Acquisition Protocols and Correction Methods for Estimation of the Heart-to-Mediastinum Ratio in ¹²³I-Metaiodobenzylguanidine Cardiac Sympathetic Imaging

Abstract

Septal penetration of high-energy photons affects quantitative results in imaging of 123 I-labeled tracers. We investigated acquisition protocols (collimator choice and energy window setting) and correction methods for estimating the heart-to-mediastinum (H/M) ratio in cardiac 123 I-metaiodobenzylguanidine (MIBG) imaging. Methods: Four hours after 123 I-MIBG injection, 40 patients successively underwent planar anterior chest imaging with the medium-energy (ME) (ME method) and low-energy high-resolution (LEHR) (LEHR method) collimators. A 20% energy window was used for both collimators. Another 40 patients were imaged successively with the ME collimator and a 20% window (ME method), the low-medium-energy (LME) collimator and a 20% window (LME20 method), and the LME collimator and a 15% window (LME15 method). The H/M ratios obtained by the LEHR, LME20, and LME15 methods were corrected using their correlations with the H/M ratio obtained by the ME method (empiric correction). The 123 I-dual-window (IDW) correction was also applied to remove the influence of high-energy photons. Results: Without correction, severe underestimation of the H/M ratio was shown for the LEHR method using the ME method as a standard, and this underestimation increased with increasing H/M ratios. Underestimation substantially decreased using the LME20 method and further using the LME15 method. Empiric correction reduced the error in the H/M ratio by the LEHR method, but the error was still evident. After empiric correction, the H/M ratios with the LME collimator were comparable to those with the ME collimator. The IDW correction only partially reduced underestimation by the LEHR method and caused a small overestimation for the LME15 method. Conclusion: The use of an LME collimator appears to be acceptable for cardiac 123 I-MIBG imaging as an alternative to an ME collimator, and the application of a 15% energy window is recommended when an LME collimator is used. Empiric correction is also expected to improve exchangeability between H/M ratios calculated with ME and LME collimators. Neither the use of an LEHR collimator nor the use of IDW correction is recommended.

ASNC imaging guidelines for SPECT nuclear cardiology procedures: Stress, protocols, and tracers

“…130,131 Although most clinical literature is based on use of a LEHR, in fact the reported HMRs are severely underestimated in relation to the true value. 132 Several methods have been explored attempting to overcome this problem when an LEHR is used, including mathematical deconvolution of septal penetration (DSP), 130 image acquisition using 123 I-dual window acquisition (IDW), 133 decreasing the 159-kEV energy window to 15%. 132 Although it has been suggested that a medium-energy collimator may be preferred, 129 use of a calibration phantom to derive a conversion coefficient for each camera-collimation system may be a better approach.…”

“…132 Several methods have been explored attempting to overcome this problem when an LEHR is used, including mathematical deconvolution of septal penetration (DSP), 130 image acquisition using 123 I-dual window acquisition (IDW), 133 decreasing the 159-kEV energy window to 15%. 132 Although it has been suggested that a medium-energy collimator may be preferred, 129 use of a calibration phantom to derive a conversion coefficient for each camera-collimation system may be a better approach. 134,135 There have been recent reports on the 123 I-mIBG imaging with solid-state cameras.…”

Multicenter cross-calibration of I-123 metaiodobenzylguanidine heart-to-mediastinum ratios to overcome camera-collimator variations

“…While various methods have been proposed to improve the quantification of 123 I tracers, including a multiple energy window method,9,15 deconvolution of the septal penetration method,17 and a direct empirical conversion method,18 the calibration phantom method has an advantage, which is demonstrated as follows. Although the simplest approach was creating a linear regression equation between measured HMRs with both LE and ME collimators, the empirical method cannot be applicable to other camera-collimator combinations or multicenter study protocols.…”

Phase-1 Clinical Trial Results of High-Specific-Activity Carrier-Free 123I-Iobenguane

“…This normal cutoff value is concordant with our measurements of a normal H/M ratio on delayed planar imaging for both HSA MIBG and LSA MIBG (2.2 6 0.3 and 2.0 6 0.2, respectively). Verberne et al reported higher H/M ratios in 9 healthy volunteers using a no-carrier-added formulation (20); however, these higher H/M ratios could be attributed to acquisition on medium-energy collimators that reduce septal penetration and scatter of the higherenergy g photons from 123 I (21). As expected, all SPECT H/M ratios were higher than their respective planar values; however, the variability in normal SPECT H/M measurements was high, as previously reported (22).…”