transformed images, e) combining at least two of said weighted Fourier transformed images to produce an image with selective spectral suppression.
Claim 3
Dependent Claim
21 words
The method as defined by claim 1 , where the integral of the magnetic gradients is zero between the RF pulses.
Claim 4
Dependent Claim
28 words
The method as defined by claim 2 , where step b)i) includes applying magnetic gradients during the RF pulses, whereby the NMR signals are restricted to a slice.
Claim 5
Dependent Claim
16 words
The method as defined by claim 3 , where step d) suppresses signals from lipid spins.
Claim 6
Dependent Claim
11 words
The method of claim 3 , where two images are collected.
Claim 7
Dependent Claim
19 words
The method as defined in claim 5 , where said RF phase increments are 0 degrees and 180 degrees.
Claim 8
Dependent Claim
16 words
The method as defined in claim 6 , where said complex weighting are 1 and sqrt(−1).
Claim 9
Dependent Claim
13 words
The method as defined in claim 3 , where four images are collected.
Claim 10
Dependent Claim
19 words
The method as defined in claim 8 , where said phase increments are 0, 90, 180, and 270 degrees.
Claim 11
Independent Claim
90 words
A method of collecting image data with selective spectral suppression comprising the steps of: a) placing an object in a magnetic field, b) repeatedly applying a sequence of two or more RF excitation pulses to the object at a repetition rate, whereby a repeated sequence of two or more substantially different spectrally selective steady state magnetizations are established, c) applying magnetic gradients between said RF pulses, d) acquiring NMR signals during the time said magnetic gradients are applied, e) combining said signals to produce an image with selective spectral suppression.
Claim 12
Independent Claim
90 words
A method of collecting image data with selective spectral suppression comprising the steps of: a) placing an object in a magnetic field, b) repeatedly applying a sequence of two or more RF excitation pulses to the object at a repetition rate, whereby a repeated sequence of two or more substantially different spectrally selective steady state magnetizations are established, c) applying magnetic gradients between said RF pulses, d) acquiring NMR signals during the time said magnetic gradients are applied, e) combining said signals to produce an image with selective spectral suppression.
Claim 13
Dependent Claim
21 words
The method as defined by claim 10 , where the integral of the magnetic gradients is zero between the RF pulses.
Claim 14
Dependent Claim
27 words
The method as defined in claim 11 , where a magnetic gradient is applied during said RF pulses, whereby the NMR signals are restricted to a slice.
Claim 15
Dependent Claim
17 words
The method as defined in claim 12 , where said RF excitation pulses alternate between two phases.
Claim 16
Dependent Claim
17 words
The method as defined in claim 13 , where said RF phases are 0 and 90 degrees.
Claim 17
Dependent Claim
20 words
The method as defined in claim 14 , where the RF repetition rate is half of the water-fat difference frequency.
Claim 18
Dependent Claim
28 words
The method as in claim 15 , where one steady state signal is primarily from water spins, and the second steady state signal is primarily from lipid spins.
Claim 19
Independent Claim
138 words
A method of collecting image data with selective spectral suppression using steady-state free precession magnetic resonance imaging comprising the steps of: a) placing an object in a magnetic field, b) applying time varying magnetic gradients along three axes to the object, c) applying a plurality of RF excitation pulses to the object at a sequence repetition rate, the phase of the RF pulses being related by a fixed phase increment and the repetition rate being selected to suppress nuclei spins within a selected spectral range, d) obtaining multiple datasets after applying multiple RF excitation pulses, e) computing discrete Fourier transformed data sets for each pixel in the multiple data sets, f) applying complex weighting to the Fourier transformed data sets, and g) combining the weighted Fourier transformed data sets to produce a data set with selective spectral suppression.
Claim 20
Independent Claim
138 words
A method of collecting image data with selective spectral suppression using steady-state free precession magnetic resonance imaging comprising the steps of: a) placing an object in a magnetic field, b) applying time varying magnetic gradients along three axes to the object, c) applying a plurality of RF excitation pulses to the object at a sequence repetition rate, the phase of the RF pulses being related by a fixed phase increment and the repetition rate being selected to suppress nuclei spins within a selected spectral range, d) obtaining multiple datasets after applying multiple RF excitation pulses, e) computing discrete Fourier transformed data sets for each pixel in the multiple data sets, f) applying complex weighting to the Fourier transformed data sets, and g) combining the weighted Fourier transformed data sets to produce a data set with selective spectral suppression.
Claim 21
Dependent Claim
24 words
The method as defined by claim 17 wherein step d) includes spin rephasing after obtaining each acquisition using refocusing gradients along the three axes.
Claim 22
Dependent Claim
24 words
The method as defined by claim 18 wherein flip angles for the RF excitation pulses are chosen to obtain a desired passband and stopband.
Claim 23
Dependent Claim
27 words
The method as defined by claim 19 wherein large flip angles yield large passbands and narrow stopbands, and smaller flip angles produce narrower passbands and wider stopbands.
Claim 24
Dependent Claim
13 words
The method as defined by claim 20 wherein step c) suppresses lipid spins.
Claim 25
Dependent Claim
31 words
The method as defined by claim 18 wherein phase of the plurality of RF excitation pulses is varied and the multiple datasets are selectively combined to obtain a desired spectral profile.
Claim 26
Dependent Claim
19 words
The method as defined by claim 22 wherein the plurality of RF excitation pulses are varied between two phases.
Claim 27
Dependent Claim
22 words
The method as defined by claim 23 wherein datasets are obtained with two sequences with RF excitation phase of 0-0 and 0-180.
Claim 28
Dependent Claim
19 words
The method as defined by claim 22 wherein the plurality of RF excitation pulses are varied between four phases.
Claim 29
Dependent Claim
25 words
The method as defined by claim 25 wherein datasets are obtained with the four phases with RF excitation phase being 0-0-0-0, 0-90-180-270, 0-180-0-180, and 0-270-180-90.
Claim 30
Dependent Claim
24 words
The method as defined by claim 22 wherein step d) includes spin rephasing using refocusing gradients along the three axes after obtaining each acquisition.
Claim 31
Dependent Claim
24 words
The method as defined by claim 27 wherein flip angles of the RF excitation pulses are chosen to obtain a desired passband and stopband.
Claim 32
Dependent Claim
27 words
The method as defined by claim 28 wherein larger flip angles yield larger passbands and narrower stopbands, and smaller flip angles produce narrower passbands and wider stopbands.
Claim 33
Dependent Claim
24 words
The method as defined by claim 17 wherein phase of the RF excitation pulses is varied for parsing of data to form multiple images.
Claim 34
Dependent Claim
135 words
Magnetic resonance imaging apparatus for collecting image data with selective spectral suppression using steady-state free precession magnetic resonance imaging comprising a) means for establishing a magnetic field through an object to be imaged, b) means for applying magnetic gradients along three axes through the object, c) means for applying a plurality of RF excitation pulses to the object at a sequence repetition rate, the repetition rate being selected to suppress nuclei spin within a spectral range, d) means for obtaining multiple datasets after applying multiple RF excitation pulses, and e) means for computing discrete Fourier transformed data sets for each pixel in the multiple data sets, f) applying complex weighting to the Fourier transformed data sets, and g) means for combining weighted Fourier transformed data sets to produce a data set with selective spectral suppression.
Claim 35
Dependent Claim
135 words
Magnetic resonance imaging apparatus for collecting image data with selective spectral suppression using steady-state free precession magnetic resonance imaging comprising a) means for establishing a magnetic field through an object to be imaged, b) means for applying magnetic gradients along three axes through the object, c) means for applying a plurality of RF excitation pulses to the object at a sequence repetition rate, the repetition rate being selected to suppress nuclei spin within a spectral range, d) means for obtaining multiple datasets after applying multiple RF excitation pulses, and e) means for computing discrete Fourier transformed data sets for each pixel in the multiple data sets, f) applying complex weighting to the Fourier transformed data sets, and g) means for combining weighted Fourier transformed data sets to produce a data set with selective spectral suppression.
Claim 36
Dependent Claim
30 words
Apparatus as defined by claim 31 wherein the means for applying magnetic gradients includes means for applying spin rephasing using refocusing gradients along the three axes after obtaining each dataset.
Claim 37
Dependent Claim
35 words
Apparatus as defined by claim 32 wherein the means for applying a plurality of RF excitation pulses produce flip angles for the RF excitation pulses which are chosen to obtain a desired passband and stopband.
Claim 38
Dependent Claim
16 words
Apparatus as defined by claim 33 wherein the flip angles are chosen to suppress lipid spins.
Claim 39
Dependent Claim
37 words
Apparatus as defined by claim 31 wherein the means for applying a plurality of RF excitation pulses varies phase of the RF excitation pulses and the multiple datasets are selectively combined to obtain a desired spectral profile.
Claim 40
Dependent Claim
13 words
Apparatus as defined by claim 35 wherein the phases vary between two phases.
Claim 41
Dependent Claim
32 words
Apparatus as defined by claim 35 wherein phases are varied between four phases (0, 90, 180, 270) and the multiple datasets are selectively combined for the phases 0-0-0-0, 0-90-180-270, 0-180-0-180, and 0-270-180-90.
Claim 42
Dependent Claim
19 words
The method as defined by claim 1 wherein step d) includes use of homodyne detection of magnetic resonant signals.
Claim 43
Dependent Claim
18 words
The method as defined by claim 1 wherein step a) includes applying a contrast agent to the object.
Claim 44
Dependent Claim
25 words
The method as defined by claim 1 wherein step e) includes setting all bright pixels in one image (fat) to zero in another image (water).
Claim 45
Dependent Claim
19 words
The method as defined by claim 1 wherein step e) includes subtracting one image (fat) from another image (water).
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) | 2004-10-22 | 2005-04-23 | 2005-10-23 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2008-10-22 | 2009-04-23 | 2009-10-23 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2012-10-22 | 2013-04-23 | 2013-10-23 | $7700.00 | Window Closed / Lapsed |