1930年代后期发明的断层合成技术：概念：移动-叠加

1.1 Invention of Tomosynthesis in the Late 1930s

1.1 1930年代后期发明的断层合成技术

1.1.1 Concept: Shift and Add

Tomosynthesis addresses one of the primary weaknesses of conventional single-projection x-ray imaging, the superposition of objects in the image. This superposition may result in the obscuring of an object of interest and/or the production of pseudoobjects that mimic a disease (e.g., pseudomasses or a reduction in bone joint space). Tomosynthesis decreases superposition by generating slice images of the body from a series of projections taken at a variety of angles. In this sense, it is much like computed tomography (CT); however, instead of acquiring projections over 360° as in CT, the projections for tomosynthesis are acquired over a limited range of angles (e.g., 10° or 60°). The resulting tomosynthesis images have much better spatial resolution than CT within the slice, but poorer resolution in the depth direction, between the slices. The basic tomosynthesis principle is illustrated in Figure 1.1. A series of snapshot radiographs (films) are taken, each from a different viewing angle, as an x-ray tube translates across a patient. These snapshots are later combined by shifting the snapshots relative to one another and superimposing (adding) them to bring different planes within the patient in focus. Today, we use digital radiographs instead of films and more sophisticated reconstruction algorithms like those employed in CT instead of the “shift-and-add” technique.

Figure 1.1 illustration of the shift-and-add technique whereby the positions of images obtained at different angles (left) are shifted relative to one another and superimposed (added) to bring different planes (e.g., plane 1 and plane 2) within the object (patient) in focus (right).

1.1.1 概念：移动-叠加

断层合成解决了一个传统单投影X射线摄影的主要缺陷，即图像中物体的叠加。这种叠加可能导致目标物体的模糊和产生模仿病灶的伪对象（例如：假性瘤或骨关节间隙的缩小）。断层合成从一系列不同角度拍摄的投影中产生身体的切片图像，来减少重叠。从这个意义上来说，它很像计算机断层扫描（CT）。然而，不同于CT中采集360°的投影信息，断层合成的投照是在有限的角度范围内采集得到的（例如：10°或60°）。所得到的断层合成图像在每一层上空间分辨率远高于CT，但其每一层间深度方向的分辨率较差。断层合成的基本原理如图1.1所示。当X射线管在病人身上移动时，从不同的角度获得了一些列快速拍摄的照片。这些照片随后通过互相移动和叠加它们来组合，以使得患者的不同平面在焦点上。今天，我们使用数字X光摄影代替胶片，用类似CT中的更加复杂的重建算法代替“移动-叠加”技术。

图1.1 移动-叠加技术示意图，即通过不同角度上物体的位置相互移动和叠加，将不同平面（例如:平面1和平面2）置于对象（患者）的焦点内。