Hiroshi Asahina

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

Flat-panel detector (FPD) is the driving force for realizing the next generation of x-ray systems. The purpose of this study was to develop a selenium-based FPD for both radiography and fluoroscopy. The detector uses amorphous selenium (a-Se) and a thin-film transistor (TFT) array. The simple construction of the a-Se layer permits real-time readout. The unique response characteristics of the FPD, which can be saturated over permitted x-ray doses, are provided by the TFT structure. Our prototype FPD was designed to acquire images at 30 frames per second (fps). A high modulation transfer factor was obtained: 0.63 at 2.0 Lp/mm. Sequential fluoroscopic images were acquired at up to 30 fps. The linear characteristics of the detector covered the commonly employed range of clinical exposure dose. Less than 1.5% image lag was measured at 30 fps.

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.

Reconstruction of Pediatric 3D Blood Vessel Images from Biplane Angiograms

In pediatric cardiac angiography, there are several peculiarities such as limitation of both x-ray dose and the amount of contrast medium in comparison with conventional angiography. Due to these peculiarities, the catheter examinations are accomplished in a short time with biplane x- ray apparatus. Thus, it is often difficult to determine 3D structures of blood vessels, especially those of pediatric anomalies. Then a new 3D reconstruction method based on selective biplane angiography was developed in order to support diagnosis and surgical planning. The method was composed of particular reconstruction and composition. Individual 3D image is reconstructed with the particular reconstruction, and all 3D images are composed into standard coordinate system in the composition. This method was applied to phantom images and clinical images for evaluation of the method. The 3D image of the clinical data was reconstructed accurately as its structures were compared with the real structures described in the operative findings. The 3D visualization based on the method is helpful for diagnosis and surgical planning of complicated anomalies in pediatric cardiology.