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Instrumentation
Published in Clive R. Bagshaw, Biomolecular Kinetics, 2017
For a volume change of 15 cm3 mol−1, a change in pressure of 150 bar would give about a 9% shift in the equilibrium constant. As with temperature jump, whether this shift is sufficient to give an observable signal depends on the value of the equilibrium constant (Figure 7.14). When the pressure is released, the system will relax back to its original value with a time course dependent on the rate constants of interconversion. This is the basis of the pressure-jump method.
The histotripsy spectrum: differences and similarities in techniques and instrumentation
Published in International Journal of Hyperthermia, 2023
Randall P. Williams, Julianna C. Simon, Vera A. Khokhlova, Oleg A. Sapozhnikov, Tatiana D. Khokhlova
As mentioned above, the main requirement for the focal waveform in boiling histotripsy is that the shock amplitude is sufficient for reaching 100 °C in under 10 ms; for most tissues this implies the shock amplitude being over 60 MPa, for frequencies higher than 1 MHz. Typically, boiling histotripsy exposures utilize the output power at or above the formation of fully developed shocks – when the focal peak positive pressure p+ equals shock amplitude [51]. The shock amplitude is defined in this case as a pressure jump within the steepest part of the acoustic waveform, between the time points where the time derivative of pressure decreases to a certain value, typically 2.5% of the maximum value [67]. With this definition, it has been shown that shock-wave heating predicted by the weak shock theory corresponds well to the heating calculated in direct numerical simulations [13,67]. Conversely p- is ideally kept low, to avoid the formation of incidental bubble clouds prefocally. Those bubbles may shield the focus and prevent the initiation of boiling, yet produce little to no mechanical disruption by themselves [17]. Due to their incidental nature, the threshold for prefocal bubble formation decreases with HIFU frequency.