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

<div><p>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.</p></div

Relative estimation error for three different imaging conditions: Ideal (no scatter medium), scatter and attenuation medium without corrections, and scatter and attenuation medium with corrections.

<p>Relative estimation error for three different imaging conditions: Ideal (no scatter medium), scatter and attenuation medium without corrections, and scatter and attenuation medium with corrections.</p

Energy spectra of ¹²³I and ¹²⁵I for the MGP collimator.

<p>Energy spectra of ¹²³I and ¹²⁵I for the MGP collimator.</p

Illustrations of model components.

<p>a). GATE model of Siemens Inveon SPECT system configured with two MGP collimators. b). MWB collimator. c). MOBY attenuation phantom.</p

Stacked bar plots of energy ratios and relative activity measurements.

<p>a). Low-to-high energy ratio e123 under different imaging conditions. b). Total ¹²³I activity in both high and low-energy windows.</p

Estimated low-to-high energy (e123) ratios for selected organs in different sized mice.

<p>Estimated low-to-high energy (e123) ratios for selected organs in different sized mice.</p

Comparison of real and simulated data.

<p>The top row shows real data for the uncorrected low energy window, high energy window, and the corrected low energy window. The bottom row shows the same information but for the simulated MOBY phantom data.</p

Descriptive statistics for group 2 using the low-dose CT detector.

<p>Descriptive statistics for group 2 using the low-dose CT detector.</p

3^rd generation detector technology with the X-ray source and detector rotating about the subject.

<p>3^rd generation detector technology with the X-ray source and detector rotating about the subject.</p

Descriptive statistics for group 1 using the low-dose detector.

<p>Descriptive statistics for group 1 using the low-dose detector.</p