Feasibility of using lateral mode coupling method for a large scale ultrasound phased array for noninvasive transcranial therapy.

Authors: Song J, Hynynen K

A hemispherical-focused, ultrasound phased array was designed and fabricated using 1372 cylindrical piezoelectric transducers that utilize lateral coupling for noninvasive transcranial therapy. The cylindrical transducers allowed the electrical impedance to be reduced by at least an order of magnitude, such that effective operation could be achieved without electronic matching circuits. In addition, the transducer elements generated the maximum acoustic average surface intensity of 27 W/cm(2). The array, driven at the low (306-kHz) or high frequency (840-kHz), achieved excellent focusing through an ex vivo human skull and an adequate beam steering range for clinical brain treatments. It could electronically steer the ultrasound beam over cylindrical volumes of 100-mm in diameter and 60-mm in height at 306 kHz, and 30-mm in diameter and 30-mm in height at 840 kHz. A scanning laser vibrometer was used to investigate the radial and length mode vibrations of the element. The maximum pressure amplitudes through the skull at the geometric focus were predicted to be 5.5 MPa at 306 kHz and 3.7 MPa at 840 kHz for RF power of 1 W on each element. This is the first study demonstrating the feasibility of using cylindrical transducer elements and lateral coupling in construction of ultrasound phased arrays.

Introduction

Purpose Thermal ablation

Study Objective To design, fabricate, and demonstrate the feasibility of a hemispherical-focused ultrasound phased array using cylindrical laterally-coupled piezoelectric transducers for noninvasive transcranial therapy.

Animal model / Human subject Human (ex vivo skull); strain: N/A; age: None; sex: None

Outcomes and Safety

Summary of Outcomes A hemispherical phased array of 1372 laterally-coupled cylindrical transducers achieved effective transcranial focusing through an ex vivo human skull with a maximum acoustic surface intensity of 27 W/cm2 and predicted geometric-focus pressures of 5.5 MPa at 306 kHz and 3.7 MPa at 840 kHz, while lateral coupling reduced element impedance enabling operation without matching circuits; electronic steering volumes were 100 mm diameter × 60 mm height at 306 kHz and 30 mm diameter × 30 mm height at 840 kHz.

Safety-related matter The paper contains no discussion of safety assessments or adverse effects; no adverse effects were reported. Experiments were ex vivo (human skull) and no in vivo safety data are provided.

Brain Region

Visualization unavailable

Ultrasound Parameters

FUS Frequency 306 kHz, 840 kHz

FUS Intensity 27 W/cm2

FUS Pressure 5.5 MPa (306 kHz), 3.7 MPa (840 kHz)

Focal Characteristics Focal depth: None; Focal length: None; Aperture size: None

We are open to feedback. If you see a mistake or have a suggestion, please contact us.