Mouse embryo imaging with a 40 mhz annular array

Current high frequency ultrasound imaging, or ultrasound biomicroscopy (UBM) systems use fixed-focus trans- ducers, which are limited in depth of field (DOF). One important application for UBM is in the area of mouse embryo imaging. Depending on the gestational age of the embryo, regions of interest in the image can extend well beyond the DOF for a fixed-focus transducer. This shortcoming makes it impossible, in many cases, to post-process 3-D datasets for volumetric rendering of the developing embryonic anatomy. High frequency annular arrays can provide a solution to this problem, extending the DOF through variable focusing in depth. A 5-element, 40-MHz annular array transducer has been developed, and imaging of a wire phantom showed an increase in DOF from 1-2 mm (fixed- focus) to more than 10 mm with array focusing. We have now used this annular array system to acquire images from mouse embryos between gestational ages 11 (E11.5) and 13 (E13.5) with this annular array system. Our results show the superior image definition and quality compared to fixed-focus images and an increased DOF of close to 6 mm. The images reveal the entire extent of anatomical structures such as cerebral ventricles and the amniotic membrane, enabling robust volumetric rendering of these structures from 3-D image data.