Journal
ULTRASOUND IN MEDICINE AND BIOLOGY
Volume 39, Issue 10, Pages 1785-1793Publisher
ELSEVIER SCIENCE INC
DOI: 10.1016/j.ultrasmedbio.2013.04.010
Keywords
High-intensity focused ultrasound; Peri-nephric fat; Attenuation; De-focusing; Thermal ablation; Renal cancer; Kidney
Funding
- Oxford Biomedical Research Centre [A90104]
- EPSRC [EP/F02617X/1] Funding Source: UKRI
- Engineering and Physical Sciences Research Council [EP/F02617X/1] Funding Source: researchfish
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High-intensity focused ultrasound (HIFU) is an attractive therapy for kidney cancer, but its efficacy can be limited by heat deposition in the pre-focal tissues, notably in fat around the kidney (peri-nephric fat), the acoustic properties of which have not been well characterized. Measurements of attenuation were made using a modified insertion-loss technique on fresh, unfixed peri-nephric fat obtained from patients undergoing kidney surgery for cancer. The de-focusing effect of changing the position of the fat layers was also investigated using fresh subcutaneous fat from euthanized pigs. The mean attenuation of human peri-nephric fat was found to be 11.9 +/- 0.9 Np/m (n = 10) at 0.8 MHz, the frequency typically used for HIFU ablation of kidney tumors, with a frequency dependence of f(1.2). A typical 2- to 4-cm thickness of peri-nephric fat would result in a de-rated intensity of 3%-62% at 0.8 MHz compared with a hypothetical patient with no peri-nephric fat. Through the use of freshly excised porcine subcutaneous fat, the presence of fat 100 mm in front of the focus was found to have a defocusing effect of approximately 1 mm in both transverse directions, which corresponds to a full HIFU beam width off-target. Peri-nephric fat may significantly affect both the intensity and accuracy of HIFU fields used for the ablation of kidney cancer. (E-mail: robritchie1@gmail.com or robritchie@doctors.org.uk) (C) 2013 World Federation for Ultrasound in Medicine & Biology.
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