A doppler is a medical device that uses ultrasound and the doppler effect to measure the movement of objects – e.g. fetal heartbeat or bloodflow in a body. There are different types of doppler:
Fetal Doppler
Invented in 1958 by Dr. Edward H. Hon a Fetal Doppler or fetal heart rate monitor is a hand-held device used to detect the heart beat of a fetus for prenatal care (baby in the womb).
Fetal Dopplers are commonly referred to simply as “Dopplers”. To use them, a small amount of ultrasound gel and a doppler probe is placed on a pregnant woman’s lower abdomen. The probe sends sound waves (ultrasound) into the body and when the position of the fetal heartbeat reflects the ultrasound waves, the frequency or pitch of the waves are changed. If the fetal heartbeat is moving toward the probe, this produces a higher frequency and a lower frequency if it is moving away from the probe. The Doppler effect detects the change in frequency of the fetal heartbeat and therefore can measure the sound of the baby’s heartbeat. This sound is then amplified through a speaker in the doppler.
Some fetal dopplers also contain an LCD screen to display the Fetal Heart rate (FHR) on an LCD screen.
Fetal dopplers are generally able to be used from 12 weeks of pregnancy. Originally they were used by midwives and healthcare professionals, but it is becoming increasingly popular to find companies offering fetal dopplers to buy or hire for home use / personal use as well as professional use.
Fetal dopplers can help reduce anxiety during pregnancy, offering reassurance especially during the early stages before it is possible to feel the baby moving. Dopplers also help to involve other family members in the pregnancy experience such as young siblings, partners and grandparents..
Ultrasound vascular doppler
An ultrasound vascular doppler is a device that uses ultrasound to measure blood flow and blood pressure. High frequency sound waves ultrasound) are bounced off circulating red blood cells to identify blood flow.
A vascular doppler can estimate how fast blood flows by measuring the rate of change in its pitch (frequency). The doppler probe is pressed against the area of your body being examined, moving from one area to another as necessary. This test may be done as an alternative to more-invasive procedures such as arteriography and venography, which involve injecting dye into the blood vessels so that they show up clearly on X-ray images.
An ultrasound vascular doppler may help diagnose many medical conditions such as:
- Blocked arteries otherwise known as arterial occlusion
- Blood clots
- Bulging arteries known as Aneurysms
- Narrowing arteries
- Heart valve defects and congenital heart disease
- Problems with valves in leg veins causing pooling of blood or fluids, otherwise known as venuous insufficiency
- Decreased leg blood circulation known as peripheral artery disease
- An ultrasound vascular Doppler may also help to check for injuries to your arteries or to monitor certain treatments to your veins and arteries
What is the Doppler effect?
The Doppler effect (or Doppler shift), named after Austrian physicist Christian Doppler who proposed it in 1842, is the change in frequency of a wave for an observer moving relative to the source of the waves. It is commonly heard when a vehicle sounding a siren approaches, passes and recedes from an observer. The received frequency is increased (compared to the emitted frequency) during the approach, it is identical at the instant of passing by, and it is decreased during the recession. This variation of frequency also depends on the direction the wave source is moving with respect to the observer; it is maximum when the source is moving directly toward or away from the observer, and diminishes with increasing angle between the direction of motion and the direction of the waves, until when the source is moving at right angles to the observer, there is no shift.
What is Ultrasound?
Ultrasound is a medical detection technique that uses high frequency sound waves and their echoes. The technique is similar to the method used by bats, whales and dolphins to navigate, as well as SONAR used by submarines. Ultrasound devices transmit sound pulses using a probe / transducer, which are reflected back to the probe once they come across an object. The time taken for the pulse to get returned is translated into a picture or sound.
