Effective Attenuation Coefficient Research Articles

A new formulation of polymer gel dosimeter with reduced toxicity: Dosimetric characteristics and radiological properties

The present study aimed to produce a new, less toxic, and cost-effective polymer gel dosimeter using potassium salt of 2-acrylamido-2 methyl-propane sulfonic acid (AMPS) monomer. The new formulation was called PAKAG. The irradiation of PAKAG polymer gel dosimeter was performed using a 6 MV clinical linear accelerator, and its response was evaluated using magnetic resonance imaging. The obtained images were post-processed to produce related R2 maps. Afterward, the Dose–R2 calibration curves were obtained. Response dependence on the imaging temperature was examined. Furthermore, response stability over time was investigated. To investigate the radiological characteristics, the elemental composition, effective atomic number, electron density, and photon attenuation coefficient of PAKAG polymer gel dosimeter were calculated. A maximum sensitivity of 0.152±0.007 with the goodness of fit of R2=0.999 in a dynamic range of 0–6Gy at 12h post-irradiation time was found. Such as other polymer gel dosimeter, the response of PAKAG polymer gel dosimeter was dependent on post-irradiation time and imaging temperature. Finally, it was concluded that the PAKAG polymer gel dosimeter could be used as a less toxic and cost-effective polymer gel dosimeter.

Comparison of Dosimetry Characteristics from Some Bolus Materials for 6 and 10 MV Photons Beam Radiation Therapy

In radiation therapy, bolus material is often used for increased surface dose, compensate for surface irregularities and internal heterogeneities. Bolus has properties equivalent to water and soft tissue. In this study, the mixture of Silicone Rubber (SR) and Bismuth was used for bolus fabrication and then compared to commercial boluses such as Paraffin, Play-Doh, and Paraffin Wax. The study aims to evaluate the comparison of relative electron density (RED), effective mass attenuation coefficient, transmission factor, percentage of surface dose (PSD), and Percentage Depth Dose (PDD) for all boluses. The bolus was made with the size 11 × 11 × 0.5 cm3. Physical density of the synthesized bolus was assessed by computerized tomography (CT) Scanning. The results of the RED analysis for the mixture of Silicone Rubber (SR) and Bismuth, Paraffin, Play-Doh, and Paraffin Wax were 0.954; 0.743; 0.933; and 0.878, respectively. The values of RED for all boluses has a similar to water and soft tissue. These results prove that the bolus is equivalent to soft tissue density such as fat, breast, lungs, and liver. Furthermore, for other dosimetry tests such as transmission factors and attenuation coefficients using Linear Accelerator (LINAC) with photon energy sources 6 and 10 MV. In general, Percentage of surface dose at 6 MV is higher than 10 MV. The highest percentage of the surface dose was achieved by paraffin wax at 6 MV energy by 85%. For effective mass attenuation coefficient result, the highest is the mixture of silicone rubber and bismuth at -0.0030 cm2/g for 6 MV and Play-Doh at -0.0114 cm2/g for 10 MV.

Investigations of effective attenuation coefficients (EACs) of multi-layered polymers using Monte Carlo method

In the present study, a Monte Carlo model has been developed to compute the EACs of some multi-layered materials, especially polymers for the first time. Different mono-energetic gamma rays with energy range between 59.5 and 1332.5 keV were considered to accomplish this goal. A comparison was made between the simulation results and those derived from a theoretical formula based on available measured attenuation coefficients and data taken from the XCOM program. A highly agreement was achieved. This study shows an improvement over Al-Arif an Kakil’s work, in the sense that the modified model is appropriate enough to estimate the EACs within ±1.5%. It was indicated that changing the order of the materials did not vary the results significantly. The results showed that the proposed model can be used to determine radiation properties of multi-layer polymers in cases where no analogous experimental data exist or it is expensive to test.

The Nonlinear Effective Attenuation Coefficient of Spaceborne Oceanic Lidar Signal

Multiple scattering is an inevitable effect in spaceborne oceanic lidar because of the large footprint size and the high optical density of seawater. The effective attenuation coefficient klidar in oceanic lidar equation, which indicates the influence of the multiple scattering effect on the formation of lidar returns, is an important parameter in the retrieval of inherent optical properties (IOPs) of seawater. In this paper, the nonlinearity of klidar and the relationships between klidar and the IOPs of seawater are investigated by solving the radiative transfer equation with an improved semianalytic Monte Carlo model. klidar is found to decrease exponentially with the increase of depth in homogeneous waters. klidar is given as an exponential function of depth and IOPs of seawater. The results in this paper can help to have a better understanding of the multiple scattering effect of spaceborne lidar and improve the retrieval accuracy of the IOPs of seawater using spaceborne lidar.

Ultraviolet light (365 nm) transmission properties of articular cartilage as a function of depth, extracellular matrix, and swelling.

Current tissue engineering approaches for treatment of injured or diseased articular cartilage use ultraviolet light (UV) for in situ photopolymerization of biomaterials to fill chondral and osteochondral defects as well as resurfacing, stiffening and bonding the extracellular matrix and tissue interfaces. The most commonly used UV light wavelength is UVA 365 nm, the least cytotoxic and deepest penetrating. However, little information is available on the transmission of UVA 365 nm light through the cartilage matrix. In the present study, 365 nm UV light transmission was measured as a function of depth through 100 μm thick slices of healthy articular cartilage removed from mature bovine knees. Transmission properties were measured in normal (Native) cartilage and after swelling equilibration in phosphate-buffered saline (Swollen). Single-factor and multiple linear regression analyses were performed to determine depth-dependencies between the effective attenuation coefficients and proteoglycan, collagen and water contents. For both cartilages, a significant depth-dependency was found for the effective attenuation coefficients, being highest at the articular surface (superficial zone) and decreasing with depth. The effective attenuation coefficients for full-thickness cartilages were approximately a third lower than the total attenuation coefficients calculated from the individual slices. Analysis of absorption and scattering effects due to the ECM and chondrocytes found that UV light scatter coefficients were ∼10 times greater than absorption coefficients. The greater transmittance of UV light through the thicker cartilage was attributed to the collagen within the ECM causing significant backscatter forward reflectance.

Quantitative techniques for extraction of blood oxygenation from multispectral optoacoustic measurements

We report on the comparison of two approaches to the reconstruction of oxygen saturation (StO2) within blood vessels from multispectral optoacoustic (OA) measurements. The spatially-resolving approach is based on determination of the optical absorption coefficient µa from OA signal amplitudes, while the calibration-free approach is based on evaluation of the effective optical attenuation coefficient µeff derived from the in-depth OA signal decay. Both approaches were verified in phantom experiments as well as in in vitro and in vivo measurements. The results demonstrate good agreement of µa spectra derived from OA signal amplitudes with the published data indicating this approach to be preferable for the in vivo determination of StO2. Reconstruction of µa spectra from the in vivo measured OA signal amplitudes in a rat yields StO2 values of 0.57 ± 0.08 and 0.50 ± 0.07 for two veins of the thoracic spine. We demonstrate that for cost-effective measurements a dual-probing wavelength scheme can be employed instead of multiple wavelength probing. We found that the probing wavelength of 700 nm combined with a wavelength from the range of 850–1069 nm provides reconstructed StO2 values close to the reference ones derived from multiple wavelength measurements in the entire range of 658‒1069 nm.

Differential pathlength factor in continuous wave functional near-infrared spectroscopy: reducing hemoglobin's cross talk in high-density recordings.

Functional near-infrared spectroscopy (fNIRS) estimates the functional oscillations of oxyhemoglobin and deoxyhemoglobin in the cortex through scalp-located multiwavelength recordings. Hemoglobin oscillations are inferred through temporal changes in continuous-wave (CW) light attenuation. However, because of the diffusive multilayered head tissue structures, the photon path is longer than the source-detector separation, complicating hemoglobin evaluation. This aspect is incorporated in the modified Beer-Lambert law where the source-detector distance is multiplied by the differential pathlength factor (DPF). Since DPF estimation requires photons' time-of-flight information, DPF is assumed a priori in CW-fNIRS. Importantly, errors in the DPF spectrum induce hemoglobin cross talk, which is detrimental for fNIRS. We propose to estimate subject-specific DPF spectral dependence relying on multidistance high-density measurements. The procedure estimates the effective attenuation coefficient (EAC), which is proportional to the geometric mean of absorption and reduced scattering. Since DPF depends on the scattering-to-absorption ratio, EAC limits the spectral dependence assumption to scattering. This approach was compared to a standard frequency-domain multidistance procedure. A good association between the two methods ( ) was obtained. This approach could estimate low-resolution maps of the DPF spectral dependence through large field of view, high-density systems, reducing hemoglobin cross talk, and increasing fNIRS sensitivity and specificity to brain activity without instrumentation modification.

The Optical Effective Attenuation Coefficient as an Informative Measure of Brain Health in Aging.

Aging is accompanied by widespread changes in brain tissue. Here, we hypothesized that head tissue opacity to near-infrared light provides information about the health status of the brain’s cortical mantle. In diffusive media such as the head, opacity is quantified through the Effective Attenuation Coefficient (EAC), which is proportional to the geometric mean of the absorption and reduced scattering coefficients. EAC is estimated by the slope of the relationship between source–detector distance and the logarithm of the amount of light reaching the detector (optical density). We obtained EAC maps across the head in 47 adults (age range 18–75 years), using a high-density dual-wavelength optical system. We correlated regional and global EAC measures with demographic, neuropsychological, structural and functional brain data. Results indicated that EAC values averaged across wavelengths were strongly associated with age-related changes in cortical thickness, as well as functional and neuropsychological measures. This is likely because the EAC largely depends on the thickness of the sub-arachnoid cerebrospinal fluid layer, which increases with cortical atrophy. In addition, differences in EAC values between wavelengths were correlated with tissue oxygenation and cardiorespiratory fitness, indicating that information about cortical health can be derived non-invasively by quantifying the EAC.

Dosimetry analysis of homemade bolus using propylene glycol for photon MegaVoltage and electron radiation therapy

Bolus is widely used to protect and reduce irradiation in organ at risk in the process of radiotherapy. Generally, the bolus was made from polymer material due to had property is similar or equivalent to tissue. This study aimed to determine the density, transmission factor, effective mass attenuation coefficient on bolus with radiation of photons and electrons. The bolus material (B) was used Propylene Glycol (PG), Silicon Rubber (SR) and Aluminium Powder (Al), and had four types of bolus namely B - PG 24%, B - PG 24%; SR 8%, B - PG 24%; SR 8%; Al 0,5%, and B - PG 24%; SR 8%; Al 1,5% with dimensions of 11 × 11 cm and thickness of 1 and 1.5 cm. The bolus density is evaluated through the mass of each volume. The measured data revealed that all of the boluses have density values which are similar to tissue or water and air in the range from 0,864 - 1,202 g/cm3. For dosimetry testing, the bolus is irradiated using Linear Accelerator with 6 and 10 MV for photon source and 6 and 12 MeV for an electron source. The results showed that B - PG 24%; SR 8%; Al 1.5% for dosimetry testing both 6 and 10 MV photons obtained properties that resemble soft tissue. Meanwhile, for both dosimetry testing of 12 MeV electrons, the B - PG 24%; SR 8% with addition silicone rubber and aluminum have nature closest to soft tissue. All of the boluses that have been fabricated have properties similar to soft tissue for photon therapy whereas the addition of more aluminum making a bolus has features as a shield on the process of radiotherapy.

Comparative analysis of the transmission properties of tissue equivalent materials

Phantom objects have as main requirement to have the effective atomic number and linear attenuation coefficient approximately equal to the human tissue to be simulated. The present work aims to characterize samples of materials radiologically equivalent to water for dose studies in patients in the diagnostic energy range. Water was chosen as reference material representing human tissue, which is composed mostly of it. A set of samples was formulated and submitted to radiation transmission tests in four different values of tension applied to an X-ray tube. Mass densities of the samples were evaluated using the Arquimedes method. The samples were identified as A, B, C and D. By transmission curves, it was possible to estimate the samples transmission factors corresponding to the water transmission factor for different thicknesses. Moreover, the thicknesses of samples equivalent to water thickness for different values of transmission factor were also evaluated. All the samples densities were bigger than the density of water. For the same thickness of water and the samples, the radiation transmission of the developed materials are in better agreement for thicknesses of 10 mm and 30 mm. The lowest percentage difference between the water transmission and the transmission of any of the samples obtained was approximately 0.6% for the sample A in the thickness of 30 mm under voltage of 60 kV. The correspondence between the transmission factors and the thicknesses showed that the compounds studied in this work are potential materials to develop phantoms that simulate the transmission properties of human tissue.

An Investigation on Effective Atomic Numbers and Mass Attenuation Coefficients of Some Bioactive Glasses

A bioactive material is known as a natural or man-made material that prompts a specific biological response from the body such as bonding to tissue. They have numerous applications in the repair and reconstruction of diseased and damaged tissue, and tissue and hard tissue (bone) re-engineering. In this study, we have evaluated the same gamma-ray shielding parameters such as mass attenuation coefficient (μ/ρ), effective atomic number (Z eff ), half value layer (HVL), mean free path (MFP) for selected bioactive glasses. The shielding effectiveness of the selected glasses is found comparable each other. Effective atomic number (Z eff ) is convenient parameters used to characterize the radiation response of a multi-element material in the technical and industrial applications, radiation shielding design, absorbed dose. Thus, it is very significant to choose accurate method to determine this parameter unambiguously. In the present study, effective atomic number of different type of material has been calculated by using calculation method for total photon interaction in the energy region of 1 keV to 100 GeV. The results obtained from this study show that effective atomic number depends strongly on the chemical composition of the interaction material in the lower as well as higher energy region, but in the intermediate energy region, the chemical composition dependence becomes very weak. This result can be interpreted that an increase in P 2 O 5 content in the composition of bioactive glasses results as an in increase of bioactivity of that particular materials. Therefore, this study underlines the finding that bioactive glasses would be potential biomaterials for biomedical applications.

VALIDATION OF A BEAMNRC MONTE CARLO SIMULATION OF A BROAD BEAM DIAGNOSTIC X-RAY UNIT.

A BEAMnrc Monte Carlo simulation of a diagnostic X-ray unit in a broad beam geometry intended for the derivation of effective linear attenuation coefficients was validated against measurements made on the X-ray unit on which the simulation was based. The validation process assessed the size of the beam, the first and second half value layer, the variation in kerma with anode-heel effect and the accuracy of values of effective linear attenuation coefficient for water and solid water attenuators. The agreement between the simulated and measured results for all tests was consistently within the experimental uncertainty for the measurements. The average deviation between values of effective linear attenuation coefficient for simulated and measured results is 3.8%, with the highest individual deviation 7.1%. The simulation can be used to produce values of effective linear attenuation coefficient for a range of kVp, field size and attenuator thickness that are close to those measured.

Passive seismic measurement of seismic attenuation in Delaware Basin

Local earthquake activity can be employed to measure attenuation (the effective quality factor [Q]) and characterize production in the Delaware Basin, Texas, USA. To illustrate this, we employed data from the recently installed Texas Seismic Network (TexNet) seismic stations collected in the west Texas area between April 2017 and March 2018. Earthquake activity in the Delaware Basin has increased in comparison to the previous 20 years, which has resulted in numerous high-quality events suitable for this analysis. The high signal-to-noise ratio events were used to estimate effective Q factors using the peak frequency method on the sediments of the Delaware Basin. The effective attenuation of the sedimentary basin is 90 for P-waves and 140 for S-waves (both with uncertainty of approximately 30), indicating an unusually low attenuation (high Q) for S-waves relative to the P-waves. This is consistent with attenuation of a saturated sedimentary basin because the saturation results in less attenuation of S-waves. Additionally, we observe an increase of the effective Q factor with distance between the station and events consistent with rays sampling the deeper, less-attenuating, and less-saturated portions of the basin and even basement. Inverted effective attenuation coefficients were used to calculate moment magnitudes, which were consistent with those seen in the TexNet array.

Correction of beam hardening in X-ray radiograms.

The intensity of a monochromatic X-ray beam decreases exponentially with the distance it has traveled inside a material; this behavior is commonly referred to as Beer-Lambert's law. Knowledge of the material-specific attenuation coefficient μ allows us to determine the thickness of a sample from the intensity decrease the beam has experienced. However, classical X-ray tubes emit a polychromatic bremsstrahlung-spectrum. And the attenuation coefficients of all materials depend on the photon energy: photons with high energy are attenuated less than photons with low energy. In consequence, the X-ray spectrum changes while traveling through the medium; due to the relative increase in high energy photons, this effect is called beam hardening. For this varying spectrum, the Beer-Lambert law only remains valid if μ is replaced by an effective attenuation coefficient μeff which depends not only on the material but also on its thickness x and the details of the X-ray setup used. We present here a way to deduce μeff(x) from a small number of auxiliary measurements using a phenomenological model. This model can then be used to determine an unknown material thickness or in the case of a granular media its volume fraction.

Measurement of coherent surface acoustic wave attenuation in polycrystalline aluminum

Attenuation of Rayleigh-type surface acoustic waves induced by grain-boundary scattering is studied experimentally and theoretically by an effective medium approach. A frequency domain opto-acoustic laboratory setup, capable of measuring a coherent Rayleigh wave response by emulating an ensemble average via spatial averaging, is presented. Measurements are conducted on polycrystalline aluminum at ultrasonic frequencies from 10 MHz to 130 MHz. A constant effective phase velocity of 2893 m s−1 is found below 80 MHz. The effective attenuation coefficient varies in the whole frequency range by nearly two orders of magnitude, and shows classical scattering behavior, comprising stochastic and geometric scattering regimes. A semi-analytical attenuation model is presented, valid below the geometric limit. The model incorporates the material’s spatial two-point correlation function obtained from metallurgical micrographs. Comparisons to experimentally obtained attenuation coefficients show good quantitative agreement, with differences in the frequency power-law dependence. This study attempts to elucidate microstructure induced surface acoustic wave attenuation experimentally by means of a statistical approach. The proposed method and the obtained findings contribute to the understanding of wave propagation in heterogeneous media, and promote the use of surface acoustic waves in non-destructive microstructure characterization.

Relationship between the effective attenuation coefficient of spaceborne lidar signal and the IOPs of seawater.

Multiple scattering is an inevitable effect in spaceborne oceanic lidar because of the large footprint size and the high optical density of seawater. The effective attenuation coefficient klidar in the oceanic lidar equation, which indicates the influence of the multiple scattering effect on the formation of lidar returns, is an important parameter in the retrieval of inherent optical properties (IOPs) of seawater. In this paper, the relationships between klidar of the spaceborne lidar signal and the IOPs of seawater are investigated by solving the radiative transfer equation with an improved semianalytic Monte Carlo model. Apart from the geometric loss factors, klidar is found to decrease exponentially with the increase of depth in homogeneous waters. klidar is given as an exponential function of depth and IOPs of seawater. The mean percentage errors between klidar calculated by the exponential function and the simulated ones in three typical stratified waters are within 0.5%, proving the effectiveness and applicability of this klidar-IOPs function. The results in this paper can help researchers have a better understanding of the multiple scattering effect of spaceborne lidar and improve the retrieval accuracy of the IOPs and the chlorophyll concentration of case 1 water from spaceborne lidar measurements.

Semi-analytic Monte Carlo radiative transfer model of laser propagation in inhomogeneous sea water within subsurface plankton layer

Current Monte Carlo simulation methods of laser propagation in sea water are mostly based on the assumption of homogeneous water. In this study, a semi-analytic Monte Carlo radiative transfer model is developed to study laser propagation in inhomogeneous sea water within subsurface plankton layer. It is based on analytical estimate of the probability of collection by a remote receiver of scattered or emitted photons; in particular, the water optical input parameter of vertical profile is no longer simply set as a constant. In the new transfer model, the input optical vertical profile can vary with a resolution as high as 0.11 m. Using this model, we study the influences of water optical properties, multiple scattering, wind-driven sea surface condition, and lidar incident angle. The effective lidar attenuation coefficient is found to depend on the field of view of the lidar system: it approaches attenuation coefficient with a narrow field of view, and approaches absorption coefficient with a wide-enough field of view. We also find the lidar transmittance through the air-sea interface decreases significantly as the wind speed increases to greater than 7 m/s, and the transmittance can even be reduced by half when the wind speed reaches 18 m/s. Finally, we compare the simulations by our new model with airborne lidar measurements. We find that the simulation curve is quite similar to that of the lidar measurements. The absolute error of normalized simulation signals compared with the measurements is within 0.05, suggesting the effectiveness and applicability of our approach for inhomogeneous water.

Parametrization of the Propagation of Elastic Waves in a Medium with Ensembles of Disc-Shaped Inclusions

We propose a method for the determination of effective (mean) velocities and attenuation coefficients of elastic waves in a medium with two ensembles of distributed disc-shaped compliant and low-contrast inclusions. The inclusions are characterized by both their own ensemble volume concentrations and ordered (or random) space orientations. The realization of this method is connected with the application of the Foldy dispersion relation with the use of the solutions of problems of scattering of elastic waved by local inhomogeneities. We also perform the numerical analysis of the influence of volume concentrations of various types of inclusions and the wave number on the effective velocity of elastic longitudinal waves.

Density scaling of phantom materials for a 3D dose verification system.

In this study, the optimum density scaling factors of phantom materials for a commercially available three‐dimensional (3D) dose verification system (Delta4) were investigated in order to improve the accuracy of the calculated dose distributions in the phantom materials. At field sizes of 10 × 10 and 5 × 5 cm2 with the same geometry, tissue‐phantom ratios (TPRs) in water, polymethyl methacrylate (PMMA), and Plastic Water Diagnostic Therapy (PWDT) were measured, and TPRs in various density scaling factors of water were calculated by Monte Carlo simulation, Adaptive Convolve (AdC, Pinnacle3), Collapsed Cone Convolution (CCC, RayStation), and AcurosXB (AXB, Eclipse). Effective linear attenuation coefficients (μ eff) were obtained from the TPRs. The ratios of μ eff in phantom and water ((μ eff)pl,water) were compared between the measurements and calculations. For each phantom material, the density scaling factor proposed in this study (DSF) was set to be the value providing a match between the calculated and measured (μ eff)pl,water. The optimum density scaling factor was verified through the comparison of the dose distributions measured by Delta4 and calculated with three different density scaling factors: the nominal physical density (PD), nominal relative electron density (ED), and DSF. Three plans were used for the verifications: a static field of 10 × 10 cm2 and two intensity modulated radiation therapy (IMRT) treatment plans. DSF were determined to be 1.13 for PMMA and 0.98 for PWDT. DSF for PMMA showed good agreement for AdC and CCC with 6 MV x ray, and AdC for 10 MV x ray. DSF for PWDT showed good agreement regardless of the dose calculation algorithms and x‐ray energy. DSF can be considered one of the references for the density scaling factor of Delta4 phantom materials and may help improve the accuracy of the IMRT dose verification using Delta4.

Elastic wave dispersion and attenuation caused by multiple types of disc-shaped inclusions

PurposeThe purpose of this paper is to numerically investigate time-harmonic elastic wave propagation with the analysis of effective wave velocities and attenuation coefficients in a three-dimensional elastic composite consisting of infinite matrix and uniformly distributed soft, low-contrast and absolutely rigid disc-shaped micro-inclusions.Design/methodology/approachWithin the assumptions of longitudinal mode of a propagating wave as well as dilute concentration and parallel orientation of inclusions in an infinite elastic matrix, Foldy’s dispersion relation is applied for introducing a complex and frequency-dependent wavenumber of homogenized structure. Then, the effective wave velocities and attenuation coefficients are directly defined from the real and imaginary parts of wavenumber, respectively. Included there a far-field forward scattering amplitude by a single low-contrast inclusion given in an analytical form, while for the other types of single scatterers it is determined from the numerical solution of boundary integral equations relative to the displacement jumps across the surfaces of soft inclusion and the stress jumps across the surfaces of rigid inclusion.FindingsOn the frequency dependencies, characteristic extremes of the effective wave velocities and attenuation coefficients are revealed and analyzed for different combinations of the filling ratios of involved types of inclusions. Anisotropic dynamic behavior of composite is demonstrated by the consideration of wave propagation in perpendicular and tangential directions relatively to the plane of inclusions. Specific frequencies are revealed for the first case of wave propagation, at which inclusion rigidities do not affect the effective wave parameters.Originality/valueThis paper develops a micromechanical study that provides a deeper understanding of the effect of thin-walled inclusions of diversified rigidities on elastic wave propagation in a three-dimensional composite. Described wave dispersion and attenuation regularities are important for the non-destructive testing of composite materials by ultrasonics.