Ex Vivo HIFU Experiments Using a $32 \times 32$ -Element CMUT Array.

Area of Science:

• Biomedical Engineering
• Ultrasound Technology
• Medical Devices

Background:

• High-intensity focused ultrasound (HIFU) offers noninvasive therapeutic treatment for various diseases.
• Capacitive micromachined ultrasonic transducers (CMUTs) present advantages over traditional piezoelectric transducers for HIFU applications.
• Developing advanced transducer arrays is crucial for enhancing HIFU efficacy and precision.

Purpose of the Study:

• To design and fabricate a 32x32-element 2D CMUT array for HIFU applications.
• To investigate a novel element grouping strategy to simplify system complexity for addressing 1024 transducer elements.
• To evaluate the performance of the CMUT array in generating therapeutic ultrasound pressures and creating lesions in biological tissues.

Main Methods:

• Fabrication of an 8x8 mm^2, 32x32-element 2D CMUT array.
• Implementation of an element grouping scheme into eight HIFU channels based on phase delay for simplified addressing.
• Utilizing a custom application-specific integrated circuit (ASIC) for channel control.
• Characterization of transducer performance, including surface pressure and focal pressure measurements.
• Ex vivo tissue experiments to demonstrate lesion creation capabilities.

Main Results:

• The CMUT array was designed to focus at an 8-mm depth with a 5-MHz excitation frequency.
• A surface pressure of 1.2 MPa (peak-to-peak) was achieved with 40-V DC bias and 60-V peak-to-peak AC excitation.
• The focal peak-to-peak output pressure reached 8.5 MPa, sufficient for lesion generation within a minute based on thermal simulations.
• Successful ex vivo lesion creation was demonstrated in bovine muscle and liver tissue.

Conclusions:

• The developed 32x32-element 2D CMUT array is suitable for HIFU therapeutic applications.
• The proposed element grouping strategy effectively reduces system complexity for addressing a large number of elements.
• The CMUT array demonstrates significant potential for noninvasive tissue ablation and lesion generation.