Vogel Wouter V, van Dalen Jorn A, Schinagl Dominic A X, Kaanders Johannes H A M, Huisman HenkJan, Corstens Frans H M, Oyen Wim J G
Department of Nuclear Medicine, Radboud University Nijmegen Medical Centre, The Netherlands.
Nucl Med Commun. 2006 Jun;27(6):515-9. doi: 10.1097/00006231-200606000-00007.
Clinical work in software positron emission tomography/computed tomography (PET/CT) image fusion has raised suspicion that the image sizes of PET and CT differ slightly from each other, thus rendering the images suboptimal for image fusion. The aim of this study was to evaluate the extent of the relative image size difference between PET and CT and the impact of the correction of this difference on the accuracy of image fusion.
The difference in real image size between PET and CT was evaluated using a phantom study. Subsequently, 13 patients with cancer in the head/neck area underwent both CT and [(18)F]fluorodeoxyglucose PET in a custom-made mask for external beam radiotherapy, with multimodality markers for positional reference. The image size of PET relative to CT was determined by evaluating the distances between the markers in multiple directions in both scans. Rigid-body image fusion was performed using the markers as landmarks, with and without correction of the calculated image size difference.
Phantom studies confirmed a difference in real image size between PET and CT, caused by an absolute error in PET image size calibration. The clinical scans demonstrated an average relative difference in image size of 2.0% in the transverse plane and 0.8% along the longitudinal axis, the PET images being significantly smaller. Image fusion using original images demonstrated an average registration error of 2.7 mm. This error was decreased to 1.4 mm after size correction of the PET images, a significant improvement of 48% (P<0.001).
A significant deviation in PET image size may occur, either as a real image size deviation or as a relative difference from CT. Although possibly not clinically relevant in normal diagnostic procedures, correction of such a difference benefits image fusion accuracy. Therefore, it is advisable to calibrate the PET image size relative to CT before performing high-accuracy rigid-body image fusion.
软件正电子发射断层扫描/计算机断层扫描（PET/CT）图像融合的临床工作引发了一种怀疑，即PET和CT的图像大小彼此略有不同，从而使图像在用于图像融合时并非最优。本研究的目的是评估PET和CT之间相对图像大小差异的程度以及校正这种差异对图像融合准确性的影响。
使用体模研究评估PET和CT之间实际图像大小的差异。随后，13例头颈部癌症患者在定制的用于外照射放疗的面罩中接受了CT和[（18）F]氟脱氧葡萄糖PET检查，并使用多模态标记物进行位置参考。通过评估两次扫描中多个方向上标记物之间的距离来确定PET相对于CT的图像大小。使用标记物作为地标进行刚体图像融合，分别在不校正和校正计算出的图像大小差异的情况下进行。
体模研究证实PET和CT之间实际图像大小存在差异，这是由PET图像大小校准中的绝对误差引起的。临床扫描显示，在横断面中图像大小的平均相对差异为2.0%，沿纵轴为0.8%，PET图像明显较小。使用原始图像进行图像融合显示平均配准误差为2.7毫米。在对PET图像进行大小校正后，该误差降至1.4毫米，显著改善了48%（P<0.001）。
PET图像大小可能会出现显著偏差，既可能是实际图像大小偏差，也可能是与CT的相对差异。尽管在正常诊断程序中可能与临床无关，但校正这种差异有利于提高图像融合的准确性。因此，在进行高精度刚体图像融合之前，建议对PET图像大小相对于CT进行校准。
