# Basics of ultrasound imaging

### Ultrasound transducer physics

Therefore, multiple reflected waves return to the probe and the machine uses this information to display an image showing the different tissues. Doppler shift; difference between emitted and received frequencies. Note: the specific Doppler calculation will not be explained further in this course. The wave that returns to the probe also has a certain frequency. Posterior sound transmission is a good tool to differentiate a cyst from a solid lesion fig. Resolution is the ability to see two things as two things. The reflected sound waves produce the ultrasound image. The human ear can hear between frequencies of about 20 Hz to 20, Hz. This is called deflection. Photo courtesy Philips Research Ultrasound examination during pregnancy In this edition of How Stuff Works , we will look at how ultrasound works, what type of ultrasound techniques are available and what each technique can be used for.

Additionally, we want adequate depth of penetration to see deeper structures. The optimum frequency is one that will give you just the adequate amount of depth necessary to see the structures of interest.

So in clinical practice, you might think that using the lowest frequency is the best because it gives a longer depth of penetration. The commands from the operator are translated into changing electric currents that are applied to the piezoelectric crystals in the transducer probe.

When ultrasound enters the body, some of it undergoes: 1. The Doppler shift is shown on the vertical line, time on the horizontal line fig.

### Ultrasound basics for medical students

Unfortunately, these artifacts cannot all be discussed in this course. Figure Orientation tip when attending a live examination: the top of the image is the location where the sound waves enter the patient first. For this reason, it is common to use a thick liquid jelly between the probe and the patients skin. Since the image is redrawn so rapidly, one can see size changes e. Figure 6. It uses different colours to show the direct and speed of flow. Acoustic impedance is a somewhat complicated concept, but basically depends on the density of the substance and the speed of ultrasound in that substance. Blood flowing towards the transducer has a positive Doppler shift and is shown above the line. More energy will therefore be left to reflect to the transducer. The following happens: You remove your clothes all of your clothes or only those over the area of interest. Years ago, doctors use to perform this procedure blindly; however, with accompanying use of ultrasound, the risks of this procedure have dropped dramatically. Kossoff G. The sound waves bounce on objects such as the strawberry.

Unfortunatelybats always have the night shift. Various frequencies and wave lengths in flowing blood. The linear transducer emits parallel sound waves, achieving high resolution of surface structures including skin lesions. Whenever the returned wave has a frequency different to the frequency of the transmitted wave, the machine knows that the place where those waves bounced back from have moving objects.

In color Doppler, frequency changes are converted into color on screen.

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