oscillation、down-the-barrel (end-on)？

Vertebral augmentation is typically performed with fluoroscopic guidance. High-quality fluoroscopy allows realtime, continuous monitoring of needle positioning and cement injection. Fixed fluoroscopic equipment is recommended over mobile C-arms due to higher image quality and lower risk of radiation exposure to the patient and practitioner. Biplane fluoroscopy (two perpendicular image detectors utilized simultaneously) is recommended, as it allows swift oscillation between imaging places without needing to move equipment or realign the projection.Image guidance strategies may be anteroposterior (AP) or ‘down-the-barrel’ (end-on). For the latter strategy, ipsilateral oblique rotation of the image intensifier places the needle tract and fluoroscopy beam parallel to each other.CT is a potential adjunctive tool for image guidance, particularly for the detection of small cement leaks due to its superior contrast resolution. However, it does not allow real-time monitoring of needle placement or cement injection [17, 18].

椎体充填扩张术通常需要在X线引导下进行。高质量的影像可以实时、连续地监测穿刺针定位和骨水泥注射。建议使用更高影像质量和较低辐射暴露的固定式透视设备而不是移动式C形臂。推荐使用可以满足影像位置之间的快速振荡，而无须移动设备或重新校正投影的双平面荧光透视（该透视同时使用2个垂直的图像探测器）。影像引导策略可以是“正位”或“上下”（头尾两端）。对于后一种策略，将影像增强器向同侧倾斜旋转使针道和透视光束彼此平行。CT 是影像引导的潜在辅助工具，由于其更优越的造影剂分辨率可用于微小骨水泥渗漏的检查。但CT 不允许用于实时监测针放置或骨水泥注射

oscillation、down-the-barrel’ (end-on)？怎么理解？谢谢