Most institutions now have a suite of imaging tools to follow mouse models of human disease. Micro-ultrasound is one of these tools and is second after whole-mouse fluorescence or bioluminescent imaging, in terms of installed systems. We report in this paper the first commercially available array transducer-based ultrasound imaging system that enables micro-ultrasound imaging at center frequencies between 15 and 50 MHz. At the heart of the new scanner is a laser-machined high-frequency 256 element, linear transducer array capable of forming dynamic diffraction limited beams. The power of the linear array approach is embodied in the uniform high resolution maintained over the full field of view. This leads to greatly expanded scope for real-time functional imaging that is demonstrated in this paper. The unprecedented images made with the new imaging system will enable many new applications not previously possible. These include real-time visualization of flow in the mouse placenta, visualization of flow development in the embryo, studies of embryonic to adult cardiac development/disease, and studies of real-time blood flow in mouse models of tumour angiogenesis.