TY - JOUR
T1 - Evaluation of the unscanned soft-tissue thermal index
AU - O'Brien, William D.
AU - Scott Ellis, D.
N1 - Manuscript received December 7, 1998; accepted July 6, 1999. This work was supported in part by the NIH CA09067, NIH HD21687, and NIH HL58218. W. D. O’Brien, Jr., is with the Bioacoustics Research Laboratory, Department of Electrical and Computer Engineering, University of Illinois, Urbana, IL 61801 (e-mail: [email protected]). D. S. Ellis is with Andersen Consulting, Washington, DC 20006.
PY - 1999
Y1 - 1999
N2 - The monopole-source solution was used to calculate the three-dimensional complex acoustic pressure field for focused circular apertures in a medium having homogeneous acoustic and thermal properties. The three source diameters were 1, 2, and 4 cm and the eight transmit f-numbers (ratio of the radius of curvature/source diameter) were 0.7, 1.0, 1.3, 1.6, 2.0, 3.0, 4.0, and 5.0. For these focused field geometries, eight ultrasonic frequencies were evaluated (1, 2, 3, 4, 5, 7, 9, and 12 MHz) from which the three-dimensional temperature distribution was calculated using the bio-heat transfer equation in homogeneous, perfused media (attenuation = absorption = 0.3 dB/cm-MHz; perfusion length: 1.0 cm). For each of the 192 cases, the acoustic field was normalized to the derated spatial peak, temporal average intensity (ISPTA.3) of 720 mW/cm2, the maximum value allowed by the FDA 510(k) diagnostic ultrasound equipment approval process. Using the normalized acoustic field, the axial temperature increase profiles and the maximum temperature increases (ΔTmax) were determined for each case. Also, from the normalized acoustic field, the unscanned soft-tissue thermal index (TIS) was determined. In general, ΔTmax, TIS, and source power increase with increasing transmit f-number, source diameter, or frequency. The TIS generally underestimates (is less than) ΔTmax for f-numbers≤2, conditions for which ΔTmax≤0.30 °C and TIS≤0.40. This suggests that, for transmit f-numbers≤2, TIS would not need to be displayed according to the ODS display requirements. With the exception of the longer-focus, larger-diameter, higher-frequency sources, TIS generally tracks ΔTmax for f-numbers≥3. These exceptions suggest a breakdown of the ODS procedures for calculating TIS.
AB - The monopole-source solution was used to calculate the three-dimensional complex acoustic pressure field for focused circular apertures in a medium having homogeneous acoustic and thermal properties. The three source diameters were 1, 2, and 4 cm and the eight transmit f-numbers (ratio of the radius of curvature/source diameter) were 0.7, 1.0, 1.3, 1.6, 2.0, 3.0, 4.0, and 5.0. For these focused field geometries, eight ultrasonic frequencies were evaluated (1, 2, 3, 4, 5, 7, 9, and 12 MHz) from which the three-dimensional temperature distribution was calculated using the bio-heat transfer equation in homogeneous, perfused media (attenuation = absorption = 0.3 dB/cm-MHz; perfusion length: 1.0 cm). For each of the 192 cases, the acoustic field was normalized to the derated spatial peak, temporal average intensity (ISPTA.3) of 720 mW/cm2, the maximum value allowed by the FDA 510(k) diagnostic ultrasound equipment approval process. Using the normalized acoustic field, the axial temperature increase profiles and the maximum temperature increases (ΔTmax) were determined for each case. Also, from the normalized acoustic field, the unscanned soft-tissue thermal index (TIS) was determined. In general, ΔTmax, TIS, and source power increase with increasing transmit f-number, source diameter, or frequency. The TIS generally underestimates (is less than) ΔTmax for f-numbers≤2, conditions for which ΔTmax≤0.30 °C and TIS≤0.40. This suggests that, for transmit f-numbers≤2, TIS would not need to be displayed according to the ODS display requirements. With the exception of the longer-focus, larger-diameter, higher-frequency sources, TIS generally tracks ΔTmax for f-numbers≥3. These exceptions suggest a breakdown of the ODS procedures for calculating TIS.
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U2 - 10.1109/58.808870
DO - 10.1109/58.808870
M3 - Article
C2 - 18244343
AN - SCOPUS:0033308014
SN - 0885-3010
VL - 46
SP - 1459
EP - 1476
JO - IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control
JF - IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control
IS - 6
ER -