HIFU Power Monitoring Using Combined Instantaneous Current and Voltage Measurement

Abstract

During HIFU therapy it is important that the electrical power delivered to the transducer is monitored to avoid under or over exposure, ensure patient safety and to protect the transducer itself. Due to ease of measurement, the transducer's potential difference may be as an indicator of power delivery. However, even when a transducer's complex impedance is well characterised at small amplitudes and matching networks are used, voltage-only (VO) monitoring cannot account for the presence of drive waveform distortion, changes to the acoustic path or damage to the transducer. In this study, combined current and voltage (CCV) is proposed as an MRIcompatible, miniature alternative to bi-directional power couplers that is compatible with switched amplifiers. For CCV power measurement, current probe data was multiplied by the voltage waveform and integrated in the frequency domain. Transducer efficiency was taken into account to predict acoustic power. The technique was validated with a radiation force balance (RFB). When using a typical HIFU transducer and amplifier, VO predictions and acoustic power had a maximum difference of 20%. However, under the same conditions, CCV only had a maximum difference of 5%. The technique was applied to several lesioning experiments and it was shown that when VO was used as a control between two amplifiers there was up to a 38% difference in lesion area. This greatly reduced to a maximum of 5% once CCV was used instead. These results demonstrate that CCV can accurately predict real-time electrical power delivery leading to safer HIFU treatments.

Lead‐free versus PZT: Acoustic characterization of ultrasonic immersion transducers fabricated with lead‐free NBT‐BT piezoceramic

“…From theory, input electrical power can be measured with a combination of probes measuring voltage and current across the terminals of the transducer provided the load is purely real [16]. On the basis that the electrical impedance matching of the transducers was sufficient to approximate their impedance as ($$50 + j0)\;\Omega $$ and the drive waveform contained only a single frequency.…”

“…Measurements of supplied electrical power were made using current and voltage probes as per Figure 3. Drive voltage was measured at a T-piece on the output of the amplifier using a high impedance passive probe whilst the current was monitored at the same junction where a short section of coaxial cable From theory, input electrical power can be measured with a combination of probes measuring voltage and current across the terminals of the transducer provided the load is purely real [16]. On the basis that the electrical impedance matching of the transducers was sufficient to approximate their impedance as (50 + j 0) Ω and the drive waveform contained only a single frequency.…”

High-Power Gallium Nitride HIFU Transmitter With Integrated Real-Time Current and Voltage Measurement

“…Techniques have been presented for the use of power monitoring circuitry measuring the output voltage and current when the system is driving a transducer load in order to calculate the true output power of the system [29], [30], with [29] presenting the argument that electrical output power can be correlated directly to the acoustic power delivered based on the conversion efficiency of the transducer. In both of these examples, the measurement approach was based around the use of an oscilloscope with current and voltage probes in order to measure the power.…”

Gallium Nitride Based High-Power Switched HIFU Pulser with Real-Time Current/Voltage Monitoring

“…This is typically achieved by simply estimating the power based on scaled radiation force balance measurements of the transducer output [17]. An alternate approach is to measure both current and voltage of the output of the drive waveform in real time to directly calculate power delivered in order to achieve a more accurate calculation of power delivered [18].…”