The Experts below are selected from a list of 5868 Experts worldwide ranked by ideXlab platform
Tomy Varghese - One of the best experts on this subject based on the ideXlab platform.
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signal to noise ratio comparisons for ultrasound Attenuation Slope estimation algorithms
Medical Physics, 2014Co-Authors: Eenas A Omari, Tomy VargheseAbstract:Purpose: Attenuation imaging has a promising role in the detection of tissue abnormalities. The authors have previously compared three different frequency domain ultrasound Attenuation estimation methods, for accuracy and bias. The mean estimated Attenuation value in a region of interest has been the determining factor of how well a method performs; however, the noise level has not been quantified for Attenuation estimated using different methods. Methods: The authors compare three different frequency domain ultrasound Attenuation estimation methods [the reference phantom method (RPM), the centroid downshift method (CEN), and the hybrid method (HYB)] using the signal to noise ratio (SNR) metric. Both simulated and experimental tissue-mimicking phantoms are used in the performance comparison study, evaluating the impact of the variation in acoustical properties. Results: For Attenuation estimation in a tissue-mimicking phantom with a known Attenuation coefficient of 0.5 dB/cm/MHz, all the three methods estimated the Attenuation coefficient to be ≈ 0.49 dB/cm/MHz for a transmit center frequency of 6 MHz, however, the signal to noise ratio obtained was found to be 8.5, 5.7, and 2.2 for the HYB, RPM, and CEN methods, respectively. These results demonstrate the need for the SNR metric in the comparison of different algorithms and to evaluate the impact of varying different ultrasound system and tissue parameters. Conclusions: In this paper, the authors demonstrate that although the estimated mean Attenuation value with a region of interest may be closely estimated using different methods, the signal to noise ratio obtained of the estimates can vary significantly. The centroid downshift method presented with the lowest signal-to-noise ratio of the methods compared. The hybrid method was the least susceptible to changes in the acoustical properties and provided unbiased Attenuation coefficient estimates with the highest signal-to-noise ratios.
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theoretical and phantom based investigation of the impact of sound speed and backscatter variations on Attenuation Slope estimation
Ultrasonics, 2011Co-Authors: Eenas A Omari, Heichang Lee, Tomy VargheseAbstract:Quantitative ultrasound features such as the Attenuation Slope, sound speed and scatterer size, have been utilized to evaluate pathological variations in soft tissues such as the liver and breast. However, the impact of variations in the sound speed and backscatter due to underlying fat content or fibrotic changes, on the Attenuation Slope has not been addressed. Both numerical and acoustically uniform tissue-mimicking experimental phantoms are used to demonstrate the impact of sound speed variations on Attenuation Slope using clinical real-time ultrasound scanners equipped with linear array transducers. Radiofrequency data at center frequencies of 4 and 5 MHz are acquired for the experimental and numerical phantoms respectively. Numerical phantom sound speeds between 1480 and 1600 m/s in increments of 20 m/s for Attenuation coefficients of 0.3, 0.4, 0.5, 0.6, and 0.7 dB/cm/MHz are simulated. Variations in the Attenuation Slope when the backscatter intensity of the sample is equal, 3 dB higher, and 3 dB lower than the reference is also evaluated. The sound speed for the experimental tissue-mimicking phantoms were 1500, 1540, 1560 and 1580 m/s respectively, with an Attenuation coefficient of 0.5 dB/cm/MHz. Radiofrequency data is processed using three different Attenuation estimation algorithms, i.e. the reference phantom, centroid downshift, and a hybrid method. In both numerical and experimental phantoms our results indicate a bias in Attenuation Slope estimates when the reference phantom sound speed is higher (overestimation) or lower (underestimation) than that of the sample. This bias is introduced via a small spectral shift in the normalized power spectra of the reference and sample with different sound speeds. The hybrid method provides the best estimation performance, especially for sample Attenuation coefficient values lower than that of the reference phantom. The performance of all the methods deteriorates when the Attenuation coefficient of the reference phantom is lower than that of the sample. In addition, the hybrid method is the least sensitive to sample backscatter intensity variations.
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hybrid spectral domain method for Attenuation Slope estimation
Ultrasound in Medicine and Biology, 2008Co-Authors: Hyungsuk Kim, Tomy VargheseAbstract:Attenuation estimation methods for medical ultrasound are important because Attenuation properties of soft tissue can be used to distinguish between benign and malignant tumors and to detect diffuse disease. The classical spectral shift method and the spectral difference method are the most commonly used methods for the estimation of the Attenuation; however, they both have specific limitations. Classical spectral shift approaches for estimating ultrasonic Attenuation are more sensitive to local spectral noise artifacts and have difficulty in compensating for diffraction effects because of beam focusing. Spectral difference approaches, on the other hand, fail to accurately estimate Attenuation coefficient values at tissue boundaries that also possess variations in the backscatter. In this paper, we propose a hybrid Attenuation estimation method that combines the advantages of the spectral difference and spectral shift methods to overcome their specific limitations. The proposed hybrid method initially uses the spectral difference approach to reduce the impact of system-dependent parameters including diffraction effects. The normalized power spectrum that includes variations because of backscatter changes is then filtered using a Gaussian filter centered at the transmit center frequency of the system. A spectral shift method, namely the spectral cross-correlation algorithm is then used to compute spectral shifts from these filtered power spectra to estimate the Attenuation coefficient. Ultrasound simulation results demonstrate that the estimation accuracy of the hybrid method is better than the centroid downshift method (spectral shift method), in uniformly attenuating regions. In addition, this method is also stable at boundaries with variations in the backscatter when compared with the reference phantom method (spectral difference method). Experimental results using tissue-mimicking phantom also illustrate that the hybrid method is more robust and provides accurate Attenuation estimates in both uniformly attenuating regions and across boundaries with backscatter variations. The proposed hybrid method preserves the advantages of both the spectral shift and spectral difference approaches while eliminating the disadvantages associated with each of these methods, thereby improving the accuracy and robustness of the Attenuation estimation.
M Appleberg - One of the best experts on this subject based on the ideXlab platform.
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preliminary results from Attenuation Slope mapping of plaque using intravascular ultrasound
Ultrasound in Medicine and Biology, 1994Co-Authors: L S Wilson, Michael Neale, H E Talhami, M ApplebergAbstract:Excised femoral and iliac artery segments have been examined with 20 MHz intravascular ultrasound followed by histological assessment. During the ultrasound examinations, radio-frequency (RF) data were recorded digitally, and used for calculating local values of Attenuation Slope throughout the tissue, using a frequency-domain technique. The RF data were also reconstructed as conventional ultrasound images, and the Attenuation-Slope information presented as a thresholded colour overlay. Areas identified as degenerative plaque in the histological assessments were usually found to correspond to areas of high Attenuation Slope, and were clearly identified from the pattern of colours on the combined image. Some examples are presented, illustrating the appearance of various pathologies imaged by this technique.
William D Obrien - One of the best experts on this subject based on the ideXlab platform.
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method for estimating total Attenuation from a spatial map of Attenuation Slope for quantitative ultrasound imaging
Ultrasonic Imaging, 2013Co-Authors: Alexander D Pawlicki, William D ObrienAbstract:Estimating total ultrasound Attenuation from backscatter data is essential in the field of quantitative ultrasound (QUS) because of the need to compensate for Attenuation when estimating the backscatter coefficient and QUS parameters. This work uses a reference phantom method of Attenuation estimation to create a spatial map of Attenuation Slope (AS) from backscatter radio-frequency (RF) data of three phantoms and a rat mammary adenocarcinoma tumor (MAT). The Attenuation maps show changes in Attenuation between different regions of the phantoms and the MAT tumor. Analyses of the Attenuation maps of the phantoms suggest that the AS estimates are in good quantitative agreement with the known values for the phantoms. Furthermore, estimates of total Attenuation from the Attenuation maps are likewise in good quantitative agreement with known values.
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algorithm for estimating the Attenuation Slope from backscattered ultrasonic signals
Internaltional Ultrasonics Symposium, 2009Co-Authors: Alexander Haak, Timothy J Hall, Zachary T Hafez, Janelle J Anderson, Mariateresa Herd, Kibo Nam, Ernest L Madsen, Timothy A Bigelow, William D ObrienAbstract:In vivo Attenuation Slope measurements usually utilize the backscattered signal from pulse/echo ultrasound. In this work the down shift of the center frequency of an emitted ultrasound pulse with penetration depth is utilized to estimate the Attenuation Slope. A diffraction correction of the focused ultrasound source is performed by measuring the reflection from a planar surface positioned throughout the depth of focus. A focused single element transducer with a measured center frequency of 8.2 MHz and a fractional band width of 72% was used to interrogate four tissue mimicking phantoms. The scatterers in the tissue mimicking phantoms were glass spheres embedded in a gelatin/milk matrix. In one set of the phantoms, the backscattering strength was varied; in the other set of phantoms the Attenuation Slope was varied. The Attenuation Slope (AS BS ) was estimated using pulse/echo data obtained by scanning the phantoms. The “true” Attenuation Slope (AS Thru ) was obtained from two independent insertion loss measurements performed at two different laboratories. The relative error of AS BS was investigated for different regions of interest (ROI) for all phantoms. Three different axial and lateral ROI sizes were tested. It was observed that the average relative error (average over all four phantoms) changed by less than three percent when the lateral size of the ROI was decreased by seventy percent. The axial size of the ROI was changed by thirty percent whereas the average error changed by less then three percent.
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in vivo ultrasonic Attenuation Slope estimates for detecting cervical ripening in rats preliminary results
Journal of the Acoustical Society of America, 2008Co-Authors: Timothy A Bigelow, William D Obrien, Barbara L Mcfarlin, Michael L OelzeAbstract:To effectively postpone preterm birth, cervical ripening needs to be detected and delayed. As the cervix ripens, the spacing between the collagen fibers increases and fills with water, hyaluronan, decorin, and enzymes suggesting that the ultrasonic Attenuation of the cervix should decrease. The decrease in ultrasonic Attenuation may be detectable, leading to an effective means of detecting cervical ripening. Herein, the traditional Attenuation Slope-estimation algorithm based on measuring the downshift in center frequency of the ultrasonic backscattered signal with propagation depth was modified and applied to the cervix of rats. The modified algorithm was verified using computer simulations and an ex vivo tissue sample before being evaluated in in vivo animal studies. Spherically-focused f/3 transducers with 33-MHz center frequencies and with 9-mm focal lengths were used in both the simulations and experiments. The accuracy was better than 15% in the simulations, and the Attenuation Slope of the cervix in the ex vivo experiment was 2.6+/-0.6 dB/cm-MHz, which is comparable to 2.5+/-0.4 dB/cm-MHz measured using a through-transmission insertion loss technique. For the in vivo experiments, a statistically significant effect of ultrasonic Attenuation with gestational age was not observed. The large variances in the in vivo results were most likely due to the natural variation in Attenuation for biological tissue between animals.
H Hatayama - One of the best experts on this subject based on the ideXlab platform.
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wide dynamic range and channel number free thulium doped fibre amplifiers utilizing variable Attenuation Slope compensators vascs
European Conference on Optical Communication, 2002Co-Authors: M Kakui, H Hatayama, T Shitomi, C Hirose, M ShigematsuAbstract:The mid-stage VASC scheme has successfully maintained the gain-profile of the TDFA within 0.2 dB under the operational conditions where the channel number is from 4 to 32 and the dynamic range is 8 dBp-p
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variable Attenuation Slope compensator vasc using silica based planar lightwave circuit technology for active gain Slope control in edfas
Optical Fiber Communication Conference, 2000Co-Authors: H Hatayama, Chisai Hirose, Koichi Koyama, N Akawsaka, M NishimuraAbstract:A novel planar lightwave circuit device called variable Attenuation Slope compensator (VASC) is proposed for active gain Slope control in EDFAs. Its Attenuation Slope is electrically controllable with the average Attenuation unchanged.
L S Wilson - One of the best experts on this subject based on the ideXlab platform.
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preliminary results from Attenuation Slope mapping of plaque using intravascular ultrasound
Ultrasound in Medicine and Biology, 1994Co-Authors: L S Wilson, Michael Neale, H E Talhami, M ApplebergAbstract:Excised femoral and iliac artery segments have been examined with 20 MHz intravascular ultrasound followed by histological assessment. During the ultrasound examinations, radio-frequency (RF) data were recorded digitally, and used for calculating local values of Attenuation Slope throughout the tissue, using a frequency-domain technique. The RF data were also reconstructed as conventional ultrasound images, and the Attenuation-Slope information presented as a thresholded colour overlay. Areas identified as degenerative plaque in the histological assessments were usually found to correspond to areas of high Attenuation Slope, and were clearly identified from the pattern of colours on the combined image. Some examples are presented, illustrating the appearance of various pathologies imaged by this technique.
