Abstract: A method of measuring blood flow through a blood vessel is provided using a single quasi-continuous mode probe that can support multiple frequencies without increasing the probe tip size. A plurality of elements are provided in the probe tip. Each element emits ultrasound waves using a long pulsed signal with each element having a different resonant frequency. Each element also receives ultrasound energy in a continuous mode. A selector is manually controlled by a practitioner to select the active element. The output may take a variety of forms. For example, the output may be printed, displayed, recorded to a memory, and/or played through a speaker or headset.