Expert: Myocardial perfusion SPECT may no longer be best noninvasive test for heart disease
BOSTON—While the era for cardiac SPECT imaging continues to be exciting, the nuclear cardiology community needs to address the challenges of increased throughput efficiency, lower cost delivery and reduced dosimetry to remain competitive and cutting edge, according to an analysis presented Sept. 12 by Timothy M. Bateman, MD, at the American Society of Nuclear Cardiology (ASNC) conference.

Bateman, a professor of medicine at the University of Missouri-Kansas City in Miss., said that the past of myocardial perfusion SPECT imaging (MPS) has been characterized by tremendous growth (one of the fastest growing CPT codes in the past decade and one of the largest Medicare payment codes); an aggressive push by the industry for further growth; as well as unusual and inappropriate expansion of high-tech imaging into non-specialized sites of service.

He said that MPS quickly became known as the:
1. Best noninvasive test for diagnosing coronary artery disease (CAD) in patients with intermediate CAD likelihood;
2. Best noninvasive test for triaging between medical therapy and revascularization; and
3. Best noninvasive test for short-term risk stratification.
As a result of these characteristics, along with the focus on procedural guidelines and appropriateness criteria, SPECT experienced tremendous growth, according to Bateman.

However, he also noted that there have failings that also characterize the history of SPECT. For example, the pharmaceutical companies have not produced any new tracers, “despite widely known limitations.” There has been minimal evolution in camera technologies—and most evolutions have focused on the low-end. Also, he said that there is limited support for technologic evolution without new payments on the part of the providers.

As a result of the failings, Bateman said that “many disinterested outsiders would say that MPS is inefficient, over-valued, over-utilized and [emits] excessive radiation.”

Bateman reference a clinical trial, in which Ronaldo S. Lima, MD, PhD, et al. assessed the incremental value of combined perfusion and function over perfusion alone by gated MPS for detection of severe three-vessel CAD in 143 patients (JACC 2003;42:64-70).
“Importantly, the study found that with combined perfusion and function assessment, only about 60 percent of the subjects were identified as having multi-vessel CAD,” he said. “The study pointed out the importance of going beyond perfusion.”

In another trial, which evaluated the detection of significant left main CAD in 101 patients imaged with dual-isotope SPECT, Daniel S. Berman, MD, et al. found no significant perfusion defects in about 13 percent of patients (J Nucl Cardiol 2007;14:521-528). In this trial, Bateman said that “a lot of patients were under detected and the extent of their disease was under appreciated.”

“To remain vital long-term, we must improve,” said Bateman, based on the findings in these trials and others.

However, he commented on several of the newest cameras to enter the U.S. market, such as Spectrum Dynamics’ D-SPECT and CardiArc, which seem to reduce scan time and patient discomfort.

Also, Bateman said that some of the new software approaches could make strides toward improving: iterative reconstruction, ordered subset maximation, noise reduction, resolution recovery, performing the same number of angular projects in less time with less stops. The vendors producing the new software approaches are: UltraSPECT; Philips’ Astonish; Siemens’ Flash 3D; GE Healthcare’s Evolution; and Digirad’s nSPEED.

“We made big strides with the most recent methods,” he added.

Despite the advances, he said that several factors have yet to be shown, including:
  • Reduced acquisition time improves throughout efficiency and economics;
  • Reduced acquisition time compatible with good patient outcomes;
  • Several approaches not yet validated for one or more of the following: obese patients, women, 16-frame stress gating, 8-frame rest gating and thallium-201.
Bateman suggested that if the new methods produce the same quality within “half-time acquisition, then better results could be attained by using same dosages and imaging for current times, or lower dosimetry could be realized by imaging for the same times but using lower dosages.”

In order to maintain its diagnostic superiority, Bateman concluded that cardiac SPECT needs to produce better image quality and diagnostic certainty; earlier CAD detection; improved recognition of multi-vessel disease; and simultaneous acquisition of perfusion and metabolic tracers.