http://academic.oup.com/milmed/article-pdf/146/7/506/24126715/milmed-146-7-506.pdf

Goodman and Gilman's The Pharmacological Basis of Therapeutics

Elastic Moduli of Breast and Prostate Tissues under Compression

Shear wave elasticity imaging (SWEI) is a new approach to imaging and characterizing tissue structures based on the use of shear acoustic waves remotely induced by the radiation force of a focused ultrasonic beam. SWEI provides the physician with a virtual "finger" to probe the elasticity of the internal regions of the body. In SWEI, compared to other approaches in elasticity imaging, the induced strain in the tissue can be highly localized, because the remotely induced shear waves are attenuated fully within a very limited area of tissue in the vicinity of the focal point of a focused ultrasound beam. SWEI may add a new quality to conventional ultrasonic imaging or magnetic resonance imaging. Adding shear elasticity data ("palpation information") by superimposing color-coded elasticity data over ultrasonic or magnetic resonance images may enable better differentiation of tissues and further enhance diagnosis. This article presents a physical and mathematical basis of SWEI with some experimental results of pilot studies proving feasibility of this new ultrasonic technology. A theoretical model of shear oscillations in soft biological tissue remotely induced by the radiation force of focused ultrasound is described. Experimental studies based on optical and magnetic resonance imaging detection of these shear waves are presented. Recorded spatial and temporal profiles of propagating shear waves fully confirm the results of mathematical modeling. Finally, the safety of the SWEI method is discussed, and it is shown that typical ultrasonic exposure of SWEI is significantly below the threshold of damaging effects of focused ultrasound.

Shear wave elasticity imaging: a new ultrasonic technology of medical diagnostics

A detailed review of the literature on ultrasonic propagation properties of mammalian tissues and organs has revealed 144 papers containing compilable data. Over 1300 lines of parametric data are listed, including the tissue, species, age, specimen preparation, anatomical structure, pathology, temperature, measurement method, frequency, velocity, attenuation, acoustic impedance, and density.

Comprehensive compilation of empirical ultrasonic properties of mammalian tissues

The clinical viability of a method of acoustic remote palpation, capable of imaging local variations in the mechanical properties of soft tissue using acoustic radiation force impulse (ARFI) imaging, is investigated in vivo. In this method, focused ultrasound (US) is used to apply localized radiation force to small volumes of tissue (2 mm(3)) for short durations (less than 1 ms) and the resulting tissue displacements are mapped using ultrasonic correlation-based methods. The tissue displacements are inversely proportional to the stiffness of the tissue and, thus, a stiffer region of tissue exhibits smaller displacements than a more compliant region. Due to the short duration of the force application, this method provides information about the mechanical impulse response of the tissue, which reflects variations in tissue viscoelastic characteristics. In this paper, experimental results are presented demonstrating that displacements on the order of 10 microm can be generated and detected in soft tissues in vivo using a single transducer on a modified diagnostic US scanner. Differences in the magnitude of displacement and the transient response of tissue are correlated with tissue structures in matched B-mode images. The results comprise the first in vivo ARFI images, and support the clinical feasibility of a radiation force-based remote palpation imaging system.

Acoustic radiation force impulse imaging: in vivo demonstration of clinical feasibility.

The compilation of the literature on ultrasonic propagation properties of mammalian tissues [J. Acoust. Soc. Am. 64, 423 (1978)] is continued with the addition of 45 papers yielding over 700 lines of parametric data.

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Compilation of empirical ultrasonic properties of mammalian tissues. II

The ultrasonic absorption was determined, by the transient thermoelectric method, for brain, heart, kidney, liver, tendon, and testis from cat, mouse, pig and beef. Comparison of these absorption (α) values with published values of attenuation ( A ) shows: (1) that the α and A coefficients have nearly the same frequency dependencies in the range 0.5–7 MHz, (2) that the magnitudes of α and A differ appreciably and that difference depends upon the method of measurement and tissue type, and (3) that there appears to be little species difference, at least as revealed by measurement of liver and tendon.

/pdf/ultrasonic-absorption-and-attenuation-in-mammalian-tissues-ib7e1me94w.pdf

Ultrasonic absorption and attenuation in mammalian tissues

It is argued that the elastic properties of soft tissues are largely responsible for their echographic visualizability and that these are determined, for the most part, by structural collagen‐containing components.

/pdf/correlation-of-echographic-visualizability-of-tissue-with-625or7eo9p.pdf

Correlation of echographic visualizability of tissue with biological composition and physiological state

The nonlinearity parameter B/A has been determined for various biological solutions and soft tissues using the thermodynamic and finite amplitude methods. Agreement between the two methods is better than 10% for the tissues and 1% for the solutions. Fat has a B/A value around 11, the highest among soft tissues studied. Other soft tissues including liver, muscle, brain, and heart muscle have B/A values close to 7. Based on the observed linear relation between the B/A value and solute concentration in protein solutions, and also the lack of dependence of the B/A value on solute molecular weight in dextran solutions, it is postulated that the nonlinearity in these solutions is due to solute-solvent interactions. The general trend of increasing B/A value with specimen structural hierarchy suggests that the nonlinearity of biological materials is related to this feature. These observations suggest the use of the nonlinearity parameter B/A in tissue characterization, particularly since structural alteration often attends the pathological state.

Floyd Dunn

Papers

Comprehensive compilation of empirical ultrasonic properties of mammalian tissues

Compilation of empirical ultrasonic properties of mammalian tissues. II

Ultrasonic absorption and attenuation in mammalian tissues

Correlation of echographic visualizability of tissue with biological composition and physiological state

Determination of the nonlinearity parameter B/A of biological media