Overcoming detector limitations of x-ray photon counting for preclinical microcomputed tomography.

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Abstract

Spectral computed tomography (CT) using photon counting detectors (PCDs) can provide accurate tissue composition measurements by utilizing the energy dependence of x-ray attenuation in different materials. PCDs are especially suited for K-edge imaging, revealing the spatial distribution of select imaging probes through quantitative material decomposition. We report on a prototype spectral micro-CT system with a CZT-based PCD (DxRay, Inc.) that has

16
×
16
  
pixels

of

0.5
×
0.5
  

mm

2

, a thickness of 3 mm, and four energy thresholds. Due to the PCD’s limited size (

8
×
8
  

mm

2

), our system uses a translate-rotate projection acquisition strategy to cover a field of view relevant for preclinical imaging (

∼
4.5
  
cm

). Projection corrections were implemented to minimize artifacts associated with dead pixels and projection stitching. A sophisticated iterative algorithm was used to reconstruct both phantom and ex vivo mouse data. To achieve preclinically relevant spatial resolution, we trained a convolutional neural network to perform pan-sharpening between low-resolution PCD data (

247
–
μ
m

voxels) and high-resolution energy-integrating detector data (

82
–
μ
m

voxels), recovering a high-resolution estimate of the spectral contrast suitable for material decomposition. Long-term, preclinical spectral CT systems such as ours could serve in the developing field of theranostics (therapy and diagnostics) for cancer research.