Localised two-dimensional correlated spectroscopy based on Hadamard encoding technique

A new pulse sequence based on Hadamard encoding technique, dubbed as Hadamard encoded localised correlation spectroscopy (HLCOSY) was devised to speed up the acquisition of localised two-dimensional (2D) nuclear magnetic resonance (NMR) correlation spectroscopy (LCOSY). Direct frequency-domain (F2) excitation with an array of different radiofrequencies has been used to speed up 2D NMR experiments by a large factor. Multiplex excitation in the indirect frequency (F1) dimension is restricted to the signal-bearing regions and is encoded according to a Hadamard matrix of order N, where N is a relatively small number. The detected signals are decoded by reference to the same Hadamard matrix. An HLCOSY spectrum of a two-compartment phantom was obtained with a total acquisition time of 32 s, with its volume localisation confirmed. The success in achieving 2D LCOSY spectrum of pig marrow within 40 s shows the feasibility of HLCOSY for the detection of biological tissues. It may provide a promising way for in vivo and in vitro NMRs.