Magnetic resonance tomography method with screening of signals from tissues with long transverse relaxation times
First Claim
1. A method for operating a nuclear magnetic resonance tomography apparatus for examining first tissue in an examination subject having a first T2 time, the subject also containing tissue having a second T2 time which is longer than said first T2 time, said method comprising the steps of:
- exciting nuclear spins in each of said first and second tissues in said subject, beginning at an excitation time, under transverse magnetization which decays with said first and second T2 time constants, obtaining a first group and a second group of locus-encoded nuclear magnetic resonance signals from said subject;
obtaining said first group of nuclear magnetic resonance signals shortly after said excitation time;
obtaining said second group of nuclear magnetic resonance signals after said first group in a time interval following said excitation time at which said second tissue having said second time constant supplies a predominant signal contribution to the nuclear magnetic resonance signals; and
reconstructing an image of said examination subject containing said first and second tissues on the basis of differences in the respective content of said first and second groups of locus-encoded nuclear magnetic resonance signals having identical locus encoding.
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Abstract
In a nuclear magnetic resonance tomography apparatus and a method in the form of a pulse sequence for operating the apparatus, after an excitation of spins in a subject, two groups of nuclear magnetic resonance signals are obtained in two time intervals at different chronological spacings from the excitation time. An image is obtained on the basis of the signal differences of nuclear magnetic resonance signals of the first and second groups with corresponding locus-encoding. Signal contributions from tissues with longer T2 relaxation time can thereby be screened out.
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Citations
10 Claims
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1. A method for operating a nuclear magnetic resonance tomography apparatus for examining first tissue in an examination subject having a first T2 time, the subject also containing tissue having a second T2 time which is longer than said first T2 time, said method comprising the steps of:
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exciting nuclear spins in each of said first and second tissues in said subject, beginning at an excitation time, under transverse magnetization which decays with said first and second T2 time constants, obtaining a first group and a second group of locus-encoded nuclear magnetic resonance signals from said subject; obtaining said first group of nuclear magnetic resonance signals shortly after said excitation time; obtaining said second group of nuclear magnetic resonance signals after said first group in a time interval following said excitation time at which said second tissue having said second time constant supplies a predominant signal contribution to the nuclear magnetic resonance signals; and reconstructing an image of said examination subject containing said first and second tissues on the basis of differences in the respective content of said first and second groups of locus-encoded nuclear magnetic resonance signals having identical locus encoding. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A nuclear magnetic resonance tomography apparatus for examining first tissue in an examination subject having a first T2 time, said subject also containing second tissue having a second T2 time which is longer than said first T2 time, said apparatus comprising:
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transmission means for emitting a plurality of 90°
radio-frequency excitation pulses for exciting nuclear spins in said examination subject, and for subsequently emitting a plurality of 180°
refocusing radio-frequency pulses;reception means for receiving a first group of nuclear magnetic resonance signals at a short chronological distance from a selected 90°
radio-frequency pulse and for receiving a second group of nuclear magnetic resonance signals at a larger chronological distance from said selected 90°
radio-frequency pulse;a first memory for storing said first group of nuclear magnetic resonance signals and a second memory for said second group of nuclear magnetic resonance signals; subtraction means for subtracting corresponding nuclear magnetic resonance signals in said first and second groups respectively stored in said first and second memories to obtain a difference; and image reconstruction means for reconstructing an image of said subject including said first and second tissues from said difference.
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Specification