GATE Validation of Standard Dual Energy Corrections in Small Animal SPECT-CT

Abstract

This paper addresses 123I and 125I dual isotope SPECT imaging, which can be challenging because of spectrum overlap in the low energy spectrums of these isotopes. We first quantify the contribution of low-energy photons from each isotope using GATE-based Monte Carlo simulations for the MOBY mouse phantom. We then describe and analyze a simple, but effective method that uses the ratio of detected low and high energy 123I activity to separate the mixed low energy 123I and 125I activities. Performance is compared with correction methods used in conventional tissue biodistribution techniques. The results indicate that the spectrum overlap effects can be significantly reduced, if not entirely eliminated, when attenuation and scatter is either absent or corrected for using standard methods. In particular, we show that relative activity levels of the two isotopes can be accurately estimated for a wide range of organs and provide quantitative validation that standard methods for spectrum overlap correction provide reasonable estimates for reasonable corrections in small-animal SPECT/CT imaging.

177Lu SPECT imaging in the presence of 90Y: does 90Y degrade image quantification? a simulation study

“…Our study is unique as there have been no other simulation studies, to the best of our knowledge, performing SPECT imaging of 177 Lu and 90 Y combined. Dual-isotope SPECT imaging based on Monte Carlo simulations have been performed for radioisotope pairs such as 99m Tc/ 123 I [35] 123 I/ 125 I [36], and combinations of 99m Tc, 111 In, 123 I, 177 Lu, and 201 Tl [37], but not 177 Lu and 90 Y. Dosimetry simulations of 177 Lu and 90 Y therapy have been performed [38,39] which highlights the importance of a study such as ours; dosimetry is impractical outside of a simulation if imaging cannot be performed quantitatively. Imaging has been performed in dual-isotope PRRT with 177 Lu and 90 Y [40], but dosimetry was not performed.…”

Feasibility and Initial Performance of Simultaneous SPECT-CT Imaging Using a Commercial Multi-Modality Preclinical Imaging System

“…The primary issue would be to develop a method by which the gammas emitted from 125 I could be separated from any CT X-rays. One approach would be to use a Monte Carlo model that would enable a statistical method of removing the X-rays from the 125 I SPECT projection data, such as the GATE model created for this platform by Lee et al [ 17 , 18 ].…”

Dual-Energy SPECT and the Development of Peptide p5+14 for Imaging Amyloidosis

“…We have recently developed methods for performing dualenergy studies using 125 I-and 123 I-labeled peptides that circumvent the confounding issues associated with low-energy X-ray emission from the latter. 15 With respect to the relatively greater hepatic and splenic uptake of SAP in the AA mice, we consider that these 2 highly vascularized, heavily amyloid-laden organs in the mouse sequestered the SAP, perhaps in a first-pass manor, and given that SAP irreversibly binds amyloid in the mouse, this prevented uptake in less accessible anatomic sites such as the intestines, pancreas, and likely the heart. This was not the case for p5þ14.…”

“…We have recently developed methods for performing dual-energy studies using 125 I- and 123 I-labeled peptides that circumvent the confounding issues associated with low-energy X-ray emission from the latter. 15 …”