Signal envelope recovery in NMR signal acquisition at low SNR In Nuclear Magnetic Resonance (NMR), the frequency of the acquired signal depends on the applied magnetic field, and the SNR is usually poor. One method recently proposed to study the dependence of relaxation time (T2) on the applied magnetic field requires the application of the magnetic field by an electromagnet, that suffers from field instabilities. Magnetic field instabilities don’t allow the cumulation of I/Q components to improve SNR because of the frequency drift of the signal; the envelope (modulus) of the signal has to be cumulated instead. In presence of additive noise on the I/Q components, the amplitude (envelope) of the signal follows Rice statistics, so the cumulation of the envelope results in a bias error, that becomes important at low SNR of the acquired I/Q components. A model of the acquisition system has been developed, and a suitable correction algorithm is beeing studied to recovery the envelope of the NMR signal in presence of magnetic field instabilities, even at low SNR in presence of additive noise.

Signal envelope recovery in NMR signal acquisition at low SNR

MARTINI, GIUSEPPE;SVELTO, VITO
2008-01-01

Abstract

Signal envelope recovery in NMR signal acquisition at low SNR In Nuclear Magnetic Resonance (NMR), the frequency of the acquired signal depends on the applied magnetic field, and the SNR is usually poor. One method recently proposed to study the dependence of relaxation time (T2) on the applied magnetic field requires the application of the magnetic field by an electromagnet, that suffers from field instabilities. Magnetic field instabilities don’t allow the cumulation of I/Q components to improve SNR because of the frequency drift of the signal; the envelope (modulus) of the signal has to be cumulated instead. In presence of additive noise on the I/Q components, the amplitude (envelope) of the signal follows Rice statistics, so the cumulation of the envelope results in a bias error, that becomes important at low SNR of the acquired I/Q components. A model of the acquisition system has been developed, and a suitable correction algorithm is beeing studied to recovery the envelope of the NMR signal in presence of magnetic field instabilities, even at low SNR in presence of additive noise.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11571/147790
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