MGy Dose Levels Research Articles

Development and Application of a Virtual Imaging Trial framework for Airway Quantifications via CT.

Chronic obstructive pulmonary disease (COPD) is one of the top three causes of death worldwide, characterized by emphysema and bronchitis. Airway measurements reflect the severity of bronchitis and other airway-related diseases. Airway structures can be objectively evaluated with quantitative computed tomography (CT). The accuracy of such quantifications is limited by the spatial resolution and image noise characteristics of the imaging system and can be potentially improved with the emerging photon-counting CT (PCCT) technology. This study evaluated the quantitative performance of PCCT against energy-integrating CT (EICT) systems for airway measurements, and further identified optimum CT imaging parameters for such quantifications. The study was performed using a novel virtual imaging framework by developing the first library of virtual patients with bronchitis. These virtual patients were developed based on CT images of confirmed COPD patients with varied bronchitis severity. The human models were virtually imaged at 6.3 and 12.6 mGy dose levels using a scanner-specific simulator (DukeSim), synthesizing clinical PCCT and EICT scanners (NAEOTOM Alpha, FLASH, Siemens). The projections were reconstructed with two algorithms and kernels at different matrix sizes and slice thicknesses. The CT images were used to quantify clinically relevant airway measurements ("Pi10" and "WA%") and compared against their ground truth values. Compared to EICT, PCCT provided more accurate Pi10 and WA% measurements by 63.1% and 68.2%, respectively. For both technologies, sharper kernels and larger matrix sizes led to more reliable bronchitis quantifications. This study highlights the potential advantages of PCCT against EICT in characterizing bronchitis utilizing a virtual imaging platform.

Gamma Ray Effects on Multi-Colored Commercial Light-Emitting Diodes at MGy Level

Light-emitting diodes (LEDs) are of interest for implementation in radiation environments, such as part of illumination systems of radiation-tolerant cameras able to provide images at high doses (>MGy). It is then mandatory to characterize the radiation effects on all of the LED key properties exploited for such applications. To this aim, the evolution of the optical properties of commercial LEDs after they have been exposed to γ-rays, up to total ionizing dose (TID) levels of 2 MGy(air) at room temperature, is discussed. The devices under test include four LEDs of different colors (red, green, blue and white) in the same package. This allows a direct comparison between the responses of the different structures and technologies, as the proximity between the diodes ensures the uniformity of their irradiation conditions. The radiation effect on the electron–photon conversion mechanisms inside these LEDs is investigated through the evolution of their external quantum efficiency (EQE) vs. current characteristics. The spectral emission pattern of LEDs after irradiation at different dose levels is then characterized to estimate the TID effects on the lens which surrounds the LED package. The presented results show a monotone radiation-induced EQE decrease as a function of the TID, especially in the red LEDs. For the tested red LEDs, the EQE decreased up to 78% after a TID of 1 MGy when they were OFF during irradiation, and up to 8% when they were ON during irradiation. A visual inspection of the devices after irradiation shows a mechanical degradation of the lens shared among the four diodes. However, the emission pattern analysis does not show any significant radiation-induced changes in the optical properties of the lens. Based on these results, it appears possible to design LED-based illumination systems able to survive to MGy dose levels that can be integrated as subsystems of radiation-hardened cameras.

Photon-counting CT versus conventional CT for COPD quantifications: intra-scanner optimization and inter-scanner assessments using virtual imaging trials.

Chronic obstructive pulmonary disease (COPD) is a chronic inflammatory lung disease and a major cause of death and disability worldwide. Quantitative CT is a powerful tool to better understand the heterogeneity and severity of this disease. Quantitative CT is being increasingly used in COPD research, and the recent advancements in CT technology have made it even more encouraging. One recent advancement has been the development of photon-counting detectors, offering higher spatial resolution, higher image contrast, and lower noise levels in the images. However, the quantification performance of this new technology compared to conventional scanners remains unknown. Additionally, different protocol settings (e.g., different dose levels, slice thicknesses, reconstruction kernels and algorithms) affect quantifications in an unsimilar fashion. This study investigates the potential advantages of photon-counting CT (PCCT) against conventional energy-integrating detector (EID) CT and explores the effects of protocol settings on lung density quantifications in COPD patients. This study was made possible using a virtual imaging platform, taking advantage of anthropomorphic phantoms with COPD (COPD-XCAT) and a scanner-specific CT simulator (DukeSim). Having the physical and geometrical properties of three Siemens commercial scanners (Flash, Force for EID and NAEOTOM Alpha for PCCT) modeled, we simulated CT images of ten COPD-XCAT phantoms at 0.63 and 3.17 mGy dose levels and reconstructed at three levels of kernel sharpness. The simulated CT images were quantified in terms of "Lung mean absolute error (MAE)," "LAA -950," "Perc 15," "Lung mass" imaging biomarkers and compared against the ground truth values of the phantoms. The intra-scanner assessment demonstrated the superior qualitative and quantitative performance of the PCCT scanner over the conventional scanners (21.01% and 22.74% mean lung MAE improvement, and 53.97% and 68.13% mean LAA -950 error improvement compared to Flash and Force). The results also showed that higher mAs, thinner slices, smoother kernels, and iterative reconstruction could lead to more accurate and precise quantification scores. This study underscored the qualitative and quantitative benefits of PCCT against conventional EID scanners as well as the importance of optimal protocol choice within scanners for more accurate quantifications.

Low-contrast detectability and potential for radiation dose reduction using deep learning image reconstruction—A 20-reader study on a semi-anthropomorphic liver phantom

BackgroundA novel deep learning image reconstruction (DLIR) algorithm for CT has recently been clinically approved. PurposeTo assess low-contrast detectability and dose reduction potential for CT images reconstructed with the DLIR algorithm and compare with filtered back projection (FBP) and hybrid iterative reconstruction (IR). Material and methodsA customized upper-abdomen phantom containing four cylindrical liver inserts with low-contrast lesions was scanned at CT dose indexes of 5, 10, 15, 20 and 25 mGy. Images were reconstructed with FBP, 50% hybrid IR (IR50), and DLIR of low strength (DLL), medium strength (DLM) and high strength (DLH). Detectability was assessed by 20 independent readers using a two-alternative forced choice approach. Dose reduction potential was estimated separately for each strength of DLIR using a fitted model, with the detectability performance of FBP and IR50 as reference. ResultsFor the investigated dose levels of 5 and 10 mGy, DLM improved detectability compared to FBP by 5.8 and 6.9 percentage points (p.p.), and DLH improved detectability by 9.6 and 12.3 p.p., respectively (all p < .007). With IR50 as reference, DLH improved detectability by 5.2 and 9.8 p.p. for the 5 and 10 mGy dose level, respectively (p < .03). With respect to this low-contrast detectability task, average dose reduction potential relative to FBP was estimated to 39% for DLM and 55% for DLH. Relative to IR50, average dose reduction potential was estimated to 21% for DLM and 42% for DLH. Conclusions:Low-contrast detectability performance is improved when applying a DLIR algorithm, with potential for radiation dose reduction.

Noise and spatial resolution properties of a commercially available deep learning-based CT reconstruction algorithm.

To characterize the noise and spatial resolution properties of a commercially available deep learning-based computed tomography (CT) reconstruction algorithm. Two phantom experiments were performed. The first used a multisized image quality phantom (Mercury v3.0, Duke University) imaged at five radiation dose levels (CTDIvol : 0.9, 1.2, 3.6, 7.0, and 22.3mGy) with a fixed tube current technique on a commercial CT scanner (GE Revolution CT). Images were reconstructed with conventional (FBP), iterative (GE ASiR-V), and deep learning-based (GE True Fidelity) reconstruction algorithms. Noise power spectrum (NPS), high-contrast (air-polyethylene interface), and intermediate-contrast (water-polyethylene interface) task transfer functions (TTF) were measured for each dose level and phantom size and summarized in terms of average noise frequency (fav ) and frequency at which the TTF was reduced to 50% (f50% ), respectively. The second experiment used a custom phantom with low-contrast rods and lung texture sections for the assessment of low-contrast TTF and noise spatial distribution. The phantom was imaged at five dose levels (CTDIvol : 1.0, 2.1, 3.0, 6.0, and 10.0mGy) with 20 repeated scans at each dose, and images reconstructed with the same reconstruction algorithms. The local noise stationarity was assessed by generating spatial noise maps from the ensemble of repeated images and computing a noise inhomogeneity index, , following AAPM TG233 methods. All measurements were compared among the algorithms. Compared to FBP, noise magnitude was reduced on average (± one standard deviation) by 74±6% and 68±4% for ASiR-V (at "100%" setting) and True Fidelity (at "High" setting), respectively. The noise texture from ASiR-V had substantially lower noise frequency content with 55±4% lower NPS fav compared to FBP while True Fidelity had only marginally different noise frequency content with 9±5% lower NPS fav compared to FBP. Both ASiR-V and True Fidelity demonstrated locally nonstationary noise in a lung texture background at all radiation dose levels, with higher noise near high-contrast edges of vessels and lower noise in uniform regions. At the 1.0mGy dose level values were 314% and 271% higher in ASiR-V and True Fidelity compared to FBP, respectively. High-contrast spatial resolution was similar between all algorithms for all dose levels and phantom sizes (<3% difference in TTF f50% ). Compared to FBP, low-contrast spatial resolution was lower for ASiR-V and True Fidelity with a reduction of TTF f50% of up to 42% and 36%, respectively. The deep learning-based CT reconstruction demonstrated a strong noise magnitude reduction compared to FBP while maintaining similar noise texture and high-contrast spatial resolution. However, the algorithm resulted in images with a locally nonstationary noise in lung textured backgrounds and had somewhat degraded low-contrast spatial resolution similar to what has been observed in currently available iterative reconstruction techniques.

Investigations of the MGy dose level radiation effects on the photometric budget of a radiation-hardened CMOS-based camera.

We studied the impact of ionizing radiation at high dose levels (megagray, MGy) on the photometric budget of a radiation-resistant complementary metal oxide semi-conductor (CMOS)-based camera. This is achieved by measuring the radiation-induced degradation of each subpart, namely its illumination system, its optical system, and its CMOS image sensor. The acquired experimental results allow performing a rather realistic simulation of the radiation effects at the system level. Thanks to appropriate mitigation techniques, limited image darkening and color change are obtained at MGy dose levels. The presented results confirm the feasibility of a CMOS-based camera able to resist to MGy dose level of ionizing radiations with an acceptable degradation of the image quality, opening the way to its implementation in the most challenging harsh environments.

Distributed Optical Fiber Sensor Allowing Temperature and Strain Discrimination in Radiation Environments

We evaluate the potential of a new architecture of distributed optical fiber sensor (DOFS) to discriminate between the temperature and strain changes along a single optical fiber exposed to radiation. This DOFS exploits the measurements of both the Landau–Placzek ratio (LPR) and the Brillouin frequency shift (BFS) to achieve the discrimination between the two parameters on up to 10 km of fiber with a spatial resolution of 1 m. We demonstrate that the LPR remains unaffected up to MGy(SiO2) dose levels, whereas the BFS is only slightly shifted by the radiation. The measured radiation-induced BFS is strongly reduced in radiation-hardened fluorine-doped single-mode optical fibers. Combining the DOFS architecture and the fiber allows discriminating temperature and strain using a single optical fiber up to megagray dose levels.

Effect of cobalt-60 gamma radiation on total hemocyte content and biochemical parameters in Macrobrachium rosenbergii (De Man, 1879)

Purpose: The effect of low level cobalt-60 (60Co) gamma radiation on the freshwater prawn Macrobrachium rosenbergii was evaluated by observing their hemocyte counts and biochemical parameters.Materials and methods: Prawns were exposed to 3, 30, 300 and 3000 milligray (mGy) dose levels and their tissues of gills, hepatopancreas and muscle were analyzed.Results: The results showed that the number of hemocytes in the hemolymph and concentrations of protein and carbohydrate were significantly reduced in irradiated groups than compared to the control prawn. Increased aspartate transaminase (AST), alanine transaminase (ALT), lactate dehydrogenase (LDH), alkaline phosphatase (ALP), Acetyl choline esterase (AChE) in the irradiated groups reflects tissue damage.Conclusions: Hence, this study concludes that even low level of ionizing radiation (60Co gamma) can cause acute damages in gills, hepatopancreas and muscles in irradiated groups.Highlights60Co exposures effect the THC and biochemical of prawn M. rosenbergii.Different dose levels such as 3, 30, 300 and 3000 mGy.Biochemical parameters serve as reliable indicators of physical status of organism.Self-regulating mechanisms might be the reason for preventing from the lethality.Suggested that nuclear industries should manage below 3 mGy.

A novel Lab-on-Fiber Radiation Dosimeter for Ultra-high Dose Monitoring

In this work, we report on the first demonstration of Lab on Fiber (LOF) dosimeter for ionizing radiation monitoring at ultra-high doses. The new dosimeter consists in a metallo-dielectric resonator at sub-wavelength scale supporting localized surface plasmon resonances realized on the optical fiber (OF) tip. The resonating structure involves two gold gratings separated by a templated dielectric layer of poly(methyl methacrylate) (PMMA). Two LOF prototypes have been manufactured and exposed at the IRRAD Proton Facility at CERN in Geneva to 23 GeV protons for a total fluence of 0.67 × 1016 protons/cm2, corresponding to an absorbed dose of 1.8 MGy. Experimental data demonstrated the “radiation resistance” feature of the LOF devices and a clear dependence of the reflected spectrum versus the total dose, expressed by a cumulative blue-shift of ~1.4 nm of the resonance combined with a slight increase of 0.16 dBm in the reflected spectrum. The numerical analysis carried out to correlate the experimental results with the dimensional and physical properties of the resonator, expected to be tightly connected to the absorbed dose, suggests that the main phenomenon induced by exposure to proton beam and able to explain the measured spectral behavior is the reduction of the PMMA thickness, which is also consistent with past literature in the field. Preliminary results demonstrated the potentiality of the proposed platform as dosimeter at MGy dose levels for high energy physics experiments.

Growth and Decay Kinetics of Radiation-Induced Attenuation in Bulk Optical Materials

Using a dedicated setup, the growth and decay kinetics of the radiation-induced attenuation (RIA) have been characterized during and after steady-state 40-keV X-ray exposures of bulk (1-cm thickness) optical materials. Such materials served to design the lenses of radiation-hardened cameras of the FURHIS Project intended to withstand MGy (SiO2) dose levels associated with ITER remote handling operations. RIA is monitored in situ in the 400- to 800-nm spectral domain for glass types ranging from radiation sensitive (BK7) to radiation hardened ones: pure silica, BK7G18, K5G20, and SF6G05 from SCHOTT. In addition to the detailed characterization of these various glasses, our study highlights the systematic underestimation of the RIA measured by the usual qualification approach consisting in postirradiation RIA measurements after dose steps. The error due to this underestimation is shown to strongly depend on the glass type, very large for the BK7G18 glass. This material is associated with high transient RIA, its loss levels exceed the ones of its nonrad-hard counterpart (BK7) at low dose levels. For the development of MGy radiation-hardened systems using these glasses, a vulnerability study of the in situ response of glass lenses appears mandatory. By improving our knowledge on the origin of these transient losses, appropriate hardening techniques to maintain the camera photometry budget will be tested in the future.

Investigating energy deposition within cell populations using Monte Carlo simulations

In this work, we develop multicellular models of healthy and cancerous human soft tissues, which are used to investigate energy deposition in subcellular targets, quantify the microdosimetric spread in a population of cells, and determine how these results depend on model details. Monte Carlo (MC) tissue models combining varying levels of detail on different length scales are developed: microscopically-detailed regions of interest (>1500 explicitly-modelled cells) are embedded in bulk tissue phantoms irradiated by photons (20 keV–1.25 MeV). Specific energy (z; energy imparted per unit mass) is scored in nuclei and cytoplasm compartments using the EGSnrc user-code egs_chamber; specific energy mean, , standard deviation, , and distribution, , are calculated for a variety of macroscopic doses, D. MC-calculated are compared with normal distributions having the same mean and standard deviation. For ∼mGy doses, there is considerable variation in energy deposition (microdosimetric spread) throughout a cell population: e.g. for 30 keV photons irradiating melanoma with 7.5 μm cell radius and 3 μm nuclear radius, for nuclear targets is , and the fraction of nuclei receiving no energy deposition, fz=0, is 0.31 for a dose of 10 mGy. If cobalt-60 photons are considered instead, then decreases to , and fz=0 decreases to 0.036. These results correspond to randomly arranged cells with cell/nucleus sizes randomly sampled from a normal distribution with a standard deviation of 1 μm. If cells are arranged in a hexagonal lattice and cell/nucleus sizes are uniform throughout the population, then decreases to and for 30 keV and cobalt-60, respectively; fz=0 decreases to 0.25 and 0.000 94 for 30 keV and cobalt-60, respectively. Thus, specific energy distributions are sensitive to cell/nucleus sizes and their distributions: variations in specific energy deposited over a cell population are underestimated if targets are assumed to be uniform in size compared with more realistic variation in target size. Bulk tissue dose differs from for nuclei (cytoplasms) by up to () across all cell/nucleus sizes, bulk tissues, and incident photon energies, considering a 50 mGy dose level. Overall, results demonstrate the importance of microdosimetric considerations at low doses, and indicate the sensitivity of energy deposition within subcellular targets to incident photon energy, dose level, elemental compositions, and microscopic tissue model.

Vulnerability and Hardening Studies of Optical and Illumination Systems at MGy Dose Levels

In the framework of the fusion for energy radiation hard imaging system project, the main radiation effects affecting the image quality of a miniaturized complementary metal–oxide–semiconductor-based camera exposed to radiation doses up to 1 MGy(SiO2) are investigated for ITER applications. The radiation effects related to two of the three subcomponents of the camera are investigated: the optical system (OS) and the illumination system (IS). Subsystem demonstrators have been manufactured selecting radiation tolerant or hardened materials and components to demonstrate the feasibility to withstand such high dose levels while fulfilling the ITER remote handling needs in terms of optical performances and miniaturization. Regarding the OS, the observed degradation of the radiation-hardened optical glasses used for the OS lenses is characterized in terms of both radiation-induced attenuation and radiation-induced refractive-index change. At the system level, impact of these phenomena on the OS demonstrator performances is discussed in terms of image contrast. Radiation test results highlight the high radiation tolerance of manufactured monochrome and color OS to both degradation mechanisms. Regarding the IS, the selected architecture consists in a ring of 20 commercially available light-emitting diodes (LEDs) with monochrome (amber) or white emissions. An appropriate choice for the LEDs allows designing an IS with the requested performances and slight degradation of its output power at the MGy dose levels. From the obtained results, developing miniaturized IS and OS subcomponents for MGy dose operation levels appears realistic using commercially available technologies and appropriate hardening procedures.

Radiation-Hardened Fiber Bragg Grating Based Sensors for Harsh Environments

Fiber Bragg Grating (FBG) based sensors are nowadays used for several applications, but, even if they present advantages for their incorporation into radiation environments, commercial-off-the-shelf devices cannot still be used in harsh conditions. We recently reported a procedure for fabricating FBGs resistant to severe constraints combining both high radiation doses up to MGy levels and operation temperatures exceeding 200°C (RadHard FBGs). Following these results, the European project HOBAN was granted by Kic InnoEnergy with the aim of developing and marketing FBG-based temperature and strain monitoring systems suitable for harsh nuclear environments (350°C temperature and MGy dose levels), with their associated instrumentation devices. In this framework, we present an accurate study about the robustness of the radiation-response of these RadHard FBGs against the main grating inscription parameters. Up to the accumulated X-ray dose of 1 MGy(SiO2), no significant radiation induced Bragg wavelength shift is observed meaning that radiations induce errors below ± 0.4°C in the temperature estimation. Moreover, a study about the dose-rate dependence (1 to 50 Gy/s) of the gratings response is also reported and confirms the high radiation hardness of our RadHard FBGs at all dose rates.

Investigation of Coating Impact on OFDR Optical Remote Fiber-Based Sensors Performances for Their Integration in High Temperature and Radiation Environments

The response of optical frequency-domain reflectometry-based temperature sensors is here investigated in harsh environments (high temperature, high radiation dose) focusing the attention on the impact of the fiber coating on the sensor performances in such conditions. Our results demonstrate that the various coating types evolve differently under thermal treatment and/or radiations, resulting in a small ( ${C_T}s$ ) remain identical within 1% fluctuations up to 10 MGy dose, and that permanent radiation-induced attenuation reached values stands for the development of high-spatial resolved distributed temperature for harsh environment associated with high temperature (up to 300 ° C) and ionizing radiation up to the MGy dose level.

Image texture and radiation dose properties in CT.

The aim of this study was to compare image noise properties of GE Discovery HD 750 and Toshiba Aquilion ONE. The uniformity section of a Catphan 600 image quality assurance phantom was scanned with both scanners, at different dose levels and with extension rings simulating patients of different sizes. 36 datasets were obtained and analyzed in terms of noise power spectrum. All the results prove that introduction of extension rings significantly altered the image quality with respect to noise properties. Without extension rings, the Toshiba scanner had lower total visible noise than GE (with GE as reference: FC18 had 82% and FC08 had 80% for 10 mGy, FC18 had 77% and FC08 74% for 15 mGy, FC18 had 80% and FC08 77% for 20 mGy). The total visible noise (TVN) for 20 and 15 mGy were similar for the phantom with the smallest additional extension ring, while Toshiba had higher TVN than GE for the 10 mGy dose level (120% FC18, 110% FC08). For the second and third ring, the GE images had lower TVN than Toshiba images for all dose levels (Toshiba TVN is greater than 155% for all cases). The results indicate that GE potentially has less image noise than Toshiba for larger patients. The Toshiba FC18 kernel had higher TVN than the Toshiba FC08 kernel with additional beam hardening correction for all dose levels and phantom sizes (120%, 107%, and 106% for FC18 compared to 110%, 98%, and 97%, for FC08, for 10, 15 and 20 mGy doses, respectively).PACS number(s): 87.57.Q‐, 87.57.nf, 87.57.C‐

Ultralow-dose CT with tin filtration for detection of solid and sub solid pulmonary nodules: a phantom study.

To investigate the diagnostic performance of advanced modelled iterative reconstruction (ADMIRE) to filtered back projection (FBP) when using an ultralow-dose protocol for the detection of solid and subsolid pulmonary nodules. Single-energy CT was performed at 100 kVp with tin filtration in an anthropomorphic chest phantom with solid and subsolid pulmonary nodules (2-10 mm, attenuation, 20 to -800 HU at 120 kVp). The mean volume CT dose index (CTDIvol) of the standard chest protocol was 2.2 mGy. Subsequent scans were obtained at 1/8 (0.28 mGy), 1/20 (0.10 mGy) and 1/70 (0.03 mGy) dose levels by lowering tube voltage and tube current. Images were reconstructed with FBP and ADMIRE. One reader measured image noise; two readers determined image quality and assessed nodule localization. Image noise was significantly reduced using ADMIRE compared with FBP (ADMIRE at a strength level of 5 : 70.4% for 1/20; 71.6% for 1/8; p < 0.001). Interobserver agreement for image quality was excellent (k = 0.88). Image quality was considered diagnostic for all images at 1/20 dose using ADMIRE. Sensitivity of nodule detection was 97.1% (100% for solid, 93.8% for subsolid nodules) at 1/20 dose and 100% for both nodule entities at 1/8 dose using ADMIRE 5. Images obtained with 1/70 dose had moderate sensitivity (overall 85.7%; solid 95%; subsolid 73.3%). Our study suggests that with a combination of tin filtration and ADMIRE, the CTDIvol of chest CT can be lowered considerably, while sensitivity for nodule detection remains high. For solid nodules, CTDIvol was 0.10 mGy, while subsolid nodules required a slightly higher CTDIvol of 0.28 mGy. Detection of subsolid nodules is feasible with ultralow-dose protocols.

TU‐G‐204‐04: A Unified Strategy for Bi‐Factorial Optimization of Radiation Dose and Contrast Dose in CT Imaging

Purpose:To substantiate the interdependency of contrast dose, radiation dose, and image quality in CT towards the patient‐ specific optimization of the imaging protocolsMethods:The study deployed two phantom platforms. A variable sized (12, 18, 23, 30, 37 cm) phantom (Mercury‐3.0) containing an iodinated insert (8.5 mgI/ml) was imaged on a representative CT scanner at multiple CTDI values (0.7–22.6 mGy). The contrast and noise were measured from the reconstructed images for each phantom diameter. Linearly related to iodine‐concentration, contrast‐to‐noise ratio (CNR), were calculated for 16 iodine‐concentration levels (0–8.5 mgI/ml). The analysis was extended to a recently developed suit of 58 virtual human models (5D XCAT) with added contrast dynamics. Emulating a contrast‐enhanced abdominal image procedure and targeting a peak‐enhancement in aorta, each XCAT phantom was “imaged” using a simulation platform (CatSim, GE). 3D surfaces for each patient/size established the relationship between iodine‐concentration, dose, and CNR. The ratios of change in iodine‐concentration versus dose (IDR) to yield a constant change in CNR were calculated for each patient size.Results:Mercury phantom results show the image‐quality size‐ dependence on CTDI and IC levels. For desired image‐quality values, the iso‐contour‐lines reflect the trade off between contrast‐material and radiation doses. For a fixed iodine‐concentration (4 mgI/mL), the IDR values for low (1.4 mGy) and high (11.5 mGy) dose levels were 1.02, 1.07, 1.19, 1.65, 1.54, and 3.14, 3.12, 3.52, 3.76, 4.06, respectively across five sizes. The simulation data from XCAT models confirmed the empirical results from Mercury phantom.Conclusion:The iodine‐concentration, image quality, and radiation dose are interdependent. The understanding of the relationships between iodine‐concentration, image quality, and radiation dose will allow for a more comprehensive optimization of CT imaging devices and techniques, providing the methodology to balance iodine‐concentration and dose based on patient's attributes.

High Total Ionizing Dose and Temperature Effects on Micro- and Nano-Electronic Devices

This paper investigates the vulnerability of several micro- and nano-electronic technologies to a mixed harsh environment involving high total ionizing dose at MGy levels and high temperature. Such operating conditions emerge today for several applications like new security systems in existing or future nuclear power plants, fusion experiments, or deep space missions. In this work, the competing effects of ionizing radiations and temperature are characterized in elementary devices made of MOS transistors from several technologies. First, devices are irradiated using a radiation laboratory X-ray source up to MGy dose levels at room temperature. Devices are either grounded or biased during irradiation to simulate two major circuit cases: a circuit which waits for a wake up signal, representing most of the lifetime of an integrated circuit operating in a harsh environment, and a nominal circuit function. Devices are then annealed at several temperatures to discuss the post-irradiation behavior and to determine whether an elevated temperature is an issue or not for circuit function in mixed harsh environments.

Radiation tolerant fiber Bragg gratings for high temperature monitoring at MGy dose levels

We report a method for fabricating fiber Bragg gratings (FBG) resistant to very severe environments mixing high radiation doses (up to 3 MGy) and high temperatures (up to 230°C). Such FBGs have been written in two types of radiation resistant optical fibers (pure-silica and fluorine-doped cores) by exposures to a 800 nm femtosecond IR laser at power exceeding 500 mW and then subjected to a thermal annealing treatment of 15 min at 750°C. Under radiation, our study reveals that the radiation induced Bragg wavelength shift (BWS) at a 3 MGy dose is strongly reduced compared to responses of FBGs written with nonoptimized conditions. The BWS remains lower than 10 pm for temperatures of irradiation ranging from 25°C to 230°C without noticeable decrease of the FBG peak amplitude. For an applicative point of view, this radiation induced BWS corresponds to an additional error on the temperature measurements lower than 1.5°C, opening the way to the development of radiation-tolerant multi-point temperature sensors for nuclear industry.

LONG-PERIOD FIBER GRATING–BASED NUCLEAR RADIATION SENSORS FOR HIGH-LEVEL DOSE APPLICATIONS

We present for first time the detailed investigation on the effect of MGy (106 Gy) dose level of gamma radiation on the parameters of CO2 laser-written long-period fiber gratings (LPFGs) in B/Ge-doped single-mode fibers with particular attention to lower-order modes and higher order nonturnaround point (non-TAP) modes. Wavelength shifts up to 11 nm for 100 kGy dose and a further shift of 20 nm (1.5 nm/100 kGy) for dose of 900 kGy (total 1 MGy) were observed. Further, the radiation-induced shifts of resonant modes did not saturate up to a 1 MGy dose. No remarkable changes were observed in width and amplitude of the resonant dips during in-situ measurements up to the full dose irradiation. The radiation sensitivity up to 100 kGy was found to be independent of the grating period. This study shows that LPFGs in boron-doped fibers are strong candidates for very high-dose sensing applications such as in super Large Hadron Collider (LHC) and International Thermonuclear Experimental Reactor (ITER).