Detection Properties Research Articles

Clinical applications of spectral molecular imaging: potential and challenges

Spectral molecular imaging is a new X-ray-based imaging technology providing highly specific 3D imaging at high spatial resolution that has the potential to measure disease activity and response to treatment noninvasively. The ability to identify and quantify components of tissue and biomarkers of disease activity derive from the properties of the photon-processing detector. Multiple narrow sections of the energy spectrum are sampled simultaneously, providing a range of energy dependent Hounsfield units. As each material has a specific measurable X-ray spectrum, spectroscopic imaging allows for multiple materials to be quantified and differentiated from each other simultaneously. The technology, currently in its infancy, is set to grow rapidly, much as magnetic resonance did. The critical clinical applications have not yet been established, but it is likely to play a major role in identifying and directing treatment for unstable atherosclerotic plaque, assessing activity and response to treatment of a range of inflammatory diseases, and monitoring biomarkers of cancer and its treatment. If combined with Positron-emission tomography (PET), spectral molecular imaging could have a far greater effective role in cancer diagnosis and treatment monitoring than PET-CT does at present. It is currently used for small animal and specimen imaging. There are many challenges to be overcome before spectral imaging can be introduced into clinical medicine - these include technological improvements to detector design, bonding to the semiconductor layer, image reconstruction and display software, identifying which biomarkers are of most relevance to the disease in question, and accelerating drug discovery enabled by the new capabilities provided by spectral imaging.

Stable numerosity representations irrespective of magnitude context in macaque prefrontal cortex

Cognitively demanding tasks require neurons of the prefrontal cortex (PFC) to encode divergent behaviorally relevant information. In discrimination tasks with arbitrary and learned categories, context-specific parameters shape and adapt the tuning functions of PFC neurons. We explored if and how selectivity of PFC neurons to visual numerosities, a 'natural' abstract category, may change depending on the magnitude context. Two monkeys discriminated visual numerosities (varying numbers of dot items) in a delayed match-to-sample (DMS) task while single-cell activity was recorded from the lateral PFC. During a given recording session, the numerosity task was either presented in isolation or randomly intermixed with DMS tasks with line lengths and colors as discriminative stimuli. We found that the context of numerosity discriminations did not influence the response properties of numerosity detectors. The numerosity tuning curves of selective neurons, i.e. the preferred numerosity and the sharpness of tuning, remained stable, irrespective of whether the numerosity task was presented in a pure numerosity block or a mixed magnitude block. Our data suggest that numerosity detectors in the PFC do not adapt their response properties to code stimuli according to changing magnitude context. Rather, numerosity representations seem to rely on a sparse and stable 'labeled line' code. In contrast to arbitrarily learned categories, numerosity as a 'natural' category may possess a privileged position and their neuronal representations could thus remain unaffected by magnitude context.

Determination of iron by Z-GFAAS and the influence of short-term precision and long-term precision

Abstract A detailed method validation of graphite-furnace atomic absorption spectrometry (GFAAS) with Zeeman background correction was performed. The aim is to perform a detailed investigation of short-term precision as opposed to long-term precision. It was suggested that release of graphite flakes into the light path during measurement significantly influenced the performance of the method. It was found that significant deviations with respect to the certified values were frequent and an estimate of reliable uncertainties was obtained only after a high number of repetitions. Uncertainty of Interlaboratory testing was evaluated as a method to estimate uncertainties that are comparable to uncertainties that were obtained by Interlaboratory testing and to uncertainties predicted by the Horwitz curve. To a large extent, the uncertainty in measurement that was predicted by pooled calibrations corresponded to the uncertainties that were obtained from multiple determinations of unknowns. It was thus proposed that a large proportion of the difference in uncertainty in measurement between laboratories could be explained by properties of the different detectors. In order to support accuracy, it is suggested that a higher level of uncertainty should be accepted in analytical investigations.

Evaluation of the dosimetric properties of a synthetic single crystal diamond detector in high energy clinical proton beams

To investigate the dosimetric properties of a synthetic single crystal diamond Schottky diode for accurate relative dose measurements in large and small field high-energy clinical proton beams. The dosimetric properties of a synthetic single crystal diamond detector were assessed by comparison with a reference Markus parallel plate ionization chamber, an Exradin A16 microionization chamber, and Exradin T1a ion chamber. The diamond detector was operated at zero bias voltage at all times. Comparative dose distribution measurements were performed by means of Fractional depth dose curves and lateral beam profiles in clinical proton beams of energies 155 and 250 MeV for a 14 cm square cerrobend aperture and 126 MeV for 3, 2, and 1 cm diameter circular brass collimators. ICRU Report No. 78 recommended beam parameters were used to compare fractional depth dose curves and beam profiles obtained using the diamond detector and the reference ionization chamber. Warm-up∕stability of the detector response and linearity with dose were evaluated in a 250 MeV proton beam and dose rate dependence was evaluated in a 126 MeV proton beam. Stem effect and the azimuthal angle dependence of the diode response were also evaluated. A maximum deviation in diamond detector signal from the average reading of less than 0.5% was found during the warm-up irradiation procedure. The detector response showed a good linear behavior as a function of dose with observed deviations below 0.5% over a dose range from 50 to 500 cGy. The detector response was dose rate independent, with deviations below 0.5% in the investigated dose rates ranging from 85 to 300 cGy∕min. Stem effect and azimuthal angle dependence of the diode signal were within 0.5%. Fractional depth dose curves and lateral beam profiles obtained with the diamond detector were in good agreement with those measured using reference dosimeters. The observed dosimetric properties of the synthetic single crystal diamond detector indicate that its behavior is proton energy independent and dose rate independent in the investigated energy and dose rate range and it is suitable for accurate relative dosimetric measurements in large as well as in small field high energy clinical proton beams.

Efficiency of dislocation density reduction during heteroepitaxial growth of diamond for detector applications

The development of dislocation density and micro-strain in heteroepitaxial diamond films on iridium was measured over more than two decades of thickness up to d ≈ 1 mm. Simple mathematical scaling laws were derived for the decrease of dislocation density with increasing film thickness and for its correlation with micro-strain. The Raman line width as a measure of micro-strain showed a huge decrease to 1.86 cm−1, close to the value of perfect single crystals. The charge collection properties of particle detectors built from this material yield efficiencies higher than 90% in the hole-drift mode, approaching the performance of homoepitaxial films.

Super-thin single crystal diamond membrane radiation detectors

We propose to use the non-electronic grade (nitrogen content 5 ppb < [N] < 5 ppm) single crystal (sc) chemical vapour deposited (CVD) diamond as a thin-membrane radiation detector. Using deep Ar/O2 plasma etching it is possible to produce self-supported few micrometres thick scCVD membranes of a size approaching 7 mm × 7 mm, with a very good surface quality. After metallization and contacting, electrical properties of diamond membrane detectors were probed with 5.486 MeV α-particles as an ionization source. Despite nitrogen impurity, scCVD membrane detectors exhibit stable operation, charge collection efficiency close to 100%, with homogenous response, and extraordinary dielectric strength up to 30 V/μm.

화재모델링 예측성능 개선을 위한 이온화식 연기감지기의 장치물성 측정

성능위주 소방설계(PBD)의 과정에서 화재 및 피난모델링의 신뢰성을 확보하기 위해서는 화재감지기 모델의 높은 예측성능이 필수적으로 요구된다. 본 연구의 목적은 FDS와 같은 대와동모사(Large Eddy Simulation) 화재모델에 적용될 수 있는 연기감지기의 정확한 작동 개시시간을 예측하기 위한 수치적 입력정보를 측정하는 것이다. 이를 위해 화재감지기의 장치특성을 측정할 수 있는 FDE (Fire Detector Evaluator)를 제작하였으며, 이온화식 연기감지기에 대한 Heskestad 및 Cleary 모델의 입력변수가 측정되었다. 또한 일반적으로 사용되는 FDS의 기본 값과 측정된 값이 적용된 연기감지기의 작동 개시시간을 정량적으로 비교하였다. 주요 결과로써, 본 연구에서 검토된 이온화식 연기감지기의 장치 물성은 FDS에 적용된 기본 값과 매우 큰 차이를 보이고 있으며, 연기감지기 작동 개시시간이 최대 15분 이상 차이가 발생되었다. PBD의 신뢰성을 향상시키기 위하여 향후 연구에서는 보다 다양한 연기 및 열감지기의 장치물성에 대한 데이터베이스(DB)가 구축될 예정이다. The high prediction performance of fire detector models is essentially needed to assure the reliability of fire and evacuation modeling in the process of PBD (Performance Based fire safety Design). The main objective of the present study is to measure input information in order to predict the accurate activation time of smoke detector into a Large Eddy Simulation (LES) fire model such as FDS (Fire Dynamics Simulator). To end this, FDE (Fire Detector Evaluator) which can measure the device properties of detector was developed, and the input information of Heskestad and Cleary's models was measured for a ionization smoke detector. In addition, the activation times of smoke detectors predicted using default values into FDS and measured values in the present study were systematically compared. As a result, the device properties of smoke detector examined in the present study showed a significant difference compared to the default values used into FDS, which resulted in the considerable difference of up to 15 minutes or more in terms of the activation time of smoke detector. The database (DB) on device properties of various smoke and heat detectors will be built to improve the reliability of PBD in future studies.

Influence of the starting materials used in the crystal growth process of CZT for gamma ray radiation applications

The influences of two different ways of crystal growth preparations by using different starting materials on the detector properties have been investigated. The characterization has been carried out in terms of structural, optical, and electrical properties of the materials grown with the vertical gradient freeze method. The distributions of Zn and In at different axial positions with different crystals have been compared by using the Induced Coupled Plasma-Mass Spectroscopy technique. The size and density of Te inclusions within the materials have been identified by Infrared Microscopy. The luminescence behaviors have been investigated by studying the defects levels. Particularly, the current–voltage characteristics and Gamma-ray Spectroscopy have been investigated by comparing the performance of detectors achieved from different axial directions of the ingots.

The Effect of Vibration Noise for Cavity Ring Down Time Extraction

A continue-wave cavity ring down experimental system is established surrounding the micro-sphere cavity. In the experiments of measuring micro-spheres cavity quality factor (Q) upon the system, it is found that photoelectric detectors with different response characteristic have different response to the optical signal which is shut off rapidly. The vibration noise caused by changes of external environment, meanwhile, can be transformed following the change of photoelectric detector properties. With the build of photoelectric detector response model, the mean-square deviation of repeated experiments under the same conditions is used for charactering level of the error caused by vibration noise. The influence of vibration noise to photoelectric detector is discussed in detail, and further analyzes the effect for the cavity ring down time extraction. Then the optimal photoelectric detector (Newfocus1434, 15V/W) is selected to optimize the experimental system. The level of error caused by vibration noise has been decreased from 0.191ns to 1.562ps. Finally, the Q value of micro-sphere cavity is calculated according to fitted value of cavity ring down time, and the experimental correctness is verified by the line-width law.

Evaluation of the Timepix chip radiation hardness using a 60Co source

Radiation damage is a widely studied topic for its effects on detectors and supporting electronics in various practical applications. Radiation hardness and stability of the detector properties are critical parameters in applications of semiconductor radiation detectors. The 0.25μm CMOS technology used in fabrication of the Medipix2 and Timepix chips provides high degree of inherent radiation hardness. We present the study of operational, detection and signal processing properties of the irradiated Timepix chip exposed to a high-flux 60Co source reaching the operational limits of the chip.

Ultra-fast silicon detectors

We propose to develop a fast, thin silicon sensor with gain capable to concurrently measure with high precision the space (∼10μm) and time (∼10ps) coordinates of a particle. This will open up new application of silicon detector systems in many fields. Our analysis of detector properties indicates that it is possible to improve the timing characteristics of silicon-based tracking sensors, which already have sufficient position resolution, to achieve four-dimensional high-precision measurements. The basic sensor characteristics and the expected performance are listed, the wide field of applications are mentioned and the required R&D topics are discussed.

SU-E-T-104: Evaluation of the Dosimetric Properties of a Synthetic Single Crystal Diamond Detector in Clinical Proton Beams

Purpose: To investigate the dosimetric properties of a new synthetic single crystal diamond Schottky diode for accurate relative dose measurements in clinical proton beams. Methods: The dosimetric properties of the synthetic single crystal diamond detector (SCDD) were assessed by comparison with a reference parallel plate ionization chamber (PTW Markus Chamber 23343) and a micro ionization chamber (Exradin A16). The diamond detector was operated at zero bias voltage at all times. Comparative dose distribution measurements were performed by means of percent depth dose curves and lateral beam profiles using the diamond detector and a reference ionization chamber in clinical proton beams of energies 155MeV and 250 MeV for a 14cm square cerrobend aperture and 126 MeV for 3cm, 2cm and 1cm diameter circular brass collimators. ICRU 78 recommended beam parameters are used to compare the percent depth dose curves and lateral profiles obtained using the SCDD and the reference ionization chamber. The warm‐up/stability of the detector response, dose linearity and dose‐rate dependency were also evaluated in a 250 MeV proton beam. Results: During warm‐up/stability the diamond detector was irradiated 6 times and the maximum deviation from the average reading was less than 0.5%. The detector response shows a good linear behavior as a function of dose with observed deviations below 0.5% over a dose range of 50cGy to 500cGy. The detector response is dose rate independent, with deviations below 0.5% in the investigated dose‐rates of 64cGy/min,47.5cGy/min and 17.5cGy/min. Percent depth dose curves and lateral beam profiles obtained with the diamond detector were in good agreement with those obtained using reference dosimeters. Conclusion: The observed dosimetric properties of the SCDD indicate that its behavior is proton energy independent in the investigated energy range and it is suitable for accurate relative dosimetric measurements in large field and small field clinical proton beams.

WE‐B‐137‐01: Plastic Scintillation Detectors: Present Status and Their Application for Quality Assurance and in Vivo Dosimetry

Development of plastic scintillation detector (PSD) systems for dosimetry has been evolving for two decades now. The subject area has been a topic of a keen research interest that has generated lot of publications lately. PSD systems are being introduced in the market place. Numerous PSD systems for External Beam Radiation Therapy and Brachytherapy have been proposed, most times differentiating from the original systems by slight changes in one or more components, such as the photodetector. However, few major technological and engineering innovations have enabled this new technology to be embraced by the community which helped launching these systems for commercialization (Standard Imaging, Radiadyne, etc.). Scintillation materials (plastic, scintillating fibers and liquid) have many properties that make them ideal for dosimetry including water equivalence and energy independence for MV photons, linearity with dose, dose rate independence, high spatial resolution and nanosecond fast response time. Therefore, these detectors do not require the usual conversion and/or correction factors used for other commonly used detectors to convert the dosimeter reading to absorbed dose. This evolution started with point detectors and has led to matrix arrays to respond to the ever‐increasing complexity of radiotherapy treatment fields such as IMRT, small field dosimetry or incorporating them within special patient applicators to monitor the dose in real time. This lecture will provide a brief overview of the dosimetric characteristics and properties of PSDs when exposed to high‐energy photon beams. We will present few recent applications of PSD systems as applied for EBRT and Brachytherapy (quality assurance and in vivo dosimetry applications). We will briefly present the available and soon to come commercial products related to this type of dosimetry.Learning Objectives:1. Review the underlying physics of organic scintillation materials and the properties of plastic scintillation detectors used in radiation dosimetry.2. Understand the principles of the methods associated with recent innovations of PSDs in EBRT and Brachytherapy.3. Identify potential applications that could benefit from these PSD systems.

Measurement of thermal and optical properties of CR-39 solid-state nuclear detector by photothermal deflection

The thermal and optical properties of the nuclear detector CR-39 were studied in light of the demand for CR-39 and its novel physical properties, as well as its technological implications in many fields. Thermal diffusivity is the most important parameter when this detector is exposed to nuclear radiation and when consequent heat transfer processes influence the photothermal deflection spectroscopy. Thermal-induced effects on the surface of the CR-39 detector were studied using transient heat diffusion simulations. The resulting thermal deformation due to alpha particle irradiation of CR-39 will be presented. Irradiation of CR-39 by α-particles was found to lower the refractive index change with temperature. The temperature distribution was studied numerically by solving the heat diffusion equation to illustrate the effects of α-particle exposure on the CR-39. The thermal diffusivity of exposed CR-39 is the primary subject of this article.

Investigation of charge collection in a CdTe-Timepix detector

Energy calibration of CdTe detectors is usually done using known reference sources disregarding the exact amount of charge that is collected in the pixels. However, to compare detectorand detector model the quantity of charge collected is needed. Wecharacterize the charge collection in a CdTe detector comparing testpulses, measured data and an improved TCAD simulation model [1]. The 1mm thick detector is bump-bonded to a TIMEPIX chip and operating inTime-over-Threshold (ToT) mode. The resistivity in the simulation wasadjusted to match the detector properties setting a deep intrinsicdonor level [2]. This way it is possible to adjust properties liketrap concentration, electron/hole lifetime and mobility in thesimulation characterizing the detector close to measured data cite[3].

Analysis and Interpretation of the Cramér-Rao Lower-Bound in Astrometry: One-Dimensional Case

ABSTRACTIn this article we explore the maximum precision attainable in the location of a point source imaged by a pixel array detector in the presence of a background, as a function of the detector properties. For this we use a well-known result from parametric estimation theory, the so-called Cramér-Rao lower bound. We develop the expressions in the one-dimensional case of a linear array detector in which the only unknown parameter is the source position. If the object is oversampled by the detector, analytical expressions can be obtained for the Cramér-Rao limit that can be readily used to estimate the limiting precision of an imaging system, and which are very useful for experimental (detector) design, observational planning, or performance estimation of data analysis software: In particular, we demonstrate that for background-dominated sources, the maximum astrometric precision goes as B/F2, where B is the background in one pixel, and F is the total flux of the source, while when the background is negligible, this precision goes as F-1. We also explore the dependency of the astrometric precision on: (1) the size of the source (as imaged by the detector), (2) the pixel detector size, and (3) the effect of source decentering. Putting these results into context, the theoretical Cramér-Rao lower bound is compared to both ground- as well as space-based astrometric results, indicating that current techniques approach this limit very closely. It is furthermore demonstrated that practical astrometric estimators like maximum likelihood or least-squares techniques cannot formally reach the Cramér-Rao bound, but that they approach this limit in the one-dimensional case very tightly, for a wide range of signal-to-noise ratio (S/N) of the source. Our results indicate that we have found in the Cramér-Rao lower variance bound a very powerful astrometric “benchmark” estimator concerning the maximum expected positional precision for a point source, given a prescription for the source, the background, the detector characteristics, and the detection process.

Advantages and challenges of high-dose thermoluminescent detectors

The current status of high-dose luminescent detector investigations is discussed. The examples of successful applications of various materials for medium and high-dose luminescent detector creation are presented. High-dose irradiation effect on luminescence of TLD-500 (α-Al2O3:C) detectors has been described. The challenges of detector properties restoration after high-dose irradiation are considered.

3D imaging of radiation damage in silicon sensor and spatial mapping of charge collection efficiency

Radiation damage in semiconductor sensors alters the response and degrades the performance of many devices ultimately limiting their stability and lifetime. In semiconductor radiation detectors the homogeneity of charge collection becomes distorted while decreasing the overall detection efficiency. Moreover the damage can significantly increase the detector noise and degrade other electrical properties such as leakage current. In this work we present a novel method for 3D mapping of the semiconductor radiation sensor volume allowing displaying the three dimensional distribution of detector properties such as charge collection efficiency and charge diffusion rate. This technique can visualize the spatially localized changes of local detector performance after radiation damage. Sensors used were 300 μm and 1000 μm thick silicon bump-bonded to a Timepix readout chip which serves as an imaging multichannel microprobe (256 × 256 square pixels with pitch of 55 μm, i.e. all together 65 thousand channels). Per pixel energy sensitivity of the Timepix chip allows to evaluate the local charge collection efficiency and also the charge diffusion rate. In this work we implement an X-ray line scanning technique for systematic evaluation of changes in the performance of a silicon sensor intentionally damaged by energetic protons.

The effect of different gamma doses on some properties of a CR-39 detector

In the current study, the bulk etch rate, the removal thickness percentage and the track density have been examined for gamma-irradiated at doses ranging from 0 to 100 kGy. After irradiating CR-39 detectors, they got etched at 70°C in different concentration of NaOH solutions for various time intervals. Results indicate that the bulk etch rate and the removal thickness percentage increase with the increase of gamma absorbed dose and the etchant solution concentration. The track density increases with increase of the etchant solution concentration for irradiated samples (0, 10, 50 kGy) up to 6.25 N NaOH, and then it decreases with the increase of the etchant solution concentration for un-irradiated samples and those irradiated with 10 kGy, and with the high doses the samples' surface got damaged.

Lanthanum halide nanoparticle scintillators for nuclear radiation detection

Nanoparticles with sizes <10 nm were fabricated and characterized for their nanocomposite radiation detector properties. This work investigated the properties of several nanostructured radiation scintillators, in order to determine the viability of using scintillators employing nanostructured lanthanum trifluoride. Preliminary results of this investigation are consistent with the idea that these materials have an intrinsic response to nuclear radiation that may be correlated to the energy of the incident radiation.