Infographics / Ultrasound Physics

Thermal bioeffects and mechanisms of tissue heating

A comparison of ultrasound-induced heating in three tissue scenarios. Homogeneous soft tissue (thermal index TIS) has low absorption and the smallest temperature rise. Bone within the beam near the focus (TIB) and cranial bone near the transducer surface (TIC) have high absorption and the largest temperature rise, because local temperature rise is proportional to twice the absorption coefficient times intensity, and bone absorbs far more than soft tissue. A panel lists factors that increase the temperature rise: higher time-averaged intensity, longer dwell time, lower perfusion, and additive baseline plus probe self-heating.

Ultrasound tissue heating compared by tissue type and thermal index A comparison of ultrasound-induced heating in three tissue scenarios. Homogeneous soft tissue (thermal index TIS) has low absorption and the smallest temperature rise. Bone within the beam near the focus (TIB) and cranial bone near the transducer surface (TIC) have high absorption and the largest temperature rise, because local temperature rise is proportional to twice the absorption coefficient times intensity, and bone absorbs far more than soft tissue. A panel lists factors that increase the temperature rise: higher time-averaged intensity, longer dwell time, lower perfusion, and additive baseline plus probe self-heating. Ultrasound tissue heating: soft tissue versus bone Tissue Index Absorption Relative tissue heating (qualitative) Soft tissue homogeneous TIS low Bone in beam at or near the focus TIB high Cranial bone near transducer surface TIC high greater temperature rise Local temperature rise is proportional to 2αI (absorption coefficient α × intensity I); bone's α far exceeds soft tissue's. What increases the temperature rise Higher time-averaged intensity, ISPTA — pulsed Doppler heats more than B-mode Longer dwell time holding the beam on one location Lower tissue perfusion — less heat carried away by blood flow Higher baseline temperature and probe self-heating add to the total
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