间歇式屏气CBCT图像采集优选模式研究

目的 旨在建立一种实用型间歇式屏气CBCT图像采集优选模式。方法 利用自制呼吸运动模型模拟肿瘤患者膈肌附近肿块在屏气和自由呼吸状态下的运动情况并行CBCT扫描。扫描模式有常规屏气CBCT扫描(主要分为屏气间隙暂停扫描、进行自由呼吸、自由呼吸不计入扫描过程)及间歇式屏气CBCT扫描Ⅰ型和Ⅱ型(主要分为若干个屏气和自由呼吸时段,以近3∶1比例作间歇式调配并一次完成扫描),将常规屏气CBCT扫描作为标准技术,与2种间歇式屏气CBCT扫描就图像质量及使用该图像实现三维配准的精度进行量化比较分析。间歇式屏气CBCT图像质量参数与常规屏气CBCT图像行配对t检验。结果 2种间歇式屏气CBCT图像均产生运动伪影,其重建像素值与常规扫描相比较为一致(P>0.05),均匀性无明显改变(P=0.02、0.53),但图像信噪比分别减少30%和60%(P<0.05)。图像配准误差除上下方向最大为0.4 cm以外,其余均在0.1 cm以内。结论 在体模研究阶段,间歇式屏气CBCT扫描图像采集模式并未明显降低图像质量和配准精度,其实际临床的可行性还需在大量患者身上进一步得到验证。

Investigation of image guidance strategy for intermittent breath-hold cone beam CT

Objective To develop a practical image acquisition strategy using intermittent breath-hold cone beam computed tomography (CBCT). Methods A breathing phantom was used to simulate the movement of tumor near the diaphragm during free breathing and breath hold and scanned by conventional breath-hold CBCT and type Ⅰ/Ⅱ intermittent breath-hold CBCT. In the conventional breath-hold CBCT, scan paused and free breathing occurred at the break of breath hold and free breathing was not included in the scan. In the intermittent breath-hold CBCT, one scan covered several breath holds separated by free breathing in a ratio of 3 vs1. Image quality and three-dimensional registration accuracy were quantitatively compared between conventional breath-hold CBCT and type Ⅰ/Ⅱ intermittent breath-hold CBCT. Comparison of image quality parameters between conventional breath-hold CBCT and intermittent breath-hold CBCT was made by paired t test. Results Motion artifacts arose in type I and Ⅱ intermittent breath-hold CBCT scans. There were no significant differences in the reconstructed pixel value or uniformity between intermittent breath-hold CBCT and conventional breath-hold CBCT (P>0.05, and P=0.02,0.53). Compared with conventional breath-hold CBCT images, the signal-to-noise ratios of type I and Ⅱ intermittent breath-hold CBCT images were reduced by 30% and 60%, respectively (P<0.05). The registration errorwas up to 0.4 cm in the anterior-posterior direction and less than 0.1 cm in other directions. ConclusionsThe phantom study shows that intermittent breath-hold CBCT does not significantly reduce image quality or registration accuracy compared with conventional breath-hold CBCT. The feasibility of intermittent breath-hold CBCT in clinical application needs to be further validated among a large number of patients.