3D small animal imaging with high-frequency ultrasound (20 MHz) using limited-angle spatial compounding

For ultrasound imaging of small animals often standard systems for human medicine or special high frequency ultrasound systems are used. The former are limited to frequencies below 15 MHz, and therefore their spatial resolution often is not sufficient. High-frequency ultrasound (HFUS) imaging systems working at frequencies up to 40 MHz offer a rather high resolution, but high ultrasound frequencies and mainly used fixed-focus transducers lead to a limited depth of field (DOF). In this paper, a 20 MHz HFUS imaging system operating in a limited angle spatial compounding (LASC) mode is applied. It representing a good compromise between depth of field and spatial resolution with an improved image quality due to the LASC operation mode. By stepwise moving the transducer along the elevational direction, three-dimensional (3D) echo datasets are recorded. The system was characterized in terms of axial, lateral, and elevational resolution by means of wire phantom measurments. For further evaluation, measurements on fresh cadavers of 1-day-old rat pups were carried out. Spatial compound images show reduced speckle, a more complete and detailed depiction of tissue structures and less shadowing artifacts compared to conventional B-mode images. The increase of signal-to-noise ratio is analyzed by speckle statistics. Cross sectional images of 3D datasets as well as maximum intensity projections (MIP) and mean intensity projections (MeanIP) are presented.