BSI PD IEC/TR 62799:2013
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Models for evaluation of thermal hazard in medical diagnostic ultrasonic fields
| Published By | Publication Date | Number of Pages |
| BSI | 2013 | 48 |
IEC/TR 62799:2013(E), which is a technical report, provides background information for users of IEC 62359 to understand the relative merits of several of the potential replacements for the thermal index as described in IEC 60601-2-37 and IEC 62359. The report discusses parameters related to thermal aspects of diagnostic ultrasonic fields; and methods for the determination of an exposure parameter relating to temperature rise in theoretical tissue-equivalent models, resulting from absorption of ultrasound. The report is intended to be used: – by those involved in the development and maintenance of IEC 62359; – manufacturers of medical electrical equipment for risk assessment; – and health care regulatory authorities, test houses and other organizations responsible for implementing standards for medical electrical equipment.
PDF Catalog
| PDF Pages | PDF Title |
|---|---|
| 4 | CONTENTS |
| 6 | FOREWORD |
| 8 | 1 Scope 2 Normative references 3 Terms and definitions |
| 12 | 4 Background 4.1 General |
| 13 | 4.2 Limitations of the existing standard 4.2.1 Linear display |
| 14 | 4.2.2 Equilibrium temperature 4.2.3 Tissue parameters 4.2.4 Transducer self-heating 4.2.5 Safety limits |
| 15 | 5 Options for improvement of the existing standard 5.1 General 5.2 Exponential display of the current TI 5.2.1 Theory |
| 17 | 5.2.2 Illustrative results for the new thermal index display 5.2.3 Advantages of the new display Figures Figure 1 – Comparison of the values of thermal index that would be displayed under the proposed definition, TInew, with that displayed currently, TIcur Figure 2 – Expanded view of the comparison of Figure 1 for smaller values of TIcur |
| 18 | 5.2.4 Shortcomings of the new display 5.3 Replacement of the TI with the thermally equivalent time index (TETI) 5.3.1 Theory |
| 20 | Figure 3 – Thermal-equivalent core temperature elevations vs time |
| 21 | Figure 4 – Temperature-time curve (solid line) that represents a conservative boundary for non-foetal exposure durations, particularly for exposure durations of less than 5 s |
| 22 | 5.3.2 Illustrative results for the TETI Tables Table 1 – Thermally equivalent time thresholds for chronic damage in various tissues, t43; see [21]. |
| 23 | Figure 5 – Thermally equivalent time index (solid curves) vs foetal exposure duration for TI = 1, 2, 3 and 4 |
| 24 | 5.3.3 Advantages of the TETI 5.3.4 Shortcomings of the TETI Table 2 – Foetal exposure durations for a thermally equivalent time index value of 1 Table 3 – Non-foetal exposure durations for a thermally equivalent time index value of 1 |
| 25 | 5.4 Replacement of the TI with the time to threshold (TT) 5.4.1 Theory |
| 26 | 5.4.2 Illustrative results for the TT |
| 27 | Figure 6 – Temperature rise for distance (z0 > 3 cm) for four models as a function of US exposure time |
| 28 | Figure 7 – Relation between TT (time to threshold) and power parameters that give a temperature rise of ΔTthr = 4 °C |
| 29 | 5.4.3 Advantages of the TT 5.4.4 Shortcomings of the TT Figure 8 – The ratio of temperature rise to acoustic absorption coefficient, ΔT/μ , vs exposure duration for the non-scanning soft tissue model with Pa = 100 mW |
| 30 | 5.5 Replacement of the TI with the safe use time (SUT) 5.5.1 Theory |
| 31 | Figure 9 – A typical example of temperature rise due to diagnostic ultrasound |
| 32 | 5.5.2 Illustrative results for the SUT |
| 33 | Figure 10 – Values of temperature rise as a function of insonation time |
| 34 | Figure 11 – The thermal load as a function of time and f-number Table 4 – SUT values when including and ignoring the contribution of temperatures lower than ΔTmax for the four exposure conditions and the corresponding values of ΔTmax |
| 35 | 5.5.3 Advantages of the SUT 5.5.4 Shortcomings of the SUT Table 5 – Values of W, Wa, and ΔTmax for the case of SUT = 500 s. |
| 36 | 5.6 Replacement of the TI with the thermally equivalent time displayed (TETD) 5.6.1 Theory |
| 37 | 5.6.2 Illustrative results for the TETD |
| 38 | Figure 12 – A comparison of thermally equivalent times (t43) for the temperature profiles shown in Figure 6 |
| 39 | Figure 13 – Probability of birth defect or kidney necrosis as a function of thermally equivalent time (t43) |
| 40 | 5.6.3 Advantages of the TETD Figure 14 – Probabilities of kidney necrosis estimated for the thermally equivalent times (t43) shown in Figure 12 |
| 41 | 5.6.4 Shortcomings of the TETD Figure 15 – Probabilities of birth defect estimated for the thermallyequivalent times (t43) shown in Figure 12 |
| 42 | 6 Summary Table 6 – Comparison of significant characteristics of the possible replacements for the TI. |
| 43 | 7 Recommendations 7.1 General 7.2 Thermally equivalent time index 7.3 Other models |
| 44 | Bibliography |
