In vivo volumetric imaging of the mouse embryonic brain using chirp‐coded excitation and a high‐frequency annular‐array. Free

Many genetically engineered mice display abnormal development of the central nervous system (CNS) and high‐frequency ultrasound (HFU) offers great potential for efficient, serial in vivo phenotyping of the developing embryonic mouse brain. However, HFU mouse‐embryo imaging remains challenging because of the orientation of the embryos and of the limited acoustic penetration depth of HFU. In this study, a 34‐MHz, five‐element annular array was excited using conventional mono‐cycle and chirp‐coded excitations. Synthetic focusing and pulse compression (for the chirp excitation) were used to form images with increased depth of field and penetration depth (for the chirp excitation). In utero, in vivo 3‐D data sets were acquired from 48 embryos over four stages from embryonic days E10.5 to E13.5, and CNS volume renderings were obtained. The chirp‐based renderings were more morphologically accurate than the mono‐cycle‐based renderings, and the chirp provided sufficient penetration depth to correctly segment the brain ventricles lying deep inside the mother. The chirp renderings indicated that the early CNS architecture was dominated by the third and fourth brain ventricles, with the lateral ventricles contributing more at later stages. [Work supported by NIH Grant nos. NS038461 and EB008606.]