A step forward in the use of SPECT imaging with I-123 MIBG

Excerpt

With the publication of the AdreView Myocardial Imaging for Risk Evaluation in Heart Failure Study (ADMIRE-HF), it has become clear that a simple ratio of heart-to-mediastinum (H/M) activity of I-123 metaiodobenzylguanidine (MIBG), on an anterior planar image is a strong predictor of cardiac prognosis in heart failure patients with a reduced left ventricular ejection fraction and New York Heart Association class II or III symptoms. The planar I-123 MIBG H/M ratio provides predictive information for outcome in heart failure patients beyond that available from clinical variables, left ventricular ejection fraction, and b-type natriuretic peptide.1 It remains unclear, however, whether further improvement in the prognostic information available from the planar I-123 MIBG H/M ratio can be provided through the use of single-photon emission computed tomography (SPECT). Previously, Chen et al.2 compared the accuracy of planar and SPECT imagings for noninvasive quantitation of I-123 MIBG activity in a cardiac phantom model. They noted that SPECT imaging with iterative reconstruction produced more accurate heart-to-calibration ratios than planar imaging. Cardiac SPECT imaging is usually performed with a low-energy, high-resolution (LEHR) collimator. In addition to its predominant 159 keV energy, I-123 has a low abundance, high-energy photon that penetrates the septa of a LEHR collimator, blurring the MIBG images, and impairing the accuracy of quantitative estimates. Those authors had previously reported that deconvolution of septal penetration (DSP) by those high-energy photons combined with iterative reconstruction yielded quantitative estimates of I-123 MIBG activity that were similar to measurements without septal penetration using a medium-energy all-purpose collimator.2,3 This suggests that the combination of iterative reconstruction and DSP might substantially improve quantitation of I-123 MIBG activity in the heart in patient studies. These previous investigations notwithstanding, the I-123 MIBG H/M ratio from SPECT imaging has not entered into common use due to a lack of a standardized and practical method for calculation of the H/M ratio, as well as the technical challenges of calculating the H/M ratio in heart failure patients with very low uptake of the tracer into the myocardium. …