Optimization Of Bone Mineral Density Measurement Parameters For Gemstone Spectral CT Based On European Spine Phantom

Purpose To investigate the effect of scanning parameters for BMD measurements by GSCT material separation technology,trying under the condition of as much as possible low radiation dose accurately measures BMD,and compare accuracy,precision and radiation dose of this method and QCT measuring BMD.Material and Methods（1）Using the ESP Number 145,the vertebral body of50mg/cm³ of cancellous hydroxyapatite（HAP）were labeled as L₁,the vertebral body of100mg/cm³ were labeled as L₂,and the vertebral body of 200mg/cm³ were labeled as L₃.（2）The 14 groups of GSCT spectral protocols were used to scan the ESP model for10 times.The material separation technology was used to measure the hydroxyapatite-water based material density（ρHAP-H₂O）of the cancellous bone of intermediate layer of each vertebral body,namely the BMD.（3）The ESP model was scanned 10 times using QCT protocol on the same CT machine,and the BMD values of the vertebral bodies in the corresponding region of interests were obtained by QCT BMD analysis software.（4）One-way ANOVA was used to compare the measured values of different scanning parameters.Single sample t test was used to compare the measured values of GSCT and QCT with the true BMD values of ESP.The relative standard deviation（RSD）and relative error（RE）of the measured BMD values of each group were calculated to represent the precision and accuracy of measurement,respectively.Results（1）The measured values of the three inserts at different exposure levels were statistically significant（P<0.05）.（2）When the L₁ was measured,the measured values of 0.7s/r 260 m A,0.8s/r260 m A,0.5s/r 630 m A and 0.6s/r 640 m A groups had no statistical significance compared with the actual vertebral body values;The measured values in the 0.8s/r 260 m A group,0.5s/r 630 m A group,and 0.6s/r 640 m A group were not significantly different from the actual ESP values for L2.However,the measured values at all the protocols were significantly different from the actual values for the L₃（P<0.05）.（3）When the L₁ and L₂ were measured by QCT,the difference between the measured values and the actual values were statistically significant（P<0.05）,while the difference between the measured values of L₃ and the actual values were not statistically significant.（4）The radiation dose under all protocols of spectral CT was higher than that of QCT,and the difference was statistically significant.Conclusion The BMD measured by the GSCT material separation technology was affected by tube current and tube speed.Under the appropriate scanning protocols,CT gemstone spectral imaging（GSI）can accurately measure the BMD value of ESP,but there may be a certain threshold,when beyond the high reliability of the interval,the quantitative analysis of GSI may be biased,Taking the radiation dose into consideration,it is recommended to adopt the scanning condition of 0.8s/r 260 m A when using GSCT to measure the BMD of ESP.Under this scanning protocol,the measurement accuracy of GSCT in vertebrae with low BMD was higher than that of QCT,but the measurement accuracy of vertebrae with high BMD was lower than that of QCT.In this study,the precision of GSCT was worse than that of QCT,suggesting that the reproducibility of GSCT material separation technology was slightly poor.