The Pulser and Power Control

The pulser is the component in an ultrasound machine that gets everything started!  

The pulser sends the excitation voltage to the transducer which converts the voltage into an ultrasound pulse.  One pulser voltage generates one pulse of ultrasound.  The number of ultrasound pulses produced by the transducer per second is known as the pulse repetition frequency (PRF).  Thus, the pulser sets the PRF. 

The sonographer indirectly influences the PRF by setting the depth of field.  A deep depth of field will tell the pulser to reduce the PRF in order to wait for the deeper echoes to return to the transducer.  A shallow depth of field tells the pulser that it can increase the PRF since the system does not need to wait as long between pulses.

The pulser also serves as the system's master clock.  The pulser tells the receiver when each pulse is transmitted so that the go-return time for each pulse-echo can be accurately measured.

The power control controls the amplitude of the excitation voltages from the pulser.  A high amplitude excitation voltage produces a high amplitude ultrasound pulse.  Reducing the amplitude of the excitation voltage reduces the amplitude of the ultrasound pulse.  

The sonographer directly controls the ultrasound power using the power control.  The operating principle should be the ALARA principle (use as low power as is reasonably achievable).

Here is a short video on the pulser and power control...