Tomography Attenuation Research Articles

Imaging characteristics of intravascular spherical contrast agents for grating-based x-ray dark-field imaging \u2013 effects of concentrations, spherical sizes and applied voltage

This study investigates the x-ray scattering characteristics of microsphere particles in x-ray-grating-based interferometric imaging at different concentrations, bubble sizes and tube voltages (kV). Attenuation (ATI), dark-field (DFI) and phase-contrast (PCI) images were acquired. Signal-to-noise (SNR) and contrast-to-noise ratios with water (CNRw) and air as reference (CNRa) were determined. In all modalities, a linear relationship between SNR and microbubbles concentration, respectively, microsphere size was found. A significant gain of SNR was found when varying kV. SNR was significantly higher in DFI and PCI than ATI. The highest gain of SNR was shown at 60 kV for all media in ATI and DFI, at 80 kV for PCI. SNR for all media was significantly higher compared to air and was slightly lower compared to water. A linear relationship was found between CNRa, CNRw, concentration and size. With increasing concentration and decreasing size, CNRa and CNRw increased in DFI, but decreased in PCI. Best CNRa and CNRw was found at specific combination of kV and concentration/size. Highest average CNRa and CNRw was found for microspheres in ATI and PCI, for microbubbles in DFI. Microspheres are a promising contrast-media for grating-based-interferometry, if kV, microsphere size and concentration are appropriately combined.

Accuracy of Two-Dimensional Shear Wave Elastography and Attenuation Imaging for Evaluation of Patients With Nonalcoholic Steatohepatitis

We evaluated the accuracy of a multiparametric approach using attenuation imaging and 2-dimensional shear wave elastography (2D-SWE) for the detection of steatosis and fibrosis in patients with nonalcoholic fatty liver disease (NAFLD). We studied 102 patients with increased levels of liver enzymes or suspicion of NAFLD, examined by attenuation imaging and 2D-SWE, immediately before biopsy collection and analysis (reference standard), from January 2018 to July 2019. We collected data on the attenuation coefficient (dB/cm/MHz) from attenuation imaging, liver stiffness measurements, and shear wave dispersion slope (SWDS, [m/s]/kHz) from 2D-SWE. Multivariate linear regression analysis was performed to identify factors associated with each parameter. Diagnostic performance was determined from area under the receiver operating curve (AUROC) values. The attenuation coefficient was associated with steatosis grade (P < .01) and identified patients with steatosis grades S1 or higher, S2 or higher, and S3 or higher, with AUROC values of 0.93, 0.88, and 0.83, respectively. Liver stiffness associated with fibrosis stage (P < .01) and lobular inflammatory activity was the only factor associated with SWDS (P < .01). SWDS detected inflammation grades I1 or higher, I2 or higher, and I3 or higher with AUROC values of 0.89, 0.85, and 0.78, respectively. We developed a risk scoring system to detect steatohepatitis based on the attenuation coefficient (score of 1 for 0.64 < attenuation coefficient ≤ 0.70; score of 2 for 0.70 < attenuation coefficient ≤ 0.73; and score of 3 for attenuation coefficient >0.73) and SWDS (score of 2 for 10.5 [m/s]/kHz < SWDS ≤ 11.7 [m/s]/kHz; and score of 3 for SWDS >11.7 [m/s]/kHz), using an unweighted sum of each score. Based on histopathology analysis, 55 patients had steatohepatitis. Risk scores correlated with NAFLD activity score (rho= 0.73; P < .01). Our scoring system identified patients with steatohepatitis with an AUROC of 0.93-this valuewassignificantly higher than that of other parameters (P < .05), except SWDS (AUROC, 0.89; P= .18). In the evaluation of patients with suspected NAFLD, the attenuation coefficient can identify patients with steatosis and liver stiffness can detect fibrosis accurately. SWDS was associated significantly with lobular inflammation. We developed a risk scoring system based on the attenuation coefficient and SWDS that might be used to detect steatohepatitis.

Deep-JASC: joint attenuation and scatter correction in whole-body 18F-FDG PET using a deep residual network

We demonstrate the feasibility of direct generation of attenuation and scatter-corrected images from uncorrected images (PET-nonASC) using deep residual networks in whole-body 18F-FDG PET imaging. Two- and three-dimensional deep residual networks using 2D successive slices (DL-2DS), 3D slices (DL-3DS) and 3D patches (DL-3DP) as input were constructed to perform joint attenuation and scatter correction on uncorrected whole-body images in an end-to-end fashion. We included 1150 clinical whole-body 18F-FDG PET/CT studies, among which 900, 100 and 150 patients were randomly partitioned into training, validation and independent validation sets, respectively. The images generated by the proposed approach were assessed using various evaluation metrics, including the root-mean-squared-error (RMSE) and absolute relative error (ARE %) using CT-based attenuation and scatter-corrected (CTAC) PET images as reference. PET image quantification variability was also assessed through voxel-wise standardized uptake value (SUV) bias calculation in different regions of the body (head, neck, chest, liver-lung, abdomen and pelvis). Our proposed attenuation and scatter correction (Deep-JASC) algorithm provided good image quality, comparable with those produced by CTAC. Across the 150 patients of the independent external validation set, the voxel-wise REs (%) were - 1.72 ± 4.22%, 3.75 ± 6.91% and - 3.08 ± 5.64 for DL-2DS, DL-3DS and DL-3DP, respectively. Overall, the DL-2DS approach led to superior performance compared with the other two 3D approaches. The brain and neck regions had the highest and lowest RMSE values between Deep-JASC and CTAC images, respectively. However, the largest ARE was observed in the chest (15.16 ± 3.96%) and liver/lung (11.18 ± 3.23%) regions for DL-2DS. DL-3DS and DL-3DP performed slightly better in the chest region, leading to AREs of 11.16 ± 3.42% and 11.69 ± 2.71%, respectively (p value < 0.05). The joint histogram analysis resulted in correlation coefficients of 0.985, 0.980 and 0.981 for DL-2DS, DL-3DS and DL-3DP approaches, respectively. This work demonstrated the feasibility of direct attenuation and scatter correction of whole-body 18F-FDG PET images using emission-only data via a deep residual network. The proposed approach achieved accurate attenuation and scatter correction without the need for anatomical images, such as CT and MRI. The technique is applicable in a clinical setting on standalone PET or PET/MRI systems. Nevertheless, Deep-JASC showing promising quantitative accuracy, vulnerability to noise was observed, leading to pseudo hot/cold spots and/or poor organ boundary definition in the resulting PET images.

Multi-parameter wavefield reconstruction inversion for wavespeed and attenuation with bound constraints and total variation regularization

Wavefield reconstruction inversion (WRI) extends the search space of Full Waveform Inversion (FWI) by allowing for wave equation errors during wavefield reconstruction to match the data from the first iteration. Then, the wavespeeds are updated from the wavefields by minimizing the source residuals. Performing these two tasks in alternating mode breaks down the nonlinear FWI as a sequence of two linear subproblems, relaying on the bilinearity of the wave equation. We solve this biconvex optimization with the alternating-direction method of multipliers (ADMM) to cancel out efficiently the data and source residuals in iterations and stabilize the parameter estimation with appropriate regularizations.Here, we extend WRI to viscoacoustic media for attenuation imaging. Attenuation reconstruction is challenging because of the small imprint of attenuation in the data and the crosstalks with velocities. To address these issues, we recast the multivariate viscoacoustic WRI as a triconvex optimization and update wavefields, squared slowness, and attenuation factor in alternating mode at each WRI iteration. This requires to linearize the attenuation-estimation subproblem via an approximated trilinear viscoacoustic wave equation. The iterative defect correction embedded in ADMM corrects the errors generated by this linearization, while the operator splitting allows us to tailor ℓ1 regularization to each parameter class. A toy numerical example shows that these strategies mitigate crosstalk artifacts and noise from the attenuation reconstruction. A more realistic example representative of the North sea further shows the ability of the method to jointly reconstruct the wavespeed and the attenuation starting from a very crude attenuation-free initial model, the moderate strength of the crosstalk artifacts and the sensitivity of the multi-parameter reconstruction to noise.

Probabilistic seismic hazard assessment for Iraq

Probabilistic seismic hazard assessments (PSHA) form the basis for calculating seismic loads in most contemporary seismic provisions in building codes around the world. The current building code of Iraq, which was published in 1997, is currently undergoing a significant engineering update. This study was undertaken in order to support the building code update and to satisfy the need in Iraq for a contemporary assessment of seismic hazard in terms of spectral accelerations. Seismic source characterization largely relies on a newly compiled earthquake catalog since sufficiently detailed information is not available on active faulting in the country even though there are numerous known active faults. There is also a lack of locally recorded strong-motion data. As a result, we make use of attenuation tomography studies in the region to compare local attenuation characteristics with that in other parts of the world where ground-motion prediction equations are available for use in PSHA. For most of the country, the attenuation of 1HzLg waves indicates an attenuation rate that is slower than active tectonic regions but faster than stable continental regions. Hence, we use ground-motion prediction equations from active tectonic and stable continental regions, weighted equally. The PSHA results are presented for a 2% chance of being exceeded in 50 years and on a reference ground condition of the National Earthquake Hazards Reduction Program (NEHRP) site class B. The probability level and reference ground conditions were selected to be consistent with the update of Iraq’s building code. The largest hazard, and consequently the design ground motions, is in the northern cities of Sulaymaniyah and Erbil, consistent with the fact that they are the two urban areas closest to major tectonic features to the north and east of Iraq. Additionally, the Badra–Amarah fault zone is a significant contributor to seismic hazard in the country; therefore, urban areas near it exhibit high seismic hazard.

Rayleigh Wave Attenuation Tomography of the Chinese Mainland

Rayleigh Wave Attenuation Tomography of the Chinese Mainland

Development of Physical Breast Phantoms for X-ray Imaging Employing 3D Printing Techniques

Objective: This study aims to investigate the use of 3D printing techniques for the fabrication of physical breast phantoms, suitable for conventional and phase contrast breast imaging. Such phantoms could provide essential information for the design, development and optimization of emerging X-ray imaging modalities. Materials and Methods: Physical phantoms were constructed using two 3D printing techniques: Fused Deposition Modeling and Stereolithography. Eight materials suitable for 3D printing, including thermoplastic filaments and photopolymer resins, were investigated for the optimal representation of breast tissues, based on their attenuation and refractive characteristics. The phantoms consisted of a 3D-printed mold, which was then manually filled with paraffin wax. Additionally, a 3D complex-patterned layer and details representing abnormalities were embedded in different depths. Images of the phantoms were obtained in attenuation and phase contrast mode. Experiments were conducted using an X-ray microfocus tube with Tungsten anode set to 55kVp, combined with a photon-counting detector. The distance between source and detector was 56.5cm. The images were acquired at different object-to-detector distances starting from 5cm up to 40cm in a free space propagation set-up. Results and Conclusion: Results show that among all combinations with paraffin used as an adipose substitute, phantoms created with the Stereolithography technique and resins (especially Flex) as glandular equivalent, were found to be more appropriate for both attenuation and phase contrast imaging. The edge enhancement effect was well observed in the experimental images acquired at 35cm object-to-detector distance, indicating the potential for improved feature visualization using this set-up in phase contrast compared to attenuation mode.

Epidemiological and initial clinical characteristics of patients with family aggregation of COVID-19

BackgroundSince December 2019, a new outbreak of the coronavirus disease 2019 (COVID-19) in Wuhan (Hubei, China) and rapidly spread throughout China, however, confirmed cases are still increasing worldwide. ObjectivesTo investigate the epidemiological history and initial clinical characteristics of 10 patients with family aggregation of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in Western Chongqing, China. Study designTen patients positive for SARS-CoV-2 nucleic acid detection by real time Reverse Transcription-Polymerase Chain Reaction (RT-PCR), were collected from The People's Hospital of Dazu District, Chongqing. Epidemiological data and laboratory and imaging results were collected on the first day of admission, and analyzed based on the Diagnosis and Treatment Guideline for COVID-19 (5th edition, China). ResultsOf the 10 cases, case A had a history of a temporary stay in Wuhan and transmitted the virus to the others through family gathering, living together, and sharing vehicles. The average age was 56.5 years (± 11.16), six patients were males, and the incubation period was 2–14 days. Dry cough was the main symptom, followed by fever and fatigue. Most patients were clinically classified as ordinary-type, with three cases being severe-type. Chest computed tomography results were nonspecific, mainly with ground-glass attenuation and/or shadow images. Extensive lesion distribution was seen in severe cases. CD4+ lymphocyte counts were 61, 180, and 348 cells/uL in severe-type patients, respectively. Notably, viral nucleic acid values in nasopharyngeal swabs were lower (19, 25, and 26) than those of ordinary-type patients, suggesting a higher viral load. Neutrophil-lymphocyte ratio (NLR) was also higher in severe-type patients ConclusionsInitial examination results of lower CD4+ lymphocyte counts and RT-PCR-CT values coupled with higher NLR may indicate the severity of COVID-19 infection for these family clusters.

X-ray Dark-Field Radiography: Potential for Visualization of Monosodium Urate Deposition.

The aim of this study was to evaluate the potential of x-ray dark-field radiography for the noninvasive detection of monosodium urate (MSU) crystals as a novel diagnostic tool for gout. Contrast-to-noise ratios of MSU crystals in conventional radiography and dark-field radiography have been compared in a proof of principle measurement. Monosodium urate crystals have been injected into mouse legs in an ex vivo experimental gout setup. Three radiologists independently evaluated the images for the occurrence of crystal deposits in a blinded study for attenuation images only, dark-field images only, and with both images available for a comprehensive diagnosis. All imaging experiments have been performed at an experimental x-ray dark-field setup with a 3-grating interferometer, a rotating anode tube (50 kVp), and a photon-counting detector (effective pixel size, 166 μm). X-ray dark-field radiography provided a strong signal increase for MSU crystals in a physiological buffer solution compared with conventional attenuation radiography with a contrast-to-noise ratio increase from 0.8 to 19.3. Based on conventional attenuation images only, the reader study revealed insufficient diagnostic performance (sensitivity, 11%; specificity, 92%) with poor interrater agreement (Cohen's coefficient κ = 0.031). Based on dark-field images, the sensitivity increased to 100%, specificity remained at 92%, and the interrater agreement increased to κ = 0.904. Combined diagnosis based on both image modalities maximized both sensitivity and specificity to 100% with absolute interrater agreement (κ = 1.000). X-ray dark-field radiography enables the detection of MSU crystals in a mouse-based gout model. The simultaneous avaliability of a conventional attenuation image together with the dark-field image provides excellent detection rates of gout deposits with high specificity.

Parametric imaging of attenuation by optical coherence tomography: review of models, methods, and clinical translation.

.Significance: Optical coherence tomography (OCT) provides cross-sectional and volumetric images of backscattering from biological tissue that reveal the tissue morphology. The strength of the scattering, characterized by an attenuation coefficient, represents an alternative and complementary tissue optical property, which can be characterized by parametric imaging of the OCT attenuation coefficient. Over the last 15 years, a multitude of studies have been reported seeking to advance methods to determine the OCT attenuation coefficient and developing them toward clinical applications.Aim: Our review provides an overview of the main models and methods, their assumptions and applicability, together with a survey of preclinical and clinical demonstrations and their translation potential.Results: The use of the attenuation coefficient, particularly when presented in the form of parametric en face images, is shown to be applicable in various medical fields. Most studies show the promise of the OCT attenuation coefficient in differentiating between tissues of clinical interest but vary widely in approach.Conclusions: As a future step, a consensus on the model and method used for the determination of the attenuation coefficient is an important precursor to large-scale studies. With our review, we hope to provide a basis for discussion toward establishing this consensus.

X-ray interferometry without analyzer for breast CT application: asimulation study.

.Purpose: We investigate an analyzer-less x-ray interferometer with a spatially modulated phase grating (MPG) that can deliver three modalities (attenuation image, phase image, and scatter images) in breast computed tomography (BCT). The system can provide three x-ray modalities while preserving the dose to the object and can achieve attenuation image sensitivity similar to that of a standard absorption-only BCT. The MPG system works with a source, a source-grating, a single phase grating, and a detector. No analyzer is necessary. Thus, there is an approximately 2x improvement in fluence at the detector for our system compared with the same source–detector distance Talbot–Lau x-ray interferometry (TLXI) because the TLXI has an analyzer after the object, which is not required for the MPG.Approach: We investigate the MPG BCT system in simulations and find a clinically feasible system geometry. First, the mechanism of MPG interferometry is conceptually shown via Sommerfeld–Rayleigh diffraction integral simulations. Next, we investigate source coherence requirements, fringe visibility, and phase sensitivity dependence on different system parameters and find clinically feasible system geometry.Results: The phase sensitivity of MPG interferometry is proportional to object–detector distance and inversely proportional to a period of broad fringes at the detector, which is determined by the grating spatial modulation period. In our simulations, the MPG interferometry can achieve about 27% fringe visibility with clinically realistic BCT geometry of a total source–detector distance of 950 mm and source–object distance of 500 mm.Conclusions: We simulated a promising analyzer-less x-ray interferometer, with a spatially sinusoidal MPG. Our system is expected to deliver the attenuation, phase and scatter image in a single acquisition without dose or fluence detriment, compared with conventional BCT.

Three-dimensional mapping of the attenuation coefficient in optical coherence tomography to enhance breast tissue microarchitecture contrast.

Effective intraoperative tumor margin assessment is needed to reduce re-excision rates in breast-conserving surgery (BCS). Mapping the attenuation coefficient in optical coherence tomography (OCT) throughout a sample to create an image (attenuation imaging) is one promising approach. For the first time, three-dimensional OCT attenuation imaging of human breast tissue microarchitecture using a wide-field (up to ~45 × 45 × 3.5 mm) imaging system is demonstrated. Representative results from three mastectomy and one BCS specimen (from 31 specimens) are presented with co-registered postoperative histology. Attenuation imaging is shown to provide substantially improved contrast over OCT, delineating nuanced features within tumors (including necrosis and variations in tumor cell density and growth patterns) and benign features (such as sclerosing adenosis). Additionally, quantitative micro-elastography (QME) images presented alongside OCT and attenuation images show that these techniques provide complementary contrast, suggesting that multimodal imaging could increase tissue identification accuracy and potentially improve tumor margin assessment.

Image quality and attenuation values of multidetector CT coronary angiography using high iodine-concentration contrast material: A comparison of the use of iopromide 300 and iopromide 370

Abstract Background Iodine concentration is one of the main determinants of arterial enhancement in CTA, and current low-osmolar and iso-osmolar nonionic CM for intravascular administration still come in a handful of molecules, but a relatively wide range of different iodine concentrations. This gives the opportunity to optimize CTA protocols as a function of several factors such as patient characteristics, CT technology, and CM features in an attempt to maximize the diagnostic yield of CTA examinations while considering patient safety and avoiding unnecessary extra costs. Objective To compare image quality and attenuation values of multidetector CT coronary angiography (MDCT) between iopromide 300 and iopromide 370 and to evaluate whether the higher iodine contrast material has better image quality or not. Material and Methods Patients were prospectively enrolled and were randomized into two groups (group A, 30 patients received iopromide 300, iodine flux 1.2g I/s; group B, 30 patients received iomeprol 370, iodine flux 1.48g I/s). CT attenuation values were measured in the proximal end coronary arteries,ascending aorta and main pulmonary artery. The image quality of 15 coronary artery segments was graded by cardiologist in consensus with the use of a four-point scale (1 excellent enhancement to 4 poor enhancement). Non-parametric statistical approaches were used to compare the two groups. Results No statistically significant differences were found between the mean attenuation values (302 HU for iopromide 300 and 326 HU for iopromide 370, P = 0.175) in the coronary arteries in the two groups. The mean attenuation value of the proximal ascending aorta (AA)and main pulmonary artery (MPA) was found to be 345+/-63 HU and 241+/- 89 in group A respectively, whereas the mean attenuation value in proximal ascending aorta and main pulmonary artery in group B was found to be 348+/-74 and 238+/- 50 respectively. No significant difference was found between iopromide 300 and iopromide 370 in terms of contrast enhancement at the level of great arteries, P value AA = 0.826 and P value for MPA = 0.884. 92.9% of coronary arterial segments got score (range 1–2) in group A whereas 93.6 of coronary arterial segments got score (range 1-2) in group with no statistically significant difference P value = 0.755. Conclusion With the current CT technology iopromide 300 is not inferior to iopromide 370 in terms of coronary artery attenuation values and image quality. Iopromide 300 provides similar enhancement of coronary arteries and excellent image quality as compared with iopromide 370 using identical amount of total iodine with fewer cost and less estimated adverse effects owing to low iodine concentration of iopromide 300.

Quantitative research on the interaction between cerebral edema and peripheral cerebral blood perfusion using swept-source optical coherence tomography.

Ischemic cerebral edema (CE) is a major leading cause of death in patients with ischemic stroke. The CE progression is closely related to the local cerebral blood perfusion (LCBP) level surrounding the edema area. Quantitative studying the interaction between the CE and peripheral LCBP may provide new inspiration for control and even treatment of CE. Photothrombosis ischemia mouse model was established and observed for 9 hours using swept-source optical coherence tomography (SS-OCT). OCT-based angiography and OCT-based attenuation imaging techniques were used to reconstruct the angiograms reflecting the cerebral blood perfusion (CBP) level and optical attenuation coefficient (OAC) maps reflecting the edema state. The influence of edema on LCBP was analyzed by quantifying the blood perfusion in different spatial locations around the edema tissue, and the influence of LCBP on CE progression was revealed by comparing the changes of the edema area and LCBP level over time. Preliminary studies show that the effect of edema tissue on LCBP is very significant, which shows a clear spatial dependence. LCBP near the edema tissue is 15-20% lower than that far away from the edema tissue. When the LCBP drops to around 60% of the initial value, the edema area increases sharply. In addition, the level of CBP in the contralateral hemisphere also decreases with time. When the contralateral CBP drops to around 60%, there is a certain probability that contralateral edema will occur. CE progression is not only related to the LCBP around the edema tissue but also related to the CBP of non-edematous regions. Controlling the CBP level of non-edematous regions may play a positive role in the treatment of CE. This work provides a new method and inspiration for exploring the mechanism of ischemic CE progression.

Velocity-attenuation model from check-shot drift trends in North Sea well data

Seismic attenuation distorts phase and narrows bandwidth in seismic surveys. It is also an exploration attribute, as, for example, gas or overpressure, may create attenuation anomalies. Compensating attenuation in imaging requires accurate models. Detailed attenuation models may be obtained using full-waveform inversion (FWI) or attenuation tomography, but their accuracy benefits from reliable starting models and/or constraints. Seismic attenuation and velocity dispersion are necessarily linked for causal linear wave propagation such that higher frequencies travel faster than lower frequencies in an attenuative medium. In publicly released well data from the Norwegian North Sea, we have observed systematic positive linear trends in check-shot drift when comparing (lower frequency) time-depth curves with (higher frequency) integrated sonic transit times. We observe velocity dispersion consistent with layers having constant seismic attenuation. Adapting a previously published method, and assuming an attenuation-dispersion relationship, we use drift gradients, measured over thick stratigraphic units, to estimate interval P-wave attenuation and tentatively interpret its variation in terms of porosity and fluid mobility. Reflectivity modeling predicts a very low attenuation contribution from peg-leg multiples. We use the attenuation values to develop a simple regional relationship between P-wave velocity and attenuation. Observed low drift gradients in some shallower units lead to an arch-shaped model that predicts low attenuation at both low and high velocities. The attenuation estimates were broadly comparable with published effective attenuation values obtained independently nearby. This general methodology for quickly deriving a regional velocity-attenuation relationship could be used anywhere that coincident velocity models are available at seismic and sonic frequencies. Such relationships can be used for fast derivation (from velocities) of starting attenuation models for FWI or tomography, constraining or linking velocity and attenuation in inversion, deriving models for attenuation compensation in time processing, or deriving background trends in screening for attenuation anomalies in exploration.

Maximum likelihood activity and attenuation estimation using both emission and transmission data with application to utilization of Lu-176 background radiation in TOF PET.

We present a new method for joint reconstruction of activity and attenuation images using both emission and transmission data and demonstrate its advantage over the standard maximum likelihood activity and attenuation (MLAA) reconstruction using emission data alone. We define a joint likelihood function including both time-of-flight (TOF) emission data and transmission data. The latter can be obtained from an external source or from Lu-176 background radiation. Activity and attenuation images are estimated jointly by maximizing the likelihood function. The proposed method solves the undetermined scale problem in the conventional MLAA. A monotonically convergent algorithm was derived to optimize the objective function. Furthermore, we present a theoretical analysis of the noise propagation in the joint reconstruction. Simulations and phantomexperiments were conducted to validate the feasibility of the proposed method. Quantitatively correct and less noisy images were reconstructed with the proposed method. Artifacts in the attenuation map reconstructed from the standard MLAA were removed by incorporating transmission data. Noise analysis was validated with different transmission sources and transmission count levels. The theoretical prediction indicated that noise of activity map would not change in a large range of transmission count level and a very low transmission count level could result in good estimation. The results demonstrate the feasibility of obtaining quantitatively correct images in TOFPET by using both emission and (weak) transmission data. The noise analysis also provides guidance for choosing a proper transmission source configuration to reduce noise propagation.

Simultaneous emission and attenuation reconstruction in time-of-flight PET using a reference object

BackgroundSimultaneous reconstruction of emission and attenuation images in time-of-flight (TOF) positron emission tomography (PET) does not provide a unique solution. In this study, we propose to solve this limitation by including additional information given by a reference object with known attenuation placed outside the patient. Different configurations of the reference object were studied including geometry, material composition, and activity, and an optimal configuration was defined. In addition, this configuration was tested for different timing resolutions and noise levels.ResultsThe proposed strategy was tested in 2D simulations obtained by forward projection of available PET/CT data and noise was included using Monte Carlo techniques. Obtained results suggest that the optimal configuration corresponds to a water cylinder inserted in the patient table and filled with activity. In that case, mean differences between reconstructed and true images were below 10%. However, better results can be obtained by increasing the activity of the reference object.ConclusionThis study shows promising results that might allow to obtain an accurate attenuation map from pure TOF-PET data without prior knowledge obtained from CT, MRI, or transmission scans.

Supercritical CO2 source for underground seismic exploration

Underground seismic exploration is a technical assurance for the geological transparency of the mining face. However, seismic exploration with explosive seismic source has shortcomings such as acquisition difficulties and serious safety hazards. Besides, dynamic detection of the mining face with explosive source is challenging. To this end, the study proposes a supercritical CO2 source based on the underground seismic geological condition of the roadway. The phase change blasting mechanism of the supercritical source was revealed, and the equivalent energy of the source was calculated. Additionally, a field test was also carried out. The results show that the seismic signals of the CO2 source have clear P-waves, S-waves, and channel waves; the signal excited by the source has strong energy and rich frequency bands; the signal-to-noise ratio of single CO2 source is high; and the attenuation images of transmitted channel wave excited by the source shows high resolution and the result is consistent with field validation data. CO2 source can be used as a new source of underground in-seam seismic exploration and it also helps in reducing the dependence of explosive seismic source. Besides, the study can achieve early warnings of dynamic geological disasters in the working face and has the advantages of high efficiency, safe, low cost, and environmentally friendly.

Ultrasound-Based Attenuation Imaging for the Non-Invasive Quantification of Liver Fat - A Pilot Study on Feasibility and Inter-Observer Variability.

Attenuation imaging is a novel, ultrasound-based technique to objectively detect and quantify liver steatosis. In this study, we evaluated the performance and inter-observer variability of attenuation imaging and compared it to a known quantification method of liver fat, the hepatorenal index (HRI). Two observers measured attenuation coefficients (AC) in an attenuation phantom, 20 healthy volunteers and 27 patients scheduled for biopsy for suspected diffuse liver disease. Results were compared with the HRI and histological findings. Both observers were blinded to the results of the biopsy and the measurements of the other observer. Our results showed that patients with moderate (S2, 33-66%) and severe fatty infiltration of the liver (S3, >66%) showed significantly higher ACs in comparison to patients with a liver fat fraction of less than 33% (S0/1). There was no significant difference in AC-values of patients with fatty infiltration of less than 5% (S0) and 5-32% (S1). In the Receiver Operating Characteristic (ROC)-analysis, the area under the curve (AUC)-values for the detection of moderate and severe steatosis were excellent at 0.98. Cut-off values were 0.64 dB/cm/MHz for the detection of S2- and 0.68 dB/cm/MHz for the detection of S3-steatosis. The inter-observer agreement of attenuation imaging was very good with an intraclass correlation coefficient (ICC) of 0.92 in patient and 0.96 in phantom measurements. The ICC decreased with depth in the phantom measurements. In summary, attenuation imaging showed very good inter-observer agreement and is a promising tool for the detection and quantification of moderate and severe hepatic steatosis.

A Combined Regularization Method Using Prior Structural Information for Sound-Speed Image Reconstruction of Ultrasound Computed Tomography

Ultrasound computed tomography (USCT) is a promising technique for breast imaging. It provides three modalities: echo image, sound speed image (SSI), and attenuation image. The echo image reveals structural details of the breast with high resolution but is not quantitative. The SSI is quantitative, but its resolution is generally lower than that of the echo image. The SSI reconstruction is an ill-posed problem, thus the Tikhonov or total variation (TV) regularization methods are generally used. Tikhonov regularization is stable, but it tends to smooth the SSI and results in low resolution. TV regularization can preserve the sharp edges and provide higher resolution, but it may result in staircase artifacts. To combine the advantages of Tikhonov and TV regularizations, this article proposes a combined regularization method using prior structural information from the echo image. The proposed method mainly includes three steps. First, the echo image is reconstructed using the synthetic aperture (SA) technique and then segmented into breast and water regions. The segmentation result is used as prior structural information. Second, the USCT sound propagation forward model was built. Finally, with a penalty term according to the prior structural information, the combined regularization method is used to reconstruct the SSI. Both simulation and ex vivo experiments were conducted for evaluation. In the simulation, the proposed method has a low root-mean-square-error (13.78 m/s), a high correlation coefficient (0.812), a high structural similarity (0.755), and a low standard deviation of water sound speed (2.33 m/s). In the ex vivo experiment, the method has a low standard deviation of water sound speed (1.44 and 3.13 m/s for small and large objects, respectively), a low contrast to noise ratio (3.09 and 5.08), and a high Dice coefficient (0.92 and 0.97). Thus, the proposed combined regularization method using prior structural information can improve reconstruction quality.