Figure 2. Graphic representation of a pulsed ultrasound signal. A series of n pulses with a period which is determined by the frequency is presented. The pulse duration equals n times the period. The pulse sequence is repeated after the pulse repetition time. The maximal and minimal pressures during a pulse train are indicated by p₊ (peak positive pressure) and p_- (peak negative pressure). The mechanical effects are mainly determined by the pressure of the pulse train. The pulse duration:pulse repetition time ratio modulates the heat load. If ultrasound is administered in short bursts, heat accumulation is limited.