Reduction of the Beam Hardening Artifacts in the X-Ray Computer Tomography: Energy Discrimination with a Photon-Counting Detector

The material identification is a pressing requirement for the sensitive security applications. Dual-energy X-ray computer tomography (DXCT) has been investigated for material identification in the medical and security fields. It requires two tomographic images at sufficiently different energies. To discriminate dangerous materials of light elements such as plastic bombs in luggage, it is needed to measure accurately with several tens of kilo electron volts where such materials exhibit significant spectral differences. However, CT images in that energy region often include artifacts from beam hardening. To reduce these artifacts, a novel reconstruction method has been investigated. It is an extension of the Al-gebraic Reconstruction Technique and Total Variation (ART-TV) method that reduces the artifacts in a lower-energy CT image by referencing it to an image obtained at higher energy. The CT image of a titanium sample was recon-structed using this method in order to demonstrate the artifact reduction capability.

X-ray photon counting detectors for preclinical and clinical applications

Photon counting detectors(PCDs) have attained w ide use in X-ray imaging for various preclinical and clinical applications in the past decade. This paper briefly review s the preclinical and clinical applications of PCDs based X-ray imaging systems.Starting with an introduction of X-ray single photon detection mechanism,the brief review first describes tw o major advantages of utilizing PCDs: photon energy resolving capability and electronic noise elimination. Compared to energy integrating detectors(EIDs),the aforementioned advantages make PCDs more favorable in X-ray imaging with profound benefits such as enhanced tissue contrast,decreased image noise,increased signal to noise ratio,decreased radiation dose to the small animals and patients,and more accurate material decomposition. The utilizations of PCDs in X-ray projection radiography and computed tomography(CT)including micro-CT,dedicated breast CT,K-edge CT,and clinical CT are then review ed for the imaging applications ranging from phantoms to small animals and humans. In addition,optimization methods aiming to improve the imaging performance using PCDs are briefly review ed. PCDs are not flaw less though,and their limitations are also discussed in this review. Nevertheless,PCDs may continuously contribute to the advancement of X-ray imaging techniques in future preclinical and clinical applications.

The intensity detection of single-photon detectors based on photon counting probability density statistics

Single-photon detectors possess the ultra-high sensitivity, but they cannot directly respond to signal intensity. Conven- tional methods adopt sampling gates with fixed width and count the triggered number of sampling gates, which is capable of obtaining photon counting probability to estimate the echo signal intensity. In this paper, we not only count the number of triggered sampling gates, but also record the triggered time position of photon counting pulses. The photon counting probability density distribution is obtained through the statistics of a series of the triggered time positions. Then Minimum Variance Unbiased Estimation （MVUE） method is used to estimate the echo signal intensity. Compared with conventional methods, this method can improve the estimation accuracy of echo signal intensity due to the acquisition of more detected information. Finally, a proof-of-principle laboratory system is established. The estimation accuracy of echo signal intensity is discussed and a high accuracy intensity image is acquired under low-light level environments.

Detailed calibration of the PI-LCX：1300 high performance single photon counting hard x-ray CCD camera

X-ray charge-coupled-device（CCD） camera working in single photon counting mode is a type of x-ray spectrometer with high-sensitivity and superior signal-to-noise performance. In this study, two single photon counting CCD cameras with the same mode（model： PI-LCX： 1300） are calibrated with quasi-monochromatic x-rays from radioactive sources and a conventional x-ray tube. The details of the CCD response to x-rays are analyzed by using a computer program of multi-pixel analyzing and event-distinguishing capability. The detection efficiency, energy resolution, fraction of multi-pixel events each as a function of x-ray energy, and consistence of two CCD cameras are obtained. The calibrated detection efficiency is consistent with the detection efficiency from Monte Carlo calculations with XOP program. When the multi-pixel event analysis is applied, the CCDs may be used to measure x-rays up to 60 ke V with good energy resolution（E /？E ≈ 100 at60 ke V）. The difference in detection efficiency between two CCD cameras is small（5.6% at 5.89 ke V）, but the difference in fraction of the single pixel event between them is much larger（25% at 8.04 ke V）. The obtained small relative error of detection efficiency（2.4% at 5.89 ke V） makes the high accurate measurement of x-ray yield possible in the laser plasma interaction studies. Based on the discrete calibration results, the calculated detection efficiency with XOP can be used for the whole range of 5 ke V–30 ke V.

An FPGA-Based Pulse Pile-up Rejection Technique for Photon Counting Imaging Detectors

A novel FPGA-based pulse pile-up rejection method for single photon imaging detectors is reported. Tile method is easy to implement in FPGAs for real-time data processing. The rejection principle and entire design are introduced in detail. The photon counting imaging detector comprises a micro-channel plate （MCP） stack, and a wedge and strip anode （WSA）. The resolution mask pattern in front of the MCP can be reconstructed after data processing in the FPGA. For high count rates, the rejection design can effectively reduce the impact of the pulse pile-up on the image. The resolution can reach up to 140μm. The pulse pile-up rejection design can also be applied to high-energy physics and particle detection.

Photon-Counting Spectrometers Based on Superconducting Nanowire Single-Photon Detectors

Optical spectrum analysis provides a wealth of information about the physical world.Throughout the development of optical spectrum analysis,sensitivity has been one of the major topics and has become essential in applications dealing with faint light.Various high-sensitivity optical detection technologies have been applied in optical spectrum analysis to enhance its sensitivity to single-photon level.As an emerging single-photon detection technology,superconducting nanowire single-photon detectors(SNSPDs)have many impressive features such as high detection efficiency,broad operation bandwidth,small timing jitter,and so on,which make them promising for enhancing the performance of optical spectral analysis.Diverse schemes for photon-counting spectrometers based on SNSPDs have been demonstrated.This article reviews these impressive works and prospects for the future development of this technology.Further breakthroughs can be expected in its theories,device performance,applications,and combinations with in-sensor computing,promoting it to be a mature and versatile solution for optical spectrum analysis on ultra-faint light.

Direct Measurement of Non-Classical Photon Statistics with a Multi-Pixel Photon Counter

Photon number resolving detectors with high accuracy bring broad applications in long-distance laser ranging, ultrafast spectroscopy, and quantum optics. In this paper, we observed the non-classical photon number distribution directly with a multi-pixel photon counter (MPPC) instead of a classic Hanbury-Brown and Twiss (HBT) system. The detector’s photon-number resolving ability was characterized by quantum detector tomography. To show the quantum feature of the detector, we further plotted the Wigner function, which was obtained corresponding to the positive operator value measure (POVM) elements. Finally, we declared the observation of non-classical photon statistics from a single color center in nanodiamond by using this detector.

Dual-Energy X-Ray Computed Tomography Scanner Using Two Different Energy-Selection Electronics and a Lutetium-Oxyorthosilicate Photomultiplier Detector

To obtain two kinds of tomograms at two different X-ray energy ranges simultaneously, we have constructed a dual-energy X-ray photon counter with a lutetium-oxyorthosilicate photomultiplier detector system, three comparators, two microcomputers, and two frequency-voltage converters. X-ray photons are detected using the detector system, and the event pulses are input to three comparators simultaneously to determine threshold energies. At a tube voltage of 100 kV, the three threshold energies are 16, 35 and 52 keV, and two energy ranges are 16 - 35 and 52 - 100 keV. X-ray photons in the two ranges are counted using microcomputers, and the logical pulses from the two microcomputers are input to two frequency-voltage converters. In dual-energy computed tomography (CT), the tube voltage and current were 100 kV and 0.29 mA, respectively. Two tomograms were obtained simultaneously at two energy ranges. The energy ranges for gadolinium-L-edge and K-edge CT were 16 - 35 and 52 - 100 keV, respectively. The maximum count rate of dual-energy CT was 105 kilocounts per second with energies ranging from 16 to 100 keV, and the exposure time for tomography was 19.6 min.

感应读出延时线阳极光子计数探测器研究

针对空间天文、生物荧光、光谱测量等领域对高灵敏、大面阵探测器的应用需求,研制出基于感应读出方式的延迟线阳极光子计数成像探测器。该探测器由微通道板、延时线阳极以及读出电路组成,其中延时线阳极的性能直接影响探测器的成像质量。作为一种电荷感应读出延时线阳极,该阳极利用信号到达的时间差解码入射光子的位置,可获得高的探测灵敏度和大的成像面积,同时简化了工艺难度并提升了可靠性。设计了感应读出延时线阳极,理论分析了探测器不同设计参数及材料对感应电荷量的影响,提出了解决异层电极间感应电荷量难以平衡的方法。据此研制出了收集面积为40 mm×40 mm的位敏阳极。测试结果表明该阳极信号传输衰减小于10%,极间串扰小于3%。利用该阳极进行了光子计数成像实验,获得了优于150μm的空间分辨率,为研制可应用于天文紫外光谱测量的大面阵、高灵敏探测器提供了理论依据及实验指导。

光子计数探测器技术应用进展

光子计数探测器(PCD)是一种用于检测X射线光子的装置,能够将光子能量直接转化为电信号,从而实现对光子的计数和测量。基于PCD的能谱CT技术(PCD-CT)可以提供额外的能谱成像信息,改善成像质量,同时降低辐射剂量。相较于能量积分探测器(EID),PCD具有能量转换效率高、成像质量好、结构设计精巧、应用范围广等优势,在超低剂量CT、特定病症检验及工业检测中具有广阔的应用前景。综述PCD-CT在能谱CT成像中的应用,为其在临床医疗诊断与工业应用提供有益参考。

基于自研ASIC芯片HEPS中硅微条探测器读出电子学原型系统设计与测试

时间分辨X射线粉末衍射技术是探测物质晶体结构及其演变的重要手段。单光子计数型硅微条探测器因其灵敏度高和死时间低,在高能同步辐射光源(HEPS)的X射线粉末衍射实验中发挥着重要作用。研制适用于单光子计数型一维硅微条探测器的专用ASIC读出芯片(SSDROC)及其读出电子学系统,并采用一种新标定方法解决了SSDROC各通道对同一输入输出响应不一致的问题,该方法可显著提高各通道数据一致性并减小衍射实验数据的统计误差。探测器完成各项性能测试,结果表明整体系统线性优秀、能量分辨能力强、噪声低以及计数率高,为将来大覆盖角度一维硅微条探测器系统研制奠定坚实基础。

超高分辨率冠状动脉CT血管造影的可行性和图像表征研究

目的评估CT(CT)在高冠状动脉钙负荷患者的超高分辨率冠状动脉计算机断层血管造影(CCTA)的可行性和质量。方法纳入20例患者接受PCDCCTA,使用离散视觉量表评估图像噪声和冠状动脉斑块和邻近血管腔,表征图像噪声纹理。结果CCTA在所有患者中都是可行的。在Bv40核和0.6 mm层厚重建的患者中,虚化伪影最大(55.2%±9.8%),血管锐度最低(477.1±73.6ΔHU/mm),信噪比最高(27.4±5.6),CNR最高(32.9±6.6),噪声最低(17.1±2.2 HU)。考虑到薄片厚度为0.2mm的重建,图像噪声、信噪比、CNR、血管清晰度和虚化伪影在不同核之间存在显著差异(P<0.001)。随着内核清晰度的提高,信噪比和CNR不断降低,图像噪声和血管清晰度增加,其中Bv89内核的清晰度最高(2383.4±787.1ΔHU/mm)。结论超高分辨率CCTA结合CT是可行的,可以实现钙化冠状动脉的可视化,图像质量好,清晰度高。

Experimental research of the energy bins for K-edge imaging using a photon counting detector:a phantom and mice study

Purpose K-edge imaging based on the photon counting detectors(PCDs)is an effective enhanced imaging method because the PCDs are conducive to the K-edge imaging due to the adjustable energy thresholds.The energy bins significantly affect the image quality of the K-edge imaging,but the conventional energy bins used for K-edge imaging are continuous which weaken the K-edge signal and decline the image quality.Hence,how to get a better K-edge signal by the optimized energy bins is the key point for the K-edge imaging based on the PCDs.Method This paper experimentally studied the influence of the energy bins used for the K-edge imaging based on the PCDs.The conventional energy bins were determined by the theoretical-attenuation method(TAM),and the optimized energy bins were determined by the threshold-scan method(TSM).For the phantom and mice imaging,we performed both the K-edge subtraction algorithm and the K-edge decomposition algorithm on the projections obtained by the energy bins which were determined by the TAM and TSM.The image quality was compared using the CNR of the objective area.Results The experimental results showed that the energy bins identified by the TSM had a better performance than the TAM in both imaging methods.The TSM improved the CNR by~39%than the TAM in the phantom results and could better highlight the areas where the contrast agents are enriched(such as the kidney).Conclusions The optimized energy bins can better highlight the K-edge signal than the conventional energy bins which can improve the image quality and have the potential to reduce the amount of the contrast agents.

Enhanced K-Edge Radiography Using a High-Spatial-Resolution Cadmium Telluride Array Detector

To confirm the imaging effect of a dual-energy (DE) cadmium telluride (CdTe) array detector (XCounter, Actaeon) and to perform fundamental studies on DE computed tomography, we performed enhanced K-edge radiography using iodine (I) and gadolinium (Gd) media. DE radiography was performed using an X-ray generator with a 0.1-mm-diam-focus tube and a 0.5-mm-thick beryllium window, a 1.0-mm-thick aluminum filter for absorbing extremely low-energy photons, and the CdTe array detector with pixel dimensions of 0.1 × 0.1 mm2. Each pixel has a charge-sensitive amplifier and a dual-energy counter, and the event pulses from the amplifier are sent to the counter to determine two threshold energies. The tube current was a maximum value of 0.50 mA, and the tube voltages for I- and Gd-K-edge radiograms were 60 and 80 kV, respectively. In the I-K-edge radiography of a dog-heart phantom at an energy range of 33 - 60 keV, the muscle density increased, and fine coronary arteries were visible. Utilizing Gd-K-edge radiography of a rabbit head phantom at an energy range of 50 - 80 keV, the muscle density increased, and fine blood vessels in the nose were observed at high contrasts. Using the DE array detector, we confirmed the image-contrast variations with changes in the threshold energy.

月基极紫外相机光子计数成像探测器Ge膜的空间质子辐照稳定性

光子计数成像探测器是月基极紫外相机等空间成像载荷的核心成像器件。Ge膜作为探测器的电荷感应层,在空间质子辐照环境下的稳定性直接影响系统的成像质量。采用Monte-Carlo法仿真了500 nm Ge膜被10、50和100 keV高能质子辐照后,Ge膜内部的质子浓度分布与空位缺陷分布。仿真结果表明,50 keV质子在Ge膜内部产生的空位缺陷对膜层内部损伤最大。对100、230、350和500 nm厚度Ge膜分别进行50 keV质子辐照实验,经方阻仪测试显示,越厚的薄膜辐照后方阻变化越大,500 nm比100 nm Ge膜方阻增加量高约500 MΩ/。通过原子力显微镜(AFM)表征发现,500 nm Ge膜辐照后出现膜层凸起与分离,均方根表面粗糙度由1.63 nm增至约10 nm。研究结果表明,在满足方阻要求的前提下,通过对Ge膜厚度的合理设计,可以有效减小高能质子辐照带来的损伤。

光子计数探测器CT在骨肌系统疾病中的研究进展

光子计数探测器(PCD)-CT可以直接进行单光子成像,兼有常规CT检查的功能,具有物质分析准确、扫描剂量低、影像质量高的优势,对减少影像金属伪影、骨肌系统疾病分级等具有重要价值。综述PCD-CT的基本原理,及其在骨关节炎分析、骨肿瘤定量诊断、儿童骨肌低剂量扫描、骨骼微结构显示及骨关节假体评估中的应用进展。

大型客体光子计数成像技术的发展与挑战

具有光子计数能力的探测器给辐射成像领域带来了技术革新,具有巨大的应用潜力。光子计数探测器凭借其能量分辨能力将有助于提高辐射图像质量、降低辐射剂量、提高检测效率。目前,光子计数成像技术在医学诊断和行包安检等低能领域已有广泛和深入的研究,比如在能谱CT、乳腺检查、PET等领域诞生了许多成果,但是在集装箱检测及车辆安检等大型客体检测的中高能(MeV)领域研究较少,还需进一步克服技术上的困难,以达到中高能射线和高计数率条件的应用要求。本研究重点介绍了光子计数成像技术的特征优势、在X/γ射线医学诊断、安全检查辐射成像系统中的研究现状及面临的挑战,分析了其在大型客体检测中的应用现状和需要进一步突破的技术难点。

淋巴管平滑肌瘤病及肺部影像诊断研究进展

淋巴管平滑肌瘤病(lymphangio leiomyomatosis,LAM)是一种罕见的多系统肿瘤性疾病,主要影响育龄期和绝经前女性。LAM病变可累及肺[即肺淋巴管平滑肌瘤病(pulmonary Lymphangioleiomyomatosis,PLAM)]、肾[如血管平滑肌脂肪瘤(angiomyolipoma,AML)]和淋巴系统(如淋巴管平滑肌瘤、乳糜渗出)。随着病程的进展,LAM会破坏肺组织、改变肺结构,并导致胸、腹部淋巴管肌瘤的出现。LAM患者在早期症状较为轻微,临床表现缺乏特异性,极易被误诊,常因肺功能衰歇,反复发生气胸而死亡,肺移植是目前唯一有效的治疗方法,尽管移植后复发率较高。胸部高分辨CT(high resolution computer tomography,HRCT)是诊断LAM的关键手段,不仅有助于LAM的确诊,也可用于评估患者的病情严重程度和预后。随着医学影像技术的快速发展,特别是光子计数探测器CT(photon counting detector CT,PCD-CT)的应用,因其高分辨率和噪声减少能力,可以显著提高图像质量,与传统CT扫描相比,PCD-CT的辐射剂量可减少35.7%,非常适合用于LAM的诊断和长期随访。

Measurement of X-ray photon energy and arrival time using a silicon drift detector

Detecting the X-ray emission of pulsars and obtaining the photons＇ time of arrival are the foundational steps in autonomous navigation via X-ray pulsar measurement.The precision of a pulse＇s time of arrival is mainly determined by the precision of photon arrival time measurement.In this work,a silicon drift detector is used to measure photon energy and arrival time.The measurement system consists of a signal detector,a processing unit,a signal acquisition unit and a data receiving unit.This system acquires the energy resolution and arrival time information of photons.In particular,background noise with different energies disturbs pulse profile forming,the system can also achieve a high signal-to-noise ratio profile.Ground test results show that this system can be applied in autonomous navigation based on X-ray pulsar measurement.

光子计数CT成像技术的临床应用

光子计数CT是近10年来CT影像领域最具影响力的技术。利用光子计数探测器可以对X线进行计数,以获取高分辨力、低剂量的三维解剖结构和功能信息。光子计数CT探测器结构的变革使图像的分辨力得到明显提高,进一步拓宽了临床应用的范围。随着光子计数CT临床的广泛应用,有望挖掘出更多、更高效的功能和优势。因此,对于光子计数CT探测器的原理、材料及光子计数CT的优势、临床应用以及挑战的全面了解是非常必要的。