James Gessert

Challenges and regulatory considerations in the acoustic measurement of high-frequency (>20 mhz) ultrasound

This article examines the challenges associated with making acoustic output measurements at high ultrasound frequencies (>20 MHz) in the context of regulatory considerations contained in the US Food and Drug Administration industry guidance document for diagnostic ultrasound devices. Error sources in the acoustic measurement, including hydrophone calibration and spatial averaging, nonlinear distortion, and mechanical alignment, are evaluated, and the limitations of currently available acoustic measurement instruments are discussed. An uncertainty analysis of acoustic intensity and power measurements is presented, and an example uncertainty calculation is done on a hypothetical 30‐MHz high‐frequency ultrasound system. This analysis concludes that the estimated measurement uncertainty of the acoustic intensity is +73%/−86%, and the uncertainty in the mechanical index is +37%/−43%. These values exceed the respective levels in the Food and Drug Administration guidance document of 30% and 15%, respectively, which are more representative of the measurement uncertainty associated with characterizing lower‐frequency ultrasound systems. Recommendations made for minimizing the measurement uncertainty include implementing a mechanical positioning system that has sufficient repeatability and precision, reconstructing the time‐pressure waveform via deconvolution using the hydrophone frequency response, and correcting for hydrophone spatial averaging.

Color Flow Imaging Display Modes and Data Acquisition Parameters

The recent development and refinement of color flow imaging systems has led to some confusion as to the relative merit or proper use of various display parameters available to the operator. Still in its infancy, color flow imaging represents an exciting extension of pulsedDoppler technology in the evaluation of physiological events associated with the intracardiac movement of blood. As with any new technology, the initial excitement must soon turn toward a serious evaluation of the extent to which it may be applied in assisting the physician in the proper management of his patient. In order to effectively use color flow Doppler, as either a qualitative or quantitative modality, the physician and sonographer must have a clear understanding of the instrument and the parameters of data acquisition in which the instrument will operate. While considerable experience concerning the potential clinical efficacy of color flow imaging has already been reported, few data are available from commercial manufacturers as to how their systems acquire data, how data is processed, the inherent limitations of color flow data acquisition, why one display mode seems to work better than another in certain circumstances, and the ever-looming problem of instrumentation pitfalls. This review examines how color flow data is obtained, processed, and displayed. The limitations of color flow imaging and potential pitfalls of the various displays are also addressed.

Development of a High Intensity Focused Ultrasound (HIFU) Hydrophone System

The growing clinical use of High Intensity Focused Ultrasound (HIFU) has driven a need for reliable, reproducible measurements of HIFU acoustic fields. We have previously presented data on a reflective scatterer approach, incorporating several novel features for improved bandwidth, reliability, and reproducibility [Proc. 2005 IEEE Ultrasonics Symposium, 1739–1742]. We now report on several design improvements which have increase the signal to noise ratio of the system, and potentially reduced the cost of implementation. For the scattering element, we now use an artificial sapphire material to provide a more uniform radiating surface. The receiver is a segmented, truncated spherical structure with a 10 cm radius; the scattering element is positioned at the center of the sphere. The receiver is made from 25 micron thick, biaxially stretched PVDF, with a Pt‐Au electrode on the front surface. In the new design, a specialized backing material provides the stiffness required to maintain structural stability, wh...

Development of a high intensity focused ultrasound (HIFU) hydrophone system.

The growing use of high intensity focused Ultrasound (HIFU) has driven a need for reliable, reproducible measurements of HIFU acoustic fields. A reflective scatterer approach, incorporating several novel features for improved bandwidth, reliability, and reproducibility has been demonstrated [M. E. Schafer, J. Gessert, and W. Moore, Proc. IEEE Ultrasonics Symposium, 1739–1742 (2005)]. Several design improvements which have increase the signal‐to‐noise ratio of the system, and potentially reduced the cost of implementation, are now presented. For the scattering element, an artificial sapphire material is used to provide a more uniform radiating surface. The receiver is a segmented, truncated spherical structure with a 10 cm radius, made from 25 micron thick, biaxially stretched PVDF, with a Pt‐Au electrode on the front surface. A specialized backing material provides the stiffness required to maintain structural stability, while at the same time providing both electrical shielding and ultrasonic absorption....