TITLE:
Detection of Spherical Gold Fiducials in kV X-Ray Images Using Intensity-Estimation-Based Method
AUTHORS:
Masaki Kokubo, Masahiro Yamada, Akira Sawada, Nobutaka Mukumoto, Yuki Miyabe, Takashi Mizowaki, Masahiro Hiraoka
KEYWORDS:
Fiducial Marker Detection, Intensity Estimation
JOURNAL NAME:
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology,
Vol.7 No.1,
February
28,
2018
ABSTRACT: Fiducial
marker detection algorithms in kilovoltage x-ray images using physical
characteristics of transmission x-ray have been proposed. It, however, has been
suggested recently that factors besides transmission x-ray affect x-ray images.
The purpose of this study was to develop a new fiducial detection algorithm using
fiducial intensity estimation based on physical characteristics of x-ray images
with gold fiducials. First, x-ray images of a fiducial on a water-equivalent
phantom were acquired. It was observed that the ratio of background to fiducial
intensity in the images decreased as phantom thickness increased. Based on the
negative correlation, we identified a function for estimating fiducial
intensity that consists of background intensity and the amount of scattered
radiation by the other x-ray source of an orthogonal imaging system and a
treatment beam. Then, we developed an algorithm that extracts fiducial
candidates using the estimation function. Its performance was measured using
x-ray images which had 3824 fiducials altogether. The average number of
false-positive detection of the proposed algorithm in single image was
one-tenth of an algorithm considering only transmission x-ray. The proposed
algorithm detected 99.5% of all fiducials under an error of 1.0 mm, while the
other algorithm detected 94.7% or less (Clinical
trial number: UMIN000005324).