Contrast enhancement of EPID images via difference imaging: a feasibility study

Abstract

In this study, the feasibility of difference imaging for improving the contrast of electronic portal imaging device (EPID) images is investigated. The difference imaging technique consists of the acquisition of two EPID images (with and without the placement of an additional layer of attenuating medium on the surface of the EPID) and the subtraction of one of these images from the other. The resulting difference image shows improved contrast, compared to a standard EPID image, since it is generated by lower-energy photons. Results of this study show that, firstly, this method can produce images exhibiting greater contrast than is seen in standard megavoltage EPID images and secondly, the optimal thickness of attenuating material for producing a maximum contrast enhancement may vary with phantom thickness and composition. Further studies of the possibilities and limitations of the difference imaging technique, and the physics behind it, are therefore recommended.

Enhancement of megavoltage electronic portal images for markerless tumor tracking

“…However, amplification of noise is also observed. Noise has been reported to be increased slightly during contrast improvement and deblurring, and incorporation of another filter was suggested to limit artifacts 29, 30. In our study, however, the increase of noise was neglected to simulate the minimal processing time, and noise influence on image interpretation was marginal.…”

Electronic portal image enhancement based on nonuniformity correction in wavelet domain

“…Among the reviewed studies, improving the quality of the portal images has led to very good results by the modification of the detector configuration. 15,16 However, for EPIDs that have been clinically commissioned, the detectors modification is not practical due to the high cost and operational difficulty. 1 So far, many studies have been performed on the enhancement of portal images in spatial and frequency domains.…”

“…14 Moreover, some studies focused on the development of high detective quantum efficiency (DQE) detector configurations, which may improve quality of EPID imaging. As an example, Kairn et al 15 inserted an additional attenuating layer on the surface of the detector to reduce the photon's energy.…”

Contrast enhancement for portal images by combination of subtraction and reprojection processes for Compton scattering

“…The portal images with and without the proposed image processing were evaluated by the image contrast profile C ( x , y ) that was used by Kairn et al16 C ( x , y ) was calculated by the following equation:$Cfalse(x,yfalse)=\frac{Pfalse(x,yfalse)-P_{\mathrm{normalref}}}{P_{\mathrm{ref}}},$where P ref is the mean signal of the reference region that is indicated as a square in Fig. 3(a).…”