Abstract
BackgroundThe heart-to-mediastinum (H/M) ratio is a commonly used parameter to measure cardiac I-123 metaiodobenzylguanidine (MIBG) uptake. Since the H/M ratio is substantially influenced by the collimator type, we investigated whether an empirical linear conversion of H/M ratios between camera systems with low-energy (LE) and medium-energy (ME) collimator is possible.MethodsWe included 18 patients with parkinsonism who were referred to one of the two participating molecular imaging facilities for the evaluation of cardiac sympathetic innervation by MIBG scintigraphy. Two consecutive planar image datasets were acquired with LE and ME collimators at 4 h after MIBG administration. Linear regression analyses were performed to describe the association between the H/M ratios gained with both collimator settings, and the accuracy of a linear transfer of the H/M ratio between collimators and across centers was assessed using a leave-one-out procedure.ResultsH/M ratios acquired with LE and ME collimators showed a strong linear relationship both within each imaging facility (R2 = 0.99, p < 0.001 and R2 = 0.90, p < 0.001) and across centers (H/M-LE = 0.41 × H/M-ME + 0.63, R2 = 0.97, p < 0.001). A linear conversion of H/M ratios between collimators and across centers was estimated to be very accurate (mean absolute error 0.05 ± 0.04; mean relative absolute error 3.2 ± 2.6%).ConclusionsThe present study demonstrates that a simple linear conversion of H/M ratios acquired with different collimators is possible with high accuracy. This should greatly facilitate the exchange of normative data between settings and pooling of data from different institutions.
Highlights
The heart-to-mediastinum (H/M) ratio is a commonly used parameter to measure cardiac I-123 metaiodobenzylguanidine (MIBG) uptake
The present study demonstrates that a simple linear conversion of H/ M ratios acquired with different collimators is possible with high accuracy
H/M ratio acquired with LE collimators exhibited highly significant linear correlations with the corresponding ratio obtained with ME collimators, both when contemplating each center separately and when pooling the data of both centers together (H/M-LE = 0.41 × H/M-ME + 0.63, R2 = 0.97, p < 0.001; Fig. 1c)
Summary
The heart-to-mediastinum (H/M) ratio is a commonly used parameter to measure cardiac I-123 metaiodobenzylguanidine (MIBG) uptake. For an ongoing bi-center study on the diagnostic performance of MIBG scintigraphy in comparison to F-18 fluorodeoxyglucose and positron emission tomography in neurodegenerative parkinsonism, we sought to extend few earlier findings by providing additional data on these particular patient population who were scanned on current SPECT/CT systems. Such a comparison will be of great interest for future multi-center studies including the data from various institutions and camera settings in the fields of cardiology (e.g., ischemic heart disease, cardiomyopathy, congestive heart failure) and neurology (e.g., parkinsonism, dementia). We hypothesized that a relatively small number of MIBG scans (≤ 10) employing both LE and ME collimators suffices to reliably describe the relationship and allows for an empiric conversion
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