Active control of simply supported cylindrical shells using the weighted sum of spatial gradients control metric.

It is often desired to reduce sound radiated from cylindrical shells. Active structural acoustic control (ASAC) provides a means of controlling the structural vibration in a manner to efficiently reduce the radiated sound. Previous work has often required a large number of error sensors to reduce the radiated sound power, and the control performance has been sensitive to the location of error sensors. The ultimate objective is to provide global sound power reduction using a minimal number of local error measurements, while also minimizing any dependence on error sensor locations. Recently, a control metric referred to as weighted sum of spatial gradients (WSSG) was developed for ASAC. Specific features associated with WSSG make this method robust under a variety of conditions. In this work, the WSSG control metric is extended to curved structures, specifically a simply supported cylindrical shell. It is shown that global attenuation of the radiated sound power is possible using only one local error measurement. It is shown that the WSSG control metric provides a solution approximating the optimal solution of attenuating the radiated sound power, with minimal dependence on the error sensor location. Numerical and experimental results are presented to demonstrate the effectiveness of the method.

A Fully Electronically Steerable Therapeutic Ultrasound Phased Array With MR-Guidance.

Recently, MRI-guided focused ultrasound (FUS) has shown great promise in treating various conditions non-invasively. OBJECTIVE: The focus of this article is to introduce an MRI-guided FUS device, which can provide full electronic steering range without mechanical movement and with low near-field heating. A pilot study was conducted in order to investigate the feasibility, and safety of the device in a large animal model and a pilot clinical trial. METHODS: A flat, fully steerable FUS phased array with 4096 elements was designed and manufactured to be compatible with an MR scanner. Pre-clinical experiments were carried out for testing the accuracy of the focus at different steering angles as well as evaluating the ablation efficiency using MR thermometry. Eleven patients with uterine fibroids were treated in the pilot clinical trial. RESULTS: Pre-clinical results showed successful ablation at various steering angles with reasonable targeting accuracy and no off-target heating. During the pilot clinical study, effective fibroid ablation was achieved with significant symptom reduction observed over time. In general, the treatment results showed the system to be effective in ablating deep tissue volumes. The device was successful at efficiently ablating large volumes with minimal near-field heating and eliminating the need for mechanical translation. CONCLUSIONS: Being capable of providing high acoustic power, full electronic steering range in 3D for large volume ablations, this device can provide a safe and efficient treatment option as an outpatient procedure for uterine fibroids and other pelvic and abdominal tumors.

Thermal Therapy With a Fully Electronically Steerable HIFU Phased Array Using Ultrasound Guidance and Local Harmonic Motion Monitoring.

The method of localized harmonic motion (LHM) monitoring has been proposed as an ultrasound-based monitoring technique for in vivo real-time ultrasound-guidance during thermal surgery. OBJECTIVE: The focus of this paper is to study the performance of LHM monitoring in vivo in order to assess the tissue coagulation during ultrasound surgery of bone metastases. This is done through a pre-clinical study on large scale animals (pigs) as well as a first-in-human pilot study, using a hand held ultrasound-guided HIFU phased array. METHODS: A flat, fully steerable HIFU phased array system (1024 elements, 100 mm diameter, 516 kHz), in combination with a co-aligned 64 element imaging system, is used to perform thermal surgery and monitor tissue coagulation using the LHM technique. The in vivo experiments are conducted using thirteen animals, followed by a first-in-human pilot study in which nine patients are enrolled. RESULTS: The pre-clinical results show that the LHM monitoring method is able to detect about 80% of the observed coagulated tissue volumes visible in dissection. In the pilot study, six out of nine patients have durable pain reduction with good correlation observed from LHM detections. CONCLUSION: In general, the results suggest that the LHM monitoring performance is promising in detecting thermal tissue coagulation during focused ultrasound surgery in tissues close to the bone. SIGNIFICANCE: The LHM technique can offer a very accessible and cost-efficient monitoring solution during ultrasound surgery within a clinical setting.