CT-based attenuation correction on the FLEX Triumph™ preclinical PET/CT scanner

Abstract

Positron Emission Tomography (PET) has emerged as a very valuable molecular imaging modality for quantitative measurement of biochemical processes in the clinical and preclinical imaging domains. However, PET imaging suffers from various physical degrading factors including photon attenuation, which can be corrected using CT-based attenuation correction (CTAC) on combined PET/CT scanners. The attenuation map is calculated by converting CT numbers derived from low-energy polyenergetic x-ray spectra to linear attenuation coefficients at 511 keV. In this study, we implemented and evaluated tube voltage-dependent attenuation correction on the FLEX Triumph <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TM</sup> preclinical PET/CT scanner. The impact of both bilinear and quadratic polynomial calibration curve methods obtained at different CT tube voltages was assessed. Correlation coefficients and best fit equations were calculated for both techniques. Phantoms and rodents' PET images were used to assess improvements in image quality and quantitative accuracy. It was observed that the slopes of the bilinear calibration curves for CT numbers greater than 0 HU increase with increasing tube voltage. Significantly higher correlation coefficients were obtained using the quadratic polynomial calibration curve method. Acquired phantoms and rodents' PET data were successfully corrected for photon attenuation using the CTAC procedure thus enabling more accurate quantitative analysis of biochemical processes in vivo.