Patent FR-2836553-A1 (FR)
Title: Quantitative NMR determination of spins in rapid exchange between at least two different compartments of mixture, e.g. physico-chemical mixture, comprises making two measurements, each with authorized relaxation time
Inventor: LIBES FRANCOIS
IPC: G01R33/44
Filed: 2002-02-25
Abstract: Two measurements are made, each with an authorized relaxation time. The first time (t1) allows total relaxation of the spins of all components present. The second time(s) (t2) only allow partial longitudinal relaxation of at least one spin category, i.e. of one component. The results are treated to determine a quantitative parameter relative to at least one of the spin categories in the sample  The spins are determined independently of the volume analyzed, using two consecutive measurement phases each carried out on any volume of sample to be analyzed with a sequence or series of impulses. The first measurement phase is done with a relaxation time (t1) before measurement of the order of and preferably equal to the time (teqL) taken to return to thermodynamic equilibrium for the component with the greatest spin-resolution relaxation time T1. The second phase is done and repeated with a relaxation time (t2) before measurement much less than (teqL). Each repetition of the second phase is done with a different relaxation time and the results from the first and second phases are used for the quantitative determination of spins or spin concentration for at least one component of the sample analyzed. For a sample with n components, the second measurement phase is repeated n-1 times, preferably with authorized relaxation times spread over the range of values between (teqL) and (1/5 teqR), where (teqR) is the time to return to equilibrium of the component with the lowest spin relaxation time. The first measurement phase includes repetition between 1 and 10 times of an NMR excitation and measurement sequence with a repetition time (TR) between two consecutive sequences equal to (t1) and the second measurement phase involves the repetition between 10 and 100 times of an NMR excitation and measurement sequence with a repetition time (TR') between two sequences equal to (t2). The sequence(s) for the first and/or second measurement phase are chosen from impulsion at an angle alpha, a spin echo sequence at m echos with m a whole number greater than or equal to 1 and preferably 2, or an inversion recovery sequence which can be followed by a spin echo. The second measurement phase is preceded by or integrates a series of pre-saturation impulses. The excitation sequences for the second measurement phase are repeated a number of times without measurement at the start of the second phase or before it (dummy scans). The repetition time (TR) is reduced by applying a supplementary (flip-back) impulse after acquisition of the measurement concerned. The sample to be analyzed is channeled into the analysis zone by a sampling circuit (6), for example a bypass circuit (4) on a pipe (7) carrying the mixture. The temperature of the circuit is regulated around the analysis zone. An Independent claim is also included for an apparatus for carrying out the above process.