Porphyrin metabolism in Gilbert's, Dubin-Johnson, and Rotor's syndromes.

Abstract

<b>373</b> <h3><b>Objectives</b></h3> In pre-clinical 3D PET imaging, quantification of iodine-124 (I-124) imaging is especially challenging due to the complex decay scheme of I-124 and the relative long positron range. The objective of this study was to tackle these issues by developing a LOR-OSEM reconstruction method using a system matrix (SM) based on Monte Carlo (MC) simulations. <h3><b>Methods</b></h3> The SM required in iterative reconstruction was pre-calculated with MC simulations taking into account the transport of particles in the phantom and in the detector. Three MC SM were computed modelling: only the detector PSF (SM2), the detector PSF + I-124 in water (SM3), the detector PSF + I-124 in heterogeneous media (SM4). A ray-tracing Siddon algorithm was also developed (SM1) for comparison purpose. Two heterogeneous phantoms with water, lungs and bones were simulated, with hot (contrast 4:1) and cold (contrast 0:1) regions. I-124 activity was inserted in all media for the first phantom and only in water-filled regions for the second phantom. For the first phantom, the contrast recovery coefficients (C_Hot and C_Cold) in water and the activity ratio (R) between lung and water were calculated (ideal R=1). For the second phantom, profiles through the five different regions were plotted to assess contrast recovery. <h3><b>Results</b></h3> For the first phantom, C_Hot and C_Cold were closer to 100% with SM4 than with all other SM (table). Moreover, R was 0.92 with SM4 while it was less than 0.33 with all other SM. Additionally, when the complexity of SM increased, the contrast recovery coefficients were higher for all regions for the second phantom (varying from 55% to 80% for the biggest region). <h3><b>Conclusions</b></h3> This work suggests that the use of an SM including a thorough modelling of the detector response and physical effects in the object is essential for achieving a high quantitative accuracy in pre-clinical PET imaging.