TY - JOUR
T1 - Multifrequency Ultrasound Transducers for Conformal Interstitial Thermal Therapy
AU - Chopra, Rajiv
AU - Luginbuhl, Chris
AU - Foster, F. Stuart
AU - Bronskill, Michael J.
N1 - Funding Information:
Manuscript received February 12, 2002; accepted December 3, 2002. This work was supported by a Terry Fox Program Project grant from the National Cancer Institute of Canada. Rajiv Chopra was supported by a Research Studentship from the National Cancer Institute of Canada.
PY - 2003/7
Y1 - 2003/7
N2 - Control over the pattern of thermal damage generated by interstitial ultrasound heating applicators can be enhanced by changing the ultrasound frequency during heating. The ability to change transmission frequency from a single transducer through the use of high impedance front layers was investigated in this study. The transmission spectrum of multifrequency transducers was calculated using the KLM equivalent circuit model and verified with experimental measurements on prototype transducers. The addition of a quarter-wavelength thick PZT (unpoled) front layer enabled the transmission of ultrasound at two discrete frequencies, 4.7 and 9.7 MHz, from a transducer with an original resonant frequency of 8.4 MHz. Three frequency transmission at 3.3, 8.4, and 10.8 MHz was possible for a transducer with a half-wavelength thick front layer. Calculations of the predicted thermal lesion size at each transmission frequency indicated that the depth of thermal lesion could be varied by a factor of 1.6 for the quarter-wavelength front layer. Heating experiments performed in excised liver tissue with a dual-frequency applicator confirmed this ability to control the shape of thermal lesions during heating to generate a desired geometry. Practical interstitial designs that enable the generation of shaped thermal lesions are feasible.
AB - Control over the pattern of thermal damage generated by interstitial ultrasound heating applicators can be enhanced by changing the ultrasound frequency during heating. The ability to change transmission frequency from a single transducer through the use of high impedance front layers was investigated in this study. The transmission spectrum of multifrequency transducers was calculated using the KLM equivalent circuit model and verified with experimental measurements on prototype transducers. The addition of a quarter-wavelength thick PZT (unpoled) front layer enabled the transmission of ultrasound at two discrete frequencies, 4.7 and 9.7 MHz, from a transducer with an original resonant frequency of 8.4 MHz. Three frequency transmission at 3.3, 8.4, and 10.8 MHz was possible for a transducer with a half-wavelength thick front layer. Calculations of the predicted thermal lesion size at each transmission frequency indicated that the depth of thermal lesion could be varied by a factor of 1.6 for the quarter-wavelength front layer. Heating experiments performed in excised liver tissue with a dual-frequency applicator confirmed this ability to control the shape of thermal lesions during heating to generate a desired geometry. Practical interstitial designs that enable the generation of shaped thermal lesions are feasible.
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U2 - 10.1109/TUFFC.2003.1214507
DO - 10.1109/TUFFC.2003.1214507
M3 - Article
C2 - 12894921
AN - SCOPUS:0042764331
SN - 0885-3010
VL - 50
SP - 881
EP - 889
JO - IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control
JF - IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control
IS - 7
ER -