Zhao Zhanqi, Frerichs Inéz, Pulletz Sven, Müller-Lisse Ullrich, Möller Knut
Institute of Technical Medicine, Furtwangen University, VS-Schwenningen, Germany Department of Radiology, University of Munich, Munich, Germany.
Department of Anaesthesiology and Intensive Care Medicine, University Medical Center Schleswig-Holstein, Campus Kiel, Kiel, Germany.
J Xray Sci Technol. 2014;22(6):797-807. doi: 10.3233/XST-140464.
Due to the ill-posed problem, the electrical impedance within the thorax cannot be exactly reconstructed.
The aim of our study was to prove that reconstruction with individual thorax geometry improved the quality of EIT (electrical impedance tomography) images.
Seven mechanically ventilated patients with acute respiratory distress syndrome were examined by EIT. The thorax contours were determined from routine computed tomography (CT) images based on automatic threshold filtering. EIT raw data was reconstructed offline with (1) back-projection with circular forward model; (2) GREIT reconstruction method with circular forward model and (3) GREIT with individual thorax geometry. The resulting EIT images were compared to rescaled CT images. The distance between the lung contour and the thorax contour was calculated for each method and the differences to that in CT were denoted as position differences. Shape differences was defined as the ratio of thorax (or lungs) size in EIT and that in rescaled CT.
Method (3) has the smallest position differences (6.6 ± 2.8, 5.3 ± 3.3, 2.3 ± 1.4 in pixel, for each reconstruction method respectively; mean ± SD). The thorax and lungs sizes in the transformed CT images were 514 ± 73 and 177 ± 39. Shape differences of thorax were 1.81 ± 0.26, 1.81 ± 0.26, 1.10 ± 0.12 and that of lungs were 1.69 ± 0.45, 1.52 ± 0.45, 1.34 ± 0.35 for each method respectively.
The reconstructed images using the GREIT method with individual thorax geometry were more realistic. Improvement of EIT image quality may foster the acceptance of EIT in routine clinical use.
由于不适定问题，胸部内的电阻抗无法精确重建。
我们研究的目的是证明使用个体胸部几何形状进行重建可提高电阻抗断层成像（EIT）图像的质量。
对7例患有急性呼吸窘迫综合征的机械通气患者进行EIT检查。基于自动阈值滤波从常规计算机断层扫描（CT）图像确定胸部轮廓。EIT原始数据通过以下方式离线重建：（1）使用圆形正向模型的反投影；（2）使用圆形正向模型的GREIT重建方法；（3）使用个体胸部几何形状的GREIT。将所得的EIT图像与重新缩放的CT图像进行比较。计算每种方法的肺轮廓与胸轮廓之间的距离，并将与CT中的距离差异表示为位置差异。形状差异定义为EIT中胸部（或肺部）大小与重新缩放的CT中胸部（或肺部）大小的比率。
方法（3）的位置差异最小（每种重建方法分别为6.6±2.8、5.3±3.3、2.3±1.4像素；均值±标准差）。变换后的CT图像中胸部和肺部大小分别为514±73和177±39。每种方法的胸部形状差异分别为1.81±0.26、1.81±0.26、1.10±0.12，肺部形状差异分别为1.69±0.45、1.52±0.45、1.34±0.35。
使用具有个体胸部几何形状的GREIT方法重建的图像更逼真。EIT图像质量的提高可能会促进EIT在常规临床应用中的接受度。
