Method and apparatus for acquisition of magnetic resonance data with fat saturation pulses radiated with respectively different flip angles
In a method and apparatus for magnetic resonance imaging of an examination subject using an acquisition sequence that includes at least one acquisition cycle, wherein the acquisition cycle includes a readout block set with at least two readout blocks, and a saturation pulse set with at least two saturation pulses, the saturation pulses of the saturation pulse set are respectively associated with respective readout blocks of the readout block set, and the saturation pulses of the saturation pulse set have respectively varying flip angles.
1. A method for acquiring magnetic resonance data from an examination subject using an acquisition sequence that includes at least one acquisition sequence, comprising:
operating a magnetic resonance data acquisition unit to read out magnetic resonance data from a plurality of slices in a stack in the examination subject, in a readout block set comprised of a readout block for each of said slices in the stack;
preceding each readout block of said readout block set, radiating one saturation pulse that saturates nuclear spins of fat in a respective slice of the examination subject from which the magnetic resonance data in the respective readout block are readout;
operating the magnetic resonance data acquisition unit to radiate the respective saturation pulses with varying flip angles in at least three of said readout blocks that occur in succession in said acquisition sequence, to give the respective saturation pulses of said at least three readout blocks respectively different flip angles that decrease from a largest flip angle for a first-occurring of said at least three readout blocks, to a smallest flip angle for a last-occurring of said at least three readout blocks; and
operating the magnetic resonance data acquisition unit, also in said acquisition sequence, to radiate the respective saturation pulses in at least two further readout blocks, other than said at least three of said readout blocks, respectively with equal flip angles.
2. A method as claimed in claim 1 comprising decreasing said flip angle according to a monotonically decreasing mathematical function.
3. A method as claimed in claim 1 comprising repeating said acquisition sequence multiple times, and varying the respective flip angles of the saturation pulses of said at least three readout blocks dependent on a duration between a saturation pulse of a current acquisition sequence, and a saturation pulse of an immediately preceding acquisition sequence.
4. A method as claimed in claim 3 comprising setting a flip angle of a saturation pulse in a current acquisition cycle to be larger when a longer duration elapses between said saturation pulse and an immediately preceding saturation pulse.
5. A method as claimed in claim 1 comprising operating said magnetic resonance data acquisition unit to acquire magnetic resonance data in multiple, successive acquisition sequences, with a first of said multiple acquisition cycles occurring chronologically before a second of said multiple acquisition cycles, and wherein a time interval, which is larger than a time interval of two readout blocks of a readout block set, being situated between a chronologically last readout block of the readout block set of the first acquisition sequence and the chronologically first readout block of the readout block set of the second acquisition sequence.
6. A magnetic resonance apparatus comprising:
a magnetic resonance data acquisition unit;
a control unit configured to operate the magnetic resonance data acquisition unit to execute an acquisition sequence in order to read out magnetic resonance data from a plurality of slices in a stack in the examination subject, in a readout block set comprised of a readout block for each of said slices in the stack;
said control unit being configured to operate the magnetic resonance data acquisition unit to radiate, preceding each readout block of said readout block set, one saturation pulse that saturates nuclear spins of fat in a respective slice of the examination subject from which the magnetic resonance data in the respective readout block are readout;
said control unit being configured to operate the magnetic resonance data acquisition unit to radiate the respective saturation pulses with varying flip angles in at least three of said readout blocks that occur in succession in said acquisition sequence, to give the respective saturation pulses of said at least three readout blocks respectively different flip angles that decrease from a largest flip angle for a first-occurring of said at least three readout blocks, to a smallest flip angle for a last-occurring of said at least three readout blocks; and
said control unit being configured to operate the magnetic resonance data acquisition unit, also in said acquisition sequence, to radiate the respective saturation pulses in at least two further readout blocks, other than said at least three of said readout blocks, respectively with equal flip angles.
7. A non-transitory, computer-readable data storage medium encoded with programming instructions, said data storage medium being loaded into a computerized control unit of a magnetic resonance apparatus that also comprises a magnetic resonance data acquisition unit, said programming instructions causing said computerized control unit to:
operating the magnetic resonance data acquisition unit to execute an acquisition sequence in order to read out magnetic resonance data from a plurality of slices in a stack in the examination subject, in a readout block set comprised of a readout block for each of said slices in the stack;
operate the magnetic resonance data acquisition unit to radiate, preceding each readout block of said readout block set, one saturation pulse that saturates nuclear spins of fat in a respective slice of the examination subject from which the magnetic resonance data in the respective readout block are readout;
operate the magnetic resonance data acquisition unit to radiate the respective saturation pulses with varying flip angles in at least three of said readout blocks that occur in succession in said acquisition sequence, to give the respective saturation pulses of said at least three readout blocks respectively different flip angles that decrease from a largest flip angle for a first-occurring of said at least three readout blocks, to a smallest flip angle for a last-occurring of said at least three readout blocks; and
operate the magnetic resonance data acquisition unit, also in said acquisition sequence, to radiate the respective saturation pulses in at least two further readout blocks, other than said at least three of said readout blocks, respectively with equal flip angles.