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. These attenuation artifacts can lead to a false positive result. According to Juni, 10 to 15 percent of SPECT studies have some potential for false positive findings with women and obese patients at the highest risk. Most systems can measure absorption with an attenuation map created by a CT scan.

Wackers confirms, "The primary benefit of hybrid SPECT/CT cameras is attenuation correction." In fact, Yale is upgrading from its Hawkeye with a one-slice CT scanner to GE Healthcare's Infinia, which incorporates a four-slice CT scanner. "The quality of attenuation correction will improve, but we still won't have diagnostic quality CT scans," notes Wackers.

Park Nicollet Heart and Vascular Center in St. Louis Park, Minn., recently deployed Siemens Medical Solutions Symbia T2 SPECT/CT system. "The primary benefit of the scanner is the CT attenuation correction, which is quite helpful in reducing interpretation time and increasing certainty of diagnosis," says Cynthia Toher, MD, director of cardiology. The center does use attenuation correction on every case, which increases scan time slightly and exposes all patients to radiation. On the downside, the new camera does not completely eliminate artifacts and even creates some of its own, and techs must make sure to register anatomic and functional images correctly.

Baptist Hospital of Miami is taking the next step and has installed the first of two Philips Medical Systems Precedence SPECT/CT cameras. The hybrid scanners include a 16-slice CT camera. "Our goal is to image all patients [who present with chest pain] with the SPECT/CT cameras. We gain the additional ability to complete calcium scoring, which is useful to exclude patients with significant coronary artery disease. We also expect the hybrid scanner to yield more accurate results in women and overweight men, who are prone to attenuation artifacts," Janowitz says.

The hospital initially considered using the SPECT/CT systems for CT angiograms, but decided its stand-alone 64-slice CT was better suited to the task as CT angiograms benefit from the higher resolution.

Despite the progress and the marriage of SPECT and multislice CT, attenuation correction remains a work in progress, says Juni. The technology is still evolving, and correction devices are not routinely used in practice. Juni predicts that attenuation correction methods will improve in the next few years, with "very good" methods hitting the market in two to four years.

Coming soon: Lighter, smaller, better SPECT cameras

The next generation of SPECT cameras will include some diminutive options. In January, the FDA approved CardiArc's CardiArc SPECT camera. The pint-sized SPECT system reinvents the modality.

For starters, CardiArc measures a mere 3.5x4.5 feet and fits neatly in a 6x7 room. A conventional system, in contrast, requires a 14x18 room, and other new, "small" options squeeze into a 10x12 space. The size makes it ideal for the outpatient cardiology office. Typically, the cardiology practice that wants to invest in SPECT must combine three rooms, which may be economically impractical.

Currently, when a cardiologist sees a patient with suspected acute coronary syndrome he calls the imaging center or hospital to schedule a study, which can take two to three weeks. Tack on another week or two to share results. "That's a risky delay in care for someone with serious disease. SPECT is the best way to evaluate cardiac disease, and this system delivers immediate results to the point of care," explains Juni.

The new generation of SPECT cameras delivers additional results, says Juni. Conventional cameras entail a 12- to 20-minute scan. During the scan, the patient lies on his back with his arms over his head, which can cause shoulder discomfort and claustrophobia. The patient may move, leading to a false positive result or creating the need for a second study.

During a CardiArc scan, the patient sits upright, and scan time drops to between 30 seconds and two minutes.

PACS & nuke med: Making friends

Most PACS workstations remain unfriendly to SPECT and other nuclear medicine studies. "PACS does not handle fusion data really well," states Janowitz. As a result, the radiologist must use the SPECT workstation for image viewing and interpretation. "It's not as convenient as being able to read from PACS. It is a workflow issue," continues Janowitz. Another option is a third-party viewing station optimized for nuclear cardiology.

"PACS is evolving, and image management systems are incorporating improved nuclear medicine capabilities," concludes Juni.

Park Nicollet Heart and Vascular Center has determined a reasonable multipurpose cardiac imaging reading solution with the Siemens Leonardo workstation. Cardiologists can read SPECT, CT and MR studies from the same workstation, which benefits workflow, says Toher.

Future directions

As PACS vendors tackle the nuances of nuclear imaging, clinicians are wrestling with the role of SPECT and other cardiac imaging solutions. "The future is hybrid imaging," predicts Wackers, "and I'm always in favor of smaller equipment."

"We are trying to determine how SPECT and coronary CT angiograms fit together," says Janowitz. One possibility is the development of a hybrid 64-slice SPECT/CT scanner. "It would be useful for calcium scoring," admits Janowitz, "but it's not efficient to have a 64-slice scanner sitting idle during SPECT studies."

The raging either-or argument of SPECT vs. cardiac CTA may not be the right way to frame the discussion, says Juni. In the future, the two exams may be used in a complementary fashion. "SPECT studies are often performed to guide therapy or plan medical management on patients who have had invasive catheterizations. There could be a role for SPECT with non-invasive [CT] catheterization," notes Juni.

Toher also sees SPECT and 64-slice CT playing complementary, rather than mutually exclusive, roles. "It's hard to determine which lesions are functionally significant on a CTA," she explains. The site can overlay 64-slice CTs on SPECT images to help sort out indeterminate lesions on CT studies or view anatomy on SPECT exams.

Wackers promotes a continuum among SPECT, PET and CT in the lab. "Not every patient needs a high-end study. Low-risk patients can be referred for a simple SPECT study. Obese patients and women may require attenuation correction, and the highest risk category may be referred for a PET-CT study."

Janowitz also sees more small cameras that can be attached to CT scanners and falling acquisition speeds, which could aid throughput and yield better images. "The combination of higher-slice CT and nuclear studies will be important for groups that don't have a dedicated cardiac CT unit," adds Toher.

Cardiac SPECT remains a modality in evolution. Vendors are launching new hybrid cameras, which lessen the impact of attenuation and result in greater diagnostic confidence. The other new development is the small SPECT camera, which will expand the outpatient market and enable cardiologists to provide results more quickly and at the point of care. A final and critical area of development is the PACS workstation; vendors do recognize that systems do not meet nuclear medicine needs and are developing viable stations that incorporate nuclear medicine functionality.

The upshot? "SPECT will be around for the foreseeable future," Juni says.