![Nonlinear Derating of High Intensity Therapeutic Ultrasound Beams using Decomposition of Gaussian Mode için kapak resmi Nonlinear Derating of High Intensity Therapeutic Ultrasound Beams using Decomposition of Gaussian Mode için kapak resmi](/client/assets/d79c3e4af2b6d196/ctx/images/no_image.png)
Nonlinear Derating of High Intensity Therapeutic Ultrasound Beams using Decomposition of Gaussian Mode
Başlık:
Nonlinear Derating of High Intensity Therapeutic Ultrasound Beams using Decomposition of Gaussian Mode
Yazar:
Dibaji, Seyed Ahmad Reza, author.
ISBN:
9780438093621
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (127 pages)
Genel Not:
Source: Dissertation Abstracts International, Volume: 79-10(E), Section: B.
Committee members: Rupak Banerjee, Ph.D P.E.; Michael Kazmierczak, Ph.D.; Jay Kim, Ph.D.; Matthew R. Myers, Ph.D.; Sang Young Son, Ph.D.
Özet:
Techniques for predicting high intensity focused ultrasound (HIFU) pressure fields in tissue using measured pressures in water are called derating techniques. These techniques are valuable for characterizing the HIFU systems prior to use in animals or humans. One common technique, called linear derating, assumes linear wave propagation in both water and tissue and involves reducing the measured pressures in water by the tissue attenuation to account for the losses in tissue. However, neglecting nonlinear propagation effects in the derating process can cause significant errors.
This dissertation presents a nonlinear derating technique to estimate HIFU nonlinear pressure fields and temperature rise in tissue using pressure measurements made in water. The method is based on an evolution equation in tissue which is derived assuming a Gaussian functional dependence for each harmonic in the radial direction. The nonlinear term in the evolution equation is modeled using modal amplitudes measured in water and suitably reduced using a combination of source derating (lower acoustic source pressure in water than in tissue) and endpoint derating (reduction in amplitudes at the target location). The resulting linear ordinary differential equations are solved to obtain an estimate of the tissue modal amplitudes.
Numerical validation of the derating technique is performed using the computed acoustic pressure measurements in water for transducers with Gaussian and uniform shadings. The simulated modal amplitudes in water for the three different transducer gains of 20, 40 and 60 are used in the nonlinear derating algorithm to estimate the focal acoustic pressures in tissue. In addition, the derated modal amplitudes for the transducers with uniform shadings are used in the Green function solution of the bioheat equation to predict the HIFU induced focal temperature rise in tissue. The estimated acoustic pressures and temperature rises by the derating technique are compared with the direct computations in tissue. The numerical computations shows that, with proper combination of source derating and endpoint derating, direct computations of acoustic pressure and temperature rise in tissue can be reproduced by derating with less than 10% error for each applied gain.
Experimental validation of the derating technique is performed by measuring the acoustic pressures in water by hydrophones. A HIFU transducer, operated at fundamental and third harmonic modes, is used to produce the pressure fields. The recorded axial pressures in water are Fourier transformed and the resulted modal amplitudes are used in the nonlinear derating algorithm to estimate the focal acoustic pressures and temperature rises in a tissue phantom. The derated acoustic pressures are compared with direct measurements in the tissue phantom by hydrophones. In addition, the derated temperature rises are compared with direct measurements in a tissue phantom embedded with eight thin wire thermocouples. The derated focal pressures are within 20% agreement with direct measurements in tissue phantom at both fundamental and third harmonic operational frequencies. The agreement between the focal temperature rises by derating and direct measurement in tissue phantom is about 20% at the fundamental frequency, while it is about 72% at the third harmonic operational frequency.
Notlar:
School code: 0045
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Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
---|---|---|---|
XX(687108.1) | 687108-1001 | Proquest E-Tez Koleksiyonu | Arıyor... |
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