Spectral Log Research Articles

Influences of Variability in Attenuation Compensation on the Estimation of Backscatter Coefficient of Median Nerves in Vivo.

Peripheral nerves remain a challenging target for medical imaging, given their size, anatomical complexity, and structural heterogeneity. Quantitative ultrasound (QUS) applies a set of techniques to estimate tissue acoustic parameters independent of the imaging platform. Many useful medical and laboratory applications for QUS have been reported, but challenges remain for deployment in vivo, especially for heterogeneous tissues. Several phenomena introduce variability in attenuation estimates, which may influence the estimation of other QUS parameters. For example, estimating the backscatter coefficient (BSC) requires compensation for the attenuation of overlying tissues between the transducer and the underlying tissue of interest. The purpose of this study is to extend prior studies by investigating the efficacy of several analytical methods of estimating attenuation compensation on QUS outcomes in the human median nerve. Median nerves were imaged at the volar wrist in vivo and beam-formed radiofrequency (RF) data were acquired. Six analytical approaches for attenuation compensation were compared: 1-2) attenuation estimated by applying spectral difference method (SDM) and spectral log difference method (SLDM) independently to regions of interest (ROIs) overlying the nerve and to the nerve ROI itself; 3-4) attenuation estimation by applying SDM and SLDM to ROIs overlying the nerve, and transferring these properties to the nerve ROI; and 5-6) methods that apply previously published values of tissue attenuation to the measured thickness of each overlying tissue. Mean between-subject estimates of BSC-related outcomes as well as within-subject variability of these outcomes were compared among the 6 methods. Compensating for attenuation using SLDM and values from the literature reduced variability in BSC-based outcomes, compared to SDM. Variability in attenuation coefficients contributes substantially to variability in backscatter measurements. This work has implications for the application of QUS to in vivo diagnostic assessments in peripheral nerves and possibly other heterogeneous tissues.

Enhancing ultrasonic attenuation images through multi-frequency coupling with total nuclear variation.

Quantitative ultrasound is a non-invasive image modality that numerically characterizes tissues for medical diagnosis using acoustical parameters, such as the attenuation coefficient slope. A previous study introduced the total variation spectral log difference (TVSLD) method, which denoises spectral log ratios on a single-channel basis without inter-channel coupling. Therefore, this work proposes a multi-frequency joint framework by coupling information across frequency channels exploiting structural similarities among the spectral ratios to increase the quality of the attenuation images. A modification based on the total nuclear variation (TNV) was considered. Metrics were compared to the TVSLD method with simulated and experimental phantoms and two samples of fibroadenoma in vivo breast tissue. The TNV demonstrated superior performance, yielding enhanced attenuation coefficient slope maps with fewer artifacts at boundaries and a stable error. In terms of the contrast-to-noise ratio enhancement, the TNV approach obtained an average percentage improvement of 34% in simulation, 38% in the experimental phantom, and 89% in two in vivo breast tissue samples compared to TVSLD, showing potential to enhance visual clarity and depiction of attenuation images.

Improving attenuation imaging of the breast with the spectral log difference technique and full angular spatial compounding

Ultrasound tomography is an imaging technique for the breast that can create maps of the sound speed and acoustic attenuation simultaneously. By use of wave-based methods, images of speed of sound are of high quality, but the attenuation images are of inferior quality. The Spectral Log Difference (SLD) is a technique based on the ultrasonic backscatter that can provide estimates of the attenuation coefficient slope (ACS). However, SLD requires a large amount of data to provide a low variance of the estimate. This estimate variance can be reduced through compounding, which decreases spatial resolution of SLD images. Due to the nature of tomography, the tradeoff between estimate variance of SLD and spatial resolution can be reduced by using full angular spatial compounding. Using the data from a breast tomography scanner, the results demonstrated that the SLD technique with full angular spatial compounding could generate an accurate attenuation map with low bias and variance. As a result, SLD with full spatial angular compounding can provide improved attenuation images for breast diagnostics.

Spatially Variant Ultrasound Attenuation Mapping Using a Regularized Linear Least-Squares Approach

Quantitative ultrasound methods aim to estimate the acoustic properties of the underlying medium, such as the attenuation and backscatter coefficients, and have applications in various areas including tissue characterization. In practice, tissue heterogeneity makes the coefficient estimation challenging. In this work, we propose a computationally efficient algorithm to map spatial variations of the attenuation coefficient. Our proposed approach adopts a fast, linear least-squares strategy to fit the signal model to data from pulse-echo measurements. As opposed to existing approaches, we directly estimate the attenuation map, that is, the local attenuation coefficient at each axial location by solving a joint estimation problem. In particular, we impose a physical model that couples all these local estimates and combine it with a smooth regularization to obtain a smooth map. Compared to the conventional spectral log difference method and the more recent ALGEBRA approach, we demonstrate that the attenuation estimates obtained by our method are more accurate and better correlate with the ground-truth attenuation profiles over a wide range of spatial and contrast resolutions.

Comparison of two spectral-based techniques for estimating the attenuation coefficient from human cervix

This study uses in vivo radiofrequency ultrasound data acquired from human cervices to compare two commonly used spectral-based techniques for estimating the ultrasonic attenuation coefficient (AC): the spectral difference (SD) and the spectral log difference (SLD) techniques. The AC is a fundamental quantitative ultrasound (QUS) parameter useful for tissue characterization to improve diagnostics, e.g., cervix characterization to predict preterm birth. The selection of appropriate AC techniques is a critical step for QUS tissue characterization. The advantages and disadvantages of various AC estimation techniques have been studied using physical phantoms and computational simulations. However, the heterogeneous nature of real tissue cannot be fully simulated with phantoms and computations. In this study, the SD and SLD techniques were evaluated using human cervices from 214 pregnant women (enrollment still ongoing). Each participant underwent 1-2 cervical QUS exams during each visit. In each exam, 10 acquisitions of radiofrequency ultrasound and one acquisition of a physical phantom were made using a Siemens MC9-4 transvaginal ultrasound transducer (center frequency: 5.25 MHz) with a Siemens S2000 ultrasound system. Preliminary analysis yielded correlated AC estimates (Pearson’s r = 0.66; <0.001) between the two AC techniques and better precision (e.g., inter-sonographer reproducibility) with the SLD technique. [No. R01HD089935.]

Measurement and compensation of frequency-dependent attenuation in ultrasonic backscatter signal from cancellous bone

Ultrasonic backscatter has been gradually applied to the assessment and diagnosis of bone disease. The heavy frequency-dependent attenuation of ultrasound results in weak ultrasonic signals with poor signal-to-noise ratio and serious wave distortions during propagation in cancellous bone. Ultrasonic attenuation measured with the through-transmission method is an averaged result of ultrasonically interrogated tissues (including the soft tissue, cortical bone and cancellous bone). Therefore, the through-transmission measurements can not accurately provide ultrasonic attenuation of cancellous bone of interest. The purpose of this study is to estimate ultrasonic frequency-dependent attenuation with ultrasonic backscatter measurements and to compensate for the frequency-dependent attenuation in an ultrasonic backscatter signal from cancellous bone. <i>In-vitro</i> ultrasonic backscatter and through-transmission measurements are performed on 16 cancellous bone specimens by using 1.0-MHz transducers. Spatial scans are performed in a 10 mm × 10 mm scanned region with a spatial interval of 0.5 mm for each bone specimen. The frequency slope of ultrasonic attenuation is measured with the ultrasonic through-transmission signals serving as a standard value. Four different algorithms (the spectral shift method, the spectral difference method, the spectral log difference method, and the hybrid method) are used to estimate the frequency slope of ultrasonic attenuation coefficient from ultrasonic backscatter signal. The results show that the frequency-dependent attenuation coefficient ranges from 2.3 dB/mm/MHz to 6.2 dB/mm/MHz for the bovine bone specimens. The through-transmission measured frequency slope of ultrasonic attenuation coefficient is (4.14 ± 1.14) dB/mm/MHz (mean ± standard deviation), and frequency slopes of ultrasonic attenuation coefficient are estimated by four backscattering methods to be (3.88 ± 1.15) dB/mm/MHz, (4.00 ± 0.98) dB/mm/MHz, (3.77 ± 0.84) dB/mm/MHz, and (4.05 ± 0.85) dB/mm/MHz, respectively. The estimated frequency-dependent attenuation is significantly correlated with the standard attenuation value (<i>R</i> = 0.78－0.92, <i>p</i> < 0.01), in which the spectral difference method (<i>R</i> = 0.91, <i>p</i> < 0.01) and the hybrid method (<i>R</i> = 0.92, <i>p</i> < 0.01) are more accurate with an estimated error less than 20%. The results prove that it is feasible to measure the frequency-dependent attenuation from ultrasonic backscatter signal of cancellous bone. Based on Fourier transform-inverse Fourier transform, the frequency-dependent attenuation can be compensated.The compensated ultrasonic signals are with significantly improved signal intensity and improved signal-to-noise ratio. This study is conducive to the subsequent ultrasonic backscatter measurement and ultrasonic imaging of cancellous bone.

Comprehensive Interpretation of the Laboratory Experiments Results to Construct Model of the Polish Shale Gas Rocks

More than 70 rock samples from so-called sweet spots, i.e. the Ordovician Sa Formation and Silurian Ja Member of Pa Formation from the Baltic Basin (North Poland) were examined in the laboratory to determine bulk and grain density, total and effective/dynamic porosity, absolute permeability, pore diameters size, total surface area, and natural radioactivity. Results of the pyrolysis, i.e., TOC (Total Organic Carbon) together with S1 and S2 – parameters used to determine the hydrocarbon generation potential of rocks, were also considered. Elemental composition from chemical analyses and mineral composition from XRD measurements were also included. SCAL analysis, NMR experiments, Pressure Decay Permeability measurements together with water immersion porosimetry and adsorption/ desorption of nitrogen vapors method were carried out along with the comprehensive interpretation of the outcomes. Simple and multiple linear statistical regressions were used to recognize mutual relationships between parameters. Observed correlations and in some cases big dispersion of data and discrepancies in the property values obtained from different methods were the basis for building shale gas rock model for well logging interpretation. The model was verified by the result of the Monte Carlo modelling of spectral neutron-gamma log response in comparison with GEM log results.

On the development of a non-linear calibration relationship for the purpose of clay content estimation from the natural gamma ray log

The Shurijeh Formation of Early Cretaceous age is an important clastic sandstone reservoir rock in the Gonbadli field, NE Iran. The quantitative determination of Shurijeh clay minerals has been considered to be a very important and challenging task due to the heterogeneity of formation. The calibrated gamma ray log has been traditionally used as the primary estimator of volume of clay in the subsurface formations. The comparison between the core-measured values and the resulting estimates from the old calibration methods in Shurijeh Formation revealed that despite of applying old calibrations, the Shurijeh clay contents suffers from overestimations. Thus, the most accurate calibration for natural gamma ray log was developed, using the integration of quantitative mineralogical analyses from 76 core samples to estimate the volume of clay in Shurijeh Formation. The least percent relative error, i.e., 11.4%, was achieved in developing a new regression relationship in the form of a rational function acting as the most accurate non-linear clay indicator. The reliability of it was verified by the excellent correlation between the laboratory-measured clay contents in the core samples from another wells drilled in the mentioned Formation and the estimated values. The spectral log ratios have also been used to estimate the Formation depositional environment and different clay minerals types in it. It could truly be inferred that the Shurijeh was deposited in a marine environment with most of data having a thorium to uranium (Th/U) ratio in the range of 1–10. However, the indirect clay typing accomplished by several cross-plots, did not provide consistent results with the laboratory-determined types from the XRD test.

Regularized Spectral Log Difference Technique for Ultrasonic Attenuation Imaging.

The attenuation coefficient slope (ACS) has the potential to be used for tissue characterization and as a diagnostic ultrasound tool, hence complementing B-mode images. The ACS can be valuable for the estimation of other ultrasound parameters such as the backscatter coefficient. There is a well-known tradeoff between the precision of the estimated ACS values and the data block size used in the spectral-based techniques such as the spectral-log difference (SLD). This tradeoff limits the practical usefulness of the spectral-based attenuation imaging techniques. In this paper, the regularized SLD (RSLD) technique is presented in detail, and evaluated with simulations and experiments with physical phantoms, ex vivo and in vivo. The RSLD technique allowed decreasing estimation variance when using small data block sizes, i.e., fivefold reduction in the standard deviation of percentage error when using data block sizes larger than and more than a tenfold reduction when using data blocks. The precision improvement was obtained without sacrificing estimation accuracy (i.e., estimation bias improved in 70% of the cases by 10% of the ground truth-value on average while degraded in 30% of the cases by 3% of the ground truth-value on average). The improvements in precision allowed for better differentiation of inclusions especially when using small data blocks (i.e., smaller than ) where the contrast-to-noise ratio improved by an order of magnitude on average. The results suggest that the RSLD allows for the reconstruction of attenuation coefficient images with an improved tradeoff between spatial resolution and estimation precision.

Technogenic-tectonic earthquakes of the Dnieper–Donets aulacogen

The Mikhnevo Seismic Group of the Institute of Geosphere Dynamics, Russian Academy of Sciences (IGD RAS), and the Malin mini-group in the region of the Dnieper–Donets aulacogen, within which prospecting and mountain-explosion works were carried out from 2007 to 2015 on industrial scales, recorded a series of seismic events. Special attention has been focused on analysis of the nature of three earthquakes in 2015. Application of the spectral discrimination method log(Pg/Lg) and cross-correlation tools allowed us to identify the seismic events in 2015 as a special technogenic-tectonic type.

Evaluation of a frequency-domain ultrasonic imaging attenuation compensation technique.

Ultrasound attenuation is typically compensated for in clinical scanners by using time gain compensation (TGC). However, TGC operates in a frequency-independent fashion and therefore the spatial resolution of the echographic images degrades as the examination depth increases. In the current study, the capability of a multi-band attenuation compensation (MBAC) TGC technique to recover both magnitude and spatial resolution in lossy media was evaluated. Simulations were performed using a 5-MHz transducer for imaging point targets embedded in a medium with attenuation coefficient slope (ACS) of 0.5 dB/(cm.MHz). For performance assessment, the magnitude and spatial resolution of the reflected point spread functions (PSFs) were compared to the ones obtained from point targets embedded in a lossless medium. The results showed a complete recovery of the spectral content when using MBAC for all depths when compared to the lossless case. Both the magnitude and spatial resolution of the compensated PSFs were in agreement with the lossless result (i.e., less than 1 dB and 3 % difference in PSF magnitude and spatial resolution, respectively). The MBAC was then applied to in vivo liver imaging using a scanner equipped with a 5-MHz linear array. Attenuation compensation was performed using ACSs reported in the literature for skin, fat and muscle, and experimentally estimated ACS using the spectral log difference technique for the liver. The lateral and axial extent of the autocorrelation function was estimated in the liver tissue. The experimental MBAC image exhibited only 6 % and 11 % variation in speckle magnitude and lateral autocorrelation length for depths between 2.5 and 4 cm. These results suggest that MBAC technique may enhance speckle uniformity in homogeneous tissue regions.

Attenuation Coefficient Estimation of the Healthy Human Thyroid In Vivo

Previous studies have demonstrated that attenuation coefficients can be useful towards characterizing thyroid tissues. In this work, ultrasonic attenuation coefficients were estimated from healthy human thyroids in vivo using a clinical scanner. The selected subjects were five young, healthy volunteers (age: 26 ± 6 years old, gender: three females, two males) with no reported history of thyroid diseases, no palpable thyroid nodules, no smoking habits, and body mass index less than 30kg/m2. Echographic examinations were conducted by a trained sonographer using a SonixTouch system (Ultrasonix Medical Corporation, Richmond, BC) equipped with an L14-5 linear transducer array (nominal center frequency of 10MHz, transducer footprint of 3.8cm). Radiofrequency data corresponding to the collected echographic images in both transverse and longitudinal views were digitized at a sampling rate of 40MHz and processed with Matlab codes (MathWorks, Natick, MA) to estimate attenuation coefficients using the spectral log difference method. The estimation was performed using an analysis bandwidth spanning from 4.0 to 9.0MHz. The average value of the estimated ultrasonic attenuation coefficients was equal to 1.34 ± 0.15dB/(cm.MHz). The standard deviation of the estimated average attenuation coefficient across different volunteers suggests a non-negligible inter-subject variability in the ultrasonic attenuation coefficient of the human thyroid.

Audio bandwidth extension based on temporal smoothing cepstral coefficients

In this paper, we propose a wideband (WB) to super-wideband audio bandwidth extension (BWE) method based on temporal smoothing cepstral coefficients (TSCC). A temporal relationship of audio signals is included into feature extraction in the bandwidth extension frontend to make the temporal evolution of the extended spectra smoother. In the bandwidth extension scheme, a Gammatone auditory filter bank is used to decompose the audio signal, and the energy of each frequency band is long-term smoothed using minima controlled recursive averaging (MCRA) in order to suppress transient components. The resulting ‘steady-state’ spectrum is processed by frequency weighting, and the temporal smoothing cepstral coefficients are obtained by means of the power-law loudness function and cepstral normalization. The extracted temporal smoothing cepstral coefficients are fed into a Gaussian mixture model (GMM)-based Bayesian estimator to estimate the high-frequency (HF) spectral envelope, while the fine structure is restored by spectral translation. Evaluation results show that the temporal smoothing cepstral coefficients exploit the temporal relationship of audio signals and provide higher mutual information between the low- and high-frequency parameters, without increasing the dimension of input vectors in the frontend of bandwidth extension systems. In addition, the proposed bandwidth extension method is applied into the G.729.1 wideband codec and outperforms the Mel frequency cepstral coefficient (MFCC)-based method in terms of log spectral distortion (LSD), cosh measure, and differential log spectral distortion. Further, the proposed method improves the smoothness of the reconstructed spectrum over time and also gains a good performance in the subjective listening tests.

Cervical attenuation as a measure of preterm delivery: impact of different region of interest sizes.

One to five transvaginal ultrasound scans were taken of 63 women to estimate the microstructural changes in cervix using ultrasonic attenuation. Spectral log difference algorithm showed a clear decrease in attenuation as the time to delivery comes closer. The decrease in attenuation occurs earlier in preterm birth compared to full term birth which can be used as a predictor for preterm birth. Attenuation estimate did not improve as the ROI size increased.

A theoretical comparison of attenuation measurement techniques from backscattered ultrasound echoes

Accurate characterization of tissue pathologies using ultrasonic attenuation is strongly dependent on the accuracy of the algorithm that is used to obtain the attenuation coefficient estimates. In this paper, computer simulations were used to compare the accuracy and the precision of the three methods that are commonly used to estimate the local ultrasonic attenuation within a region of interest (ROI) in tissue; namely, the spectral log difference method, the spectral difference method, and the hybrid method. The effects of the inhomgeneities within the ROI on the accuracy of the three algorithms were studied, and the optimal ROI size (the number of independent echoes laterally and the number of pulse lengths axially) was quantified for each method. The three algorithms were tested for when the ROI was homogeneous, the ROI had variations in scatterer number density, and the ROI had variations in effective scatterer size. The results showed that when the ROI was homogeneous, the spectral difference method had the highest accuracy and precision followed by the spectral log difference method and the hybrid method, respectively. Also, when the scatterer number density varied, the spectral difference method completely failed, while the log difference method and hybrid method still gave good results. Lastly, when the scatterer size varied, all of the methods failed.

Lithofacies characterization of fluvial sandstones from outcrop gamma-ray logs (Loranca Basin, Spain): the influence of provenance

Natural gamma spectral (NGS) log motifs and cluster analysis were used to characterize outcropping sandstone bodies formed in braided and high-sinuosity streams of the Tertiary Tórtola fluvial system of the Loranca Basin (Spain). Five coarse-grained lithofacies comprise these deposits and determine distinct NGS log motif. Cross-plots and cluster analysis of NGS log data of the lithofacies suggest three distinct clusters. These clusters reflect distinct values for sandstones with small sets of ripple lamination, cross-stratification, and conglomerates and pebbles. Ripple-laminated sandstones show the most variability in NGS signature, whereas conglomeratic sandstones show the most uniform signature. Such cluster analysis may be used to assign NGS log data points of unknown origin to a specific fluvial lithofacies under conditions of equal rock provenance and diagenetic history. A sedimentaclastic (i.e. sedimentary parent rock) origin of sediments appears to be the main control on detrital composition that, in turn, varies with grain size.

Spectral shape analysis for contaminant logging at the Hanford site

A spectral shape factor log has been developed to provide information on the spatial distribution of gamma-ray-emitting contaminants detected by passive logging of boreholes that surround the buried high-level nuclear waste tanks at the U.S. Department of Energy's Hanford Site near Richland, Washington. Many boreholes intersect plumes of contaminants that leaked from the tanks. Spectral shape analysis has been able to distinguish /sup 137/Cs and /sup 60/Co uniformly distributed in the formation from borehole-localized and radially remote distributions of these contaminants. A uniform distribution is evidence for a formation-migration plume while a borehole-localized contaminant distribution indicates that the borehole was a preferential pathway for contaminant migration. Knowledge of the contaminant distribution assists the process of formation contamination assessment and of estimation of remediation costs. In a few cases, the shape factor log has identified the bremsstrahlung-producing contaminant /sup 90/Sr//sup 90/Y. Shape factor data processing and interpretation methods were optimized using results of Monte Carlo simulations of the logging measurements. The accuracy of the Monte Carlo simulations was confirmed through experiments with known source distributions.

Use of Gamma-Ray Spectral Log to Recognize Exposure Surfaces and Associated Water Tables in a Midcontinent Carbonate Sequence, Kansas: ABSTRACT

Use of Gamma-Ray Spectral Log to Recognize Exposure Surfaces and Associated Water Tables in a Midcontinent Carbonate Sequence, Kansas: ABSTRACT

MULTIPARAMETER GEOPHYSICAL LOGGING AT THE YAVA LEAD DEPOSIT: A STATISTICAL APPROACH1

The present study describes multiparameter geophysical logging carried out at the Yava sandstone lead deposit, Nova Scotia, Canada. Statistical analysis of the multiparameter data set shows that the spectral gamma-gamma ratio log (SGG ratio) is the most useful technique for characterizing the disseminated sulphide mineralization. Principal component analysis (PCA) indicates that the apparent chargeability (IP parameter) responds to the presence of clay minerals in the sandstone in addition to disseminated sulphides, so that the induced polarization method (IP) does not accurately delineate the disseminated galena content as was originally assumed in the preliminary log interpretation. PCA has also confirmed that the SGG ratio and density are related to lead content and that lithological variations can be delineated with natural radioactivity and resistivity. The zinc content of the deposit was poorly characterized by geophysical logs. Sphalerite occurrences seem to be localized as narrow bands (< 1 cm) which were not geophysically detectable.

A New Approach to Lithologic and Sedimentary Structure Analysis from Well Logs

A new method is presented which visually integrates lithologic and sedimentary structure data from well logs. Lithology is classified using a new technique based on formation mineralogy determined from spectral well logs. Geologic interpreta­ tion is enhanced by combining the lithologic results with sedimentary structure analysis from wellbore images. This meth­ od has been used successfully in studies of Gulf Coast fluvio-deltaic deposits to map lithofacies and depositional facies changes, for correlation between wells and for interpretation of reservoir quality. Rock classification is achieved by determining mineral concentrations from spectral and other log responses, using mineral-suite models applicable to the region. Rock classification is based on the widely used scheme of Pettijohn el a\. (1982) (arenite-graywacke-mudstone). Percent fine-grained matrix in the rock is the principal classification variable in their scheme, and is assumed to be a function of percent total clay volume. This approach to classification has the added advantage in petroleum exploration of emphasizing rocks of high reservoir quality. Sedimentary structures interpreted from high resolution wellbore images are summarized independently of the litholog­ ic analysis. Sedimentary structure analysis yields information on such practical factors as bedding thickness, directional permeability, and petroleum reservoir potential. When combined with the lithologic data, distribution of the sedimentary structures significantly enhances construction of reservoir models. While great detail is available from lithologic and sedimentary feature analysis, studies undertaken in the Gulf Coast indicate that a broader overview of lithologic and sedimentary features leads to a better synthesis of these data. Offshore and onshore Gulf Coast examples are shown which illustrate the method and its results.