Effect of phantom-making error in the calculation of quantitative values of single-photon emission computed tomography/computed tomography using system planar sensitivity.

This study aimed to clarify the effect of the accuracy of phantom-making on quantification accuracy in the measurement of system planar sensitivity using a disc source. We measured the system planar sensitivity using the method recommended by the equipment manufacturer. A container of^99mTc solution was placed at a height of 10 cm from the surface of the collimator using styrofoam. The system planar sensitivity was the average of the values obtained from the two detectors, the measurements were taken thrice. The system planar sensitivity values obtained when the disc source size (5.0, 14.5 and 20 cm), solution volume (50, 100 and 150 ml) and radioactivity (nine points between 36 MBq and 505 MBq) changed were used to evaluate the quantification accuracy. The relative error for the 5.0 cm source significantly exceeded for the other source sizes (p < 0.05); however, no statistically significant difference was observed between the 14.5 cm and 20.0 cm sources. The smaller the solution volume, the smaller the relative error and the higher the quantification accuracy. The quantification accuracy increased as radioactivity decreased. The relative error was lowest at 36 MBq and highest at 505 MBq, with a difference of approximately 10%. Quantification accuracy improved as the size of the surface source exceeded 14.5 cm and the amount of solution decreased. Radioactivity at the time of measurement significantly affected quantification accuracy and 73-103 MBq of radioactivity was sufficient for repeatable and quantification accuracy.