The mesomechanics of geotechnical materials are closely related to the macromechanical properties,especially the mesoscale evolution of shear bands,which is helpful for understanding the failure mechanism of geotechni...The mesomechanics of geotechnical materials are closely related to the macromechanical properties,especially the mesoscale evolution of shear bands,which is helpful for understanding the failure mechanism of geotechnical materials.However,there is lack of effective quantitative analysis method for the complex evolution mechanism of threedimensional shear bands.In this work,we used X-ray computed tomography(CT)to reconstruct volume images and used the digital volume correlation(DVC)method to calculate the three-dimensional strain fields of granite residual soil samples at different loading stages.The trend of the failure surface of the shear bands was obtained by the planar fitting method,and the connectivity index was constructed according to the projection characteristics of the shear bands on the failure trend surface.The results support the following findings:the connectivity index of the shear band increases rapidly and then slowly with increasing axial strain,which is characterized by a near'S'curve.As the stress reaches the peak value,the connectivity index of the shear bands almost exceeds 0.7.The contribution of the new shear band volume to the connectivity of the shear bands becomes increasingly small with increasing axial loading.Affected by quartz grains and stress at the initial stage,the dip angle gradually and finally approaches the included angle of the maximum shear stress from the discrete state with increasing axial loading.The tendency and dip angle of the resulting shear bands are dynamic,and the tendency slightly deflects with increasing loading.展开更多
目的针对锥形束CT(CBCT)引导的图像引导放疗中无儿童合理扫描模式的现状,探讨采用成人头部扫描模式进行学龄前儿童腹部肿瘤扫描,以降低CBCT额外辐射的可行性及价值。方法利用仿真头模引入人为误差的方法,比较CBCT的头部扫描模式与腹盆...目的针对锥形束CT(CBCT)引导的图像引导放疗中无儿童合理扫描模式的现状,探讨采用成人头部扫描模式进行学龄前儿童腹部肿瘤扫描,以降低CBCT额外辐射的可行性及价值。方法利用仿真头模引入人为误差的方法,比较CBCT的头部扫描模式与腹盆部扫描模式在摆位误差方面有无区别。选取2019-01-02-2019-12-31行图像引导放疗的25例学龄前儿童腹部肿瘤患者,分别交替采用头部和腹盆部模式进行CBCT扫描,比较2种CBCT扫描模式下患者在x、y、z方向上的摆位误差有无区别,并对结果进行t检验,同时比较头部和腹盆部扫描模式在图像质量、额外辐射、耗时等方面的差别。结果经仿真头模20次测试,CBCT的头部与腹盆部扫描模式在模体x、y、z方向摆位误差方面差异无统计学意义,t值分别为-0.579、1.445和-1.000,P值分别为0.574、0.161和0.327。25例患儿获得CBCT头部和腹盆部模式图像共50组,头部扫描模式下x、y、z方向上的摆位误差分别为(1.26±2.77)、(0.48±3.31)和(-0.52±2.85) mm;腹盆部扫描模式下摆位误差分别为(1.04±2.83)、(0.84±3.09)和(-0.42±3.57) mm, 2种模式误差差异均无统计学意义,t值分别为0.482、-0.579和-0.149,P值分别为0.632、0.565和0.882,2种扫描模式的图像质量均可满足图像引导需要;而与腹盆扫描模式相比,头部扫描模式的单次辐射降低77.97%(3.9 mGy vs 17.7 mGy),扫描耗时减少44.4%(40 s vs 72 s)。结论 CBCT的头部与腹盆部扫描模式在发现患者摆位误差方面差异无统计学意义,但头部扫描模式扫描要比腹盆部模式的辐射更小、耗时更短。在CBCT引导的学龄前儿童腹部肿瘤的放疗中,宜采用头部模式进行扫描。展开更多
基金supported by the Building Fund for the Academic Innovation Team of Shantou University (CN)(NTF21017)the Special Fund for Science and Technology of Guangdong Province in2021 (STKJ2021181)the National Natural Science Foundation of China (Grant nos.12272394)
文摘The mesomechanics of geotechnical materials are closely related to the macromechanical properties,especially the mesoscale evolution of shear bands,which is helpful for understanding the failure mechanism of geotechnical materials.However,there is lack of effective quantitative analysis method for the complex evolution mechanism of threedimensional shear bands.In this work,we used X-ray computed tomography(CT)to reconstruct volume images and used the digital volume correlation(DVC)method to calculate the three-dimensional strain fields of granite residual soil samples at different loading stages.The trend of the failure surface of the shear bands was obtained by the planar fitting method,and the connectivity index was constructed according to the projection characteristics of the shear bands on the failure trend surface.The results support the following findings:the connectivity index of the shear band increases rapidly and then slowly with increasing axial strain,which is characterized by a near'S'curve.As the stress reaches the peak value,the connectivity index of the shear bands almost exceeds 0.7.The contribution of the new shear band volume to the connectivity of the shear bands becomes increasingly small with increasing axial loading.Affected by quartz grains and stress at the initial stage,the dip angle gradually and finally approaches the included angle of the maximum shear stress from the discrete state with increasing axial loading.The tendency and dip angle of the resulting shear bands are dynamic,and the tendency slightly deflects with increasing loading.
文摘目的针对锥形束CT(CBCT)引导的图像引导放疗中无儿童合理扫描模式的现状,探讨采用成人头部扫描模式进行学龄前儿童腹部肿瘤扫描,以降低CBCT额外辐射的可行性及价值。方法利用仿真头模引入人为误差的方法,比较CBCT的头部扫描模式与腹盆部扫描模式在摆位误差方面有无区别。选取2019-01-02-2019-12-31行图像引导放疗的25例学龄前儿童腹部肿瘤患者,分别交替采用头部和腹盆部模式进行CBCT扫描,比较2种CBCT扫描模式下患者在x、y、z方向上的摆位误差有无区别,并对结果进行t检验,同时比较头部和腹盆部扫描模式在图像质量、额外辐射、耗时等方面的差别。结果经仿真头模20次测试,CBCT的头部与腹盆部扫描模式在模体x、y、z方向摆位误差方面差异无统计学意义,t值分别为-0.579、1.445和-1.000,P值分别为0.574、0.161和0.327。25例患儿获得CBCT头部和腹盆部模式图像共50组,头部扫描模式下x、y、z方向上的摆位误差分别为(1.26±2.77)、(0.48±3.31)和(-0.52±2.85) mm;腹盆部扫描模式下摆位误差分别为(1.04±2.83)、(0.84±3.09)和(-0.42±3.57) mm, 2种模式误差差异均无统计学意义,t值分别为0.482、-0.579和-0.149,P值分别为0.632、0.565和0.882,2种扫描模式的图像质量均可满足图像引导需要;而与腹盆扫描模式相比,头部扫描模式的单次辐射降低77.97%(3.9 mGy vs 17.7 mGy),扫描耗时减少44.4%(40 s vs 72 s)。结论 CBCT的头部与腹盆部扫描模式在发现患者摆位误差方面差异无统计学意义,但头部扫描模式扫描要比腹盆部模式的辐射更小、耗时更短。在CBCT引导的学龄前儿童腹部肿瘤的放疗中,宜采用头部模式进行扫描。
