Pointing the way toward heart disease screening.
Cardiologists contend every day with the worst of the worst, the conditions that continue to rank the highest in mortality and reach the farthest through society. To do this, and to provide the best possible patient care, they rely on an increasing array of medications, treatments, and examinations. But there’s still something missing.
“Cardiovascular disease is the leading cause of death for both women and men in the United States and worldwide,” said Claudio Smuclovisky, MD, director of South Florida Medical Imaging Cardiovascular Institute in Boca Raton, Fla. “It kills many more people than any other disease, and yet we don’t have a comprehensive and effective screening process. No matter all the wonderful treatments that are out there, we still have people dying every minute, and every day, people that sometimes had no idea they had heart disease.”
With the advent of Step-and-Shoot cardiac imaging technology, many cardiologists and radiologists are spotting a potential means of effective heart disease screening without the significant radiation dose of current methods.
Behind the creation of cardiac CT options, and the evolution of the Step-and-Shoot line of products, is the critical nature of the issue. As cardiologists know well, heart disease can be deadly and unexpected: for one-fifth of all patients, the first symptom of heart trouble is sudden death. Heart disease affects more than 60 million people in the United States, according to the American Heart Association; put another way, one person in five suffers from some form of heart disease, including high blood pressure, coronary heart disease, stroke, congenital cardiovascular defects, and congestive heart failure.
|The Brilliance iCT features Essence technology, consisting of new x-ray tubes, detectors, and reconstruction design elements.|
Cardiac imaging has improved the situation, but the current roster of technological options is limited. To understand what is truly happening in the heart, physicians are often required to rely on invasive cath lab and other procedures. For noninvasive imaging, traditional helical CT imaging and prospective data acquisitions (calcium score) enable a close look at blockages in the heart and arteries, but in practice they can determine only approximately 20% of the actual plaque burden. Other imaging tests, including nuclear perfusion imaging, cardiac MRI, and more, are similarly limited in scope.
When thinking about the commonly used CT methods, more limitations become apparent. Obtaining heart images through conventional cardiac spiral retrospective gating can result in an average radiation dose of 12 to 25 millisieverts (mSv), a significant amount considering the normal background radiation dose is around 3 mSv. The speed of processing, image quality, and time of acquisition also are limitations cardiologists must contend with.
Step-and-Shoot technology, then, represents an exciting advance for cardiologists and radiologists, and an important tool in the fight against heart disease. It’s a relatively simple idea. With standard spiral CT image acquisition, the x-ray tube is on at all times as the table moves at a constant speed. The radiation is delivered and imaging is taken even during periods when a patient’s heart is at an undesirable phase for diagnostic imaging. With Step-and-Shoot technology, the patient is moved through the same distance in steps, but the x-ray tube is only at the discrete acquisition point. Moreover, a bigger area of the heart is covered with each gantry rotation. As a result, the radiation dosage is reduced, and the time needed for imaging is shrunk.
“The CT scan is essentially a camera with a shutter,” said Furqan Tejani, MD, director, advanced cardiovascular imaging, Long Island College Hospital. “Both cheap and expensive cameras can take pictures, and the only thing that sets them apart is shutter speed; the ability of the camera eye to blink faster gets you better pictures. Cardiologists need a camera fast enough to capture the heart in motion. If the speed of the heart is faster, we’ll see a blur. By the same token, if the shutter speed is faster than the heart’s motion, will see crystal-clear images. The Step-and-Shoot method capitalizes on this and provides reduced radiation as a benefit. In addition, not only does the camera need a good shutter, it needs good film. The new systems are making the film (detectors) more sensitive, more receptive to light and dark, and more able to crunch the data coming through them, creating much faster, crisper images.”
With radiation reduced as much as 83%, and image quality and processing time enhanced, cardiologists are now using CT scanning with Step-and-Shoot with confidence.
“Step imaging enables us to acquire coronary CTA images with doses roughly equivalent to ambient annual background radiation exposure,” said James K. Min, MD, assistant professor of medicine and radiology and director of the Cardiac Computed Tomography Laboratory, Weill Cornell Medical College and New York Presbyterian Hospital. “It is a dramatic reduction in radiation that has been coupled with an improvement in overall image quality. In addition, as the technology requires radiation exposure during only a portion of the cardiac cycle, fewer unnecessary images are acquired, which can expedite the clinician’s ability to determine a diagnosis.”
Step-and-Shoot also opens up CT imaging to patient populations previously not well addressed.
“At our center, it’s now the standard of care,” Smuclovisky said. “It opens up the possibility of evaluating people you typically wouldn’t use CT imaging with before, including younger patients.”
Since the technology is still relatively new, hiccups do exist. Variable heart rates will degrade the image, excluding patients with excessive or unstable heart rates due to arrhythmias. In addition, obese patients, anxious patients, and those who have difficulty following breathing instructions are excluded.
|GE moves forward with the new Lightspeed CT 750 HD.|
While the Step-and-Shoot method is increasingly embraced in clinical care, the market for technology and products is still relatively young. The major players have demonstrated the ability for the technology to effectively address some of cardiologists’ major challenges, and are introducing product lines to an increasingly wider audience.
GE pioneered the Step-and-Shoot method for CT scanning, bolstered by the idea that the excessive radiation dosage for cardiac CT could not be adequately balanced with the imaging results. For CT imaging to be more readily available to a wider range of patients, GE reasoned, lowering the radiation dose was critical. Using GE’s SnapShot Pulse feature, images can be obtained with up to an 83% reduction in dose for cardiac scans. Scans are achieved with an average 3 to 5 mSv; for some patients, the radiation can be as low as 0.6 mSv.
To expand upon its Step-and-Shoot line, GE is going for a “game-changing” product called the Lightspeed CT 750 HD.
“It’s a fundamental paradigm shift based in new detector technology and materials, new x-ray tech, and new reconstruction technology,” said Gene Saragnese, vice president and general manager, molecular imaging and CT, GE Healthcare. “We asked radiologists and cardiologists what was important to them. They’re in the business of making very difficult diagnoses that are in many ways life and death, so they asked for better images to make more confident diagnoses and better ways to differentiate between calcium and contrast. We increased the resolution by 47% in order to see finer structures, blockages, and more. We also expanded the radiation dose reduction capabilities. Now, we keep the dose reduction for cardiac scans and add dose reduction for the entire body by up to 50%.”
The CT 750 continues the tradition of low-dose, step-and-shoot scanning all with higher spatial resolution. The machine structure includes the first new detector material in 20 years, made from garnets with altered molecular structure. The Gemstone high-definition imaging uses up to 2,496 views per rotation (a 2.5x increase) to deliver improved spatial resolution and image quality across the entire field of view. It also allows for accurate stenosis quantification (measuring 75% stenosis on a 3-mm vessel within 100 microns in bench testing) and delivers a 40% low-contrast detection improvement in bench testing.
Philips also offers evolved Step-and-Shoot technology options. The Brilliance iCT features Essence technology, consisting of new x-ray tubes, detectors, and reconstruction design elements. The system is able to provide clear images of the entire heart in two beats.
The scan is touted as the fastest system on the market, with the gantry rotating four times in a single second, 22% faster than current systems. Brilliance iCT offers 256 slices for the speed, power, coverage, and dose utility. While the radiation dose is reduced by around 80%, sample density is improved for better spatial resolution, and high temporal resolution is provided through adaptive, rate-responsive techniques to arrest patient motion.
With the significantly reduced radiation dose and imaging quality, the power of the Step-and-Shoot technology is its potential of becoming the best noninvasive screening test for the evaluation of coronary artery disease.
“This is one of the most significant, life-saving tests to come out in the last 20 years,” said Smuclovisky, who uses the Philips line of Step-and-Shoot products. “I’ve used cardiac CTA in over 6,000 cases, including people with normal cholesterol and normal stress tests but an underlying, undetected heart disease, and have been able to save many lives. There’s an enormous possibility for this tool for screening purposes, particularly for those in their early 40s with a family history of heart disease, diabetes, and hypertension.”
There are barriers, however, to widespread use of the technology. Scientific data supports the efficacy and safety of the method, but still parts of the cardiology community have been reluctant to opt for Step-and-Shoot over other diagnostic imaging.
“The problem is economics,” Smuclovisky said. “Cardiologists with nuclear cameras generate lots of revenue, and it’s not easy to give this up to a technology that’s not yet profitable. Unless the cardiac CT becomes profitable, its future is very questionable. If they reimbursed cardiac CT appropriately, we would see a lot more utilization and overall savings in health care costs. It’s that phenomenal of a study.”
The issue of financial investment, and sufficient financial reimbursement, is one the Step-and-Shoot producers have top of mind.
“Our intent is to make this technology available more broadly,” Saragnese said. “We’re trying to balance superpremium offerings with bringing better health care to everyone. We recognize not every institution will be able to afford it, but even in a health care system with low reimbursement, we should have access to lower dose and uncompromised image quality. Our goal is to solve unmet clinical needs and be responsive to those needs.”
Cardiologists are looking at their options and the ways in which Step-and-Shoot technology can be incorporated in their practices. Some, like Min, who uses the GE line of products, believe an ultimate solution might be a combination of traditional and newer technology. The Step-and-Shoot method could be used as a low-dose screening tool, with the retrospective helical gating method as a secondary measure to preserve functional data.
Ultimately, Step-and-Shoot offers cardiologists hope for more effective patient care, and many in the field are excited about the potential for the future.
“We’re making leaps of imagination that have the capability of giving us answers to questions we have now, and questions we’ll have in the future,” Tejani said. “We’re gaining the ability to truly look inside the body without using a scalpel. In that aspect, this will become an all-encompassing modality for the field.”
Amy Lillard is a contributing writer for Medical Imaging. For more information, contact .