Artery stenosis or occlusive diseases of the lower extremities refer to a group of diseases caused by atherosclerosis,thromboembolic vasculitis,aorticitis,trauma and other factors of the lower extremities.Artery stenosis or even occlusion of the lower extremities.Atherosclerosis mostly occurs in the middle and large arteries,while thromboembolic vasculitis mainly involves the small and medium arteries of the lower limbs and their accompanying veins,and the lesions are segmented.

Artery stenosis or occlusion of the lower extremities mainly manifests the symptoms and signs of lower limb ischemia.The early symptoms are mild,but they can only be manifested as coldness,coldness,numbness and paresthesia of the limbs,especially the toes;the condition continues to progress,intermittent lameness occurs,and when the advanced arterial ischemia is severe,the affected limb may experience resting pain,and even toe ulcers and gangrene.The severity of symptoms depends on the degree and scope of artery stenosis or occlusion,the establishment of lateral branch circulation,and the speed of disease progress.For patients in the minor complaint period,only early diagnosis and early intervention can effectively reduce the incidence of adverse consequences such as amputation and improve the quality of life of patients.

At present,the main imaging examination methods for lower limb artery stenosis or occlusive diseases are:color Doppler ultrasound(CDU),percutaneous artery digital subtraction angiography(DSA),multilayer spiral CT vascular imaging(MSCTA),nuclear magnetic resonance arterial imaging(MRA)and so on.

Color Doppler ultrasound(CDU)

Color Doppler examination is currently one of the ideal methods for diagnosing arteriosclerotic diseases of the lower extremities.Using color Doppler ultrasound,the two-dimensional structure of blood vessels,the flow rate and direction of blood flow in the blood vessel cavity,the filling of color blood flow,and the Doppler waveform can be clearly displayed.

(1)The two-dimensional image can observe the structure of the artery wall of the lower extremity,the thickness of the inner-middle membrane,the size of the plaque,and the degree and range of lumen stenosis.When the artery is stenosis,the thickness of the inner-middle membrane of the stenosis site thickens,and strong or low echo plaques of varying sizes and forms can be seen,or intrauterine exploration and solid echo filling can be seen.Ultrasound diagnosis of arterial stenosis adopts the diameter stenosis rate,and it has become a widely accepted diagnostic specification for the degree of peripheral arterial stenosis.(2)Color Doppler normal lower limb artery lumen is full of blood flow signals,the blood flow toward the probe is red,and the blood flow away from the probe is blue.The flow rate during the systolic period is high and the color is bright,and the flow rate during the diastolic period is low and the color is dim.Due to the color reversal in the early diastolic stage,the blood flow signal in the lumen shows a rapid“red-blue-red”transition.When the artery is stenosis,color Doppler shows that the color blood flow beam becomes thinner and varies in thickness,showing segmented light and dark changes,colorful inlays or weak colored blood flow in dots and strips.(3)Spectral doppler The Doppler spectrum of normal lower limb arteries is a typical three-phase waveform.The spectrum begins with high-speed forward blood flow caused by heart contraction,then reverse blood flow in the early diastolic stage,and finally forward low-speed blood flow in the middle and late diastolic stage.When the artery is stenosis,the blood flow rate at the stenosis accelerates,the frequency band widens,and the peak speed of the reverse wave during the diastolic period decreases or disappears.The stenosis or occlusion of the remote artery becomes a low-resistance blood flow,which is manifested as an extension of the acceleration time of the systolic period and a decrease in acceleration.Many authors tend to judge the degree of artery stenosis based on the characteristics of pulse Doppler spectrum changes.

There are reports that:for narrow arteries with a stenosis of more than 50%above the popliteal artery and below the iliac artery,the sensitivity and specificity of color ultrasound are more than 90%.Research by Jager et al.found that in each segment of the lower limb artery,the sensitivity of ultrasound to distinguish between normal and diseased arteries was 96%and the specificity was 81%,and the sensitivity to distinguish between pipe diameter reduction of less than and greater than 50%was 77%and the specificity was 98%.Studies by Kohler and others have shown that for arterial stenosis that causes significant pressure gradation or>50%reduction in pipe diameter,the sensitivity of ultrasound is 82%,the specificity is 92%,the positive predictive value is 80%,and the negative predictive value is 93%.

Limitations:(1)Ultrasound cannot accurately diagnose the degree of artery stenosis.(2)Ultrasound cannot clearly provide the state of blood vessels below the stenosis site,nor can it construct the true form of blood vessels well,and it is susceptible to interference by gas and other factors during the examination;if the artery wall has strong echo calcification,it is easy to lose the Doppler signal and interfere with the examination.

Therefore,color Doppler ultrasound can be used as a means to roughly judge the site and degree of vascular stenosis,which is of high clinical value for early diagnosis.Ultrasound can be used as a common indicator to evaluate blood vessel function after vascular transplantation,and can be used as the preferred method for judging the efficacy and long-term follow-up of patients and monitoring of changes in their condition.

Department of Ultrasound Liu Hao