Cardiac SPECT Maintaining Its Niche: A Technology in Evolution

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hiit040506b.jpgCardiac SPECT may not seem like the latest and greatest cardiac imaging technique. The fuzzy, low-resolution SPECT images may appear far less glamorous (and perhaps, to the untrained eye, less convincing) than 64-slice cardiac CT — but don't be counting cardiac SPECT out of the cardiac care paradigm just yet. The nuclear medicine study remains quite relevant, and it will likely continue to play a key, yet evolving, role in the cardiology department of the future.

The typical cardiac SPECT camera is used to evaluate patients who present to the emergency room with chest pain. In the not-too-distant future, it could play a larger role in the outpatient cardiology office. That's because some new cameras offer a small footprint that is quite manageable in a private-office setting. And as another breed of new SPECT cameras are combined with higher-slice CT cameras, physicians will gain the ability to complete calcium scoring in conjunction with a SPECT study.

IT capabilities are limited in this realm and mainly focus around image viewing. Most PACS still do not display SPECT/CT and other nuclear medicine studies well, which necessitates the workflow disruption of moving to a dedicated SPECT workstation to read images. But that will change too as vendors are getting closer to viable PACS workstation solutions that incorporate full SPECT functionality.

SPECT & other cardiac modalities

SPECT is one of several tools used evaluate and diagnose heart disease. The arsenal also includes cardiac CT, ECG stress testing and echocardiography. But for many facilities, SPECT is the preferred solution.

The cardiovascular nuclear imaging laboratory at Yale University in New Haven, Conn., relies on GE Healthcare's Hawkeye SPECT camera to image 90 percent of patients suspected or known to have heart disease, says Frans Wackers, MD, professor of diagnostic radiology and medicine and director, cardiovascular nuclear imaging and exercise laboratories. Other possibilities are an ECG stress test or an echocardiogram. But the sensitivity of an ECG is substantially lower than SPECT. With an ECG, sensitivity sits at the 60 percent range, while SPECT sensitivity hovers in the 90 percent range. Echocardiograms also are plagued by a higher false positive rate than SPECT.

What's more, SPECT is a healthcare bargain. At many sites, the state-of-the-art ER chest pain workup consists of a 12- to 24-hour hold. During the hold, cardiac enzymes are measured and an EKG is ordered. Yet 8 percent of released patients suffer a heart attack within 30 days of being released. SPECT may improve those odds.

"Nuclear SPECT scanning identifies almost everyone with acute coronary syndrome," offers Jack Juni, MD, nuclear medicine specialist at Beaumont Hospital in Royal Oak, Mich., and chairman and chief technology officer of CardiArc. Other studies show that hospitals can save nearly $1,000 per patient by incorporating SPECT. That's because many patients can be sent home safely and others can be admitted to a lower-intensity bed.

The other major issue is the role of cardiac SPECT vs. the coronary CT angiogram (CTA), says Warren Janowitz, MD, medical director of nuclear medicine services at Baptist Hospital of Miami in Florida. "It's almost become a religious argument," adds Juni.

Sixty-four slice CT does offer some fairly significant advantages. "It's fast, and it provides a direct view of the coronary anatomy. CT gives immediate answers and pinpoints the locations of any blockages," explains Juni. On the other hand, 64-slice CT remains fairly unproven clinically, although several studies are now underway comparing it to the cath lab performance. "There is little data to show how accurate it is," continues Juni. In addition, cardiac CT requires x-ray contrast, which could cause a reaction; and it entails radiation exposure to the tune of 10 to 20 times more than a SPECT study.

The radiation issue is a particular concern for stent and bypass patients who require annual follow-up. Is it feasible, safe or practical to subject this population to annual cardiac CTs for 10 to 20 years, asks Juni.

A final barrier to cardiac CT is its cost. SPECT cameras are a veritable bargain at one-half to one-third the price of a multi-slice CT scanner.

Attenuation, slice count and more

At the same time, SPECT technology is far from perfect. One of the primary problems with SPECT is attenuation, the phenomenon that occurs when fat or breast tissue absorbs radiation before it reaches the heart.