The evolutionary density and the scatter of densities of the short fatigue cracks on the surface of 1Cr18Ni9Ti pipe-weld metal were observed by local and overall viewpoints, respectively. The local viewpoint, which is...The evolutionary density and the scatter of densities of the short fatigue cracks on the surface of 1Cr18Ni9Ti pipe-weld metal were observed by local and overall viewpoints, respectively. The local viewpoint, which is in accordance with a so-called "effectively short fatigue crack criterion", paid attention to the dominant effective short fatigue crack (DESFC) initiation zone and the zones ahead of the DESFC tips. The overall viewpoint focused on the whole test piece of specimen. The results revealed that the density and scatter evolution exhibited a significant character of microstructural short crack and physical short crack stages. The evolutionary behavior by the local viewpoint was sensitive to the increase of DESFC size and tip location. The mechanism of the short crack growth associated with the general test observations that the DESFC acted gradually as a long crack and the scatter of DESFC growth rates tended gradually to that of a long crack was well revealed. Intrinsic causes of the random cyclic strain-life relations and stress-strain responses are appropriately given. In contrast, the evolutionary behavior by the overall viewpoint was non-sensitive and violated the general test observations. Therefore, the intrinsic localization and randomization of material evolutionary fatigue damage should be more appropriately revealed from the observations by the local viewpoint.展开更多
Size evolution of the surface short fatigue cracks of lCrl8Ni'9Ti weld metal was investigated. A local viewpoint is applied to be agreement with a so-called 'effectively short fatigue crack criterion'. Att...Size evolution of the surface short fatigue cracks of lCrl8Ni'9Ti weld metal was investigated. A local viewpoint is applied to be agreement with a so-called 'effectively short fatigue crack criterion'. Attention was paid to the dominant effectively short fatigue crack (DESFC) initiation zone and the zones ahead of the DESFC tips. The results revealed that the evolutionary size shows a significant character of microstructural short crack (MSC) and physical short crack (PSC) stages. In the MSC stage, fatigue damage is due to mainly the initiation and irregular growth of the effectively short fatigue cracks (ESFCs). In the PSC stage, the damage is conversely due to mainly the DESFC growth and partially, the growth of the ESFCs and the coalescence of the ESFCs themselves with the DESFC. The process involves from a non-ordered/chaotic state in the initiation of MSC stage, gradually to an independently random state at the transition point between the MSC and PSC stages and then, to an ordered/history-dependent random state. Interactive effect of the collective cracks is stronger and shows an increase in the MSC stage, it reaches a maximum value at the transition point and then, tends to a decrease in the PSC stage. The DESFC acts as a result of the interactive cracks and thus, is deemed suitable to describe the behaviour of collective cracks.展开更多
目的比较优化短反转恢复(Short TI Inversion Recovery,STIR)和三点非对称法脂肪抑制技术(Iterative Dixon of Water-fat with Echo Asymmetry and Least-squares Estimation,IDEAL)对金属植入物磁共振成像(Magnetic Resonance Imaging,...目的比较优化短反转恢复(Short TI Inversion Recovery,STIR)和三点非对称法脂肪抑制技术(Iterative Dixon of Water-fat with Echo Asymmetry and Least-squares Estimation,IDEAL)对金属植入物磁共振成像(Magnetic Resonance Imaging,MRI)图像质量的影响。方法选取腰椎金属内固定术后需行MRI检查的患者30例,行常规序列以及优化STIR、IDEAL序列扫描,通过对感兴趣区信号的强度值分别计算信噪比(Signal to Noise Ratio,SNR)和信噪比(Contrast to Noise Ratio,CNR),对数据结果做统计学分析;对脂肪抑制均匀性、金属伪影大小进行主观评价。结果优化STIR和IDEAL两种方法图像信噪比分别为:19.26±0.96、20.26±1.24(t=-2.94,P<0.01);图像噪声比分别为:7.03±0.94、8.28±0.97(t=-6.07,P<0.01);主观评分脂肪抑制的均匀性分别为:3.47±0.51、3.63±0.50(t=1.37,P>0.05);金属伪影的大小分别为:3.68±0.67,3.74±0.65(t=-0.57,P>0.05)。结论IDEAL技术在脂肪抑制均匀性、金属伪影、图像信噪比等图像质量方面和优化STIR脂肪抑制技术相当,并且可以得到更好的SNR和CNR。因此在机器条件允许的情况下,对于金属植入物的患者可以选择IDEAL脂肪抑制技术进行检查。展开更多
Objective To evaluate the clinical impact of whole body diffusion weighted imaging （WB-DWI） on diagnosis and staging of malignant lymphoma. Methods Thirty-one patients with suspected lymphadenopathy were enrolled. ...Objective To evaluate the clinical impact of whole body diffusion weighted imaging （WB-DWI） on diagnosis and staging of malignant lymphoma. Methods Thirty-one patients with suspected lymphadenopathy were enrolled. WB-DWI was performed by using short TI inversion recovery echo-planar imaging sequence with free breathing and built-in body coil. Axial T2- weighted imaging images of the same location were used as reference. The results of WB-DWI were compared with pathological results and other imaging modalities. The mean apparent diffusion coefficient （ADC） values of different kinds of lymph nodes were compared. Results WB-DWI was positive in all 18 cases with lymphoma, 5 cases with metastatic lymph nodes and 4 of 8 eases with benign lymphadenopathy. The mean ADC value of lymphomatous, metastatic and benign lymph nodes was （0.87 ± 0.17） × 10^3, （0.98± 0.09） × 10^3 and （1.20 ± 0.10） × 10^3 mm^2/s. There was significant difference in ADC value between benign lymph nodes and other two groups （P 〈 0.01）. The sensitivity, specificity and accuracy of WB-DWI in diagnosis of lymphoma were 100% （18/18）, 30.8% （4/13） and 71.0% （22/31）. When an ADC value of 1.08 × 10^-3 mm^2/s was used as the threshold value for differentiating malignant from benign lymph nodes, the best results were obtained with sensitivity of 87.8% and specificity of 91.3%. Sixteen of eighteen cases （88.9%） of lymphoma were accurately staged in accordance with clinical staging. Conclusions WB-DWI is a sensitive, but less specific technique for diagnosis of lymphoma. It is difficult to differentiate lymphnmatous from metastatic lymph nodes using WB-DWI. However, it is a valuable imaging modality for staging of patients with malignant lymphoma.展开更多
目的:探讨T23D SPACE序列在腰骶丛神经根中的应用及其参数优化。方法:前瞻性招募并收集46名正常志愿者的临床与影像资料,所有志愿者均行常规T23D SPACE(方法A)、优化后T23D SPACE(方法B)磁共振扫描,并比较2种方法的扫描时间,第4~5腰神...目的:探讨T23D SPACE序列在腰骶丛神经根中的应用及其参数优化。方法:前瞻性招募并收集46名正常志愿者的临床与影像资料,所有志愿者均行常规T23D SPACE(方法A)、优化后T23D SPACE(方法B)磁共振扫描,并比较2种方法的扫描时间,第4~5腰神经、第1~4骶神经、坐骨神经的神经显示情况,第5腰神经根节中、节前、节后的信噪比(SNR)、对比度噪声比(CNR)_(神经-肌肉)、对比度(CR)_(神经-肌肉值)。优化后T23D SPACE序列(方法B)主要优化了TR、TE、加速因子(回波链)、脂肪抑制方式、血液抑制方式、层厚等参数。结果:(1)方法A扫描时间为356 s,方法B扫描时间为229 s。(2)在神经显示评分比较中,第4、5腰神经,第1~4骶神经和坐骨神经的显示评分在2种方法之间差异无统计学意义。(3)第5腰神经根的节中SNR值(286.842±75.822 vs 376.784±111.880)、CNR_(神经-肌肉值)(389.199±106.824 vs 522.683±159.883)、CR_(神经-肌肉值)(0.798±0.037 vs 0.830±0.038)在2种方法间比较,差异均有统计学意义(P<0.05)。(4)第5腰神经根的节前SNR值(198.758±52.966 vs 260.378±79.631)、CNR_(神经-肌肉值)(254.720±74.904 vs344.948±112.041)、CR_(神经-肌肉值)(0.718±0.070 vs 0.762±0.056)在2种方法间比较,差异均有统计学意义(P<0.05)。(5)第5腰神经根的节后SNR值(161.400±46.883 vs 206.849±59.706)、CNR_(神经-肌肉值)(197.684±63.776 vs 263.240±80.910)、CR_(神经-肌肉值)(0.663±0.068 vs 0.711±0.058)在2种方法间比较,差异均有统计学意义(P<0.05)。结论:常规T23D SPACE序列与优化后的序列均可以显示腰骶神经,优化后扫描更快,神经显示中第5腰神经根的信噪比、对比度均比常规T23D SPACE序列高。展开更多
分析我院2004年～2007年123例早期股骨头无菌坏死患者的X线平片、CT以及MRI检查。123例患者在MRI检查中应用短时反转恢复(short TI Inversion-Recovery)序列通过抑制正常骨髓高信号及周围肌肉组织间脂肪高信号,使病变早期轻微水肿高信...分析我院2004年～2007年123例早期股骨头无菌坏死患者的X线平片、CT以及MRI检查。123例患者在MRI检查中应用短时反转恢复(short TI Inversion-Recovery)序列通过抑制正常骨髓高信号及周围肌肉组织间脂肪高信号,使病变早期轻微水肿高信号显示出来,诊断早期股骨头无菌坏死,跟踪追查1至3年,93例患者出现股骨头塌陷,临床证实为股骨头无菌坏死,进一步明确诊断。展开更多
Background Detection rate of retropharyngeal lymph node metastasis in patients with nasopharyngeal carcinoma （NPC） needs to be improved. The purpose of this study was to compare three magnetic resonance （MR） seque...Background Detection rate of retropharyngeal lymph node metastasis in patients with nasopharyngeal carcinoma （NPC） needs to be improved. The purpose of this study was to compare three magnetic resonance （MR） sequences for detecting lymph nodes in patients with NPC. Methods Between July 2007 and March 2008, MR staging of pre-treated tumor was conducted on 120 patients with pathologically confirmed NPC. The outcome of three different sequences for MR NPC staging were compared： coronal short T1 inversion recovery （STIR）, axial proton density fat-suppressed （PDWI fs）, and coronal contrast enhanced fast spin echo T1 weighted fat-suppressed （CE FSE TlWl fs）. Nodal classification method （1999） was applied to count the number of retropharyngeal and cervical lymph nodes discovered by each MR sequence. Paired t tests were used for statistical analysis. Results A total of 2575 lymph nodes were found using coronal STIR sequence; 1816 lymph nodes for coronal CE FSE TIWI fs sequence and 2638 lymph nodes for axial PDWl fs sequence. Significant differences existed in the number of lymph nodes detected by axial PDWI fs and coronal CE FSE T1WI fs sequence （paired t test, P 〈0.05）, with the former sequence getting higher numbers. Statistical differences also existed between coronal STIR and coronal CE FSE TlWl fs sequence （paired ttest, P 〈0.05）, with the former sequence getting higher numbers. No significant difference was found between coronal STIR sequence and axial PDWI fs sequence （paired ttest, P 〉0.05）. Conclusions For the detection of retropharyngeal and cervical lymph nodes, coronal STIR sequence and axial PDWI fs sequence have similar performance and both sequences showed better detection than CE FSE TIWI fs sequence. Furthermore, by combining coronal STIR sequence and axial PDWI fs sequence, we can improve the detection of lymph nodes in NPC N-staging before treatment, especially for lymph nodes located in the thoracic entrance.展开更多
文摘The evolutionary density and the scatter of densities of the short fatigue cracks on the surface of 1Cr18Ni9Ti pipe-weld metal were observed by local and overall viewpoints, respectively. The local viewpoint, which is in accordance with a so-called "effectively short fatigue crack criterion", paid attention to the dominant effective short fatigue crack (DESFC) initiation zone and the zones ahead of the DESFC tips. The overall viewpoint focused on the whole test piece of specimen. The results revealed that the density and scatter evolution exhibited a significant character of microstructural short crack and physical short crack stages. The evolutionary behavior by the local viewpoint was sensitive to the increase of DESFC size and tip location. The mechanism of the short crack growth associated with the general test observations that the DESFC acted gradually as a long crack and the scatter of DESFC growth rates tended gradually to that of a long crack was well revealed. Intrinsic causes of the random cyclic strain-life relations and stress-strain responses are appropriately given. In contrast, the evolutionary behavior by the overall viewpoint was non-sensitive and violated the general test observations. Therefore, the intrinsic localization and randomization of material evolutionary fatigue damage should be more appropriately revealed from the observations by the local viewpoint.
基金Present work is supported by the National Natural Science Foundation of China (50075073), the Special Foundation for the Authors of National Excellent Ph.D. Theses (2002067), the Excellent Young Teachers Program of MOE, PRO (EYTP 2101) and the Provincial
文摘Size evolution of the surface short fatigue cracks of lCrl8Ni'9Ti weld metal was investigated. A local viewpoint is applied to be agreement with a so-called 'effectively short fatigue crack criterion'. Attention was paid to the dominant effectively short fatigue crack (DESFC) initiation zone and the zones ahead of the DESFC tips. The results revealed that the evolutionary size shows a significant character of microstructural short crack (MSC) and physical short crack (PSC) stages. In the MSC stage, fatigue damage is due to mainly the initiation and irregular growth of the effectively short fatigue cracks (ESFCs). In the PSC stage, the damage is conversely due to mainly the DESFC growth and partially, the growth of the ESFCs and the coalescence of the ESFCs themselves with the DESFC. The process involves from a non-ordered/chaotic state in the initiation of MSC stage, gradually to an independently random state at the transition point between the MSC and PSC stages and then, to an ordered/history-dependent random state. Interactive effect of the collective cracks is stronger and shows an increase in the MSC stage, it reaches a maximum value at the transition point and then, tends to a decrease in the PSC stage. The DESFC acts as a result of the interactive cracks and thus, is deemed suitable to describe the behaviour of collective cracks.
文摘目的比较优化短反转恢复(Short TI Inversion Recovery,STIR)和三点非对称法脂肪抑制技术(Iterative Dixon of Water-fat with Echo Asymmetry and Least-squares Estimation,IDEAL)对金属植入物磁共振成像(Magnetic Resonance Imaging,MRI)图像质量的影响。方法选取腰椎金属内固定术后需行MRI检查的患者30例,行常规序列以及优化STIR、IDEAL序列扫描,通过对感兴趣区信号的强度值分别计算信噪比(Signal to Noise Ratio,SNR)和信噪比(Contrast to Noise Ratio,CNR),对数据结果做统计学分析;对脂肪抑制均匀性、金属伪影大小进行主观评价。结果优化STIR和IDEAL两种方法图像信噪比分别为:19.26±0.96、20.26±1.24(t=-2.94,P<0.01);图像噪声比分别为:7.03±0.94、8.28±0.97(t=-6.07,P<0.01);主观评分脂肪抑制的均匀性分别为:3.47±0.51、3.63±0.50(t=1.37,P>0.05);金属伪影的大小分别为:3.68±0.67,3.74±0.65(t=-0.57,P>0.05)。结论IDEAL技术在脂肪抑制均匀性、金属伪影、图像信噪比等图像质量方面和优化STIR脂肪抑制技术相当,并且可以得到更好的SNR和CNR。因此在机器条件允许的情况下,对于金属植入物的患者可以选择IDEAL脂肪抑制技术进行检查。
文摘Objective To evaluate the clinical impact of whole body diffusion weighted imaging （WB-DWI） on diagnosis and staging of malignant lymphoma. Methods Thirty-one patients with suspected lymphadenopathy were enrolled. WB-DWI was performed by using short TI inversion recovery echo-planar imaging sequence with free breathing and built-in body coil. Axial T2- weighted imaging images of the same location were used as reference. The results of WB-DWI were compared with pathological results and other imaging modalities. The mean apparent diffusion coefficient （ADC） values of different kinds of lymph nodes were compared. Results WB-DWI was positive in all 18 cases with lymphoma, 5 cases with metastatic lymph nodes and 4 of 8 eases with benign lymphadenopathy. The mean ADC value of lymphomatous, metastatic and benign lymph nodes was （0.87 ± 0.17） × 10^3, （0.98± 0.09） × 10^3 and （1.20 ± 0.10） × 10^3 mm^2/s. There was significant difference in ADC value between benign lymph nodes and other two groups （P 〈 0.01）. The sensitivity, specificity and accuracy of WB-DWI in diagnosis of lymphoma were 100% （18/18）, 30.8% （4/13） and 71.0% （22/31）. When an ADC value of 1.08 × 10^-3 mm^2/s was used as the threshold value for differentiating malignant from benign lymph nodes, the best results were obtained with sensitivity of 87.8% and specificity of 91.3%. Sixteen of eighteen cases （88.9%） of lymphoma were accurately staged in accordance with clinical staging. Conclusions WB-DWI is a sensitive, but less specific technique for diagnosis of lymphoma. It is difficult to differentiate lymphnmatous from metastatic lymph nodes using WB-DWI. However, it is a valuable imaging modality for staging of patients with malignant lymphoma.
文摘目的:探讨T23D SPACE序列在腰骶丛神经根中的应用及其参数优化。方法:前瞻性招募并收集46名正常志愿者的临床与影像资料,所有志愿者均行常规T23D SPACE(方法A)、优化后T23D SPACE(方法B)磁共振扫描,并比较2种方法的扫描时间,第4~5腰神经、第1~4骶神经、坐骨神经的神经显示情况,第5腰神经根节中、节前、节后的信噪比(SNR)、对比度噪声比(CNR)_(神经-肌肉)、对比度(CR)_(神经-肌肉值)。优化后T23D SPACE序列(方法B)主要优化了TR、TE、加速因子(回波链)、脂肪抑制方式、血液抑制方式、层厚等参数。结果:(1)方法A扫描时间为356 s,方法B扫描时间为229 s。(2)在神经显示评分比较中,第4、5腰神经,第1~4骶神经和坐骨神经的显示评分在2种方法之间差异无统计学意义。(3)第5腰神经根的节中SNR值(286.842±75.822 vs 376.784±111.880)、CNR_(神经-肌肉值)(389.199±106.824 vs 522.683±159.883)、CR_(神经-肌肉值)(0.798±0.037 vs 0.830±0.038)在2种方法间比较,差异均有统计学意义(P<0.05)。(4)第5腰神经根的节前SNR值(198.758±52.966 vs 260.378±79.631)、CNR_(神经-肌肉值)(254.720±74.904 vs344.948±112.041)、CR_(神经-肌肉值)(0.718±0.070 vs 0.762±0.056)在2种方法间比较,差异均有统计学意义(P<0.05)。(5)第5腰神经根的节后SNR值(161.400±46.883 vs 206.849±59.706)、CNR_(神经-肌肉值)(197.684±63.776 vs 263.240±80.910)、CR_(神经-肌肉值)(0.663±0.068 vs 0.711±0.058)在2种方法间比较,差异均有统计学意义(P<0.05)。结论:常规T23D SPACE序列与优化后的序列均可以显示腰骶神经,优化后扫描更快,神经显示中第5腰神经根的信噪比、对比度均比常规T23D SPACE序列高。
文摘分析我院2004年～2007年123例早期股骨头无菌坏死患者的X线平片、CT以及MRI检查。123例患者在MRI检查中应用短时反转恢复(short TI Inversion-Recovery)序列通过抑制正常骨髓高信号及周围肌肉组织间脂肪高信号,使病变早期轻微水肿高信号显示出来,诊断早期股骨头无菌坏死,跟踪追查1至3年,93例患者出现股骨头塌陷,临床证实为股骨头无菌坏死,进一步明确诊断。
基金This study was supported by a grant from the Natural Science Foundation of Fujian Province （No. 2004Y008）.
文摘Background Detection rate of retropharyngeal lymph node metastasis in patients with nasopharyngeal carcinoma （NPC） needs to be improved. The purpose of this study was to compare three magnetic resonance （MR） sequences for detecting lymph nodes in patients with NPC. Methods Between July 2007 and March 2008, MR staging of pre-treated tumor was conducted on 120 patients with pathologically confirmed NPC. The outcome of three different sequences for MR NPC staging were compared： coronal short T1 inversion recovery （STIR）, axial proton density fat-suppressed （PDWI fs）, and coronal contrast enhanced fast spin echo T1 weighted fat-suppressed （CE FSE TlWl fs）. Nodal classification method （1999） was applied to count the number of retropharyngeal and cervical lymph nodes discovered by each MR sequence. Paired t tests were used for statistical analysis. Results A total of 2575 lymph nodes were found using coronal STIR sequence; 1816 lymph nodes for coronal CE FSE TIWI fs sequence and 2638 lymph nodes for axial PDWl fs sequence. Significant differences existed in the number of lymph nodes detected by axial PDWI fs and coronal CE FSE T1WI fs sequence （paired t test, P 〈0.05）, with the former sequence getting higher numbers. Statistical differences also existed between coronal STIR and coronal CE FSE TlWl fs sequence （paired ttest, P 〈0.05）, with the former sequence getting higher numbers. No significant difference was found between coronal STIR sequence and axial PDWI fs sequence （paired ttest, P 〉0.05）. Conclusions For the detection of retropharyngeal and cervical lymph nodes, coronal STIR sequence and axial PDWI fs sequence have similar performance and both sequences showed better detection than CE FSE TIWI fs sequence. Furthermore, by combining coronal STIR sequence and axial PDWI fs sequence, we can improve the detection of lymph nodes in NPC N-staging before treatment, especially for lymph nodes located in the thoracic entrance.
