New pulse sequences for T₁- and T₁/T₂-contrast enhancing in NMR imaging

Improved pulse sequences DIFN (abbreviation of the words: DIFferentiation by N pulses), 90°- τ₁ - 180°- τ₁ - ... 180°- τ(n), with optimised time intervals τ₁ for T₁ measurement and contrast enhancing in NMR imaging are presented. The pulse sequences DIFN have a better sensitivity to T₁ than the well-known pulse sequence SR. In contrast to the IR pulse sequence, the information given by the DIFN pulse sequence is more reliable, because the NMR signal does not change its sign. For a given time interval τ₀ ≤ (0.1-0.3) T₁' the DIFN pulse sequences serve as T₁- filters. They pass the signal components with relatively short T₁ < T₁' and suppress the components with relatively long T₁ < T₁'. The effects of the radiofrequency field inhomogeneity and inaccurate adjusting of pulse lengths are also considered. It is also proposed in this work to use the joint T₁- T₂-contrast in NMR imaging obtained as a result of applying the DIFN pulse sequences in combination with the well-known Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence. The region of interest, where the contrast should be especially enhanced, is specified by the two times at which measurements are performed, which allow the amplitudes of pixels to reach some defined levels by spin-lattice and spin-spin relaxation.