Propagation of quantum noise in multiplexed x-ray imaging

Multiplexed x-ray imaging was recently proposed as a way to possibly reduce x-ray source power requirements while maintaining temporal resolution and imaging speed. Rather than measuring projections sequentially, with multiplexing multiple sources send photons to the same detector corresponding to different projections. Data for the multiple projections that are measured by the same detector are separated by energizing the sources with different temporal sequences. This concept could be used for radiography, tomosynthesis, or CT imaging. Multiplexed measurements are used very successfully in other modalities. For example, in magnetic resonance imaging (MRI) data from multiple voxels, perhaps even the entire object, can be measured through a single channel. In MRI, the simultaneous interrogation of multiple regions has no SNR penalty. It is important to examine the noise impact of multiplexing/demultiplexing in x-ray imaging. We examined the propagation of noise due to the quantum statistics of the measured x-rays. The analysis showed that for quantum limited acquisitions, the noise penalty of multiplexing can be severe. Indeed, if both the multiplexed and sequential methods are quantum limited, the simpler sequential method always outperforms multiplexing.