Ultrasonic Thermometry Hirad Karimi MBP1028

Outline Introduction US thermometry Summary and Discussions Current methods US thermometry Physics Different techniques Summary and Discussions

Thermometry 3D distribution of temperature Different techniques Crucial for the extent of damage Controlling heat delivery Protecting healthy tissues from thermal exposure Ensuring adequate thermal dosimetry Different techniques Magnetic Resonance Imaging Impedance Tomography Microwave Radiometry Backscattered Ultrasound techniques

Ultrasound Thermometry Why US Thermometry? Non-invasive Relatively low cost Real-time data collection and signal processing Deep penetration Good spatial and temporal localization Compatibility with US therapeutic technologies

Physical and Biological effects When a region of tissue heated: Speed of sound Thermal expansion Changes in tissue stiffness Tissue US attenuation Leads to time-shifts between backscattered US RF-echoes

Speed Vs Temperature Nasoni et al Techavipoo et al

Attenuation Coef. Vs Temperature Techavipoo et al

Techniques Frequency dependent attenuation (Ueno et al) Tracking changes in acoustic properties before and after heating

Techniques (cont’d) Backscattered power (Straube et al) Measuring backscattered power differences between power measured before and after heating

Techniques (cont’d) Speed of sound and Thermal expansion (Simon et al) 1D: tracking frequency variation of the echo components in the spectral domain 2D: tracking echo time-shifts in the time domain

Techniques (cont’d) Optical-flow (Mehrabani et al) Detecting shifts in speckle pattern location of ultrasound B-Mode digital images from a region of tissue undergoing thermal therapy

Limitations Signal-to-noise ratio Time-consuming process Low spatial resolution Time-consuming process Low temporal resolution Motion artifacts Compromises time-shift estimations

References Mehrabani, Bahram M., Tavakoli, Vahid, Abolhassani, Mohammad D., Alirezaie, Javad and Ahmadian, Alireza. An efficient temperature estimation using optical-flow in ultrasound B-mode digital images 2008 Nasoni, R. L., Bowen, T., Connor, W. G. and Sholes, R. R. In vivo temperature dependence of ultrasound speed in tissue and its application to noninvasive temperature monitoring 1979 Simon, C., VanBaren, P. and Ebbini, E. S. Two-dimensional temperature estimation using diagnostic ultrasound 1998 Straube, W. L., Arthur, R. M. Theoretical estimation of the temperature dependence of backscattered ultrasonic power for noninvasive thermometry 1994 Ueno, S., Hashimoto, M., Fukukita, H. and Yano, T. Ultrasound thermometry in hyperthermia 1990 Vaezy, Shahram, Shi, Xuegong, Martin, Roy W., et al. Real-time visualization of high-intensity focused ultrasound treatment using ultrasound imaging 2001 Techavipoo U, Varghese T, Chen Q, Stiles TA, Zagzebski JA, Frank GR. Temperature dependence of ultrasonic propagation speed and attenuation in excised canine liver tissue measured using transmitted and reflected pulses. Journal of the Acoustical Society of America 2004;115:2859–2865.