Search

The purpose of this work is to investigate the factors determining the magnitude and nature of the lag effect (residual signal) in the Varian PaxScan 4343CB flat-panel detector. Depending on the detector mode, typical value of residual signal is 1-2% after single exposed frame, increasing up to 3% after multiple exposures. The lag effect is the cause of up to 3.6% error of average flat-field signal measurement if used for averaging series of continuously exposed frames, which leads to incorrect assessment of X-ray attenuation coefficients. Spatial dependence of the lag effect is confirmed; the results of correction of projection images using spatially localized impulse response functions are demonstrated.

The shape and size of the projection of the focal spot of an x-ray tube largely depend on the direction of the beam, which results in a spatial difference of the point spread function (PSF) of the imaging system. A model developed for determining the PSF at an arbitrary point of the radiation field is presented in this article. The input data for the model are the geometric parameters of the system, the measured magnified projection of the effective focal spot, and the PSF in the internal structure of the detector. The difference in the width of the profiles of the PSF between the experimental and modeled data does not exceed 7.2%. The projection images are reconstructed by means of a deconvolution algorithm using the modeled PSF. The frequency–contrast characteristics of the images show improvement compared with the initial image.

A system currently under development for remote radiotherapy based on a 6 MeV linac and cone-beam computer tomograph is presented. Its distinguishing design features and solutions are described: compact 5-cm wavelength electron accelerator, solid-state modulator, visualization in the bremsstrahlung beam with low nominal energy 2.5 MeV, bremsstrahlung beam without a compensating filter, cone-beam computer tomography, multi-leaf collimator, adaptive radiotherapy, and a therapeutic table with six degrees of freedom. The system is compared with foreign analogs.

Main parameters of digital flat panel detectors, to be taken into account in developing imaging systems are considered. Various factors affecting obtained images are presented. Experimental results presented confirm the necessity of image correction.

The online version of the original article can be found at https://doi.org/10.1007/s10512-019-00490-9