Mr. Zihui Jin Profile

Zihui Jin

at KTH Physics of Medical Imaging

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Proceedings Article | 1 April 2024 Presentation + Paper

Experimental evaluation of a micron-resolution CT detector

Rickard Brunskog, Mats Persson, Zihui Jin, Mats Danielsson

Proceedings Volume 12925, 129250B (2024) https://doi.org/10.1117/12.2692858

KEYWORDS: Sensors, Electrodes, Simulations, Monte Carlo methods, X-rays, Signal attenuation, Prototyping, Diffusion, Photon counting, Optical simulations

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Current photon-counting detectors are limited to a pixel size of 0.3mm to 1mm, as decreasing the pixel size further generally introduces degraded dose efficiency and energy resolution from excessive charge sharing. In this work, we present experimental measurements of the first photon-counting detector prototype designed to leverage the charge sharing to estimate the photon interaction position, where simulations indicate a theoretical resolution of around 1μm using a similar geometry. The goal of the measurements is to validate our Monte-Carlo simulation for further development. DAC sweeps are performed with an x-ray beam at specified locations on the sensor front, with the beam at 20keV and 35keV, as well as with different sensor biases with the beam at 35keV. The experimental data are then compared to a Monte Carlo simulation combined with a charge transport model. In this first prototype wire bonds are used, and as such only a few channels are connected. The experimental data agree generally well with the simulated data with the beam close to the electrodes, with the simulated data diverging from the experiments with the beam further away from the electrodes. The induced charge cloud signal exhibits a fairly linear dependency on the beam position, indicating that any estimation techniques will yield more precise position when the photon interacts further away from the electrodes, rather than closer. With the experimental data and the simulations agreeing generally well, together with the same software previously indicating a resolution of around 1μm, we expect an ultra-high-resolution detector to be in reach, and are encouraged to continue development.

SPIE Journal Paper | 1 February 2024 Open Access

First experimental evaluation of a high-resolution deep silicon photon-counting sensor

Rickard Brunskog, Mats Persson, Zihui Jin, Mats Danielsson

JMI, Vol. 11, Issue 01, 013503, (February 2024) https://doi.org/10.1117/12.10.1117/1.JMI.11.1.013503

KEYWORDS: Sensors, Monte Carlo methods, Electrodes, Optical simulations, Silicon, Prototyping, Photodetectors, Calibration, Image resolution, X-rays

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PurposeCurrent photon-counting computed tomography detectors are limited to a pixel size of around 0.3 to 0.5 mm due to excessive charge sharing degrading the dose efficiency and energy resolution as the pixels become smaller. In this work, we present measurements of a prototype photon-counting detector that leverages the charge sharing to reach a theoretical sub-pixel resolution in the order of 1 μm. The goal of the study is to validate our Monte-Carlo simulation using measurements, enabling further development.ApproachWe measure the channel response at the MAX IV Lab, in the DanMAX beamline, with a 35 keV photon beam, and compare the measurements with a 2D Monte Carlo simulation combined with a charge transport model. Only a few channels on the prototype are connected to keep the number of wire bonds low.ResultsThe measurements agree generally well with the simulations with the beam close to the electrodes but diverge as the beam is moved further away. The induced charge cloud signals also seem to increase linearly as the beam is moved away from the electrodes.ConclusionsThe agreement between measurements and simulations indicates that the Monte-Carlo simulation can accurately model the channel response of the detector with the photon interactions close to the electrodes, which indicates that the unconnected electrodes introduce unwanted effects that need to be further explored. With the same Monte-Carlo simulation previously indicating a resolution of around 1 μm with similar geometry, the results are promising that an ultra-high resolution detector is not far in the future.

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