The present invention is directed to a novel target detecting device comprising an excitation transducer generating a low frequency pulses of weakly focused ultrasonic energy and a sensing transducer. The present invention also includes a method of aligning a treatment transducer to a target by mapping the target in situ by sending a low frequency ultrasound signal and receiving reflected signals from the target. These inventions provide a simpler way of determining the location of a target and aligning a treatment transducer without the need to generate and interpret an image and then translate the image back onto the target.