Review of Quantitative Ultrasound: Envelope Statistics and Backscatter Coefficient Imaging and Contributions to Diagnostic Ultrasound

Abstract

Conventional medical imaging technologies, including ultrasound, have continued to improve over the years. For example, in oncology, medical imaging is characterized by high sensitivity, i.e., the ability to detect anomalous tissue features, but the ability to classify these tissue features from images often lacks specificity. As a result, a large number of biopsies of tissues with suspicious image findings are performed each year with a vast majority of these biopsies resulting in a negative finding. To improve specificity of cancer imaging, quantitative imaging techniques can play an important role. Conventional ultrasound B-mode imaging is mainly qualitative in nature. However, quantitative ultrasound (QUS) imaging can provide specific numbers related to tissue features that can increase the specificity of image findings leading to improvements in diagnostic ultrasound. QUS imaging techniques can encompass a wide variety of techniques including spectral-based parameterization, elastography, shear wave imaging, flow estimation and envelope statistics. Currently, spectral-based parameterization and envelope statistics are not available on most conventional clinical ultrasound machines. However, in recent years QUS techniques involving spectral-based parameterization and envelope statistics have demonstrated success in many applications, providing additional diagnostic capabilities. Spectral-based techniques include the estimation of the backscatter coefficient, estimation of attenuation, and estimation of scatterer properties such as the correlation length associated with an effective scatterer diameter and the effective acoustic concentration of scatterers. Envelope statistics include the estimation of the number density of scatterers and quantification of coherent to incoherent signals produced from the tissue. Challenges for clinical application include correctly accounting for attenuation effects and transmission losses and implementation of QUS on clinical devices. Successful clinical and pre-clinical applications demonstrating the ability of QUS to improve medical diagnostics include characterization of the myocardium during the cardiac cycle, cancer detection, classification of solid tumors and lymph nodes, detection and quantification of fatty liver disease, and monitoring and assessment of therapy.

Real-time envelope detection of ultrasound radiofrequency signals using OpenCV GPU framework

“…Envelope detection of ultrasound backscattered signals is an essential step in many ultrasonic applications, such as envelope statistics based tissue characterization [4][5][6][7][8][9][10]. Real-time envelope detection is desired for fast analysis of ultrasound RF signals.…”

“…Constructed from the amplitude of ultrasound echo signals, ultrasound B-mode images suffer from the drawbacks as being qualitative and operator-dependent [1]. To complement B-mode imaging, quantitative ultrasound (QUS) explores frequency, phase, or statistical information of backscattered ultrasound signals for tissue characterization [3][4][5][6][7][8][9][10]. In the context of QUS, parameters including backscatter coefficient, acoustic attenuation, speed of sound, envelope statistics, scatterer properties, and tissue elasticity can be quantified for tissue characterization [4,11,12].…”

“…Envelope statistics are directly related to tissue microstructures and are able to characterize structural alterations in tissues that are not apparent on ultrasound B-mode images [4][5][6][7][8][9][10]. Thus, they are useful for quantitative description of pathological state of tissues.…”

“…Thus, they are useful for quantitative description of pathological state of tissues. Envelope detection of ultrasound RF data is essential for envelope statistics analysis [4][5][6][7][8][9][10]. In order to ensure real-time backscattered envelope analysis, the time efficiency of the envelope detection algorithm is demanded.…”

Temperature Monitoring during Focused Ultrasound Treatment by Means of the Homodyned K Distribution

“…This model describes the statistics of backscattered echo with three parameters and is considered to be highly effective in scattering properties characterization [15]. The homodyned K distribution was reported to be useful for tissue characterization [16], especially in the case of breast lesion classification [17,18]. Parameters of the homodyned K distribution describe different aspects of the acoustic scattering, namely the mean intensity of backscattered echo, number of scatterers per resolution cell and their spatial organization.…”