3D Reconstructions and Models As Planning Tools for Surgery
Author: Linda Brookes, MSc
Cardiac surgeons and radiologists at Great Ormond Street Hospital for Children (GOSH), London, collaborate in the treatment of children with congenital heart disease (CHD). Faster imaging produces 3D reconstructions and models to be used as planning tools for surgery and in communication with patients and their parents. Consultant radiologist Catherine Owens, MD, and consultant surgeon Martin Kostolny, MD, spoke about their work at GOSH.
Photos: Andrea Artz
One in every 180 babies in the UK is born with congenital heart disease (CHD) – a structural malformation of the heart or major blood vessels.1 CHD is the most common congenital anomaly and causes more deaths in the first year of life than any other birth defect. Twenty to thirty years ago, only 15% of babies in the UK with the most complex CHD survived beyond 18 years, but since then deaths from CHD in childhood have fallen by 83% so that over 90% of these children now survive into adulthood.1 This improvement has been attributed to better imaging and improved understanding of the anatomy of a child’s heart. In addition, new, often highly complex surgical techniques have been developed, and use of sophisticated cardiac catheters for minimally invasive interventional procedures to correct the defects avoids the need for more risky open-heart surgery.
Most cases of CHD require surgery or interventional procedures to restore the heart’s normal function. Great Ormond Street Hospital for Children (GOSH) in London is the largest pediatric center for cardiac surgery in the UK. Between 2012 and 2015, surgeons at GOSH carried out 2,995 major pediatric CHD procedures, with a 30-day survival rate, (the benchmark used to judge outcomes) of 99% – the highest in the country.2 At GOSH, the type of heart defect a child has is usually identified initially by a pediatric cardiologist using an echocardiogram. This information is limited, however, so a multidisciplinary team of cardiologists, surgeons, intensivists, imagers, and nurses then meet in a ‘joint cardiology conference’ to discuss the symptoms and decide on the type of additional imaging that will provide the surgeon with the optimal tools for planning the necessary operative procedures or medical interventions.
Individualized 3D models Martin Kostolny, MD, has been a consultant cardiothoracic surgeon at GOSH since 2006. He is the lead in neonatal cardiac surgery, performing between 200 and 240 operations annually. For more common defects, such as transposition of the great arteries, where surgical intervention is needed within the first two weeks of life, “the only information I need is in the form of an echocardiogram,” Martin Kostolny explains. “For the more complex heart defects, we usually need a combination of imaging modalities to help the team reach the right decision. What is important for me as a surgeon is that you can combine these imaging modalities to get an understanding of a 3D image,” he stresses. A recently introduced application of the 3D datasets from CT and MRI imaging is the production of individualized models of patient’s hearts built by deploying a 3D printer using a technique known as “rapid prototyping.” These models provide surgeons with a valuable clinical planning tool and can be used to help parents and patients understand the complex anatomy of congenital heart defects. They are also used in teaching. “Not everyone can visualize a 3D image in their heads, so this is a very important development,” explains Kostolny. The department of radiology at GOSH provides diagnostic imaging and interventional radiology services for children from newborns to 16 years of age. Among their equipment is a CT scanner, a Siemens SOMATOM Force, installed in 2015. Up to that time, the department was using a SOMATOM Definition for CT scanning, which lacked the high-speed Turbo Flash scan mode.
State-of-the-art CT scanner “We went straight from a firstgeneration dual source CT scanner to a state-of-the-art third-generation device, notes Catherine Owens, MD, consultant radiologist at GOSH. “We were very happy with the previous scanner,” she stresses. “We spent a lot of time modifying it to get to a place where our radiation doses were very low. Our images were good and diagnostic, but they were nowhere near the diagnostic quality of the images we are getting now, with significantly reduced radiation dose compared with the previous scanner,” she says. “The new scanner has a number of new technologies, but the Turbo Flash mode (increasing scan speed to 737 mm/s), rapid acquisition (0.25 s compared with 0.33 s per rotation on the previous scanner), and hence high temporal resolution (66 ms compared with 83 ms) have all made a huge difference for us.” In the year since the SOMATOM Force scanner was installed, there has been a marked increase in the number of cardiothoracic CT examinations performed at GOSH, rising from around 800 in the previous year with the previous scanner to almost 1000 in 2015.
“The average time taken for a CT scan is less than five seconds – the actual time of the scan is tiny compared with the average time of an MR, which is about half an hour,” Owens explains. Martin Kostolny appreciates the advantage of being able to run a fast CT in cases such as hypoplastic left heart syndrome, one of the most complex cardiac defects seen in the newborn and probably the most challenging to manage; without treatment, the syndrome is always fatal, often within the first hours or days of life. “I do an operation called a Norwood-type procedure in which I reconstruct the aortic arch and provide a source of pulmonary blood flow,” Kostolny explains. “The echocardiogram can tell me everything about the function of the valves inside the heart, but can only give limited information about the shape and size of the aortic arch. So if there are any doubts about the clinical picture, then I can ask for a CT. The patient is fed, swaddled, put into the CT scanner, and we have the image in two seconds, with no concern about radiation,” he says.
The ultimate test “Children really are the ultimate test of a good CT machine,” Owens admits. “They are small – many of the hearts operated on are about the size of a walnut – and the rapid heart rates and faster breathing in children cause motion artifacts; and older children may be uncooperative. In a child, it is not uncommon to see a heart rate of 150–180 bpm,” she says. However, the extended coverage of SOMATOM Force means an entire heart can be covered in approximately 150 ms.
Radiation remains a concern in pediatric CT imaging, “and rightly so,” Owens acknowledges, although “the data associating radiation in diagnostic use with cancer risk are very sparse and the potential risks probably very low,” she adds. As current President of the European Society of Paediatric Radiology, Catherine Owens is involved in a number of initiatives for radiation safety in medical imaging, including EuroSafe, the European Society of Radiology’s campaign for medical radiation protection.
Reduced doses In the UK, requests for an examination using radiation must be clinically ‘justified’ by the referring clinician. Owens explains that before performing a CT scan, a risk-benefit analysis is carried out that involves asking whether an examination is really necessary and if so, whether another form of imaging that does not involve ionizing radiation, such as MR, could be used instead. After justification, the CT scanner will be optimized to provide the best quality image that is ‘fit for purpose,’ that is, clear enough to see any abnormality at the lowest possible diagnostic radiation dose.
“Since the installation of the SOMATOM Force scanner, we’ve reduced our doses radically” Owens notes. “The test of our work is with patients and the clinicians,” she says. “We have a very close-knit multidisciplinary team and through regular meetings we help plan patients’ therapy and educate clinicians about imaging and the tools that are valuable for each potential diagnosis. The bottom line is that you justify your examination; you do it for a reason that will benefit the patient, and you perform the scan to the best of your ability, working with your scanner.”
Linda Brookes is a freelance medical writer and editor who divides her time between London and New York, working for a variety of clients in the healthcare and pharmaceutical fields.
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Townsend N, Bhatnagar P, Wickramasinghe K, et al; British Heart Foundation Health Promotion Research Group, Department of Public Health, University of Oxford. Children and young people statistics 2013. London, UK: British Heart Foundation; 2013.https://www.bhf.org.uk/-/media/files/research/heart-statistics/g694-bhfchildren-and-young-peoplestatistics-2013.pdf
Franklin R, Cunningham D, Tracy Whittaker T, Denne L. National congenital heart disease audit 2015. London, UK: National Institute for Cardiovascular Outcomes Research (NICOR), Institute of Cardiovascular Science, University College London: 2016. https://nicor4.nicor.org.uk/chd/an_paeds.nsf/9791867eff401e0d8025716f004bb8f2/5983f27e0b3ff3b080257d5d005cec4a/$FILE/NCHDA%20Aggregate%20report%202012_15%20v1%202%20published%2027042016.pdf
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