Ultrasound pulse generation length

Each pulse is the same duration and consists of two to four cycles. The pulse length is constant; it is not changed by the ultrasonographer. The pulse repetition period consists of the pulse duration plus the listening period, which is the time during which the device listens for returning echoes. The pulse repetition frequency is the inverse of the pulse repetition period, or the number of pulse repetitions per unit of time. If the ultrasonographer increases the imaging depth, the listening time increases (to allow for return of more distant echoes), so the pulse repetition period increases, and thus the pulse repetition frequency decreases.