Yasutaka Konno

Comparison of flat-panel detector and image-intensifier detector for cone-beam CT

We evaluated a flat-panel detector (FPD) (scintillator screen and a-Si photo-sensor array) for use in a cone-beam computed tomography (CT) detector and compared it with an image-intensifier detector (IID). The FPD cone-beam CT system has a higher spatial resolution than the IID system. At equal pixel sizes, the standard deviation of noise intensity of the FPD system is equal to that of the IID system. However, the circuit noise of the FPD must be reduced, especially at low doses. Our evaluations show that the FPD system has a strong potential for use as a cone-beam CT detector because of high-spatial resolution.

Development and evaluation of a digital radiography system using a large-area flat-panel detector

A new DR system using a large-area flat panel detector (FPD) with a 40 by 30 cm active area and a 194 micrometers pixel pitch, has been developed to compare with a conventional image intensifier and charge-coupled device camera type DR system. After measuring basic characteristics of the new DR system such as signal-to-noise ratio, modulation transfer function, and detective quantum efficiency, we applied the FPD to a Gastro-Intestinal study with contrast media, and discussed its potential for clinical use with a medical doctor. In radiography mode, the new DR system with a large-are FPD has superior image quality compared with the conventional I.I.- CCD camera type DR system because of high SNR and DQE. In fluoroscopy mode, the SNR of the new DR system at the exposure range of over 2(mu) R/frame is similar with the conventional I.I.-CCD camera type DR system. As a result, we considered that new DR system with a large-area FPD could be applied to a clinical study replacing an I.I.-CCD camera type. In the evaluation using various clinical images taken with the new DR system by a medical doctor, the new DR system with a large-are FPD performed sufficiently for a GI study.

MO-D-330A-06: Development of the X-Ray Detector with Sequential Readout Circuits for Multidetector-Row Computed Tomography

Purpose: To develop a low‐cost X‐ray detector with sequential readout circuits, to realize enough low noise for multidetector‐row computed tomography(MDCT), and to evaluate image quality. Method and Materials: We have developed an X‐ray detector that has a MOS‐switch for each pixel, connects many pixels of a common column with the electric readout circuit, and outputs the signals of these pixels from one circuit by turning on lines of switches in order. It has fewer readout circuits than a conventional MDCT detector, but new design is necessary to realize enough low noise for MDCT. First, to make the required noise specific, we simulated the relation of the detectornoise and imagenoise (simulation(A)). Second, to consider how to realize it, we simulated the detectornoise with the circuit noise model (simulation(B)). Third, we constructed the detector in order to evaluate its noise. Last, we developed a test CTsystem with these detectors to evaluate imagenoise with phantoms. Results: The result of the simulation(A) indicated that detectornoise had to be less than about 10‐k rms electrons, and we found to be able to achieve it by optimizing the circuit parameters of the low pass filter and the data line as a result of the simulation(B). We constructed the detectors with these parameters to evaluate these noise, and it turned out that it was about 10.5‐k rms electrons and the required noise was achieved. Moreover, the result to evaluate the noise from images with phantoms indicated that the main was X‐ray quantum noise and the detectornoise was low enough to be ignored when the object was a cylindrical water‐filled phantom less than about 30 cm in diameter and the slice thickness of the images was 0.625 mm. Conclusion: We developed a low‐noise X‐ray detector with sequential readout circuits for MDCT.