Longitudinal relaxation time measurement in MR with transient-state magnetization

To measure the relaxation times T-1 of polarized gases an unusual method has been proposed that makes use of the transient state of the magnetization of the nuclei being measured. The transient state is the result of multiple excitations by RF pulses with a small flip angle and an appropriate repetition time T-R. The method was designed and experimentally tested for measuring the relaxation times T-1 of polarized gases with transient-state magnetization, based on measuring the MR signal levels after the termination of RF pulses. For a higher precision of determining T-1 two measurements with different repetition times were performed. The relaxation time was calculated from one or two measurements, using an optimization method. In the method described no precise calibration of the flip angle of RF pulses is necessary. The measuring precision achieved was better than 1%, and it depends on a precise determination of the magnitude of MR signal. The technique described will be used when measuring the properties of polarized gases or even liquids in porous materials.