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Real-Time Solutions
— Flat-Panel Angiography Offers 3-D Views in the Interventional
Suite Digital flat-panel fluoroscopy systems are providing CT-like 3-D images interventionalists can use without moving patients from the angiography suite. Interventionalists using the new systems’ capability believe it will change how they practice. The 15-year-old girl had a spontaneous gastric perforation, a very rare but serious condition. Surgeons at Cincinnati Children’s Hospital Medical Center were able to operate and repair the perforation. However, five days after surgery, the child developed a fever and remained seriously ill. Her physicians decided to take her to the interventional suite where, using contrast fluoroscopy, they looked for leakage outside the bowel. Fluoroscopy showed a vague pooling of contrast at the lesser curvature of the stomach. “But it was difficult to tell where it was coming from,” says John M. Racadio, MD, chief of interventional radiology at the hospital. Ordinarily, the patient, even though seriously ill, would have been moved to the CT scanner to determine the leak’s origin. However, Cincinnati Children’s recently became the first pediatric medical center to receive a new linear, solid-state detector XperCT matched with the Allura 3D-RA from Philips Medical Systems. Its XperCT was installed in late December 2005 and has been available for use since January. Using the XperCT, a rotational study was done that provided 3-D images of the area around the suspected leak. Overlaying the images from the fluoroscopy with the CT-like images from the XperCT on the workstation enabled the physicians to pinpoint the leak’s origin. Immediate Response “From that data, under live fluoroscopy, we were able to pull the drainage catheter back and place it outside the stomach,” Racadio says. The patient benefited greatly from her physicians being able to diagnose, treat, then reposition the catheter all in one room. “Not having to move a very sick patient was an incredible help for that child,” Racadio says. The case, which Racadio spoke about at the 31st annual meeting of the Society of Interventional Radiology in Toronto in March and April, is an example of the future of the interventional lab that for some early adopters of flat-panel CT-like technology is already here. Three major manufacturers—Philips, GE Healthcare, and Siemens Medical Solutions—now have flat-panel CT-like detectors that can be combined with interventional x-ray systems to sometimes eliminate the need to move patients from one room or table to another for diagnostics and treatment. Fluoroscopy Acquisition Interventional radiologists believe the new technology means they will be able to perform the minimally invasive procedures that they do now with more skill and in less time than traditionally. They also believe the technology will allow them to add new procedures, such as advanced cancer treatments, to their practices. “This is very new technology and I think applications will be coming out in the next year as people have this new tool at their disposal,” says Atul Gupta, MD, director of interventional radiology at the Main Line Health System’s Paoli (Pa.) Hospital, which recently acquired an FD20 with XperCT for its suite. “They’ll find new uses for it.” The quality of the images acquired with flat-panel CT-like detectors is obviously not as good as those taken with a multislice CT scanner. “It’s not the same technology,” Gupta says. However, the interventional radiologists who have been using it agree the quality of the 3-D and CT images the flat-panels produce is good enough for them to perform interventional procedures with much more ease. “It’s actually very, very impressive, and it’s very, very quick,” Gupta says. The XperCT has a less than three-minute reconstruction time from acquisition to display. Besides, Racadio says, when performing some interventional procedures, the need isn’t always for the sharpest images. “Basically, what you need is the 3-D relationships and not really that fine, fine detail to perform or assist you in your intervention. If, for some reason, you need the [most crisp] pictures possible, then you would need to bring the patient to a multislice CT scanner.” Gerald Niedzwiecki, MD, president of Advanced Intervention in Clearwater, Fla., who recently acquired an Innova 4100 for his stand-alone practice, finds it provides even better contrast than more traditional imaging equipment because it uses dynamic range management (DRM) as well as subtraction technology. “DRM compares each part of the picture with the part immediately adjacent to it, so you don’t get any overexposed or underexposed areas across the entire picture,” he explains. “It gives you a very true and pleasant representation of what you’re looking at. There are no harsh areas where it’s so bright here and so dark there that you can’t see what’s going on.” With subtraction technology—which takes before-and-after
pictures and leaves only what’s new in the second image—it’s
easy to get artifacts if the patient moves even slightly, Niedzwiecki
says. The key advantage of the flat-panel CT-like systems is they enable patients to undergo procedures performed in the interventional suite—including device placement, ablation, and embolization—without being moved to the CT scanner for follow-up or confirmation. A good example is uterine fibroid embolization (UFE), which is performed for the treatment of symptomatic fibroids. During the procedure, the interventional radiologist uses real-time fluoroscopic imaging to guide a catheter through the tiny arteries that supply blood to the fibroid tumors. The physician then releases tiny embolic particles the size of grains of sand into the arteries. The particles block the blood flow to the fibroid tumor, causing it to shrink and die. “In the old days,” Gupta says, “we would do the UFE in the interventional suite and the patient would go home. If her symptoms continued, we would go back and repeat the angiogram to try and find the source of the fibroid we didn’t embolize.” With flat-panel CT-like imaging available, “I can use it to see—while the patient is on the table having the procedure done—if I missed a fibroid and we can take care of it right then and there,” he says. Another example is when stenting carotid arteries or arteries in the brain for patients who had strokes. If the patient starts behaving inappropriately during the interventional procedure, physicians would have to stop what they were doing and send the patient for a CT scan. In one case, Gupta says, because the XperCT was available, a flat-panel scan was done while the patient was on the table. “It showed the patient was bleeding into the brain, and they were able to stop the bleed right then and there,” he says. “If they had the old technology, they would have had to take the patient from the room to the scanner, and it would have been at least a half-hour to an hour until he came back. You know that when you’re bleeding in the head, seconds count.” Gupta says the technology is also useful in another common interventional procedure, vertebroplasty, which is used to treat spinal fractures. Vertebroplasty stabilizes the collapsed vertebra with the injection of medical-grade bone cement into the spine. With the XperCT, Gupta says, before he finishes the procedure, he can scan the patient’s back bone to confirm that the cement is where he wants it. “If I’m not happy and want to put more cement in, or it’s not exactly where I want it, I can do it right then and there before the patient is off the table,” he says. “In the old days,” Gupta adds, “you do a vertebroplasty, take the needles out, and put the bandages on. You send the patient for a CT scan afterward. That’s great, but what happens if the CT scan shows you the cement is not exactly where you want it? You can’t bring the patient back and repeat the whole procedure. This is an example of how XperCT can change the way we practice and make it easier and safer.” Cancer Treatments Another treatment for liver cancer is radiofrequency ablation (RFA). Currently, RFA is performed with CT. Niedzwiecki expects that with flat-panel CT-like technology, the venue for the procedure could change to the interventional suite because radiologists will be able to better guide the needles that deliver the therapy under a combination of fluoroscopy and flat-panel CT-like images. Rajiv Gupta, MD, PhD, director of the Volume CT Lab at Massachusetts General Hospital in Boston, who is working with the Siemens flat-panel detector technology, sees future applications in musculoskeletal imaging. He has been experimenting with imaging the trabecular structure of bone—the spongy bone that makes up the interior of most bones—in animals. “You get very nice details of the trabecular bone,” he says. “With the spatial resolution available using this technology, we can assess fracture healing, effect of medications on the skeleton, and other pathologies such as osteoporosis.” Also, Rajiv Gupta also expects the flat-panel detector to eventually play a major role in functional or volume perfusion studies and dynamic imaging of temporally evolving processes. Because each rotation of the gantry acquires a complete volumetric data set, by continuously spinning the gantry, it is possible to observe the dynamics of a contrast of bolus as it passes through the vascular system, he says. With further improvements in temporal resolution, it should be possible to detect partial or complete coronary artery blockages. “The scanners also enable you to see the composition of atherosclerotic plaque in the vascular system and coronary arteries, and the micro-circulation of the cardiac muscle,” he says. Another potential advantage to the flat-panel detector technology is that it may prove safer for the patient and physician because procedures may require less radiation. Traditionally, interventional radiologists spend a lot of time and radiation just hunting for the artery they are treating, Atul Gupta says. “The reason you potentially use less radiation with flat-panel technology is that you spend less time hunting for the artery,” he says. With flat-panel 3-D technology, “right from the get-go you can do a 3-D scan. My Philips system takes exactly four seconds from start to finish to create the 3-D angiogram—the fastest system currently available. Those four seconds could potentially save a half an hour or an hour of searching for a vessel later. You know right away exactly what angle and what projection you need to find the artery,” Atul Gupta says. “It makes the rest of the procedure go very, very quickly. You no longer have to hunt and seek to find the artery. You’re no longer blindly passing a needle several times looking for something.” It’s also a safer way of doing interventional procedures, Atul Gupta says, “because every time you pass a needle, there is the risk of bleeding.” Even though interventional radiologists wear lead, they still get hit with scatter radiation that bounces off the patient. X-ray exposure is cumulative. Flat-panel technology, by the nature of its construction, uses less radiation to get the same or better images compared with standard image intensifiers, Niedzwiecki says. “So baseline, there is less radiation to the patient and physician.” Additionally, if flat-panel detector technology allows the radiologist to perform procedures with more accuracy, they will take less time and therefore further reduce the exposure to radiation to the patient as well as the physician, Niedzwiecki says. Niedzwiecki expects that in the next two to three years, flat-panel detector technology will begin to replace the image intensifiers now found in angiography suites. “There may be a used market for image intensifiers, but you won’t see anybody buying them new,” he says. The life expectancy of angiography suite equipment is approximately 10 years, Niedzwiecki says. So when physicians need to replace their imaging equipment, they are likely to opt for the newest technology. Racadio agrees that flat-panel CT-like detectors “will set the stage for broad changes in the practice of interventional radiology. Within the next couple of years, everyone is going to have this and it’s going to change how and what we are capable of doing.” — Beth W. Orenstein is a freelance medical
writer who lives in Northampton, Pa., and is a regular contributor to
Radiology Today.
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June
5, 2006
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