Ready for Prime Time: Cardiac CT Quickens the Beat
Imaging the beating heart presents a significant challenge, and until recently, cardiac CT was a tenuous proposition at best. Although 16-slice scanners can perform the task adequately for some patients, its utility is far from universal. Enter the 64-slice scanner. CT's big gun is ideally suited to cardiac imaging and has thrust open the door to cardiac CT (and sales are going great guns, too!).Cardiac CT is quickly convincing the clinical community of its capabilities. Michael Poon, MD, chief of cardiology at Cabrini Medical Center (New York City) and president-elect of the Society for Cardiovascular CT, explains, "CT is the only imaging modality to non-invasively view the lumen of the coronary arteries and provide information about vessel walls where plaque develops. Other cardiac modalities provide information at the end state of the disease process."
Jeffery Goldman, MD, director of cardiac CT and MR at Manhattan Diagnostic Radiology (New York City), adds, "Cardiac CT is ready for prime time. Sixty-four slice technology has the potential to completely change the way cardiac patients are managed."
A study in the May issue of the Journal of the American Medical Association supports cardiac CT aficionados. The study indicated multi-slice CT can provide high accuracy for coronary artery disease detection and may complement conventional coronary angiography. (See sidebar, "JAMA Study Supports Cardiac CT.")
Hospitals and independent practices are catching on. Ask anyone, especially facilities with a cardiac flare, about upcoming purchases. Chances are 64-slice CT is near the top of the list, and cardiac CT is one of the primary applications of the uber scanner. Sites that have taken the plunge into cardiac CT are deploying the scanner for coronary CT angiographies as well as studies of the carotids, aorta and pulmonary arteries and peripheral vascular scans.
But before joining the crowd, cardiac CT-wannabes need to understand appropriate applications as well as the benefits and challenges of implementing cardiac CT. This includes staff training, radiology-cardiology workload, technology to support cardiac CT and economics.
16 to 64
Washington Hospital Center (Washington, D.C.) is a typical cardiac CT site. The hospital has relied on a Philips Brilliance CT 16 Power for cardiac imaging and plans to upgrade to a 64-slice scanner in a few months. "Adequate coronary imaging can take place with a 16-slice scanner," asserts Guy Weigold, MD, director, cardiac CT program. Weigold says the 16-slice scanner is optimized for cardiac imaging with an x-ray tube and upgraded processing hardware to provide the horsepower and speed to facilitate cardiac CT. This is a good starting point for cardiac CT, says Weigold.
But Weigold foresees several advantages with the 64-slice scanner. The 20- to 30-second scan times with the 16-slice scanner will drop to 10 to 15 seconds, an easy, single breath-hold for most patients. And 64-slice is less prone to artifacts, resulting in better image quality. "We'll produce excellent quality scans in more patients," predicts Weigold.
Indeed the experience at Manhattan Diagnostic Radiology proves the point. "The problem with the 16-slice scanner is that at least one-third of studies are difficult to read because of motion artifacts. With the 16, we had to read a lot of cases without confidence," explains Craig Sherman, MD, managing partner. The practice upgraded to a Toshiba Aquilion 64 CFX scanner in March. "The improvement is greater than we expected. Almost all studies are diagnostic quality," continues Sherman.
Cabrini's Poon, who upgraded from a Siemens Sensation 16 to a SOMATOM Sensation Cardiac 64 in May, adds resolution to the list of 64-slice advantages. Siemens' 16-slice scanner has a resolution of 0.6 millimeters; the 64-slice upgrade drops resolution to 0.4. millimeters. "That's phenomenal compared to the gold standard of x-ray angiography, an invasive procedure with a resolution of 0.2 millimeters," claims Poon.
Cardiac applications: the short list
The Heart Center of Indiana in Indianapolis has relied on Siemens Medical Solutions SOMATOM Sensation Cardiac 64 as its cardiac powerhorse since early this year. "The primary benefit is that a 64-slice coronary study can replace a cardiac catheterization in a certain patient population," notes Ronald Razmi, MD, director of cardiovascular MR/CT. This includes patients with a low index of suspicion who don't have a lot of calcium in the coronary arteries and those with an abnormal stress test that seems suspicious.
For many facilities, CT angiography represents a new procedure and a dramatic improvement over the traditional cardiac catheterization. "This is a study that typically occurs in the hospital. It's an invasive surgical procedure that has a recovery period and is not without risk. In contrast, CT angiography is a very short in-office procedure that can be completed in five heartbeats, and the images parallel or are better those obtained in the cardiac cath lab," says Vance Chunn, administrator for Cardiology Associates of Mobile, Ala. Cardiology Associates deployed a GE LightSpeed VCT in April.
Chunn predicts that the number of normal catheterizations performed in the cath lab will drop from the current rate of 18 to 25 percent as more CT angiographies are performed. Goldman foresees fewer diagnostic caths.
"The number of therapeutic catheterizations will go up. Cardiologists will be able to develop more comprehensive pre-operative plans because they will know what the problems are prior to surgery," continues Goldman. Poon adds that a 64-slice scan can provide information that will enable cardiologists to prevent heart attacks and unstable angina by aggressively treating patients with statins and aspirin to reduce the plaque burden. In contrast, other tests such as stress tests can not provide information until the end state of the disease process - after the vessel is destroyed. A final plus? Cardiac CT benefits aren't limited to patient care; CT angiography has lower costs than the traditional cardiac catheterization.
Another promising arena for cardiac CT is the triple rule-out. That is, a cardiac scan can be used to quickly evaluate the patient who presents to the ER with chest pain for aortic dissection, pulmonary embolism and coronary disease. ER physicians may love the concept, but the jury is out on whether or not the triple rule-out will become standard of care. Weigold explains, "There may not be a high enough prevalence of aortic dissection and pulmonary embolism to justify the use of cardiac CT in this manner. It will take research and studies to determine a standard." Other cardiac applications include evaluation of bypass grafts and studies of the aorta and pulmonary arteries.
Despite the promise and hype surrounding cardiac CT, there are some clinical challenges. For example, it remains difficult to image patients with a significant amount of coronary disease; vessel wall calcification hinders imaging and makes it difficult to determine the degree of stenosis in the vessel interior. It's also difficult to obtain an accurate reading of patients with a very fast heart rate or cardiac arrthymia.
Tech Talk
As with any sophisticated imaging solution, there are technical issues to consider when deploying cardiac CT. "Sites need a robust PACS as well as a solid network to handle the images," says Manhattan Diagnostic Radiology's Sherman. The facility plans to upgrade from two T1 lines to a fiber optic network between its two offices to meet cardiac CT requirements. The practice plans to store cardiac CT images on a separate server because image size could tax its current system. Manhattan Diagnostic Radiology also intends to upgrade its three Vital Images Vitrea workstations to 64-bit processors for optimum cardiac functionality with radiologists clamoring for more speed and power. "A cardiac scan can yield 10 series of 400 or more images to reconstruct. That's a lot of data, and you need power to manipulate it," confirms Goldman. And 64-slice image size is a hefty 0.5 megabytes. To minimize the PACS burden, Manhattan Diagnostic Radiology limits data saved on PACS, selecting the best reconstructions to archive.
Other facilities are prepping for the onslaught of cardiac CT data. St. Petersburg Independent Diagnostic Radiology (St. Petersburg, Fla.) is one, which reads for 42 imaging centers across the state of Florida. The practice installed a fixed, wireless 45 megabit-per-second internet connection and an additional 300 gigabyte (GB) drive for storage. Finally, St. Petersburg Diagnostic Radiology plans to bump its memory to 2 GB to 4 GB. Owner Mark Herbst, MD, PhD explains, "Memory is the most important [IT] factor in handling datasets with a lot of slices."
Developing CT expertise
Cardiac CT presents some human resources challenges, too. Chunn says, "This is a fairly tech-intensive option. Centers need a well-trained technologist because cardiac CT differs from CT in the past."
Razmi confides, "Training techs is one of the more time-consuming aspects of deploying a 64-slice scanner." Nursing staff must know how to complete beta blocking and manage cardiac events.
The Society for Cardiovascular CT, American College of Cardiology and American Heart Association expect to release a consensus statement recommending two months of training for technologists at facilities that intend to independently perform cardiac CT. Currently, Cabrini Medical Center and a handful of other sites offer a one-week training course for physicians and ancillary staff. The course covers technical issues, patient prep, interpretation and contraindications, with experts providing overreads for 100 cases after the course.
Sherman outlines one issue confronting the cardiac CT world, asking who controls the technology - the cardiologist or radiologist. He opines, "The bottom line is patient care, and patients are best served by a collaborative effort between the two disciplines."
The all-cardiologist Cardiology Associates has developed a model collaborative program, deploying cardiac CT without an on-site radiologist. Staff cardiologists read the cardiovascular portion of CT angiographies. An offsite radiologist provides QA and reviews selected datasets for soft-tissue tumors and other problems. The practice relies on a T1 connection, mini-PACS for image storage and compression and a GE Advantage Workstation and Vital Images' Vitrea workstation to keep its cardiology-radiology partnership humming. Chunn says GE's remote diagnostics program is another technical plus; the program enables GE engineers to complete remote diagnostics on the scanner and provides a resource for techs with a database and expert Q&As.
Finally, the facility must create new protocols for cardiac CT. "Be vigilant with protocols. Practices will need different protocols for different types of patients," recommends Razmi. For example, obese patients typically require a higher radiation dose to improve the odds of a diagnostic scan.
Reconstruction realities
Cardiac CT reading and post-processing can take 20 to 30 minutes for each case. Sherman repeats the radiology mantra - workflow is the key to success. Manhattan Diagnostic Radiology streamlined its cardiac CT workflow by training techs to complete post-processing.
3D reconstruction workstations can simplify post-processing. Take for example the Center for Advanced Imaging Research at Medical University of South Carolina in Charleston, which relies on Vital Images' Vitrea workstation for three applications - calcium scoring, coronary CT angiography and cardiac function analysis - for images acquired from its 64-slice scanner.
"Vitrea very intuitively puts each calcium scoring patient into perspective with an age and gender-based chart that can be configured as a report and sent to PACS," explains U. Joseph Schoepf, MD, director, CT research and development. The workstation simplifies CT angiography with a VesselProbe tool that automatically removes the rib cage, extracts the course of a coronary artery and displays the artery in a curved multiple planar reformation (MPR). The perpendicular, cross-sectional views enable users to accurately detect and grade lesions and stenosis in minimal time, says Schoepf. Other options that could provide similar information include axial or manual segmentation and manual MPRs or MIPs (maximum intensity projections). Schoepf estimates that it would take 15 to 20 minutes to obtain the same results for each coronary artery with the manual alternatives; Vitrea completes the process in a matter of seconds.
Schoepf admits echocardiography and MRI provide superior cardiac function analysis tools, and stresses that CT should not be performed primarily for cardiac function analysis. Nonetheless, CT angiographies contain functional information. Instead of disposing of the data, Schoepf generates a cardiac function dataset on the 64-slice scanner and sends it to Vitrea for automatic left ventricle volume calculations when appropriate.
Another cardiac post-processing option is Voxar's VESSELMETRIX. "I use VESSELMETRIX for three purposes: problem-solving, creating high-quality images to communicate with referring physicians and automatic measurement of stenosis and cardiac volumes," says Herbst of St. Petersburg Independent Diagnostic Radiology. Herbst describes VESSELMETRIX as smart software that automatically subtracts bones and veins in two or three keystrokes to simplify 3D reconstruction. An automatic vessel tracking tool detects the center point, contours, minimum and maximum diameter of a blood vessel, and it displays the area and diameter of stenosis. "It's like computer-aided detection of stenosis," sums Herbst. The software also includes report templates to streamline the reporting process.
The financial factor
Cardiac CT requires a hefty investment in a nascent technology. How can facilities ensure a healthy return on that investment? Cardiology Associates purchased its 64-slice scanner confident that cardiac CT would add to its revenue stream as well as benefit patients. Chunn explains, "The literature indicates that sites need about 10 cardiologists to afford the scanner and a large enough patient volume to justify the cost." The practice has ramped up cardiac CT volume over several months, giving techs and cardiologists time to learn about the scanner. Chunn estimates that the 25-cardiologist practice will eventually complete 20 to 24 cardiac CT studies daily.
On the reimbursement front, Medicare and some private companies reimburse for cardiac CT. Cardiology Associates launched an educational campaign focused on value, efficiency and clinical indications for cardiac CT to foster acceptance and reimbursement among companies that don't reimburse for the study.
Conclusion
Cardiac CT is hitting its stride, promising to improve patient care by providing high-quality, non-invasive diagnostic information for a significant portion of cardiac patients. With 64-slice CT, cardiologists may be able to detect and treat coronary artery disease before a cardiac event occurs. CT angiography promises to better prepare patients for surgery by providing accurate pre-surgical information for stent planning and bypass grafts. Other potential CT cardiac applications include the triple rule-out.
Developing a healthy cardiac CT program hinges on planning, staff training and technical infrastructure. Scores of pioneering sites across the country have demonstrated that cardiac CT can be successfully implemented to enhance the practice and improve patient care.
JAMA Study Supports Cardiac CT
The May 25th issue of the Journal of the American Medical Association contained a study comparing 16-slice CT to invasive coronary angiography in 103 patients with suspected coronary artery disease. The study indicated multislice CT can provide high accuracy for coronary artery disease detection and may complement conventional coronary angiography.
The study demonstrated that multislice CT provides specificity, sensitivity and positive and negative predictive values comparable to conventional angiography for detection of significant lesions greater than 50 percent stenosis.
The downside of coronary angiography is a small risk of serious, potentially life-threatening events such as arrhythmia, stroke, coronary artery dissection and access site bleeding. The procedure also requires follow-up care. CT, on the other hand, is non-invasive, but does not eliminate the risks of radiation exposure or use of contrast agents.
The authors, Martin H. K. Hoffmann, MD, of University Hospital, Ulm, Germany and colleagues, concluded that CT shows reasonably high accuracy for detecting significant obstructive coronary artery disease when assessed at a patient level and indicated CT may be used to substantially reduce likelihood of clinically important coronary artery disease in patients with suspected disease. The authors also hypothesized that CT may evolve from a useful complement to invasive angiography to a clinically viable alternative as the technology improves.