An ultrasound medical system has an end effector including a medical ultrasound transducer and an acoustic coupling medium. The acoustic coupling medium has a transducer-proximal surface and a transducer-distal surface. The medical ultrasound transducer is positioned to emit medical ultrasound through the acoustic coupling medium from the transducer-proximal surface to the transducer-distal surface. The end effector is adapted to change a property (such as the shape and/or the temperature) of the acoustic coupling medium during emission, and/or between emissions, of medical ultrasound from the medical ultrasound transducer during a medical procedure on a patient. In one example, such changes are used to change the focus and/or beam angle of the emitted ultrasound during the medical procedure.