The effects of residual temperature rise on ultrasound heating

Abstract

In recent theoretical studies, the temperature rise produced by diagnostic ultrasound was estimated by solving the Bioheat Transfer Equation (BHTE) but ignoring the initial temperature rise. The temperature rise was determined in our study by the BHTE including an initial temperature rise. We discuss how the initial temperature rise occurs during an ultrasound examination, and how the initial temperature rise affects subsequent ultrasound heating. We theoretically show that the temperature rise produced by the ultrasound examination (exposure time of 500 s) in a tissue sample having an initial temperature rise was higher than that in a tissue sample with no initial temperature rise that was exposed to ultrasound (exposure time of 1200 s). The theoretical results for these two cases were 5.64 degrees C and 3.58 degrees C, respectively. In our experimental study, the highest temperature rise was measured in the presence of an initial temperature rise as in the theoretical study under the same exposure conditions. Mean temperature rises for tissue without an initial temperature rise and for tissue with an initial temperature rise were 2.42 +/- 0.13 degrees C and 3.62 +/- 0.17 degrees C, respectively. Both theoretical and experimental studies show that unless the initial temperature rise produced by the first ultrasound examination decreases to 0 degrees C, the next ultrasound examination on the same tissue sample may cause the temperature rise to be higher than expected.

A Generic Bioheat Transfer Thermal Model for a Perfused Tissue

“…Several diagnostic and therapeutic protocols require the determination of in vivo temperatures to plan and optimize the protocols [1–5]. To manage computational costs, temperatures in a tissue embedded with ‘small’ (< 1 mm in diameter) more frequent blood vessels are determined using approximate thermal models known as the bioheat transfer models (BHTMs) [6–8].…”

The Effects of Residual Temperature Rise on Ultrasound Heating

“…It should be noted that also in the earlier paper of Karagoz and Kartal (2005), the same error in the theoretical calculation of the temperature drop in the cooling period occurs. That paper seems to contain in their Fig.…”

“…In our previous papers (Karagoz and Kartal 2005;2006), we calculated the residual temperature rise (RTR) at the focus of a transducer by assuming that the uniform temperature field occurs at the end of the first ultrasound examination to obtain worst-case temperature rise. After all, Lubbers (2006) theoretically proposed that there is no need to consider the effect of residual temperature rise for the case of a single stationary transducer.…”

“…In our previous papers, we calculated an RTR at focus (Karagoz and Kartal 2005;2006). In this study, we also obtained the temperature rise at other locations in the presence of the RTR.…”

Noninvasive measurement of temperature for simulated tissue based on piezoelectric micromachined ultrasonic transducers

“…thermal therapy has the advantage of delivering ultrasonic energy to treatment volume in a non-invasive manner [5,6]. During actual clinical, temperature monitoring of the treatment volume directly affects the therapeutic effect, which requires a certain temperature to destroy cancer cells without damage to normal cells [7,8]. Moreover, noninvasive treatments require noncontact temperature measurements to avoid additional harm to patients [9].…”