Estimating rotation angle from asymmetric projection of chest

Article type: Research Article

Authors: Wu, Zhonghang^{a; b} | Hou, Pengfei^c | Li, Wei^d | Zhu, Tianbao^e | Wang, Peipei^f | Yuan, Mingyuan^{f; *} | Sun, Jiuai^{d; *}

Affiliations: [a] Department of Scientific Research, Shanghai University of Medicine and Health Sciences Affiliated Zhoupu Hospital, Shanghai, China | [b] Shanghai Key Laboratory of Molecular Imaging, Shanghai University of Medicine and Health Sciences, Shanghai, China | [c] School of Medical Instrument and Food Engineering, University of Shanghai for Science and Technology, Shanghai, China | [d] School of Medical Imaging, Shanghai University of Medicine and Health Sciences, Shanghai, China | [e] Shanghai Shanghe Intelligent Technology Co., Ltd., Shanghai, China | [f] Department of Radiology, Shanghai University of Medicine and Health Sciences Affiliated Zhoupu Hospital, Shanghai, China

Correspondence: [*] Corresponding authors. Mingyuan Yuan, Department of Radiology, Shanghai University of Medicine and Health Sciences Affiliated Zhoupu Hospital, Shanghai, 201318, China. E-mail: [email protected]. and Jiuai Sun, School of Medical Imaging, Shanghai University of Medicine and Health Sciences, Shanghai 201318, China. E-mail: [email protected].

Abstract: BACKGROUND:Manual or machine-based analysis of chest radiographs needs the images acquired with technical adequacy. Currently, the equidistance between the medial end of clavicles and the center of spinous processes serves as the only criterion to assess whether a frontal PA chest radiograph is taken with any rotation. However, this measurement is normally difficult to implement because there exists overlapping of anatomies within the region. Moreover, there is no way available to predict exact rotating angles even the distances were correctly measured from PA chest radiographs. OBJECTIVE:To quantitatively assess positioning adequacy of PA chest examination, this study proposes and investigates a new method to estimate rotation angles from asymmetric projection of thoracic cage on radiographs. METHOD:By looking into the process of radiographic projection, generalized expressions have been established to correlate rotating angles of thorax with projection difference of left and right sides of thoracic cage. A trunk phantom with different positioning angles is employed to acquire radiographs as standard reference to verify the theoretical expressions. RESULTS:The angles estimated from asymmetric projections of thoracic cage yield good agreement with those actual rotated angles, and an approximate linear relationship exists between rotation angle and asymmetric projection of thoracic cage. Under the experimental projection settings, every degree of rotation corresponds to the width difference of two sides of thoracic cage around 13–14 pixels. CONCLUSION:The proposed new method may be used to quantify rotating angles of chest and assess image quality for thoracic radiographic examination.

Keywords: Technical adequacy, PA chest images, rotation angle of thorax, asymmetric radiographic projection, thoracic cage

DOI: 10.3233/XST-210990

Journal: Journal of X-Ray Science and Technology, vol. 29, no. 6, pp. 1139-1147, 2021