Isaac Chan PhD, Abstract Co-Author: Nothing to Disclose

Chin-Yuan Ho, Abstract Co-Author: Nothing to Disclose

Heng-Yin Chen, Presenter: Nothing to Disclose

Ming Hua Yeh, Abstract Co-Author: Nothing to Disclose

Flat-panel thin-film transistor (TFT) detector is a proven technology for digital radiography. However, its resolution, sensitivity, and readout speed (frame rate) are limited as the pixel size is reduced to sub-100-μm, a prominent need for mammography and breast tomosynthesis. A novel and simple amplified pixel sensor (APS) architecture is introduced to overcome the drawbacks in conventional flat-panel X-ray detectors.

Rather than using single amorphous silicon (a-Si) TFT to simply transfer the electronic charge signals converted from the X-rays, a second TFT is added to convert the charges into an amplified current in the pixel, which can be rapidly read out by external electronics. Overlaying with amorphous selenium (a-Se) as the X-ray conversion layer with 100% effective fill factor, the amplified pixel detector with high resolution, low dose, and high speed performance can be realized

The performance of the new detector is evaluated in terms of dark current, signal conversion gain, and readout speed. The output dark current of the fabricated 50-μm amplified pixel constructed with two a-Si TFTs and the a-Se sensor is below the 1-fA measurement limit of the low-noise probe station, due to zero-bias state of the amplifier (amp) TFT during the X-ray detection period. 50-μm pixel size represents a Nyquist resolution limit of 10 lp/mm, which is sufficient for mammography. The output voltage signal gain is as high as 35 times the input charge signal from the a-Se sensor, giving a comparable sensitivity as for a 300-μm pixel pitch detector without the signal gain. Furthermore, the designable gain factor can be appreciated in the light-on brightness test of the 160x160 APS prototype array with different width-to-length (W/L) ratios (26/5, 32/5, 40/5, and 50/5) of the amp TFT. It can be shown that a readout rate above 60 frames per second (fps) is attainable by appropriate pixel design.

Given the fA-range low dark current noise, high signal gain, and fast readout performance, coupled with the mature a-Si TFT array technology, the proposed APS detector is promising for advancing both scintillator-based indirect conversion or photoconductor-based direct conversion X-ray imaging.

Flat-panel amplified pixel sensor array can be integrated into digital X-ray imaging systems for mammography, breast tomosythesis, fluoroscopy, dental imaging, and cone-beam CT applications.

Chan, I, Ho, C, Chen, H, Yeh, M, 50-μm Pitch Amplified Pixel Sensor Array for Low Dose, High Resolution, and High Frame Rate Digital Radiography.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12023148.html