Design and Development of a New Multi-Projection X-Ray System for Chest Imaging

Abstract

Overlapping anatomical structures may confound the detection of abnormal pathology, including lung nodules, in conventional single-projection chest radiography. To minimize this fundamental limiting factor, a dedicated digital multi-projection system for chest imaging was recently developed at the Radiology Department of Duke University. We are reporting the design of the multi-projection imaging system and its initial performance in an ongoing clinical trial. The system is capable of acquiring multiple full-field projections of the same patient along both the horizontal and vertical axes at variable speeds and acquisition frame rates. These images acquired in rapid succession from slightly different angles about the posterior-anterior (PA) orientation can be correlated to minimize the influence of overlying anatomy. The developed system has been tested for repeatability and motion blur artifacts to investigate its robustness for clinical trials. Excellent geometrical consistency was found in the tube motion, with positional errors for clinical settings within 1%. The effect of tube-motion on the image quality measured in terms of impact on the Modulation Transfer Function (MTF) was found to be minimal. The system was deemed clinic-ready and a clinical trial was subsequently launched. The flexibility of image acquisition built into the system provides a unique opportunity to easily modify it for different clinical applications, including tomosynthesis, correlation imaging (CI), and stereoscopic imaging.

Keywords: Chest radiography; correlation imaging; lung cancer; stereoscopy; tomosynthesis.

Fig. 1

Schematic of a new multi-projection x-ray imaging system capable of multiple oblique-angled acquisitions about the PA orientation for chest imaging. (a) top-view showing the system’s trajectory along horizontal axis, and (b) side-view showing motion along the vertical axis.

Fig. 2

Snapshot of the multi-projection x-ray imaging system installed at the Radiology Dept. of Duke University as applicable for chest radiography. Also shown are motion-regulating switches (indicated by arrows) to achieve iso-centric motion of the tube along vertical axis.

Fig. 3

Pictures of the multi-projections system depicting its trajectory along vertical (a–c) and horizontal axis (d–e). The tube motion is depicted via pictures of the tube at three different locations (PA and two extremities) along the two axes. Also shown is the angulated railing arrangement and the servo-motor coupling (pointed by the arrows in c & d) that enable the iso-centric motion of the tube along vertical and horizontal axes, respectively.

Fig. 4

Schematic of the interface developed to achieve synchronization of image acquisitions between the detector, x-ray generator and the positional coordinates of the moving x-ray tube. The corresponding timing diagram is shown in Fig. 5.

Fig. 5

Timing diagram for continuous acquisition. The system is capable of both step-and-shoot and continuous operations.

Fig. 6

Comparison of MTFs computed from images of an edge device acquired at PA orientation with the stationary tube and with the tube moving in the negative direction with a velocity 2.5 cm/sec (a), in the positive direction at 2.5 cm/sec (b), in the negative direction at 2.5 and 5 cm/sec (c), and at 2.5 cm/sec with exposure times of 5 and 10 ms (d).

Fig. 7

Example PA images of a complex thoracic phantom (Kyoto Kagaku. Co., Ltd, Kyoto, Japan) acquired with (a) and without (b) tube motion. The tube speed was fixed at 2.5 cm/sec corresponding to the speed used in our clinical trial. Anatomical details rendered in the image acquired with static tube are preserved in that acquired with the tube in motion, indicating minimal impact of tube motion on clinical image quality.

Fig. 8

Sample clinical images of three volunteers acquired at +3° (a), 0° (b), and −3° (c) about the PA orientation using a recently developed multi-projection chest imaging system. While the top row shows images of a healthy volunteer, the bottom two rows show subjects with lung nodules. The locations of the nodules were identified by a radiologist and are denoted by arrows. Most noteworthy is the relative displacement of lesion locations across different views. This information is used by multi-projection imaging technique to improve the accuracy of nodule detection.

Fig. 9

Tomosynthesis slices of the Kyoto thoracic phantom as a proof of concept for potential tomosynthesis application of the new multi-projection system. The precision in image acquisition of the system enabled tomosynthesis acquisition resulting in slices that rendered anatomical features in greater details.

Fig. 10

Stereoscopic display unit at Duke Laboratory that enables 3D rendition of medical images, such as chest x-rays.