Three-Dimensional Reconstruction Algorithm for a Reverse-Geometry Volumetric CT System With a Large-Array Scanned Source

We have proposed a CT system design to rapidly produce volumetric images with negligible cone beam artifacts. The investigated system uses a large array scanned source with a smaller array of fast detectors. The x-ray source is electronically steered across a 2D target every few milliseconds as the system rotates. The proposed reconstruction algorithm for this system is a modified 3D filtered backprojection method. The data are rebinned into 2D parallel ray projections, most of which are tilted with respect to the axis of rotation. Each projection is filtered with a 2D kernel and backprojected onto the desired image matrix. To ensure adequate spatial resolution and low artifact level, we rebin the data onto an array that has sufficiently fine spatial and angular sampling. Due to finite sampling in the real system, some of the rebinned projections will be sparse, but we hypothesize that the large number of views will compensate for the data missing in a particular view. Preliminary results using simulated data with the expected discrete sampling of the source and detector arrays suggest that high resolution

Noise Simulations For an Inverse-Geometry Volumetric CT System

This paper examines the noise performance of an inverse-geometry volumetric CT (IGCT) scanner through simulations. The IGCT system uses a large area scanned source and a smaller array of detectors to rapidly acquire volumetric data with negligible cone-beam artifacts. The first investigation compares the photon efficiency of the IGCT geometry to a 2D parallel ray system. The second investigation models the photon output of the IGCT source and calculates the expected noise. For the photon efficiency investigation. the same total number of photons was modeled in an IGCT acquisition and a comparable multi-slice 2D parallel ray acquisition. For both cases noise projections were simulated and the central axial slice reconstructed. In the second study. to investigate the noise in an IGCT system, the expected x-ray photon flux was modeled and projections simulated through ellipsoid phantoms. All simulations were compared to theoretical predictions. The results of the photon efficiency simulations verify that the IGCT geometry is as efficient in photon utilization as a 2D parallel ray geometry. For a 10 cm diameter 4 cm thick ellipsoid water phantom and for reasonable system parameters, the calculated standard deviation was approximately 15 HU at the center of the ellipsoid. For the same size phantom with maximum attenuation equivalent to 30 cm of water, the calculated noise was approximately 131 HU. The theoretical noise predictions for these objects were 15 HU and 112 HU respectively. These results predict acceptable noise levels for a system with a 0.16 second scan time and 12 lp/cm isotropic resolution

Access Denied—Using Procedure to Restrict Tort Litigation: The Israeli-Palestinian Experience

Procedural barriers which limit individuals’ ability to bring lawsuits—like conditioning litigation upon the provision of a bond—are a subtle way to reduce the volume of tort litigation. The use of such procedural doctrines often spares legislatures from the need to debate the substance of legal rights, especially when those rights are politically controversial. This Article presents a case study of this phenomenon which has escaped scholarly attention, in the intriguing context of the Israeli-Palestinian Conflict. On the books, a unique mechanism enables non-Israeli citizen Palestinians of the West Bank and Gaza Strip to bring civil actions for damages against Israel before Israeli civil courts. Yet, since the early 2000s, Israel began using a host of procedural obstacles to restrict Palestinians’ access to its civil courts, effectively precluding their ability to bring claims arising from Israeli military actions. Through fifty-five in-depth interviews with lawyers, policy makers, plaintiffs, and other key stakeholders, alongside a host of secondary sources such as parliamentary protocols and NGO reports, this Article considers the impact this process has on Palestinians’ access to justice. While the use of procedure to encroach on an injured person’s right to compensation may be considered a taking of property, and thus, conceptualized as a dignity taking, such an analysis overlooks a key component of the harm caused to these individuals. Procedural restrictions that block access to the courts also deny Palestinians of their right to participate in the litigation process. Focusing only on property rights—the “end game” of the litigation—ignores benefits derived from the litigation process, including accountability, transparency, and recognition, which may be particularly important when it comes to plaintiffs from vulnerable, disadvantaged groups

Collateral Damages: Domestic Monetary Compensation for Civilians in Asymmetric Conflict

The armed conflicts of the twenty-first century, which often take place among civilian populations rather than on traditional battlefields, push states to acknowledge and rectify the resulting harm to foreign civilians. In particular, asymmetric conflicts, which involve confronting non-state actors within civilian populations, tend to cause more of what has come to be known as ‘collateral damage.’ Such harm to civilians can be inflicted, for instance, in checkpoint shootings, drone attacks, or riot control efforts. How should these losses be addressed? This Article examines two competing models. The U.S. military provides compensation to civilians injured by its activity in Iraq and Afghanistan through a military-run program, governed by the Foreign Claims Act and condolence payments. In contrast, Israel enables non-citizen Palestinians injured by Israeli military actions to bring tort lawsuits before Israeli civil courts. Notwithstanding the differences between these two conflicts, both entail military forces engaging with civilians while assuming quasi-military or policing roles. Yet, scholars have not yet juxtaposed the distinct compensation mechanisms applied in each conflict, vis-à-vis the goals of monetary damages under tort law. This Article seeks to fill this gap. Drawing on tort theory, social psychology, and socio-legal studies, the Article examines the structure of domestic conflict compensation programs. It utilizes data from public records, interviews with relevant stakeholders, NGO reports, and Freedom of Information Act requests to compare the American and Israeli compensation paradigms. Through this analysis, the Article offers guidelines for designing compensation programs that address both government accountability and victims’ needs to effectively redress the harm modern-day conflict causes to civilians

Technical Note: Phantom study to evaluate the dose and image quality effects of a computed tomography Organ-based Tube Current Modulation Technique

Purpose This technical note quantifies the dose and image quality performance of a clinically available organ-dose-based tube current modulation (ODM) technique, using experimental and simulation phantom studies. The investigated ODM implementation reduces the tube current for the anterior source positions, without increasing current for posterior positions, although such an approach was also evaluated for comparison. Methods Axial CT scans at 120 kV were performed on head and chest phantoms on an ODM-equipped scanner (Optima CT660, GE Healthcare, Chalfont St. Giles, England). Dosimeters quantified dose to breast, lung, heart, spine, eye lens, and brain regions for ODM and 3D-modulation (SmartmA) settings. Monte Carlo simulations, validated with experimental data, were performed on 28 voxelized head phantoms and 10 chest phantoms to quantify organ dose and noise standard deviation. The dose and noise effects of increasing the posterior tube current were also investigated. Results ODM reduced the dose for all experimental dosimeters with respect to SmartmA, with average dose reductions across dosimeters of 31% (breast), 21% (lung), 24% (heart), 6% (spine), 19% (eye lens), and 11% (brain), with similar results for the simulation validation study. In the phantom library study, the average dose reduction across all phantoms was 34% (breast), 20% (lung), 8% (spine), 20% (eye lens), and 8% (brain). ODM increased the noise standard deviation in reconstructed images by 6%–20%, with generally greater noise increases in anterior regions. Increasing the posterior tube current provided similar dose reduction as ODM for breast and eye lens, increased dose to the spine, with noise effects ranging from 2% noise reduction to 16% noise increase. At noise equal to SmartmA, ODM increased the estimated effective dose by 4% and 8% for chest and head scans, respectively. Increasing the posterior tube current further increased the effective dose by 15% (chest) and 18% (head) relative to SmartmA. Conclusions ODM reduced dose in all experimental and simulation studies over a range of phantoms, while increasing noise. The results suggest a net dose/noise benefit for breast and eye lens for all studied phantoms, negligible lung dose effects for two phantoms, increased lung dose and/or noise for eight phantoms, and increased dose and/or noise for brain and spine for all studied phantoms compared to the reference protocol

Application of Fractal Dimension for Quantifying Noise Texture in Computed Tomography Images

Purpose Evaluation of noise texture information in CT images is important for assessing image quality. Noise texture is often quantified by the noise power spectrum (NPS), which requires numerous image realizations to estimate. This study evaluated fractal dimension for quantifying noise texture as a scalar metric that can potentially be estimated using one image realization. Methods The American College of Radiology CT accreditation phantom (ACR) was scanned on a clinical scanner (Discovery CT750, GE Healthcare) at 120 kV and 25 and 90 mAs. Images were reconstructed using filtered back projection (FBP/ASIR 0%) with varying reconstruction kernels: Soft, Standard, Detail, Chest, Lung, Bone, and Edge. For each kernel, images were also reconstructed using ASIR 50% and ASIR 100% iterative reconstruction (IR) methods. Fractal dimension was estimated using the differential box‐counting algorithm applied to images of the uniform section of ACR phantom. The two‐dimensional Noise Power Spectrum (NPS) and one‐dimensional‐radially averaged NPS were estimated using established techniques. By changing the radiation dose, the effect of noise magnitude on fractal dimension was evaluated. The Spearman correlation between the fractal dimension and the frequency of the NPS peak was calculated. The number of images required to reliably estimate fractal dimension was determined and compared to the number of images required to estimate the NPS‐peak frequency. The effect of Region of Interest (ROI) size on fractal dimension estimation was evaluated. Feasibility of estimating fractal dimension in an anthropomorphic phantom and clinical image was also investigated, with the resulting fractal dimension compared to that estimated within the uniform section of the ACR phantom. Results Fractal dimension was strongly correlated with the frequency of the peak of the radially averaged NPS curve, having a Spearman rank‐order coefficient of 0.98 (P‐value \u3c 0.01) for ASIR 0%. The mean fractal dimension at ASIR 0% was 2.49 (Soft), 2.51 (Standard), 2.52 (Detail), 2.57 (Chest), 2.61 (Lung), 2.66 (Bone), and 2.7 (Edge). A reduction in fractal dimension was observed with increasing ASIR levels for all investigated reconstruction kernels. Fractal dimension was found to be independent of noise magnitude. Fractal dimension was successfully estimated from four ROIs of size 64 × 64 pixels or one ROI of 128 × 128 pixels. Fractal dimension was found to be sensitive to non‐noise structures in the image, such as ring artifacts and anatomical structure. Fractal dimension estimated within a uniform region of an anthropomorphic phantom and clinical head image matched that estimated within the ACR phantom for filtered back projection reconstruction. Conclusions Fractal dimension correlated with the NPS‐peak frequency and was independent of noise magnitude, suggesting that the scalar metric of fractal dimension can be used to quantify the change in noise texture across reconstruction approaches. Results demonstrated that fractal dimension can be estimated from four, 64 × 64‐pixel ROIs or one 128 × 128 ROI within a head CT image, which may make it amenable for quantifying noise texture within clinical images

Reduction of voluntary dehydration during effort in hot environments

During an experimental marching trip the daily positive fluid balance was preserved by providing a wide choice of beverages during the hours of the day. It was found that the beverage most suitable for drinking in large quantities during periods of effort was a cold drink with sweetened (citrus) fruit taste. Carbonated drinks, including beer, but milk also, were found unsuitable for this purpose

Far-red switching DNA probes for live cell nanoscopy

Herein we present DNA probes composed of Hoechst 33258 and spontaneously blinking far-red hydroxymethyl silicon-rhodamine (HMSiR). The best performing probe, 5-HMSiR-Hoechst, contains the 5′-regioisomer, shows ∼400-fold fluorescence increase upon DNA binding and is compatible with wash-free single molecule localization and 3D stimulated emission depletion microscopy of chromatin nanostructures in living cells

Geometry Analysis of an Inverse-Geometry Volumetric CT System With Multiple Detector Arrays

An inverse-geometry volumetric CT (IGCT) system for imaging in a single fast rotation without cone-beam artifacts is being developed. It employs a large scanned source array and a smaller detector array. For a single-source/single-detector implementation, the FOV is limited to a fraction of the source size. Here we explore options to increase the FOV without increasing the source size by using multiple detectors spaced apart laterally to increase the range of radial distances sampled. We also look at multiple source array systems for faster scans. To properly reconstruct the FOV, Radon space must be sufficiently covered and sampled in a uniform manner. Optimal placement of the detectors relative to the source was determined analytically given system constraints (5cm detector width, 25cm source width, 45cm source-to-isocenter distance). For a 1x3 system (three detectors per source) detector spacing (DS) was 18deg and source-to-detector distances (SDD) were 113, 100 and 113cm to provide optimum Radon sampling and a FOV of 44cm. For multiple-source systems, maximum angular spacing between sources cannot exceed 125deg since detectors corresponding to one source cannot be occluded by a second source. Therefore, for 2x3 and 3x3 systems using the above DS and SDD, optimum spacing between sources is 115deg and 61deg respectively, requiring minimum scan rotations of 115deg and 107deg. Also, a 3x3 system can be much faster for full 360deg dataset scans than a 2x3 system (120deg vs. 245deg). We found that a significantly increased FOV can be achieved while maintaining uniform radial sampling as well as a substantial reduction in scan time using several different geometries. Further multi-parameter optimization is underway