Abstract: A method and apparatus for ultrasonically detecting an embolus in blood flow includes an ultrasound transducer for transmitting ultrasound pulses into the blood flow being interrogated and receiving reflections from acoustic impedance changes in the body. The reflected signals are converted to an electronic signal representation which is subsequently processed to detect and classify emboli in the blood flow. A short duration, broad bandwidth ultrasound signal is used to preserve the polarity of the reflected signal. The polarity is then used to classify the emboli based on a positive or negative reflection coefficient. Emboli having a negative reflection coefficient are classified as either gaseous or fat particles, and emboli having a positive reflection coefficient are classified as solid particles. The emboli can be further classified based on the amplitude of the reflected signal, or designated features of the time waveform or FFT of the reflected signal.