Large-area sensors for medical imaging

Engineers at the University of Sheffield and at the Science and Technology Facilities Council’s Rutherford Appleton Laboratory in Didcot, both in the UK, have developed a large-area CMOS-based imager for medical body scanners. With active pixel sensors with an imaging area of ~6 cm², the device may produce more sensitive images more quickly and at a lower cost, aiding in the analysis of medical screening tests and in the early detection of cancer.

The intersection of four ~6-cm² imagers before dicing.

The silicon imager, comprising a 1400 × 1400 array of 40-μm pixels with a total active area of 56 × 56 mm², has been designed for x-ray and electron diffraction studies as well as for clinical diagnostic applications such as x-ray imaging and low-dose mammography. The novel stitched sensor design was developed by a consortium of 11 research centers as part of a £4.5million, four-year project called Multidimensional Integrated Intelligent Imaging, or M-I³, funded by the UK Research Council Basic Technology program.

Each pixel on an active pixel sensor device contains a photosensitive element and several transistors. Currently, the fabrication process allows for about 30 transistors per pixel. According to Nigel M. Allinson, project leader from the university, technology advances allowing for up to 300 transistors per pixel will enable users of the imaging device to isolate particular features of an image and to obtain readouts very quickly. Very large area active pixel sensors could reduce the need for film in medical imaging. The next step is to manufacture wafer-scale imagers that can produce images of widths closer to that of the human torso, eliminating the need for expensive and inefficient lenses.