Measurements, phantoms, and standardization

Zeqiri, Bajram; Hodnett, Mark

doi:10.1243/09544119jeim647

Cited by 11 publications

(7 citation statements)

References 49 publications

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“…One approach is to perform measurements in lossy media to more closely match in vivo imaging. 29,30 This approach was used to obtain the green lines in Figure 2, using a modified attenuating fluid recipe (evaporated milk and water). Challenges of this approach include establishing a standard medium with specific acoustic properties, calibrating and maintaining the hydrophone in the new medium, and satisfying the need for ease of maintenance and repeatability (as water does), which would be required for commercial implementation.…”

Section: Challenges With Estimation Of In Situ Pressuresmentioning

confidence: 99%

Conditionally Increased Acoustic Pressures in Nonfetal Diagnostic Ultrasound Examinations Without Contrast Agents: A Preliminary Assessment

Nightingale

Church

Harris

et al. 2015

J of Ultrasound Medicine

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The mechanical index (MI) has been used by the US Food and Drug Administration (FDA) since 1992 for regulatory decisions regarding the acoustic output of diagnostic ultrasound equipment. Its formula is based on predictions of acoustic cavitation under specific conditions. Since its implementation over 2 decades ago, new imaging modes have been developed that employ unique beam sequences exploiting higher-order acoustic phenomena, and, concurrently, studies of the bioeffects of ultrasound under a range of imaging scenarios have been conducted. In 2012, the American Institute of Ultrasound in Medicine Technical Standards Committee convened a working group of its Output Standards Subcommittee to examine and report on the potential risks and benefits of the use of conditionally increased acoustic pressures (CIP) under specific diagnostic imaging scenarios. The term “conditionally” is included to indicate that CIP would be considered on a per-patient basis for the duration required to obtain the necessary diagnostic information. This document is a result of that effort. In summary, a fundamental assumption in the MI calculation is the presence of a preexisting gas body. For tissues not known to contain preexisting gas bodies, based on theoretical predications and experimentally reported cavitation thresholds, we find this assumption to be invalid. We thus conclude that exceeding the recommended maximum MI level given in the FDA guidance could be warranted without concern for increased risk of cavitation in these tissues. However, there is limited literature assessing the potential clinical benefit of exceeding the MI guidelines in these tissues. The report proposes a 3-tiered approach for CIP that follows the model for employing elevated output in magnetic resonance imaging and concludes with summary recommendations to facilitate Institutional Review Board (IRB)-monitored clinical studies investigating CIP in specific tissues.

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Section: Challenges With Estimation Of In Situ Pressuresmentioning

confidence: 99%

Conditionally Increased Acoustic Pressures in Nonfetal Diagnostic Ultrasound Examinations Without Contrast Agents: A Preliminary Assessment

Nightingale

Church

Harris

et al. 2015

J of Ultrasound Medicine

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“…The basic approach in these standards is to rely on measurements in water, comprising direct hydrophone measurements of the pressure field and radiation force measurements that determine acoustic power over a range of output levels. [21][22][23] Pressures and intensities inferred from these measurements are then derated to estimate in situ values that account for acoustic propagation in tissue rather than water. 24,25 In practice, this basic approach can produce incomplete or erroneous results.…”

Section: Introductionmentioning

confidence: 99%

Acoustic holography as a metrological tool for characterizing medical ultrasound sources and fields

Sapozhnikov

Tsysar

Khokhlova

et al. 2015

The Journal of the Acoustical Society of America

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Acoustic holography is a powerful technique for characterizing ultrasound sources and the fields they radiate, with the ability to quantify source vibrations and reduce the number of required measurements. These capabilities are increasingly appealing for meeting measurement standards in medical ultrasound; however, associated uncertainties have not been investigated systematically. Here errors associated with holographic representations of a linear, continuous-wave ultrasound field are studied. To facilitate the analysis, error metrics are defined explicitly, and a detailed description of a holography formulation based on the Rayleigh integral is provided. Errors are evaluated both for simulations of a typical therapeutic ultrasound source and for physical experiments with three different ultrasound sources. Simulated experiments explore sampling errors introduced by the use of a finite number of measurements, geometric uncertainties in the actual positions of acquired measurements, and uncertainties in the properties of the propagation medium. Results demonstrate the theoretical feasibility of keeping errors less than about 1%. Typical errors in physical experiments were somewhat larger, on the order of a few percent; comparison with simulations provides specific guidelines for improving the experimental implementation to reduce these errors. Overall, results suggest that holography can be implemented successfully as a metrological tool with small, quantifiable errors.

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“…As described in several review articles [7]–[9], relevant measurement standards are available for diagnostic ultrasound, but remain in development for therapeutic applications that utilize high acoustic intensities. As defined by the International Electrotechnical Commission (IEC), standards for characterizing the acoustic field generated by an ultrasound transducer involve measurements of acoustic pressure and power in water.…”

Section: Introductionmentioning

confidence: 99%

“…The derating of exposimetry measurements for estimating in situ pressures also poses particular challenges for intense fields. Typical derating strategies such as that included in the AIUM/NEMA standard for diagnostic ultrasound [9] assume linear acoustic propagation; however, it is well established that nonlinear propagation effects can significantly affect the in situ acoustic field for both diagnostic and therapeutic applications [11]–[13]. Accordingly, methods for modeling nonlinear propagation for intense ultrasound fields has received significant attention in recent years [14]–[18].…”

Section: Introductionmentioning

confidence: 99%

Characterization of a multi-element clinical HIFU system using acoustic holography and nonlinear modeling

Kreider

Yuldashev

Sapozhnikov

et al. 2013

IEEE Trans. Ultrason., Ferroelect., Freq. Contr.

122

113

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High-intensity focused ultrasound (HIFU) is a treatment modality that relies on the delivery of acoustic energy to remote tissue sites to induce thermal and/or mechanical tissue ablation. To ensure the safety and efficacy of this medical technology, standard approaches are needed for accurately characterizing the acoustic pressures generated by clinical ultrasound sources under operating conditions. Characterization of HIFU fields is complicated by nonlinear wave propagation and the complexity of phased-array transducers. Previous work has described aspects of an approach that combines measurements and modeling, and here we demonstrate this approach for a clinical phased array transducer. First, low-amplitude hydrophone measurements were performed in water over a scan plane between the array and the focus. Second, these measurements were used to holographically reconstruct the surface vibrations of the transducer and to set a boundary condition for a 3-D acoustic propagation model. Finally, nonlinear simulations of the acoustic field were carried out over a range of source power levels. Simulation results were compared to pressure waveforms measured directly by hydrophone at both low and high power levels, demonstrating that details of the acoustic field including shock formation are quantitatively predicted.

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Measurements, phantoms, and standardization

Cited by 11 publications

References 49 publications

Conditionally Increased Acoustic Pressures in Nonfetal Diagnostic Ultrasound Examinations Without Contrast Agents: A Preliminary Assessment

Conditionally Increased Acoustic Pressures in Nonfetal Diagnostic Ultrasound Examinations Without Contrast Agents: A Preliminary Assessment

Acoustic holography as a metrological tool for characterizing medical ultrasound sources and fields

Characterization of a multi-element clinical HIFU system using acoustic holography and nonlinear modeling

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