Gated metabolic imaging: A single agent method in detecting hibernating myocardium

Purpose: Positron emission tomography (PET) using perfusion and metabolic imaging is the gold standard for detecting hibernating myocardium (HM). HM is defined by continuing metabolic activity in an ischaemic region at rest (mismatch defect). We investigated whether, using a single agent, detecting metabolic activity in an impaired myocardial region is capable of achieving the same diagnostic results. Methods: PET was performed using ¹³N-ammonia (NH₃) and ¹⁸F-Fluorodeoxyglucose (FDG) for perfusion and metabolic imaging, respectively. Etectrocardiographic (ECG) gating of the metabolic images, over 8 phases within a cardiac cycle, allows collection of data on myocardial wall thickening. The results of the ECG-gated FDG images were compared to the results of the combined perfusion and metabolic imaging. Results: There were 45 patients (37 males) in sinus rhythm, and impaired left ventricular contraction who underwent PET imaging. Combined perfusion and metabolic PET imaging revealed perfusion-metabolic mismatch defects suggestive of HM in 26 patients. Using the data from ECG-gated FDG imaging, continuing metabolic activity in areas with impaired myocardial thickening was found in 26 patients. The results were concordant in 43 of the 45 patients. Therefore, the use of the new method has a positive and negative predictive accuracies of 96% and 95%, respectively, when compared to the perfusion-metabolic mismatch defects. Conclusion: ECG gated FDG imaging may be helpful in detecting hibernating myocardium in patients with sinus rhythm. Prospective validation of this method is necessary.