NEW PULSE SEQUENCES FOR T-1-CONTRAST AND T-1 T-2-CONTRAST ENHANCING IN NMR IMAGING/

Improved pulse sequences DIFN (abbreviation of the words: DIFferentiat ion by N pulses), 90 degrees - tau(1) - 180 degrees - tau(1) - ...180 degrees - tau(n), with optimised time intervals tau(1) for T-1 measure ment and contrast enhancing in NMR imaging are presented. The pulse se quences DIFN have a better sensitivity to T-1 than the well-known puls e sequence SR. In contrast to the IR pulse sequence, the information g iven by the DIFN pulse sequence is more reliable, because the NMR sign al does not change its sign. For a given time interval tau(0) less tha n or equal to (0.1 - 0.3) T-1' the DIFN pulse sequences serve as T-1-f ilters, They pass the signal components with relatively short T-1 < T- 1' and suppress the components with relatively long T-1 < T-1'. The ef fects of the radiofrequency field inhomogeneity and inaccurate adjusti ng of pulse lengths are also considered. It is also proposed in this w ork to use the joint T1T2-contrast in NMR imaging obtained as a result of applying the DIFN pulse sequences in combination with the well-kno wn Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence. The region of inte rest, where the contrast should be especially enhanced, is specified b y the two times at which measurements are performed, which allow the a mplitudes of pixels to reach some defined levels by spin-lattice and s pin-spin relaxation, (C) 1998 Elsevier Science Inc.