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Okay, so welcome back everybody. After our short delay we can go back to our lecture

and we will talk about interventional medical image processing. Today we want to discuss

3D ultrasound and in particular the application how to reconstruct 3D volumes from 2D ultrasound

slices. Okay, we will first have a couple of historical remarks on the history of ultrasound,

then a couple of facts on ultrasound, a bit of the physics. Remember that these things

won't be relevant for the written exam, but rather the factorization methods that we will

focus on in the second part of the lecture. So we will then describe factorization methods

and factorization methods we will find extremely useful because with those kind of methods

we will be able to reconstruct a set of 3D positions while also reconstructing the camera

poses without any additional input. So this is a really nice algorithm and you will find

it extremely useful, it's also very popular, it's also been cited a lot of times in literature.

Good, so a couple of historical remarks. So actually medical ultrasound was discovered

in 1942 and it was the first time actually used for medical purposes, but the entire

theory and first applications actually come from a military background. You will see that

this technology was found to be extremely useful if you want to detect submarines. So

this is where many of the basics come from. And again you can see that a lot of technology

is useful in a medical sense, you can use it to help people, but on the other hand a

very similar kind of technology can also be used in military applications. So you can

always think about that when you are actually driving science, that you should also think

about ethics and the actual application of your science. Then in 1984 the first 3D ultrasound

system was reported by Barber and here you can actually see that the very first applications

also go back to a commentary by Aristotle, so it has a long history. Very well, so what

we are actually interested in is propagation of waves and measurement of reflectance. In

order to do that we are generating pressure waves and they are generated by periodic motion

and this way we are able to send out waves along into a medium. There's a couple of things

that happen with those waves, so first of all they can be reflected, so if the boundary

between two media is in a certain condition you will realise that the wave will be reflected

and they will not be transmitted. Then there's the effect of refraction, this can also happen

that your waves are bended and you can experience absorption and absorption will be that if

you have acoustic energy that will be absorbed by the tissue and then it will attenuate the

wave, so the wave will get weaker the further it propagates into tissue and in between every

time you have an intersection between media it can be either reflected or refracted. Down

here you see a couple of ultrasound machines and you can notice that ultrasound is a modality

where you, if you have a look at the user interface you will see that it is, it seems

rather complicated but people are really well used to it and they can operate these systems

very well and securely and here you can also see another more newer device of an ultrasound

system here to the right hand side. Actually there has been further developments in ultrasound

and nowadays you can even produce ultrasound sensors and also ultrasound displays that

are hand held so you can actually use ultrasound in for example in an ambulance. So this is

also a nice thing about ultrasound, the technology is very very well available so you have ultrasound

in many clinics, many doctors use it and it's a rather cheap technology compared to the

other modalities that we've seen in the lecture so far. So an ultrasound device is much cheaper

than a CT system and it's also much cheaper than an MR system. So MR is really really

expensive and in 2D ultrasound you can deploy it even in an ambulance. These are a couple

of images and of course everybody knows ultrasound from fetal imaging and another reason of course

why ultrasound is very popular is it's not using any ionizing radiation so you're merely

using acoustic properties, reflection of sound waves and they are not ionizing the tissue

so you don't have any radiation exposure and this is also why it's very popular in fetal

imaging so that you can create images of the growing fetus and you can also measure different