Purpose

We are developing a monolithic deep-silicon photon-counting sensor targeting spatial resolution on the order of 1 μm. This work investigates how pixel pitch, noise level, threshold number, and threshold placement affect the achievable tangential and wafer-thickness resolution to guide the CMOS electronics and sensor design.

Approach

Allpix Squared simulations were used to evaluate pixel pitches with two noise levels and two threshold-placement schemes over varying threshold numbers. Interaction position was estimated in both dimensions using lookup tables trained on the thresholded pixel output, and performance was quantified using the MTF.

Results

Decreasing pixel pitch strongly improved tangential resolution for Compton interactions, whereas photoelectric interactions showed a weaker dependence on pixel pitch and threshold placement. Equal-counting thresholds approached the achievable resolution with fewer thresholds than equidistant thresholds. For eight equal-counting thresholds, the 10% MTF across the studied pixel sizes ranged from 1284 lp/cm to 2452 lp/cm in the tangential direction and from 15 to 71 lp/cm in the wafer-thickness direction for Compton interactions, compared with 409 to 507 lp/cm and 18 to 79 lp/cm, respectively, for photoelectric interactions. RMSE analysis further showed that some interactions for the 25 μm pitch reached below 2 μm tangentially and a few tens of micrometers in the wafer-thickness direction.

Conclusions

Spatial resolution improved with a threshold number up to about 8 to 10, beyond which additional programmable thresholds gave only modest gain. The achieved tangential resolution also suggests that analyzer-free phase-contrast imaging is feasible for realistic geometries and expected interference patterns.

Photon counting CT with ever finer detector pixels, microbeam cancer therapy and recent methods for non-destructive evaluation demand minimized X-ray focal spots and improved photon flux from keV bremsstrahlung X-ray sources. Compared with X-ray detection, the performance improvement of high-performance X-ray tubes with rigid target materials has substantially fallen behind in recent decades. Rigid anode technology has become a serious bottleneck for improvement. Our group has previously shown that rapidly moving tungsten microparticle streams could be powerful X-ray targets and have potential for novel system design. Compared with rotating anode tubes we simulated a potential output intensity gain of almost an order of magnitude for high tube voltage and focal spots at the low end of the realistic human diagnostic CT range. Our current work further supports our expectation that an essential property is fulfilled, namely that the particle stream remains neutral upon electron impact for realistic tube voltages and suitable tungsten microparticle streams. In addition, we now add that, in contrast to conventional rigid targets, microparticle targets enable full space angle or at least triple-sided X-ray emission that would allow to achieve extraordinarily high image resolution for central objects on the reference axis of the imaging system. The anode angle would be zero. A thin and fast moving microparticle target can simultaneously emit in conventional reflection mode, transmission mode, and sideways to enhance image resolution, object size and total output.

コンピュータ断層撮影（ＣＴ）における機械学習画像再構成のための１つ以上の信頼度表示を決定するための方法及びシステムが提供される。この方法は、（Ｓ１）エネルギー分解Ｘ線データを取得することと、（Ｓ２）少なくとも１つの機械学習システムに基づいてエネルギー分解Ｘ線データを処理して、少なくとも１つの再構成基底画像又はその画像特徴の事後確率分布の表現を生成することとを備える。本方法は更に、事後確率分布の表現に基づいて、前記少なくとも１つの再構成基底画像、又は前記少なくとも１つの再構成基底画像に由来する少なくとも１つの派生画像、又は前記少なくとも１つの再構成基底画像又は前記少なくとも１つの派生画像の画像特徴に対する１つ以上の信頼度表示を生成する（Ｓ３）ことを含む。【選択図】図６Ａ

Purpose: We aim to investigate the feasibility of developing a tabletop photon-counting micro-computed tomography (CT) device that can perform intraoperative virtual histopathology on tumor specimens, showing the demarcation between the tumor and surrounding tissue. By enabling fast imaging and tissue analysis during surgery, the micro-CT device would enhance the accuracy of tumor excision and thus minimize harm to the patient by reducing the need for re-operations. Approach: A simulation using a Python package called SpekPy is used to investigate the potential capabilities of a tabletop micro-CT device on tumor specimens.1 We use existing micro-CT systems as a model for the tube parameters (filters, voltage, power, and current), and we assume an ideal detector in order to understand the upper limit of detection capabilities. Results: The simulated data indicate that when the contrast-to-noise ratio (CNR) is normalized for time, higher tube voltage is optimal across all tissue thicknesses. In contrast, when the CNR is normalized for dose, lower tube voltage ranges are preferable for thinner tissues. Since shorter acquisition times are desirable in this application and dose is not a concern (as the tissue is not live), it is useful to know that the highest applied voltage will yield the highest CNR, and thus the best capability for tumor differentiation. Additionally, the data suggest that the device can distinguish features as small as 33 microns within soft tissue, facilitating precise assessment of tumor margins. Conclusions: The simulation demonstrates that a micro-CT device with these specifications is capable of effectively performing intraoperative tumor margin assessment.

Purpose: Evaluation of a new sensor for micrometer-resolution photon-counting CT. Approach: DAC-sweeps are performed using a commercial x-ray tube and are compared to simulations. An edge-scan using a 250 µm tungsten wafer without any interaction logic is also performed, as well as single interaction readout of the energy spectrum that is compared to simulations. Results: The edge-scan shows a line spread function with a full width at half maximum of 11.6 µm and a 5% modulation transfer function at 850 lp/cm. Conclusions: Fair agreement with simulations indicated that employing the interaction can further significantly improve spatial resolution.

【課題】改良されたＸ線検出器システムを提供する。【解決手段】Ｘ線源からのＸ線放射を検出するフォトンカウンティングＸ線検出器（２０）、及び前記Ｘ線検出器における光子相互作用の時間に関する情報と、前記Ｘ線検出器に対する前記Ｘ線源の位置に関する情報とに基づいて、前記Ｘ線検出器に入射する放射線に関する情報を決定する及び／又は取得する同時計数検出システム（６０）を含むＸ線検出器システム（５）を提供する。このようなＸ線検出器システムを含むＸ線イメージングシステム、並びに対応する同時計数検出システム及び対応する方法も提供する。【選択図】図２Ｂ

The input power density of eroding rotating anode X-ray sources restricts the achievable spatial image resolution in X-ray systems, especially for medical computed tomography (CT). The development of anodes that sustain higher input power density has stalled in recent decades, despite substantial investment and sophisticated material analysis. The grain structure of the conversion layer, typically sintered and forged tungsten/rhenium, erodes during tens of millions of thermal cycles. Anodes of high-performance tubes are under extreme thermomechanical stress and rotate near angular burst velocities. To overcome this challenge, we propose a paradigm shift using a stream of very fast moving tungsten microparticles. Volume heating, twice the mass heat capacity and much shorter residence times under electron impact may render an order of magnitude improvement of the focal spot input power density. This corresponds to a threefold improvement of the source MTF in each orthogonal direction for a standard focal spot. We made sure by Monte-Carlo simulation, that the new microparticle target would not charge negatively upon electron impact in the tube voltage range of medical imaging. Hence, it would be electrically compatible with the spectral requirements. We propose technical implementations. We further suggest a source of high intensity and highly monochromatic bremsstrahlung based on microparticle technology that may replace synchrotrons for a variety of experiments. After thorough simulations we believe that the remaining engineering problems, such as separating the microparticle space from the cathode region, storage, acceleration, capturing, cooling, and recycling, can be solved in the near future.

The input power density of rotating anode X-ray sources and hence the spatial image resolution of the X-ray system must be fundamentally restricted due to the erosion of anode material. The efficacy of computed tomography would benefit from much smaller X-ray focal spots with equal or increased photon output. A switch to carbon fiber reinforced rotor members that may enable higher rotor velocity has been suggested, or increasing the tube voltage for deeper implantation of electronic input power. Alternatively, we are proposing a new fast moving tungsten microparticle target that avoids focal track erosion, offers high mass heat capacity from increased temperature swing and reduced material residence time in the electron beam. This novel technology concept promises to eliminate the bottleneck and allow for an order of magnitude improvement of the focal spot input power density. However, before investing in implementation the ultimate limitations of current technology should be better known than currently. To gain knowledge, we improved the modeling of electron transport and target erosion of rotary anodes. We infer a criticality parameter that enables predicting the risk of anode erosion for a wide range of technique factors and focal spot sizes based on a few reference life cycle tests. In conclusion, despite the deficits of assumptions made in the classic Müller-Oosterkamp theory that ignores tube voltage, the derived specifications of commercial X-ray tubes are justified. Limited by anode erosion, the gain of permitted power density with increasing tube voltage is smaller than predicted by some alternative volume heating models. We further discovered the necessity to introduce a correction for calculations of the applied patient X-ray dose and pointed to the related error in the standards for radiation safety.

Objective. We strive to overcome the challenges posed by ring artifacts in x-ray computed tomography (CT) by developing a novel approach for generating training data for deep learning-based methods. Training such networks require large, high quality, datasets that are often generated in the data domain, time-consuming and expensive. Our objective is to develop a technique for synthesizing realistic ring artifacts directly in the image domain, enabling scalable production of training data without relying on specific imaging system physics. Approach. We develop 'Syn2Real,' a computationally efficient pipeline that generates realistic ring artifacts directly in the image domain. To demonstrate the effectiveness of our approach, we train two versions of UNet, vanilla and a high capacity version with self-attention layers that we call UNetpp, with & ell;2 and perceptual losses, as well as a diffusion model, on energy-integrating CT images with and without these synthetic ring artifacts. Main Results. Despite being trained on conventional single-energy CT images, our models effectively correct ring artifacts across various monoenergetic images, at different energy levels and slice thicknesses, from a prototype photon-counting CT system. This generalizability validates the realism and versatility of our ring artifact generation process. Significance. Ring artifacts in x-ray CT pose a unique challenge to image quality and clinical utility. By focusing on data generation, our work provides a foundation for developing more robust and adaptable ring artifact correction methods for pre-clinical, clinical and other CT applications.

Background

The permitted input power density of rotating anode x-ray sources is limited by the performance of available target materials. The commonly used simplified formulas for the focal spot surface temperature ignore the tube voltage despite its variation in clinical practice. Improved modeling of electron transport and target erosion, as proposed in this work, improves the prediction of x-ray output degradation by target erosion, the absolute x-ray dose output and the quality of diagnostic imaging and orthovolt cancer therapy for a wide range of technique factors.

Purpose

Improved modeling of electronic power absorption to include volume effects and surface erosion, to improve the understanding of x-ray output degradation, enhance the reliability of x-ray tubes, and safely widen their fields of use.

Methods

We combine Monte Carlo electron transport simulations, coupled thermoelasticity finite element modelling, erosion-induced surface granularity, and the temperature dependence of thermophysical and thermomechanical target properties. A semi-empirical thermomechanical criterion is proposed to predict the target erosion. We simulate the absorbed electronic power of an eroded tungsten-rhenium target, mimicked by a flat target topped with a monolayer of spheres, and compare with a pristine target.

Results

The absorbed electronic power and with it the conversion efficiency varies with tube voltage and the state of erosion. With reference to 80 kV (100%), the absorption of a severely eroded relative to a pristine target is 105% (30 kV), 99% (100 kV), 97% (120 kV), 96% (150 kV), 93% (200 kV), 87% (250 kV), and 79% (300 kV). We show that, although the simplistic Müller–Oosterkamp model of surface heating underestimates the benefit of higher tube voltages relative to operation at 80 kV, the error is limited to below −6% for 30 kV (reduction advised) and +13% for 300 kV (input power increase permitted).

Conclusions

Correcting the x-ray conversion efficiency of eroded target material, that is typically not accessible by measuring the tube current, may imply corrections to existing x-ray dose calculations. The relative increase of the allowable anode input power of rotating anode x-ray tubes with increasing tube voltage is substantially smaller than predicted by volume heating models that only rely on the focal spot surface temperature. The widely used voltage agnostic Müller–Oosterkamp formalism fails to predict the tube voltage dependency of the surface temperature of rotating anode targets, ignores the temperature dependency of the thermal diffusivity of tungsten-rhenium, and the granularity of the material. Nevertheless, we show theoretically why, backed by experience, the practical use of the Müller–Oosterkamp formalism is justified in medical imaging and provides a basis for comparison with new microparticle based targets. The reason for this surprising finding is that voltage dependent material erosion must be primarily considered as a precursor of thermal runaway effects.