Kouhei Suzuki

Development and evaluation of a large-area selenium-based flat-panel detector for real-time radiography and fluoroscopy

The x-ray flat panel detector (FPD) is a key component of the next generation x-ray imaging systems which promote digitization of x-ray images. By developing FPD applicable to both fluoroscopy and radiography, it is expected that x-ray diagnostic systems will change dramatically not only in terms of performance, but also in shape and form. The purpose of this research is to develop a selenium-based FPD applicable to both radiography and fluoroscopy. This report presents the results of the work on new technology which can be applied to create clinically-useful view size detector. The prototype detector adopts 1000 micron thick selenium as the photoconductor, 23 cm square of field of view, 150 X 150 micron pixel pitch, 1536 X 1536 pixel number, and is capable of capturing images at up to 30 frames/second. The features of this prototype detector are: simple-structure selenium suitable for real-time readout, and a high voltage protection structure for the TFT array which acts at x-ray overexposure. To realize large field of view, the field uniformity performance of the selenium and TFT array has been improved, and noise from the TFT array has been minimized. In this paper, new physical performance related to MTF, input- and-output characteristics, image lag, blooming, etc., are discussed.

Multi-field driving method for reducing LCD power consumption

We have developed a multi-field driving method for TFT-LCDs in which a displayed image was divided into at least three interlaced sub-field images where visible flicker did not occur as the image refresh rate was decreased. This method made it possible not only to reduce driving-power consumption in the case of still images to less than half, compared to that of conventional methods, but also to ensure that large-area flicker and line flicker were invisible to the human eye.

High Speed and High Resolution Contact-Type Image Sensor Using an Amorphous Silicon Photodetector Array

A contact-type image sensor has been developed with 16 elements/mm resolution and 0.8 ms/line scanning speed. This surpasses all previously reported devices of this type. These features are achieved by a newly developed highly integrated low noise hybrid circuit technology and a novel photodetector structure. This sensor is very compact with 3456 picture elements in a 216 mm active length. The reason why previous sensors had low speed, how this high performance sensor has been developed, and what remains to be improved is discussed.

A dynamic model of an a-Si:H photoconductive sensor

A dynamic model of an a-Si:H photoconductive sensor under a pulse driven condition is proposed. In this model, it is assumed that a high rate of recombination at the interface between a-Si:H and the substrate occurs due to hole drift along the interface when a driving voltage is applied between the electrodes. Calculated results agree with experimental results to an accuracy of 10%. It is shown that the localized state density of the bulk a-Si:H is one of the dominant factors determining the photoresponse of the a-Si:H photoconductive sensor under a pulse driven condition, and that the minimum photoresponse time of this sensor is about 5 ms. >

An a-Si:H photoconductive sensor with a gate electrode

A hydrogenated amorphous silicon photoconductive sensor with a gate electrode is developed for a matrix-driven linear image sensor array. The photoresponse time for this new sensor is about 1/3 of that for a conventional photoconductive sensor. A new dynamic model is proposed to analyze the photoresponse characteristics for this sensor. The minimum photoresponse time predicted by the calculation is about 2 ms. This value is markedly short compared with that for a conventional photoconductive sensor (about 5 ms). >