Doppler ultrasound is the first diagnostic test for chronic venous disease. Doppler ultrasound provides information about venous anatomy and blood flow. Unlike arterial testing, veins are affected by gravity and valve insufficiency; therefore, the posture of the patient, the method of inducing reflux, and the location of the ultrasound probe and test vessel are important. Generally, the reflux diagnosis for saphenous veins is based on 0.5 seconds, and the reflux standard for deep veins is based on 1 second (1). Throughout this article, we refer to standardized reflux testing methods.

The characteristic change in blood flow direction in venous insufficiency can be assessed by measuring the augmentation waveform caused by calf compression and the reflux waveform due to retrograde flow. These waveforms are positioned in opposite directions along the baseline of pulse wave analysis, allowing for a clear indication of the directionality of blood flow. It is preferable to measure and record the augmentation waveform below the baseline and the reverse flow waveform above the baseline (1-7).

A longitudinal view allows for a more accurate assessment of the length and curvature of blood vessels compared to a transverse view. Therefore, it enables a more precise evaluation of issues, such as stenosis or occlusion, caused by venous thrombosis, providing a higher resolution of the vascular structure. This high resolution aids the examiner in easily identifying and interpreting subtle changes within the blood vessels. Additionally, when measuring in a longitudinal view in duplex or triplex ultrasound, the likelihood of mistaking temporary turbulence or pulsatile flow as reflux is reduced (6-14). Turbulence around valves may be misinterpreted as reflux when measuring in a transverse view (15).

Color Doppler allows for the visualization of blood flow direction by using two colors. Additionally, pulsed-wave Doppler provides information such as flow direction, velocity, and cycle that cannot be solely analyzed using color Doppler. Therefore, to effectively demonstrate the persistence of reflux over a specific period, it is recommended to primarily base it on pulsed-wave Doppler examination and supplement it with color Doppler (6,7,9,10,12).

Perforating veins can be an anatomically intricate and tortuous network, making measurements in a longitudinal view challenging. In a longitudinal view, the primary goal is to follow the vessel length, making it difficult to measure complex vascular branching or transverse sections accurately. In such cases, measurements can be performed more effectively in a transverse view.

Reflux refers to retrograde blood flow opposite to normal venous flow. To verify venous reflux using ultrasound, standardized ultrasound images are required. Unlike the transverse view, the longitudinal view allows for visualization of both the direction of the blood flow and the ultrasound incidence angle, facilitating an objective assessment of the presence or absence of reflux. Furthermore, the probe must measure blood flow in a fixed position to detect the Doppler frequency shift accurately. The Doppler effect is sensitive to the relative movement between the probe and blood flow. Therefore, performing the reflux provocation test using the standardized position and method provided here is of great significance.