Cancer ablation by high intensity focused ultrasound
Law, Berlinda Siu Kwun
Date of Issue2017-05-11
School of Mechanical and Aerospace Engineering
High intensity focused ultrasound (HIFU) shows promising potential as a non-invasive treatment for medical conditions. HIFU depends on identical principle as traditional ultrasound and has advantages such as non-invasion, non-ionization and fewer problems arising after treatment. The main mechanisms of HIFU are thermal and mechanical effects. Initially, single frequency was used in HIFU ablation, however dual frequency has been proven to be more effective for surgical uses. In this study, various parameters were used for comparison of lesion formation between single and dual frequency excitations. After ablation for each of the parameters, all lesions were carefully handled and measured using ImageJ program to accurately determine the size of lesions in terms of their area, length, width and perimeter. Lesions were statistically calculated using Student’s t-test to determine if the size of lesions for dual frequency is significantly larger than that of single frequency in which a p value of lesser than 0.05 would be calculated. Using varying pulse repetition frequency (PRF), the area of lesions ablated by dual frequency was larger than the area of lesions ablated by single frequency. However, it was found that the area of lesions did not increase with increasing PRF for dual frequency. The area of lesions for PRF of 100 Hz for dual frequency was measured to be the lowest out of all the PRFs for dual frequency. This could be due to the presence of residual clouds seeding the subsequent bubble clouds which affected the area of lesions for PRF of 100 Hz. In terms of lesion size (length, width and perimeter), it followed an increasing trend of lesion size with increasing PRF. For varying duty cycle and ablation time, lesions were observed to be increasing as duty cycle level increase and the lesions produced by dual frequency were significantly larger than the single frequency’s lesions with a p value lesser than 0.05. Varied parameters (amplitude ratio, phase differences and frequency differences) for dual frequency were conducted. It was observed that increasing amplitude ratio resulted in an increase of lesion size while increasing frequency differences for dual frequency has led to a decrease in lesion size. Dual frequency with phase difference of π/2 yielded the largest lesion in terms of its size, followed by 0, π and 3π/2.
Final Year Project (FYP)
Nanyang Technological University