Dan Li BS, Presenter: Nothing to Disclose

Wei Zhao PhD, Abstract Co-Author: Nothing to Disclose

To investigate the application of parallel electron beam readout method in a flat-panel detector with avalanche gain and field emitter array (FEA) readout, and its impact on detector temporal performance, electronic noise and readout speed.

Previously we proposed a new detector called SAPHIRE to improve the imaging performance at low dose with high resolution (50µm). Such a detector in large area (20cm×25cm) will contain up to 4000×5000 pixels, which poses tremendous challenge for the readout speed and electronic noise of the detector. Parallel electron beam readout is necessitated to overcome these problems. It can be implemented by dividing the signal electrode of the detector into N parallel strips, each of which is connected to an external amplifier. The FEA is addressed such that one pixel per strip, i.e. N pixels, are turned simultaneously to provide parallel readout. Usually N is much smaller than the number of pixels in one direction, i.e. multiple rows of pixels share the same signal strip and amplifier. Within each strip the FEA pixels are addressed sequentially.

Since FEA uses passive driving circuitry, the gate pulses experience delay due to line resistance and capacitances. The time τ taken for the gate potential to reach 90% of its value is ~40nS, which makes real-time readout impossible using a single signal electrode. With N=128, the readout time for each pixel can be up to 213nS at 30 fps. More strips also reduce the input load capacitance of the amplifier, which is the dominant source of electronic noise of the detector. N=128 reduces the amplifier noise from 48000 to 530 e-/pixel. This is to be compared with the signal per absorbed x-ray of 3600 electrons, which means that the detector is x-ray quantum noise limited down to a single x-ray level. The readout lag with N=128 is <5% for the first frame, which is acceptable.

Parallel beam readout method can increase readout speed, reduce amplifier noise and lag for the proposed detector with FEA readout.

SAPHIRE with high spatial resolution, low noise and real-time readout is still at conceptual level. It can potentially be applied to mammography, fluoroscopy and cone beam CT.

Li, D, Zhao, W, SAPHIRE (Scintillator Avalanche Photoconductor with High Resolution Emitter Readout): Investigation of Parallel Beam Readout.  Radiological Society of North America 2007 Scientific Assembly and Annual Meeting, November 25 - November 30, 2007 ,Chicago IL. http://archive.rsna.org/2007/5014594.html