Sonography (Video)
The ultrasound, also called ultrasonography, became widespread in the 1980s. The two key elements of the physical principle are echoes and ultrasounds.
Ultrasounds are acoustic waves, just like sound waves, but with a higher frequency than the highest-pitched sounds a human ear can perceive.
These waves can go through tissues but some are reflected anywhere there are density changes in the body.
It is these reflected waves, called echoes, which are detected and changed into images, hence the name ‘ultrasonography’ which literally means “the trace of the sound.
The apparatus is made up of several elements:
- A probe, called a transducer, which can emit ultrasounds as well as receive the echoes sent back by the organs. The probe converts these ultrasounds into electric signals.
- The computer system then interprets the signals according to the levels of intensity and the delay of propagation. An image is re-constructed by computer processing.
- Finally, a console which displays but also analyses the obtained image. The doctor can then take certain measurements in real time.
Images appear in different shades of grey. Tissues which send back a lot of echoes show up in white. This is the case for bones but also, oddly enough, gas and air.
Liquids without any particles in suspension such as urine send back little or no echo and appear in black on the screen.
Liquids with particles in suspension, such as blood or soft tissues, send back a weak echo and they appear in grey.
A medical specialist carries out the examination because it is necessary to look for and choose the areas to be studied and then interpret them in real time. It is thus an obstetrician-gynecologist, a cardiologist or a radiologist.
In the case of an external pre-natal ultrasound, the probe is placed on the body’s surface.
Beforehand, the skin is coated with a special gel which prevents the ultrasounds from being dispersed in the air.
The doctor moves the probe while looking at the screen. With rare exceptions, the images are in 2D which explains the incessant movements of the probe to observe a specific area.
Here is a sagittal section view of the spinal column of a fetus.
The ultrasound image makes it possible to study the morphology in order to determine if a structure or an organ is normal.
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computer tools are used to take measures of length or diameter as in the case of this femur
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or, as we see here, a cephalic perimeter measure.(…)
Both hemispheres of the brain are clearly distinguished in this cross section.
For the abdominal cross section, the position of the stomach can be seen …and here there is the umbilical vein.
Here you can see the bone structures: vertebrae and ribs.
An ultrasound makes it possible to study morphology but it is also a dynamic examination resulting in a functional analysis.
The Doppler sonography depends on the coupling of two technologies based on the use of ultrasounds:
- Image technology: sonography
- Movement detection technology: the Doppler
Doppler sonography is used to study blood flow in the heart cavity or in the umbilical cord.
The ultrasound plays an important role in medical imagery.
It is widely-used; it is simple, rapid and non-invasive.
However, it is sometimes less efficient if the patient is obese, for example, because fat absorbs the ultrasound waves.
Furthermore, because it is a dynamic test, a deferred reading of the images is very tricky.
No negative secondary effects have been found due to the use of ultrasounds. However, the frequency and length of the tests are limited to what is necessary for the diagnosis.
