Magnetic resonance imaging system

Apparatus for magnetic resonance imaging (MRI), comprising:

• a magnetic field generator which is adapted to impose N sets of steady-state free precession (SSFP) sequences on an object to be Imaged, the sequences comprising respective initial radio-frequency (RF) excitation pulses, each initial RF excitation pulse having a predetermined phase shift relative to the other initial RF excitation pulses, wherein N is a value chosen from a set of whole numbers larger than one and less than six, and wherein the phase shift of the RF pulse of an Mth sequence is substantially equal to 2 ⁢ π ⁡ ( M - 1 ) N
• radians, wherein M is chosen from a set of whole numbers larger than 0 and less than or equal to N,
• a signal processor which is adapted to receive a respective set of image signals from the object responsive to the N sets of SSFP sequences, and to process the set of received image signals so as to generate an image of the object;
• and
• wherein the first SSFP sequence in each of the N sets of sequences is preceded by a de-phasing magnetic gradient and an RE pre-pulse which generates a flip angle substantially equal to 90°.

Apparatus for magnetic resonance imaging (MRI), comprising:

• a magnetic fluid generator which is adapted to impose N sets of steady-state free precession (SSFP) sequences on an object to be imaged, the sequences comprising respective initial radio-frequency (RF) excitation pulses, each initial RF excitation pulse having a predetermined phase shift relative to the other initial RF excitation pulses, wherein N is a value chosen from a set of whole numbers larger than one and less than six, and wherein the phase shift of the RF pulse of an sequence is substantially equal to 2 ⁢ π ⁡ ( M - 1 ) N
• radians, wherein M is chosen from a set of whole numbers larger than 0 and less than or equal to N;
• a signal processor which is adapted to receive a respective set of image signals from the object responsive to the N sets of SSFP sequences, and to process the set of received image signals so us to generate an image of the object;
• and
• wherein the object comprises water and fat, and wherein the magnetic field generator is adapted to:
• set a frequency of a frequency synthesizer generating the N sets of SSFP sequences to be substantially equal to an average of a water resonance frequency νW and a fat resonance frequency νF;
• set a repetition time (TR) of each of the sequences to be substantially equal to a first odd integral of a time period τ, wherein τ = 1 2 ⁢ ( v F - v W ) ;
• and
• wherein the signal processor is adapted to:
• receive a first set of image signals at a first readout time substantially equal to a second odd integral of the time period τ and less than the first odd integral;
• receive a second Set of image signals at a second readout time substantially equal to the second odd integral incremented by τ;
• process the first and the second set of image signals to form respective processed first and second signals;
• and
• generate a water image and a fat image responsive to the first processed signals and the second processed signals.

A method for magnetic resonance imaging (MRI), comprising:

• imposing N sets of steady-state free precession (SSFP) sequences on an object to be imaged, the sequences comprising respective initial radio-frequency (RF) excitation pulses, each initial RF excitation pulse having a predetermined phase shift relative to the other initial RF excitation pulses, wherein N is a value chosen from a set of whole numbers larger than one and less than six;
• setting the phase shift of the RF pulse of the sequences so that the phase shift of the RF pulse of an Mth sequence is substantially equal to 2 ⁢ π ⁡ ( M - 1 ) N
• radians, wherein M as a value chosen from a set of whole numbers larger than 0 and less than or equal to N;
• receiving a respective set of image signals from the object responsive to the N sets of SSFP sequences;
• and
• processing the set of received image signals so as to generate an image of the object, wherein the object comprises a region having a resonant frequency varying by a factor Δf, and wherein a repetition time (TR) of each sequence of the N sets of SSFP sequences comprises a time greater than a reciprocal of 2Δf.

A method for magnetic resonance imaging (MRI), comprising:

• imposing N sets of steady-state free precession (SSFP) sequences on an object to be imaged, the sequences comprising respective initial radio-frequency (RF) excitation pulses, each initial RF excitation pulse having a predetermined phase shift relative to the oilier initial RF excitation pulses, wherein N is a value chosen from a set of whole numbers larger than one and less than six and wherein the first SSFP sequence in each of the N sets of sequences is preceded by a de-phasing magnetic gradient and an RE pre-pulse which generates a flip angle substantially equal to 90°,
• setting the phase shift of the RF pulse of the sequences so that the phase shift of the RF pulse of an Mth sequence is substantially equal to 2 ⁢ π ⁡ ( M - 1 ) N
• radians, wherein M is a value chosen from a set of whole numbers larger than 0 and less than or equal to N;
• receiving a respective set of image signals from the object responsive to the N sets of SSFP sequences;
• and processing the set of received image signals so as to generate an image of the object.

A method for magnetic resonance imaging (MRI), comprising:

• imposing N sets of steady-state free precession (SSFP) sequences on an object to be imaged, the sequences comprising respective initial radio-frequency (RE) excitation pulses, each initial RE excitation pulse having a predetermined phase shill relative to the other initial RF excitation pulses, wherein N is a value chosen from a set of whole numbers larger than one and less than six;
• setting the phase shift of the RE pulse of the sequences so that the phase shift of the RF pulse of an Mth sequence is substantially equal to 2 ⁢ π ⁡ ( M - 1 ) N
• radians, wherein M is a value chosen from a set of whole numbers larger than 0 and less than or equal to N;
• receiving a respective set of image signals from the object responsive to the N sets of SSFP sequences;
• and
• processing the set of received image signals so as to generate an image of the object, wherein the object comprises water and fat;
• setting a frequency of a frequency synthesizer generating the N sets of SSFP sequences to be substantially equal to an average of a water resonance frequency νW and a fat resonance frequency νF;
• setting a repetition time (TR) of each of the sequences to be substantially equal to a first odd integral of a time period τ, wherein τ = 1 2 ⁢ ( v F - v W ) ;
• and wherein receiving the respective set of image signals comprises:
• receiving a first set of image signals at a first readout time substantially equal to a second odd integral of the tune period τ and less than the first odd integral;
• and
• receiving a second set of image signals at a second readout time substantially equal to the second odd integral incremented by τ;
• and
• wherein processing the set of received image signals comprises:
• processing the first and the second set of image signals to form respective processed first and second signals;
• and
• generating a water image and a fat image responsive to the first processed signals and the second processed signals.

A method for magnetic resonance imaging (MRI), comprising:

• imposing N sets of steady-state free precession (SSFP) sequences on an object to be imaged, the sequences comprising respective initial radio-frequency (RF) excitation pulses, each initial RF excitation pulse having a predetermined phase shift relative to the other initial RE excitation pulses wherein N is a value chosen from a set of whole numbers larger than one and less than six;
• setting the phase shift of the RE pulse of the sequences so that the phase shift of the RE pulse of an Mth sequence is substantially equal to 2 ⁢ π ⁡ ( M - 1 ) N
• radians, wherein M is a value chosen from a set of whole numbers larger than 0 and less than or equal to N;
• receiving a respective set of image signals substantially absent of signals from the object responsive to the sets of SSFP sequences, wherein at least a portion of the image signals is dependent on an angle of precession Φ;
• and
• processing the set of received image signals so as to generate an image of the object, wherein the image of the object is substantially independent of Φ.

A method for magnetic resonance imaging (MRI), comprising:

• creating a gradient field about an object to be imaged, the gradient field having a field strength greater than 1.5T;
• imposing N sets of steady-state free precession (SSFP) sequences on the object to be imaged, the sequences comprising respective initial radio-frequency (RF) excitation pulse and occurring during a repetition time (TR), each initial RF excitation pulse having a predetermined phase shift relative to the other initial RF excitation pulses, wherein N is a value chosen from a set of whole numbers larger than one and less than six and wherein the TR of each sequence is unrestricted;
• setting the phase shift of the RE pulse of the sequences so that the phase shift of the RF pulse of an Mth sequence is substantially equal to 2 ⁢ π ⁡ ( M - 1 ) N
• radians, wherein M is a value chosen from a set of whole numbers larger than 0 and less than or equal to N;
• receiving a respective set of image signals from the object responsive to the N sets of SSFP sequences;
• and
• processing the set of received image signals so as to generate an image of the object.

A method for magnetic resonance imaging (MRI) with water and fat separation, comprising:

• imposing N sets of steady-state free precession (SSFP) sequences on an object to be imaged, the sequences comprising respective initial radio-frequency (RF) excitation pulses, each initial RF excitation pulse having a predetermined phase shift relative to the other initial RF excitation pulses, wherein N is a value chosen from a set of whole numbers larger than one and less than six;
• setting the phase shift of the RE pulse of the sequences so that the phase shift of the RE pulse of an Mth sequence is substantially equal to 2 ⁢ π ⁡ ( M - 1 ) N
• radians, wherein M is a value chosen from a set of whole numbers larger than 0 and less than or equal to N;
• receiving a respective set of image signals without the object responsive to the N sets of SSFP sequences, and
• processing the set of received image signals so as to generate separate water and fat images of the object.