Recent advances in biomedical imaging systems

Current medical imaging technology for computed tomography (CT) and radiographic applications are based on either indirect or direct integrating x-ray detectors. The resulting image contrast is based on the differences between the x-ray absorption properties of the object being imaged. Contrast in biomedical samples that contain soft tissues can be poor due to similar densities and elemental composition of mainly carbon (C), hydrogen (H) and oxygen (O). Work is needed to improve the differentiation between these elements, as greater contrast between tissues types will allow improved detection and possibly earlier diagnosis of disease. To overcome the challenges of contrast at a reasonable dose, a direct conversion hybrid pixel detector is being developed that is different to conventional systems in two ways. First, photon counting is used to reduce noise in the image, and second, each photon is energy resolved which provides a new degree of information that, together with knowledge of the elemental properties of the phantom can be used to provide improved imaging capabilities. A hybrid detector system has a detector layer consisting of a pixelated compounded semiconductor operating in direct conversion mode to increase detection efficiency and provide reasonable energy resolution. This layer produces a charge that is proportional to the incoming x-ray photon energy. The detector layer is bonded to an in house designed multi channel application specific integrated circuit (ASIC) which converts the charge to a digital value. Each pixel has its own data acquisition chain and this parallel approach allows both large numbers of photons to be processed and positional information to be determined simultaneously.