IEC TR 62799:2013
(Main)Models for evaluation of thermal hazard in medical diagnostic ultrasonic fields
Models for evaluation of thermal hazard in medical diagnostic ultrasonic fields
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.
General Information
Standards Content (Sample)
IEC/TR 62799 ®
Edition 1.0 2013-09
TECHNICAL
REPORT
Models for evaluation of thermal hazard in medical diagnostic ultrasonic fields
IEC/TR 62799:2013(E)
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IEC/TR 62799 ®
Edition 1.0 2013-09
TECHNICAL
REPORT
Models for evaluation of thermal hazard in medical diagnostic ultrasonic fields
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
X
ICS 11.040.50 ISBN 978-2-8322-1099-4
– 2 – TR 62799 © IEC:2013(E)
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Background . 10
4.1 General . 10
4.2 Limitations of the existing standard . 11
4.2.1 Linear display . 11
4.2.2 Equilibrium temperature . 12
4.2.3 Tissue parameters . 12
4.2.4 Transducer self-heating . 12
4.2.5 Safety limits . 12
5 Options for improvement of the existing standard . 13
5.1 General . 13
5.2 Exponential display of the current TI . 13
5.2.1 Theory . 13
5.2.2 Illustrative results for the new thermal index display . 15
5.2.3 Advantages of the new display . 15
5.2.4 Shortcomings of the new display . 16
5.3 Replacement of the TI with the thermally equivalent time index (TETI) . 16
5.3.1 Theory . 16
5.3.2 Illustrative results for the TETI . 20
5.3.3 Advantages of the TETI. 22
5.3.4 Shortcomings of the TETI . 22
5.4 Replacement of the TI with the time to threshold (TT). 23
5.4.1 Theory . 23
5.4.2 Illustrative results for the TT. 24
5.4.3 Advantages of the TT . 27
5.4.4 Shortcomings of the TT . 27
5.5 Replacement of the TI with the safe use time (SUT) . 28
5.5.1 Theory . 28
5.5.2 Illustrative results for the SUT . 30
5.5.3 Advantages of the SUT . 33
5.5.4 Shortcomings of the SUT . 33
5.6 Replacement of the TI with the thermally equivalent time displayed
(TETD) . 34
5.6.1 Theory . 34
5.6.2 Illustrative results for the TETD . 35
5.6.3 Advantages of the TETD . 38
5.6.4 Shortcomings of the TETD . 39
6 Summary . 40
7 Recommendations . 41
7.1 General . 41
7.2 Thermally equivalent time index . 41
7.3 Other models . 41
Bibliography . 42
TR 62799 © IEC:2013(E) – 3 –
Figure 1 – Comparison of the values of thermal index that would be displayed under
the proposed definition, TI , with that displayed currently, TI . 15
new cur
Figure 2 –Expanded view of the comparison of Figure 1 for smaller values of TI . 15
cur
Figure 3 – Thermal-equivalent core temperature elevations vs time . 18
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 . 19
Figure 5 – Thermally equivalent time index (solid curves) vs foetal exposure duration
for TI = 1, 2, 3 and 4 . 21
Figure 6 – Temperature rise for distance (z > 3 cm) for four models as a function of
US exposure time . 25
Figure 7 – Relation between TT (time to threshold) and power parameters that give a
temperature rise of ∆T = 4 °C. 26
thr
Figure 8 – The ratio of temperature rise to acoustic absorption coefficient, ∆T/µ, vs
exposure duration for the non-scanning soft tissue model with P = 100 mW. . 27
a
Figure 9 – A typical example of temperature rise due to diagnostic ultrasound . 29
Figure 10 – Values of temperature rise as a function of insonation time . 31
Figure 11 – The thermal load as a function of time and f-number . 32
Figure 12 – A comparison of thermally equivalent times (t ) for the temperature
profiles shown in Figure 6 . 36
Figure 13 – Probability of birth defect or kidney necrosis as a function of thermally
equivalent time (t ) . 37
Figure 14 – Probabilities of kidney necrosis estimated for the thermally equivalent
times (t ) shown in Figure 12 . 38
Figure 15 – Probabilities of birth defect estimated for the thermally equivalent times
(t ) shown in Figure 12 . 39
Table 1 – Thermally equivalent time thresholds for chronic damage in various tissues,
t ; see [21]. . 20
Table 2 – Foetal exposure durations for a thermally equivalent time index value of 1 . 22
Table 3 – Non-foetal exposure durations for a thermally equivalent time index value
of 1 . 22
Table 4 – SUT values when including and ignoring the contribution of temperatures
lower than ∆T for the four exposure conditions and the corresponding values of
max
∆T . 32
max
Table 5 – Values of W, W , and ∆T for the case of SUT = 500 s. . 33
a max
Table 6 – Comparison of significant characteristics of the possible replacements for
the TI. . 40
– 4 – TR 62799 © IEC:2013(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
MODELS FOR EVALUATION OF THERMAL HAZARD
IN MEDICAL DIAGNOSTIC ULTRASONIC FIELDS
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