We describe a fully automatic three-dimensional (3-D)-segmentation tec
hnique for brain magnetic resonance (MR) images, By means of Markov ra
ndom fields (MRF's) the segmentation algorithm captures three features
that are of special importance for MR images, i.e., nonparametric dis
tributions of tissue intensities, neighborhood correlations, and signa
l inhomogeneities, Detailed simulations and real MR images demonstrate
the performance of the segmentation algorithm, In particular, the imp
act of noise, inhomogeneity, smoothing, and structure thickness are an
alyzed quantitatively, Even single-echo MR images are well classified
into gray matter, white matter, cerebrospinal fluid, scalp-bone, and b
ackground, A simulated annealing and an iterated conditional modes imp
lementation are presented.