EP0745865A1
Expired / Lapsed
EP
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A magnetic resonance imaging method and apparatus
Assignee: Philips Nuclear Medicine Inc
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Filing: 1996-05-13
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Granted: —
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Expires: 2016-05-13
Abstract
Abstract Magnetic resonance is excited (50) in first and second species dipoles of a subject in a temporally constant magnetic field. The resonance is refocused (52) to generate a spin echo (54) centered at a time when the first and second species resonance signals are in-phase. Gradients echoes (64, 68) are generated, centered at a time (2n+1)π/δω before and after the spin echo, where δω is a difference between the first and second species resonance frequencies. In this manner, the first and second species signals are 180° out-of-phase in the gradient echoes. The resonance is refocused (82) one or more times to generate additional spin and gradient echoes with different phase encodings (78) . The sequence is repeated with yet more phase encodings, and magnetic resonance signals from the spin echo and the two gradient echoes are reconstructed (86) into a spin echo image (s 0 ) and a pair of gradient echo images (s +1 , s -1 ) . A phase map is generated (90) from the spin and gradient echo images. One of the gradient echo images is corrected (116) with the phase map. The phase corrected gradient image is additively combined (118) with the spin echo image to generate a first species image (112) and is subtractively combined (120) to generate a second species image (114) .
Inventors
- 👤 Rao P. Gullapalli
- 👤 Liu Haiying
- 👤 Mark J. Loncar
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-07 16:23
CPC Classifications
G; G01; G01R; G01R33/00; G01R33/20; G01R33/44; G01R33/48; G01R33/4828
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
110 words
A magnetic resonance imaging method in which a resonance excitation pulse and a resonance refocusing pulse are applied to generate a spin echo (54) and in which read gradients are reversed in order to induce first and second gradient echoes (64, 68) in association with each spin echo, characterized by: inducing the spin echo (54) when resonance signals of a first and second species are substantially in-phase; and, generating the gradient echoes (64, 68) at a time when the resonance signals of the first and second species are substantially 180° out-of-phase such that an in-phase spin echo and out-of-phase gradient echoes are generated in each repetition of the imaging sequence.
Claim 2
Dependent Claim
124 words
A method as claimed in claim 1, including: reconstructing a spin echo image from the spin echo signals from a plurality of repetitions of the imaging sequence; generating first and second gradient echo images from the gradient echo signals of the plurality of repetitions of the imaging sequence; generating a phase correction map from the spin echo image and the first and second gradient echo images; correcting phase error in the first gradient echo image in accordance with the phase map; additively combining the spin echo image with the phase corrected first gradient echo image to generate a first species image (112); and subtractively combining the spin echo image with the phase corrected first gradient echo image to generate a second species image (114).
Claim 3
Dependent Claim
52 words
A method as claimed in claim 2, further including: generating the first gradient echo (64) a time Π/δω before the spin echo, where δω is a difference in the resonance frequencies of the first and second species; and, generating the second gradient echo (68) at a time Π/δω after the spin echo.
Claim 4
Dependent Claim
77 words
A method as claimed in claim 3, further including: generating the spin echo (54) at a time when resonance signals of the first species, second species, and a third species are all in-phase; generating a third gradient echo (130) at a time Π/δω' after the spin echo, where δω' is a difference in the resonance frequencies between the first and third species; and generating a fourth gradient echo (132) at a time Π/δω' before the spin echo.
Claim 5
Independent Claim
24 words
A method as claimed in any of the preceding claims, wherein the first species (112) is water and the second species (114) is fat.
Claim 6
Independent Claim
71 words
A method as claimed in any of the preceding claims, further including: applying an additional refocusing RF pulse after the spin echo and the first and second gradient echoes to induce a second spin echo at a time when the first and second species are again in-phase; and, generating a pair of additional gradient echoes after the second refocusing pulse at times when the first and second species are 180° out-of-phase.
Claim 7
Independent Claim
31 words
A method as claimed in any of the preceding claims, further including phase encoding the spin and gradient echoes with a common phase encoding in each of a plurality of repetitions.
Claim 8
Dependent Claim
202 words
A magnetic resonance imaging apparatus which includes a primary magnet (12) for generating a temporally constant magnetic field, a gradient magnetic field coil (22) for generating magnetic field gradients across an imaging region, one or more radio frequency coils (26) for inducing and refocusing magnetic resonance of dipoles of first and second species within the imaging region and for receiving magnetic resonance signals from the resonating first and second species dipoles in the examination region, the first and second species dipoles having resonance frequencies which differ by a frequency difference δω, characterized by: a timing and control circuit (40, 42) for controlling the radio frequency and gradient coils to (1) excite magnetic resonance, (2) refocus the magnetic resonance to induce a spin echo (54), and (3) induce gradient echoes (64, 68) centered at times nΠ/δω before and after a center of the spin echo, where n is an odd integer; a reconstruction processor (86) for (1) reconstructing magnetic resonance signals from the spin echo into a spin echo image, (2) reconstructing magnetic resonance signals from the first gradient echo into a first gradient echo image, and (3) reconstructing magnetic resonance signals from the second gradient echo into a second gradient echo image.
Claim 9
Dependent Claim
110 words
A magnetic resonance imaging apparatus as claimed in claim 8, further including: a phase map generator (90) which generates a phase correction map from the spin echo image and the first and second gradient echo images; a circuit (110, 116) which corrects one of the gradient echo images with the phase map to generate a phase map corrected gradient echo image; an image adder (118) which adds the spin echo and the phase corrected gradient echo images to generate a first species dipole image (112); an image subtractor (120) which subtractively combines the spin echo and the phase corrected gradient echo images to generate a second species dipole image (114).
References Cited (Backward Citations)
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