Advanced Visualization Aids Cardiac Imaging
The use of advanced visualization software has become a necessity due to the vast image data sets produced by cardiac computed tomography (CT) and magnetic resonance imaging (MR). The technology is known for making pretty, color 3D pictures, but users say the technology goes a long way to help increase efficiency, speed diagnoses, and can guide procedures in the OR and cath lab. “There is a huge advantage,” said Ahmed M. Gharib, MB Ch.B., staff radiologist, National Institutes of Health, diagnostic radiology department, Warren G. Magnuson Clinical Center. He specializes in multimodality cardiovascular imaging and uses advanced visualization sofware from AZE, Vital Images, Philips, Siemens and Toshiba. “You are not only getting slices through the heart, you are getting 300 slices through the heart, and you are getting 10 sets of images to capture all the phases of the heartbeat,” he said. “So, you are have 10 times 300 slices you need to go through.” He said the software eases the upload of the thousands of images and enables easier manipulation of the data sets. “It makes your life easier.” While each scanner comes with its own proprietary software, Dr. Gharib said issues arise when you want to view images from other manufacturers’ scanners. For that reason he prefers third party advanced visualization systems, which can manipulate images from all CT and MR scanners. He also said third party systems have more features. “They tend to have an edge, and they try to package everything together in one system,” Dr. Gharib said. The buttons and the format of the third party systems tend to be similar, but can vary greatly between proprietary systems. Tony DeFrance, M.D., FACC, interventional cardiologist clinical associate professor at Stanford Medical School, and a board member of the Society of Cardiac Computed Tomography (SCCT), uses software from Vital Images, TeraRecon and Ziosoft to help read CTA and peripheral vascular studies. “These three systems are all very robust – all three are excellent,” he said. He said each has different bells and whistles and they perform much better than the vendor software that comes with the scanners. “I have a lot more control with some of these systems than working with the software from the vendors,” Dr. DeFrance said. Proprietary systems usually only have three sets of image views. Dr. DeFrance said you can get views from other angles, but it requires pulling lines and manipulating images with extra steps that are not required with third party software. “I don’t want to spend 10 minutes pulling lines to create an angle,” he said. “(With third party systems) I can literally rotate it at many thousands of angles. They are really good at it, and they are easy to use.” Advanced visualization software can also help cut radiation dose, said Robert Schwartz, M.D., FACC, medical director, Minneapolis Heart Institute, who uses software from Siemens, Vital Images and TeraRecon. He said the multiplaner viewing with these systems allows instant changes in orientation to get a better view of target vessels. In the old days, patients had to be sent back in for additional imaging to get different views, increasing imaging times and radiation exposure. He said Minnesota Heart uses the software in combination with the a duel-source CT scanner for CT angiography. The combination cut doses to about 2-3 mSv, where as a typical CTA dose is 3-5 mSv.
Helping Analyze Images
Dr. Gharib said the software helps visualize the coronary arteries during the cardiac cycle, which is difficult due to the heart’s constant movement. “You are essentially imaging spaghetti jumping on a trampoline, and you are trying to assess the insides of the spaghetti,” he said. In coronary analysis the software can extract each vessel for separate evaluation. Dr. Gharib said the software also saves a lot of time by automatically subtracting out surrounding tissue, such as the ribs and lungs. While this is a big time-saver, he said you need to be aware of what the software is removing. “You have to be careful because software can automatically take things out that you many not want it to take out,” he explained. The software can also be fooled into subtracting areas of heavy contrast in vessels, or contrast pooling in the tissue. Tumors can sometimes be subtracted from the final images, so he said it is a good idea to reference the source images. “The computer will not do everything for you – you have to check it,” Dr. Gharib said. He said the software is also very good at taking gated images and piecing them together for cine loops for wall motion and heart valve assessment. “You download 5,000 images and you put them in the software so you can see the cine loops,” Dr. Gharib said. In the old days, he said CT slices were loaded into the PACS and slices had to be selected and flipped through to create a cine effect. “It’s the difference between watching a cartoon, or flipping the pages to make it look like a cartoon.”
Using 3D Images
Dr. DeFrance uses the 3D images produced by the software to look for gross anatomical problems, such as structural heart issues like ASDs, PFOs or aneurisms. However, he only uses 3D for about 5 percent of his reads. “It’s a lot of show and great for teaching, but it is not good for the day to day reviews,” he said. “Three-D is great for structural heart, and for gross anatomy it’s awesome. But, you can’t use it to look at coronary disease. If you do, you will be wrong a lot.” The false color 3D images are reconstructions of data based on what the software thinks it should look like, so for a true representation of the anatomy you really need to use the source grayscale, multiplanar review (MPR) images, said Dr. Gharib. “You want to go back to the source images to do your assessment, because the color can be misleading,” he explained. “It’s a huge mistake to do your diagnosis off of the color images.” However, the colorful 3D images do have a role for procedure planning. Dr. Gharib said cardiac surgeons like to evaluate structural heart problems on 3D prior to surgery so they have a better picture of what they will find in the OR. “Surgeons like it for surgical planning, and they like to review the pre- and post-procedural images to see the functional results,” he said. The 3D images can also aid in patient education. “The patients love the images – they get to see a great image of their own heart and they get a better understanding of the anatomy. They can see the blockages and they can see why they need the procedure,” said Dr. Schwartz.
Imaging for the Cath Lab
“There is a huge future in cath lab imaging,” Dr. Schwartz said of advanced visualization. He said CT or MR images can be fused with live cath lab angiography, which will rotate the anatomical image to match the actual anatomy as the C-arm is moved. He said this will be a big help in navigating vessels. Minnesota Heart already uses the software to help navigate chronic total occlusions (CTOs) and to help with transcatheter structural repair planning. Dr. Schwartz said this will become even more important as transcatheter valve replacements become more common. Minnesota Heart already uses CoreValve in clinical trials and uses the advanced visualization all the time for procedure planning and guidance. “I think it’s incredibly valuable to have the CT data before you go into the cath lab,” said Dr. DeFrance. In addition to guidance, he said CT images help with planning by determining the length of the lesion and vessel diameter. He agrees advanced visualization images are ideal when treating CTOs, because unlike fluoro images that leave cardiologists blind beyond the start of the occlusion, CT scans will show the entire vessel path. He said this is a big help in determining the length of the occlusion, vessel tortuosity, if there are any side branches and even the degree of calcification. “You may even decide not to attack that lesion based on the images,” said Dr. DeFrance. He said CT data sets have made him re-evaluate his sizing of stents, usually opting for larger stents. He said poor apposition from under-deployed stents is a major cause of restenosis and you get a more realistic view of the vessel size from CT scans rather than from angiography.
Dr. Schwartz believes future improvements to advanced visualization will include better artificial intelligence for computer-aided evaluation of coronary artery blockages. The systems may also automatically determine the best viewing angles for procedures to treat the lesions in the cath lab. Minnesota Heart is one of a handful of test sites for a prototype computer-aided detection system for CT and MR coronary artery scans. The artificial intelligence conducts a preread, which Dr. Schwartz said detects the vessels and then evaluates any stenosis it finds. The system then categorizes each stenosis as critical or noncritical and helps speed up reads by highlighting areas of interest for the cardiologist. “I think the future is in quantification. The advancement will come when you can make measurements,” Dr. Gharib said. He said the current technology allows for good 3D images and basic measurements, but what is needed are detailed sets of measurements. He agrees more automation will some day help identify noncalcified plaques and allow quantifiable perfusion imaging. Ideally he said the systems should be able to act as a detailed computer-aided detection (CAD) system to help identify areas of particular interest in a first read. However, in terms of today’s technology used for cancer detection, he said, “CAD is detection, not measurement.” “I think we will see more advanced visualization image fusion with cath/CT, cath/MR and cath/nuclear,” said Dr. DeFrance. He also said CT perfusion imaging will likely become available in the next year or so, and advanced visualization software will be very important to allow quick processing and rendering of these very large data sets.
“These are not plug and play systems, you need to sit down and get trained on how to use them, which requires a time investment from the doctors,” said Dr. DeFrance. “You have to play with the systems and make sure they can do multiplanar imaging easily. Look at the workflow – more buttons is not necessarily better. I would sit down with someone who uses these systems and watch their workflow.” He also suggests asking the vendor what they can offer in terms of education and support.
An Example of Advanced Visualization Functionality
The biggest advantages of using advanced visualization software is it enables quick, automated measurements, centerline references, helps calculate calcium scoring, and can measure ejection fraction, said Donna Wefers, RT (R), TeraRecon’s clinical training manager. She said the automation also saves time and boosts efficiency. “The computer will allow automation to save time, but you do need to review the images,” she said.
The cardiologist can pick a vessel and the software will automatically find the vessel’s centerline. The software can also automatically remove bone and other surrounding tissue and label the surrounding anatomy. The automated feature can quickly pull images of specific vessel segments, such as the left main, circumflex, right main, aortic root, the entire heart, or expanded coronaries.
In the multiplaner review (MPR) mode the software has a quick anatomical reference feature, allowing the operator to click on a vessel or other feature and the software will place a dot and identify what it is.
Wefers said some advanced visualization software vendors require designated workstations, but TeraRecon’s system can be used on any terminal. The software allows each physician to maintain their own personalized template, which allows for customized imaging templates and specific projections the physician commonly uses.
In addition to helping diagnose stenosis and calculating lesion length and vessel diameter for stenting, Wefers said the TeraRecon software can also aid in transcatheter abdominal aortic aneurism (AAA) repair. The cardiologist or vascular surgeon can click on the aorta and manipulate marks to outline an aneurism and the software will automatically calculate the volume and dimensions of the AAA. The software can sort through a list of stent graft vendor specified measurements to help determine what endografts are needed for the procedure. The system will also generate a specific device order form for each vendor.
The reports generated on the TeraRecon system can be saved. The file can be converted to a DICOM format for storage on a PACS. The information and images can also be sent to other physicians using a secure Web link, which allows the images to be manipulated from the remote location.