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动脉穿支（arterial perforator）是指起源于主（母）动脉，并穿过肌间/隔皮/肌皮平面以供应深部组织的血管。 如今，动脉穿支已成为针对因烧伤、创伤或外周血管闭塞性病变继发坏疽等损伤引发的营养性或浅表软组织缺损，开展穿支皮瓣重建手术的主流术式。 尽管当前有关动脉穿支解剖的研究资料浩如烟海且持续增多，但目前尚无系统方法可用于定位下肢的穿动脉。这主要源于个体间存在大量解剖变异，且不对称是人体普遍存在的规律；即便在同一受试者的双侧下肢之间，动脉穿支的解剖分布也存在不对称现象。 因此，皮瓣手术的术前规划自然无法依托任何预先制定的统一准则。必须对每位患者进行独立评估，并将穿支的解剖变异纳入术前血管映射的考量范畴。 ### 连续波多普勒（CW Doppler） 连续波多普勒（CW Doppler）是多普勒成像中较为简易的配置形式，由两种不同的换能器组成：接收换能器与发射换能器。发射换能器的核心作用是产生预设频率的连续超声波束输出。随后，接收换能器接收该发射信号。将接收信号与发射信号进行叠加，可生成包含拍频的波形，该拍频等于多普勒频移频率。但连续波多普勒无法提供分析点深度或产生多普勒频移的运动点位置相关信息¹。 ### 脉冲波多普勒（PW Doppler） 脉冲波多普勒（PW Doppler）的研发初衷是获取感兴趣区域的深度感知信息，该区域正是产生多普勒频移现象的位置。脉冲波多普勒系统仅包含一个换能器，该换能器可同时完成信号的发射与接收。脉冲波多普勒所使用的脉冲与B型超声成像所用的脉冲存在显著差异。系统采用电子门控技术，对发射脉冲与接收脉冲之间的时间间隔进行计时，这使得操作者能够对发射波束长轴上的特定点进行分析。脉冲波多普勒的主要输出为可听信号。将脉冲波多普勒与B型超声成像相结合，即称为双工超声成像，可使操作者同时分析两种成像信息，并聚焦于B型超声图像中的特定点以开展多普勒分析。