Medical X-ray Detectors Research Articles

Perovskite-Based X-ray Detectors.

X-ray detection has widespread applications in medical diagnosis, non-destructive industrial radiography and safety inspection, and especially, medical diagnosis realized by medical X-ray detectors is presenting an increasing demand. Perovskite materials are excellent candidates for high-energy radiation detection based on their promising material properties such as excellent carrier transport capability and high effective atomic number. In this review paper, we introduce X-ray detectors using all kinds of halide perovskite materials along with various crystal structures and discuss their device performance in detail. Single-crystal perovskite was first fabricated as an active material for X-ray detectors, having excellent performance under X-ray illumination due to its superior photoelectric properties of X-ray attenuation with μm thickness. The X-ray detector based on inorganic perovskite shows good environmental stability and high X-ray sensitivity. Owing to anisotropic carrier transport capability, two-dimensional layered perovskites with a preferred orientation parallel to the substrate can effectively suppress the dark current of the device despite poor light response to X-rays, resulting in lower sensitivity for the device. Double perovskite applied for X-ray detectors shows better attenuation of X-rays due to the introduction of high-atomic-numbered elements. Additionally, its stable crystal structure can effectively lower the dark current of X-ray detectors. Environmentally friendly lead-free perovskite exhibits potential application in X-ray detectors by virtue of its high attenuation of X-rays. In the last section, we specifically introduce the up-scaling process technology for fabricating large-area and thick perovskite films for X-ray detectors, which is critical for the commercialization and mass production of perovskite-based X-ray detectors.

Contemporary review of commercially available medical X-ray detectors

Contemporary review of commercially available medical X-ray detectors

Spectral response tuning of organic photodetectors using strong microcavity effects for medical X-ray detector application

An X-ray detector system was fabricated with an organic small molecule photodetector and a terbium-doped gadolinium oxysulfide (Gd2O2S:Tb) scintillating screen. Though the microsphere cluster structure of the Gd2O2S film had advantage in low material cost, wavelength matching to the proper photodetector is challenging due to its scintillating performance property in the relatively narrow emission spectrum range. To tune the absorption spectrum of the organic photodetector to that of the emission spectrum of the Gd2O2S, a microcavity effect was applied by controlling the thickness of the C60 layer. The peak wavelength of the absorption spectrum was tuned over a broad region of wavelengths, from 461 nm to 776 nm. The fabricated X-ray detector system was demonstrated in a medical X-ray radiography system.

Effect of X-ray irradiation on a-IGZO and LTPS thin-film transistors for radiography applications

The effects of X-ray irradiation on amorphous indium-gallium-zinc oxide (a-IGZO) and low-temperature polysilicon (LTPS) thin-film transistors (TFTs) were investigated. A comparison of the electrical characteristics of the TFTs at different stages of exposure to X-rays was conducted. After X-ray irradiation, the a-IGZO TFTs maintained their performance, while the LTPS TFTs showed considerable performance degradation. A distinct negative threshold voltage shift occurred in the LTPS TFTs under X-ray irradiation. In addition, the electrical parameters including mobility, subthreshold swing and off-current were significantly deteriorated. In addition, the binding energy shift of Si 2p peaks in the phase transition region of the interlayer between Si and SiO2 was confirmed by XPS depth profile analysis. This result indicates that permanent damage to the LTPS crystalline structure was induced under X-ray exposure. Under the same doses of X-ray irradiation, the a-IGZO film did not exhibit any notable change, indicating the tolerance of a-IGZO to X-ray irradiation. Therefore, we expect a-IGZO to be applied in the active matrix backplane of medical X-ray detectors for use for prolonged periods of time. This work not only provides systemic studies on the effects of X-rays on semiconductor materials but also proposes an alternative material to highly endurable X-ray detectors.

Spray printing of organic semiconducting single crystals.

Single-crystal semiconductors have been at the forefront of scientific interest for more than 70 years, serving as the backbone of electronic devices. Inorganic single crystals are typically grown from a melt using time-consuming and energy-intensive processes. Organic semiconductor single crystals, however, can be grown using solution-based methods at room temperature in air, opening up the possibility of large-scale production of inexpensive electronics targeting applications ranging from field-effect transistors and light-emitting diodes to medical X-ray detectors. Here we demonstrate a low-cost, scalable spray-printing process to fabricate high-quality organic single crystals, based on various semiconducting small molecules on virtually any substrate by combining the advantages of antisolvent crystallization and solution shearing. The crystals' size, shape and orientation are controlled by the sheer force generated by the spray droplets' impact onto the antisolvent's surface. This method demonstrates the feasibility of a spray-on single-crystal organic electronics.

Growth of Polycrystalline Cd0.8Zn0.2Te Thick Films for X-Ray Detectors

Cd 1-x Zn x Te is known as promising medical X-ray detector material but CdZnTe as a single crystal is not available in large sizes. As an alternative to single crystal, CdZnTe thick film was grown by vacuum thermal evaporator to 100 μm thickness. The characteristics of thick films were analyzed by XRD, EDS, SEM and current-voltage measurements. Zn composition is x = 0.2 and resistivity is higher than 10 9 Ω cm.

Requirements on amorphous semiconductors for medical X-ray detectors

Solid state X-ray detectors based on large-area amorphous semiconductors, such as amorphous silicon or selenium, have been developed. The requirements for various applications in medical diagnosis determine the boundary conditions for different detectors. Key parameters are image-receptor size, spatial resolution, image frequency, signal-to-noise ratio, and long-term stability. Conventional thorax radiographs are 43×35 cm2 in size. Therefore, to replace film, large detectors are required. Mammograms need to display microcalcifications of some 100 μm in detail. Fluoroscopic images are taken at a rate of 30 images/s, or even faster. Moreover, all detectors need to deliver optimum image quality at the lowest tolerable dose. The lifetime should be at least 10 years. In this paper we discuss different types of detectors that could fulfill those needs. Two fundamental concepts are compared: a scintillator coupled to a photodiode and a direct converting semiconductor, both being arranged on an amorphous silicon-switching matrix.

Requirements on amorphous semiconductors for medical X-ray detectors

Solid state X-ray detectors based on large-area amorphous semiconductors such as amorphous silicon or selenium have been developed. The requirements for various applications in medical diagnosis determine the boundary conditions for different detectors. Key parameters are image receptor size, spatial resolution, image frequency, signal-to-noise ratio and long-term stability. Conventional thorax radiographs are 43×35 cm 2 in size. Therefore, to replace film, large detectors are required. Mammograms need to display microcalcifications of some 100 μm in detail. Fluoroscopic images are taken at a rate of 30 images/s or even faster. Moreover, all detectors need to deliver optimum image quality at the lowest tolerable dose. The lifetime should be at least 10 years. In this paper we discuss different types of detectors that could fulfill those needs. Two fundamental concepts are compared: A scintillator coupled to a photodiode and a direct converting semiconductor, both being arranged on an amorphous silicon switching matrix.

Calculation of inelastic cross-sections for the interaction of electrons with amorphous selenium

Research into medical x-ray detectors based on amorphous selenium (a-Se) has seen a resurgence lately due to the advent of flat-panel active matrix technology. There is presently no quantitative theory, however, to explain the signal formation due to the interaction of ionizing radiation with a-Se. One of the main obstacles in the characterization of this process is the lack of suitable interaction cross-sections. In this work we develop an expression for the calculation of inelastic electron cross-sections from a dipole oscillator strength distribution, which includes relativistic and exchange effects. We construct the oscillator strength distribution from known experimental results and calculate the total and cumulative differential cross-sections for incident electron energies ranging from a few eV to 23 MeV. The total cross-section agrees with that of isolated Se atoms at high energies, as expected, and provides the low energy cross-sections which depend on the dielectric properties of the amorphous state. From these cross-sections, Monte Carlo codes can be developed which simulate the creation of individual electron-hole pairs, which will lead to a better understanding of the signal-formation process in a-Se based x-ray detectors.

Ceramic innovations in the 20th century

Ceramic innovations in the 20th century

An evaluation of the Y2O3:Eu3+ scintillator for application in medical x-ray detectors and image receptors.

The suitability off a Y2O3:Eu3+ scintillator for use in radiation detectors and medical image receptors was studied. Y2O3:Eu3+ was used in the form of laboratory prepared screens of different coating thicknesses. The x-ray luminescence efficiency of the screens was measured for tube voltages between 50-200 kVp and in both transmission and reflection modes of observation. The intrinsic x ray to light conversation efficiency (nc) and other parameters of the Y2O3:Eu3+ phosphor material related to optical scattering, absorption, and reflection were determined. These were used in the calculation of the image transfer characteristics, MTF and zero frequency DQE, for various screen coating thicknesses and x-ray tube voltages. The light emission spectrum of Y2O3:Eu3+ was measured (narrow band peak at 613 nm) and its spectral compatibility to the spectral sensitivity of several commonly employed optical photon detectors was determined. The x-ray luminescence efficiency varied with x-ray tube voltage, attaining maximum value at about 80 kVp for all screen thicknesses. It also varied with coating thickness reaching 25 microW m(-2)/mR s(-1) and 18 microW m(-2)/mR s(-1) at 175 mg/cm2 for reflection and transmission modes, respectively. The intrinsic x ray to light conversion efficiency and the image transfer characteristics were found to be comparable to several commercially used phosphors: nc = 0.095, MTF0.05 ranged between 10 and 25 line pairs per mm and peal values of DQE(0) varied between 0.33 and 0.14 in the coating thickness and kVp ranges useful for x-ray imaging. Spectral compatibility to some red sensitive optical photon detectors was excellent (0.9 or better). Results indicated that Y2O3:Eu3+ is a medium to high overall performance material that could be used in medical x-ray detectors and image receptors.