Single photon counting x-ray imaging system using a micro hole and strip plate

Abstract

A single photon counting x-ray imaging system based on a MicroHole and Strip Plate (MHSP) using a resistive charge division method was implemented. The MHSP is a hybrid microstructure that combines within the same device the features of the Gas Electron Multiplier (GEM) and the Micro-strip Gas Chamber (MSGC). The MHSP presents two multiplication stages thus allowing reaching high gains. Two thin orthogonal resistive lines of about 100 between each strip (top side) and between each anode strip (bottom side) allows us to obtain the actual position in both x and y directions. The readout electronics use only two charge preamplifiers in each dimension and a TNT module with four independent ADCs controlled through FPGAs that allow converting and registering the four signals through the USB port of a computer. Position resolution in both dimensions as a function of the detector parameters are presented for a 30 keV copper-target x-ray tube. Detector position resolution of x =130 m and y =250 m were achieved for 8keV, making it suitable for many applications in single photon x-ray imaging. The first x-ray images produced by the system are also presented together with a discussion of the image quality and the future prospects.

X-ray imaging detector based on a position sensitive THCOBRA with resistive line

“…For the second dimension, the top copper side is also structured in several different strips perpendicular to the anode strips. Two resistive lines of about 50 Ω/mm, one for each dimension, are orthogonally disposed, connecting respectively the anode strips and the top strips of the 2D-THCOBRA, similarly to the 2D-MHSP [1] (see figure 1).…”

“…By controlling the voltage difference between the circular-cathode strips and the anodes (V AC , typically 150 V), a second multiplication can occur. The charge is collected at the anode strips [1,2,7].…”

“…The charge collected on the anode and the induced charge on the top strips are read from both ends of each resistive line and the interaction position is determined according to the principle of resistive charge division [1]. This simple readout system composed by resistive lines is very cost effective since it requires only 4 electronic channels to process the signals and therefore obtain an image [1].…”

“…The signals were digitally shaped and amplified by applying the Jordanov trapezoid algorithm to determine the signal amplitudes. For more details on the readout electronics please see reference [1].…”

“…Following the success of the 2D-Micro-Hole and Strip Plate (2D-MHSP) obtained for single photon X-ray detection and imaging [1], a new detector based on a similar concept is presented. The Thick-COBRA (THCOBRA) structure [2] was developed with 2D capability for X-ray imaging (2D-THCOBRA) (figure 1).…”