The thickness of the dura mater was obtained from ultrasound probes on the skull and fast Fourier transform-Cepstrum through a probability process at various intracranial pressures (ICP), measured with pressure transducers, in 12 anesthetized dogs. There was a constant relationship between changes in thickness (micron) and changes in ICP (mmHg) from 5 to 80 mmHg. The estimated thickness at 0 mmHg of pressure and values obtained from measurements of dural samples were very similar. Our method provides estimations of ICP, and holds promise for measuring thicknesses below 1000 microns in biological systems in general.