According to the characteristics of color Doppler flow imaging, it is important to determine the direction of blood flow, the speed of blood flow and the nature of blood flow. At the same time, it is also valuable for the display of vascular morphology including the vessel diameter, travel, distribution and the richness of blood vessels. High-performance color Doppler ultrasonography can display small vessels with diameters of 2 mm or less, as well as low flow velocities and low flow rates of 2 to 3 mm/s. It can be used to evaluate organ perfusion and lesion blood supply characteristics.
However, because the vasculature in the organ or lesion is not perfectly straight and is affected by the angle of sound beam detection, it is often difficult to show the complete vasculature, and only a certain section or part of it may be observed. As a result, the vasculature may appear as colored dots, short lines or dendrites on the image. The degree of abundance is also evaluated based on the number of dots, short lines, or dendrites shown. Richer flow may show more dendritic or reticulated flow, or even fireballs.
Quantitative flow velocity studies or hemodynamic measurements are based on spectral Doppler testing, generally based on the Doppler spectrum curve of a particular site as shown by color Doppler. The Doppler spectrum curve shows the magnitude and distribution of the Doppler difference frequency (frequency shift) over time. The vertical coordinate is the frequency shift axis, and if the angle between the sound beam and blood flow is corrected (<60°), it can directly express the flow velocity magnitude; the horizontal coordinate is the time axis.
The spectrum curve has a certain width, i.e., the spectral width, which represents the distribution range of different flow velocities. The upper envelope of the curve represents the variation of the highest flow velocity, its lower envelope represents the variation of the lowest flow velocity, and the brightness on the curve indicates the intensity of a velocity component in the flow velocity distribution.
Through this spectrum curve, the following indexes are commonly used in the detection of abdominal and peripheral vascular hemodynamics: maximum systolic velocity (SP), end-diastolic velocity (Ed), mean velocity (mv), acceleration (av), acceleration time (at), resistance index (RI), pulsatility index (PI), congestion index (CI), etc.
The resistance index (RI) and pulsatility index (PI) can reflect the distal resistance of the measured vessel and the elasticity of the arterial wall and other comprehensive factors within a certain range, and exclude the influence of the angle between the acoustic beam and the blood flow, and have a greater reference value, which are calculated by the following formulas:
PI=(sP-Ed)/SP Note: SP: maximum systolic blood flow velocity
Ed: end-diastolic blood flow velocity
RI=(sP-P-P)/MEANNote: P-P: the lowest value of the curve
MEAN: Mean value of blood flow velocity
CI: A/mvNote: mv. mean blood flow velocity
A-Transected area of the vessel (cm)
Since the intravascular flow velocity distribution is not piston-shaped and is influenced by heartbeat, respiration and many other factors, it is wrong to use the simple calculation of Q=A-TAV-60 and A=π/4D2.
The determination of blood flow requires a specially designed instantaneous (10ms) flow velocity profile display technique. The flow velocity data is intercepted in segments on the flow velocity profile and multiplied by the corresponding intra-lumen ring area to obtain the zonal ring flow; the sum of all ring flows is the instantaneous blood flow. 100 consecutive instantaneous blood flows are summed to the blood flow per second. This is then multiplied by 60 to obtain blood flow per minute. This method, called CVIQ technique, is in accordance with the flow measurement principle.
