Method for the phase correction of MR inversion recovery images
First Claim
1. In a method of determining a nuclear magnetization distribution in a region of a body which is situated in a steady, uniform magnetic field, generating spin resonance signals in the region of the body in first and second sequences by high-frequency excitation pulses, measuring said signals in the presence of magnetic field gradients superposed on the uniform magnetic field, the excitation pulse in one sequence being preceded by a high-frequency inversion pulse which inverts the nuclear magnetization, using a transformation to form a first image of complex image values from the first sequence and a second image of complex image values from the second sequence, said images representing nuclear magnetization distributions, the improvement comprising the step of determining the value of a sign function for each corresponding complex image value of the first image and the second image, each corresponding value of the sign function being determined from the phase difference between the corresponding complex image values of the first image and the second image.
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Abstract
During known MRI measurements, for example spin echo and inversion recovery measurements, phase errors occur in pixels, inter alia due to eddy currents caused by the application or interruption of magnetic field gradients during a measurement. There is proposed an inversion recovery method combined with a method where the magnetization is not inverted in advance in order to determine for each pixel the phase error in an image obtained by means of an inversion recovery method, so that inversion recovery images can be obtained which do not contain phase errors.
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10 Claims
- 1. In a method of determining a nuclear magnetization distribution in a region of a body which is situated in a steady, uniform magnetic field, generating spin resonance signals in the region of the body in first and second sequences by high-frequency excitation pulses, measuring said signals in the presence of magnetic field gradients superposed on the uniform magnetic field, the excitation pulse in one sequence being preceded by a high-frequency inversion pulse which inverts the nuclear magnetization, using a transformation to form a first image of complex image values from the first sequence and a second image of complex image values from the second sequence, said images representing nuclear magnetization distributions, the improvement comprising the step of determining the value of a sign function for each corresponding complex image value of the first image and the second image, each corresponding value of the sign function being determined from the phase difference between the corresponding complex image values of the first image and the second image.
- 7. In a method for determining a nuclear magnetic distribution in a region of a body wherein spin resonance signals are generated in the region of the body in first and second sequences and wherein transformations are used to form a first image of complex image values from the first sequence of spin resonance signals and a second image of complex image values from the second sequence of spin resonance signals, the improvement comprising determining the value of a sign function for each corresponding complex image value of the first image and the second image, each corresponding value of the sign function being determined from the phase difference between the corresponding complex image values of the first image and the second image.
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