Urikura Atsushi, Ichikawa Katsuhiro, Hara Takanori, Nishimaru Eiji, Nakaya Yoshihiro
Department of Diagnostic Radiology, Shizuoka Cancer Center, 1007 Shimonagakubo, Nagaizumi, Sunto, Shizuoka, 411-8777, Japan,
Radiol Phys Technol. 2014 Jul;7(2):358-66. doi: 10.1007/s12194-014-0273-2. Epub 2014 Jun 1.
The purpose of our study was to investigate the validity of a spatial resolution measuring method that uses a combination of a bar-pattern phantom and an image-averaging technique, and to evaluate the spatial resolution property of iterative reconstruction (IR) images with middle-contrast (50 HU) objects. We used computed tomography (CT) images of the bar-pattern phantom reconstructed by the IR technology Adaptive Iterative Dose Reduction 3D (AIDR 3D), which was installed in the multidetector CT system Aquilion ONE (Toshiba Medical Systems, Otawara, Japan). The contrast of the bar-pattern image was set to 50 HU, which is considered to be a middle contrast that requires higher spatial resolution clinically. We employed an image-averaging technique to eliminate the influence of image noise, and we obtained averaged images of the bar-pattern phantom with sufficiently low noise. Modulation transfer functions (MTFs) were measured from the images. The conventional wire method was also used for comparison; in this method, AIDR 3D showed MTF values equivalent to those of filtered back projection. For the middle-contrast condition, the results showed that the MTF of AIDR 3D decreased with the strength of IR processing. Further, the MTF of AIDR 3D decreased with dose reduction. The image-averaging technique used was effective for correct evaluation of the spatial resolution for middle-contrast objects in IR images. The results obtained by our method clarified that the resolution preservation of AIDR 3D was not sufficient for middle-contrast objects.
我们研究的目的是探究一种空间分辨率测量方法的有效性，该方法结合了条形图案体模和图像平均技术，并评估具有中等对比度（50 HU）物体的迭代重建（IR）图像的空间分辨率特性。我们使用了由安装在Aquilion ONE多探测器CT系统（东芝医疗系统公司，日本大田原）中的IR技术自适应迭代剂量降低3D（AIDR 3D）重建的条形图案体模的计算机断层扫描（CT）图像。条形图案图像的对比度设置为50 HU，这被认为是临床上需要更高空间分辨率的中等对比度。我们采用图像平均技术来消除图像噪声的影响，并获得了具有足够低噪声的条形图案体模的平均图像。从这些图像中测量调制传递函数（MTF）。还使用传统的金属丝法进行比较；在该方法中，AIDR 3D显示出与滤波反投影相当的MTF值。对于中等对比度条件，结果表明AIDR 3D的MTF随着IR处理强度的增加而降低。此外，AIDR 3D的MTF随着剂量降低而降低。所使用的图像平均技术对于正确评估IR图像中中等对比度物体的空间分辨率是有效的。我们的方法所获得的结果表明，AIDR 3D对于中等对比度物体的分辨率保留是不够的。
