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Facial topometry using pulsed holography

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Facial topometry using pulsed holography
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Planning, simulation and documentation of interventions in maxillofacial surgery require high resolution soft tissue information of the human face. Topometric data may be gained with various methods (CT, optical, contact), and these all have their advantages and drawbacks. We developed a topometry system using pulsed holography to capture the surface of objects. In topometry it is necessary to avoid movement of the object during measurement. For static objects this is hardly of influence, however, movement artefacts are the primary cause of errors in measurements of living or moving objects. In this case either the recording time needs to be sufficiently short, or the object needs to be immobilized as much as possible. Most current topometric techniques feature overall capture times ranging around or just below one second. Although their nominal accuracy, which is defined on static objects, might be good, the surface quality is often questionable. Therefore, great efforts are being made to speed up the measurement.
Pulse (signal processing) Theory of relativity Computer animation Physicist Cartesian coordinate system Belegleser
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OK and everyone and although and the physicist I'm not gonna talk about relativity up and the north and Minkowski we have more down to earth approach to application full pulse photography and hence the uh garden us this to presented here in the hope that it will be inspiring to of the community 0 we've been developing a method cool facial top parliamentary using pulse holography at the Caesar Institute or its foundation in Bonn Germany and it all came from the demand from maxillofacial surgeons they say that they like to plan their interventions and they try to digitize the patients and with the methods they had at hand with the line-scan us all of them greater than the other men methods they they use and white light scanners and so this we don't recognize so patients anymore and don't have a better method at hand and so and we were looking around and came to to the poles holography but
let me show some I would say inspirational pictures for and what they can do already see this girl on the left side she has I that a distance the younger and the next syllable so it needs to be extended extended it's not just in this article question but it's a functional question as well since um when she gets older she will have troubles to eat drink and breathe and so the end the whole and excellent needs to be extended on the right side you see the amazing result that year and the next 1 is
even more difficult it's what they call by max and so you need to cut away parts of the mix so long and extended and in the upper part of the job so you get a real small and appearance of the of the patient again and the final aim is that with a good dataset the surgeon can plan the intervention in advance he says you know and if I said that the maximum 4 5 millimeters 0 6 mm how well my patient look like and so in the end they want to simulations to cut away the bone how the soft tissue behave and for this we not only need the the data from the city but you will need to a very good surface dataset and
so that was a key question we had an it might be familiar to you that you can do reported holograms but for the Inter-Parliamentary what metrology community it was not that clear so when we needed a fast method and you always already see that that asks for holography and so we do a two-step approach and that you have to know an advance it's a pulsed hollow-gram do at 1st it with a very short exposure time of 21 35 nanoseconds depending on the system used and then at the 2nd stage we do reconstruction optical reconstruction of the real image and digitized and that's where whether tomography comes in we digitize the real image slice by slice and we can do the metrology on this digitized image and the 3rd part is then you have a complete volumes and then you do surface extraction from this volume so this is
the 2nd camera MIT stationary system from July and and then we approach David to develop a mobile system so together with the sign they have system more camera with the axis and it's on on the 5 30 to 9 meters then doubled and specified to 1 dual pulse energy so it's quite a lot but it can deliver 1 . 4 things for that and the it has quite a high coherence length and uh and we can easily set up the the the system in the field within 20 minutes once in the room and that's what's very important to us is the the whole system is I say saved in they captures very
easy the the patient sits in front of it the black box you see there's a is a shot on the next image you want to close the book on this 1 and what you see is all that there being scheme and I get an error here there so the reference beam is delivered over that little hole up here goes through 1st and there are 2 of a 2nd up to the plate and and here on on the 2 sides you have the uh and the nomination ports yeah you
see that better even under the illumination ports on the right and left side and the the first 1 shows this rolling shutter so what it does it has occurred roles 1 time and exposes the hollow-gram the holographic plate 50 milliseconds so we can we can actually do although GM in daylight conditions and we already did some studies with this and that and there it says probably record with a 50 holograms and 1 day of all 50 portraits and that was lying and sitting in patients and developed and so what we did quite some investors quite some work with this so this is all holographic systems we use standard terms large plates and with the conventional processing within SM 6 and to build the bleaching event this is now the
2nd step with a CW laser we use the Korean for that but that basically doesn't matter forming the 1st thing is forming the conjugate and then you get the real image and then displaying that's worth I said we do that we do the tomography have uh before we used with the diffuses the screen and and recorded that with the camera but now we have a direct scanner in here and it's and it's about as quick as they can be the pictures with the with the camera and then this this diffuse all the scanner vice-versa is achieved through the real image of this linear position on the table but what you get them and
yet on on this on this plane that we that we project on you have the focus contour and the unfocused surroundings due to the point spread function that's a normal thing and so we have to separate the focus from the unfocused information and that's the 3rd part of the surface reconstruction and they
gave me an error for that so here you OK so here this is
just this is a scan this is a scan through this volume not 1st this see also I replayed again at 1st and that's coming the slices are going from from the from the with the back so at 1st you see the the tip of the nose being done in focus and then it goes over the eyes into the cheek and back to what's the the region so here's is you see the the nose and on the ice and OK and what you can imagine right away is what's that
received in each slice you have a very fine band of from a focused information and um in the focal depth of our really image is well below mm so it's I think it's about point 1 milimeter and that's what we . 1 2 . 4 million that's what we so that's what we found out
and no OK now we have this image stacks and usually take 200 50 or 500 images this depth and then I the idea you know that only when you go through this in a stack on 1 line there's only 1 point in focus because you won't have any of the because because 1 goal behind each other you won't have any occlusions so and that's in basic that's a 2 and a half deep approach and so when you found that point on the 1
hand side you have you can say at which position it isn't exactly know where it is since we positioned there but the 2nd thing is you can retrieve the intensity at a point to so you have so you have the height information plus the texture information the 2 things and the the textual information is in the in the real images and its intrinsic and it's not projected onto the onto the onto the surface like with the photogrammetric methods on like um so when you
combine these them to you have on the left side you see the surface it's just from the snapshots from the left 1 from a representation and that's just the surface of the surface model the 2nd 1 is the parallel we project a texture which overlay and the that 1 that's what you get that's the that's the textured 3 D models and then these you can
and this can be then used for for the planning and documentation of the surgery a 2nd application that we had is to establish a soft tissue database and where does the the and the study that into that before was that exactly that immediate and young patients between 18 and 25 and 25 of these of these and to the idea is to to earn we had we had 2 questions the 1st 1 was how thick in forensics when you find a skull which you can't and say where the person belongs to because and you you need to you want to know the parents of of this human being and what it what it once was because you don't have any such soft tissue anymore when you have skull so what they did their approaches that plastered it on the on the skull directly on the skull and what we are trying to do is to establish a database of some of landmarks we say you have the thicknesses of the soft tissue and that in respect to gender age of ethnic origin body mass index and and so forth and so on but there is the efforts done already in that direction but they had to and that different approaches which with from ultrasonic devices or if a student with needles and so that's that's what we trying to the best we can try and which you get is an
overlay usage and a transparent overlay of of also has over a segment of city skull and the 2nd question we had this and that this study was what's the soft tissue shift between an upright person and reclined position so we did actually did holograms and I would like to show you a picture of how we only finally realize the refined pictures and and what
without method since we have the intrinsic the intrinsic and texture we can say exactly how much the the shift is and that is not only a volumetric difference but that is really because we can follow you can for for those skin poles and so and even even tho the difference between sitting in line that's what we what we saw in in these investigations is about 3 . 5 mm the the real shift and in the cheek for example 15 millimetres because it goes back to the gravity really pulls it back a lot further and then you would just judged by and by the differences in involved
and OK here's another that's another example but we did
the captured a black person we because we weren't sure if all of that technology would be able to to display them and it will have enough of that person would have enough reflectivity but it showed that and it it worked extremely well since some there was an it it in fact had
extremely high contrast him because he had to the reflections on the skin will vary extremely bright and speculate and the and the
background was nonetheless paradoxically could do an extremely good and surface reconstruction of these models as well but as the
next 1 OK he actually
picture of the of the the texture of that we that we have and that's as far as we pushed all scanning right now that's the as you can probably see detail of the of the nose and nostril and that is already in extracted texture from the from the real image and you can see skin pores and substructures and the the scanning is done with fight 40 microns so can imagine how big data than Texas already get here and there but this this text
erected there resolution is extremely important especially when we're looking toward small children 1 target patient for us this is some this class intervention children and the especially for for babies or young children and these interventions are usually done within the 1st year of life and they won't stay still you can't tell them and wondering what light skin and please stay still for 1 2nd and the normal form they and nobody was ever offered it except that preceded them and that's not indicated for that kind of thing and you can't capture the surface and and that's the way we succeeded in new that's expression that really and specialty here and then the next 1 that you see
how the process goes on this is in a 3 D CAD program but we can import the surfaces and you already see the the red and the blue that's outlines of the of the lips and the clefts and and that's what you see here is the that's all actual state of the art and that that's what we're working on so just give you some snapshots of this
uh um the next thing we expanded and then that goes back to the reclined ones as well is that we engaged in the indeed and the portrait set up so on here see top view and on the left and the right you see a mirror sites upon patient in a 45 degree angle so from the view of the whole play you
see the patient and the reflection from the 1 side you can see that from the outside as well and on the left you see denoted the that's the tumorous standing on the on the right and the left of the patients you just see there and the chair from the bottom and and the left is the that's all stationary system that's the and I showed you and
that's not what we get you have a from you you have side you ought to side views and then you can register the Andes and I'm coming to withstand already uh and and then you register the sense with this report we were able to do 270 degrees the to commentary which 1 single shot so that's the that's
obviously messed up the funds but you can read that so the captain reclined position and then here we did it the other way round the position at 45 degrees over the patient's annotation lies reclined opens in front of the of the camera and I
couldn't even take the 2 minutes and that's already the summary we can do with the culture of the weekend to commentary with them in accuracy of point 4 mill and the extremely short exposure time of 35 nanoseconds definitely does have to be resolved uh movement artifacts and the yes right now we are moving towards completely digital method but the young results are not as far that we you want to presented here but I I hope that was already some extensions of the tomography people be fairly the the yeah I think you will find do you know that this is a lot of yes you you you you you you are it's it's basically over the contrast but you can calculate the contrast in different in different ways and you usually have taken area of interest around the year you take an area of interest around the end the point of interest there and you see how big the modulation is and the higher the modulation is the more you will be in in in the focus because of the focus the point spread function simply blows everything that's that's a simple approach and you can modify this contrast measure and that's what we did and to to enlarge the the the area of interest or make it smaller depending on how big the modulation so that's basically what we do and that's that was a lot of development work as well to refine the and working