I179] SPECT/CT quantitative reconstruction techniques

Abstract

The last years, the clinical interest in quantitative SPECT/CT imaging is increasing. Especially in the rapidly growing field of radionuclide therapy, quantitative imaging is essential to provide nuclear medicine physicians with accurate dosimetric data. As a result, manufacturers now focus on producing SPECT/CT systems that are intrinsically quantitative. SPECT quantification is more challenging than PET quantification. In fact, the correction for photon absorption is relatively straightforward to apply in PET. In addition, in SPECT, we need to consider a variety of radionuclides with different photon energies and energy windows, different collimators and the potential for drifts in performance due to the greater number of moving parts in a SPECT system. With SPECT/CT, the coregistered CT data provide accurate information on the density of the body tissues, which can be used in algorithms that correct for photons that have been Compton-scattered or attenuated within the body. State-of-the-art reconstruction techniques are based on statistical iterative methods such as the ordered-subset maximum-likelihood expectation maximization algorithm (OSEM). In this approach, the physical characteristics of the acquisition process can be completely modeled in the reconstruction. In this presentation, an overview of all factors affecting SPECT image quantification will be presented. The latest developments to achieve quantitative SPECT/CT reconstruction will be discussed, together with calibration issues to finally obtain radioactivity concentrations per unit volume (kBq/ml).