Synonyms in a broader sense
Ultrasound examination, sonography, sonography
Definition
Sonography or ultrasound – examination is the application of ultrasound waves to examine organic tissue in medicine. A sonogram/ultrasound is an image created with the help of sonography. The examination works with inaudible sound waves on the echo principle, comparable to the echo sounder used in seafaring.
Physically, ultrasound refers to sound waves above the human auditory range. The human ear can perceive sounds up to about 16 -18. 000 Hz.
The ultrasonic range lies between 20. 000 Hz – 1000 MHz. Bats use ultrasonic waves for orientation in the dark.
Tones of even higher frequency are called hypersonic. Below the sound audible to humans, we speak of infrasound. Ultrasonic waves of the sonography device are generated with so-called piezoelectric crystals.
Piezoelectric crystals oscillate when ultrasound is applied with a corresponding alternating voltage and thus emit the ultrasound waves. The prerequisite for ultrasound examination in medicine is liquid. Air-filled cavities such as lungs and intestines cannot be examined and evaluated, or only to a limited extent.
In ultrasound examination, the ultrasound probe, which is both a transmitter and receiver, sends an ultrasound pulse into the tissue. If this is reflected in the tissue, the pulse returns and is registered by the receiver. The depth of the reflected tissue can be determined by the duration of the emitted impulse and its registration by the receiver.
The introduction of ultrasound diagnostics in orthopedics goes back to Prof. R. Graf in 1978. Graf started to use ultrasound on the child’s hip joint in order to be able to detect hip dysplasia in infancy, since X-rays do not provide any information due to the missing skeleton. In the further course of time, the indication for the use of sonography in orthopedics grew continuously (see indications).
In general, the so-called B-mode is used for examination. In this mode, not a single pulse is emitted, but a “pulse wall” is used over a line of several centimeters. As a result, the sonographer calculates a slice image of the tissue being scanned. In orthopedics, depending on the required penetration depth, transducers with frequencies between 5 – 10 MHz are used for an ultrasound.
