T2-weighted fast MR imaging with true FISP versus HASTE: Comparative efficacy in the evaluation of normal fetal brain maturation

OBJECTIVE, This study compares the relative efficacy of two fast T2-weighte d MR imaging techniques-fast imaging with steady-state free precession (tru e FISP) and half-Fourier acquisition single-shot turbo spin-echo (HASTE)-in the evaluation of the normal fetal brain maturation during the second and third trimesters of gestation. SUBJECTS AND METHODS. The brain maturation of 10 normal nonsedated fetuses (5 during the second trimester and 6 during the third trimester of gestatio n [1 fetus underwent 2 examinations]) was examined by both techniques using a Vision + 1.5-T MR system. We specifically looked for developing events, including white matter myelination, neuronal migration, and cortical sulcat ion. Image quality was graded according to the presence or absence of undes irable blurring. RESULTS. The specific absorption rate was lower for true FISP than for HAST E by a factor of 3 at equivalent imaging conditions. HASTE and true FISP pr ovide comparable image quality in the second trimester when myelination of the cerebrum has not begun. Neuronal migration could be recognized as hypod ense bands on both sequences during the second trimester. Myelination begin ning at the third trimester was better delineated with true FISP than with HASTE because of point spread function-related blurring effects inherent in HASTE that hampered visualization of short-T2 structures. Cortical sulcati on was well delineated by both sequences. CONCLUSION. With relatively superior image quality and significantly lower radiofrequency absorption than HASTE, true FISP is a safer and more effecti ve alternative in the prenatal evaluation of normal fetal brain.