The present invention relates to a device (8) for determining tissue layer boundaries of a body (14), comprising a probe (10) for acquiring (S12) two or more ultrasound images (36) at adjacent positions of a surface (12) of the body (14), a converter (44) for converting (S14) said ultrasound images (36) separately to depth signals (46), wherein a depth signal (46) is obtained by summing intensities of one of said ultrasound images (36) along a line (66) of substantially constant depth in the body (14), a detector (48) for detecting (S16) a set of candidate tissue layer boundaries (50) for an ultrasound image (36) by thresholding the depth signal (46) obtained for said ultrasound image (36), a selection means (52) for selecting (S18) from a set of candidate tissue layer boundaries (50) a nearest candidate tissue layer boundary (54) that is nearest to the surface (12) of the body (14), and a processing means (56) for determining (S20) an actual tissue layer boundary (58) from the nearest candidate tissue layer boundaries (54) obtained for various ultrasound images (36).
