Characterization of and Correction for Inter-Layer Scatter In Material Decomposition Using Dual-Layer Flat-Panel Detector
Abstract
Purpose
The dual-layer flat-panel detector (FPD) has great potential in dual-energy cone-beam CT imaging. However, like the scatters from the detector housing in conventional single-layer FPD, the scatters from the top layer and some aluminum or carbon panels between the two detector layers, called the inter-layer scatter, can be collected by the bottom layer and may have a non-negligible impact on the accuracy of material decomposition. We characterize the impact of the inter-layer scatter by Monte Carlo simulation for a prototype dual-layer FPD and perform a correction to reduce the decomposition error from it.
Methods
For the dual-layer FPD, the detector housing, top-layer scintillator and the inter-layer buffer material are all the potential source of scattering to the bottom-layer detector. We perform Monte Carlo simulation to quantify the fraction and point-spread function (PSF) of inter-layer scatter. To apart the inter-layer scatter from the scatter from the object to be scanned, the experimental verification is conducted in narrow fan-beam scan. In such case, the object scatter can be ignored, so we can focus on the response of inter-layer scatter which is concentrated in a neighborhood of the target pixel. The inter-layer scatter is estimated by convolution process and thus subtracted from the measurements. Noted that the same operation should be done for the air image before the logarithmization.
Results
The fraction of inter-layer scatter PSF could be more than 10% of bottom-layer detector signal . According to the PSF by simulation for 120 kVp X-ray input, the inter-layer scatter correction is performed for the experimental data. The decomposition error near the tissue-bone boundary can be greatly reduce by the proposed correction and the image quality of VMIs is also improved.
Conclusion
Our study demonstrates that the inter-layer scatter for dual-layer is nonnegligible and related correction for it is necessary.