EP0567194A2
Expired / Lapsed
EP
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Method and apparatus for rapid spin echo magnetic resonance imaging
Assignee: Koninklijke Philips NV
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Filing: 1993-04-21
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Granted: —
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Expires: 2013-04-21
Abstract
Abstract In a spin-echo magnetic resonance sequence a phase encoding gradient magnetic field (39) is applied after the 180° rephasing pulse (32₁). After detection of the spin-echo signal (33) the position dependent phases are compensated for by applying a further gradient magnetic field (39'), identical in size but opposite in sign. The phase difference (φ 32,1 -φ 31,1 ) between the RF-pulses (31₁,32₁) applied within a sequence is constant over the sequences. With no position dependent effects left at the end of a sequence the next sequence can be stated immediately following the earlier one. A repetition time TR substantially shorter than the spin-spin relaxation time T₂ is feasible, thereby developing a steady state of the magnetisation. A TR of 50 ms or less can be obtained, as well as strong signals for long T₂ substances and good T₂ contrast. RF spoiling by changing phases of RF-pulses in subsequent sequences can destroy the T₂ signal and provide images with pure T₁ contrast.
Inventors
- 👤 Gerrit H. c/o INT. OCTROOIBUREAU B.V. Van Yperen
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-07 21:07
CPC Classifications
G; G01; G01R; G01R33/00; G01R33/20; G01R33/44; G01R33/48; G01R33/54; G01R33/56; G01R33/561; G01R33/565
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
183 words
Method for magnetic resonance imaging of a body placed in a stationary and substantially homogeneous main magnetic field, the method comprising repeated execution of a sequence including the following steps: - application of a first RF-pulse for excitation of at least a portion of the body, - application of at least a first gradient magnetic field for phase encoding of the excited portion, - application of a second RF-pulse at a time τ after the first RF-pulse, - detection of a magnetic resonance spin-echo signal around a time 2τ after the first RF-pulse, - whereby a repetition time between first RF-pulses in subsequent sequences is shorter than a transversal relaxation time T₂ of a relevant substance of the body, characterised in that - said first gradient magnetic field is applied after the application of the second RF-pulse, and in that - a second gradient magnetic field for compensation of the phase encoding caused by the first gradient magnetic field is applied in the interval after occurrence of the magnetic resonance spin-echo signal and before application of the first RF-pulse in a next sequence.
Claim 2
Dependent Claim
53 words
Method as claimed in Claim 1, characterised in that - a selection gradient magnetic field is applied during application of the first RF-pulse for selection of a slice of the body, and in that - a third gradient magnetic field is applied during detection of the magnetic resonance spin-echo signal for frequency encoding.
Claim 3
Dependent Claim
29 words
Method as claimed in Claim 1 or 2 characterised in that phase differences between the first RF-pulse and the second RF-pulses within a sequence are equal over the sequences.
Claim 4
Dependent Claim
32 words
Method as claimed in Claim 3, characterised in that the first RF-pulses in subsequent sequences have zero phase difference and in that the second RF-pulses in subsequent sequences have zero phase difference.
Claim 5
Dependent Claim
28 words
Method as claimed in Claim 3, characterised in that the phases of the first and second RF-pulses in subsequent sequences are mutually different, thereby forming an RF-spoiling scheme.
Claim 6
Dependent Claim
29 words
Method as claimed in Claim 5, characterised in that the phases of the first and second RF-pulses are changed from one sequence to another according to a non-repetitive scheme.
Claim 7
Dependent Claim
36 words
Method as claimed in Claim 6, characterised in that the phases of the first and second RF-pulses in successive sequences differ with a linear increasing or decreasing value proportional to the rank number of the sequence.
Claim 8
Dependent Claim
26 words
Method as claimed in any of the preceding Claims, characterised in that the repetition time TR is about 50 milliseconds or less, preferably about 30 milliseconds.
Claim 9
Dependent Claim
255 words
Apparatus for magnetic resonance imaging according to a method as claimed in any of the preceding Claims, comprising means for establishing a stationary and substantially homogeneous main magnetic field, means for generating gradient magnetic fields superimposed upon the main magnetic field, means for radiating RF-pulses towards a body placed in the main magnetic field, control means for steering the generation of the gradient magnetic fields and the RF-pulses, and means for receiving and sampling magnetic resonance signals generated by sequences of RF-pulses and switched gradient magnetic fields, said control means being arranged for - applying a first radio-frequency pulse for excitation of at least a portion of the body, - applying at least a first gradient magnetic field for phase encoding of the excited portion, - applying a second RF-pulse at a time τ after the first RF-pulse, and - detecting a magnetic resonance spin-echo signal around a time 2τ after the first RF-pulse, within a period that allows a repetition time TR between first RF-pulses in subsequent sequences to be shorter than a transversal relaxation time T₂ of a relevant substance of the body, characterised in that the control means are further arranged for - applying said first gradient magnetic field after the application of the second RF-pulse, and - applying a second gradient magnetic field in the interval after occurrence of the magnetic resonance spin-echo signal and before application of the first RF-pulse in a next sequence, the second gradient magnetic field compensating the phase encoding caused by the first gradient magnetic field.
References Cited (Backward Citations)
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