Skin Acceleration Levels Estimated by a Neck-surface Accelerometer during Phonation Are Affected by The Mechanical Properties of The Anterior Cervical Skin.

OBJECTIVES: The aim of the present study was to assess whether skin acceleration levels (SAL) estimated by a neck-surface accelerometer (ACC) are affected by the anterior neck skin condition. METHODS: Each of six healthy non-dysphonic participants wore a headset microphone (MIC), had an ACC sensor fitted on the skin over the cervical trachea, and were subsequently asked to gradually increase the vocal loudness during sustained phonation of the vowel /e:/ (crescendo task), while the sound pressure levels on a sound level meter (SPLSLM) and MIC/ACC signals were simultaneously recorded. Root mean squared values were calculated from the MIC and ACC signals as the sound pressure level (SPLMIC) and SAL, respectively, and the relationships between SPLSLM and SAL were compared between neck anteflexion and retroflexion or between outward and inward skin retraction on both sides of the sensor. RESULTS: In the total samples for the successful crescendo performance in a natural head position, the SPLMIC and SPLSLM showed a strong linear correlation (r=0.980), whereas the correlation between the SAL and SPLSLM showed a distorted regression line (r=0.765) with individual differences. In all participants, the anteflexion and inward skin retraction decreased the SAL value at the same SPLSLM value, whereas the retroflexion increased the SAL value at the same SPLSLM value. CONCLUSION: These results demonstrate that the signal intensity of a neck-surface ACC is affected by the condition of the anterior cervical skin, perhaps leading to inter-individual variability in SAL measurements.

The Feasibility of a Neck-Surface Accelerometer for Estimating the Amount of Acoustic Output During Phonation Regardless of the Difference in the Mouth Configuration.

OBJECTIVES: This study aimed to assess the feasibility of a neck-surface accelerometer (ACC) for estimating the amount of acoustic output produced during phonation regardless of individual differences or the mouth configuration. METHODS: The sound pressure levels (SPL) and signals of a neck-surface ACC were simultaneously recorded, while each of healthy nondysphonic speakers was asked to perform the following phonatory tasks: (1) repetitive phonation of the vowel /e:/ at various loudness levels; (2) gradually increasing vocal loudness (crescendo) during sustained phonation of the vowel /e:/; (3) repetitive smooth transition between phonation of the vowel /a:/ and /u:/ with the same vocal effort or between phonation of the vowel /e:/ and production of a hum /m:/. The skin acceleration levels (SAL) were calculated from the ACC signals. RESULTS: Although the correlations between the SPL and SAL values were nearly linear in both repetitive-vowel-phonation and vowel-crescendo tasks, the crescendo task showed a higher correlation within individuals than the repetitive task, but with substantial individual differences. The correlation between the increments in the SPL and SAL was higher than that between the SPL and SAL. In the smooth-transition tasks, the SAL-but not the SPL-showed no significant differences between the vowels or hum. CONCLUSION: These results show that the signal intensity of a neck-surface ACC reflects the amount of acoustic output during phonation irrespective of the mouth configuration, but shows nonnegligible individual differences. The use of the increment in the SAL is suggested to be suitable for comparing the amount of acoustic output.

Hydrophone Spatial Averaging Artifacts for ARFI Beams from Array Transducers.

This paper reports underestimation of peak compressional pressure (p c), peak rarefactional pressure (p r ), and pulse intensity integral (pii) due to hydrophone spatial averaging of acoustic radiation force impulse (ARFI) beams generated by clinical linear and phased arrays. Although a method exists for correcting for hydrophone spatial averaging for circularly-symmetric beams, there is presently no analogous method for rectangularly-symmetric beams generated by linear and phased arrays. Consequently, pressure parameters (p c, p r , and pii) from clinical arrays are often not corrected for spatial averaging. This can lead to errors in Mechanical Index (MI) and Thermal Index (TI), which are derived from pressure measurements and are displayed in real-time during clinical ultrasound scans. ARFI beams were generated using three clinical linear array transducers. Output pressure waveforms for all three transducers were measured using five hydrophones with geometrical sensitive element sizes (dg) ranging from 85 to 1000 µm. Spatial averaging errors were found to increase with hydrophone sensitive element size. For example, if dg = 500 µm (typical membrane hydrophone), frequency = 2.25 MHz and F/# = 1.5, then average errors are approximately -20% (pc), -10% (pr), and -25% (pii). Therefore, due to hydrophone spatial averaging, typical membrane hydrophones can exhibit significant underestimation of ARFI pressure measurements, which likely compromises exposure safety indexes.

Correction for Spatial Averaging Artifacts for Circularly-Symmetric Pressure Beams Measured with Membrane Hydrophones.

This paper investigates experimental underestimation of pressure measurements due to spatial averaging across a hydrophone sensitive element. Empirical relationships are measured to enable correction for hydrophone spatial averaging errors in peak compressional pressure (p c ), peak rarefactional pressure (p r ), and pulse intensity integral (pii). The empirical relationships show, for example, that if a 3-MHz, F/2 transducer is driven to moderate nonlinear distortion and measured at the focal point with a 500-µm membrane hydrophone, then spatial averaging errors are approximately 16% (p c ), 12% (p r ), and 24% (pii).

Ultrasound biosafety: Knowledge and opinions of health practitioners who perform obstetric scans in South Africa.

BACKGROUND: Diagnostic ultrasound is generally considered as a safe test in pregnancy. To date there is no evidence that ultrasound has caused harm to the developing foetus. However, with the number of obstetric scans on the rise and the steep increase in acoustic output achieved by modern machines, the lack of evidence of absolute safety remains a concern. Acoustic output is under the direct control of the operator and is therefore the operator's responsibility to keep the intensity as low as reasonably achievable. A situation analysis in the South African context was deemed necessary to determine end user knowledge and opinions on safe antenatal ultrasound practice. AIM: The aim of this quantitative descriptive, cross-sectional study was to evaluate the knowledge and practice of health practitioners who perform antenatal scans regarding safety aspects of diagnostic ultrasound. SETTING: A self-administered questionnaire was distributed at two national congresses, hosted by the South African Society of Ultrasound and Obstetrics (SASUOG) and South African Society of Obstetricians (SASOG) committees. METHOD: Quota non-probability sampling allowed for the identification of professional categories capable of providing information relevant to the study objectives. The sample represented a population with experience in obstetric ultrasound. RESULTS: Compared to international studies, South African end users demonstrated better knowledge of safety indices than their international counterparts. It is, however, discouraging that end users still demonstrate insufficient knowledge regarding factors contributing to adverse biological effects. CONCLUSION: With room for improvement, an effort should be made to comply with international standards through increased training efforts and raising awareness.

Evaluating the Benefit of Elevated Acoustic Output in Harmonic Motion Estimation in Ultrasonic Shear Wave Elasticity Imaging.

Harmonic imaging techniques have been applied in ultrasonic elasticity imaging to obtain higher-quality tissue motion tracking data. However, harmonic tracking can be signal-to-noise ratio and penetration depth limited during clinical imaging, resulting in decreased yield of successful shear wave speed measurements. A logical approach is to increase the source pressure, but the in situ pressures used in diagnostic ultrasound have been subject to a de facto upper limit based on the Food and Drug Administration guideline for the mechanical index (MI <1.9). A recent American Institute of Ultrasound in Medicine report concluded that an in situ MI up to 4.0 could be warranted without concern for increased risk of cavitation in non-fetal tissues without gas bodies if there were a concurrent clinical benefit. This work evaluates the impact of using an elevated MI in harmonic motion tracking for hepatic shear wave elasticity imaging. The studies indicate that high-MI harmonic tracking increased shear wave speed estimation yield by 27% at a focal depth of 5 cm, with larger yield increase in more difficult-to-image patients. High-MI tracking improved harmonic tracking data quality by increasing the signal-to-noise ratio and decreasing jitter in the tissue motion data. We conclude that there is clinical benefit to use of elevated acoustic output in shear wave tracking, particularly in difficult-to-image patients.

Quantifying Image Quality Improvement Using Elevated Acoustic Output in B-Mode Harmonic Imaging.

Tissue harmonic imaging has been widely used in abdominal imaging because of its significant reduction in acoustic noise compared with fundamental imaging. However, tissue harmonic imaging can be limited by both signal-to-noise ratio and penetration depth during clinical imaging, resulting in decreased diagnostic utility. A logical approach would be to increase the source pressure, but the in situ pressures used in diagnostic ultrasound are subject to a de facto upper limit based on the U.S. Food and Drug Administration guideline for the mechanical index (<1.9). A recent American Institute of Ultrasound in Medicine report concluded that an effective mechanical index ≤4.0 could be warranted without concern for increased risk of cavitation in non-fetal tissues without gas bodies, but would only be justified if there were a concurrent improvement in image quality and diagnostic utility. This work evaluates image quality differences between normal and elevated acoustic output hepatic harmonic imaging using a transmit frequency of 1.8 MHz. The results indicate that harmonic imaging using elevated acoustic output leads to modest improvements (3%-7%) in contrast-to-noise ratio of hypo-echoic hepatic vessels and increases in imaging penetration depth on the order of 4 mm per mechanical index increase of 0.1 for a given focal depth. Difficult-to-image patients who suffer from poor ultrasound image quality exhibited larger improvements than easy-to-image study participants.

[Study of Acoustic Output Power Measurement of Transcranial Doppler Diagnostic & Monitor System].

The fundamental concept, measuring and calculating of Transcranial Doppler Diagnostic & Monitor System acoustic output power are introduced according to hydrophone scanning method and pulsing sequences principle. Then, the feasibility of the method is demonstrated. Finally, the detail calculating method of Transcranial Doppler Diagnostic & Monitor System has been derived.

Thermal safety simulations of transient temperature rise during acoustic radiation force-based ultrasound elastography.

Ultrasound transient elastography is a new diagnostic imaging technique that uses acoustic radiation force to produce motion in solid tissue via a high-intensity, long-duration "push" beam. In our previous work, we developed analytical models for calculating transient temperature rise, both in soft tissue and at a bone/soft tissue interface, during a single acoustic radiation force impulse (ARFI) imaging frame. The present study expands on these temperature rise calculations, providing applicable range assessment and error analysis for a single ARFI frame. Furthermore, a "virtual source" approach is described for temperature and thermal dose calculation under multiple ARFI frames. By use of this method, the effect of inter-frame cooling duration on temperature prediction is analyzed, and a thermal buildup phenomenon is revealed. Thermal safety assessment indicates that the thermal dose values, especially at the absorptive bone/soft tissue interface, could approach recommended dose thresholds if the cooling interval of multiple-frame ARFI elastography is too short.

Trends in diagnostic ultrasound acoustic output from data reported to the US Food and Drug Administration for device indications that include fetal applications.

OBJECTIVES: A survey was conducted of acoustic output data received by the US Food and Drug Administration for diagnostic ultrasound devices whose indications for use include fetal applications to assess trends in maximum available acoustic output over time. METHODS: Data were collected from 124 regulatory submissions received between 1984 and 2010. Data collection excluded transducers not indicated for diagnostic fetal imaging. The output parameters of ultrasonic power, mean center frequency, and bone thermal index (TIB) were extracted or computed from the submissions for 3 periods: 1984-1989, 1992-1997, and 2005-2010. The data were stratified according to the following imaging modes: M-mode, B/M-mode, pulsed wave Doppler, color flow Doppler, and continuous wave Doppler. RESULTS: Ultrasonic power and maximum TIB values have increased roughly an order of magnitude from pre-1991 to post-1991 periods; the center frequency has decreased somewhat (4.2 to 3.4 MHz). The percentage of Doppler-mode transducers has increased substantially over time, with the majority of the diagnostic fetal imaging transducers currently designed to operate in Doppler modes; this increase is particularly important, since Doppler modes generate much higher TIB levels than B/M-modes. Color flow Doppler ultrasound currently operates at the highest mean ultrasonic power level (with a 14-fold increase over time). CONCLUSIONS: The observed trends in increased acoustic output for both Doppler and non-Doppler modes underscore the widely recognized importance of adherence to the ALARA (as low as reasonably achievable) principle and prudent use in fetal ultrasound imaging.

Development of portable acoustic output measurement system for medical ultrasonic diagnostic equipment / 医疗卫生装备

Objective To develop a portable acoustic output measurement system in order to satisfy the requirements of military itinerant inspection. Methods A hydrophone was used as energy converting equipment to collect wave of acoustic pressure in the field of ultrasound. Through some calculations using approximated formulas, a serious of acoustic output parameters were achieved. Results Main acoustic output parameters could be measured with permitted error. Conclusion This method is feasible, which can make up for the defects of current measurement.