![]() ![]() ![]() With complete occlusion of ICA, the external carotid doppler waveform can change from high resistance to low resistance due to the development of low resistance collateral pathways. Alternating peak systolic height in line with cardiac rhythm is called pulsus alternans, which can be seen in myocardial disease, metabolic disease, or IVC compression. Pulsus Bisferiens denotes two prominent systolic peaks with mid systolic retraction and is usually found in hypertrophic cardiomyopathy and aortic valvular disease. The Pulsus Parvus and Pulsus Tardus waveform results from delayed and diminished arterial pulsation and is observed distal to stenosis in 91% of cases. The resistive index is the term used to describe waveforms, which signifies resistance of the vessel distal to the examined vessel. ICA demonstrates low resistance flow, ECA has high resistance flow, while CCA has a hybrid of ICA and ECA (Figure 2, 3, 4). Spectral Doppler waveform evaluation gives critical information about flow dynamics at the point of sampling, which depends on hemodynamic factors affecting a proximal or distal portion of the vessel. Spectral analysis including peak systolic velocity (PSV), peak diastolic velocity (PDV), mean maximum velocity, and pulsatility index can then be obtained. Color Doppler should be evaluated at the minimum at (a) “long axis of the distal common carotid artery” (b) “long axis of proximal and mid internal carotid artery” (c) “long axis of the external carotid artery” (d) “long axis of the vertebral artery.” Any abrupt change in the systolic velocity or area of slow flow should be carefully evaluated and documented. Sample volume should be placed into the center of the lumen and should be moved along the entire vessel. ![]() Gain is adjusted so that color is seen only within the lumen of the vessel to avoid bleeding artifact. The velocity of the common carotid artery is usually 30-40 cm/sec but may vary in a diseased vessel. The technologist needs to correctly set the angle correction parallel to the flow direction to correctly calculate the velocity (the calculated velocity will be incorrect if calculated using an inaccurate angle, not corresponding to flow direction). The actual angle of insonation / Doppler angle should be less than <60 degrees (as close as possible to parallel) to improve the accuracy of measurements (the calculated velocity will be less precise if calculated/extrapolated from a nearly perpendicular angle). There are many parameters that should be optimally adjusted to achieve reliable results. This is then followed by the Doppler examination. At the jugular notch, the transducer is angulated causally, while at the angle of the mandible, it is cephalic angulated. Some vessels, especially if they are tortuous, require the angle of the probe to be adjusted accordingly. The time-gain compensation should be optimized to account for ultrasound attenuation from deeper structures. irregular), and presence of calcification should be assessed and reported. The plaque echogenicity, surface characteristic (i.e., regular vs. The vulnerable plaques are more prone to rupture and acute thrombosis. The morphology of plaque is associated with the severity of atherosclerotic disease. B-mode imaging evaluates the course and caliber of the vessel with the evaluation of intimal-media thickness and quality of plaque. Grayscale imaging, which is also called B (brightness)-mode, is usually performed first, where carotid arteries are evaluated in their entirety from the jugular notch to the angle of the mandible in the transverse and longitudinal plane. This allows the determination of the speed and direction of the flow. Velocity is calculated using the Doppler formula, where frequency shift is proportional to the velocity times the cosine of the Doppler angle. The technique is built on the principle of the Doppler effect, with measurement of the change in the frequency and wavelength of a sound wave transmitted and reflected by moving red blood cells within the vessel, termed as Doppler frequency shift. ![]()
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