Digital filter for NMR an MRI applications

A method for operating a nuclear magnetic resonance (NMR) or a magnetic resonance imaging (MRI) spectrometer using a digital filter which is installed in a low-frequency region of a receiver system, the digital filter having an input which is fed with an NMR signal of time length TA and with an output signal consisting essentially of a rising oscillation B1 of time length TB, a signal portion [F]′, which consists of a filtered FID or echo signal of time length TA, and a decaying oscillation B2 of time length TB, wherein this output signal is initially modified using a calculation process RV and subsequently transformed into a desired NMR spectrum through Fourier transformation, the method comprising the steps of:

• a) initially selecting, during the calculation process RV only the signal portion [F]′;
• b) subsequently generating at least N copies of the rising oscillation B1 in positive time shifts TA relative to each other;
• c) positioning the at least N copies of the rising oscillation B1 on the signal portion [F]′ in time such that an end of a first rising oscillation is positioned at an end of the signal portion [F]′;
• d) generating at least N copies of the decaying oscillation B2 in negative time shifts TA relative to each other;
• e) positioning the at least N copies of the decaying oscillation B2 on the signal portion [F]′ in time such that a start of a first decaying oscillation is positioned at a start of the signal portion [F]′;
• f) adding all N copies of the rising oscillation B1, defined in this manner, and all N copies of the decaying oscillation B2, defined in this manner, to the signal portion [F]′;
• and
• g) selecting, following step f), only portion TA which contains the signal portion [F]″ as a resulting signal F″ of the calculation process RV, wherein the number N is calculated using the formula N=TB/TA and rounded to a next higher integer number.