Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, New York 10065, USA.
Med Phys. 2013 Apr;40(4):041717. doi: 10.1118/1.4795336.
Methods of reducing respiratory motion blurring in cone-beam CT (CBCT) have been limited to lung where soft tissue contrast is large. Respiration-correlated cone-beam CT uses slow continuous gantry rotation but image quality is limited by uneven projection spacing. This study investigates the efficacy of a novel gated CBCT technique.
In gated CBCT, the linac is programmed such that gantry rotation and kV image acquisition occur within a gate around end expiration and are triggered by an external respiratory monitor. Standard CBCT and gated CBCT scans are performed in 22 patients (11 thoracic, 11 abdominal) and a respiration-correlated CT (RCCT) scan, acquired on a standard CT scanner, from the same day serves as a criterion standard. Image quality is compared by calculating contrast-to-noise ratios (CNR) for tumors in lung, gastroesophageal junction (GEJ) tissue, and pancreas tissue, relative to surrounding background tissue. Congruence between the object in the CBCT images and that in the RCCT is measured by calculating the optimized normalized cross-correlation (NCC) following CBCT-to-RCCT rigid registrations.
Gated CBCT results in reduced motion artifacts relative to standard CBCT, with better visualization of tumors in lung, and of abdominal organs including GEJ, pancreas, and organs at risk. CNR of lung tumors is larger in gated CBCT in 6 of 11 cases relative to standard CBCT. A paired two-tailed t-test of lung patient mean CNR shows no statistical significance (p = 0.133). In 4 of 5 cases where CNR is not increased, lung tumor motion observed in RCCT is small (range 1.3-5.2 mm). CNR is increased and becomes statistically significant for 6 out of 7 lung patients with > 5 mm tumor motion (p = 0.044). CNR is larger in gated CBCT in 5 of 7 GEJ cases and 3 of 4 pancreas cases (p = 0.082 and 0.192). Gated CBCT yields improvement with lower NCC relative to standard CBCT in 10 of 11, 7 of 7, and 3 of 4 patients for lung, GEJ, and pancreas images, respectively (p = 0.0014, 0.0030, 0.165).
Gated CBCT reduces image blurring caused by respiratory motion. The gated gantry rotation yields uniformly and closely spaced projections resulting in improved reconstructed image quality. The technique is shown to be applicable to abdominal sites, where image contrast of soft tissues is low.
在锥形束 CT（CBCT）中，减少呼吸运动模糊的方法仅限于软组织对比度较大的肺部。呼吸相关的锥形束 CT 使用缓慢的连续旋转机架，但图像质量受到不均匀的投影间距限制。本研究调查了一种新型门控 CBCT 技术的疗效。
在门控 CBCT 中，通过编程使旋转机架和千伏图像采集在门周围的呼气末期进行，并由外部呼吸监测器触发。对 22 例患者（11 例胸部，11 例腹部）进行标准 CBCT 和门控 CBCT 扫描，同一天从标准 CT 扫描仪获取的呼吸相关 CT（RCCT）扫描作为标准。通过计算肺、胃食管交界处（GEJ）组织和胰腺组织中肿瘤与周围背景组织的对比噪声比（CNR）来比较图像质量。通过计算 CBCT 图像与 RCCT 图像之间的优化归一化互相关（NCC），测量 CBCT 图像中的物体与 RCCT 图像中的物体之间的一致性。
与标准 CBCT 相比，门控 CBCT 可减少运动伪影，使肺肿瘤和腹部器官（包括 GEJ、胰腺和危险器官）的可视化效果更好。在 11 例中有 6 例肺肿瘤的门控 CBCT 的 CNR 大于标准 CBCT。对肺患者的平均 CNR 进行配对双侧 t 检验，无统计学意义（p = 0.133）。在 RCCT 中观察到肺肿瘤运动较小（范围 1.3-5.2mm）的 5 例中，肺患者的 CNR 没有增加。在有 >5mm 肿瘤运动的 6 例中有 6 例，CNR 增加且具有统计学意义（p = 0.044）。在 7 例肺、5 例 GEJ 和 3 例胰腺病例中，门控 CBCT 的 CNR 大于标准 CBCT（p = 0.082 和 0.192）。在 11 例、7 例和 4 例肺、GEJ 和胰腺患者中，门控 CBCT 的 NCC 相对于标准 CBCT 降低，改善程度分别为 10/11、7/7 和 3/4（p = 0.0014、0.0030 和 0.165）。
门控 CBCT 减少了呼吸运动引起的图像模糊。门控机架旋转产生均匀且紧密间隔的投影，从而提高了重建图像质量。该技术适用于软组织对比度较低的腹部部位。
