Abstract
PurposeIn this study, the robustness and feasibility of a noise elimination method using continuous wave response of therapeutic ultrasound signals were investigated when tissue samples were moved to simulate the respiration-induced movements of the different organs during actual high-intensity focused ultrasound (HIFU) treatment. In addition to that, the failure conditions of the proposed algorithm were also investigated.MethodsThe proposed method was applied to cases where tissue samples were moved along both the lateral and axial directions of the HIFU transducer to simulate respiration-induced motions during HIFU treatment, and the noise reduction level was investigated. In this experiment, the speed of movement was increased from 10 to 40 mm/s to simulate the actual movement of the tissue during HIFU exposure, with the intensity and driving frequency of HIFU set to 1.0–5.0 kW/cm2 and 1.67 MHz, respectively. To investigate the failure conditions of the proposed algorithm, the proposed method was applied with the HIFU focus located at the boundary between the phantom and water to easily cause cavitation bubbles. The intensity of HIFU was set to 10 kW/cm2.ResultsAlmost all HIFU noise was constantly able to be eliminated using the proposed method when the phantom was moved along the lateral and axial directions during HIFU exposure. The noise reduction level (PRL in this study) at an intensity of 1.0, 3.0, and 5.0 kW/cm2 was in the range of 28–32, 38–40, and 42–45 dB, respectively. On the other hand, HIFU noise was not basically eliminated during HIFU exposure after applying the proposed method in the case of cavitation generation at the HIFU focus.ConclusionsThe proposed method can be applicable even if homogeneous tissues or organs move axially or laterally to the direction of HIFU exposure because of breathing. A condition under which the proposed algorithm failed was when instantaneous tissue changes such as cavitation bubble generation occurred in the tissue, at which time the reflected continuous wave response became less steady.
Highlights
High-intensity focused ultrasound (HIFU) treatment is one of the less invasive surgeries for treating cancer, where ultrasound is generated and focused outside the body and induces a temperature rise at the target tissue [1,2,3,4,5]
In a previous study [11, 12], a noise elimination method using the continuous wave (CW) response of HIFU was proposed and applied to static cases where the target tissue sample was not moved. Another suggested noise reduction method for HIFU treatment using the notch filter or pulse inversion exposure was applied to cases without respiration, which induced repetitive movement of the body and organs such as liver, kidney, and pancreas in actual surgery
These results show that HIFU noise was not basically eliminated during HIFU exposure, and the difference between the noiseeliminated and reference RF signals (B-mode images) became large
Summary
High-intensity focused ultrasound (HIFU) treatment is one of the less invasive surgeries for treating cancer, where ultrasound is generated and focused outside the body and induces a temperature rise at the target tissue [1,2,3,4,5]. In a previous study [11, 12], a noise elimination method using the continuous wave (CW) response of HIFU was proposed and applied to static cases where the target tissue sample was not moved. Another suggested noise reduction method for HIFU treatment using the notch filter or pulse inversion exposure was applied to cases without respiration, which induced repetitive movement of the body and organs such as liver, kidney, and pancreas in actual surgery. The failure conditions of the proposed algorithm were investigated
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