Doppler in Ultrasound:
Overview
In the last decades, there have been significant advances in non-invasive vascular studies, mainly with techniques such as magnetic resonance imaging and computed tomography.
The Doppler in ultrasound technique has been available in clinical practice for 40 years, constituting a fundamental diagnostic method and most of the time, a frontline approach for the diagnosis of vascular pathology.
Doppler in ultrasound effect.
When an emitter produces a wave of a certain frequency (sound or light), this wave travels freely through the air at a certain speed, reaching the receiver who will receive exactly the same emitted frequency. When this happens, it is not a Doppler effect (wave a).
If the emitter or receiver moves, either away or towards, although the wave speed remains the same, it will be compressed (if approaching) or expanded (if moving away), so the frequency received by the receiver is different from the emitted frequency. This is known as the Doppler effect (waves b and c).
The difference between the emitted and received frequencies is called “frequency shift” or “frequency displacement”.
What is venous ultrasound?
Doppler in ultrasound is primarily a first-line diagnostic method for patients with vascular pathology.
In medical practice, Doppler is used to evaluate blood flow by measuring the movement of red blood cells, which act as small reflectors that return sound as an echo, allowing information to be obtained about vascular permeability, presence of stenosis, direction of blood flow, vascular resistance, and vascularization of lesions.
Doppler in ultrasound, techniques
Color Doppler: A system is used to transform measurements into colors. The color image is superimposed onto the standard ultrasound, making it easier to visualize the velocity of the blood flow.
Power Doppler: Allows for more detailed images of the flow of localized vessels. It is useful for observing whether there is blood flow in an organ or tumor, but this method does not indicate the direction of the flow.
Spectral Doppler: Shows the results of blood flow measurement in a different graph, with the velocity of the blood flow registered at a given time.
Benefits of Doppler in Ultrasound:
- Non-invasive
- Painless
- Does not use ionizing radiation (X-rays)
- Outpatient; can be performed in a doctor’s office
- No anesthesia or sedation is needed
- Very safe and not associated with any known risks
What does Doppler in ultrasound detect in arterial or venous scans?
- Obstruction or occlusion in the arteries of the neck (carotid arteries), lower or upper limbs (stenosis or absence of flow)
- Blood clots in the veins of the legs (venous thrombosis)
- Reduced blood circulation in the upper or lower limbs (peripheral arterial disease)
- Enlarged arteries (aneurysms)
- Abnormalities in the venous valves of the legs (venous insufficiency)
- Arteriovenous fistula (pathological or surgical, for dialysis)
- Abdominal arterial Doppler evaluates renal and intra-abdominal arteries. Scrotal Doppler evaluates the vessels of the testicle and detects varicocele. Doppler’s ultrasound has various important clinical applications, including the characterization of tumor tissues, which sometimes have abnormal vascularization.
¿What is the preparation for the exam?
It is a process similar to conventional ultrasound. On the day of the study, it is suggested to wear comfortable and loose clothing, without jewelry that may interfere with obtaining the images.
When performing the study, the patient should wear a gown and remove clothing from the area that will be examined. Gel is then placed on the skin in the region to be examined, and the transducer is placed on the skin and slid gently, sometimes exerting very slight pressure.
During the study, the sound of blood flow through the examined vessels will be heard. When the study is complete, the gel is easily removed with paper towels. This gel does not stain clothes and dries quickly. Since no anesthesia or sedation is administered, the patient can continue with their usual activities without any inconvenience after the study.
The exam takes between 30 and 45 minutes to complete.
In some cases, Doppler ultrasound can be an alternative to more invasive procedures such as arteriography; in other cases, additional studies may be necessary to complete the evaluation.
