Characterization and Testing of LAS: A Prototype `Large Area Sensor´ With Performance Characteristics Suitable for Medical Imaging Applications

The Large Area Sensor (LAS) is a 1350 times1350 array of active pixels on a 40 Im pitch fabricated in a 0.35 im CMOS process. Stitching technology is employed to achieve an area of 5.4 cm times5.4 cm. The sensor includes ´regions of reset´, whereby three different integration times can be set on the array to achieve a large imaging range for static scenes. Characterization of the noise performance included temporal and fixed pattern sources. LAS was found to have a read noise of 62 e^-, a full well capacity of 61 times10³ e^- and a conversion gain of 5 e^- per digital number (DN). The fixed pattern noise (FPN) was evaluated at half saturation; within a single stitched section of the array, column-to-column FPN was found to be 0.6%, while the pixel-to-pixel FPN was 3%. Both FPN sources were found to be gain related and could be corrected via flat fielding. Based on the results of characterization, LAS was coupled to a structured CsI:Tl scintillator and included in an X-ray diffraction system developed for the analysis of breast biopsy samples. Data acquired with plastic test objects agrees with that acquired by a previous prototype sensor. It is demonstrated that an imaging output range of 140 dB can be achieved using integration times of 0.1 ms to record the transmitted X-ray beam and 2.3 s to record the lower intensity scattered radiation.