Use of high intensity focused ultrasound to destroy subcutaneous fat tissue

Thesis

Given the great promise of High Intensity Focused Ultrasound (HIFU) as a therapeutic modality, the aim of the present study is to develop and optimise a technique that uses externally applied focused ultrasound energy and remote, ultrasound-based treatment monitoring to destroy subcutaneous fat safely, effectively and non-invasively. Based on initial cavitation and temperature measurements performed ex vivo in excised porcine fat at four different frequencies (0.5, 1.1, 1.6 & 3.4MHz) over a range of pressure amplitudes and exposure durations, it was concluded that 0.5MHz is the optimal frequency for this application since it is capable of instigating inertial cavitation at relatively modest pressures while enhancing focal heat deposition. Histological assessment of tissue treated above the cavitation threshold at 0.5MHz both ex vivo and in vivo demonstrated damage to adipocytes and connective tissue. Furthermore, a good correlation was identified between the energy of broadband emissions detected by the passive cavitation detector (PCD) and the focal temperature rise at 0.5MHz during ex vivo experimentation, which could be exploited as a tool for non-invasive monitoring of successful treatment delivery. In addition, localisation of cavitation activity by means of passive cavitation detection was achieved and shown to provide a strong indicator of the location of induced histological damage. Based on the specific requirements identified during initial experimentation, an application-specific HIFU transducer, cavitation detector and real-time treatment monitoring software was developed and tested ex vivo. This treatment system was found capable of producing extensive damage to adipocytes and collagen confined to the subcutaneous fat layer at the desired treatment depth, which coincided with the location of cavitation activity as displayed by the real-time treatment monitoring software.

Authors: Kyriakou, Z

• Publication date: 2010
• DOI: 10.5287/ora-n18vdrgk5
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: subcutaneous fat tissue; high intensity focused ultrasound
• Subjects: Biomedical engineering