Department of Medical Imaging, Royal University Hospital, University of Saskatchewan, 103 Hospital Dr, Saskatoon, SK, Canada S7N 0W7.
Radiology. 2011 Aug;260(2):560-7. doi: 10.1148/radiol.11101575. Epub 2011 May 9.
To compare the effective fetal dose reduction at different stages of gestation during maternal computed tomographic (CT) pulmonary angiography by using traditional lead apron and bismuth-antimony shields combined with limited z-axis and tube current.
Phantom with gravid prosthesis, 0.5-mm lead, and two grades of bismuth-antimony shield was used. Thermoluminescent dosimeters (TLDs) measured radiation in the first- to third-trimester uterus. Fetal dose was determined for each gestation by using 100 kVp to the costophrenic angles (CPAs) with and without shielding for a total of 12 scans. Eight third-trimester scans were used to compare shields using 120 kVp to CPAs versus those using 100 kVp to the diaphragm.
Average fetal dose increased with gestation with use of 100 kVp to CPAs, from 0.11 mGy in first trimester to 0.50 mGy in third trimester. Average third-trimester unshielded fetal dose was reduced from 0.82 mGy by using 120 kVp to CPAs to 0.17 mGy (79%, P < .001) by using 100 kVp to the diaphragm. Lead apron reduced dose more than either of the bismuth-antimony shields (72%-79% vs 57%-81%) with use of 100 kVp to CPAs. Shields reduced the dose by 73% (lead), 62% (90% attenuation bismuth-antimony), and 72% (95% attenuation bismuth-antimony) (P < .01) at 120 kVp to CPAs. No significant difference between shields was demonstrated with 100 kVp to the diaphragm (P < .01). Maternal dose was 8.13 mSv at 120 kVp to CPAs, 4.90 mSv at 100 kVp to CPAs, and 4.02 mSv at 100 kVp to the diaphragm.
Reducing voltage and limiting z-axis is more effective than shields at reducing fetal dose. Shielding improves reduction with no significant difference between lead and bismuth-antimony shields when conservative scanning parameters are observed.
通过使用传统铅围裙和含铋-锑屏蔽物结合有限 Z 轴和管电流，比较母体 CT 肺动脉造影在不同妊娠阶段的有效胎儿剂量减少。
使用带有妊娠假体的体模、0.5mm 铅和两级含铋-锑屏蔽物。热释光剂量计（TLDs）测量第一至第三孕期子宫内的辐射。对每个孕期进行胎儿剂量测定，使用 100kVp 至肋膈角（CPAs），有和没有屏蔽，总共 12 次扫描。8 次第三孕期扫描用于比较使用 120kVp 至 CPAs 与使用 100kVp 至膈肌的屏蔽物。
使用 100kVp 至 CPAs 时，随着妊娠的进展，胎儿剂量平均增加，从第一孕期的 0.11mGy 增加到第三孕期的 0.50mGy。未屏蔽的第三孕期胎儿剂量平均从使用 120kVp 至 CPAs 的 0.82mGy 减少到使用 100kVp 至膈肌的 0.17mGy（79%，P<0.001）。铅围裙比任何一种含铋-锑屏蔽物减少剂量更多（使用 100kVp 至 CPAs 时为 72%-79%，57%-81%）。使用 100kVp 至 CPAs 时，屏蔽物将剂量降低了 73%（铅）、62%（90%衰减的含铋-锑）和 72%（95%衰减的含铋-锑）（P<0.01）。在使用 100kVp 至膈肌时，屏蔽物之间没有显示出显著差异（P<0.01）。在使用 120kVp 至 CPAs 时，母体剂量为 8.13mSv，在使用 100kVp 至 CPAs 时为 4.90mSv，在使用 100kVp 至膈肌时为 4.02mSv。
与屏蔽物相比，降低电压和限制 Z 轴更能有效降低胎儿剂量。当观察到保守的扫描参数时，屏蔽物可改善剂量减少，且铅和含铋-锑屏蔽物之间没有显著差异。
