半剂量 OSEM 重建在单光子发射型门控心肌灌注显像中的可行性研究

Feasibility study on half - dose OSEM reconstruction in gated myocardial perfusion imaging with single photon emission tomography

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。

Objective To evaluate the feasibility and values of half - dose and ordered subset expectation maximization（ OSEM）reconstruction in single photon gated myocardial perfusion imaging （G-MPI）. Methods Patients with suspected or confirmed coronary artery diseases（ CAD）underwent G-MPIs were divided into two groups. One group underwent SPECT G-MPI with routine 25 s acquisition time,and 50 s acquisition time for another group. After completion of acquisitions,raw-data in each group were respectively reconstructed with filtered back projection（ FBP）and OSEM. Each subgroup images were evaluated with five-point scores for image-quality evaluation,and five-point summed scores were calculated on base of left ventricle 17 segment model. Image quality scores,summed stress score （SSS）or summed rest score（SRS）and left ventricle ejection fraction（LVEF）were respectively calculated and compared for FBP or OSEM images of each subgroup. Percentage of excellent images（score 4）was calculated and compared for OSEM images of routine acquisition time group or doubling time group. Results For half-dose and routine 25 s acquisition time group,the FBP image quality scores were less than those for OSEM group（t = - 3. 72,P 0. 05）. For half-dose and doubling acquisition time group,there were no significant differences in image quality scores,summed radioactive scores or LVEF between FBP and OSEM images（P all 〉 0. 05）. There was no significant differences in percentage of excellent images（score 4）between routine 25 s acquisition time group and doubling acquisition time group（ χ2 = 1. 00,P 〉0. 05）. Conclusions Under the circumstance of half-dose injection,the image qualities reconstructed with OSEM are superior to those reconstructed with FBP for routine 25 s acquisition time group,and images reconstructed with FBP may overestimate the severity. FBP or OSEM image qualities are comparable for doubling acquisition time group,and there are no significant differences in summed radioactive score and LVEF. So half-dose,routine acquisition time and OSEM reconstruction provide good image qualities,and no need for additional acquisition time,and radiation doses for patients are also simultaneously reduced because of low injection dose,which has good feasibility and values in the clinical applications.