ROLE OF CONTINUOUS WAVE VS PULSE WAVE AND COLOR DOPPLER IN IDENTIFYING ARTERIAL PERFORATORS OF LOWER LIMB

An arterial perforator is a vessel, which arises from a main (parent) artery and passes through the intermuscular/septocutaneous/myocutaneous plane to supply blood to the deeper structures.

In the present day, arterial perforators have become the mainstay of perforator flap reconstructive surgeries after trophic or superficial soft tissue defects, secondary to insults like burns, trauma or gangrene secondary to peripheral vaso-occlusive pathology.

Even though there is voluminous and ever-increasing knowledge of anatomy, there is no systematic approach to locate the perforating arteries in the lower limb. This is mainly due to high amount of anatomical variation amongst individuals and asymmetry being the general rule in every individual. There is asymmetry in anatomical spread of arterial perforators between two lower limbs of one individual as well.

Therefore, it is natural that the pre-operative planning before surgical flap surgery cannot be based upon any previously laid down set of rules. Every individual must be evaluated independent Lee and anatomical variations in perforator a mapping must be taken into account.

Continuous-Wave Doppler (CW Doppler)

CW doppler is the one of the simpler configurations of Doppler imaging & consists of 2 different types of transducers: a receiving & a transmitting transducer. The main role of the transmitting transducer is to produce a continuous ultrasound beam output
at a predetermined frequency. This transmitted signal is then received by receiving

crystal. Addition of the received and transmitted signals is done, which leads to formation of a waveform which consists of a beat frequency. This beat frequency is equal to the doppler-shift frequency. There is no information or data provided the continuous wave doppler in terms of the depth of the point of analysis or at which the analyzed motion is occurring, that causes the doppler shift.1

Pulsed Wave Doppler (PW Doppler)

The main aim of development of pulse wave doppler was to primary obtain information regarding depth perception of the region of interest which is leading to the doppler shift phenomenon. Also, PW doppler system comprises of only one transducer. This same transducer does the job of transmitting and receiving signals. There is substantial difference in the pulse used for pulse wave doppler as compared to pulse which is used in B mode imaging. Electronic gating is used which times interval between the transmitted and received pulse. This allows the operator to analyze a specific point along the long axis of the transmitted beam. Main output from a PW doppler is primarily an audible signal. When combined together, PW doppler and B mode imaging are called Duplex ultrasound imaging. This lets the operator to analyze both entities together and focus on a specific point in the B mode image for doppler analysis