Enhanced thermal effect using magnetic nano-particles during high-intensity focused ultrasound
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ABSTRACT
Collateral damage and long sonication times occurring during high-intensity focused ultrasound (HIFU) ablation procedures limit clinical advancement. In this reserarch, we investigated whether the use of magnetic nano-particles (mNPs) can reduce the power required to ablate tissue or, for the same power, reduce the duration of the procedure. Tissue-mimicking phantoms containing embedded thermocouples and physiologically acceptable concentrations (0%, 0.0047%, and 0.047%) of mNPs were sonicated at acoustic powers of 5.2 W, 9.2 W, and 14.5 W, for 30 seconds. Lesion volumes were determined for the phantoms with and without mNPs. It was found that with the 0.047% mNP concentration, the power required to obtain a lesion volume of 13 mm3 can be halved, and the time required to achieve a 21 mm3 lesion decreased by a factor of 5. We conclude that mNPs have the potential to reduce damage to healthy tissue, and reduce the procedure time, during tumor ablation using HIFU. No MeSH data available. |
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Mentions: Lesion volume was computed through repeated use of the exponential integral (Eq 1), to compute the temperature at locations where it was not measured. Eq 1 requires knowledge of the on-axis absorbed energy αI0 and radius r0 of the ultrasound beam for a given set of exposure conditions (e.g. mNP concentration) and location of interest. The parameters αI0 and r0 in the T1-T2 plane were found by varying their values and choosing the pair that resulted in a temperature trace (defined by Eq (1)) that most closely matched that at the location of T1 (or T2, since the two traces were similar, the beam being equidistant from both). Varying the values for αI0 and r0 consisted of generating a grid of 11 x 11 values for the pair (αI0 and r0), each choice resulting in a change in peak temperature of about 0.5 deg C. The pair resulting in the closest root-mean-square (r.m.s.) agreement with the experimental trace was selected, provided the r.m.s. error was less than 3%. Fig 4 shows the temperature predicted by the exponential integral function alongside the experimental values, for fitting parameters of αI0 = 0.14 x 10−3 W/mm3 and r0 = 1.17 mm. The mNP concentration for Fig 4 is 0.047% and the power is 5.2 W. The quantity αI0 outside the T1-T2 plane could be obtained from the relative intensity profile for the transducer, assuming the absorption coefficient to be the same at the two locations. The profile for the fundamental frequency (obtained from the manufacturer, Sonic Concepts Inc., Bothell WA.) is shown in Fig 5. The beam width at locations outside the T1-T2 plane was computed using a conservation-of-energy relation: the product of axial intensity and the square of the beam radius is constant, except for the attenuation loss between the two axial locations. |
View Article: PubMed Central - PubMed
Collateral damage and long sonication times occurring during high-intensity focused ultrasound (HIFU) ablation procedures limit clinical advancement. In this reserarch, we investigated whether the use of magnetic nano-particles (mNPs) can reduce the power required to ablate tissue or, for the same power, reduce the duration of the procedure. Tissue-mimicking phantoms containing embedded thermocouples and physiologically acceptable concentrations (0%, 0.0047%, and 0.047%) of mNPs were sonicated at acoustic powers of 5.2 W, 9.2 W, and 14.5 W, for 30 seconds. Lesion volumes were determined for the phantoms with and without mNPs. It was found that with the 0.047% mNP concentration, the power required to obtain a lesion volume of 13 mm3 can be halved, and the time required to achieve a 21 mm3 lesion decreased by a factor of 5. We conclude that mNPs have the potential to reduce damage to healthy tissue, and reduce the procedure time, during tumor ablation using HIFU.
No MeSH data available.