常规机载气象雷达采用脉冲对法估计谱宽实现湍流检测,当信噪比较低时脉冲对法的谱宽估计误差大。晴空湍流(clear air turbulence,CAT)含水量较少,雷达回波信噪比很低,因此常规机载气象雷达无法检测CAT。为提高低信噪比下机载气象雷达回...常规机载气象雷达采用脉冲对法估计谱宽实现湍流检测,当信噪比较低时脉冲对法的谱宽估计误差大。晴空湍流(clear air turbulence,CAT)含水量较少,雷达回波信噪比很低,因此常规机载气象雷达无法检测CAT。为提高低信噪比下机载气象雷达回波谱宽估计性能,提出了一种基于降秩多级维纳滤波器(Reduced-Rank Multistage Wiener Filter,RR-MWF)的回波谱矩估计方法。该方法在机载气象雷达引入空时体制的基础上,利用空时域联合处理对湍流回波进行处理,通过空时积累改善信噪比。在最小均方误差准则下,构造了适用于分布式气象目标的自适应RR-MWF权矢量和代价函数,估计回波谱矩。仿真实验表明,提出的RR-MWF估计器在信噪比低于10 dB时明显优于常规的脉冲对法,可用于CAT检测。展开更多
Background：The difference between renal oncocytomas （RO） and renal clear cell carcinomas （RCCs） presents the greatest diagnostic challenge.The aim of this study was to retrospectively determine ifRO and RCCs coul...Background：The difference between renal oncocytomas （RO） and renal clear cell carcinomas （RCCs） presents the greatest diagnostic challenge.The aim of this study was to retrospectively determine ifRO and RCCs could be differentiated on computed tomography （CT） images on the basis of their enhancement patterns with a new enhancement correcting method.Methods：Forty-six patients with a solitary renal mass who underwent total or partial nephrectomy were included in this study.Fourteen of those were RO and 32 were RCCs.All patients were examined with contrast-enhanced CT.The pattern and degree of enhancement were evaluated.We selected the area that demonstrated the greatest degree of enhancement of the renal lesion in the corticomedullary nephrographic and excretory phase images.Regions of interest （ROI） were also placed in adjacent normal renal cortex for normalization.We used the values of the normal renal cortex that were measured at the same time as divisors.The ratios of lesion-to-renal cortex enhancement were calculated for all three phases.The Student＆#39;s t-test and Pearson＆#39;s Chi-square test were used for statistical analyses.Results：All RCCs masses showed contrast that appeared to be better enhanced than RO on all contrast-enhanced phases of CT imaging,but there was no significant difference in absolute attenuation values between these two diseases （P 〉 0.05）.The ratio of lesion-to-cortex attenuation in the corticomedullary phase showed significantly different values between RO and RCCs.The degree of contrast enhancement in RCCs was equal to or greater than that of the normal renal cortex,but it was less than that of the normal cortex in RO in the corticomedullary phase.The ratio of lesion-to-cortex attenuation in the corticomedullary phase was higher than the cut off value of 1.0 in most RCCs （84%,27/32） and lower than 1.0 in most RO （93%,13/14） （P 〈 0.05）.In the nephrographic phase,the ratio of lesion-to-cortex attenuation was higher than that in the corticomedullary phase in most RO （71%,10/14）,showing a prolonged enhancement pattern; and was lower than that in most RCCs （97%,31/32）,showing an early washout pattern （P 〈 0.05）.In the differentiation of RO from RCCs,the sensitivity was 93%,specificity 84%,positive predictive value 72%,negative predictive value 84%,and accuracy for RO was 87,if the ratio of lesion-to-cortex attenuation in a cortex phase was lower than the cutoff value of 1.0.The sensitivity was 71%,specificity was 97%,positive predictive value was 91%,negative predictive value was 91%,and accuracy for RO was 89%,if the ratio of lesion-to-cortex attenuation in nephrographic phase was higher than that in the corticomedullary phase.Conclusions：The ratios of renal lesion-to-cortex attenuation ratios may be helpful in differentiating RO from RCCs.展开更多
文摘常规机载气象雷达采用脉冲对法估计谱宽实现湍流检测,当信噪比较低时脉冲对法的谱宽估计误差大。晴空湍流(clear air turbulence,CAT)含水量较少,雷达回波信噪比很低,因此常规机载气象雷达无法检测CAT。为提高低信噪比下机载气象雷达回波谱宽估计性能,提出了一种基于降秩多级维纳滤波器(Reduced-Rank Multistage Wiener Filter,RR-MWF)的回波谱矩估计方法。该方法在机载气象雷达引入空时体制的基础上,利用空时域联合处理对湍流回波进行处理,通过空时积累改善信噪比。在最小均方误差准则下,构造了适用于分布式气象目标的自适应RR-MWF权矢量和代价函数,估计回波谱矩。仿真实验表明,提出的RR-MWF估计器在信噪比低于10 dB时明显优于常规的脉冲对法,可用于CAT检测。
文摘Background：The difference between renal oncocytomas （RO） and renal clear cell carcinomas （RCCs） presents the greatest diagnostic challenge.The aim of this study was to retrospectively determine ifRO and RCCs could be differentiated on computed tomography （CT） images on the basis of their enhancement patterns with a new enhancement correcting method.Methods：Forty-six patients with a solitary renal mass who underwent total or partial nephrectomy were included in this study.Fourteen of those were RO and 32 were RCCs.All patients were examined with contrast-enhanced CT.The pattern and degree of enhancement were evaluated.We selected the area that demonstrated the greatest degree of enhancement of the renal lesion in the corticomedullary nephrographic and excretory phase images.Regions of interest （ROI） were also placed in adjacent normal renal cortex for normalization.We used the values of the normal renal cortex that were measured at the same time as divisors.The ratios of lesion-to-renal cortex enhancement were calculated for all three phases.The Student＆#39;s t-test and Pearson＆#39;s Chi-square test were used for statistical analyses.Results：All RCCs masses showed contrast that appeared to be better enhanced than RO on all contrast-enhanced phases of CT imaging,but there was no significant difference in absolute attenuation values between these two diseases （P 〉 0.05）.The ratio of lesion-to-cortex attenuation in the corticomedullary phase showed significantly different values between RO and RCCs.The degree of contrast enhancement in RCCs was equal to or greater than that of the normal renal cortex,but it was less than that of the normal cortex in RO in the corticomedullary phase.The ratio of lesion-to-cortex attenuation in the corticomedullary phase was higher than the cut off value of 1.0 in most RCCs （84%,27/32） and lower than 1.0 in most RO （93%,13/14） （P 〈 0.05）.In the nephrographic phase,the ratio of lesion-to-cortex attenuation was higher than that in the corticomedullary phase in most RO （71%,10/14）,showing a prolonged enhancement pattern; and was lower than that in most RCCs （97%,31/32）,showing an early washout pattern （P 〈 0.05）.In the differentiation of RO from RCCs,the sensitivity was 93%,specificity 84%,positive predictive value 72%,negative predictive value 84%,and accuracy for RO was 87,if the ratio of lesion-to-cortex attenuation in a cortex phase was lower than the cutoff value of 1.0.The sensitivity was 71%,specificity was 97%,positive predictive value was 91%,negative predictive value was 91%,and accuracy for RO was 89%,if the ratio of lesion-to-cortex attenuation in nephrographic phase was higher than that in the corticomedullary phase.Conclusions：The ratios of renal lesion-to-cortex attenuation ratios may be helpful in differentiating RO from RCCs.
