Multi-channel magnetic resonance spectroscopy through time domain multiplexing

Time domain multiplexing (TDM) is presented as a viable approach to increasing the sensitivity and efficiency of magnetic resonance spectroscopic (MRS) experiments through multi-channel signal acquisition. By switching very rapidly between coils of a receive phased array, TDM receiver extensions allow the acquisition of multiple, independent spectra through a single channel magnetic resonance console. A TDM receiver extension designed for imaging and spectroscopy is described, and the impact of this hardware extension on the processing and quantitation of MRS data is addressed. The primary complication involves the use of fixed bandwidth RF band-pass filters that can not be adjusted to match the spectral width of the desired MRS experiment.MRS sequences whose bandwidths are narrower than the bandwidth provided by TDM band-pass filters can be acquired through TDM with minimal loss of SNR as long as two constraints are met. The first constraint requires that the entire bandwidth of the band-pass filters be sampled at or more rapidly than the Nyquist rate associated with their bandwidth, to prevent extra noise from aliasing into the final spectrum. The second requirement is that spectral resolution be held constant to that of the desired experiment. Results from a two-channel multiplexed MRS experiment, conducted according to these guidelines, illustrate that TDM can be used to allow acquisition of multi-channel MRS experiments through single channel console systems with a minimal loss in SNR.