Impact of CT tube-voltage and bone density on the quantitative assessment of tracer uptake in Tc-99m bone SPECT/CT: A phantom study

•This study validated quantitative accuracy of bone SPECT/CT with CT attenuation correction incorporating a bilinear model.•CT tube voltage for attenuation correction can affect the accuracy of SPECT quantification.•High CT tube voltages result in overestimation of radioactivity values in high CT density regions.•However, the degree of overestimation is less than 5% at most. To evaluate the effect of computed tomography (CT) tube voltage and CT density for CT-based attenuation correction (CTAC) on quantification of tracer uptake in single photon emission computed tomography (SPECT)/CT. A cylindrical phantom contained 7 cylinders with diameter of 30 mm. The central cylinder and background part were filled with 17 kBq/ml of 99mTc-pertechnetate solution. Of the remaining 6 cylinders, one cylinder was filled with water and 5 cylinders were filled with each own different concentration of K2HPO4 solution (120, 275, 450, 666, and 960 mg/cm3) to simulate different bone densities. The 6 cylinders also contained 99mTc-pertechnetate solution with the same radioactivity concentration (207 kBq/ml). CT scans were performed with 4 different tube voltages of 80, 100, 120, and 140 kVp for CTAC. The radioactivity concentration in the 6 cylinders were measured on the SPECT images processed with 4 different attenuation coefficient maps derived from each tube voltage of CT images. Compared with the water cylinder without K2HPO4 solution, the measured radioactivity of the highest density cylinder (K2HPO4 solution concentration: 960 mg/cm3) was found to be overestimated by 3.3 % and 4.3 %, respectively, when the tube voltage was 120 kVp and 140 kVp (p = 0.022). The use of low-tube voltage, such as 80 kVp, has improved the quantitative accuracy of bone SPECT/CT. SPECT quantitative evaluation of tracers in high-density objects tends to overestimate as tube voltage for CTAC increases. However, the overestimation in quantitative SPECT/CT evaluation in simulated bone area is less than 5% at most.