Byung-Youl Cha

Quantitative evaluation of mercuric iodide thick film for x-ray imaging device

In this paper, we investigated electrical characteristics of the X-ray detector of mercuric iodide (HgI2) film fabricated by PIB(Particle-In-Binder) Method with thicknesses ranging from approximately 200μm to 240μm. In the present study, using I-V measurements, their electrical properties such as leakage current, X-ray sensitivity, and signal-to-noise ratio (SNR),were investigated. The results of our study can be useful in the future design and optimization of direct active-matrix flat-panel detectors (AMFPD) for various digital X-ray imaging modalities.

Experimental evaluation of a-Se flat-panel X-ray detector for digital radiography

In this paper, the evaluation of a selenium-based flat-panel digital X-ray detector is described. The prototype detector has a pixel pitch of 139 mum and a total active imaging area of 14 inches times 8.5 inches, making up a total of 3.9 million pixels. Several quantitative parameters have been devised that correlate with the abilities of imaging devices to perform clinical tasks. The concepts of MTF, NPS, and DQE have been well described and are very useful descriptors of resolution, noise, and signal-to-noise ratio transfer ability. Such parameters (sensitivity, leakage current, MTF, NPS, DQE) were examined to evaluate the performance of this system. The sensitivity of 4.82 nC/mR/cm2 was measured at 10 V/mum, while leakage current was measured at 270 pA/cm2. The measured MTF at 2 lp/mm was 40%, and the DQE at 1.5 lp/mm was 16%

Quantitative evaluation of mercuric iodide and selenium for X-ray imaging device

Analog film/screen systems have been replaced with digital X-ray imaging devices using direct conversion materials. In this paper, mercuric iodide (HgI/sub 2/) and amorphous selenium (a-Se) films were deposited through the particle-in-binder (PIB) and physical vapor deposition (PVD) methods, respectively. Using the MCNP 4C code, the interaction of X-ray photons in HgI/sub 2/ and a-Se bulk, their transport, and transmitted energy spectrum of continuous X-ray, with total absorbed energy were simulated. Using I-V measurements, their electrical properties, such as leakage current, X-ray sensitivity, and signal-to-noise ratio (SNR), were investigated. The results of our study can be useful in the future design and optimization of direct active-matrix flat-panel detectors (AMFPD) for various digital X-ray imaging modalities.

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

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.

High resolution flat-panel X-ray detector for digital radiography

In this paper, the evaluation of a selenium-based flat-panel digital X-ray detector is described. The prototype detector has a pixel pitch of 139 /spl mu/m and a total active imaging area of 14 inches/spl times/8.5 inches, making up a total of 3.9 million pixels. Several quantitative parameters have been devised that correlate with the abilities of imaging devices to perform clinical tasks. The concepts of MTF, NPS, and DQE have been well described and are very useful descriptors of resolution, noise, and signal-to-noise ratio transfer ability. Such parameters (sensitivity, leakage current, MTF, NPS, DQE) were examined to evaluate the performance of this system. The sensitivity of 4.82 nC/mR/cm/sup 2/ was measured at 10 V//spl mu/m, while leakage current was measured at 270 pA/cm/sup 2/. The measured MTF at 2 lp/mm was 40%, and the DQE at 1.5 lp/mm was 16%.

X-ray response characterization of Y/sub 2/O/sub 2/S:Tb-CdS layered semiconductor

Phosphors coupled with photodetectors have been widely used in digital X-ray imaging applications. Some of the advantages of using phosphor films include X-ray conversion efficiency, spatial resolution, and integration with the imaging array. In this paper, the experimental studies of the Y/sub 2/O/sub 2/S:Tb synthesis, deposition, and characterization are reported on. Y/sub 2/O/sub 2/S:Tb powder was characterized in terms of scanning electron microscopy (SEM), X-ray diffraction (XRD), luminescence spectroscopy, and X-ray conversion efficiency. In addition, a Y/sub 2/O/sub 2/S:Tb layer was formed on cadmium sulphide (CdS) for the hybrid X-ray detector structure. The evaluation of the Y/sub 2/O/sub 2/S:Tb-CdS detector was performed by determining the leakage current, X-ray sensitivity, and linearity with respect to X-ray exposure dose. The results of the study made on the two-layered detector are compared with those from a conventional amorphous selenium (a-Se) detector.

Synthesis and luminescence characterization of fine gadolinium oxide phosphors for high resolution X-ray imaging

In this work, fine Gd/sub 2/O/sub 3/:Eu powder was synthesized using a solution-combustion method for high-resolution digital X-ray imaging detectors. The structure of the phosphors was characterized by X-ray diffraction (XRD), high-resolution scanning electron microscopy (HR-SEM). It was possible to obtain fine Gd/sub 2/O/sub 3/:Eu crystallized particles with an average particle size of only 20 nm. The optical properties investigated were photoluminescence emission and excitation spectra, luminescence decay time, and X-ray conversion efficiency. The emission corresponding to the /sup 5/D/sub 0//spl rarr//sup 7/F/sub 2/ transition at 610 nm was dominant, and the Eu/sup 3+/ ions substituted well for the Gd/sup 3+/ sites. Quenching starts at an europium concentration of 8% wt, and the strongest X-ray conversion efficiency was achieved at the phosphor with 5% wt. The mean lifetime of synthesized phosphors is 2.3-2.6 ms.