In standard interval mapping (IM) of quantitative trait loci (QTL), the QTL effect is described by a normal mixture model. When this assumption of normality is violated, the most commonly adopted strategy is to use th...In standard interval mapping (IM) of quantitative trait loci (QTL), the QTL effect is described by a normal mixture model. When this assumption of normality is violated, the most commonly adopted strategy is to use the previous model after data transformation. However, an appropriate transformation may not exist or may be difficult to find. Also this approach can raise interpretation issues. An interesting alternative is to consider a skew-normal mixture model in standard IM, and the resulting method is here denoted as skew-normal IM. This flexible model that includes the usual symmetric normal distribution as a special case is important, allowing continuous variation from normality to non-normality. In this paper we briefly introduce the main peculiarities of the skew-normal distribution. The maximum likelihood estimates of parameters of the skew-normal distribution are obtained by the expectation-maximization (EM) algorithm. The proposed model is illustrated with real data from an intercross experiment that shows a significant departure from the normality assumption. The performance of the skew-normal IM is assessed via stochastic simulation. The results indicate that the skew-normal IM has higher power for QTL detection and better precision of QTL location as compared to standard IM and nonparametric IM.展开更多
目的：应用常规显像剂的一半剂量情况下，评价有序子集最大期望值法（OSEM）重建单光子门控心肌灌注（G-MPI）图像质量及其临床应用的可行性。方法对可疑或确诊冠心病患者行 G-MPI 显像，在半剂量注射显像剂情况下分成常规25 s 采集时...目的：应用常规显像剂的一半剂量情况下，评价有序子集最大期望值法（OSEM）重建单光子门控心肌灌注（G-MPI）图像质量及其临床应用的可行性。方法对可疑或确诊冠心病患者行 G-MPI 显像，在半剂量注射显像剂情况下分成常规25 s 采集时间组和50 s 倍增采集时间组。采集完毕后每组原始数据分别按滤波反投影（FBP）和 OSEM 重建分成两个亚组，每组图像按5分法评价图像质量、按左心室17节段5点放射性评分法评价显像剂分布，计算各组 FBP 和 OSEM 重建的图像质量评分、负荷或静息累积评分（SSS 或 SRS），以及左心室射血分数（LVEF）并配对比较；计算并比较常规采集和倍增时间采集组 OSEM 重建图像的优质图像（4分）所占百分比。结果半剂量注射显像剂采用25 s 常规采集图像后，数据采用 FBP 重建图像评分差于 OSEM 重建（t ＝-3.72，P ＜0.05），放射性累积评分 FBP 组高于 OSEM 组（t ＝2.22，P ＜0.05），但在 LVEF 测定方面比较差异未见统计学意义（t ＝0.97，P ＞0.05）；半剂量注射显像剂采用50 s 倍增采集时间后，数据无论是 FBP 或 OSEM 重建，二者在图像评分、放射性分布累积评分和 LVEF 测定方面比较差异均未见统计学意义（P 均＞0.05）；半剂量注射25 s 采集 OSEM重建和半剂量注射50 s 采集 OSEM 重建的优质图像（图像评分为4分）所占比例比较差异未见统计学意义（χ2＝1.00，P ＞0.05）。结论在半剂量注射情况下，SPECT G-MPI 常规25 s 采集时 OSEM 重建图像质量优于 FBP 重建， FBP 重建会高估病变严重程度，而倍增时间采集后二者图像质量相当，在左室放射性分布累积评分和 LVEF 测量方面比较差异未见统计学意义。因此，G-MPI 半剂量注射、常规时间采集、OSEM 重建，能够在保证图像质量的前提下，无需增加采集时间，降低了患者辐射剂量，具有较好的临床应用可行性和价值。展开更多
基金Project supported in part by Foundation for Science and Technology(FCT) (No.SFRD/BD/5987/2001)the Operational ProgramScience,Technology,and Innovation of the FCT,co-financed by theEuropean Regional Development Fund (ERDF)
文摘In standard interval mapping (IM) of quantitative trait loci (QTL), the QTL effect is described by a normal mixture model. When this assumption of normality is violated, the most commonly adopted strategy is to use the previous model after data transformation. However, an appropriate transformation may not exist or may be difficult to find. Also this approach can raise interpretation issues. An interesting alternative is to consider a skew-normal mixture model in standard IM, and the resulting method is here denoted as skew-normal IM. This flexible model that includes the usual symmetric normal distribution as a special case is important, allowing continuous variation from normality to non-normality. In this paper we briefly introduce the main peculiarities of the skew-normal distribution. The maximum likelihood estimates of parameters of the skew-normal distribution are obtained by the expectation-maximization (EM) algorithm. The proposed model is illustrated with real data from an intercross experiment that shows a significant departure from the normality assumption. The performance of the skew-normal IM is assessed via stochastic simulation. The results indicate that the skew-normal IM has higher power for QTL detection and better precision of QTL location as compared to standard IM and nonparametric IM.
文摘目的：应用常规显像剂的一半剂量情况下，评价有序子集最大期望值法（OSEM）重建单光子门控心肌灌注（G-MPI）图像质量及其临床应用的可行性。方法对可疑或确诊冠心病患者行 G-MPI 显像，在半剂量注射显像剂情况下分成常规25 s 采集时间组和50 s 倍增采集时间组。采集完毕后每组原始数据分别按滤波反投影（FBP）和 OSEM 重建分成两个亚组，每组图像按5分法评价图像质量、按左心室17节段5点放射性评分法评价显像剂分布，计算各组 FBP 和 OSEM 重建的图像质量评分、负荷或静息累积评分（SSS 或 SRS），以及左心室射血分数（LVEF）并配对比较；计算并比较常规采集和倍增时间采集组 OSEM 重建图像的优质图像（4分）所占百分比。结果半剂量注射显像剂采用25 s 常规采集图像后，数据采用 FBP 重建图像评分差于 OSEM 重建（t ＝-3.72，P ＜0.05），放射性累积评分 FBP 组高于 OSEM 组（t ＝2.22，P ＜0.05），但在 LVEF 测定方面比较差异未见统计学意义（t ＝0.97，P ＞0.05）；半剂量注射显像剂采用50 s 倍增采集时间后，数据无论是 FBP 或 OSEM 重建，二者在图像评分、放射性分布累积评分和 LVEF 测定方面比较差异均未见统计学意义（P 均＞0.05）；半剂量注射25 s 采集 OSEM重建和半剂量注射50 s 采集 OSEM 重建的优质图像（图像评分为4分）所占比例比较差异未见统计学意义（χ2＝1.00，P ＞0.05）。结论在半剂量注射情况下，SPECT G-MPI 常规25 s 采集时 OSEM 重建图像质量优于 FBP 重建， FBP 重建会高估病变严重程度，而倍增时间采集后二者图像质量相当，在左室放射性分布累积评分和 LVEF 测量方面比较差异未见统计学意义。因此，G-MPI 半剂量注射、常规时间采集、OSEM 重建，能够在保证图像质量的前提下，无需增加采集时间，降低了患者辐射剂量，具有较好的临床应用可行性和价值。
