Physics News Update, Number 456

Number 456, November 9, 1999 by Phillip F. Schewe and Ben Stein

ULTRASOUND IMAGING WITHOUT PHYSICAL CONTACT between device and patient has been achieved, providing a potential solution to an unmet medical need--determining the depth and severity of serious burns in a convenient, accurate, and pain-free fashion. At the present time, physicians usually diagnose burns by inspecting them visually; however, such visual observation cannot provide direct information on whether there is damage to underlying blood vessels, a condition which requires surgery. Technologies such as conventional ultrasound or MRI are either too slow, time-consuming, or cumbersome. In addition, they are painful for the patient if they require direct contact with the burn area. This is certainly the case with conventional ultrasound, which requires direct contact with the body, or must at least be connected to the body via water. That's because generating ultrasound in a device and sending it through air causes a large proportion of the sound to bounce right back into the device. This results from a great mismatch between air and the device in the values of their "impedance," the product of the density of the substance and the velocity of sound through it. By more closely matching the impedance values between the device and air, a significantly greater proportion of sound can be transmitted to the body, and reflected back, to obtain enough of a signal for an image. In a non-contact ultrasound device described at last week's meeting of the Acoustical Society of America in Columbus, Joie Jones of UC-Irvine (949-824-6147, jpjones@uci.edu) and his colleagues pass the sound wave through a multilayered material, with each succeeding layer having an impedance value closer to that of air. The transmission is improved to the point that the researchers could image burns by holding their device about two inches away from the skin, in about a minute or so. Having tested this device on over 100 patients, the researchers plan to move to larger clinical studies and develop a device that can take images in real time.
See images at Physics News Graphics

THE OXYGEN RED PHASE gets its name from the fact that this form of solid oxygen comprised of oxygen-4 molecules is deeply red in color, and gets more red at higher pressures. The red phase has now been studied in detail by physicists in Italy and their results suggest that at pressures above 10 GPa two O₂ molecules combine into an O₄ molecule. The pressure is necessary for altering (by brute force) the chemical bonds at work inside this molecular solid. By recording the vibrational properties of oxygen solids at pressures up to 63 GPa, Roberto Bini (bini@chim.unifi.it, 011-39-055-230-7864) and his colleagues at the European Laboratory for Nonlinear Spectroscopy in Florence have concluded that the process whereby O2 molecules form into O4 units could be a kind of prelude to oxygen's transformation into longer chains (polymers) and then into a metal (superconducting oxygen was reported by Shimizu et al., in Nature, 25 June 1998), (Gorelli et al., Physical Review Letters, 15 November. Journalists can obtain the article at the Physics News Select Articles website)

IO SODIUM JET. Astronomers have previously known of a sodium cloud which precedes the moon Io in its orbit around Jupiter. The cloud is believed to arise from slow escape of sodium from Io. Now the Galileo spacecraft is providing details of another sodium feature at Io, more of a fast-escaping spray or jet, thought to come about when Io plows through Jupiter's potent magnetic field, a process which induces mega-amp currents through Io's atmosphere (see schematic at www.aip.org/png). New pictures, reported by scientists at the University of Colorado (Matthew Burger, burger@ganesh.colorado.edu, 303-492-3395, and Nicholas Schneider) and Boston University (Jody Wilson), localize the source of the sodium to a region smaller than Io's diameter, suggesting that Io's atmosphere might not be global; that is, the atmosphere might be patchy and not extend all the way to the poles. (Geophysical Research Letters, 15 November.)