体表高活性异物对PET图像的影响分析

Analysis of the Effect of High-active Foreign Bodies on the Body Surface on PET Images

目的:探讨体表高活性异物导致正电子发射断层扫描(PET)/X射线计算机断层扫描(CT)图像计数丢失的原因及改进措施。方法:用注射器吸取活度、体积相同正电子药物18F-FDG模拟体表高活性异物,分别固定在距离模型表面不同的5个位置进行PET采集;再将5种活度不同体积相同的注射器固定在距离模型表面相同的位置采集;选取其中一组对图像影响明显的数据,借助正常校正、无死时间校正、无几何校正、无散射校正及无衰减和散射校正等方法进行后处理,分析PET/CT图像数据丢失的原因,并提出相应的措施干预。结果:均完成上述模型及校正,结果表明:当注射器靠近模型表面时,其活度变化对图像影响不大(P>0.05);在一定范围内,相同活度的注射器到模型表面距离越大,对PET图像影响越明显;通过不同校正方法重建同一组图像,结果表明,去掉散射校正时丢失的计数恢复,但是会对图像信噪比产生影响。结论:体表高活性异物会引起散射分布的变化,在图像重建过程中引起过度散射校正,表现为相应层面符合计数丢失,去掉散射校正重建能使丢失数据恢复,但图像信噪比明显降低,临床使用PET检查时应充分考虑体表高活性异物对图像的影响。

Objective:To investigate the reasons and improvement measures of the loss of counts in positron emission tomography(PET)/X-ray computed tomography(CT) caused by highly active foreign bodies on the body surface.Methods:Place 5 syringes with different activities and the same activity at different distances from the radioactive source,and analyze the surface of the model;select one set of data and use normal correction,no dead time correction,and no geometric correction,Correction without scatter correction and no attenuation and scatter correction,and complete image reconstruction,analyze the causes of PET/CT image data loss,and propose corresponding measures to intervene.Results:The above models and corrections were all completed.The results showed:(1) When the radioactive source is close to the surface of the model,the change in its activity has little effect on the image(P>0.05).(2)Within a certain range,the radioactive source of the same activity to the surface of the model has a greater impact on the PET image,and the greater the distance,the more obvious the impact on the image;(3)The same set of images is reconstructed by different correction methods,and the results show :Remove the lost count recovery during scatter correction,but it will affect the image signal-tonoise ratio.Conclusion:Highly active foreign matter on the body surface will cause changes in the scattering distribution,and cause excessive scattering correction during the image reconstruction process,which is manifested as the loss of the corresponding layer coincidence count.Removing the scattering correction and reconstruction can restore the lost data,but the image signal-to-noise ratio is significantly reduced.The clinical use of PET examination should fully consider the impact of high-active foreign bodies on the body surface on the image.