Magnetic resonance imaging

Claim 1

A method of generating a magnetic resonance image comprising the application of a radio frequency resonance excitation pulse (62), a slice select gradient pulse (60), and a read gradient pulse (70) characterised in that said method further comprises: applying, in the direction of at least one of the slice select and read gradients, at least one additional motion desensitization gradient pulse (80) between the resonance excitation pulse (62) and the read gradient pulse (70), the amplitude and duration of the added motion desensitization pulse or pulses (80) being selected such that the sum of at least one of the zeroth, first, second, and third moment in time of the phase of the gradient pulses along the selected one of the slice select and read gradient directions is set equal to a preselected value.

Claim 2

A method of generating a magnetic resonance image comprising the application of a radio frequency resonance excitation pulse (62), a slice select gradient pulse (60), and a read gradient pulse (70) characterised in that said method further comprises: applying, in the direction of at least one of the slice select and read gradients, at least one additional motion desensitization gradient pulse (80) between the resonance excitation pulse (62) and the read gradient pulse (70), the amplitude and duration of the added motion desensitization pulse or pulses (80) being selected such that the sum of at least one of the zeroth, first, second, and third moment in time of the phase of the gradient pulses along the selected one of the slice select and read gradient directions is set equal to a preselected value.

Claim 10

A method according to any one of the preceding claims wherein the image generating sequence includes one of spin echo, an inversion recovery, a multi-echo, and a gradient echo imaging sequence.

Claim 11

A method according to any one of the preceding claims further including determining the duration and amplitudes of the motion desensitization gradient pulses by: selecting beginning and ending times for each gradient pulse, the number of motion desensitization gradient pulses being the same as the number of moments which are to be set to preselected values; along each of the slice select and read directions, setting the corresponding each term of the power series expansion: to one of the preselected values and solving for the amplitudes of the motion desensitization gradients where γ is the gyromagnetic ratio, G(t) is the gradient at time t, and x o (j) is the jth differential of position x at time 0.

Claim 14

A method of generating magnetic resonance images comprising: generating a generally uniform magnetic field through an image region in which a subject to be imaged is positioned; and applying a plurality of pulse sequences to the image region, each pulse sequence including the concurrent application of a first slice select gradient (60) in a slice select direction and a resonance excitation RF pulse (62), the concurrent application of a second slice select gradient pulse (64) and an RF inversion pulse (66) to invert the spin magnetization of resonating nuclei, application of a read gradient pulse (70) in a read direction concurrently with a spin echo (68), and application of a phase encode gradient pulse (72) prior to the application of said read gradient pulse (70); characterised in that the pulse sequence further includes the application of a plurality of motion desensitization gradient pulses (80,82,90,92,94) having components in the slice select and read gradient directions, the motion desensitization pulses (80,82,90,92,94) having a duration and amplitude such that the sum of at least one of the zeroth, first, second, and third moments in time of the phase along each of the slice select and read gradient directions is a preselected value.

Claim 15

A method of generating magnetic resonance images comprising: generating a generally uniform magnetic field through an image region in which a subject to be imaged is positioned; and applying a plurality of pulse sequences to the image region, each pulse sequence including the concurrent application of a first slice select gradient (60) in a slice select direction and a resonance excitation RF pulse (62), the concurrent application of a second slice select gradient pulse (64) and an RF inversion pulse (66) to invert the spin magnetization of resonating nuclei, application of a read gradient pulse (70) in a read direction concurrently with a spin echo (68), and application of a phase encode gradient pulse (72) prior to the application of said read gradient pulse (70); characterised in that the pulse sequence further includes the application of a plurality of motion desensitization gradient pulses (80,82,90,92,94) having components in the slice select and read gradient directions, the motion desensitization pulses (80,82,90,92,94) having a duration and amplitude such that the sum of at least one of the zeroth, first, second, and third moments in time of the phase along each of the slice select and read gradient directions is a preselected value.

Claim 19

A method according to any one of Claims 13 to 16 wherein the sum of the third moments along each of the slice select and read gradient directions is zero whereby magnetic resonance signals from portions of the subject moving with a pulsatile motion are rephased.

Claim 20

An apparatus for generating motion desensitized magnetic resonance images comprising: main magnetic field means (A) for generating a generally uniform magnetic field through an image region; a radio frequency pulse means (B) for selectively applying radio frequency pulses to the image region,at least some of the radio frequency pulses being configured for exciting magnetic resonance of selected dipoles in the image region; a slice selection gradient control means (32) for selectively applying magnetic field gradient pulses across the image region in a slice select direction; read gradient control means (34) for selectively applying magnetic field gradient pulses across the image region in a read direction; a phase encode gradient control means (36) for selectively applying magnetic field gradients across the image region in a phase encode direction; a radio frequency receiving means (50) for receiving radio frequency magnetic resonance signals from the image region; and image reconstruction means (52) for forming an image representation from the received magnetic resonance signals; characterised in that said apparatus further comprises: an imaging pulse sequence and motion desensitization memory means (44,46) for storing amplitude and relative timing information for each of a plurality of selectable imaging sequences including RF, slice select gradient, read gradient, and phase encode gradient pulses, and motion desensitization magnetic field gradient pulses to be applied in each of the slice select and read gradient directions; and a pulse sequence format means (40) operatively connected with the imaging pulse sequence and motion desensitization pulse memory means (44,46) and with the radio frequency pulse means (B), the slice select gradient control means (32), the read gradient control means (34) and the phase encode gradient control means (36) for causing the radio frequency pulse control means (B), the slice select gradient control means (32), the read gradient control means (34), and the phase encode gradient control means (36) to apply the selected sequence of imaging and motion desensitization pulses to the image region.

Claim 21

An apparatus for generating motion desensitized magnetic resonance images comprising: main magnetic field means (A) for generating a generally uniform magnetic field through an image region; a radio frequency pulse means (B) for selectively applying radio frequency pulses to the image region,at least some of the radio frequency pulses being configured for exciting magnetic resonance of selected dipoles in the image region; a slice selection gradient control means (32) for selectively applying magnetic field gradient pulses across the image region in a slice select direction; read gradient control means (34) for selectively applying magnetic field gradient pulses across the image region in a read direction; a phase encode gradient control means (36) for selectively applying magnetic field gradients across the image region in a phase encode direction; a radio frequency receiving means (50) for receiving radio frequency magnetic resonance signals from the image region; and image reconstruction means (52) for forming an image representation from the received magnetic resonance signals; characterised in that said apparatus further comprises: an imaging pulse sequence and motion desensitization memory means (44,46) for storing amplitude and relative timing information for each of a plurality of selectable imaging sequences including RF, slice select gradient, read gradient, and phase encode gradient pulses, and motion desensitization magnetic field gradient pulses to be applied in each of the slice select and read gradient directions; and a pulse sequence format means (40) operatively connected with the imaging pulse sequence and motion desensitization pulse memory means (44,46) and with the radio frequency pulse means (B), the slice select gradient control means (32), the read gradient control means (34) and the phase encode gradient control means (36) for causing the radio frequency pulse control means (B), the slice select gradient control means (32), the read gradient control means (34), and the phase encode gradient control means (36) to apply the selected sequence of imaging and motion desensitization pulses to the image region.