Apparent Attenuation Coefficient Research Articles

Multi-scale dynamic mathematical model of CO2 and fly ash mineralization

The multi-scale structural characteristics of micro-nano pores of fly ash are the core factors affecting the mechanisms of physical transport and chemical reaction of CO2. The existing theoretical models of mineralization do not take such characteristics into account. it is difficult to describe the mechanisms of physical transport and chemical reaction of CO2. In order to address this scientific problem, a theoretical model of multi-scale structures of pore series is established. A mathematical dynamic model of multi-scale internal diffusion-mineralization is also established for accurately describing the concentration variation law in physical transport and chemical reaction processes of CO2 in micro-nano pores of fly ash under natural static conditions. The model is simulated to analyze the key parameters affecting the transport-mineralization reaction rate in the evolutionary mechanism of CO2. The simulated results showed that if the initial apparent diffusion-mineralization coefficient is reduced by 100 times, the concentration of CO2 at the center of the particles is reduced by 25 order in magnitude. The attenuation coefficient is reduced by 2 order in magnitude and the concentration of CO2 at the center of the particles is changed by 9 order in magnitude. These findings indicate that the initial apparent diffusion-mineralization coefficient and attenuation coefficient are the factors affecting the diffusion-mineralization reaction in the evolution of CO2. The reason for the phenomenon of multi-scale evolution and mechanism of diffusion mineralization reaction of CO2 in the micro-nano pores of fly ash is revealed.

Tissue equivalence of 3D printing materials with respect to attenuation and absorption of X-rays used for diagnostic and interventional imaging.

Three-dimensional printing is a promising technology to produce phantoms for quality assurance and dosimetry in X-ray imaging. Crucial to this, however, is the use of tissue equivalent printing materials. It was thus the aim of this study to evaluate the properties of a larger number of commercially available printing filaments with respect to their attenuation and absorption of X-rays. Apparent kerma attenuation coefficients (AKACs) and absorbed doses for different X-ray spectra (tube voltages, 70-140kV) were measured and simulated by Monte-Carlo computations for a larger number of fused-deposition-modeling (FDM) materials. The results were compared with the respective values simulated for reference body tissues. In addition, the properties of polylactide acid samples printed with reduced infill densities were investigated. Measured and simulated AKACs and absorbed doses agreed well with each other and in case of AKACs also with attenuation coefficients derived from the reference database of the National Institute of Standards and Technology (NIST). For lung, adipose, muscle, and bulk soft tissue as well as for spongiosa (cancellous bone), printed materials with equivalent attenuation as well as absorption properties could be identified. In contrast, none of the considered printed materials was equivalent to cortical bone. Several FDM materials have been identified as well-suited substitutes for body tissues in terms of the investigated material characteristics. They can therefore be used for in-house production of individualized and task-specific phantoms for image quality assessment and dose measurements in X-ray imaging.

Online measurement of floc size, viscosity, and consistency of cellulose microfibril suspensions with optical coherence tomography

In this study, cellulose microfibril (CMF) suspensions were imaged during pipe flow at consistencies of 0.4%, 1.0%, and 1.6% with optical coherence tomography (OCT) to obtain images of the structure and the local velocity of the suspension. The viscosities obtained by combining pressure loss measurement with the OCT velocity data showed typical shear thinning behavior and were in excellent agreement with viscosities obtained with ultrasound velocity profiling. The structural OCT images were used to calculate the radial and the axial floc sizes of the suspension. A fit of power law to the geometrical floc size–shear stress data gave the same power law index for all consistencies, suggesting that floc rupture dynamics is independent of consistency. The dependence of viscosity and floc size on shear stress was similar, indicating that the shear thinning behavior of CMF suspensions is closely related to the rupture dynamics of flocs. The results also showed that an apparent attenuation coefficient of the OCT signal can be used to determine the consistency of CMF suspensions.

Focal spot imaging based on zero lag cross‐correlation amplitude fields: Application to dense array data at the San Jacinto fault zone

AbstractWe image the subsurface below a dense seismic array straddling the Clark branch of the San Jacinto fault zone in Southern California. The analysis is based on focal spots of surface waves associated with the zero lag amplitudes of noise cross‐correlations computed between all stations of the dense array. Local medium properties are inferred from the spatially variable focal spot size and shape based on the first zero crossing of amplitude versus distance distributions. The method provides simultaneous estimates of wave speed, apparent attenuation, and anisotropy without solving a tomographic inverse problem. The obtained images of the frequency dependent seismic velocity distributions are consistent with independent estimates from a far‐field Rayleigh wave tomography. We observe an anticorrelation between our apparent attenuation coefficient and seismic velocity, and a fault‐parallel alignment of fast propagation directions with greater structural complexity to the southwest of the fault. The results imply a complex fault zone structure including a waveguide to the northeast of the fault that is continuous across the observed depth range and a low‐velocity structure to the southwest associated with a shallow sedimentary basin.

Multimodal measurement of acoustic properties in cartilage tissue

In order to detect the disease and degeneration of cartilage early, evaluations of acoustic properties are expected, but the physical meaning should be clarified. On the other hand, we have proposed a multimodal method using ultrasound (US) and magnetic resonance (MR) images for in vivo SOS measurement. In this study, the method was applied for the tissue-engineered cartilage, and the SOS was compared with T1, T2, apparent diffusion coefficient (ADC), attenuation coefficient (ATT), and Young’s modulus (YM). All procedures were approved by the Animal Care and Use Committee of our institution. 12-week-old male rats were used, and five different types of tissue-engineered cartilage was subcutaneously implanted in the back of rat (n = 30). Under anesthesia, MR and US images including same cross-sections were acquired separately, by using a MR imager of 2 Tesla and a US device of 13 MHz. At this time, T1, T2, ADC were also measured. The SOS was determined by the thickness measurement using the MR image and the time-of-flight measurement using the US image. After that, the ATT and YM were measured by using the extracted samples of tissue-engineered cartilage. As a result, the SOS exhibits negative correlations with T1, T2, and ADC (R2 = 0.30, 0.93, 0.82), and positive correlations with ATT and YM (R2 = 0.98, 0.87). These results suggest the SOS of tissue-engineered cartilage strongly reflects the elasticity. Consequently, the physical meaning of SOS was clarified through the multimodal measurement.

Quantification of the void content of composite materials using soft X-ray transmittance

Carbon fiber reinforced thermoplastics (CFRTPs) have high potential in high-cycle (1 min) molding as a weight-reducing material for the mass production of automobile components. However, residual voids in CFRTPs lead to diminished and unstable mechanical properties; therefore, the effective quantification of the void content in CFRTP products is necessary for developing an affordable system for mass production. In a previous study, we demonstrated that the X-ray attenuation coefficient decreases with increasing void content; thus, measurements of X-ray attenuation coefficients can be used to estimate the void contents of CFRTPs. In this study, we first investigated in detail the soft X-ray attenuation coefficients of completely impregnated composite materials with three different thicknesses; we observed that the attenuation coefficients decreased with increasing composite thickness, even though they should be independent of the thickness according to the Beer–Lambert law. We next demonstrated that although no correlation exists between the X-ray transmittance and the apparent attenuation coefficient of six composites with various void contents, the true attenuation coefficient modified to account for void content exhibits a good linear relationship with the X-ray transmittance, same as fully impregnated composites. Using the approximation line between the X-ray transmittance and the modified attenuation coefficient of CFRTP, we estimated the void content on the basis of the difference between the apparent and true X-ray attenuation coefficients. The average difference in void content determined by conventional hydrostatic weighing and that determined by the proposed X-ray transmittance method was 0.43%. We therefore concluded that the void content of CFRTPs of any thickness can be estimated nondestructively using soft X-rays.

An analytical validation for the attenuation of lateral propagating light in sea ice

The attenuation of lateral propagating light (LPL) in sea ice was measured using an artificial light source in the Canadian Arctic during the 2007/2008 winter. The apparent attenuation coefficient µ(λ) for lateral propagating light was obtained from the measured logarithmic relative variation rate. In this study an analytical solution based on the strict optical theories is developed to validate the measured result. There is a good consistency between theoretical solution and measured data, by which a quite simple but very rigorous relationship among the light source, measurement geometry, and measured irradiance is established. The attenuation coefficients acquired by measurement and theory are the diffusion attenuation as an apparent optical property of ice, independent of the light source and shining condition. The attenuation ability of sea ice should be caused by the microstructure of sea ice, such as crystal size, ice density, brine volume, air inclusion, etc. It also includes the leak from both interfaces by directional scattering. It is verified that the measuring approach is operational and accurate to measure the attenuation of the LPL. The solution from this study did not tell the connection among the extinction and the inclusions of sea ice theoretically because of insufficient understanding.

Elimination of bandwidth effect in attenuation measurement with picosecond ultrasonics

We study the broadening effect of probing pulse light on the apparent attenuation of the Brillouin oscillation measured with picosecond ultrasonics. We observe experimentally that the attenuation of the Brillouin oscillation is sensitive to the bandwidth, and the apparent attenuation coefficient increases as the bandwidth increases, being far from the intrinsic attenuation coefficient. Theoretical calculation is performed to reconstruct the observed oscillations, and it is confirmed that there are several factors affecting the apparent attenuation in addition to the bandwidth. We finally propose equations that deduce the contribution of the broadening to the apparent attenuation of the Brillouin oscillation.

Three-dimensional brain phantom containing bone and grey matter structures with a realistic head contour

IntroductionA physical 3-dimensional phantom that simulates PET/SPECT images of static regional cerebral blood flow in grey matter with a realistic head contour has been developed. This study examined the feasibility of using this phantom for evaluating PET/SPECT images.MethodsThe phantom was constructed using a transparent, hydrophobic photo-curable polymer with a laser-modelling technique. The phantom was designed to contain the grey matter, the skull, and the trachea spaces filled with a radioactive solution, a bone-equivalent solution of K2HPO4, and air, respectively. The grey matter and bone compartments were designed to establish the connectivity. A series of experiments was performed to confirm the accuracy and reproducibility of the phantom using X-ray CT, SPECT, and PET.ResultsThe total weight was 1997 ± 2 g excluding the inner liquid, and volumes were 563 ± 1 and 306 ± 2 mL, corresponding to the grey matter and bone compartments, respectively. The apparent attenuation coefficient averaged over the whole brain was 0.168 ± 0.006 cm−1 for Tc-99 m, which was consistent with the previously reported value for humans (0.168 ± 0.010 cm−1). Air bubbles were well removed from both grey-matter and bone compartments, as confirmed by X-ray CT. The phantom was well adapted to experiments using PET and SPECT devices.ConclusionThe 3-dimensional brain phantom constructed in this study may be of use for evaluating the adequacy of SPECT/PET reconstruction software programs.

Apparent linear attenuation coefficients in phase contrast X-ray tomography

In the inline phase contrast X-ray tomography the reconstructed apparent linear attenuation coefficient values may be greatly larger than sample’s linear attenuation coefficients or even be negative. In this work we present a general formula to quantitatively relate the apparent linear attenuation coefficient values in cone-beam phase contrast tomography to sample’s linear attenuation coefficients and refractive indices. This formula overcomes the gross inaccuracy of the existing formula in the literature in analyzing high-resolution phase contrast tomography, and it will be useful for correctly interpreting and quantifying the apparent linear attenuation coefficients in cone-beam X-ray phase contrast tomography.

Effect of liquid embolic agents on Gamma Knife surgery dosimetry for arteriovenous malformations

The effectiveness of Gamma Knife stereotactic surgery to obliterate brain arteriovenous malformations (AVMs) may be diminished by the preoperative adjunctive use of endovascular liquid embolic agents. The purpose of the present investigation was to determine if commercially available liquid embolic agents reduce the radiation dose to the target because of attenuation of the (60)Co beam. The apparent linear attenuation coefficients for 120- to 140-keV radiographs in embolized regions were retrieved from CT scans for several patients with AVMs who had undergone embolization procedures with liquid embolic agents to reduce nidal volumes. Based on these coefficients and a virtual model of Gamma Knife surgery (GKS) with basic ray tracing, the authors obtained the path lengths and densities of the embolized regions. The attenuation of (60)Co beams was then calculated for various sizes and positions of embolized AVM regions and for the number of beams used for treatment. Published experiments for several high-atomic-number materials were used to estimate the effective (60)Co beam attenuation coefficients for the N-butyl cyanoacrylate (NBCA, suspended in ethiodized oil) and ethylene vinyl alcohol copolymer (EVOH, with suspended micronized tantalum powder, Onyx) used in the AVM embolizations. Dose reductions during GKS were calculated for a theoretical model based on the CT-documented apparent linear attenuation coefficients and for the (60)Co energy attenuation coefficient. Dose measurements were obtained in a phantom study with EVOH for comparison with the estimates generated from the two attenuation coefficients. Based on CT (keV) apparent attenuation coefficients, the authors' theoretical model predicted that the cumulative effect of either of the embolic agents decreased the number of kilovoltage photons in an embolized nidus by -8% to -15% because of the increased atomic number and density of NBCA and Onyx. However, in using the effective attenuation coefficient for the (60)Co energies as is used in GKS, the authors' theoretical model yielded only a 0.2% dose reduction per beam and a < 0.01%-0.2% dose reduction in total. These theoretical results were validated by measurements in a head phantom containing Onyx. Dose reduction due to attenuation of the (60)Co beam by the AVM embolization material was negligible for both NBCA and EVOH because of the high-energy (60)Co beam.

Theoretical Estimation of Changes in Plane Elastic Waves due to Cylindrical Inclusions

Changes in amplitude and phase shifts in plane elastic waves were theoretically estimated when they propagated through an elastic body containing cylindrical inclusions. Based on the integral equation suggested by Lavrov et al., these changes were calculated in the case when only one cylindrical inclusion was located in the body and the propagating waves have a single frequency. These calculations were expanded to more practical case when multiple cylindrical inclusions aligned in the body and the waves have some frequency band. The changes in amplitude and phase shifts calculated were associated to the changes in apparent sonic velocity and attenuation coefficient due to a structural change in the material. This theoretical approach contributes to a quantitative damage evaluation based upon structural changes in various materials by measuring the acoustical parameters such as apparent sonic velocity and attenuation coefficient.

Distribution of noise sources for seismic interferometry

SUMMARY We demonstrate that the distribution of seismic noise sources affects the accuracy of Green’s function estimates and therefore isotropic and anisotropic tomographic inversions for both velocity and attenuation. We compare three methods for estimating seismic noise source distributions and quantify the potential error in phase velocity, azimuthal anisotropy and attenuation estimates due to inhomogenous source distributions. The methods include: (1) least-squaresinversionofbeamformeroutput,(2)aleast-squaresinversionofyearlongstacked noise correlation functions assuming both a 2-D plane wave source density model and (3) a 3-D plane wave source density model. We use vertical component data from the 190 stations of the Southern California Seismic Network and some US Array stations for 2008. The good agreement between the three models suggests the 2-D plane wave model, with the fewest number of unknown parameters, is generally sufficient to describe the noise density function for tomographic inversions. At higher frequencies, 3-D and beamforming models are required to resolve peaks in energy associated with body waves. We illustrate and assess isotropic and azimuthally anisotropic phase velocity and attenuation uncertainties for the noise source distribution in southern California by inverting isotropic lossless synthetic Fourier transformed noise correlation function predictions from modelled 2-D source distribution. We find that the variation in phase velocity with azimuth from inhomogeneous source distribution yields up to 1 per cent apparent peak-to-peak anisotropy. We predict apparent attenuation coefficients from our lossless synthetics on the same order of magnitude as those previously reported for the region from ambient noise. Since noise source distributions are likely inhomogeneous varying regionally and with time, we recommend that noise correlation studies reporting attenuation and anisotropy incorporate source density information.

E-045 The effect of liquid embolic agents on gamma knife radiosurgery dosimetry for arteriovenous malformations

PurposeThe effectiveness of gamma knife stereotactic radiosurgery to obliterate brain arteriovenous malformations (AVMs) may be diminished by the preoperative adjunctive use of endovascular liquid embolic agents. The purpose of the...

Attenuation of lateral propagating light in sea ice measured with an artificial lamp in winter Arctic

The attenuation property of a lateral propagating light (LPL) in sea ice was measured using an artificial lamp in the Canadian Arctic during the 2007/2008 winter. A measurement method is proposed and applied whereby a recording instrument is buried in the sea ice and an artificial lamp is moved across the instrument. The apparent attenuation coefficient mu(lambda) for the lateral propagating light is obtained from the measured logarithmic relative variation rate. With the exception of blue and red lights, the attenuation coefficient changed little with wavelength, but changed considerably with depth. The vertical decrease of the attenuation coefficient was found to be correlated with salinity: the greater the salinity, the greater the attenuation coefficient. A clear linear relation of salinity and the lateral attenuation coefficient with R(2)=0.939 exists to address the close correlation of the attenuation of LPL with the scattering from the brine. The observed attenuation coefficient of LPL is much larger than that of the vertical propagation light, which we speculate to be caused by scattering. Part of this scattered component is transmitted out of the sea ice from the upper and lower surfaces. (C) 2010 Elsevier B.V. All rights reserved.

WE‐E‐304A‐01: Contrast Mechanism and Origin of Artifacts in Phase‐Sensitive X‐Ray Volumetric Imaging

Purpose: Phase‐sensitive x‐ray volumetric imaging has great potential for tissue contrast enhancement and radiation dose reduction, compared to conventional tissue‐attenuation based x‐ray volumetric imaging. In order to achieve quantitative and artifact‐free phase sensitive volumetric imaging, one should quantify the formed phase contrast and find the origin of artifacts formed in phase‐sensitive volumetric imaging. Method and Materials: We incorporated x‐ray Fresnel diffraction into x‐ray projection acquisitions, and reconstructed volumetric images from these phase‐sensitive projections by the filtered backprojection method. A formula for the reconstructed tissue's apparent attenuation coefficients was derived for quantitative analysis. Computer simulations of phase sensitive 3D tomography were performed, and reconstructed 3D phantom tomograms were analyzed, and the artifacts associated with phase‐contrast were identified. In order to eliminate these artifacts, we performed phase retrievals based on the phase‐attenuation duality method for each projection, and these phase‐retrieved projections were then used for new 3D tomographic reconstructions. Results: The apparent linear attenuation coefficients in 3D tomograms were found each being the sum of three parts: the tissue linear attenuation coefficient, the scaled 3D Laplacian of tissue refraction index, and the artifact depending on global distributions of tissue attenuation coefficients and refraction indices. The simulated high‐resolution 3D images of phantoms exhibit severe artifacts as the upward and downward density over‐shootings and the streaks. The phase retrieval was shown very effective for removing these artifacts and accurately reconstructing tissue attenuation coefficients in phase‐sensitive 3D tomography. Conclusion: We clarified the contrast mechanism in phase‐sensitive volumetric imaging, found the quantitative contribution of the phase contrast in reconstructed 3D images, and revealed the origin of severe artifacts. The need of the phase‐retrievals for quantitative and artifact‐free phase sensitive volumetric imaging was clearly demonstrated.Research supported in part by DoD Breast Cancer Research Program.

TH‐C‐BRD‐08: The Effect of Embolization Glue On Gamma Knife Radiosurgery of Arterio‐Venous Malformations

Purpose: Gamma Knife stereotactic radiosurgery in combination with embolization or alone is a widely recommended treatment option for patients with arterio‐venous malformations (AVM) with estimated near 90% cure rate. A recently published report suggested that the failures to obliterate the AVM nidus were caused by up to 15% dose reduction in the target volume due to the effect of the embolization materials used prior to the Gamma Knife radiosurgery. This work aimed to resolve the issue. Method and Materials: 1) The apparent linear attenuation coefficients for 120keV to 140keV x‐rays in the embolized regions were retrieved from CT scans for several patients with AVM malformations. Based on these coefficients and our virtual model of Gamma Knife with basic ray tracing, we obtained the pathlengths and densities for the embolized regions. The attenuation of Co‐60 beams was then calculated for various sizes and positions of AVM embolized regions and the number of beams used for treatment. 2) Published experiments for several high atomic number materials were used to estimate the effective Co‐60 beam attenuation coefficients for N‐butylcyanoacrylate (doped with high Z) and Onyx (ethylene‐vinyl alcohol copolymer doped with tantalum) used in the AVM embolizations. The dose reduction during Gamma Knife radiosurgery was calculated based on the Co‐60 energy attenuation coefficient. Results: Based on apparent CT (keV) attenuation coefficients, one may conclude that the cumulative effect of the glue would decrease the dose delivered in Gamma Knife radiosurgery from −8 to −15 %. However, using the true attenuation coefficient for Co‐60 energies in the dose calculation leads one to conclude that there is 0.2% dose reduction per beam and less than 0.01–0.2% dose reduction in total. Conclusion: Dose reduction due to attenuation of the Co‐60 beam by the AVM embolization glue material is negligible.

Effect of grain size on the ultrasonic parameters in stainless steels

In this study, the influence of grain size on the velocity of ultrasonic waves and ultrasonic attenuation in stainless steels was investigated. The aim of this study is to demonstrate the capability of ultrasonic techniques in the assessment of the grain size of steels. Heat treatment processes were carried out in order to obtain different grain sizes for AISI 304 stainless steel specimens. AISI 316 stainless steel specimens were produced by casting and tested in as-cast condition. Velocities of ultrasonic longitudinal and transverse waves were measured by means of pulse-echo method using contact type normal beam probes with 1 and 4 MHz frequencies. Apparent attenuation coefficient of longitudinal waves was determined at 4 MHz. Young's modulus of the specimens was also determined. The results showed that ultrasonic longitudinal and transverse wave velocities and Young's modulus were decreased with increasing grain size of the specimens. The apparent attenuation coefficient of longitudinal waves was increased with increasing grain size.

Is the Kramers-Kronig relationship between ultrasonic attenuation and dispersion maintained in the presence of apparent losses due to phase cancellation?

Phase cancellation effects can compromise the integrity of ultrasonic measurements performed with phase sensitive receiving apertures. A lack of spatial coherence of the ultrasonic field incident on a phase sensitive receiving array can produce inaccuracies of the measured attenuation coefficient and phase velocity. The causal (Kramers-Kronig) link between these two quantities in the presence of phase distortion is investigated using two plastic polymer materials, Plexiglas and Lexan, that exhibit attenuation coefficients that increase linearly with frequency, in a fashion analogous to that of soft tissue. Flat and parallel plates were machined to have a step of a thickness corresponding to an integer number of half wavelengths within the bandwidth investigated, 3 to 7 MHz. Insonification of the stepped portion of each plate produces phase cancellation artifacts at the receiving aperture and, therefore, in the measured frequency dependent attenuation coefficient. Dispersion predictions using two different forms of the Kramers-Kronig relations were performed for the flat and the stepped regions of each plastic plate. Despite significant phase distortion and a detection system sensitive to these aberrations, the Kramers-Kronig link between the apparent attenuation coefficient and apparent phase velocity dispersion remains intact.

Is the Kramers-Kronig causal relationship between ultrasonic attenuation and dispersion maintained when phase aberrations distort the field incident on a phase sensitive aperture?

The objective of this investigation was to determine whether the causality-induced link between ultrasonic attenuation and dispersion remains valid when the measured signal loss arises as a consequence of phase cancellation at the face of a phase-sensitive receiver rather than from intrinsic losses within the medium under study. The frequency-dependent apparent attenuation and phase velocity were obtained from through-transmission measurements of two flat and parallel plastic polymer plates, PlexiglasTM and LexanTM, exhibiting an approximately linear with frequency attenuation coefficient and logarithmic with frequency phase velocity. Phase distortion was achieved by machining a step into one side of each plastic plate. Through-transmission measurements were performed in a water tank using 5 MHz center frequency single element planar transmitting and receiving transducers. The causal (Kramers-Kronig) link between apparent phase velocity and the apparent attenuation coefficient in the presence of phase distortion was examined for both plastics over a bandwidth ranging from 3 to 7 MHz. Results demonstrate that the Kramers-Kronig link between the apparent attenuation coefficient and apparent phase velocity dispersion remains causally consistent even in the presence of aberrating media.