Magnetic resonance method and apparatus for correction of magnetic resonance data
In a method and apparatus to acquire correction data in connection with pulse sequences to acquire measurement data whose echo times—the duration between excitation and measurement data acquisition of the pulse sequences—are less than 500 microseconds, the pulse sequences acquire measurement data by repetition of a pulse sequence scheme, wherein different gradients for spatial coding are switched in each repetition, and correction data are acquired every n repetitions in a time window in which no gradients are switched, wherein n is a predetermined natural number. The method and apparatus enable correction of measurement data with which solid substances can be depicted without the hardware being used needing to be adapted and without external sensors being necessary.
1. A method to acquire correction data together magnetic resonance (MR) measurement data, comprising:
from a computerized control unit, operating an MR data acquisition unit, in which an examination subject is disposed, according to pulse sequence that causes excitation of nuclear spins in the examination subject and acquisition of measurement data comprising magnetic resonance signals resulting from the excited nuclear spins, and having an echo time, between said excitation and said acquisition of measurement data that is less than 500 microseconds, and, in said pulse sequence, activating a magnetic field gradient in said MR data acquisition unit that spatially codes said measurement data;
from said computerized control unit, operating said MR data acquisition unit to repeat said pulse sequence in a plurality of repetitions and, in each repetition, activating a different magnetic field gradient; and
from said computerized control unit, operating said MR data acquisition unit to acquire correction data from said examination subject during said time window in every n th repetition, in said plurality of repetitions, in which no gradient magnetic field is activated, wherein n is a predetermined natural number; and
making said measurement data and said correction data available in electronic form, in at least one data file, at an output of said control unit.
2. A method as claimed in claim 1 comprising acquiring said correction data during a free induction decay (FID) that occurs immediately following said excitation of said nuclear spins.
3. A method as claimed in claim 2 comprising providing said at least one data file to a computerized processor and, in said computerized processor, executing an FID-based movement correction algorithm, using said correction data and said measurement data, to correct said measurement data for movement of said examination subject.
4. A method as claimed in claim 3 wherein said MR data acquisition unit comprises a multi-channel reception coil comprising multiple individual coils, and acquiring said correction data with said multi-channel reception coil, and, in said FID-based movement correction algorithm, analyzing the acquired correction data on a coil-by-coil basis.
5. A method as claimed in claim 1 comprising, from said computerized control unit, operating said MR data acquisition unit by radiating an excitation pulse in said pulse sequence and activating said magnetic field gradient during radiation of said excitation pulse and, in each nth repetition of said pulse sequence, ramping down said magnetic field gradient and deactivating said magnetic field gradient to produce said time window in which said correction data are acquired.
6. A method as claimed in claim 5 wherein said MR data acquisition unit comprises a gradient coil system that is operated by said computerized control unit to activate said magnetic field gradient, and comprising ramping down said magnetic field gradient with a slew rate selected to ideally produce no mechanical stress on said gradient coil system.
7. A method as claimed in claim 5 comprising, from said computerized control unit, operating said MR data acquisition unit with a PETRA pulse sequence, as said pulse sequence.
8. A method as claimed in claim 1 comprising, from said computerized control unit, operating said MR data acquisition unit to radiate an excitation pulse that excites said nuclear spins in said pulse sequence and thereafter ramping up said magnetic field gradient in order to acquire said measurement data and, in each n th repetition, acquiring said correction data before beginning acquisition of said measurement data.
9. A magnetic resonance (MR) system comprising:
an MR data acquisition unit;
a computerized control unit configured to operate the MR data acquisition unit, in which an examination subject is disposed, according to pulse sequence that causes excitation of nuclear spins in the examination subject and acquisition of measurement data comprising magnetic resonance signals resulting from the excited nuclear spins, and having an echo time, between said excitation and said acquisition of measurement data that is less than 500 microseconds, and, in said pulse sequence, to activate a magnetic field gradient in said MR data acquisition unit that spatially codes said measurement data;
from said computerized control unit being configured to operate said MR data acquisition unit to repeat said pulse sequence in a plurality of repetitions and, in each repetition, activate a different magnetic field gradient; and
said computerized control unit being configured to operate said MR data acquisition unit to acquire correction data from said examination subject during said time window in every n th repetition, in said plurality of repetitions, in which no gradient magnetic field is activated, wherein n is a predetermined natural number; and
said control unit being configured to make said measurement data and said correction data available in electronic form, in at least one data file, at an output of said control unit.
10. 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 (MR) apparatus, said MR apparatus also comprising an MR data acquisition unit, and said programming instructions causing said computerized control unit to:
operate the MR data acquisition unit, in which an examination subject is disposed, according to pulse sequence that causes excitation of nuclear spins in the examination subject and acquisition of measurement data comprising magnetic resonance signals resulting from the excited nuclear spins, and having an echo time, between said excitation and said acquisition of measurement data that is less than 500 microseconds, and, in said pulse sequence, activate a magnetic field gradient in said MR data acquisition unit that spatially codes said measurement data;
operate said MR data acquisition unit to repeat said pulse sequence in a plurality of repetitions and, in each repetition, activating a different magnetic field gradient; and
operate said MR data acquisition unit to acquire correction data from said examination subject during a time window in every n th repetition, in said plurality of repetitions, in which no gradient magnetic field is activated, wherein n is a predetermined natural number; and
make said measurement data and said correction data available in electronic form, in at least one data file, at an output of said control unit.