Imaging babies' hearts in the womb
At various times throughout a pregnancy, women will be invited for scans to check how the baby is developing. These scans can tell us a lot - for instance how big a baby is, when it was conceived and what sex it is. But babies in the womb are tiny, with tiny organs, and there are some things we currently can’t see very well on existing scans. This is an issue if babies encounter problems during pregnancy, which we can’t pick up on before the birth. Chris Smith spoke to David Lloyd from King's College London and Evelina Children's Hospital, who has come up with a method of 3D modelling babies' hearts before they're even born. First up, Chris asked, how can we image babies in the womb currently?
David - So at the moment we use ultrasound and, as we just heard, ultrasound is used in a variety of ways. The primary one that most people will experience in their pregnancy is the screening ultrasound, so the anomaly scan which happens at around 20 weeks, and there we’re looking just to screen out major abnormalities in the baby. If we look at the heart - so if we suspect that there may be a problem with the heart then that patient will get referred on from the screening ultrasound to see a specialist so like a Foetal Cardiologist. So you’ll see a sonographer who's expert in scanning the heart with ultrasound, and a physician, a doctor who works specifically looking at babies hearts before and after birth. That's the sort of main way of doing that and actually ultrasound is still the same technique as we use for both of those scans.
But there are some limits, and even when you have those very expert operators, when you're in that very specialist environment of foetal cardiologists, there are some things that we can't necessarily see as clearly as we'd like. It's a very good tool for most things but when we get to things like the small vessels around the heart that can be very difficult to define accurately, and when you look at all the other ways we have to image postnatally and compare that to before birth, it's much more limited. So, things like CT scans that use radiation we can't use, MRI which is safe to use in pregnancy and has been used for things like say the brain for example, is very limited when it comes to the heart because it's very small and it moves very quickly. So we've developed a technique to use those types of MRI scans using lots of images that we acquire of the heart and then cleverly reconstructing them after the fact to produce these very detailed 3D images.
Chris - Cardiac abnormalities are one of the most common congenital things to go wrong, aren't they? Put simply then, you take a person who has for some reason been detected to possibly have some kind of abnormality in her developing baby's heart. You then put her in her pregnant state into your MRI scanner, and what, you just take loads and loads loads of images - slices, effectively through the pregnant uterus and then use a computer to recompile this?
David - Exactly. So, an MRI scanner works by essentially taking like a stack of photos through the baby from one side or the other side - we can choose where we want that to be - but each of those photos is just a two dimensional image. So what we do is even though the baby is moving, if you looked at those stacks of images that each image wouldn’t relate to each other so you can't actually go through that stack and make any sense of one image compared to the next image. So it's a little bit like someone’s taken a load of pictures and then just thrown them all around the room. They're all a shuffled up deck of cards.
But we still take all of those pictures, and we’ll get the woman in the scanner and we can take sometimes hundreds of individual pictures and put them into a very clever piece of software that will look for the little bit we’re interested in, and when it identifies that it will try and work out where that belongs in a three-dimensional space, and it will keep using all of the other pictures to support that sort of growing volume, as we call it, of the foetal chest and the foetal heart and eventually we'll end up with something we can interpret in three dimensions.
Chris - So this was more of a software problem, writing clever enough computer software that can sift through enormous numbers of slightly different images because there's been movement, and draw the common components back together so that you compile them to make that image? How good are the images?
David - The images are excellent. So we can resolve down to less than a millimetre in terms of the resolution, and actually one of the advantages of this technique is because we've got so much data, the dataset that we end up with is actually higher resolution than any other data we put in because it all overlaps with each other.
Chris - Presumably a surgeon then, when this baby's born, we can predict what problems it's going to have on the basis of that very detailed scan? They could even rehearse in their mind what surgery they might carry out on that individuals anatomy in order to fix the problem before it's even been born?
David - Exactly, and usually that kind of thing, really understanding to that level of detail what's happening with that baby's anatomy, would have to wait until the baby was born for many conditions. So they can have a CT scan then they can have an MRI scan once they've delivered but not before, so all of that's on hold until the baby is actually here with us. What we can do now is bring that into the antenatal domain sometimes two or even three months before the baby's there, speak to the surgeons, they can counsel the family, we can plan for how that baby is going to be treated immediately after birth and ultimately improve the outcomes for those children.