Quantitative Accuracy of Clinical ^sup 99m^Tc SPECT/CT Using Ordered-Subset Expectation Maximization with 3-Dimensional Resolution Recovery, Attenuation, and Scatter Correction

• Published in: The Journal of nuclear medicine (1978) Vol. 51; no. 6; p. 921
• Main Authors: Zeintl, Johannes, Vija, Alexander Hans, Yahil, Amos, Hornegger, Joachim, Kuwert, Torsten
• Format: Journal Article
• Language: English
• Published: New York Society of Nuclear Medicine 01.06.2010
• Subjects: Accuracy; Clinical medicine; Methods; Radiation therapy; Software; Studies
• ISSN: 0161-5505; 1535-5667

We present a calibration method of a clinical SPECT/CT device for quantitative ^sup 99m^Tc SPECT. We use a commercially available reconstruction package including ordered-subset expectation maximization (OSEM) with depth-dependent 3-dimensional resolution recovery (0SEM-3D), CT-based attenuation correction, and scatter correction. We validated the method in phantom studies and applied it to images from patients injected with ^sup 99m^Tc-diphosponate. Methods: The following 3 steps were performed to derive absolute quantitative values from SPECT reconstructed images. In step 1, we used simulations to characterize the SPECT/CT system and derive emission recovery values for various imaging parameter settings. We simulated spheres of varying diameters and focused on the dependencies of activity estimation errors on structure size and position, pixel size, count density, and reconstruction parameters. In step 2, we cross-calibrated our clinical SPECT/CT system with the well counter using a large cylinder phantom. This step provided the mapping from image counts to kBq/mL And in step 3, correction factors from steps 1 and 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 ^sup 99m^Tc-diphosponate SPECT/CT examinations of the pelvis including the bladder were acquired. The radioactivity concentration in the patients' urine served as the gold standard. Mean quantitative accuracy ana SEs were calculated. Results: In the phantom experiments, the mean accuracy in quantifying radioactivity concentration in absolute terms was within 3.6% (SE, 8.0%), with a 95% confidence interval between -19.4% and +12.2%. In the patient studies, the mean accuracy was within 1.1% (SE, 8.4%), with a 95% confidence interval between -15.4% and +17.5%. Conclusion: Current commercially available SPECT/CT technology using 0SEM-3D reconstruction, scatter correction, and CT-based attenuation correction allows quantification of ^sup 99m^Tc radioactivity concentration in absolute terms within 3.6% in phantoms and 1.1% in patients with a focus on the bladder. This opens up the opportunity of SPECT quantitation entering the routine clinical arena. Still, the imprecision caused by unavoidable measurement errors is a dominant factor for absolute quantitation in a clinical setup. [PUBLICATION ABSTRACT]