Diagnostic Services
Color Doppler Imaging has added a new to dimension to sonography. It is an established non–invasive technique, predominantly to study blood flow. Color flow imaging is being used to determine organ expansion and functioning. The technique is based on the Doppler principle, first described by Christian Doppler in 1842. The effect is a change in the perceived frequency of sound emitted by a moving source. A working example of this change is the pitch of a train whistle as it moves past a stationary observer. Though the train is whistling at the same pitch the stationary person perceives an increasing and decreasing pitch as the train moves towards and away from him respectively. 
The amount of Doppler shift can be calculated by the Doppler equation. The clinical implication of this is that if we know the frequency shift, we can calculate the velocity of blood flow. Continuous wave Doppler uses two Doppler crystals – one acting as a transmitter and the other as a receiver. Because of the continuous mode of transmitting and receiving, information about blood flow is obtained all along the ultrasound beam without any indication of the depth from which this information comes. Pulsed wave Doppler emits multiple small pulses of ultrasound beams which reach the sampling point and return, giving information of blood flow only in the area of interest. 
Detection of flow outside the area where it should be helps to identify aneurysms and tumor vascularity.
Change in the spectral waveform also determines the exact extent of vessel narrowing.