40-MHz annular array imaging of mouse embryos.

Ultrasound biomicroscopy (UBM) has emerged as an important in vivo imaging approach for analyzing normal and genetically engineered mouse embryos. Current UBM systems use fixed-focus transducers, which are limited in depth-of-focus. Depending on the gestational age of the embryo, regions-of-interest in the image can extend well beyond the depth-of-focus for a fixed-focus transducer. This shortcoming makes it particularly problematic to analyze 3-D data sets and to generate accurate volumetric renderings of the mouse embryonic anatomy. To address this problem, we have developed a five-element, 40-MHz annular array transducer and a computer-controlled system to acquire and reconstruct fixed- and array-focused images of mouse embryos. Both qualitative and quantitative comparisons showed significant improvement with array-focusing, including an increase of 3 to 9 dB in signal-to-noise ratio and an increase of at least 2.5 mm in depth-of-focus. Volumetric-rendered images of brain ventricles demonstrated the clear superiority of array-focusing for 3-D analysis of mouse embryonic anatomy.