Microbubble spectroscopy of ultrasound contrast agents

Abstract

Chair's Introduction-7:30 Invited Papers 7:355aAA1. Why we should design for optimum reverberation times in rooms for speech communication. J. S. Bradley ͑Inst. for Res. in Construction, Natl. Res. Council, Montreal Rd., Ottawa, Canada K1A 0R6͒Various texts list recommendations for optimum reverberation times as ideal goals in rooms for speech communication. However, some newer documents, such as ANSI S12.60, talk about maximum recommended reverberation times in rooms for speech communication. The source of the changed approach can be traced to interpretations of experimental results that do not consider the full implications for speech communication in real rooms, and also to the fact that reverberation time is not an ideal predictor of the quality of speech communication. In the extreme, minimizing reverberation times would lead to near anechoic rooms for speech and inadequate signal-to-noise ratios. The need for optimum reverberation times can be explained as a simple need to first achieve adequate signal-to-noise ratios. However, a more complete understanding is obtained by examining the benefits of early-arriving reflections of speech sounds on the intelligibility of the speech to listeners. Attempts to determine optimum reverberation times for normal hearing listeners, which are based on a balance between avoiding excessive reverberation and maintaining adequate signalto-noise ratios, lead to a range of acceptable values that can vary with the ambient noise level. This discussion will be supported with examples from room acoustics measurements in classrooms and meeting rooms. 7:555aAA2. The relation between speech transmission index, clarity, and reverberation time and listening difficulty in the impulse response database of AIJ. Hiroshi Sato ͑Natl. Inst. of Adv. Industrial Sci. and Technol. ͑AIST͒, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8566, Japan͒, Yoshio Nishikawa ͑Konoike Co., Ltd., Tsukuba 305-0003, Japan͒, Hayato Sato, and Masayuki Morimoto ͑Kobe Univ., Nada, Kobe 657-8501, Japan͒The Speech Communication Research Working Group of AIJ ͑Architectural Institute of Japan͒ is collecting information on rooms including digitized impulse responses ͑IRs͒ to establish a database for evaluating and designing the speech transmission quality of rooms. This database consists of 966 measured IRs. This study presents the relationships between speech transmission index ͑STI͒, clarity ͑Cx͒ and reverberation time ͑T͒ as measures to consider for the design and evaluation of the speech transmission performance of rooms. The data show a wide range of STI and Cx values for a given T, and the minimum STI at each reverberation time can be obtained by diffused field theory. STI and Cx are seen to be better indicators than T for the design of rooms for speech and that T is not as good. Relationships between STI, Cx, and listening difficulty ratings from previous studies ͓Proc. of RADS ͑2004͒, Proc. of Forum Acusticum, pp. 1713-1718 ͑2005͔͒ found both STI and Cx can be used as predictors of listening difficulty ratings. Finally, ...

Ultrasound contrast agents : dynamics of coated bubbles

“…A fit of the linearized shell model of Marmottant et al [12] then resulted in the shell elasticity and shell viscosity. In contrast to Chetty et al [40], Van der Meer et al [41] found that the shell elasticity was nearly constant while the shell viscosity decreases with decreasing dilatation rate Ṙ /R . One should note that all above experiments were performed at or in close proximity to a (capillary) wall.…”

“…The acoustic pressure was maintained below 40 kPa to ensure linear bubble dynamics. Van der Meer et al [41] indeed found an increase of the resonance frequency with respect to uncoated microbubbles.…”

“…To test the validity of the shell parameters for the very same bubble the bubble should be exposed to a set of frequencies and pressures. Van der Meer et al [41] insonified single UCA microbubbles (BR-14) consecutively with 11 ultrasound pulses, increasing the frequency for each pulse, near resonance. With this method named microbubble spectroscopy, the resonance curve was then obtained by plotting the amplitude of oscillation as a function of the applied frequency.…”

“…Van der Meer et al [41] scanned the insonation frequency at constant acoustic pressure to obtain resonance curves. The acoustic pressure was maintained below 40 kPa to ensure linear bubble dynamics.…”

Combined optical sizing and acoustical characterization of single freely-floating microbubbles

“…The measured resting radius (R meas ) of each microbubble was estimated from a selected in-focus image from an optical recording using an edge-tracking minimum cost algorithm. 24 This is a dynamic programing algorithm by first selecting a center point of a microbubble, which was then used to radially resample the bubble contour and its intensity profile until an optimal contour of the bubble was detected. The uncertainty of the optical size measurement combining the random and the systematic error was 0.1 lm based on an evaluation following Ref.…”