Feasibility study of a multi-layer liquid-crystal-based non-pixel X-ray detector

Abstract

The recent study of digital X-ray detectors in medical diagnostics has focused on high-resolution image acquisition. Digital X-ray detectors use either a direct or an indirect method of converting X-ray into an electric charge. Indirect systems have low resolution due to blurring of light from the scintillator. In contrast, direct systems have higher resolution than indirect systems, but they are expensive, and systems that have large areas are difficult. This paper proposes a new structure for a non-pixel detector in order to resolve these problems by constructing multiple layers, including photoconductor and liquid crystal (LC) cell layers. First, simulations were conducted to measure changes in the transmittance and electric field of the LC cell under different applied voltages and different thicknesses of a glass layer between the LC and the photoconductor. Subsequently, non-pixel X-ray films having an optimized structure were fabricated using the optimal glass thickness and voltage obtained from the simulation results. In a previous study, X-ray film was fabricated from an LC and a photoconductor by a single integrated production process. In this study, the fabrication process was divided into two steps to prevent damage to the X-ray conversion materials caused by the high temperature used to manufacture the LC cell. The photoconductor layer was fabricated by screen-printing at room temperature on the LC cell. HgI2 was used as the photoconductor material and an aluminum reflective layer was then deposited. The photoconductor was approximately 150–250μm thick. The linear range of LC twisting was acquired by measuring the transmittance-voltage curve; when a voltage of 1.3V to 2.2V is applied to the LC layer, the LC molecules can be twisted by 10%–90%. The charge generated in the photoconductor and the transmission efficiency of the LC were measured using the modulation potential. The results of this study indicate that an LC-based non-pixel detector is feasible for application in digital X-ray systems.