<XML><RECORDS><RECORD><REFERENCE_TYPE>0</REFERENCE_TYPE><REFNUM>7511</REFNUM><AUTHORS><AUTHOR>Mikulec,B.</AUTHOR><AUTHOR>Campbell,M.</AUTHOR><AUTHOR>Dipasquale,G.</AUTHOR><AUTHOR>Schwarz,C.</AUTHOR><AUTHOR>Watt,J.</AUTHOR></AUTHORS><YEAR>2001</YEAR><TITLE>Characterisation of a single photon counting pixel system for imaging of low-contrast objects</TITLE><PLACE_PUBLISHED> Nucl. Instr. and Meth. in Phys. Res. A 458 (2001) </PLACE_PUBLISHED><PUBLISHER>Elsevier Science</PUBLISHER><PAGES>352-359</PAGES><ISBN>0168-9002</ISBN><LABEL>Mikulec:2001:7511</LABEL><KEYWORDS><KEYWORD>Photon counting; pixel detector; X-ray imaging; Medipix; Calibration; GaAs</KEYWORD></KEYWORDS<ABSTRACT>In the framework of the Medipix collaboration the PCC, a single photon counting pixel chip, has been developed with the aim of improving the contrast resolution in medical imaging applications. The PCC consists of a matrix of 64 x 64 square pixels with 170µm side length, each pixel comprising a 15-bit counter and a pulse-height discriminator. The chip has been bump-bonded to equally segmented 200µm thick SI-LEC GaAs detectors showing a very high absorption energy for X-rays used in diagnostics. An absolute calibration of the system with a radioactive source and a synchrotron beam are described resulting in the value of the test input capactitance of ~ 24.7 fF. Using this value a full characterization of the system from electrical measurements is presented. The entire system can reach a minimum threshold of ~ 2100e- with ~ 250e- rms noise. One of the characteristic features of the PCC is the possibility to adjust the thresholds of all pixels on a pixel-by-pixel basis with 3-bit precision. The threshold distribution after adjustment is ~ 120e- rms. The spatial resolution of the system has been measured to be 3.6 lp/mm. A comparison of a tooth image taken with the PCC and with a screen-CCD-system demonstrates its imaging capabilities. </ABSTRACT></RECORD></RECORDS></XML>