Okay, now that the beam is finally working, good morning everyone. Welcome to the Monday

morning lecture on diagnostics, medical image processing. Professor Honigar can't be here

today so he asked me to give the lecture today. I'm Marco Buegel. I'm also one of the guys

doing the exercises so you'll probably see me in the next coming weeks. So what we're

talking today about is X-ray specific image processing, pre-processing using image intensifiers.

So the contents of the lecture, we will start off with some basics about X-rays and X-ray

detectors and then we will talk about the specific problem of image distortion or image

distortion correction and that's our goal to correct it. And after that maybe some remarks

and more specific problems in the approach to deal with image distortion. So what does

an X-ray system consist of? Basically we have an X-ray source and we have a detector somewhere

and in between we can put an object and the X-rays will penetrate the object and attenuate

depending on the material. And the detector can then measure the energies of the X-ray

particles. So first off in X-ray image acquisition there are different types of image artifacts.

Some are caused by the X-ray sources, some are caused by the X-ray detectors. And what

we are considering today are artifacts that are caused by the image detectors and specific

by the image intensifiers. So the image intensifiers are one of the older techniques which were

introduced in 1940 roundabout and nowadays they are still used in some hospitals and

older systems but if you were to buy a new system by Siemens or by Phillips you won't

be able to get a new system with an image intensifier anymore. So they're pretty outdated.

And nowadays all new systems are using flat panel detectors which were introduced about

15 years ago and we're mainly using in research the flat panel detectors and as I said the

new equipment only comes with flat panel detectors anymore. So image intensifiers are outdated

and we're still covering the artifacts but it's mostly for historical reasons here. So

how does an X-ray tube work? So basically we have the cathode to the right here and

it is heated up and as it is heated up electrons are released. The electrons are released in

this electric field here and are accelerated. And when they hit the anode there are the

extra particles that are released and they are released in the directions of the arrows

here. And now you can put an object in between and maybe put a film sheet behind it and then

you get the classical X-rays on film sheets as you may be seen in TV shows or maybe you

had an X-ray yourself. But with newer technology with detectors you can also capture it with

a CCD chip and display it on your computer screen. One of the problems with these X-ray

tubes is that they are very inefficient. So of that energy that is produced here 99% will

be released as heat. So we have a pretty bad cooling problem here and that is something

that was only dealt with recently in about 2005 and there is also a slide later on about

that. So there is one of the phenomena that will cause image artifacts. This is the Heal

effect here and basically what you can see here is you have the electrons that are released

here. They hit the anode and the problem is depending on the direction that the extra

particles are released they have a different energy. So if you consider the central ray

here as the 100% then you will have extra particles that are released in the direction

of the cathode that will have higher energy. And the inverse is true for extra particles

that are released away from the cathode they have even lower energy. So if you look at

an image then of an object that consists of one material you would expect for the whole

object the same intensity. But instead you will see from dark to bright from left to

right because the lower energies result in darker intensities. That is a problem of homogeneities

of the intensities and I think this will be covered in one or two lectures. So not today.

So as I mentioned the cooling problem was solved in about 2005 by engineers from Erlangen.

They developed this new x-ray tube called the Straton tube and what they did here is

they embedded the x-ray tube in an oil field here and the anode is also rotating. So the

problem while we are rotating the anode is if the electrons always hit the same spot

on the anode. First off we have the heating problem and if they always hit the same spot