An experimental method to visualize a 3D-region of interest (ROI) by means of an astigmatic Gaussian beam is proposed. This method allows to reduce the amount of image planes to be reconstructed thus saving computational time. ROI determination is performed without any computational step: particles that are located in the ROI can be distinguished from the others according to the hyperbolic shape of their diffraction pattern. Theoretical location of the ROI is determined by using the ABCD approach proposed in a previous paper [Appl. Opt. 47, 4147]. Experimental results are presented.