Original ArticleQuantitative I-123 mIBG SPECT in differentiating abnormal and normal mIBG myocardial uptake
Introduction
Assessment of sympathetic nerve activity using I-123 metaiodobenzylguanidine (mIBG) imaging in heart failure (HF) patients has been shown to provide important information for prognosis and therapy evaluation.1., 2., 3., 4., 5., 6., 7., 8., 9., 10., 11. Numerous single-center studies have shown that reduced myocardial uptake of I-123 mIBG is an independent predictor of adverse long-term outcome.12., 13., 14., 15., 16., 17. This finding has recently been confirmed in the prospective multicenter AdreView Myocardial Imaging for Risk Evaluation in Heart Failure (ADMIRE-HF) trial.18 In that study, quantitation of I-123 mIBG myocardial uptake by the heart-to-mediastinum ratio (H/M) measured from planar imaging predicted prognosis for significant cardiac events in subjects with HF and significant left ventricular dysfunction.18
Most published studies have used planar imaging to measure I-123 mIBG myocardial uptake. While single-photon emission computed tomography (SPECT) imaging has been performed as part of many trials, data analysis has primarily focused on regional abnormalities, typically quantified from summed visual scores or polar plots, rather than global assessment analogous to the planar H/M.19 However, a previous phantom study demonstrated that H/M measured from SPECT reconstructions more accurately reflected the true concentration of I-123 mIBG in the heart than that measured from planar images.20,21 In addition, as I-123 decays with emission of multiple low-abundance, high-energy photons in addition to the primary 159-keV photopeak, there is septal penetration when low-energy collimators are used, which can affect quantitation of I-123 mIBG myocardial uptake. A mathematical technique [deconvolution of septal penetration (DSP)] was therefore developed for use in reconstruction of I-123 mIBG SPECT images, which reduces the contamination of I-123 high-energy photons and improves the accuracy of quantitation of I-123 mIBG myocardial uptake.20,21
The objective of this study was to measure I-123 mIBG myocardial uptake from SPECT images reconstructed with different algorithms and to evaluate these results for differentiating between abnormal and normal mIBG uptake in comparison to H/M measured from planar imaging.
Section snippets
Patient Studies
Two groups of subjects were included in this study, a pilot group and a validation group. The pilot group was used as a training dataset for the operators to familiarize how to define heart volumes of interest (VOI) on the SPECT reconstructions, especially when the subjects had very low cardiac uptake of I-123 mIBG. The validation group was used for comparison of SPECT quantitation of mIBG uptake to that of the planar technique. None of the subjects in the pilot group came from the validation
Pilot Group
Table 1 shows the planar and SPECT H/M in the IHD and control subjects in the pilot group. For all SPECT reconstruction methods, the H/M values in the IHD patients were significantly smaller than those in the controls. Figure 2 shows the ROC curves of the SPECT H/M. Table 2 shows the optimal cutoff values, sensitivity, specificity, and AUC of the planar and SPECT H/M. There were no significant differences among the AUC, indicating that SPECT H/M had similar capability to differentiate normal
Discussion
This study presents a new quantitative tool for determining the H/M from I-123 mIBG SPECT images. Comparing the SPECT results to those from the planar H/M in a small pilot group and a large validation group, the capability to differentiate subjects with abnormal and normal mIBG uptake was equivalent, regardless of the SPECT reconstruction method used (FBP, OSEM, or DSP). In each group, SPECT H/M values were systematically larger than planar H/M values. The counts measured from planar images
Conclusion
A highly reproducible tool has been developed and validated to measure H/M from I-123 mIBG SPECT images. It showed similar capability to the planar H/M to differentiate between heart disease and control subjects, regardless of the SPECT reconstruction method used (FBP, OSEM, or DSP). This tool could be a viable quantitative SPECT alternative to the planar H/M, which can have implications for users of small field-of-view cardiac cameras and new SPECT-only systems.
Disclosure
This study was supported in part by GE Healthcare. Dr Chen, Dr Garcia, and Mr Folks receive royalties from the sale of the Emory Cardiac Toolbox. The terms of this arrangement have been reviewed and approved by Emory University in accordance with its conflict-of-interest practice. Dr Jacobson is an employee of GE Healthcare and owns shares in the General Electric Company.
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See related editorial, doi:10.1007/s12350-011-9495-4.