Basis element decomposition with spectral microCT using multi-layered, multi-colored scintillation detectors

Synchrotron-based X-ray imaging is a useful tool in biomedical research because it can nondestructively produce high-resolution, 3D images. In this technique, X-rays impinge upon a thin scintillator and the visible light emission is focused onto a CCD using microscope optics. With this type of detector, sub-micron resolution has been achieved. We have also studied the possibility of extending this detector to have multiple scintillating layers for the purposes of performing spectral microCT with polychromatic sources. When such a multi-layer detector is illuminated by a polychromatic spectrum, the first layer will preferentially stop lower-energy X-rays, and the deeper layers higher-energy X-rays, leading to limited but perfectly registered spectral resolution. This detection setup also has the advantage of efficient use of synchrotron X-rays, short scan times, and the potential adaptation to a bench top system. Here we present some of our preliminary experimental results obtained using a custom multi-layer scintillating detector in conjunction with a color CCD camera. We found that our dual-layer detector does provide a significant amount of spectral separation, which suggests that material decomposition will be possible. This will be useful in identifying the elemental stains in X-ray histology. So far we have only attempted to do the material decomposition in the image domain because it is simpler to implement and does not require very precise calibration data. In the future, we would like to develop a calibration phantom that will enable us to do the decomposition in the sinogram domain. This yields a more quantitatively rigorous decomposition and has the additional advantage of eliminating beam-hardening artifacts caused by the polychromatic spectrum.