Deep impact of superficial skin inking: acoustic analysis of underlying tissue

Abstract

Background: Skin tattoos are a common decoration, but profound scientific study whether the presence of a skin tattoo alters the acoustic response from superficial tissue, and therefore from underlying tissue, was previously lacking. Any image aberrations caused by tattoo presence may have been thought negligible, yet empirically found artifacts in brightness-mode images of tattooed skin suggest otherwise. This study investigated the nature of these artifacts theoretically and experimentally in extremely simplified cases of perfectly flat and homogenous layered media and in tattooed pork.Methods: Theory was derived for computing the acoustic response from horizontally and vertically layered media containing a thin inked layer. Experiments were performed in vitro. Artificial and pork skin were tattooed, attached to phantom material, and sonicated with a 13–6-MHz probe. The speed of sound of these materials was determined, and the perceived refraction angles was measured.Results: The measured speeds of sound of tattooed materials were higher than those of their uninked counterparts. The presence of tattoo ink was found to have increased the linear acoustic attenuation by 1 dB/cm. This value is negligible for typical tattoos of only few millimeters. The perceived critical refraction angles of adjacent materials could be detected, and their corresponding speeds of sound were quantified. These coincided with values derived from theory.Conclusion: The ratio of speeds of sound of adjacent materials was shown to create distinct highlights in brightness-mode images. The artifacts observed in in vitro and in vivo brightness-mode scans were explained from near-vertical transitions between areas of different sound speed. This is the first study correlating so-called critical refraction highlighting with speed-of-sound information. In addition, it was found that phantom material is a room-temperature acoustic alternative for experiments on live human skin. In summary, the presence of superficial tattoos has a small but quantifiable effect on the acoustic response from deeper tissues.

Rapid tablet swelling and disintegration during exposure to brightness-mode ultrasound

“…32) The sonication device was assumed to have converted two-way travel times to oneway perceived radial distances using the speed of sound in such phantom tissue. 31) The perceived distances to the tablet surface were extracted automatically from the backscattering profiles by identifying first peaks, which correspond to x-axis perceived distances, using a threshold grey value of 77. These perceived distances were represented by scatter plots as a function of time.…”

“…The speed of sound in the degassed tap water was determined from separate experiments without tablets. The instantaneous tablet thickness was computed using where is the speed of sound of the degassed tap water, is the speed of sound of phantom tissue used by the device to convert two-way time to perceived distance, 31) h(t) is the instantaneous tablet thickness as a function of time, is the fixed true distance from the probe face to the coin surface, and is the perceived distance from the probe to the tablet surface as a function of time. As an objective parameter to determine disintegration, we measured the surface displacement half-life as the time t…”

“…For sonication experiments, the sonography device was operating in two-dimensional musculoskeletal pulsed brightness mode with a mechanical index of 0.8. 31) For this imaging mode, the fixed pulse repetition frequency has been specified as 2.5 kHz. 32) Other fixed parameters that might influence disintegration, such as line density and frame rate, have not been quantified.…”

“…Subsequently, the absolute scatter amplitudes from the tablet and coin surfaces were determined in the lines extracted, as well as the perceived distances corresponding to these surfaces. 31) Tissue-mimicking phantoms had been used for the calibration of the ultrasound device. 32) The sonication device was assumed to have converted two-way travel times to one-way perceived radial distances using the speed of sound in such phantom tissue.…”