Fritz Shannon, Jones A Kyle
Department of Imaging Physics, The University of Texas, M. D. Anderson Cancer Center, 1400 Pressler St., Houston, TX, 77030, USA,
Pediatr Radiol. 2014 Mar;44(3):313-21. doi: 10.1007/s00247-013-2824-9. Epub 2013 Nov 27.
Pediatric radiography presents unique challenges in balancing image quality and patient dose. Removing the anti-scatter grid reduces patient dose but also reduces image contrast. The benefit of using an anti-scatter grid decreases with decreasing patient size.
To determine patient thickness thresholds for anti-scatter grid use by comparing scatter-to-primary ratio for progressively thinner patients without a grid to the scatter-to-primary ratio for a standard adult patient with a grid.
We used Solid Water™ phantoms ranging in thickness from 7 cm to 16 cm to simulate pediatric abdomens. The scatter-to-primary ratio without a grid was measured for each thickness at 60 kVp, 70 kVp and 80 kVp for X-ray fields of view (FOV) of 378 cm(2), 690 cm(2) and 1,175 cm(2) using indirect digital radiography (iDR) and computed radiography (CR). We determined thresholds for anti-scatter grid use by comparing the intersection of a fit of scatter-to-primary ratio versus patient thickness with a standard adult scatter-to-primary ratio measured for a 23-cm phantom thickness at 80 kVp with an anti-scatter grid. Dose area product (DAP) was also calculated.
The scatter-to-primary ratio depended strongly on FOV and weakly on kVp; however DAP increased with decreasing kVp. Threshold thicknesses for grid use varied from 5 cm for a 14 × 17-cm FOV using iDR to 12 cm for an 8 × 10-cm FOV using computed radiography.
Removing the anti-scatter grid for small patients reduces patient dose without a substantial increase in scatter-to-primary ratio when the FOV is restricted appropriately. Radiologic technologists should base anti-scatter grid use on patient thickness and FOV rather than age.
儿科放射成像在平衡图像质量和患者剂量方面面临独特挑战。移除防散射格栅可降低患者剂量，但也会降低图像对比度。随着患者体型减小，使用防散射格栅的益处会降低。
通过比较无格栅情况下逐渐变薄的患者的散射与原发射线比率和有格栅的标准成年患者的散射与原发射线比率，确定使用防散射格栅的患者厚度阈值。
我们使用厚度从7厘米到16厘米的固体水™体模来模拟儿科腹部。对于378平方厘米、690平方厘米和1175平方厘米的X射线视野（FOV），在60 kVp、70 kVp和80 kVp下，使用间接数字化X线摄影（iDR）和计算机X线摄影（CR）测量每种厚度无格栅时的散射与原发射线比率。通过比较散射与原发射线比率对患者厚度的拟合曲线与在80 kVp下使用防散射格栅对23厘米体模厚度测量的标准成年患者散射与原发射线比率的交点，我们确定了使用防散射格栅的阈值。还计算了剂量面积乘积（DAP）。
散射与原发射线比率强烈依赖于FOV，而对kVp的依赖性较弱；然而DAP随着kVp的降低而增加。使用格栅的阈值厚度从使用iDR的14×17厘米FOV的5厘米到使用计算机X线摄影的8×10厘米FOV的12厘米不等。
对于小体型患者，在适当限制FOV时，移除防散射格栅可降低患者剂量，而不会使散射与原发射线比率大幅增加。放射技师应根据患者厚度和FOV而非年龄来决定是否使用防散射格栅。
