Cardiovascular CT: A Clinical Boon

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 Philips Brilliance iCT Cardiac

Cardiovascular CT stands both at a crossroads and directly in the crosshairs. Sixty-four slice and higher slice-count scanners are proving their prowess at creating exquisite images of the heart and coronary arteries, and clinical research and experience continue to demonstrate the clinical and economic value of cardiovascular CT. That’s because cardiovascular CT provides a non-invasive means to help physicians detect heart disease earlier, limit invasive cardiac catheterizations and save money compared to nuclear stress testing and catheterization. Plus, the newest scanners effectively reduce radiation dose.

On the downside, the cardiovascular CT community finds itself facing a formidable foe. The Centers for Medicare and Medicaid Services (CMS) has proposed adoption of a national coverage determination (NCD) that could substantially limit the use of CT angiography. If implemented, the policy would replace local coverage determination in all 50 states and the District of Columbia with an NCD that restricts coverage to narrow chest pain indications.

Despite the current regulatory ambiguity, cardiovascular CT remains a valuable option in the cardiac imaging arsenal. This month, a few experienced sites share their know-how.


Cardiovascular CT at a glance



Cardiovascular CT has evolved tremendously over the last few years. Take for example cardiovascular CT pioneer Fairfax Radiological Consultants in Fairfax, Va. The outpatient radiology group began offering cardiac CT in 2003 and recently invested in a new system: the GE Healthcare VCT XT, a next-generation 64-slice scanner. The new scanner offers a number of advantages over its predecessors, says Medical Director Jay Earls, MD.

“The VCT XT pairs improved speed with high-quality images at a much lower radiation dose than before. Five years ago, it took 20 seconds or longer to scan the heart, which presented problems for patients who couldn’t hold their breath for the duration of the scan. The average acquisition time on GE VCT XT is 4 seconds.”

Abbott Northwestern Hospital in Minneapolis is a relative newcomer to cardiac CT. The hospital deployed Siemens Medical Solutions Somatom Definition dual-source CT scanner in January 2007 and completed 2,300 scans last year.

“The scanner has changed cardiac imaging and patient care,” says John Lesser, MD, director of clinical cardiology. “Cardiologists are doing fewer normal invasive catheterizations.” That’s because physicians are ordering cardiac CT rather than an invasive cardiac catheterization when a patient has an equivocal stress test. If the CT is normal, the patient can bypass the cath lab. Cardiac CT also is the test of choice for cardiac patients who can’t tolerate the exercise required for a stress test.

Other sites, like Lenox Hill Heart and Vascular Institute in New York City, turn to CT as a cardiac and vascular imaging workhorse. The real question, says Harvey Hecht, MD, director of cardiovascular CT, is not which applications are appropriate for Philips Healthcare Brilliance 64-slice CT, but which aren’t.

Cardiovascular CT data provides crucial information, helping physicians determine if a patient’s symptoms are related to coronary artery blockage and to calculate the degree of blockage. Cardiovascular CT also provides information about plaque, so cardiologists can decide the optimal course to prevent rupture. “We use the scanner for a whole range of services. It’s the first test used to evaluate cardiac patients. A cardiac CT scan is superior to a traditional stress test for determining the appropriate therapy: angiography, stenting or bypass surgery. We also use the scanner to evaluate patients with equivocal stress tests and after cardiac catheterization to answer unresolved questions,” says Hecht. For example, the institute uses cardiac CT to evaluate coronaries not adequately visualized during cardiac catheterization because of damping of the catheter or inability to cannulate the artery. CT images also help physicians determine the course of anomalous vessels and delineate the occluded segment of a chronic total occlusion. Finally, physicians use CT images to size stents.

The reason behind the effectiveness of cardiovascular CT over conventional studies is quite simple. “Cardiac CT provides a 3D view of the coronary arteries. We can rotate the arteries on the post-processing workstation. Images acquired in the cath lab are more limited,” says Hecht. In fact, Hecht and his colleagues found that CT provides a truer picture than invasive coronary artery angiography, showing healthy arteries or mild disease more clearly than the invasive study. Intravascular ultrasound (IVUS) confirms CT results in 85 percent of patients, says Hecht.

Cardiac CT also is proving useful in evaluating patients who present to the ER with chest pain. Abbott Northwestern Hospital is part of a multi-center trial comparing cardiac CT and nuclear stress testing. “Preliminary data indicate that CT is a good option from the cost, safety and accuracy perspectives,” says Lesser.


The IT angle


There is no denying the IT impact of cardiovascular CT. It is an IT behemoth, producing data-sets in the 3,000-image range in some cases. Consider Fairfax Radiological Consultants. The 16-office practice completes all cardiac scans at one site, and images are read remotely at a second office. The practice invested in a beefy IT infrastructure to support its cardiac CT program. It boasts a one gigabyte (GB) network with a sonnet ring connecting all offices, which suffices for the practice’s CT workload.

The other elements in the IT equation are the workstation and archive. Fairfax Radiological uses GE Advantage Workstation to review CT images and sends all images to its Philips Healthcare iSite PACS. The practice saves all reformats, processed images and selected images of each coronary artery for a total of approximately 1,000 images per patient. The rationale for its conservative approach is economics. “We have a generous contract with the PACS vendor and don’t pay extra to store larger files. We find it’s easier to have the images in the PACS to review at a later date if needed,” says Earls.

Abbott Northwestern Hospital also saves approximately 1,000 images from each cardiac CT study, sending one or two datasets per cycle to PACS, which meets the requirements of accrediting bodies. Lenox Hill Heart and Vascular Institute saves reconstructions used to make the diagnosis and three to four phases, including those that show ejection fraction and wall motion.


Training the masses


IT infrastructure is only one of the prerequisites necessary for a successful cardiac CT program. Radiologists, cardiologists, technologists and referring physicians all require targeted education. Physician training must be targeted to the specific needs and background experience of the audience. Radiologists and cardiologists require different types of training, says Lesser. Each needs to learn how to use post-processing workstations and interpret cardiac CT data. Radiologist training should emphasize cardiac disease, which provides them with a framework to present and discuss findings with clinicians. Cardiologists, on the other hand, may require education focused on workstation management and cross-sectional image review. In addition, practices aiming to initiate or expand cardiac CT programs should educate referring physicians, particularly cardiologists and internists, about the value of CT angiography to grow their referral base. Technologist training is more straightforward. Lenox Hill Heart and Vascular Institute sends cardiac CT techs to Philips Healthcare training programs, supplementing tech training as needed internally. For example, an internal workshop might address specific protocols or patient populations.


Meeting the dose reduction challenge


One of the critical advantages associated with the newest cardiac CT systems is lowered radiation dose. Like many other cardiac CT providers, Abbott Northwestern Hospital has taken a very proactive approach to dose reduction. “The Definition dual-source offers several options,” notes Lesser.  The hospital does use beta blockers prior to scanning, which provides a very predictable time window for scan acquisition. Siemens MinDose algorithm allows the scanner to create an image in 82 milliseconds and can be used in studies that don’t require cardiac function data. Finally, Siemens post-acquisition software can add signal back to an image if a technologist undershoots a study in an attempt to reduce dose. The three-pronged approach yields impressive dose reduction results; Abbott Northwestern typically achieves doses of 3 to 7 millisieverts (mSv)—with dose stretching as low as 0.7 mSv for pediatric cardiovascular CT scans.

The other element of dose reduction, says Lesser, is to carefully select patients by weighing the risks and benefits of cardiac CT. The ideal candidate reports chest pain but is at low to intermediate risk for severe coronary artery disease. Another trick to decrease dose is to adjust the upper and lower edges of the acquisition as tightly as possible, says Hecht.

Other systems take different, but also effective, approaches to dose reduction. For example, the GE VCT XT decreases the average dose by 83 percent via prospective triggering. How does it work? With prospective triggering, x-rays are not continuously shot as they spiral around the patient. Instead, the scanner acquires one set of 64 images and then moves before acquiring the next set of 64 images to eliminate the overlap (and excess) radiation associated with a conventional protocol. Radiation dose is less than 5 mSv for an average-sized patient. Prospective triggering delivers additional advantages, too. A recently published study in Radiology links prospective triggering to improved image quality.  According to researchers, coronary CTA studies performed with prospective triggering yield a substantial (>80%) radiation dose reduction compared to a retrospectively gated helical technique and also deliver significantly improved image quality.
   

Reimbursement economics


The prospect of an NCD is looming, which could put the brakes on cardiac CT; however, sites can remain proactive. Although the deadline for comments to CMS has passed, physicians can appeal to Congressmen and Senators, says Hecht. If the current proposal sticks, Hecht recommends that practices price cardiac CT studies so patients can pay out of pocket. “A $500 fee per procedure is affordable and allows the practice to break even at about 10 to 12 scans a day.” In addition, private practices can market general vascular studies, which lack the reimbursement dilemmas associated with cardiac CT.


A successful paradigm


Cardiac CT works. It offers an economic, non-invasive means of imaging the heart and coronary arteries to more accurately detect disease and plan therapeutic interventions. Radiation dose can be minimized via a variety of mechanisms, and although the systems produce hefty datasets, IT requirements are manageable. Despite the current reimbursement climate, insiders know cardiac CT is a winning configuration. 

 

The Next Generation…Now
The next leap forward in cardiac imaging is higher slice CT scanners like Toshiba America Medical Systems AquilionONE. The 320-slice system represents the CT workhorse of the future, says João A.C. Lima, MD, director of cardiovascular imaging at Johns Hopkins Hospital in Baltimore. Md.

Since the hospital deployed AquilionONE in October 2007, the system has become its exclusive cardiac CT imaging solution. AquilionONE improves on 64-slice CT in a number of ways, says Lima. Coverage spans 16 centimeters to cover the entire heart in one rotation and eliminate the need for helical mode. Instead, AquilionONE uses simultaneous acquisition mode; the patient does not move as the gantry rotates, bypassing the need for helical reconstruction, which can result in misalignment during the reconstruction process. The hospital uses prospective gating on most patients; all slices are obtained at the same time, which translates into greater accuracy. Finally, AquilionONE’s radiation dose of 3 to 5 millisieverts (mSv) is one-fourth to one-third of the dose of first-generation 64-slice scanners.

“The main paradigm shift with the new system is the ability to obtain perfusion studies in combination with angiographic data,” explains Lima, who predicts that the future workup of patients with suspected coronary disease will begin with a CT angiogram and calcium scoring. This first step should answer questions for about three-fourths of patients, says Lima. The remaining patients will require perfusion stress testing with adenosine. “CT imaging will be tailored to each patient’s clinical condition,” continues Lima. For example, if a patient suffered a previous infarction, the scan can measure the size of the infarct.

Cardiac CT imaging continues to develop. The newest systems offer significant improvements over earlier scanners and could make cardiac CT the test of choice for all patients with suspected coronary artery disease by producing superior quality images at a low radiation dose and eliminating the need for other studies such as nuclear stress testing for many patients.