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These data provide the first in vivo demonstration of a site-specific ultrasonic contrast agent and have potential for improved sensitivity and specificity for noninvasive diagnosis of thrombi and other pathological diseases.

Kramers–Kronig relations linking the attenuation and dispersion are presented for a linear acoustic system. These expressions are used as a starting point to derive approximate, nearly local expressions relating the ultrasonic attenuation at a specific frequency to the local frequency derivative of the phase velocity (i.e., dispersion). The validity of these approximate relationships is demonstrated in several acoustic systems exhibiting substantially different physical properties.

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