[Contrasts in the FLASH sequences in the study of musculoskeletal tumors: phantom study and theoretical calculations]

The contrast between samples simulating musculoskeletal neoplasms and muscle or bone marrow achieved with FLASH sequences, was analysed in phantom studies and was compared with theoretically calculated contrast with and without correction for flip angle distribution over the slice profile. The contrast was correlated closer with the flip angle than with TR or TE. For delineation of the tumour from muscle, only a FLASH sequence with a large flip angle following intravenous administration of Gd-DTPA can be recommended, if a tumour shows a clear Gd-DTPA uptake. With all FLASH sequences analysed, no sufficient contrast between "tumour" without Gd-DTPA uptake and muscle was obtained. Maximal contrast between "tumour" and bone marrow was achieved with small flip angles; and an additional peak was noted with large flip angles and short TR. Experimentally measured T2*-dependent contrasts were nearly identical with theoretically calculated contrasts without correction of flip angle distribution. For calculation of T1-dependent contrasts, correction of the flip angle distribution over the slice profile was of high value.