Nuclear magnetic resonance system

Claim 1

A method of deriving image information from an object using nuclear magnetic resonance signals comprising the steps of: (A) subjecting an object to a static magnetic field along an axis and performing a set of sequential preliminary steps including: (1) selectively exciting nuclear spins in a selected plane in the presence of a first gradient magnetic field oriented along said axis; (2) applying a second gradient magnetic field for encoding the phase of the selected spins to spatially resolve information along another axis being orthogonal to the direction of the first axis; (3) applying a preliminary third gradient magnetic field having a direction orthogonal to the direction of both the first and second axes; (4) applying a 180° RF pulse associated with the first gradient to produce echo refocusing; (5) applying an additional preliminary third gradient after said 180° RF pulse; (6) removing the additional third gradient; (7) applying a further second gradient; (8) measuring a spin-echo signal in the presence of said further second gradient; (9) repeating the sequence of steps (1)-(8) a plurality of times while applying a different value of the preliminary third gradient each time and while storing the respective measured values of the spin-echo signal; (10) selecting one of said stored values of the spin-echo signal in accordance with a predetermined criteria; (11) determining the value of said additional preliminary third gradient G' y (p)MAX which corresponds to said selected value of said spin-echo signal; and (B) subjecting the object to said static magnetic field and performing the measurement steps of: (12) selectively exciting nuclear spins in said selected plane in the presence of said first gradient magnetic field; (13) applying said second gradient magnetic field; (14) applying a third gradient magnetic field having a direction orthogonal to the direction of both the first and second axes; (15) applying a 180° RF pulse associated with the first gradient to produce echo refocusing; (16) applying an additional third gradient after said 180° RF pulse, said additional third gradient having a value G' y (p)MAX determined in said preliminary steps; (17) removing the additional third gradient; (18) applying a further second gradient; (19) measuring a spin-echo signal in the presence of said further second gradient; (20) repeating the sequence of steps (12)-(19) a plurality of times while applying a different value of the third gradient in step (14) while storing the respective measured values of the spin-echo signals; and (21) processing the stored values of the spin-echo signal for determining an NMR image of said object.

Claim 2

A method of deriving image information from an object using nuclear magnetic resonance signals comprising the steps of: (A) subjecting an object to a static magnetic field along an axis and performing a set of sequential preliminary steps including: (1) selectively exciting nuclear spins in a selected plane in the presence of a first gradient magnetic field oriented along said axis; (2) applying a second gradient magnetic field for encoding the phase of the selected spins to spatially resolve information along another axis being orthogonal to the direction of the first axis; (3) applying a preliminary third gradient magnetic field having a direction orthogonal to the direction of both the first and second axes; (4) applying a 180° RF pulse associated with the first gradient to produce echo refocusing; (5) applying an additional preliminary third gradient after said 180° RF pulse; (6) removing the additional third gradient; (7) applying a further second gradient; (8) measuring a spin-echo signal in the presence of said further second gradient; (9) repeating the sequence of steps (1)-(8) a plurality of times while applying a different value of the preliminary third gradient each time and while storing the respective measured values of the spin-echo signal; (10) selecting one of said stored values of the spin-echo signal in accordance with a predetermined criteria; (11) determining the value of said additional preliminary third gradient G' y (p)MAX which corresponds to said selected value of said spin-echo signal; and (B) subjecting the object to said static magnetic field and performing the measurement steps of: (12) selectively exciting nuclear spins in said selected plane in the presence of said first gradient magnetic field; (13) applying said second gradient magnetic field; (14) applying a third gradient magnetic field having a direction orthogonal to the direction of both the first and second axes; (15) applying a 180° RF pulse associated with the first gradient to produce echo refocusing; (16) applying an additional third gradient after said 180° RF pulse, said additional third gradient having a value G' y (p)MAX determined in said preliminary steps; (17) removing the additional third gradient; (18) applying a further second gradient; (19) measuring a spin-echo signal in the presence of said further second gradient; (20) repeating the sequence of steps (12)-(19) a plurality of times while applying a different value of the third gradient in step (14) while storing the respective measured values of the spin-echo signals; and (21) processing the stored values of the spin-echo signal for determining an NMR image of said object.

Claim 5

A method of deriving image information from an object using nuclear magnetic resonance signals comprising the steps of: (A) subjecting an object to a static magnetic field along an axis and performing a set of sequential preliminary steps including: (1) selectively exciting nuclear spins in a selected portion of said object in the presence of a first gradient magnetic field G z oriented along said axis; (2) applying a second gradient magnetic field G x along another axis being orthogonal to the direction of the first axis; (3) applying a preliminary third gradient magnetic field G y (p) having a direction orthogonal to the direction of both the first and second axes; (4) applying a 180° RF pulse; (5) applying an additional preliminary third gradient G y '(p) after said 180° RF pulse; (6) removing the additional third gradient; (7) applying a further second gradient G x ; (8) measuring a spin-echo signal in the presence of said further second gradient G x ; (9) repeating the sequence of steps (1)-(8) a plurality of times while applying a different value of the preliminary third gradient G y '(p) each time and while storing the respective measured values of the spin-echo signal; (10) selecting one of said stored values of the spin-echo signal in accordance with a predetermined criteria; (11) determining the value of said additional preliminary third gradient G' y (p)MAX which corresponds to said selected value of said spin-echo signal; and (B) subjecting the object to said static magnetic field and performing the measurement steps of: (12) selectively exciting nuclear spins in said selected portion of said object in the presence of said first gradient magnetic field G z ; (13) applying said second gradient magnetic field G x ; (14) applying a third gradient magnetic field G y (p) having a direction orthogonal to the direction of both the first and second axes; (15) applying a 180° RF pulse associated with the first gradient to produce echo refocusing; (16) applying an additional third gradient after said 180° RF pulse, said additional third gradient having a value G' y (p)MAX determined in said preliminary steps; (17) removing the additional third gradient; (18) applying a further second gradient; (19) measuring a spin-echo signal in the presence of said further second gradient G x ; (20) repeating the sequence of steps (12)-(19) a plurality of times while applying a different value of the third gradient G y (p) while storing the respective measured values of the spin-echo signals; and (21) processing the stored values of the spin-echo signal for determining an NMR image of said object.

Claim 6

A method of deriving image information from an object using nuclear magnetic resonance signals comprising the steps of: (A) subjecting an object to a static magnetic field along an axis and performing a set of sequential preliminary steps including: (1) selectively exciting nuclear spins in a selected portion of said object in the presence of a first gradient magnetic field G z oriented along said axis; (2) applying a second gradient magnetic field G x along another axis being orthogonal to the direction of the first axis; (3) applying a preliminary third gradient magnetic field G y (p) having a direction orthogonal to the direction of both the first and second axes; (4) applying a 180° RF pulse; (5) applying an additional preliminary third gradient G y '(p) after said 180° RF pulse; (6) removing the additional third gradient; (7) applying a further second gradient G x ; (8) measuring a spin-echo signal in the presence of said further second gradient G x ; (9) repeating the sequence of steps (1)-(8) a plurality of times while applying a different value of the preliminary third gradient G y '(p) each time and while storing the respective measured values of the spin-echo signal; (10) selecting one of said stored values of the spin-echo signal in accordance with a predetermined criteria; (11) determining the value of said additional preliminary third gradient G' y (p)MAX which corresponds to said selected value of said spin-echo signal; and (B) subjecting the object to said static magnetic field and performing the measurement steps of: (12) selectively exciting nuclear spins in said selected portion of said object in the presence of said first gradient magnetic field G z ; (13) applying said second gradient magnetic field G x ; (14) applying a third gradient magnetic field G y (p) having a direction orthogonal to the direction of both the first and second axes; (15) applying a 180° RF pulse associated with the first gradient to produce echo refocusing; (16) applying an additional third gradient after said 180° RF pulse, said additional third gradient having a value G' y (p)MAX determined in said preliminary steps; (17) removing the additional third gradient; (18) applying a further second gradient; (19) measuring a spin-echo signal in the presence of said further second gradient G x ; (20) repeating the sequence of steps (12)-(19) a plurality of times while applying a different value of the third gradient G y (p) while storing the respective measured values of the spin-echo signals; and (21) processing the stored values of the spin-echo signal for determining an NMR image of said object.