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Choosing the right Doppler

A Doppler is used to determine the speed of the blood flow in an organ or vessel. As such it is used in the detection of certain vascular pathologies such as the narrowing of the diameter of a blood vessel or detecting a damaged vein or artery. It also makes it possible to analyze the vascularization of certain organs or tissues when coupled with an ultrasound machine – this is called a Doppler ultrasound.

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  • How does a doppler work?

    Ultrasonic waves are emitted by the Doppler probe which, once reflected by the blood flow, in movement with respect to the probe, see their frequency vary. This frequency variation between the emitted ultrasound wave and the reflected ultrasound wave is used to characterize the dynamics of the blood flow-such as its velocity and direction.

    These characteristics are fundamental for determining certain cardiovascular pathologies (see next question).

  • What are the main uses of a Doppler?

    Dopplers are used to detect several cardiovascular diseases such as phlebitis, certain aneurysms, a potential heart murmur, etc. Here is a list of the main applications:

    • Detection of phlebitis (Doppler ultrasound)
    • Detection of certain aneurysms (Doppler ultrasound)
    • Detection of a potential heart murmur (Doppler ultrasound)
    • Organ vascularization analysis (Doppler ultrasound)
    • Intraoperative vascular monitoring (Doppler ultrasound)
    • Listening to a fetus and mother’s heartbeats (fetal Doppler);
    • Detection and follow-up of a cerebral embolism (transcranial Doppler);
    • Detection and follow-up of arteriovenous malformations in the brain (transcranial Doppler);
    • Head injury assessment (transcranial Doppler);
    • Diagnosis of brain death, etc.
  • What are the different types of Dopplers?

    Sonoscape color Doppler ultrasound

    A Sonoscape color Doppler ultrasound

    Different types of Dopplers present results in sound, graph or image form.

    • Acoustic Dopplers: present results in sound form. For example, the transcranial Doppler allows the speed of red blood cells in the vessels to be recorded by means of a probe that emits an RF sound signal that travels through the body. The probe then receives the wave that is reflected and it is the difference in frequency between the two that gives us information about the speed of the red blood cells.
    • Spectral dopplers: display blood flow measurements in the form of a graph representing the flow rates recorded over time.
    • Color Dopplers: in this case the Doppler is coupled with an ultrasound scanner. As such, a color Doppler makes it possible to visualize the distribution and direction of blood flow in an organ or vessel. The color mode displays the blood flow to the probe in red and the blood flow leaving the probe in blue.
  • What is the difference between a unidirectional Doppler and a bidirectional Doppler?

    An Elcat unidirectional Doppler

    An Elcat unidirectional Doppler

    Depending on the types of vessels to be analyzed, a unidirectional or bidirectional Doppler will be used.

    • Unidirectional Dopplers: are used for the analysis of vessels with blood flow that only goes in one direction.
    • Bidirectional Dopplers: are used for analyzing blood flow in both directions.
  • What is a spectral Doppler?

    A Neural Analytics Spectral Transcranial Doppler

    A Neural Analytics Spectral Transcranial Doppler

    A spectral Doppler is used to measure the speed of blood flow in certain vessels or organs. This speed is represented in the form of a diagram. The higher the amplitude, the faster the blood flow.

    There are two types of spectral Dopplers: continuous-wave or pulsed-waved.

    Sometimes, when the flow is too fast in the vessel, there is an aliasing phenomenon. The signal is no longer usable because the Doppler can no longer determine the speed and/or direction of blood flow. This problem can be corrected by increasing the Nyquist frequency, i. e. by increasing the sampling rate.

  • What does analyzing the phases of an arterial Doppler allow?

    When analyzing an artery of a resting patient, it is possible to determine its condition using an acoustic or spectral Doppler. The spectral Doppler pattern can then be triphasic, biphasic or monophasic.

    • Triphasic waveforms: when analyzing a healthy and resting patient’s artery, the waveform is triphasic, i.e. the three main phases of a heartbeat can be identified (systole, diastole, elastic recoil).
    • Biphasic waveform: when analyzing the artery of a resting patient with a mild or moderate pathology, the resulting waveform will be biphasic.
    • Monophasic waveform: lastly, in the artery of a patient at rest but suffering from a more serious pathology, the waveform will be monophasic. A more detailed examination will determine the occlusion zone.
  • What options are available for a Doppler?

    Some Dopplers have additional features that allow you to:

    • Determine the heart rate (heart rate monitor)
    • Calculate the systolic pressure index in order to detect peripheral arterial
      diseases
    • Detect AAAs (abdominal aortic aneurysms)
    • Detect embolisms (transcranial Dopplers)
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