Methods for ultrasonically imaging a heterogeneous 3D-cell population without physically probing are provided. The method can comprises: pulsing ultrasound waves having a wave frequency of about 10 MHz to about 2 GHz through a lens rod, wherein the lens rod focuses the ultrasound waves onto the cell population via a concave lens-head (e.g., comprising sapphire), and wherein the cell population is positioned on the reflective surface such that the ultrasound waves are reflected back to the lens-head; receiving the reflected waves through the lens head and the lens rod at a signal receiver; scanning the lens-head across multiple points in the x,y plane; and at each point in the x,y plane, moving the lens-head in a z-direction such that a signal is received at multiple intervals in the z-direction for each point in the x,y plane.