Focused ultrasound combined with microbubbles can locally and transiently open the blood-brain barrier (BBB) in a non-invasive and safe manner, providing a potential strategy for drug delivery into the brain. The technique is currently being used to test drugs for the treatment of different pathologies; however, the BBB opening dimensions depends on several characteristics of the ultrasonic beam. In this work we characterize the BBB opening in small animals produced by a manufactured transducer operating at frequencies 1.05 MHz (fundamental; FWHM3dB = 1.5 mm | DOF3dB = 6 mm) and 3.25 MHz (first harmonic; FWHM3dB = 0.5 mm | DOF3dB = 2 mm). The transducer has been tested in 11 mice, demonstrating its capability for different BBB opening dimensions with gadolinium (Gd) signal detected in contrast-enhanced T1-weighted MRI.