Multi-Pinhole Based X-Ray Fluorescence Computed Tomography: A Comparison with Single Pinhole Case

An x-ray fluorescence computed tomography using a pinhole collimator (p-XFCT) for medical use depicts the 3-D distribution of imaging agent by collecting the x-ray fluorescence photons emitted from the imaging agent accumulated in an organ using a pinhole collimator and a 2-D detector. However, the number of the fluorescent x-ray photons are restricted by the pinhole, leading to acquisition of low S/N projections due to the photon starvation. Simultaneous acquisition of multiple projections using a multi-pinhole scheme overcomes the photon starvation. In this research, we clarified the measurement process and described the quantitative linear relationship between the quantities to be estimated and to be measured. We solved the multi-pinhole based XFCT (mp-XFCT) as a linear inverse problem regarding the described measurement process using ML-EM (maximum likelihood expectation-maximization) algorithm. We actually constructed an mp-XFCT imaging system at beamline AR-NE7A in KEK, and performed imaging experiment using a physical phantom to demonstrate the efficacy of mp-XFCT.