KEYWORDS: Modulation transfer functions, Radiography, X-rays, Sensors, Algorithm development, Detection and tracking algorithms, Edge detection, Tungsten, Medical physics, Medical imaging
We have developed a novel method to measure the presampling modulation transfer function (MTF) in digital radiography systems using a novel edge device and algorithm. It can simultaneously measure the presampling MTFs in horizontally and vertically by utilizing its four edges. Calculation algorithm is composed of six steps, which are detection of edge, determination of angle, differentiation, composition of line spread function (LSF), fast Fourier transform (FFT) and sinc correction, respectively. Verification of the accuracy was conducted comparing with the established slit method. The repeatability of the measurement and the dose dependence was also examined. The measured MTF of edge device was coincident to that of slit within 0.02 up to the Nyquist frequency (3.125 cycles/mm). The repeatability was within 0.002 up to the Nyquist frequency. It is also confirmed that the result is not affected by the alignment error against the x-ray axis. In conclusion, an accurate and feasible method to measure the presampling MTF was established using a novel edge test device and algorithm.
We have developed a novel flat-panel detector with CsI:Tl scintillator. The detector consists of a single piece 43cm x 43cm amorphous silicon thin-film transistor (TFT) array with MIS (metal-insulator-semiconductor) photoelectric converter having a pixel pitch of 160μm coated with a needle-like crystal CsI:Tl scintillator. Signal chain was totally revised from current detector utilizing an innovative sensor technology. The novel detector and current detector were equipped to a digital radiography system allowing a quantitative and comparative study. Results show that the novel detector has a linear response covering the radiographic exposure range. It has a moderate modulation transfer function (MTF) sufficient to the radiography tasks and effective to suppress the aliasing. The detective quantum efficiency (DQE) was almost twice than the current detector. The result of contrast-detail phantom exposed with a 1/2x dose level is equivalent to that of current detector with a 1x dose level. These results show that performance of novel detector is superior to and expected to reduce the patient dose in half than current detector due to higher DQE and innovative sensor technology.
The low x-ray exposures used in fluoroscopic applications (0.1 - 10mR at the sensor surface) mean that the requirements for sensor gain and noise are particularly strict. The achievable DQE is determined by a number of factors, including the sensor quantum efficiency, x-ray absorption Swank factor, secondary quanta conversion efficiency, internal gain (e.g. the number of electrons collected per visible photon produced in the phosphor), and additive noise. The influence of these factors is examined for three direct detection x-ray sensors (PbI2, a-Se and GaAs), and one indirect detector sensor (CsI). Although the characteristics of these sensors are very different, it is demonstrated that all are appropriate for use in fluoroscopic applications as a replacement for current image intensifier based systems.
The design, development and evaluation of a portable x-ray detector are described. The completed detector has a pixel pitch of 100 micrometers , an active imaging area of 22.5 x 27.5 cm2 (9 x 11 inch2), package outer dimensions of 32.5 x 32.5 cm2, a thickness of only 20 mm, and a weight of around 2.8 kg. A number of significant advances in the design and production processes were needed to produce such a compact detector with such a small pixel pitch, while maintaining the image quality achieved a current detector (CXDI-22) which has a 160 mm pixel pitch. These include the development of a low power readout IC, advances in detector packaging design, concentrating on lightweight and strong components, and redesign of the pixel structure to improve the fill-factor. A comparison is made of the imaging characteristics of this new detector with the CXDI-22 detector, and it is shown that the new detector demonstrates improved CTF, and NEQ. The new detector is also shown to demonstrate superior performance in a contrast-detail phantom evaluation. This new detector should be useful for limb and joint examinations as it offers high spatial resolution, combined with the same freedom in positioning provided by conventional screen-film cassettes.
We have developed a brand new, large-area X-ray image sensor for Digital Radiography System (DRS). The sensor utilizes a thin film transistor (TFT)/metal insulator semiconductor (MIS)-type photoelectric converter array made from hydrogenated amorphous silicon (a-Si:H). The sensor has 2688 X 2688 pixels at a pitch of 160 micrometer. The active area is 17 inch X 17 inch. The sensor utilizes scintillator coupled to the array. The light generated by X-rays is detected by the MIS-type photoelectric converters, and the resultant signals are scanned out by switching the TFTs. The a-Si TFT/MIS-type photoelectric converter array is characterized by high signal to noise ratio (SNR) and simple fabrication process. We will describe the principle and the performance of the sensor. In addition, we will present some X-ray images of a human subject obtained with this sensor. Dynamic range of the sensor covers most of the exposure range for radiography. SNR is limited almost only by the X-ray photon noise. MTF is sufficient for digital chest radiography. X-ray images have good contrast. The experimental results and obtained images show that the brand new sensor has great advantages for replacing X-ray film. The simple fabrication process of the sensor promises high productivity and low cost of DRS.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.