Contrast Objects Research Articles

A Morphologic Contrast on Korean and Chinese Third-Person Pronouns

The purpose of this paper is to contrast the morphologic characteristics of Korean and Chinese third-person pronouns, and then to consider the similarities and differentiae of them through the perspectives of contrastive linguistics. Before the contrast, we made the analysis of preceding researches, and made them can be the contrasted objects by systemizing the analysis of preceding researches. After that, we analyzed their morphologic features through analyzing many example sentences. In addition, the contrastive analysis of them was made to identify the similarities and differentiae of their usages. From the morphologic viewpoints, whether the modification occurs or not was the point; from the syntactic viewpoints, the components of sentence and the grammatical usages were the main points. When the meaning of respecting turns up, Korean third-person pronouns have modifications, and Chinese third-person pronouns can achieve it through the change of syntactic structure.

10 Macrophage-derived wnts are required for scar-free regeneration of the neonatal mouse myocardium

Objective In contrast to the adult, neonatal mice regenerate their myocardium following injury, at least during the first week after birth. 1 Macrophages (Mx) contribute to vessel formation and scar removal following neonatal myocardial infarction (MI) 2 . In the kidney 3 liver 4,7 and gut 5 Mx-derived WNTs are required for scar free regeneration following injury. Secretion of WNTs is dependent on acylation by Porcupine (PORCN). In the present study it was hypothesised that neonatal cardiac regeneration would be impaired in mice with Csf1r-Cre driven Mx specific Porcn deletion. 5 Methods Csf1r-EGFP(MacGreen), Porcn fl/ Csf1r Cre-ve and Porcn fl /Csf1r Cre+ve mice underwent coronary artery ligation at post-natal day 1 (P1). Functional loss 1 day after MI, and recovery by P21 were assessed by high-resolution ultrasound. Heart sections were stained with isolectin B4 (vessel density) and picrosirius res (fibrosis). Myocardial gene expression was determined by PCR array in wild-type (WT) mice after injury. Results At day 1 and day 7 post-MI, Csf1r-expressing cells accumulated within the injured myocardium, consistent with a role in regeneration. 2 At day 1 post-MI, fractional area change (FAC) decreased from 40.9% ± 1.6 to 18.0% ± 2.4% (p Porcn fl/ Csf1r Cre-ve and Porcnfl/Csf1rCre-ve mice respectively. By 21 days after MI, FAC had recovered to 47.4% ± 2.5% (p Porcn fl/ Csf1r Cre-ve and 45.8% ± 1.9% (p Porcn fl/ Csf1r Cre-ve littermates. Coronary vascularisation was restored in the infarct area by 21 days in both lines, but interstitial fibrosis was significantly higher in Porcn fl/ Csf1r Cre-ve (6.0 ± 0.9% LV) compared to Porcn fl/ Csf1r Cre-ve (3.8 ± 0.5% LV, p Wnt5b and Fzd2 , genes associated with regulation of fibrosis. 8 Conclusion Mx-derived WNTs are not required for re-vascularisation or restoration of myocardial function after neonatal myocardial injury, but are necessary for scar removal during regeneration. References Porrello et al . PNAS 2013; 110 :p187–92. Aurora et al . JCI 2014; 124 :p1382–92. Lin et al . PNAS 2010; 107 :p4194–99. Boulter et al . Nat Med 2012; 18 :572–9. Saha et al . Nat Com 2016; 7 :1–16. Derlindati et al . PLoS ONE 2015; 10 :1–17. Irvine et al . Fibrogenesis Tissue Repair 2015; 8 :19–32. Laeremans et al . Cardiovascular Research 2010; 87 :514–523.

Applying a Dynamic Performance Management Framework to Wicked Issues: How Coproduction Helps to Transform Young People’s Services in Surrey County Council, UK

ABSTRACTThis article explores how a dynamic performance management (DPM) approach can give policy makers a more integrated, time-related understanding of how to address wicked problems successfully. The article highlights how an outcome-based approach to solving wicked policy problems has to balance three very contrasting objectives of stakeholders in the policy making process – improving service quality, improving quality of life outcomes and improving conformity to the principles of public governance. Simultaneous achievement of these three objectives may not be feasible, as they may form an interactive dynamic system. However the balancing act between them may be achieved by the use of DPM. Policy insights from this novel approach are illustrated through a case study of a highly successful co-production intervention to help young people with multiple disadvantages in Surrey, UK. The implications of DPM are that policy development needs to accept the important roles of emergent strategy and learning mechanisms, rather than attempting ‘blueprint’ strategic planning and control mechanisms. Some expectations about the results may indeed be justifiable in particular policy systems, as clustering of quality of life outcomes and outcomes in the achievement of governance principles is likely, because behaviours are strongly inter-related. However, this clustering can never be taken for granted but must be tested in each specific policy context. Undertaking simulations with the model and recalibrating it through time, as experience builds up, may allow learning in relation to overcoming barriers to achieving outcomes in the system.

Optimization of contrast-enhanced breast imaging: Analysis using a cascaded linear system model.

Contrast-enhanced (CE) breast imaging involves the injection contrast agents (i.e., iodine) to increase conspicuity of malignant lesions. CE imaging may be used in conjunction with digital mammography (DM) or digital breast tomosynthesis (DBT) and has shown promise in improving diagnostic specificity. Both CE-DM and CE-DBT techniques require optimization as clinical diagnostic tools. Physical factors including x-ray spectra, subtraction technique, and the signal from iodine contrast, must be considered to provide the greatest object detectability and image quality. We developed a cascaded linear system model (CLSM) for the optimization of CE-DM and CE-DBT employing dual energy (DE) subtraction or temporal (TE) subtraction. We have previously developed a CLSM for DBT implemented with an a-Se flat panel imager (FPI) and filtered backprojection (FBP) reconstruction algorithm. The model is used to track image quality metrics - modulation transfer function (MTF) and noise power spectrum (NPS) - at each stage of the imaging chain. In this study, the CLSM is extended for CE breast imaging. The effect of x-ray spectrum (varied by changing tube potential and the filter) and DE and TE subtraction techniques on breast structural noise was measured was studied and included as a deterministic source of noise in the CLSM. From the two-dimensional (2D) and three-dimensional (3D) MTF and NPS, the ideal observer signal-to-noise ratio (SNR), also known as the detectability index (d'), may be calculated. Using d' as a FOM, we discuss the optimization of CE imaging for the task of iodinated contrast object detection within structured backgrounds. Increasing x-ray energy was determined to decrease the magnitude of structural noise and not its correlation. By performing DE subtraction, the magnitude of the structural noise was further reduced at the expense of increased stochastic (quantum and electronic) noise. TE subtraction exhibited essentially no residual structural noise at the expense of increased quantum noise, even over that of the DE case. For DE subtraction, optimization of dose weighting to the HE view (fh ) results in the minimization of quantum noise. Both subtraction weighting factor (wSub ) and the iodine contrast signal were dependent on the LE and HE x-ray spectra. To best detect a 5 mm Gaussian lesion with 5 mg/ml of iodine within a 4 cm thick breast, it was found that the high energy (HE) view should be acquired with a tube potential of 47 kVp (W/Ti spectrum) and the low energy (LE) view with a potential of 23 kVp (W/Rh spectrum). Due to the complete removal of structural noise, TE subtraction produced much higher d' than DE subtraction both as a function of mean glandular dose and iodine concentration. We have shown the effect of increasing x-ray energy as well as projection domain subtraction on breast structural noise. Further, we have exhibited the utility of the CLSM for DE and TE subtraction CE imaging in the optimization of imaging parameters such as x-ray energy, fh , and wSub as well as guiding the understanding of their effects on image contrast and noise.

The effect of quality control on the function of magnetic resonance imaging (MRI), using American College of Radiology (ACR) phantom

ObjectiveTo study image quality of MRI scanner using the American College of Radiology (ACR) phantom. Material and methodsImage quality of 1.5T MRI scanner was tested using ACR phantom. A standard head coil with standard restraints was used to fix the phantom head position. The phantom included seven modules for measuring MRI scanner image quality. MRI images for each module were analyzed. ResultsFor the Geometric accuracy test the inside length of the phantom was 146mm and the inside diameter was 189.4mm. For the High-contrast spatial resolution, individual small bright spots on the image were three pairs of hole arrays and were distinguishable. For the slice thickness test, the top signal ramp length was 54.4mm and bottom signal ramp length was 54.8mm so the slice thickness was 5.46mm. For the slice position accuracy, the bar length differences of intensity uniformity a value, called percent integral uniformity (PIU), was 96.15%. For the percent-signal ghosting, ghosting ratio was 0.0002. For the low contrast object detectability, the sum of numbers of complete spokes scored was 30 spokes. ConclusionsImage quality tests were very important in acceptance of any MRI scanner after installation and during maintenance. Using ACR phantom, these tests approve that the image parameters are acceptable.

Optimizing Personalized Touristic Itineraries by a Multiobjective Evolutionary Algorithm

The paper presents an electronic tourist guide, relying on an evolutionary optimizer, able to plan personalized multiple-day itineraries by considering several contrasting objectives. Since the itinerary planning can be modeled as an extension of the NP-complete team orienteering problem with time windows, a multiobjective evolutionary optimizer is proposed to find in reasonable times near-optimal solutions to such an extension. This optimizer automatically designs the itinerary by aiming at maximizing the tourists’ satisfaction as a function of their personal preferences and environmental constraints, such as operating hours, visiting times and accessibility of the points of interests, and weather forecasting. Experimental evaluations have demonstrated that the proposed optimizer is effective in different simulated operating conditions.

Dose reduction in CT urography and vasculature phantom studies using model-based iterative reconstruction.

To evaluate the feasibility of radiation dose reduction using model‐based iterative reconstruction (MBIR) for evaluating the ureters and vasculature in a phantom, a tissue‐equivalent CT dose phantom was scanned using a 64‐channel CT scanner. Tubes of varying diameters filled with different dilutions of a contrast agent, simulating ureters or vessels, were inserted into the center of the phantom. Each combination was scanned using an existing renal protocol at 140 kVp or 120 kVp, yielding a display volumetric CT dose index (CTDIvol) of 24 mGy. The scans were repeated using reduced scan techniques to achieve lower radiation doses down to 0.8 mGy. The images were reconstructed using filtered back‐projection (FBP) and model‐based iterative reconstruction (MBIR). The noise and contrast‐to‐noise ratio (CNR) was measured for each contrast object. Comparisons between the two reconstruction methods at different dose levels were evaluated using a factorial design. At each CTDIvol the measured image noise was lower using MBIR compared to FBP (p<0.0001). At low doses, the percent change in measured image noise between FBP and MBIR was larger. For the 12 mm object simulating a ureter or large vessel with an HU of 600, the measured CNR using MBIR at a CTDIvol of 1.7 mGy was greater than the CNR of FBP at a CTIDvol of 24 mGy (p<0.0001). For the 5 mm object simulating a medium‐sized vessel with a HU of 250, the measured CNR using MBIR at a CTDIvol of 1.7 mGy was equivalent to that of FBP at a CTDIvol of 24 mGy. For the 2 mm, 100 HU object simulating a small vessel, the measured CNR using MBIR at a CTDIvol of 1.7 mGy was equivalent to that of FBP at a CTDIvol of 24 mGy. Low‐dose (3.6 mGy) CT imaging of vasculature and ureter phantoms using MBIR results in similar noise and CNR compared to FBP at approximately one‐sixth the dose. This suggests that, using MBIR, a one milliSievert exam of the ureters and vasculature may be clinically possible whilst still maintaining adequate image qualityPACS number(s): 87.57.‐s, 87.57.Q‐, 87.57.C‐, 87.57.nf, 87.57.cj, 87.57.cm

Early information processing contributions to object individuation revealed by perception of illusory figures.

To isolate multiple coherent objects from their surrounds, each object must be represented as a stable perceptual entity across both time and space. Recent theoretical and empirical work has proposed that this process of object individuation is a mid-level operation that emerges around 200-300 ms after stimulus onset. However, this hypothesis is based on paradigms that have potentially obscured earlier effects. Furthermore, no study to date has directly assessed whether object individuation occurs for task-irrelevant objects. In the present study we used electroencephalography (EEG) to measure the time course of individuation, for stimuli both within and outside the focus of attention, to assess the information processing stage at which object individuation arises for both types of objects. We developed a novel paradigm involving items defined by illusory contours, which allowed us to vary the number of to-be-individuated objects while holding the physical elements of the display constant (a design characteristic not present in earlier work). As early as 100 ms after stimulus onset, event-related potentials tracked the number of objects in the attended hemifield, but not those in the unattended hemifield. By contrast, both attended and unattended objects could be individuated at a later stage. Our findings challenge recent conceptualizations of the time course of object individuation and suggest that this process arises earlier for attended than unattended items, implying that voluntary spatial attention influences the time course of this operation.

Basic quality control in routine MRI

Aim Magnetic Resonance Imaging (MRI) has evolved a valid clinical tool in everyday practice. Its unique capabilities of imaging soft tissue human anatomy and physiology with excellent spatial, temporal and contrast resolution explain its outstanding role in clinical imaging. The aim of this lecture is to present the rationale of Quality Control (QC) and Quality Assurance (QA) in MRI and to briefly present a set of basic QC tests that can ensure MRI system’s performance and help on maintain diagnostic quality in routine clinical MRI examinations. Learning objectives • Understand the general rationale of QC and QA in MRI. • Presentation of the AAPM 100 protocol. Basic procedures and methodologies. • Presentation of accredited phantoms and tools used for basic QC and QA in MRI. • Presentation of a set of basic QC tests for assessing MRI system’s performance based solely on simple imaging post-processing methods. This will include assessments of the following system’s parameters: – H0 static field homogeneity – Signal to Noise (SNR) and Contrast to Noise (CNR) measurements – Spatial Uniformity of SNR – Chosting Ratio and MR image uniformity – Geometric Distortion and Spatial Linearity – Slice thickness – High Contrast Spatial Resolution – Low Contrast Object Detectability

Low contrast quality assesment in CT: Human and model observer comparison

Introduction Actually there is not a widely accepted method for low contrast resolution evaluation in CT scans. Purpose To test the performance of a novel ImageJ macro devoted to Catphan CTP515 low contrast automatic analysis by comparing the results with human observers. Materials and methods Software and human proportion correct curves (PCC), function of the low contrast object diameter, and corresponding Minimum Detectable Size (MDS) were determined and compared. Software PCC was obtained using the CTP515 1% contrast group of Catphan 600 images, acquired with Discovery 750 (GE healthcare) 64 slices CT scanner varying noise index (NI = 8, 12) and analysed with a non-prewhitening matched filter with an eye filter model observer. The human PCC was calculate with a known exactly signal and background experiment based on 740 canvas consisting of a template object to be recognized and two images (“background” and “signal + background”) among which the one containing the object had to be chosen. The experiment was repeated with 4 human observers. Inter-observer and human/model PC agreements were evaluated respectively with ICC test and Pearson correlation coefficient with Student t-test. Results MDS for software and human were respectively 2.77 mm and 4.42 mm (12 NI), 1.46 mm and 2.96 mm (8 NI). ICCs were 0.89 (8NI) and 0.84 (12NI); correlation coefficient was 0.89 (p = 0.02). Conclusion The high correlation between human and model showed that the macro represents a valid tool for low contrast resolution analysis. It could be useful in CT protocol optimization also thanks to its easy use. Disclosure Authors disclose any relationship that may bias their presentation.

Impact of iterative reconstructions on image noise and low-contrast object detection in low kVp simulated abdominal CT: a phantom study.

Low kilovoltage (kVp) computed tomography (CT) may be used to reduce contrast medium dose in patients at risk of contrast nephropathy, at the cost of increased image noise. To evaluate: (i) the impact of iterative reconstructions (Siemens SAFIRE) on low-contrast object detection to compensate for increased noise instead of increased tube loading when decreasing tube potential; and (ii) the change in iodine attenuation in simulated abdominal CT. A phantom was scanned at 70, 80, 100, and 120 kVp at fixed effective tube loading (170 mAsEFF) and fixed radiation dose (CTDIVOL 10 mGy). Images were reconstructed with filtered back-projection (FBP) and SAFIRE strengths S1-S5. Iodine attenuation, objective image noise, contrast-to-noise ratio (CNR), noise power spectrum (NPS), spatial resolution, and subjective detectability of low-contrast objects were evaluated. Compared with 120 kVp iodine attenuation increased by a factor 1.6 and 2.0, and image noise increased by a factor 1.9 and 2.5 at 80 and 70 kVp, respectively. Compared with FBP, SAFIRE showed objective reduction in image noise and increased CNR without loss of spatial resolution or any significant NPS alteration, with general tendency to improve subjective detectability of low-contrast objects. At 170 mAsEFF the number of discernible 1.0% contrast objects at 70 kVp/S5 and 80 kVp/S5 was similar to that at 120 kVp/FBP. With the SAFIRE algorithm image noise, CNR and detectability of low-contrast objects may be kept unchanged without increased tube loading when using low kVp settings to reduce contrast medium dose in azotemic patients.

Low contrast detectability and spatial resolution with model-based Iterative reconstructions of MDCT images: a phantom and cadaveric study.

To compare image quality [low contrast (LC) detectability, noise, contrast-to-noise (CNR) and spatial resolution (SR)] of MDCT images reconstructed with an iterative reconstruction (IR) algorithm and a filtered back projection (FBP) algorithm. The experimental study was performed on a 256-slice MDCT. LC detectability, noise, CNR and SR were measured on a Catphan phantom scanned with decreasing doses (48.8 down to 0.7mGy) and parameters typical of a chest CT examination. Images were reconstructed with FBP and a model-based IR algorithm. Additionally, human chest cadavers were scanned and reconstructed using the same technical parameters. Images were analyzed to illustrate the phantom results. LC detectability and noise were statistically significantly different between the techniques, supporting model-based IR algorithm (p < 0.0001). At low doses, the noise in FBP images only enabled SR measurements of high contrast objects. The superior CNR of model-based IR algorithm enabled lower dose measurements, which showed that SR was dose and contrast dependent. Cadaver images reconstructed with model-based IR illustrated that visibility and delineation of anatomical structure edges could be deteriorated at low doses. Model-based IR improved LC detectability and enabled dose reduction. At low dose, SR became dose and contrast dependent. • Model- based Iterative Reconstruction improves detectability of low contrast object. • With model- based Iterative Reconstruction, spatial resolution is dose and contrast dependent. • Model-based Iterative Reconstruction algorithms enable improved IQ combined with dose-reduction possibilities. • Improvement of SR and LC detectability on the same IMR data set would reduce reconstructions.

WE‐DE‐207B‐06: Artifact Reduction in Digital Breast Tomosynthesis with the Denoised Ordered‐Subset Statistically Penalized Algebraic Reconstruction Technique (DOS‐SPART) Algorithm

Purpose:Digital breast tomosynthesis (DBT) is an emerging breast imaging modality. It uses x‐ray absorption projection images acquired over a narrow angular span to provide high spatial resolution pseudo‐three dimensional images for breast cancer screening and diagnosis. Unfortunately, the narrow range used to acquire data (typically &lt;30 degrees) results in significant out of plane artifacts for high contrast objects when conventional reconstruction techniques are used. In this work, the denoised ordered‐subset statistically penalized algebraic reconstruction technique (DOS‐SPART) algorithm was adapted to breast tomosynthesis imaging to reduce out‐of‐plane blurring artifacts.Methods:The DOS‐SPART algorithm was implemented for use with DBT datasets. The ACR mammography accreditation phantom was imaged for quantitative measurement and subjective image analysis. The artifact spread function (ASF) was measured for images generated by the commercial reconstruction method as well as DOS‐SPART with different total number of iterations (5, 10, 15, and 20). The FWHM of the ASF was used to quantify out‐of‐plane blurring. A cluster of calcifications in the ACR phantom was also inspected subjectively, and images above and below the feature were examined for artifacts.Results:The DOS‐SPART algorithm was able to efficiently reconstruct sharp image at the in‐focus plane, while significantly reducing out‐of‐plane blurring artifacts (total reconstruction time &lt;90 seconds for a 1996×2457×70 voxel volume with 5 iterations). The FWHM of the ASF was reduced by as much as 35% using the algorithm. Subjectively, the out‐of‐plane artifacts from the high contrast calcification are still clearly visible in the commercial reconstruction at 1 cm above or below the in‐focus plane, whereas no artifacts from the calcification are detectable in the out‐of‐plane images generated with DOS‐SPART.Conclusion:The application of DOS‐SPART to DBT can help limit out‐of‐plane artifacts in DBT imaging, potentially improving localization of microcalcifications and image contrast for adjacent structures.Funding support: This work was support in part by NIH R01 EB020521. Disclosures: J Garrett: None. Y. Li: None. K. Li: None. GH Chen: Research funded, GE Healthcare and Siemens AX

SU‐F‐J‐159: Influence of the Elevated Posterior Position by Using the Customized Vacuum‐Bag On the Abdominal MR Image Quality: A Quantitative Phantom Study

Purpose:Signal‐to‐noise ratio(SNR) of MR abdominal imaging in diagnostic radiology is maximized by minimizing the coil‐to‐patient distance. However, for radiotherapy applications, customized vacuum‐bag is needed for abdominal immobilization at the cost of the increasing distance to the posterior spine coil. This sub‐optimized coil setting for RT applications may compromise image quality, such as SNR and homogeneity, thus potentially affect tissue delineation. In this study, we quantitatively evaluate the effect of the vertical position change on SNR and image quality change using an ACR MR phantom.Methods:An ACR MR phantom was placed on the flat couch top. Images were acquired using an 18‐channel body array coil and spine coil on a dedicated 1.5T MR‐simulator. The scan was repeated three times with the ACR phantom elevated up to 7.5cm from the couch top, with a step size of 2.5cm. All images were acquired using standard ACR test sequence protocol of 2D spin‐echo T1‐weighted(TR/TE=500/200ms) and T2‐weighted(TR/TE1/TE2=2000/20/80) sequences. For all scans, pre‐scan normalization was turned on, and the distance between the phantom and the anterior 18‐channel body array coil was kept constant. SNR was calculated using the slice with a large water‐only region of the phantom. Percent intensity uniformity(PIU) and low contrast object detectability(LCD) were assessed by following ACR test guidelines.Results:The decrease in image SNR(from 335.8 to 169.3) and LCD(T1: from 31 to 19 spokes, T2: 26 to 16 spokes) were observed with increasing vertical distance. After elevating the phantom by 2.5cm(approximately the thickness of standard vacuum‐bag), SNR change(from 335.8 to 275.5) and LCD(T1: 31 to 26 spokes, T2: 26 to 21 spokes) change were noted. However, similar PIU was obtained for all choices of vertical distance (T1: 94.5%–95.0%, T2: 94.4%–96.8%).Conclusion:After elevating the scan object, reduction in SNR level and contrast detectability but no change in image homogeneity was observed.

SU-G-IeP2-13: Toward Heavy Ion Computed Tomography with Carbon Ions: A Monte Carlo Study

Purpose: In the present Monte Carlo study, we investigated the use of Carbon ions for computed tomography (CT) with a relatively low imaging dose. This will enable us to avoid any conversion of X-ray CT numbers to the relative stopping power (or relative electron density) values and the associated uncertainties in Carbon dose calculation. Methods: In the first stage, we studied the propagation of Carbon nuclei through a water phantom using the Geant4 specially to understand their lateral displacement inside the phantom. In the second stage, we used our GPU-based Monte Carlo code, which has been cross validated against Geant4, to create the 2D map of the water equivalent path length (WEPL) inside a human head size phantom by acquiring 240 projections each 1.5° apart. Subsequently the 3D relative electron density map of the phantom was reconstructed from the 2D WEPL map using the Algebraic Reconstruction Technique (ART) coupled with total variation (TV) minimization Results: A high quality image of the relative electron density inside the phantom was reconstructed by ARTTV. The mean relative error between the reconstructed image for low contrast object (PMMA) was about 1.74%. The delivered dose per scan at the center of the phantom was about 0.1 Gy. Conclusion: We have been able to obtain a 3D map of the electron density using a human head size phantom while keeping the delivered dose to relatively low value. Using the GPU capabilities of our simulation engine, we believe that a real time CT with Carbon ions could be a reality in future.

SU‐F‐J‐26: Performance of 2.5MV Portal Imaging in Comparison with KV X‐Ray and 6MV and Flattening‐Filter‐Free 6MV Portal Imaging

Purpose:To assess image quality and imaging dose of 2.5MV electronic portal imaging in comparison to kV imaging and 6MV and Flattening‐Filter‐Free 6MV (6MVFFF) portal imaging using a DMI imager.Methods:Quantitative assessment of image quality was performed with Leeds and Las Vegas test phantoms in conjunction with qualitative evaluation of clinical patient images for kV imaging and 2.5MV, 6MV and 6MVFFF portal imaging. High and low contrast resolutions were evaluated and imaging doses were measured using these x‐rays. Phantom test was performed both in air and in solid water. Clinical patient portal images were also reviewed and qualitatively assessed for these three imaging MV energies.Results:Among the 28 objects in Las Vegas phantom, 16, 17 and 26 of them were resolved using Low Dose technique and 18, 22 and 26 were resolved using High Quality technique with 6MV, 6MVFFF and 2.5MV, respectively. The number of Leeds low contrast objects resolved by 6MV, 6MFFFF and 2.5MV was 6, 15 and 18 with Low Dose technique and 14, 17 and 18 with High Quality technique, respectively. When the test phantoms were embedded in 20cm thick solid water, the results were noticeably affected, but the performance of 2.5MV was still substantially better than 6MV and 6MVFFF. Imaging dose with 2.5MV measured at 10 cm depth was about half of that with 6MV or 6MVFFF. Clinical patient portal images were reviewed and qualitatively assessed for different sites including brain, head‐and‐neck, chest and pelvis. 2.5MV imaging provided more details and substantially higher contrast.Conclusion:While portal imaging with 6MVFFF provides noticeably better image quality than that with 6MV, the performance of 2.5MV portal imaging is substantially better than both 6MV and 6MVFFF in terms of high and low contrast resolutions as well as lower imaging dose. 2.5MV imaging provides near kV imaging quality.

SU‐G‐206‐10: Low‐Contrast Detectability Vs. Dose for CT Images Reconstructed Using Filtered Backprojection and Iterative Reconstruction: Assessment with a Model Observer

Purpose:To evaluate CT low‐contrast detectability at different dose levels in images reconstructed using filtered backprojection (FBP) and iterative reconstruction (IR).Methods:A validated channelized Hotelling observer (CHO) model was used to detect low contrast objects in images of a helical CT phantom (Model 061, CIRS) using an Aquilion Prime 160 scanner (Toshiba Medical Systems). Twenty‐one different objects of 7 diameters (2.4, 3.2, 4.6, 6.3, 9.5, and 10 mm) and 3 contrast levels (∼10, 15, and 25 HU) were evaluated. Images were acquired using 5 different tube current settings (45, 60, 90, 140, and 180 mA) and reconstructed using both FBP and IR (Adaptive Iterative Dose Reduction (AIDR) 3D). For each tube current, the phantom was scanned 100 times, yielding sets of 100 object‐present and object‐absent images at the same x‐y locations. All images were evaluated using the CHO and detectability indices (d’) for each object were calculated at all dose levels.Results:For the same tube current setting, images formed using IR yielded d’ values on average 8% higher than images reconstructed using FBP. When dose was reduced by more than 25% of the full dose, however, results showed reduced low‐contrast detectability in AIDR‐3D images compared to 100% dose, FBP images. With the vendordefault settings, dose is automatically reduced by 70‐75% when AIDR 3D reconstructions are selected, which our data indicate would significantly reduce low contrast detectability.Conclusion:At higher dose levels (minimal dose reduction), AIDR‐3D improved object detectability as compared to full‐dose FBP images. However, when dose was reduced by more than 25%, object detectability was substantially reduced for images reconstructed with AIDR‐3D compared to full‐dose FBP images.CH McCollough is supported by industry funding from Siemens Healthcare

Widefield imaging of upconverting nanoparticles on epifluorescence microscopes adapted for laser illumination with top-hat profile.

We describe a modification of epifluorescence microscopes that allows quantitative widefield imaging of samples labeled by upconverting nanoparticles (UCNP). A top-hat illumination profile on the sample was achieved with a 980-nm laser diode by using tandem microlens arrays, a moving diffuser and a telescope, which adjusts the top-hat area to the field of view. Illumination homogeneity is a critical factor for imaging of UCNP since the intensity of their luminescence typically scales with the second power of the excitation intensity. Our illuminator is combined with the epifluorescence attachment of the microscope, allowing easy switching between observation of UCNP and traditional fluorescent dyes. Illumination profile homogeneity of about 98% was measured for objectives with magnification from 4× to 100×, and the top-hat profile was also obtained with phase contrast objectives. We demonstrate capability of the illuminator by evaluating in vitro uptake of UCNP encapsulated in oleyl-hyaluronan micelles into breast cancer cells. Micelles bearing the targeting peptide were about an order of magnitude more efficient than nontargeted micelles.

GLRT subspace detection of multi-pixel targets with known and unknown spatial parameters in presence of signal-dependent background power

The video/infrared images captured at long range usually have low brightness and low contrast objects of interest with respect to surrounding background clutter. In this work, we design and analyze two detectors relying on the general likelihood ratio test (GLRT) to detect weak barely discernible multi-pixel objects with known (the first detector) and unknown shape, size and position (the second detector). The derived algorithms combine the multi-pixel matched subspace detector and multi-pixel background-plus-noise power change detector in a unique scheme. The numerical simulations and real experiments show that the first detector considerably outperforms the second one, especially in real-word situation, when the size, shape and position of the object are unknown. Finally, we compare the performances of the proposed detectors to the performances of the recently proposed modified mean subtraction filter and focused correlation (FC) detector.

Applications of the Medipix3-CT in combination with iterative reconstruction techniques

The pixelated semiconductor detectors of the Medipix family with their photon-counting abilities offer the possibility of high quality X-ray radiography as well as computed tomography. The generated signal from each photon is amplified and shaped before it is compared to an energy threshold. For a photon with an energy above the threshold the counter is incremented by one count. Photons below the operator-defined threshold do not increment the counter and therefore do not participate in the image formation. Furthermore, compared to other detectors like scintillators, an additional conversion step is dispensed due to the direct converting nature of photon-counting detectors, leading to a higher signal-to-noise-ratio. Additionally, the photon processing capabilities of photon-counting detectors allow photons to be weighted equally and not proportional to their energy as it is the case for charge integrating devices, where high energy photons are weighted stronger than low energy photons. Compared to integrating devices, this leads to an increase in contrast for images of both high and low contrast objects, hence improve object information. The use of photon-counting detectors in combination with iterative reconstruction techniques based on OSEM (ordered subset expectation maximization) algorithms is the basis of our computed tomography scans for material analysis. Due to its ability to operate with highly undersampled data sets, iterative reconstruction offers the possibility to decrease dose in CT scans. In order to identify the limits of the data set reduction, a first series of scans was performed to test, under real conditions, the CT-image quality when a strongly reduced amount of projections is used for reconstruction. In addition, the effect of a total variation minimization tool on these undersampled data sets was evaluated. Furthermore, this paper includes a number of recent CT-results with scans performed at two different setups within our facility.