Simultaneous photoacoustic and high-frequency ultrasound imaging of in vivo embryonic-mouse vasculature

Normal development of the central nervous system (CNS) and the neurovascular network are crucial to the survival and development of the mammalian embryo. Recent studies have established that the CNS and the neurovascular systems influence each other through an interplay of signalling molecules. Proper analysis of abnormalities in these complex 3D architectures necessitates an imaging technique capable of volumetrically visualizing the CNS and the neurovascular network. High-frequency ultrasound (HFUS) (>;20 MHz) is able to acquire a 3D volumetric data set of a mid-gestational embryonic head in about 2 minutes. Photoacoustic imaging (PAI) is able to produce detailed 3D images of vascular networks. The aim of this study was to integrate these two imaging modalities in order to simultaneously visualize the CNS and neurovasculature of mid-gestational mouse embryos in vivo. A 5-element, 40-MHz annular-array transducer with a geometric focus of 12 mm was integrated with a bifurcated optical-fiber assembly for delivering the light from a 532 nm, pulsed laser to the focal region of the annular array. Semi-invasive imaging was performed by exposing an intact conceptus and volumetric-image data were acquired of the embryonic heads by raster scanning the array transducer. Radio-frequency data were acquired on all five channels of the array and a delay-and-sum synthetic-focusing algorithm was utilized to form images. Preliminary results from mouse embryos imaged at E12.5 and E13.5 showed the capability of this imaging protocol to visualize morphologically correct anatomy such as the embryonic head and CNS as well as the co-registered neurovasculature. Vessels such as the as the mid-sagittal sinus, transverse sinus and basilar artery were readily identified.