Fig. 4

B-mode images do not provide a resolved signature of the tissue cellular content. a Single cells or structured connected cells forming a living tissue are providing acoustic impedance interfaces reflecting or scattering compressive waves emitted by the ultrasound probe. b These backward waves are detected by the same probe but are filtered by the “point spread function” of the ultrasound system. In other words, the limited resolution of ultrasound coupled with probe characteristics and scanner settings do not allow resolving single cell geometry. The “point spread function” can be interpreted as the image that would be produced by a single reflector much smaller than the acoustic wavelength but with enough acoustic impedance contrast with the ambient medium to provide a detected backward echo. c The B-mode image corresponds to the tissue sub-resolution characteristics filtered by the “point spread function.” The spatial distribution of reflectors and scatterers impact the final image appearance