Bibliographic record
Abstract
The existing safety standards for diagnostic ultrasound devices were developed for low frequency systems (1 to 10 MHz) under the assumption that nonlinear effects are negligible. However, the standards are now being used for relatively high frequency systems (up to 70 MHz); nonlinear effects are increasingly evident as the working frequency f0 is increased. The main goal of this project is to determine if the coverage of nonlinear effects in safety standards in terms of thermal and non-thermal effects is adequate for equipment with f0>10 MHz. To achieve this goal, a practical variation to the finite amplitude method for determination of B/A is proposed, and the values of B/A are measured from 2.25 to 20 MHz for water. It is shown that there is no statistically significant variation with f0 for the value of B/A. The appropriate value of B/A in tissue is used as input to a nonlinear pulse propagation model in the time-domain. The total heat deposition pattern due to ultrasound absorption is then calculated and used as input to a bio-heat model. The maximum peak-rarefactional pressure is also extracted from the nonlinear pulse propagation results and used to calculate the Mechanical Index MI. We propose a slight modification to MI to solve the inconsistencies associated with the coverage of nonlinear effects in MI. A modification is also required in the existing upper limit for the hydrophone calibration bandwidth to ensure that the fundamental component is fully captured at high frequencies.The thermal results show that strong higher order harmonics can significantly increase the local heat deposition rate. However, at the same time, they lead to an increase in the rate of axial and radial heat conduction, thereby reducing the net impact on the steady-state temperature rise. Also, the effect of higher order harmonics can be significant on the temperature rise at the focal point, while the maximum temperature rise always occurs close to the skin surface. We conclude that current safety standards are adequate in assessing thermal effects in B-mode imaging at high frequencies despite ignoring the extra heat deposited by higher order harmonics.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".