Time-domain quantification of multiple-quantum-filtered Na-23 signal usingcontinuous wavelet transform analysis

The application of continuous wavelet transform (CWT) analysis technique is presented to analyze multiple-quantum-filtered (MQF) Na-23 magnetic resona nce spectroscopy (MRS) data. CWT acts on the free-induction-decay (FID) sig nal as a time-frequency variable filter. The signal-to-noise ratio (SNR) an d frequency resolution of the output filter are locally increased. As a res ult, MQF equilibrium longitudinal magnetization and the apparent fast and s low transverse relaxation times are accurately estimated. A developed itera tive algorithm based on frequency signal detection and components extractio n, already proposed, was used to estimate the values of the signal paramete rs by analyzing simulated time-domain MQF signals and data from an agarose gel. The results obtained were compared to those obtained by measurement of signal height in frequency domain as a function of MQF preparation time an d those obtained by a simple time-domain curve fitting. The comparison indi cates that the CWT approach provides better results than the other tested m ethods that are generally used for MQF 23Na MRS data analysis, especially w hen the SNR is low. The mean error on the estimated values of the amplitude signal and the apparent fast and slow transverse relaxation times for the simulated data were 2.19, 6.63, and 16.17% for CWT, signal height in freque ncy domain, and time-domain curve fitting methods, respectively, Another ma jor advantage of the proposed technique is that it allows quantification of MQF Na-23 signal from a single FID and, thus, reduces the experiment time dramatically. (C) 2000 Academic Press.