Pretorius P H, Narayanan M V, Dahlberg S T, Leppo J A, King M A
Department of Radiology, Division of Nuclear Medicine, University of Massachusetts Medical School, Boston 01655, USA.
J Nucl Cardiol. 2001 May-Jun;8(3):356-64. doi: 10.1067/mnc.2001.113516.
Our objective was to study the differences in relative count distributions in the left ventricular walls with attenuation compensation (AC) versus AC and triple-energy-window scatter compensation (SC), compared with standard filtered backprojection (FBP).
Two hundred patients identified as having normal cardiac perfusion with FBP after undergoing either pharmacologically or physiologically induced stress were included in this study. Projection data were reconstructed with FBP, 10 iterations of ordered-subset expectation-maximization (OSEM) with AC, and OSEM with AC+SC. A comparison was made of average percentage of maximum counts within each of 9 regions of CEqual (Marconi Medical Systems, Inc, Cleveland, Ohio) polar maps (ie, the apex, 4 midventricular regions, and 4 basal regions). Compared with OSEM(AC), a slight decrease at the apex exists when SC is included. The elevated inferior-to-anterior count ratio in the midventricular and basal regions noted with OSEM(AC) decreased to close to 1.0 with OSEM(AC+SC). The anterior-to-lateral ratio for both regions was closest to 1.0 for OSEM(AC+SC). In the midventricular region, the lateral-to-septal ratio decreased further below 1.0 with OSEM(AC+SC) than it did with OSEM(AC). This was the only basal ratio not to improve to close to 1.0 with OSEM(AC+SC). In a subset of patients identified at the time of clinical reading as having a possible attenuation-caused decrease in the inferior region, AC elevated the inferior-to-anterior ratio to above 1.0 for the midventricular region. AC+SC resulted in a ratio of near 1.0 for this region. In another subset of patients identified as having anterior attenuation artifacts, compensation methods (either AC or AC+SC) failed to show an improvement compared with FBP.
AC and SC improve the uniformity of the polar map, especially by bringing the inferior-to-anterior ratio closer to 1.0. Further investigation is necessary to determine the cause of the increased midventricular septal polar map count. In addition, the subset of patients identified as having breast-like attenuation artifacts causing a decreased polar map count in the anterior wall (relative to the inferior wall) also needs further attention.
我们的目的是研究在左心室壁中，与标准滤波反投影（FBP）相比，使用衰减补偿（AC）与AC加三能量窗散射补偿（SC）时相对计数分布的差异。
本研究纳入了200例在接受药物或生理诱导应激后经FBP检查确定心脏灌注正常的患者。投影数据分别采用FBP、10次带AC的有序子集期望最大化（OSEM）迭代以及带AC+SC的OSEM进行重建。对CEqual（Marconi Medical Systems, Inc, Cleveland, Ohio）极坐标图的9个区域（即心尖、4个心室中部区域和4个基底区域）中每个区域的最大计数平均百分比进行了比较。与OSEM(AC)相比，加入SC后心尖处略有下降。OSEM(AC)时心室中部和基底区域观察到的下壁与前壁计数比值升高，而OSEM(AC+SC)时该比值降至接近1.0。两个区域的前壁与侧壁比值在OSEM(AC+SC)时最接近1.0。在心室中部区域，OSEM(AC+SC)时侧壁与间隔壁比值比OSEM(AC)时进一步降至1.0以下。这是唯一在OSEM(AC+SC)时未改善至接近1.0的基底比值。在临床阅片时确定为下壁可能因衰减导致计数减少的患者亚组中，AC使心室中部区域的下壁与前壁比值升高至1.0以上。AC+SC使该区域的比值接近1.0。在另一个确定为存在前壁衰减伪影的患者亚组中，与FBP相比，补偿方法（AC或AC+SC）均未显示出改善。
AC和SC改善了极坐标图的均匀性，尤其是使下壁与前壁比值更接近1.0。有必要进一步研究以确定心室中部间隔极坐标图计数增加的原因。此外，确定为存在类似乳腺的衰减伪影导致前壁（相对于下壁）极坐标图计数减少的患者亚组也需要进一步关注。
