In vivo noninvasive temperature measurement by B-mode ultrasound imaging.
OBJECTIVE
This study investigated the use of ultrasound image analysis in quantifying temperature changes in tissue, both ex vivo and in vivo, undergoing local hyperthermia.


METHODS
Temperature estimation is based on the thermal dependence of the acoustic speed in a heated medium. Because standard beam-forming algorithms on clinical ultrasound scanners assume a constant acoustic speed, temperature-induced changes in acoustic speed produce apparent scatterer displacements in B-mode images. A cross-correlation algorithm computes axial speckle pattern displacement in B-mode images of heated tissue, and a theoretically derived temperature-displacement relationship is used to generate maps of temperature changes within the tissue. Validation experiments were performed on excised tissue and in murine subjects, wherein low-intensity ultrasound was used to thermally treat tissue for several minutes. Diagnostic temperature estimation was performed using a linear array ultrasound transducer, while a fine-wire thermocouple invasively measured the temperature change.


RESULTS
Pearson correlations ± SDs between the image-derived and thermocouple-measured temperature changes were R² = 0.923 ± 0.066 for 4 thermal treatments of excised bovine muscle tissue and R² = 0.917 ± 0.036 for 4 treatments of in vivo murine tumor tissue. The average differences between the two temperature measurements were 0.87°C ± 0.72°C for ex vivo studies and 0.97°C ± 0.55°C for in vivo studies. Maps of the temperature change distribution in tissue were generated for each experiment.


CONCLUSIONS
This study demonstrates that velocimetric measurement on B-mode images has potential to assess temperature changes noninvasively in clinical applications.
Department of Radiology, University of Pennsylvania, 3400 Spruce Street, Philadelphia, PA 19104 USA. pouch@seas.upenn.edu
Alison M
AM
Pouch
Theodore W
TW
Cary
Susan M
SM
Schultz
Chandra M
CM
Sehgal
D000465:Algorithms; D000818:Animals; D002417:Cattle; D005260:Female; D006979:Hyperthermia, Induced / Q000295:instrumentation / Q000379:methods*; D007091:Image Processing, Computer-Assisted; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000628:therapy*; D051379:Mice; D008819:Mice, Nude; D013696:Temperature; D014159:Transducers; D014463:Ultrasonography / Q000379:methods*