This paper presents the image formation process in vibro-acoustography for systems based on sector array transducers. These transducers are an alternative to annular concave transducers. They represent an innovative technique deserving detailed assessment in vibro-acoustography applications. The system point-spread function (PSF) is defined in terms of the acoustic emission of a point-target in response to the dynamic ultrasound radiation force. This force is produced by two overlapping ultrasound beams. We calculate the radiation force on the target in a nonviscous fluid using the plane wave approximation for the ultrasound beams. The beamforming of sector array transducers is analyzed through linear acoustics. An expression for the velocity potential produced by sector arrays is derived, and the vibro-acoustography PSF is evaluated numerically. An experimental setup is design to validate the theory; the comparison is made using location and amplitude of sidelobes and spatial resolution defined by the PSF. Results show that the computed PSF is in full agreement with the PSF obtained experimentally.