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Research Papers

# HIFU Lesion Volume as a Function of Sonication Time, as Determined by MRI, Histology, and Computations

[+] Author and Article Information
Subhashish Dasgupta

Department of Mechanical Engineering, University of Cincinnati, Cincinnati, OH 45221

Janaka Wansapura, Ron Pratt

Department of X-Ray/Radiology, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH 45229

Prasanna Hariharan

Department of Mechanical Engineering, University of Cincinnati, Cincinnati, OH 45221; Division of Solid and Fluid Mechanics, Center for Devices and Radiological Health, U. S. Food and Drug Administration, Silver Spring, MD 20993

David Witte

Department of Histopathology, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH 45229

Matthew R. Myers

Division of Solid and Fluid Mechanics, Center for Devices and Radiological Health, U. S. Food and Drug Administration, Silver Spring, MD 20993

Rupak K. Banerjee1

Department of Mechanical Engineering and Department of Biomedical Engineering, University of Cincinnati, Cincinnati, OH 45221rupak.banerjee@uc.edu

1

Corresponding author. Also at Department of Mechanical, Industrial, and Nuclear Engineering University of Cincinnati, 593 Rhodes Hall, ML 0072, Cincinnati, OH 45221

J Biomech Eng 132(8), 081005 (Jun 15, 2010) (7 pages) doi:10.1115/1.4001739 History: Received July 04, 2009; Revised April 14, 2010; Posted May 11, 2010; Published June 15, 2010; Online June 15, 2010

## Abstract

Characterization of high-intensity focused ultrasound (HIFU) systems using ex vivo tissues is an important part of the preclinical testing for new HIFU devices. In ex vivo characterization, the lesion volume produced by the absorption of HIFU energy is quantified as operational parameters are varied. This paper examines the three methods used for lesion-volume quantification: histology, magnetic resonance (MR) imaging, and numerical calculations. The methods were studied in the context of a clinically relevant problem for HIFU procedures—that of quantifying the change in the lesion volume with changing sonication time. The lesion volumes of sonicated samples of porcine liver were determined using the three methods, at focal intensities ranging from $800 W/cm2$ to $1700 W/cm2$ and sonication times between 20 s and 40 s. It was found that histology consistently yielded lower lesion volumes than the other two methods, and the calculated values were below magnetic resonance imaging (MRI) at high applied energies. Still, the three methods agreed with each other to within a $±10%$ difference for all of the experiments. Increasing the sonication time produced much larger changes in the lesion volume than increasing the acoustic intensity, for the same total energy expenditure, at lower energy (less than 1000 J) levels. At higher energy levels, (around 1500 J), increasing the sonication time and increasing the intensity produced roughly the same change in the lesion volume for the same total energy expenditure.

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## Figures

Figure 1

Schematic of the experimental setup showing the HIFU transducer aligned with an excised tissue sample in degassed water medium. Setup is placed in the orifice of 3T MRI scanner.

Figure 2

The computational domain showing the geometry and boundary conditions used in calculating HIFU-induced temperature rise and lesion size

Figure 3

MRI image of lesions (in white) and numerically generated lesions (black outlines) are superimposed for 20 s, 30 s, and 40 s sonications at three depths (rows 1, 2, and 3)

Figure 4

Histology image of lesions at sonication times (a) 20 s, (b) 30 s, and (c) 40 s; (d) magnified view of the lesion boundary from the histology study

Figure 5

Bar charts comparing lesion volumes obtained by histology, numerical, and MRI imaging methods in rows (a) 1, (b) 2, and (c) 3. For row 3, the histology lesion size is not available.

Figure 6

HIFU lesion size versus sonication time; average of histology, numerical, and MR imaging results for the three rows

Figure 7

HIFU lesion size versus acoustic energy; average of histology, numerical, and MR imaging results for the three rows

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