3D Ultrasound – Part 3

September 7, 2006

OBGYN.net Conference CoverageFrom FIGO 2000 INTERNATIONAL FEDERATION of GYNECOLOGY & OBSTETRICS: Washington DC, USA

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Dr. Ralf L. Schild: “Ladies and gentlemen, it’s a pleasure to be here and to talk to you. My topic tonight is 3D ultrasound in obstetrics. Some of the special 3D pictures I’m going to talk to you about you saw just a few minutes ago but I’m just going to go over them briefly. This is just one of the examples of what you can do with 3D ultrasound but it’s by far the most important to me. I hope to be able to show you that you can do other things than just pretty pictures. This is a picture of Saint Louis where I currently work and this is the arch to the west. 

To cover this quickly because it’s been a long day for you, I would just like to tell you what the requirements are to do a 3D ultrasound. As far as I’m concerned, I think experience in 2D ultrasound is a must. You cannot do a 3D ultrasound without ever having scanned 2D. You should have supervised teaching in 3D ultrasound before you start, and the scanning condition should be adequate. Let’s say the patient has a habitus, which prohibits good scanning, this is not the best condition to do scanning. If the fetus is not lying your way and it’s turning his or her back to you, this is not ideal and the indications. 

How do we do that - first of all, a good 2D image is important to get a good 3D image. You just put the probe in to get a good 2D image then you start the automatic volume scanning with the probe - in obstetrics it’s a probe like this - and without moving the probe so the probe remains still, you get the multiplanar imaging. There’s the frontal, sagittal, and the transverse plane and out of these three planes the computer gets the 3D image, and this is just the schematic drawing of how this is being achieved. 

What are the advantages of 3D ultrasound? First, one of the major advantages is an additional third imaging plane, which you cannot get with 2D ultrasound. Then you can just store the whole data set and you only can do a CT-like analysis so I favor that the "Sono CT." What you can do and what I’m going to talk about in a minute is the much better volume calculation with 3D ultrasound. I’m not going to talk about that but what the positive quantitative estimation of the vessel density and the perfusion in a given area with 3D ultrasound is. 

So let’s go and talk about fetal weight calculation first. Why 3D ultrasound in fetal weight calculation is a likely question that you’re going to ask me. Two reasons, the first is the extremes of fetal weight, small or very large fetuses’ predictive value of 2D formulas is less than optimum. The second reason is because most formulas do not consider the tissue thickness. When you look at this young lady and compare her to this guy there is a slight weight difference and this is not because the length of the thigh is different or because the head circumference is slightly different. Not only because the abdominal circumference is different, this is because when you look at this upper arm and thigh, the tissue thickness or the fat content is different. That’s why others and we have developed formulas including the abdominal volume here within this point and this point and the volume of the upper arm and thigh. How is this being done? We just mark two areas, these two points here, and then we go from there to there and calculate the area, and the computer calculates the distance between each slice and calculates the volume. In 125 patients we developed a new formula of thigh volume, upper arm volume, the abdominal volume, and the BPD. Then in a different group with this formula, we tried to evaluate how good our formula was. We found that when you looked at the correlation here that was pretty good, unless you just looked at the less than 1,000-gram fetuses, and we’re currently working on that to get a special formula for those fetuses at the very low birthrate range. So what can 3D ultrasound do in obstetrics other than working in the fetal weight calculation? I’m going to show you a lot of 2D and 3D cases to show you what is possible with the help of 3D. 

First of all, what we don’t like to see is an ectopic pregnancy. This is a 2D scan and this is not difficult to see but in this case this was special because when you look at this here, this is the third plane, and the front plane of the uterus, which you do not get under normal circumstances with 2D. When you look at this, this is the ectopic here and this is inside the uterus. You see the endometrial cavity here and there’s a gap between the gestational sac and the endometrial cavity so this was a cornual pregnancy. When you have pictures like that in the first trimester, this is easy to explain to the parents how the baby looks, you get a good image, and this facilitates the bonding between the mother and the father-to-be and the fetus. 

When you look at multiple pregnancies, you can see here there are two fetuses and you cannot see a dividing membrane in between, in contrast to this slide where you see a triplet pregnancy early on at six weeks and you can see here that every fetus has a separate amnion and chorion also. When parents ask you what the sex of their baby is, it’s usually not difficult to tell them it’s a boy or a girl but sometimes it’s even better to see it in 3D when it’s obvious - this is a male fetus. Other normal findings - you get a 2D scan of the fetal spine and you can have a look at it in 3D and this just looks like an x-ray of the fetus so with the help of 3D ultrasound you can get excellent images of certain fetal parts. You can have a look at the umbilical chord and you can see here, and this is a good way to check whether the umbilical has two arteries, you look at the base of the bladder in 2D and in 3D it looks like this. This is a normal chord in contrast to the next slide where we have abnormal findings. This was a monoamniotic monochorionic twin pregnancy, and you can see here the chords are intertwined. They look similar to the next slide, which is the picture of the chord at delivery. So in pregnancies like that, 3D ultrasound can help you to show what the chord is like. 

Abnormal findings - you have here the fetus at 12 weeks with a hydrops hygroma colli and you can do that in 3D ultrasound and it can show the parents, if they ask you what that is, what the fetus looks like. You can look at the fetal head, and we’ve seen a lot of excellent slides and pictures before. This fetus has a ventriculomegaly, you can do the 3D ultrasound and you can look at the brain in different planes and have a look to see whether there’s any other pathology. You can do a neonatal scan and you can see and look for intraventricular bleeding like this case, and you can see that in all three planes. You can do that in a fetal scan with an abnormality, and this fetus had a cystic abnormality in the neck. Here in the third plane you can see this encephaloceles connected to the fetal brain and this is a cystic structure originating from the fetal brain. When you see a picture of this in the early second trimester, you know what that is, and you’ve seen pictures about holoprosencephaly. You can see in the next slide a picture of a similar case in the first trimester and here 3D ultrasound just tells you that the front brain is absent in all three planes so this facilitates you making the correct diagnosis. This case was sent to us for a cystic structure, this is a 3D rendered picture. We could confirm that this was a cystic structure in the fetal brain. Then we switched on the color and we could confirm that this is an aneurism of the vein of Galen, and you can see here the color in all three planes and this is the rendered image. You can see the blue and the red of the information of the feeding vessels. When you look at this picture you can see a face, and when you look quite closely you can see the upper lip doesn’t look okay. When you switch on your 3D and look at the 3D image, you can see here a little gap in the upper lip. We saw the same patient weeks later and we could confirm the same. Here a few weeks later you can see that this is a gap in the upper lip. Abnormal findings – you can see on this 2D ultrasound this cystic mass here in the mouth of the fetus, and switching on the 3D you can see that cystic structure here is coming out of the mouth, and again, facilitating the diagnosis and explaining to the parents what the fetus actually has. Abnormal findings, you can see in the chest here that the heart is being pushed to the other side. You can see here this echogenic mass just filling the left top of the chest and when we switched on the 3D probe, we saw that this mass filled the whole left chest, and this confirmed a cystic lung malformation. In contrast to this finding, you see an echogenic finding as well but this finding looks different, it looks encapsulated and looks rounded. This was a fetal heart tumor abruptio myoma displayed here in 3D. 

When you have a fetal head like this and compare it to this, you can see the difference. This head looks different and it looks like a lemon, and when you see a fetal head like that, you know what to do, you look at the fetal spine. When we looked at the spine, this is the corresponding picture here. We could see that myelomeningocele confirming the diagnosis of a neuro-tube defect. This is a different picture here showing MTD in a different patient, and in a plane like that with the 3D ultrasound, you can even estimate the size and which level this defect is at. Abnormal findings - in this patient with the fetal hydropsy, you can see that in all three planes. In a case like that, you can do a 3D ultrasound laparoscopy because you can see quite clearly the liver of the fetus here and this is just possible in cases like that with fluid. 

Abnormal findings - when you look at this fetus, this fetus looks pretty good, but when you get a different angle this time in 2D, you notice that the chest looks different. The chest is much smaller than the abdomen and this confirmed the skeletal abnormality in this case. And again, some pictures of skeletal abnormalities. This is a thanatophoric dysplasia, see the face - we will see that later again - the large ears, and you can see the thick and short extremities. Or in a case like this, you can see both fetuses with a kind of strange position of the wrists and the fingers and this was a trisomy 18. Or in a case like this, and this was not possible in 2D ultrasound, when you look at this arm - the upper and lower arm and hand, you see this is at a strange angle. This was a case of radial aplasia, you can see the short lower arm, and this was confirmed quite nicely by 3D ultrasound. Or in a case like this you can see that the sole of the foot looks at you, this was a talipes. Here’s another case of skeletal dysplasia, here you can see the position of the wrist, and this wasn’t a case of arthrogryposis. So what is quite important is the face, and when we look at the face we do that during our anomaly scan to see whether there’s any facial abnormality, and cases like this look normal. This fetus doesn’t want to look at us but when you look at these again, you notice that this face looks different compared to the others, and this is the fetus with the skeletal abnormality which you can see in 3D the different features of the fetal face. So the most important features, as far as I’m concerned, in obstetrics are the volume determination of organs and tumors, and the prenatal fetal weight determination. Before you all fall asleep like this fetus, I will try to get a good image out of the fetus during the live scanning. Thank you very much.”

Chairman (Paul): “Dr. Schild will be doing some live OB scanning so please bear with us. Don’t forget at the end of his talk or the end of his scanning we will be doing a question and answer and then some lucky person will walk out of here with the all new, all digital personal ultrasound machine so just bear with us.” 

Dr. Ralf L. Schild: “This is a young lady who is just so nice to show us her baby. What I’m going to do just before I start with the 3D scan is to look at the baby and see what the fetal lie is. This is a breach presentation here, and I just look at the amniotic fluid and see how much fluid we have and I have a look whether there is more than one fetus in the uterus, which isn’t the case here. That would be a surprise for you. So now I’m trying to get a good 2D image and the fetus is just about to get moving so we’ll just wait. The baby has the hand just in front of the face. It’s gone, the baby moved, but I’ll give it a try. When the baby moves, this is not the best time to do the scan because when it moves you won’t get a clear picture but I’ll try to get an even better picture. What you can do with the 3D scan now is you can have a look at the fetal face and whether the profile of the face looks good. When you can use 3D ultrasound, see whether you’re exactly midline. This is important because you cannot make a diagnosis of a fetal abnormality without being sure that you’re in midline. So what are you going to do to prove that you’re midline? You just go into the other planes and when you look at the upper right one with the green border, this is the frontal plane, and when you look at the lower left, this is the transverse plane. Now when I move the cursor you can see that in the upper left one, and when I move it up and down, this confirms that this is the midline. So just by looking at the normal 2D plane, the 3D helps you to get the right angle. This is just the 2D picture, which looks okay. Now we have a look, and there are different ways to do it. What I usually do is just have the fetus look to the ceiling, this way up, and then I’m just going to get the box a little bit smaller. Then I like to turn the baby around the axis and you will see that soon, and when you look at the lower right end, this is the 3D rendered picture, which is not ideal yet but I’m working on it. The baby has part of the chord in front of the face, and I’ll try to get a better picture. What you can then do is just switch to select a view which cuts structures just around the baby’s face so that you can get a better view of this situation. You can even go to a different mode, this mode is called cut mode. You can see the outlines of the face, it’s not that clear yet but we’re getting there. When you look at this here, you can just imagine what it looks like. Just turn it around its axis and what you can then do is just use the electronic scalpel in which you cut away all the structures that you do not want to have in the picture here and here. You shouldn’t cut away too much, and you can see here in 3D, the profile of the face. I’m going to give it another try, if you wish you can choose a different color like green or this color which is just a different color nothing else. I hope the baby stays like that. You can choose three different speeds; you can choose the slow, medium, or the fast mode, and what I’ve used here because the baby is active is the fast one. When the baby is not moving at all what you can do to get a better picture, you can use the slow speed, which is beneficial to the quality of the picture. Now I’ll give it another go. You can see while I do the scan the baby moves away. So I’ll work on that, I don’t need to scan for that. I can use the data that’s stored here on the computer. I’m just going to work on that image because that’s the best one we had so far, again, this is in 2D. You can look whether your 2D image is right in the middle and I’ll check that on the other ones. That’s okay. In the upper right plane, you can see here it’s in the middle, and you can then enlarge the 2D and this is a nice 2D shot but that’s not what we’re here for. I’ll go back again in the upper left corner with the fetus looking up, here in the upper right corner with the transverse view, and in the lower left corner with the frontal view. Now I’ll go back and start a 3D imaging, I don’t want that color. This is getting there. Now I turn the baby’s head down, and just turn it around, this is just getting even better. You can adjust the resolution here somewhat. I can then change the so-called render mode; it can just get a smooth surface. Personally I don’t like that too much, I just prefer the other one. This is just a personal thing, and then you to go to the 3D image. You can turn that. Now we decide what to cut away. You can see the hand on the right side of the face, and I just want to cut that away. I use that magic scalpel again and off the hand goes, and here you can see the profile of the face. What you can then do is enlarge that too and if you just wish to do so, you can get a different color. Do not forget to get the printout because that’s a picture to take home. I’ll give it a last try. This data you can store to work on anytime later, that’s what I just did. Again, I’ll turn this baby around, and that’s all for today. Thank you very much.”