Sandborg M, Dance D R, Carlsson G A, Persliden J
Department of Radiation Physics, Linköping University, Faculty of Health Sciences, Sweden.
Br J Radiol. 1993 Dec;66(792):1164-76. doi: 10.1259/0007-1285-66-792-1164.
A Monte Carlo computational model has been developed for the study of the performance of anti-scatter grids in diagnostic radiology. It is used here to estimate the scatter in the image plane from soft tissue phantoms (representing the patient) and to calculate image contrast and the mean absorbed dose in the phantom. Different scattering conditions, representative of various examinations, have been investigated: adult lumbar spine; small field radiography and fluoroscopy; adult chest and paediatric pelvis and chest. For each scattering condition, the combinations of tube potential and grid ratio have been found which, for a well designed grid, result in the lowest mean absorbed dose in the phantom for a fixed contrast level. In examinations which generate large amounts of scatter, the use of high grid ratios in combination with high tube potentials is favourable with regard to both mean absorbed dose in the phantom and tube charge. When less scatter is generated, either the grid ratio or the tube potential can be varied to achieve the desired contrast level. High grid ratios require shorter exposure times, but need careful alignment in the beam to prevent primary radiation cut-off. It is shown that the air gap technique can be used to reduce patient dose in examinations with small amounts of scatter, but in combinations with a lower tube potential than when a grid is used.
已开发出一种蒙特卡罗计算模型，用于研究诊断放射学中反散射格栅的性能。在此，它用于估计来自软组织体模（代表患者）的图像平面中的散射，并计算体模中的图像对比度和平均吸收剂量。已研究了代表各种检查的不同散射条件：成人腰椎；小视野射线照相和荧光透视；成人胸部以及小儿骨盆和胸部。对于每种散射条件，已找出管电压和格栅比的组合，对于精心设计的格栅，在固定对比度水平下，这些组合会使体模中的平均吸收剂量最低。在产生大量散射的检查中，就体模中的平均吸收剂量和管电荷而言，使用高格栅比并结合高管电压是有利的。当产生的散射较少时，可以改变格栅比或管电压以达到所需的对比度水平。高格栅比需要更短的曝光时间，但在射束中需要仔细对准以防止原发射线截止。结果表明，气隙技术可用于减少少量散射检查中的患者剂量，但与使用格栅时相比，其结合的管电压较低。
