Publications

The mechanical index (MI) quantifies the likelihood that exposure to diagnostic ultrasound will produce an adverse biological effect by a nonthermal mechanism. The current formulation of the MI is based on inertial cavitation thresholds in two liquids, water and blood, as calculated by a formalism assuming very short pulse durations. Although tissue contains a high proportion of water, it is not a liquid but a viscoelastic solid. Further, acoustic radiation force impulse imaging employs high-intensity pulses up to several hundred acoustic periods long. The effect of these differences was studied in water, blood and five representative tissues.

Interest in transcranial ultrasound has motivated numerous ultrasonic studies of the skull and brain; however, the ultrasonic properties of the scalp are relatively unknown. The goal of this study was to ultrasonically characterize the transmural structure of scalp tissue. Sixty-four formalin fixed specimens were prepared from four human donors and scanned in a water tank with a 25 MHz transducer to create parametric images of the speed of sound (SOS), frequency slope of attenuation (FSA), and integrated attenuation coefficient (IAC). Images revealed three distinct layers: a dermis/ epidermis layer, a subcutaneous layer, and a connective tissue layer. A statistically significant difference was observed between all layers for all parameters in most cases. Exceptions were between the dermis/epidermis layer and the subcutaneous layer for FSA and between the subcutaneous layer and the connective tissue layer for SOS.

The University of Mississippi provides a unique opportunity to study physical acoustics in two departments: the Department of Physics and Astronomy and the Department of Mechanical Engineering. It is one of the few universities in the United States where students can pursue PhD and MS degrees in Physics with a focus on physical acoustics research. The National Center of Physical Acoustics (NCPA) is an 85 000 square foot standalone facility that houses many laboratories on the campus of the University of Mississippi solely dedicated to the physics and engineering applications of acoustics over the entire frequency range, from infrasound to ultrasound. Students can study a wide range of topics including the atmosphere, ocean, weather, jet noise, porous media, acoustic metamaterials, ultrasonic properties of materials, nondestructive testing, and fluid dynamics. Our alumni work in academia, national labs, industry, and the medical field among other occupations. The University of Mississippi is a PhD granting institution with an R1 Carnegie designation placing it among schools with the highest level of research activity. It is located in Oxford, MS, a cultural mecca of the southern United States, home to William Faulkner (one of the most celebrated American authors), many artistic festivals and sporting events.

In this talk, I will present two perspectives of Rich Raspet; one from the point of view as a graduate student and the other from the point of view as a faculty colleague. As a PhD student in the University of Mississippi Physics program, he was my instructor in two courses and gave me advice whenever I requested it. Later, as a faculty member in the same department, I became Rich’s colleague where I continued to learn much from him. I will reflect on what it was like to know Rich in both modes and what I learned from him as a student and as a faculty colleague.