Basic concept and clinical applications of quantitative ultrasound (QUS) technologies

Abstract

In the field of clinical ultrasound, the full digitalization of diagnostic equipment in the 2000s enabled the technological development of quantitative ultrasound (QUS), followed by multiple diagnostic technologies that have been put into practical use in recent years. In QUS, tissue characteristics are quantified and parameters are calculated by analyzing the radiofrequency (RF) echo signals returning to the transducer. However, the physical properties (and pathological level structure) of the biological tissues responsible for the imaging features and QUS parameters have not been sufficiently verified as there are various conditions for observing living tissue with ultrasound and inevitable discrepancies between theoretical and actual measurements. A major issue of QUS in clinical application is that the evaluation results depend on the acquisition conditions of the RF echo signal as the source of the image information, and also vary according to the model of the diagnostic device. In this paper, typical examples of QUS techniques for evaluating attenuation, speed of sound, amplitude envelope characteristics, and backscatter coefficient in living tissues are introduced. Exemplary basic research and clinical applications related to these technologies, and initiatives currently being undertaken to establish the QUS method as a true tissue characterization technology, are also discussed.

Quantification of limitations in statistical analysis of ultrasound echo envelope amplitudes

“…Echo envelope statistics have been widely studied to evaluate the characteristics of scatterer distribution. 1,2) In the most common approaches for statistics-based tissue characterization, the probability density function of the echo envelope amplitudes is fitted by a model function, and the scatterer distribution characteristics are quantified by model parameters. Various model functions have been used to quantify scatterer distribution characteristics, such as Rayleigh, [3][4][5] Nakagami, [6][7][8] K, 9,10) homodyned-K, [11][12][13][14] multi-Rayleigh, [15][16][17][18] and double-Nakagami [19][20][21][22] models.…”

Appropriate indicator of modeling error for threshold-based model selection in statistics-based ultrasound tissue characterization

“…Analysis of the envelope statistics of ultrasound echo signals is effective for quantitative tissue characterization. 1,2) The most common approach for this analysis is to model a probability density function (PDF) of ultrasound echo envelope amplitudes and evaluate tissue characteristics based on the estimated model parameters.…”

Multimodality quantitative ultrasound envelope statistics imaging based support vector machines for characterizing tissue scatterer distribution patterns: Methods and application in detecting microwave-induced thermal lesions

“…Quantitative ultrasound (QUS) is a frontier ultrasound technology that can measure quantified information related to tissue microstructures [1] , [2] , [3] , [4] , [5] . Characterization of tissue microstructures is important because when a tissue undergoes a pathological change or therapy, a microstructural alteration may occur.…”

“…In the context of QUS, tissue microstructures can be characterized by extracting quantitative parameters connected with acoustic scatterers from ultrasound backscattered signals, as opposed to the commonly used B-mode ultrasound which is qualitative. The QUS parameters frequently used in ultrasound tissue characterization include backscatter coefficient [1] , [2] , [4] , [6] , acoustic attenuation [1] , [2] , [4] , speed of sound [4] , [5] , envelope statistics [1] , [2] , [3] , [4] , [6] , [7] , [8] , [9] , [10] , [11] , Lizzi–Feleppa spectral parameters [1] , [2] , [12] , [13] , [14] , mean scatterer spacing [15] , [16] , [17] , scatterer number densities [18] , [19] , and scatterer sizes [7] , [20] , [21] .…”