Abstract
583
Objectives We present a calibration method of a clinical SPECT/CT device for quantitative Tc-99m SPECT imaging based on OSEM with depth-dependent 3-dimensional resolution recovery (OSEM-3D), CT- based attenuation correction, and scatter correction. We validated this method in phantom studies and applied it to images from patients injected with Tc-99m-diphosponate.
Methods Three steps were performed to derive absolute quantitative values from SPECT reconstructed images. Step 1: We used simulations to characterize the SPECT/CT imaging system and to derive emission recovery values of variable sized spheres for various imaging parameter settings including pixel size, count density, and reconstruction parameters. Step 2: We performed a cross calibration of our clinical SPECT/CT imaging system with the well counter using a large cylinder phantom. Step 3: Correction factors from step 1 and step 2 were applied to reconstructed images. We used a cylinder phantom with variable-sized spheres for verification of the method. For in-vivo validation, SPECT/CT datasets from 16 patients undergoing Tc-99m-diphosponate SPECT/CT examinations of the pelvis including the bladder were acquired. The radioactivity concentration in the patients’ urine served as gold standard.
Results In the phantom experiments the mean accuracy in quantifying radioactivity concentration in absolute terms was 3.6% (SE 7.6%) with a 95% confidence interval between -18.5% and +11.3%. In the patient studies, the mean accuracy was 1.1% (SE 8.0%) with a 95% confidence interval between -14.6% and +16.6%.
Conclusions Current SPECT/CT technology using OSEM-3D reconstruction, scatter correction, and CT based attenuation correction allows quantification of Tc-99m radioactivity concentration in absolute terms within 3.6% in phantoms and 1.1% in patients with focus on the bladder. This opens up the opportunity of SPECT quantification entering the routine clinical arena