Method of measuring the static magnetic field distribution in an NMR inspection system

Claim 1

A method of measuring a static magnetic field distribution in a field of view of a nuclear magnetic resonance (NMR) inspection system which comprises magnetic field generating means for producing a static magnetic field, gradient magnetic fields and a high-frequency magnetic field, signal detection means for sensing nuclear magnetic resonance signals from an inspection sample, a computer for processing output signals from said signal detection means and output means for providing a computational result of said computer, said method comprising the steps of: (a) exciting nuclear spins in a sample which is disposed in said field of view by applying a 90°-pulse high frequency magnetic field; (b) applying a first gradient magnetic field pulse along a first direction; (c) applying a 180°-pulse high frequency magnetic field; (d) applying second and third gradient magnetic field pulses along at least a second direction perpendicular to said first direction so that a spin echo is formed during said third gradient magnetic field pulse and that a time interval t 1 from the center of said 90°-pulse high frequency magnetic field to the center of said 180°-pulse high frequency magnetic field is made different by a time difference t 0 from a time interval t 2 from the center of said 180°-pulse high frequency magnetic field to a peak of said spin echo; (e) sampling the signal from said signal detection means during said third gradient magnetic field pulse to obtain data of said spin echo; (f) repeating the above-described steps (a) to (e) and in each repetition of time changing the amplitude of said first gradient magnetic field pulse while maintaining the amplitude of said second and third gradient magnetic field pulses unchanged; (g) deriving image data through 2-dimensional Fourier transformation of data obtained by the repetition of the steps; and (h) calculating a static magnetic field distribution from a phase shift of said image data caused by said time difference t 0 .

Claim 2

A method of measuring a static magnetic field distribution in a field of view of a nuclear magnetic resonance (NMR) inspection system which comprises magnetic field generating means for producing a static magnetic field, gradient magnetic fields and a high-frequency magnetic field, signal detection means for sensing nuclear magnetic resonance signals from an inspection sample, a computer for processing output signals from said signal detection means and output means for providing a computational result of said computer, said method comprising the steps of: (a) exciting nuclear spins in a sample which is disposed in said field of view by applying a 90°-pulse high frequency magnetic field; (b) applying a first gradient magnetic field pulse along a first direction; (c) applying a 180°-pulse high frequency magnetic field; (d) applying second and third gradient magnetic field pulses along at least a second direction perpendicular to said first direction so that a spin echo is formed during said third gradient magnetic field pulse and that a time interval t 1 from the center of said 90°-pulse high frequency magnetic field to the center of said 180°-pulse high frequency magnetic field is made different by a time difference t 0 from a time interval t 2 from the center of said 180°-pulse high frequency magnetic field to a peak of said spin echo; (e) sampling the signal from said signal detection means during said third gradient magnetic field pulse to obtain data of said spin echo; (f) repeating the above-described steps (a) to (e) and in each repetition of time changing the amplitude of said first gradient magnetic field pulse while maintaining the amplitude of said second and third gradient magnetic field pulses unchanged; (g) deriving image data through 2-dimensional Fourier transformation of data obtained by the repetition of the steps; and (h) calculating a static magnetic field distribution from a phase shift of said image data caused by said time difference t 0 .