Section of Oral Radiology, Department of Dentistry, Aarhus University, Aarhus, Denmark.
Dentomaxillofac Radiol. 2014;43(4):20130376. doi: 10.1259/dmfr.20130376. Epub 2014 Feb 3.
The aim of this study is to assess the variation in voxel value distribution in volumetric data sets obtained by six cone beam CT (CBCT) units, and the effect of time between exposures. Six CBCT units [Cranex(®) 3D (CRAN; Soredex Oy, Tuusula, Finland), Scanora(®) 3D (SCAN; Soredex Oy), NewTom™ 5G (NEWT; QR Srl, Verona, Italy), Promax(®) Dimax 3 (Planmeca Oy, Helsinki, Finland), i-CAT (Imaging Sciences International, Hatfield, PA) and 3D Accuitomo FPD80 (Morita, Kyoto, Japan)] were tested. Two volumetric data sets of a dry human skull embedded in acrylic were acquired by each CBCT unit in two sessions on separate days. Each session consisted of 20 exposures: 10 acquired with 30 min between exposures and 10 acquired immediately one after the other. CBCT data were exported as digital imaging and communications in medicine (DICOM) files and converted to text files. The text files were re-organized to contain x-, y- and z-position and grey shade for each voxel. The files were merged to contain 1 record per voxel position, including the voxel values from the 20 exposures in a session. For each voxel, subtractions were performed between Data Set 1 and the remaining 19 data sets (1 - 2, 1 - 3, etc) in a session. Means, medians, ranges and standard deviations for grey shade variation in the subtraction data sets were calculated for each unit and session. For all CBCT units, variation in voxel values was observed throughout the 20 exposures. A "fingerprint" for the grey shade variation was observed for CRAN, SCAN and NEWT. For the other units, the variation was (apparently) randomly distributed. Large discrepancies in voxel value distribution are seen in CBCT images. This variation should be considered in studies that assess minute changes in CBCT images.
本研究旨在评估六台锥形束 CT（CBCT）设备获得的容积数据集的体素值分布变化，以及两次曝光之间的时间影响。六台 CBCT 设备[Cranex（®）3D（CRAN；Soredex Oy，图苏拉，芬兰），Scanora（®）3D（SCAN；Soredex Oy），NewTom（TM）5G（NEWT；QR Srl，维罗纳，意大利），Promax（®）Dimax 3（Planmeca Oy，赫尔辛基，芬兰），i-CAT（Imaging Sciences International，哈特菲尔德，宾夕法尼亚州）和 3D Accuitomo FPD80（森田，京都，日本）]进行了测试。每个 CBCT 设备在两天的两个不同时间段分别对一个嵌入丙烯酸的干燥人颅骨进行了两次容积数据采集。每个时间段包括 20 次曝光：10 次曝光之间间隔 30 分钟，10 次曝光连续进行。CBCT 数据以数字成像和通信在医学（DICOM）文件中导出，并转换为文本文件。文本文件重新组织为包含每个体素的 x、y 和 z 位置和灰度阴影。这些文件合并为一个记录包含每个体素位置，包括一个时间段内 20 次曝光的体素值。对于每个体素，在一个时间段内，在数据集 1 和其余 19 个数据集（1-2、1-3 等）之间进行减法运算。对于每个单位和时间段，计算减法数据集中灰度阴影变化的平均值、中位数、范围和标准差。对于所有 CBCT 设备，在 20 次曝光过程中观察到体素值的变化。CRAN、SCAN 和 NEWT 观察到灰度阴影变化的“指纹”。对于其他设备，变化（显然）是随机分布的。在 CBCT 图像中看到体素值分布的大差异。在评估 CBCT 图像中的微小变化的研究中，应该考虑这种变化。
