Reduction of cervical vertebra ghost images in panoramic radiography using vertical dual exposure

Abstract

Purpose: To evaluate the image quality of vertical dual-exposure panoramic radiography (PR), which merges two PR images taken at different focus heights to reduce ghost images of cervical vertebrae (CV) and intervertebral spaces (IVS) in the incisor region. Methods: PR images of an aluminum block, a CV phantom and a human head phantom were taken at 0 mm and merged with and subtracted from PR images taken at other heights (0, 5, 10, 15, and 20 mm) to create new images, e.g., Merg 0 + 15 mm and Sub 0 − 10 mm . The subtracted images were analyzed subjectively according to the uniformity on the line profile. Merged images were evaluated subjectively by six raters to determine the influence of the ghost images. Results: Objective evaluation revealed a positional shift in the ghost images according to the height of the focus for both phantoms. In the subjective evaluation, the normal PR (Merg 0 + 0 mm ) showed the worst score, indicating strong influence of CV and IVS ghost images. Conclusion:The vertical dual-exposure PR method, which merges PR images taken at the normal position and a higher X-ray focus, can reduce CV and IVS ghost images in the incisor region.

Vertical magnification correction in vertical dual-exposure panoramic radiography

“…In particular, when the ghost image of the IVS overlapped the apex of the incisors, periapical lesions were sometimes difficult to diagnose. Kato et al [11] proposed vertical dual-exposure PR as a method to reduce ghost imaging of the cervical vertebrae and IVS. In this method, PR images are taken twice with the X-ray focus at different heights, and these images are merged.…”

“…To solve the problem of ghost images of the IVS overlapping the incisors, Kato et al [11] proposed the vertical dual-exposure PR method. In this method, the first PR is taken in a conventional position, and the second is taken with the X-ray focus raised by 5 to 20 mm.…”

“…The two PR images taken with the X-ray focus at different heights are then merged by the least squares method. Kato et al [11] concluded that the vertical dual-exposure PR method can reduce the negative effects of ghost images of the cervical vertebrae and IVS.…”

“…However, when the X-ray focus is raised, the image of the incisors is vertically distorted because of the change in the angle of the incident X-ray beam to the incisors compared with the conventional position. Vertical dual-exposure PR therefore provides a poor merged image when there is a large difference in the length of the incisors between the two PR images [11]. Alternatively, the length of the incisors on PR depends on the tilt of the incisors in the labio-palatal direction because the magnification of the incisor varies as the distance between the incisal edge and the X-ray focus differs from the distance between the apex of the incisor and the X-ray focus in both conventional PR and vertical dual-exposure PR.…”