[Parameter-weighted MR images and their optimization: theory and example of images for the flash sequence compared to the spin-echo sequence]. / Parametergewichtete MR-Bilder und ihre Optimierung: Theorie und Bildbeispiele für die FLASH-Sequenz im Vergleich zur Spinecho-Sequenz.

ABSTRACT

In this paper the signal intensity and parameter-weighting zones of spin echo and gradient echo sequences (FLASH) have been analysed. Using information available in the literature, with additional analytical and numerical techniques, it is possible to determine parameters which maximise tissue contrast for T1, T2 and proton-weighted images. The technique is equally applicable to spin echo and FLASH sequences. The advantages of optimised gradient echo sequences compared with spin echo sequences with respect to its signal to noise ratio for short repetition times are analysed quantitatively. T2-weighted images can be generated as rapid as T1-weighted images, using the FLASH sequences when using a small angle of spin and relatively long echo. Illustrations are shown to demonstrate the numerical results (field strength 1.5 tesla). This is followed by a discussion of possible opposing effects.