Tomography Attenuation Research Articles

Nonstationary seismic inversion: joint estimation for acoustic impedance, attenuation factor and source wavelet

Seismic signal can be expressed by nonstationary convolution model (NCM) which integrates acoustic impedance (AI), attenuation factor (AF) and source wavelet (SW) into a single formula. Although it provides attractive potential to invert AI, AF and SW, simultaneously, effective joint inversion algorithm has not been developed because of the extreme instability of this nonlinear inverse problem. In this paper, we propose an alternating optimization scheme to achieve this nonlinear joint inversion. Our algorithm repeatedly alternates among three subproblems corresponding to AI, AF and SW recovery until changes in inverted models become smaller than the user-defined tolerances. Also, when we optimize one parameter, other two parameters are fixed. NCM is an explicit linear formula for AI; therefore, AI recovery is accomplished by linear inversion which is regularized by low-frequency model and isotropy total variation domain sparse constraints. However, NCM is a complicated nonlinear formula for AF. To facilitate the AF inversion, we propose a centroid frequency-based attenuation tomography method whose forward operator and observations are acquired from the time-varying wavelet amplitude spectra which is estimated according to Gabor domain factorization of NCM. SW is decoupled from NCM based on Toeplitz structure constraint, and we obtain an orthogonal wavelet transform domain sparse regularized SW inverse subproblem. Split Bregman technique is adopted to optimize AI and SW inverse subproblems. Numerical test and field data application confirm that the proposed nonstationary seismic inversion algorithm can stably generate accurate estimates of AI, AF and SW, simultaneously.

Neural MLAA for PET-enabled Dual-Energy CT Imaging.

The PET-enabled dual-energy CT method allows dual-energy CT imaging on PET/CT scanners without the need for a second x-ray CT scan. A 511 keV γ-ray attenuation image can be reconstructed from time-of-flight PET emission data using the maximum-likelihood attenuation and activity (MLAA) algorithm. However, the attenuation image reconstructed by standard MLAA is commonly noisy. To suppress noise, we propose a neural-network approach for MLAA reconstruction. The PET attenuation image is described as a function of kernelized neural networks with the flexibility of incorporating the available x-ray CT image as anatomical prior. By applying optimization transfer, the complex optimization problem of the proposed neural MLAA reconstruction is solved by a modularized iterative algorithm with each iteration decomposed into three steps: PET activity image update, attenuation image update, and neural-network learning using a weighed mean squared-error loss. The optimization algorithm is guaranteed to monotonically increase the data likelihood. The results from computer simulations demonstrated the neural MLAA algorithm can achieve a significant improvement on the γ-ray CT image quality as compared to other algorithms.

Abstract PS3-15: Imaging of the distribution of human breast ducts

Abstract While most of the anatomy of the human body is well delineated and understood, the distribution of adult female breast ducts remains largely understudied despite the fact that breast cancer, is thought to start in the lining of a breast ductal lobular unit. These anatomical features develop from stem cells located behind the nipple under the influence of the hormones of puberty. The exact patterns and number of ducts in the normal female breast has received limited attention since the work of Astley Cooper in 1840 who admitted that he had artfully displayed the ducts in two dimensions for his book. Since then, Going et al has used computerized reconstruction to map one breast and investigators in Australia have used hand-held ultrasound on lactating women to gain some insight into the nipple anatomy. The descriptions of the number of ducts exiting the breast at the nipple can be divided into those who have cannulated ducts at the nipple (6-10) and those who enumerated the number of ducts seen on transection of the nipple. (15-20). Local anesthesia can be used as a nipple block allowing duct cannulation in women. Breast cancer starts in the lining of a milk duct which opens the way for the application of new diagnostic techniques such as liquid biopsy. The limitation of this approach, however, is the absence of an imaging modality to direct sampling. In collaboration with QT Imaging, images were obtained using non-invasive 3D Transmission Ultrasound (TU) imaging of whole in vivo breasts of three patients, a postmenopausal 64 year old woman, a woman with DCIS and one with an invasive cancer. TU is a novel FDA cleared imaging device utilizing 3D ultrasound data and modelling to yield speckle free sub-mm resolution quantitative estimates of tissue characteristics. The women were lying prone with their breast immersed in a water bath with reconstruction of the projection and reflected ultrasound data resulting in co-registered 3D reflection, speed-of-sound, and attenuation images. Machine learning at a voxel level was used to quantitively differentiate and segment breast tissues types based on reconstructed voxel tissue characteristics. These tissue types were then 3D printed into anatomical models representing a normal postmenopausal breast, one with DCIS and one with invasive cancer. The images demonstrated the distribution of ductal systems in two concentric groupings unrelated to quadrants. The DCIS and the invasive ductal cancer were limited to a single ductal system each. This new non-invasive technology enables precise localization of intraductal and invasive lesions. It opens up the potential for precise anatomic intraductal liquid biopsy for diagnosis as well as intraductal therapy. In addition, it has ramifications for better directing surgical removal of intraductal and invasive lesions. Citation Format: Susan M Love, James Klock, James Wiskin. Imaging of the distribution of human breast ducts [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS3-15.

Transmission micro-focus X-ray radiographic measurements towards in-situ tracing capillary imbibition fronts and paths in ultra-thin concrete slices

In the present study, we attempted to trace the imbibition fronts and paths in concrete by controlling specimen dimensions and imbibition liquids in transmission microfocus X-ray radiographic tests. Ultra-thin concrete specimens were specifically prepared for 2D imbibitions. CsCl was used as the agent to enhance X-ray attenuation. SEM/BSE/EDS tests were used to measure the micro morphology and element distributions at local sites. Results show that the designed experiments enable the acquisition of X-ray attenuation images with the enhanced contrast, which helps identify the capillary imbibition paths and fronts in the concrete. Liquid is more likely to penetrate through the interfacial transition zone and highly porous cement paste. CsCl solution also increases the contrast gradient of BSE images. Cs and Cl gradually distribute across the imbibition fronts. The proposed measurements offer a way to instantly, continually and visually probe capillary imbibitions in concrete and other porous materials.

A Systems Approach to Estimating the Uncertainty Limits of X-Ray Radiographic Metrology

Abstract Micro- and nanomanufacturing capabilities have rapidly expanded over the past decade to include complex three-dimensional (3D) structure fabrication; however, the metrology required to accurately assess these processes via part inspection and characterization has struggled to keep pace. X-ray computed tomography (CT) is considered an ideal candidate for providing the critically needed metrology on the smallest scales, especially internal features, or inaccessible regions. X-ray CT supporting micro- and nanomanufacturing often push against the poorly understood resolution and variation limits inherent to the machines, which can distort or hide fine structures. We develop and experimentally verify a comprehensive analytical uncertainty propagation signal variation flow graph (SVFG) model for X-ray radiography in this work to better understand resolution and image variability limits on the small scale. The SVFG approach captures, quantifies, and predicts variations occurring in the system that limit metrology capabilities, particularly in the micro/nanodomain. This work is the first step to achieving full uncertainty modeling of CT reconstructions and provides insight into improving X-ray attenuation imaging systems. The SVFG methodology framework is applied to generate a complete basis set of functions describing the major sources of variation in radiographs. Five models are identified, covering variation in energy, intensity, length, blur, and position. Radiographic system experiments are defined to measure the parameters required by the SVFGs. Best practices are identified for these measurements. The SVFG models are confirmed via direct measurement of variation to predict variation within 30% on average.

Usefulness of US attenuation imaging for the detection and severity grading of hepatic steatosis in routine abdominal ultrasonography

PurposeTo assess the diagnostic performance of ultrasound (US) attenuation imaging (ATI) for diagnosis and grading of hepatic steatosis with comparison to magnetic resonance imaging-proton density fat fraction (MRI-PDFF) using mDIXON-Quant sequence. MethodsTotal 100 patients who underwent abdominal US ATI and MRI-PDFF within one month were included. Subjects were divided into three groups according to MRI-PDFF; Group 1 (no fatty liver), Q < 5.1%; Group 2 (mild fatty liver), 5.1% ≤ Q < 14.1%; and Group 3 (moderate fatty liver), Q ≥ 14.1%. US attenuation coefficients (AC) of enrolled patients were measured and correlated with MRI-PDFF. And their diagnostic performances were assessed. AC, MRI-PDFF, and liver function tests were compared among all groups. ResultsMean AC value of each group was as follows: Group 1 = 0.58 ± 0.11 dB/cm/MHz, Group 2 = 0.68 ± 0.08 dB/cm/MHz, and Group 3 = 0.77 ± 0.06 dB/cm/MHz. Mean AC value of each group of hepatic steatosis showed statistically significant difference (p < 0.001). There was a significant correlation between AC and MRI-PDFF in Pearson correlation (r = 0.751, p < 0.001). The area under the ROC curve (AUROC) of AC was 0.914 with sensitivity of 91.5%, and specificity of 80.0% for detection of mild fatty liver, and 0.935 for detection of moderate fatty liver with sensitivity of 93.3%, and specificity of 87.1%. ConclusionAC using ultrasound ATI showed high diagnostic performance and provided discriminative values for severity grading of fatty liver disease.

Total attenuation compensation for backscatter coefficient estimation using full angular spatial compounding

The backscatter coefficient (BSC) quantifies the frequency-dependent reflectivity of tissues. Accurate estimation of the BSC is only possible with the knowledge of the attenuation coefficient slope (ACS) of the tissues under examination. In this study, the use of attenuation maps constructed using full angular spatial compounding (FASC) is proposed for attenuation compensation when imaging integrated BSCs. Experimental validation of the proposed approach was obtained using two cylindrical physical phantoms with off-centered inclusions having different ACS and BSC values than the background, and in a phantom containing an ex vivo chicken breast sample embedded in an agar matrix. With the phantom data, three different ACS maps were employed for attenuation compensation: (1) a ground truth ACS map constructed using insertion loss techniques, (2) the estimated ACS map using FASC attenuation imaging, and (3) a uniform ACS map with a value of 0.5 dBcm\\protect \\relax \\special {t4ht=−}1MHz\\protect \\relax \\special {t4ht=−}1, which is commonly used to represent attenuation in soft tissues. Comparable results were obtained when using the ground truth and FASC-estimated ACS maps in term of inclusion detectability and estimation accuracy, with averaged fractional error below 2.8 dB in both phantoms. Conversely, the use of the homogeneous ACS map resulted in higher levels of fractional error (>10 dB), which demonstrates the importance of an accurate attenuation compensation. The results with the ex vivo tissue sample were consistent with the observations using the physical phantoms, with the FASC-derived ACS map providing comparable BSC images to those formed using the ground truth ACS map and more accurate than those BSC images formed using a uniform ACS. These results suggest that BSCs can be reliably estimated using FASC when a self-consistent attenuation compensation stemming from prior estimation of an accurate ACS map is used.

Double-difference seismic attenuation tomography method and its application to The Geysers geothermal field, California

SUMMARY Knowledge of attenuation structure is important for understanding subsurface material properties. We have developed a double-difference seismic attenuation (DDQ) tomography method for high-resolution imaging of 3-D attenuation structure. Our method includes two main elements, the inversion of event-pair differential ${t^*}$ ($d{t^*}$) data and 3-D attenuation tomography with the $d{t^*}$ data. We developed a new spectral ratio method that jointly inverts spectral ratio data from pairs of events observed at a common set of stations to determine the $d{t^*}$ data. The spectral ratio method cancels out instrument and site response terms, resulting in more accurate $d{t^*}$ data compared to absolute ${t^*}$ from traditional methods using individual spectra. Synthetic tests show that the inversion of $d{t^*}$ data using our spectral ratio method is robust to the choice of source model and a moderate degree of noise. We modified an existing velocity tomography code so that it can invert $d{t^*}$ data for 3-D attenuation structure. We applied the new method to The Geyser geothermal field, California, which has vapour-dominated reservoirs and a long history of water injection. A new Qp model at The Geysers is determined using P-wave data of earthquakes in 2011, using our updated earthquake locations and Vp model. By taking advantage of more accurate $d{t^*}$ data and the cancellation of model uncertainties along the common paths outside of the source region, the DDQ tomography method achieves higher resolution, especially in the earthquake source regions, compared to the standard tomography method using ${t^*}$ data. This is validated by both the real and synthetic data tests. Our Qp and Vp models show consistent variations in a normal temperature reservoir that can be explained by variations in fracturing, permeability and fluid saturation and/or steam pressure. A prominent low-Qp and Vp zone associated with very active seismicity is imaged within a high temperature reservoir at depths below 2 km. This anomalous zone is likely partially saturated with injected fluids.

The effect of water intake on ultrasound tissue characteristics and hemodynamics of adult livers.

Aim of the studyTo assess the effect of water intake on ultrasound tissue characteristics and hemodynamics of adult livers.Material and methodsIn February 2020, we prospectively performed ultrasound shear wave elastography and attenuation imaging (ATI) of the liver parenchyma, and spectral Doppler sonography of the portal vein and hepatic artery in 19 adult healthy volunteers (10 men and 9 women, mean age 27 years, mean body mass index 24.65 kg/m2). We measured liver shear wave velocity (SWV, m/s), shear wave dispersion (SWD, m/s/kHz), attenuation coefficient (dB/cm/MHz), main portal vein velocity (PVV, cm/s), hepatic artery peak systolic velocity (PSV, cm/s), and end diastolic velocity (EDV, cm/s) immediately before and at different time points (15, 30, 45, and 60 minutes) after water intake (1.0 l water and 1.5 l water for body weight < 150 lbs. and ≥ 150 lbs., respectively).ResultsThe differences in SWV, PVV, hepatic artery PSV and EDV before and after water intake were significant (p < 0.01) whereas the differences in SWD and ATI were not (p > 0.05) based on repeated measures ANOVA tests. The values of SWV, PVV, PSV, and EDV reached a peak at 30-45 minutes and returned to baseline 60 minutes after water intake. We observed positive correlations of SWV with PVV, PSV, and EDV in linear regression analyses (r2 > 0.73).ConclusionsWater intake affects the liver stiffness and hemodynamics. No water intake at least one hour prior to liver ultrasound elastography and Doppler sonography is recommended.

Quantitative Ultrasound Radiofrequency Data Analysis for the Assessment of Hepatic Steatosis in Nonalcoholic Fatty Liver Disease Using Magnetic Resonance Imaging Proton Density Fat Fraction as the Reference Standard.

ObjectiveTo investigate the diagnostic performance of quantitative ultrasound (US) parameters for the assessment of hepatic steatosis in patients with nonalcoholic fatty liver disease (NAFLD) using magnetic resonance imaging proton density fat fraction (MRI-PDFF) as the reference standard.Materials and MethodsIn this single-center prospective study, 120 patients with clinically suspected NAFLD were enrolled between March 2019 and January 2020. The participants underwent US examination for radiofrequency (RF) data acquisition and chemical shift-encoded liver MRI for PDFF measurement. Using the RF data analysis, the attenuation coefficient (AC) based on tissue attenuation imaging (TAI) (AC-TAI) and scatter-distribution coefficient (SC) based on tissue scatter-distribution imaging (TSI) (SC-TSI) were measured. The correlations between the quantitative US parameters (AC and SC) and MRI-PDFF were evaluated using Pearson correlation coefficients. The diagnostic performance of AC-TAI and SC-TSI for detecting hepatic fat contents of ≥ 5% (MRI-PDFF ≥ 5%) and ≥ 10% (MRI-PDFF ≥ 10%) were assessed using receiver operating characteristic (ROC) analysis. The significant clinical or imaging factors associated with AC and SC were analyzed using linear regression analysis.ResultsThe participants were classified based on MRI-PDFF: < 5% (n = 38), 5–10% (n = 23), and ≥ 10% (n = 59). AC-TAI and SC-TSI were significantly correlated with MRI-PDFF (r = 0.659 and 0.727, p < 0.001 for both). For detecting hepatic fat contents of ≥ 5% and ≥ 10%, the areas under the ROC curves of AC-TAI were 0.861 (95% confidence interval [CI]: 0.786–0.918) and 0.835 (95% CI: 0.757–0.897), and those of SC-TSI were 0.964 (95% CI: 0.913–0.989) and 0.935 (95% CI: 0.875–0.972), respectively. Multivariable linear regression analysis showed that MRI-PDFF was an independent determinant of AC-TAI and SC-TSI.ConclusionAC-TAI and SC-TSI derived from quantitative US RF data analysis yielded a good correlation with MRI-PDFF and provided good performance for detecting hepatic steatosis and assessing its severity in NAFLD.

Estimation of the Filling Distribution and Height Levels Inside an Insulated Pressure Vessel by Guided Elastic Wave Attenuation Tomography.

The operation efficiency and safety of pressure vessels in the oil and gas industry profits from an accurate knowledge about the inner filling distribution. However, an accurate and reliable estimation of the multi-phase height levels in such objects is a challenging task, especially when considering the high demands in practicability, robustness in harsh environments and safety regulations. Most common systems rely on impractical instrumentation, lack the ability to measure solid phases or require additional safety precautions due to their working principle. In this work, another possibility to determine height levels by attenuation tomography with guided elastic waves is proposed. The method uses a complete instrumentation on the outer vessel shell and is based on the energy conversion rates along the travel path of the guided waves. Noisy data and multiple measurements from sparsely distributed sensor networks are translated into filling levels with accuracies in the centimeter range by solving a constrained optimization problem. It was possible to simultaneously determine sand, water, and oil phases on a mock-up scale experiment, even for artificially created sand slopes. The accuracy was validated by artificial benchmarking for a horizontal vessel, giving references for constructing an affordable prototype system.

Pyroelectric ultrasound sensor model: directional response

Ultrasound is typically measured using phase-sensitive piezoelectric sensors. Interest in phase-insensitive sensors has grown recently, with proposed applications including ultrasound attenuation tomography of the breast and acoustic power measurement. One advantage of phase-insensitive detectors, in contrast to conventional phase-sensitive detectors, is that they do not suffer from a narrow directional response at high frequencies due to phase cancellation. A numerical model of a phase-insensitive pyroelectric ultrasound sensor is presented. The model consists of three coupled components run in sequence: acoustic, thermal, and electrical. The acoustic simulation models the propagation and absorption of the incident ultrasound wave. The absorbed acoustic power density is used as a heat source in the thermal simulation of the time-evolution of the temperature in the sensor. Both the acoustic and thermal simulations are performed using the k-Wave MATLAB toolbox with an assumption that shear waves are not supported in the medium. The final component of the model is a pyroelectric circuit model which outputs the sensor response based on the temperature change in the sensor. The modelled pyroelectric sensor response and directional dependence are compared to empirical data.

PET-enabled dual-energy CT: image reconstruction and a proof-of-concept computer simulation study

Standard dual-energy computed tomography (CT) uses two different x-ray energies to obtain energy-dependent tissue attenuation information to allow quantitative material decomposition. The combined use of dual-energy CT and positron emission tomography (PET) may provide a more comprehensive characterization of disease states in cancer and other diseases. However, the integration of dual-energy CT with PET is not trivial, either requiring costly hardware upgrades or increasing radiation exposure. This paper proposes a different dual-energy CT imaging method that is enabled by PET. Instead of using a second x-ray CT scan with a different energy, this method exploits time-of-flight PET image reconstruction via the maximum likelihood attenuation and activity (MLAA) algorithm to obtain a 511 keV gamma-ray attenuation image from PET emission data. The high-energy gamma-ray attenuation image is then combined with the low-energy x-ray CT of PET/CT to provide a pair of dual-energy CT images. A major challenge with the standard MLAA reconstruction is the high noise present in the reconstructed 511 keV attenuation map, which would not compromise the PET activity reconstruction too much but may significantly affect the performance of the gamma-ray attenuation image for material decomposition. To overcome the problem, we further propose a kernel MLAA algorithm to exploit the prior information from the available x-ray CT image. We conducted a computer simulation to test the concept and algorithm for the task of material decomposition. The simulation results demonstrate that this PET-enabled dual-energy CT method is promising for quantitative material decomposition. The proposed method can be readily implemented on time-of-flight PET/CT scanners to enable simultaneous PET and dual-energy CT imaging.

Practical joint reconstruction of activity and attenuation with autonomous scaling for time-of-flight PET

Recent research has showed that attenuation images can be determined from emission data, jointly with activity images, up to a scaling constant when utilizing the time-of-flight (TOF) information. We aim to develop practical CT-less joint reconstruction for clinical TOF PET scanners to obtain quantitatively accurate activity and attenuation images. In this work, we present a joint reconstruction of activity and attenuation based on MLAA (maximum likelihood reconstruction of attenuation and activity) with autonomous scaling determination and joint TOF scatter estimation from TOF PET data. Our idea for scaling is to use a selected volume of interest (VOI) in a reconstructed attenuation image with known attenuation, e.g. a liver in patient imaging. First, we construct a unit attenuation medium which has a similar, though not necessarily the same, support to the imaged emission object. All detectable LORs intersecting the unit medium have an attenuation factor of e −1≈ 0.3679, i.e. the line integral of linear attenuation coefficients is one. The scaling factor can then be determined from the difference between the reconstructed attenuation image and the known attenuation within the selected VOI normalized by the unit attenuation medium. A four-step iterative joint reconstruction algorithm is developed. In each iteration, (1) first the activity is updated using TOF OSEM from TOF list-mode data; (2) then the attenuation image is updated using XMLTR—a extended MLTR from non-TOF LOR sinograms; (3) a scaling factor is determined based on the selected VOI and both activity and attenuation images are updated using the estimated scaling; and (4) scatter is estimated using TOF single scatter simulation with the jointly reconstructed activity and attenuation images. The performance of joint reconstruction is studied using simulated data from a generic whole-body clinical TOF PET scanner and a long axial FOV research PET scanner as well as 3D experimental data from the PennPET Explorer scanner. We show that the proposed joint reconstruction with proper autonomous scaling provides low bias results comparable to the reference reconstruction with known attenuation.

Reduction of Shear Wave Elastography but Not Shear Wave Dispersion After Successful Hepatitis C Treatment With Direct-Acting Antiviral Agents.

Successful antiviral treatment in patients with hepatitis C can lead to reduced liver stiffness. In this study, we attempted to compare 2-dimensional (2D) shear wave elastography (SWE), shear wave dispersion (SWD), and attenuation imaging (ATI) with transient elastography (TE) and the controlled attenuation parameter (CAP) in patients under direct-acting antiviral (DAA) therapy. Patients with chronic hepatitis C infection undergoing DAA therapy from January 2017 to June 2020 were retrospectively examined. The results of 2D SWE, SWD, ATI, TE, and CAP were recorded before and 12 weeks after the completion of DAA therapy. A total of 122 patients with a median age of 61 years were investigated; among them, 121 (99.2%) achieved a sustained virologic response at 12 weeks after DAA therapy. Fibrosis 4, the aspartate aminotransferase-to-platelet ratio index, 2D SWE, and TE were reduced after DAA therapy. The CAP was increased; however, SWD and ATI showed no statistically significant changes after DAA therapy. Two-dimensional SWE and TE were strongly correlated (r=0.885-0.897; P < .001). Albumin and the baseline liver stiffness measurement were independent factors of liver stiffness measurement changes after DAA therapy. Direct-acting antiviral therapy can significantly decrease liver stiffness (using both 2D SWE and TE) but not SWD and ATI values in patients with hepatitis C. An increased CAP is also observed after DAA therapy.

Clinical Feasibility of Quantitative Ultrasound Imaging for Suspected Hepatic Steatosis: Intra- and Inter-examiner Reliability and Correlation with Controlled Attenuation Parameter

This study was aimed at investigating the clinical feasibility of quantitative ultrasound (QUS) imaging in the evaluation of suspected hepatic steatosis through assessment of the reliability of measurements and its correlation with the controlled attenuation parameter (CAP). This retrospective study included 117 patients who underwent liver B-mode ultrasound (US) with QUS imaging with a clinical US machine (RS85, Samsung Medison, Seoul, Korea) and CAP measurements between December 2019 and March 2020. For QUS examination, tissue attenuation imaging (TAI) and tissue scatter-distribution imaging (TSI) parameters were obtained. Intra- and inter-examiner reliability were assessed using intra-class correlation coefficients (ICCs), and QUS imaging parameters were correlated with CAP measurements using Spearman's correlation analysis. TAI and TSI revealed excellent intra- and inter-examiner reliability with ICCs of 0.994 and 0.975 and 0.991 and 0.947, respectively. Both TAI and TSI were significantly positively correlated with CAP values. QUS imaging provided good intra-and inter-observer reliability and correlated well with CAP in assessing suspected hepatic steatosis.

Quantitative accuracy of virtual non-contrast images derived from spectral detector computed tomography: an abdominal phantom study

Dual-energy CT allows for the reconstruction of virtual non-contrast (VNC) images. VNC images have the potential to replace true non-contrast scans in various clinical applications. This study investigated the quantitative accuracy of VNC attenuation images considering different parameters for acquisition and reconstruction. An abdomen phantom with 7 different tissue types (different combinations of 3 base materials and 5 iodine concentrations) was scanned using a spectral detector CT (SDCT). Different phantom sizes (S, M, L), volume computed tomography dose indices (CTDIvol 10, 15, 20 mGy), kernel settings (soft, standard, sharp), and denoising levels (low, medium, high) were tested. Conventional and VNC images were reconstructed and analyzed based on regions of interest (ROI). Mean and standard deviation were recorded and differences in attenuation between corresponding base materials and VNC was calculated (VNCerror). Statistic analysis included ANOVA, Wilcoxon test and multivariate regression analysis. Overall, the VNCerror was − 1.4 ± 6.1 HU. While radiation dose, kernel setting, and denoising level did not influence VNCerror significantly, phantom size, iodine content and base material had a significant effect (e.g. S vs. M: − 1.2 ± 4.9 HU vs. − 2.1 ± 6.0 HU; 0.0 mg/ml vs. 5.0 mg/ml: − 4.0 ± 3.5 HU vs. 5.1 ± 5.0 HU and 35-HU-base vs. 54-HU-base: − 3.5 ± 4.4 HU vs. 0.7 ± 6.5; all p ≤ 0.05). The overall accuracy of VNC images from SDCT is high and independent from dose, kernel, and denoising settings; however, shows a dependency on patient size, base material, and iodine content; particularly the latter results in small, yet, noticeable differences in VNC attenuation.

Abstract 13607: Seasonal Variation in the Attenuation of Epicardial Adipose Tissue on Cardiac Computed Tomography

Introduction: The role of epicardial adipose tissue (EAT) in the development and vulnerability of coronary artery atherosclerosis has been the focus of extensive research for the past several years. EAT is visceral fat that surrounds the coronary arteries and it consists of beige adipose tissue that is functionally similar to brown adipose tissue and has a higher computed tomography (CT) attenuation than subcutaneous white adipose tissue. Given the brown-like composition of EAT, its attenuation may be affected by several factors including seasonal temperature variations and clinical factors. Hypothesis: We investigated the effect of season on EAT attenuation and additional clinical factors that may influence attenuation measurements. Methods: Single center, retrospective study of 597 cardiac CT exams performed for coronary artery calcium (CAC) scoring obtained on a single CT scanner during winter and summer months. Summer was defined as June, July, and August. Winter was defined as December, January, and February. EAT attenuation in Hounsfield units (HU) was measured in a region of interest near the right coronary artery ostium. Subcutaneous adipose tissue (SCAD) attenuation was measured in the thoracic subcutaneous tissue. Patients’ demographic and clinical characteristics were obtained by questionnaire and chart review. Results: The clinical and demographic characteristics of patients scanned during the summer (N=253) and the winter (N=344) months were similar. One third of patients were women, one quarter used statins and anti-hypertensive drugs each and 30% had a BMI&gt;30. There was a significantly lower EAT attenuation measured during the summer than the winter months (-98.17±6.94 HUs vs -95.64±7.99 HUs; P&lt;0.001). Additionally, gender, obesity, treatment with statins and anti-hypertensive agents significantly modulated the seasonal variation in EAT attenuation. SCAD attenuation was not affected by season or any other factor. Conclusions: Our study shows that the measurement of EAT attenuation is complex and is likely affected by season, demographics and clinical factors. Attempts to use EAT attenuation as a biomarker for risk of cardiovascular events should take these potential confounders into consideration.

Abstract 16281: Non-calcified Coronary Plaque Burden is Related to Epicardial Adipose Tissue and Peri-coronary Adipose Tissue Attenuation in Heart Failure With Preserved Ejection Fraction

Introduction: Coronary inflammation may be a factor in developing heart failure with preserved ejection fraction (HFpEF). Epicardial fat volume (EFV) measured using non-contrast computed tomography (CT) and pericoronary adipose tissue (PCAT) attenuation on coronary CT angiography (CCTA) are considered to be inflammatory mediators, which play an important role in the development of coronary plaque. Hypothesis: We hypothesize that there is an interrelationship between these measures in HFpEF and no obstructive coronary artery disease (CAD). Methods: 28 subjects with HFpEF (European Society of Cardiology criteria), with coronary CCTA-documented absence of obstructive CAD. Non-calcified plaque (NCP), low-density non-calcified plaque (LDNCP), PCAT attenuation were quantified using semi-automated software and EFV was quantified using QFAT software. PCAT attenuation in Hounsfield Units (HU) was measured in a standardized 40 mm segment around the proximal right coronary artery. Statistical analysis was performed using Spearman correlation and multivariable regression models adjusted for age, BMI, EFV, and PCAT tested relations to NCP burden. Results: Overall, the mean age of 64.8±12 years, 74% women, BMI 29.3±4, total cholesterol 162±41mg/dl, LDL 85±29 mg/dl, HDL 55±14 mg/dl, systolic BP 132±22mmHg, diastolic BP 77±12mmHg, EFV 139±73 cm 3 and, PCAT attenuation -78±8 HU. Mean total NCP burden 34±13%, total LDNCP burden 3±1.8 %, and coronary calcium score (CCS) 414±920. EFV and PCAT attenuation correlated with the coronary risk markers including CCS and NCP burden variables (Table). In multivariable analysis, age and PCAT (β±SE=0.43±0.2, p=0.04, 0.64±0.3, p=0.03 per 1%-change in NCP burden respectively) were related to NCP burden. Conclusions: EFV and PCAT attenuation are associated with non-calcified plaque burden and may play an important role in the pathophysiological process of HFpEF. Further studies are needed to further understand these findings.

Dynamic Upwelling Beneath the Salton Trough Imaged With Teleseismic Attenuation Tomography

AbstractThe Salton Trough is one of the few regions on Earth where rifting is subaerial instead of submarine. We use the relative attenuation of teleseismic P phases recorded by the Salton Trough Seismic Imaging Project to investigate lithospheric and asthenospheric structures that form during extension. Map‐view analysis reveals stronger attenuation within the Salton Trough than in the adjacent provinces. We then construct tomographic models for variations in seismic attenuation with depth to discriminate between crustal and mantle signals with a damped least squares approach and a Bayesian approach. Synthetic tests show that models from damped least squares significantly underestimate the strength of attenuation and cannot separate crustal and mantle signals even if the tomographic models are allowed to be discontinuous at the lithosphere‐asthenosphere boundary (LAB). We show that a Bayesian approach overcomes these problems when inverting the same synthetic data sets and that shallow and deep signals are more clearly separated when imposing a discontinuity. With greater than 95% confidence, the results reveal first, that attenuation occurs primarily beneath the LAB; second, that the width of the attenuative region is narrower than the rift at 120 km depth; and third, that the strength of attenuation requires that the attenuative feature represents a melting‐column similar to those beneath mid‐ocean ridges. The narrow width of the melting column below the volatile‐free solidus is inconsistent with models for passive upwelling, where flow is driven only by rifting. Instead, we attribute the generation of incipient oceanic crust to mantle upwelling focused by buoyancy into a narrow diapir.