1-μm spatial resolution in silicon photon-counting CT detectors.

Christel Sundberg,Mats Danielsson,J Jacob Wikner,Mats Persson

doi:10.1117/1.jmi.8.6.063501

Christel Sundberg, Mats Danielsson + Show 2 more

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https://doi.org/10.1117/1.jmi.8.6.063501

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Abstract

Purpose: Spatial resolution for current scintillator-based computed tomography (CT) detectors is limited by the pixel size of about 1mm. Direct conversion photon-counting detector prototypes with silicon- or cadmium-based detector materials have lately demonstrated spatial resolution equivalent to about 0.3mm. We propose a development of the deep silicon photon-counting detector which will enable a resolution of , a substantial improvement compared to the state of the art. Approach: With the deep silicon sensor, it is possible to integrate CMOS electronics and reduce the pixel size at the same time as significant on-sensor data processing capability is introduced. A Gaussian curve can then be fitted to the charge cloud created in each interaction.We evaluate the feasibility of measuring the charge cloud shape of Compton interactions for deep silicon to increase the spatial resolution. By combining a Monte Carlo photon simulation with a charge transport model, we study the charge cloud distributions and induced currents as functions of the interaction position. For a simulated deep silicon detector with a pixel size of , we present a method for estimating the interaction position. Results: Using estimations for electronic noise and a lowest threshold of 0.88keV, we obtain a spatial resolution equivalent to in the direction parallel to the silicon wafer and in the direction orthogonal to the wafer. Conclusions: We have presented a simulation study of a deep silicon detector with a pixel size of and a method to estimate the x-ray interaction position with ultra-high resolution. Higher spatial resolution can in general be important to detect smaller details in the image. The very high spatial resolution in one dimension could be a path to a practical implementation of phase contrast imaging in CT.

Highlights

Photon-counting spectral detectors are predicted to evolve into a new standard for computed tomography (CT), replacing the scintillator-based technology that has been used the last 20 years
The detected energies result from an interaction of 8 keV for which Y0 1⁄4 20 μm, with the front side electrode defined as y 1⁄4 0, and X0 1⁄4 −4.8 μm, with x 1⁄4 0 corresponding to the middle of pixel 26
If a fluorescence event occurs, the resulting electron track consists of two separate parts: one track starting at the initial interaction position and one track from the interaction of the fluorescence photon at a different interaction position

Summary

Introduction

Photon-counting spectral detectors are predicted to evolve into a new standard for computed tomography (CT), replacing the scintillator-based technology that has been used the last 20 years. Individual photons can be counted and registered with respect to energy. Sundberg et al.: 1-μm spatial resolution in silicon photon-counting CT detectors higher spatial resolution and improved spectral fidelity, which will translate into higher signal-tonoise ratio in the image.[1,2,3]. Due to the low atomic number of silicon, another advantage is the absence of K-fluorescence photons, which will limit spectral and spatial resolution for high Z materials. In low Z materials like silicon, there is a significant fraction of Compton interactions, in which the incident photon only deposits some of its energy upon interacting with the detector material

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