1. Ultrasonic Thermometry Hirad Karimi MBP1028

2. Outline • Introduction • Thermometry • Current methods • US thermometry • Physics • Different techniques • Summary and Discussions

3. Thermometry • 3D distribution of temperature • 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

4. 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

5. 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

6. Speed Vs Temperature Nasoniet al Techavipooet al

7. Attenuation Coef. Vs Temperature Techavipooet al

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

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

10. 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

11. 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

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

13. 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.