The following content has been provided by the University of Erlangen-Nürnberg.

So good morning. Good morning everybody. Today we want to open the chapter on 3D ultrasound

imaging and before we look into the algorithmic part I want to introduce to you at least the

rough concept on ultrasound and I also want to point out to a few historical remarks.

Okay? Good. So let's start with the history of ultrasound. Yesterday I asked already who

got an ultrasound already and it are quite a few of you who have received an ultrasound

imaging procedure and the nice thing with ultrasound is that it's a very cheap modality.

So it's mostly with all the doctors that are out in the field. It's not harming the human

body so there is no ionization, no X-ray, no nothing. It's just sound waves that are

performed so it's easy and the tough part starts once you have a look at the images

because ultrasound images are very noisy, low quality and they just give a rough intuition

what's going on in the inner of the human body. So reading ultrasound images is a very,

very complicated thing and the second point I want to mention is if you want to perform

image processing using ultrasound images you are also not on the sunny side of life because

this is very, very hard to do smart image processing on these noisy data. And the third

part I want to mention there is no other imaging modality that is so much dependent on the

person, that depends so much on the person that is acquiring the images because you are

using the ultrasound probe and you basically guide it over the human body and there is

no way to repeat this exactly this way. This is not a well defined procedure in industry

and research is also working on standardizing the acquisition procedures for ultrasound

imaging. And ultrasound was also used in the early days in Greece when they were looking

for gold, maybe they should reconsider this option today as well. They tried to find out

what is here in the ground by sending sound waves and listening to the reflections and

sound waves you know are partially reflected if you have a transition from one material

to another material and that allows you to analyze the structure once you know how the

speed behaves in the ultrasound or the sound waves behave in different materials and how

the speed is actually in different materials. And in 1942 medical ultrasound was basically

discovered by Dusik and in 1984 the first scanners were built that do not only provide

two dimensional information but also three dimensional information so you can use ultrasound

to do 3D imaging. And if you go to your doctor he might have an ultrasound device that is

already in the years and 20 years or more but they still provide images that are sufficient

to do certain diagnosis. And how are these sound waves generated basically? You have

a periodic motion and you generate by this periodic motion these longitudinal waves that

are sent into the human body and we will not go into the technical structure of such ultrasound

probes what material is used and what technology is basically or was basically developed for

this. This will be covered in lectures on medical physics. We just accept at this point

okay there are sound waves that are generated we know that sound waves are attenuated or

reflected dependent on the tissues and we use a few of these physical properties reflection

is the most important thing. So at the boundary of two media waves are not transmitted but

partially reflected. So I send them sound wave and it comes back. If you are in the

Alps and you shout the name of your girlfriend or boyfriend and then it comes back after

a while. And if you know what the sound speed is you can compute the distance. The only

complicated thing is that you have to divide by two. The result of the standard formula

gives you twice the distance because the sound waves goes to the mountain and gets reflected.

So factor of two of one half. Then you have refraction that basically means that the sound

waves are banded. They are banded. And absorption or attenuation is the third effect that we

have. So it's basically a weakening of the signal. And there are different ways of dealing

with ultrasound. For instance if you are familiar with the CT reconstruction methods we have

discussed in winter semester. If you send sound waves to the human body through the

human body you will receive an attenuated signal on the other side. And using these