Title :
Photoacoustic thermometry for therapeutic hyperthermia
Author :
Chitnis, Parag V. ; Mamou, Jonathan ; McLaughlan, James ; Murray, Todd ; Roy, Ronald A.
Author_Institution :
F. L. Lizzi Center for Biomed. Eng., Riverside Res. Inst., New York, NY, USA
Abstract :
Local hyperthermia is widely studied as a treatment option for small tumors. This study investigates the feasibility of exploiting the photoacoustic (PA) effect to monitor the in situ temperature rise during high-intensity focused ultrasound (HIFU) exposures for therapeutic hyperthermia. Polyacrylamide phantoms with a cylindrical inclusion (3 à 20 mm) of graphite (0.01 g/ml) were heated using 30 s exposures from a 2 MHz HIFU transducer. The transducer focus was aligned to the tip of a wire thermocouple embedded in the inclusion. A 532 nm pulsed laser was used to illuminate the inclusion. A 15 MHz broadband transducer was employed as a passive receiver (PR) to detect the PA response, which was an ultrasonic pulse emanating from the inclusion due to thermoelastic expansion induced by optical absorption. The native temperature and PR signals were recorded before, during, and after HIFU exposure. Singular-value decomposition (SVD) was performed on the matrix consisting of the PR signals to extract temperature data. SVD-deduced, PA-based temperatures correlated well with the thermocouple measurements (RMS error<5°C). A temperature rise of 20°C corresponded to a 30% increase in PA amplitude. The PA temperature-measurement technique was able to track heating and cooling phases over a range of temperatures characteristic of HIFU-induced hyperthermia.
Keywords :
biomedical measurement; biomedical transducers; biomedical ultrasonics; cooling; graphite; heating; hyperthermia; phantoms; radiation therapy; thermoelasticity; HIFU-induced hyperthermia; cooling phase; cylindrical inclusion; frequency 2 MHz; graphite; heating phase; high-intensity focused ultrasound exposures; optical absorption; passive receiver; photoacoustic effect; photoacoustic thermometry; polyacrylamide phantoms; singular-value decomposition; temperature 20 degC; therapeutic hyperthermia; thermocouple measurements; thermoelastic expansion; transducers; ultrasonic pulse; Hyperthermia; Imaging phantoms; Monitoring; Neoplasms; Optical pulses; Optical receivers; Temperature; Ultrasonic imaging; Ultrasonic transducers; Wire;
Conference_Titel :
Ultrasonics Symposium (IUS), 2009 IEEE International
Conference_Location :
Rome
Print_ISBN :
978-1-4244-4389-5
Electronic_ISBN :
1948-5719
DOI :
10.1109/ULTSYM.2009.5441585