A Clear View Inside Tiny Hearts
Mark Berninger | 05.10.2017
Cinematic Rendering can display CT data as vivid three-dimensional images. Cinematic Rendering is available for research on syngo.via Frontier and is also commercially available as Cinematic VRT on syngo.via1.
A Dual Source CT scan can produce a threedimensional image of a child’s heart with minimal dose. This is highly recommended when it comes to congenital heart disease. University Hospital Erlangen is a pioneer in using this technology. It deploys diagnostic CT scans to simplify the planning and navigation involved in challenging procedures for congenital heart defects. Martin Glöckler, MD, senior attending physician for pediatric cardiology at University Hospital Erlangen, talked to us about the advantages of 3D visualization for cath lab interventions and for procedures in pediatric cardiac surgery.
Photos: Stephan Minx
Dr. Glöckler, which imaging methods were common in pediatric cardiology until now?
Glöckler: Ultrasound is still the workhorse and gold standard in pediatric cardiology because this type of imaging puts the least burden on patients and is available everywhere quickly. For complex procedures, though, we often need additional preprocedural imaging that gives us 3D navigational support. Magnetic resonance imaging is suitable for this, but the long acquisition times mean that we can normally only use it with children from about age seven.
With younger children, an MRI scan requires intubation and ventilation, which often results in critical destabilization. For about eight years now, we’ve been able to use rotational angiography as an alternative. This kind of imaging requires significant dose levels, so physicians generally only use it if they think they’ll be able to perform an interventional procedure at the same time as the diagnostic exam, or if measuring the pressure in the vessels is extremely important. But now thanks to Dual Source CT technology, with its fast acquisition times and marked reduction in dose, we have a gentle imaging method that is particularly suited to delivering optimal data for complex cases.
What advantages does Dual Source CT offer over echocardiography and MRI in pediatric cardiology?
Glöckler: One advantage is the extremely high speed. Dual Source CT allows us to acquire a full thorax within a single cardiac cycle, even in a tachycardic child with a heart rate of 180. The acquisition is so fast that we almost never have to sedate a child. The scan itself takes fractions of a second – and even with the topogram and settings, the child only spends a total of about five minutes in the exam room. The second major advantage is obviously the reduction in dose. This removed the hurdle that was stopping us from doing CT scans on newborns and infants, and it allowed us to start optimally visualizing complex heart defects in three dimensions.
How much dose does the planning CT scan save in the case of cath lab procedures?
Glöckler: In complex cases, we need around 4 to 7 mSv for a full cardiac cath if we don’t have any previous information. If we do a Dual Source CT scan before the procedure, we can reduce catheterization time by 50 to 80 percent with a tenth of that dose – 425 Gym² today compared with 3950 Gym² in the past – through evaluation of Fontan circulation. Furthermore, with a CT scan, we just use 2 mL of contrast per kilogram of bodyweight, so about 6 mL for a newborn. What’s more, a CT scan doesn’t just give us an image of the aorta; it also shows us the whole thorax in detail.
Overlay of live fluoroscopy and 3D model during stenting of the ductus arteriosus (green) in a 3.2-kg newborn with hypoplastic left heart complex.
The 3D visualization was based on a SOMATOM Force Dual Source CT scan (contrast medium: 2 mL/kg; effective radiation dose: 0.21 mSv).
Does 3D visualization also mean you can perform catheter-based procedures with less dose?
Glöckler: 3D overlay and guidance allows us to reduce the fluoroscopy time by about a quarter. The reduction in contrast medium is even higher because the angiographies that we previously needed to find the right orientation are no longer necessary. Furthermore, optimal navigation doesn’t just reduce dose; it also shortens procedure times. This effect begins right at the start of an intervention: The additional information means I have the best catheter material on hand and can ensure that the system is perfectly set up before the procedure begins. Basically, I can plan and optimize the entire navigation path and the corresponding angulations in advance. And thanks to syngo.via, we can access the original data on every workstation and view the 3D images wherever needed. This means we can use the CT datasets across the different disciplines in our team so that everyone can easily understand exactly how the detailed anatomy looks inside the child’s body.
How exactly are the CT datasets integrated with the live fluoroscopy?
Glöckler: Registration is very simple and takes a minute at most. At the start of the procedure, we just do a short scan, which is enough to register the CT dataset with the system on the basis of the trachea and the rib cage. This 2D-3D registration is very fast, and obviously also reduces dose. It’s also important that we can easily make readjustments at low dose during the procedure, for instance if the patient moves.
You’ve had a SOMATOM Force since 2014. What are the additional advantages of this system?
Glöckler: It allowed us to cut the dose substantially while retaining the same image quality. With SOMATOM Force, we’re relatively constant at 0.2 mSv per scan for newborns. Another significant aspect is the improved iterative reconstruction with ADMIRE. We’ve shown that this increases the contrast-to-noise ratio – at half the dose, as I said. The softer contouring is also helpful for 3D visualization because it keeps the number of postprocessing steps to a minimum.
How do you see the future of 3D visualization technologies in pediatric cardiology?
Glöckler: I think that all complex surgical procedures in critically ill newborns will be carried out with the support of high-resolution 3D datasets in the future. The benefits are huge, and the new CT technologies mean that the burden placed on patients is extremely small. Cardiac surgeons will simply insist on having their surgical field displayed as a 3D visualization. We’ll also increasingly rely on 3D information for catheterizations to make the interventions gentler, faster, and safer. For that to happen, though, it will have to become quicker and easier to implement the 3D data in the catheter system. Many things here are still at the prototype stage – such as the integration of triangulated 3D models in stereolitho-graphic format – but I think that 3D data will soon be available as standard on newer systems. Then there are exciting new developments like cinematic rendering, which produces fascinating realistic images that are even easier to understand. All of these factors will significantly increase the importance of preprocedural CT imaging.
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In clinical practice, the use of ADMIRE may reduce CT patient dose depending on the clinical task, patient size, anatomical location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the appropriate dose to obtain diagnostic image quality for the particular clinical task.
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