JNM: Software packages for 82Rb-gated PET/CT differ on LVEF data

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The reference range of left ventricular ejection fraction (LVEF) and LV volumes from gated 82Rb PET/CT varies significantly among available software programs and therefore cannot be used interchangeably, according to a study in the June issue of the Journal of Nuclear Medicine.

Electrocardiographic (ECG) gating is increasingly used for 82Rb cardiac PET/CT, but reference ranges for global functional parameters are not well defined, according to the authors.

In this study, Paco E. Bravo, MD, from the division of nuclear medicine and the department of radiology and radiological science at Johns Hopkins University School of Medicine in Baltimore, and colleagues sought to establish reference values for LVEF, end systolic volume (ESV) and end diastolic volume (EDV) using four different commercial software packages. Additionally, they compared two different approaches for the definition of a healthy individual.

Researchers evaluated 62 subjects (mean age 49 years; 85 percent women; mean body mass index 34 kg/m2) who underwent 82Rb-gated myocardial perfusion PET/CT. All subjects had normal myocardial perfusion and no history of coronary artery disease (CAD) or cardiomyopathy. Subgroup one consisted of 34 individuals with low pretest probability of CAD (less than 10 percent) and subgroup two comprised 28 subjects who had no atherosclerosis on a coronary CT angiogram obtained concurrently during the PET/CT session.

Bravo and colleagues calculated LVEF, ESV and EDV at rest and during dipyridamole-induced stress, using CardIQ Physio (PET software from GE Healthcare) and the three SPECT software packages (Emory Cardiac Toolbox from Philips Healthcare, Quantitative Gated SPECT from Hermes Medical and 4DM-SPECT from Invia Medical Solutions).

The authors reported that the mean LVEF was significantly different among all four software packages. They found LVEF was most comparable between CardIQ Physio (62 and 54 percent at stress and rest, respectively) and 4DM-SPECT (64 and 56 percent, respectively), whereas Emory Cardiac Toolbox yielded higher values (71 and 65 percent) and Quantitated Gated SPECT had lower values (56 and 50 percent, respectively).

Also, subgroup one (low likelihood) demonstrated higher LVEF values than did subgroup two (normal CT angiography findings), using all software packages, according to the authors. However, they noted that the mean ESV and EDV at stress and rest were comparable between both subgroups. “Intra- and interobserver agreement were excellent for all methods,” they wrote.

According to the researchers, the need for defining method-specific reference ranges was emphasized by prior studies, but because of the inclusion of “a range of health and diseases, such reference ranges could not be defined.”

The current study provides this “missing information; however, most subjects in our study were obese and female,” Bravo and colleagues wrote. “Our results may be somewhat limited when applied to the general population, but they are representative of the typical population referred for PET because SPECT is limited by artifacts specifically in those individuals.”

They also concluded that LVEF results were higher when healthy subjects were defined by a low pretest probability of CAD than by normal CT angiography results.