Experimental study of correlation between the focus-to-flat panel detector distance and entrance surface dosed in digital radiography of lumbar spine / 中华放射医学与防护杂志

ABSTRACT

Objective To investigated the correlation between the focus-to-flat panel detector distance and entrance surface dosed in digital radiography of lumbar spine.Methods The spine phantom used for bone mineral density(BMD) calibration was radiographed at different value of FFD (100 ～ 240 cm with the interval 10 cm,totally 15 times) using 70 kV and 90 kV with the automatic exposure control (AEC) mode without anti-scatter grid.The parameters measured by QUART dido 2100K type X-ray dose meter.So record the value parameters of the tube current (mAs) and entrance surface dose (ESD).The relation curve were counted between FFD,ESD,mAs and Exposure index (EI) use excle.Pearson correlation analysis and related coefficient difference analysis were performed using the SPSS 19.0 software (P ＜0.05 for the statistically significant level).The FFD and ESD values of regression equation were obtained with regression analysis.Results (1) When the tube voltage was 70 kVFFD and ESD were negative correlation (r =-0.922,P ＜ 0.001),FFD and mAs were positive correlation (r =0.991,P ＜0.001),FFD and EI negative correlation (r =-0.938,P ＜ 0.001).(2) When the tube voltage was 90 kVFFD and ESDwere negative correlation (r=-0.955,P ＜0.001),FFD and mAs were positive correlation (r=0.994,P ＜0.001),FFD and EI showed no significant correlation (r=-0.523,P＞0.05).(3) Different position correlation coefficient analysis of the difference was not statistically significant difference.(4) The regression analysis results:The regression equation of the lumbar anteriorposterior position FFD and the ESD at 70 kVy=0.805 x + 319.731 (F=74.175,P ＜0.001).The regression equation of the lumbar lateral position FFD and the ESD at 90 kVy =3.152 x + 457.613 (F =133.524,P ＜ 0.001).Conclusions The FFD and ESD in the lumbar spine X-ray radiography were relevant and highly negative correlation.It can effectively reduce the radiographic ESD of lumbar spine with the increasing of the FFD.