Multidetector CT: The Heart of Cardiac Imaging

Sixty-four slice CT is hot. Most facilities fall into one of three categories: implementers of CT’s latest workhorse, those on the brink of installing it or those actively analyzing and budgeting for the technology. In all, about 40 percent of healthcare sites across the country have added 64-slice CT to their imaging arsenal — amazing since it’s only been on the market for two years.

The primary driver for 64-slice CT is cardiac imaging; the technology truly enables non-invasive coronary artery imaging. But deploying 64-slice CT is a multi-faceted process. To fully optimize the technology, healthcare facilities need to understand its clinical utility and address issues such as post-processing, storage and business planning.

The clinical rationale

Coronary artery imaging with multidetector CT is not synonymous with 64-slice technology. Five years ago, University of Maryland Medical Center in Baltimore based its coronary imaging program on a four-slice CT system. The program graduated to 16- and 40-slice scanners and now relies on a pair of Philips Medical Systems Brilliance 64-slice CT scanners. The difference with 64-slice CT boils down to resolution and clinical capabilities.

Sixty-four slice technology offers better spatial and temporal resolution than its predecessors, yielding better coronary artery images for more patients. “This system allows us to non-invasively image the coronary arteries on a routine basis,” explains Charles White, MD, vice chairman of radiology. Improved spatial resolution is essential for contrary imaging, says Tony DeFrance, MD, medical director CVCTA Education Center in San Francisco, Calif., who uses Toshiba America Medical Systems Aquilion 64 scanner.

Sixty-four slice CT scanners generate thousands of submillimeter slices. More and thinner slices translate into better images of large coronary arteries, which measure about 4 millimeters. In addition, scan time drops to a reasonable 6 to 8 seconds, which is a feasible breath hold for most patients. The brief scan time reduces the chance of an arrhythmia or the patient releasing his breath and produces clearer images. In addition, improved temporal resolution limits blurred images and artifacts. The upshot? “Sixty-four slice CT will change the way cardiac disease is diagnosed and managed,” claims DeFrance.

The ability to visualize the coronary arteries and view and characterize plaque have taken the cardiac imaging world by storm; however, the technology is outpacing clinical trials, says DeFrance. “The field is changing rapidly,” adds James Min, MD, director of cardiac CT lab at Cornell University and a GE Healthcare Lightspeed VCT user. The current model at many sites is to use 64-slice CT as the diagnostic test of choice for low to intermediate risk chest pain patients. The scanners offer a means of rapidly deciding how to best treat these patients.

But several factors may limit adoption of 64-slice technology. DeFrance says some physicians are reluctant to adopt 64 because the return on investment can be relatively lengthy compared to other systems like cardiac nuclear cameras. What’s more, installation and education can be time-consuming, and there are disparities in reimbursement.

These barriers, however, are fairly manageable and can be overcome with comprehensive clinical and business planning. “The practice model that works best is the cooperative relationship between cardiologists and radiologists. These specialists need to understand that their strengths and weaknesses complement each other,” notes DeFrance. That is, the expertise of the radiologist is required for non-cardiac images, and the cardiac know-how addresses the cardiac portion of the scan. The benefits of the cooperative model transcend the clinical as it can be difficult to break even on cardiac scanning alone. Peripheral vascular work and non-vascular scans can round out the program to boost the bottom line.

In addition, sites need to develop a post-processing plan. Take for example University of Maryland Medical Center. For most cases, 3D technologists handle the lion’s share of post-processing for images produced on the Brilliance scanner, which includes reviewing wall motion and completing stenosis assessments and ejection fraction calculations. Then the radiologist reviews the images and fine-tunes the images as necessary. This model requires well-trained technologists, says White. The Cornell cardiac CT lab uses techs for retrospective reconstruction of different cardiac phases; radiologists and cardiologist complete the post-processing.

One exception to the 3D tech plan, however, is the triple rule-out. Most hospitals see a fair share of patients present to the ER with acute chest pain, which can be a diagnostic challenge. CT angiography offers a rapid, reliable means of ruling out coronary artery disease, aortic dissection and pulmonary embolism. The hitch, however, is the need for rapid turnaround. “Our goal is a one hour turnaround for triple-rule out, so radiologists handle the post-processing directly,” says White.

The dual-source option

Sixty-four slice CT is not the only cardiac imaging CT solution. Siemens Medical Solutions offers the SOMATOM Definition dual-source CT scanner, a new scanner that combines two x-ray sources and two detectors. In 2005 when South Jersey Radiology Associates, a nine-site group, researched its next cardiac CT investment, the group decided to deploy Definition.

“It’s clearly the way to complete cardiac scans,” explains William Muir, MD, director of body imaging. The rationale? Sixty-four slice systems are heart rate dependent. Patients may require beta blocking, which can wreak havoc on the schedule, says Muir. It can take more than an hour to beta block a patient, and the length of time needed to return to a normal heart rate varies by patient. Definition, however, is not heart rate dependent. “It produces the same high-quality images as 64-slice CT without beta blocking,” states Muir. Definition allows the practice to smoothly integrate multiple coronary CT angiograms into its daily schedule. Post-processing and storage needs are similar to conventional 64-slice systems. At South Jersey Radiology Associates, 3D techs handle basic post-processing, and images are stored in the site’s PACS.

On the 64-slice horizon

As 64-slice CT enters mainstream radiology, vendors are finding ways to improve implementation. Take for example thin-client visualization systems that offer a means of distributing 3D post-processing across the enterprise. CT vendors are developing portal solutions to distribute post-processing functionality. Today, the current generation of thin-client tools offers some utility. For example, cardiac CT angiography entails a hefty amount of negative studies, and these cases don’t hinge on the most advanced 3D toolset. “[Current] thin-client solutions may not be as robust as necessary for complete cardiac review, but they can suffice for a first approximation, or they can be used for a basic first view for after-hours studies,” says White.

One of the roadblocks to more widespread deployment and clinical use of 64-slice CT is reimbursement, but researchers are aiming to demonstrate the cost-effectiveness of CT over nuclear scans and invasive catheterizations. Positive results could sway reluctant payors and boost use.

On the CT development side, Cornell’s Min looks forward to improved spatial resolution. “We need at least 200 micron resolution to compete with invasive coronary angiography [and visualize] smaller arteries with diameters in the one millimeter range.”

Conclusion

Although the technologies are still young, 64-slice and dual-source CT are proving their utility, allowing physicians to routinely image the coronary arteries for rapid, non-invasive diagnosis of cardiac disease. Early adopters are developing best practices and demonstrating the importance of collaboration between radiology and cardiology. Another key step in the building of a successful program is the post-processing arrangement; many sites rely on 3D or super techs for the first cut. As the technology matures, physicians can look forward to a clearer definition of roles of various cardiac imaging systems and improvements in advanced visualization solutions, particularly in the thin-client arena.