Impact of bone-equivalent solution density in a thoracic spine phantom on bone single-photon emission computed...

This study aimed to evaluate the effects of dipotassium hydrogen phosphate (K₂HPO₄) solution density on single-photon emission computed tomography (SPECT) image quality and quantification. We used a JSP phantom containing six cylinders filled with K₂HPO₄ solutions of varying densities. Computed tomography (CT) was performed, and CT values and linear attenuation coefficients were measured. Subsequently, SPECT images of an SIM² bone phantom filled with ^99mTc with/without K₂HPO₄ solution were acquired using a SPECT/CT camera. The full width at half maximum (FWHM), percentage coefficient of variation (%CV), recovery coefficient, and standardized uptake value (SUV) were evaluated to investigate the impact of the K₂HPO₄ solution density. The CT values and linear attenuation coefficients increased with the K₂HPO₄ solution density. The CT values for cancellous and cortical bones were reflected by K₂HPO₄ solution densities of 0.15-0.20 and 1.50-1.70 g/cm³, respectively. FWHM values were significantly lower with the K₂HPO₄ solution than those with water alone (18.0 ± 0.9 mm with water alone, 15.6 ± 0.2 mm with 0.15 g/cm³ K₂HPO₄, and 16.1 ± 0.3 mm with 1.49 g/cm³ K₂HPO₄). Although the %CVs showed no significant differences, the recovery coefficients obtained with water alone tended to be slightly lower than those obtained with the K₂HPO₄ solution. The SUV obtained using the standard density of the K₂HPO₄ solution differed from that obtained using the optimized density. In conclusion, SPECT image quality and quantification depends on the presence and concentration of the bone-equivalent solution. The optimal bone-equivalent solution density should be used to evaluate the bone image phantoms.