Method and MR apparatus for dynamic frequency detection in MR spectroscopy
In a method for dynamic frequency detection of the resonance frequency in magnetic resonance spectroscopy, by measuring navigator signals at the same point in time in each of a number of successive sequence passes, and by comparing the navigator signals, a frequency shift of the resonance frequency is determined on the basis of which the respective individual spectrum obtained from each sequence repetition is corrected with respect to the measured frequency shift.
1. Method for dynamic frequency detection of a resonance frequency in magnetic resonance spectroscopy, comprising the steps of:
in each of a plurality of successive magnetic resonance spectroscopy pulse sequence repetitions, acquiring a navigator signal at an identical point in time in each of said repetitions, and acquiring a spectrum;
determining a frequency shift of a resonance frequency from repetition-to-repetition by comparing the respective navigator signals; and
correcting the respective spectrum obtained in each repetition dependent on said frequency shift.
2. A method as claimed in claim 1 comprising employing a pulse sequence with water suppression as said magnetic resonance spectroscopy pulse sequence.
3. A method as claimed in claim 2 comprising employing a multiple-pulse water suppression pulse sequence that includes a first RF saturation pulse, as said water suppression pulse sequence, and acquiring said navigator signal in each repetition after said first RF saturation pulse.
4. A method as claimed in claim 1 comprising acquiring said navigator signal with a duration of approximately 100 μs.
5. A method as claimed in claim 1 comprising acquiring said navigator signal through an analog-to-digital converter, and acquiring said navigator signal with a magnitude corresponding to ten measurement values of said analog-to-digital converter.
6. A method as claimed in claim 5 comprising averaging said ten measurement values of said analog-to-digital converter to form said navigator signal.
7. A method as claimed in claim 6 comprising averaging said analog-to-digital converter measurement values over all of said spectra.
8. A magnetic resonance spectroscopy apparatus comprising:
a magnetic resonance scanner, adapted to interact with an examination subject, to obtain magnetic resonance spectroscopy data from the subject;
a control unit for controlling said magnetic resonance scanner to emit a plurality of successive repetitions of a magnetic resonance spectroscopy pulse sequence, to acquire said magnetic resonance spectroscopy data as a spectrum for each repetition, and to acquire a navigator signal at an identical point in time in each of said repetitions; and
a computer supplied with said magnetic resonance spectroscopy data that determines a frequency shift of a resonant frequency from repetition-to-repetition by comparing the respective navigator signals, and that corrects each spectrum dependent on said frequency shift.