Jihee Jung

Distribution of temperature elevation caused by moving high-intensity focused ultrasound transducer

Ultrasonic thermal treatment for dermatology has been developed using a small high-intensity focused ultrasound (HIFU) transducer. The transducer moves horizontally at a constant while it emits focused ultrasound because the treatment needs a high-temperature area in skin tissue over a wide range of depths. In this paper, a tissue-mimicking phantom made of carrageenan and a thermochromic film were adopted to examine the temperature distribution in the phantom noninvasively when the focused ultrasound was irradiated from the moving transducer. The dependence of the high-temperature area on the irradiated acoustic energy and on the movement interval of the HIFU was analyzed experimentally. The results will be useful in ensuring safety and estimating the remedial value of the treatment.

Estimation of thermal distribution in tissue-mimicking phantom made of carrageenan gel

To probe the temperature elevation effect caused by ultrasound, the use of a tissue-mimicking phantom was newly suggested. Carrageenan gel was adopted to realize not only the required transparency for visualization but also the acoustic characteristics similar to those of human tissue. To visualize the temperature elevation effect inside the phantom, thermochromic film with a critical temperature of discoloration was introduced. From the visualized image, the temperature elevation due to planar and focused ultrasound in the phantom was obtained quantitatively. To verify the suggested method, the bioheat equation was solved numerically by the Fourier transform method. The theoretical results show good agreement with experimental ones regarding the temperature distribution while plane and focused ultrasound was irradiated into the phantom.

Concentration of liquid sample for gamma-ray spectroscopy with ultrasonic nebulization

Radionuclide analysis of sea water is necessary to monitor environmental contamination due to the radioactive substances from nuclear facilities. However, it is difficult to analyze the nuclides promptly with the conventional method of coprecipitation during emergencies because the method requires long precipitation times. In this study, an effective concentration method with ultrasonic nebulization was suggested for sea water samples. When a sea water sample of 40 L was concentrated, 30 h was required with the conventional method, whereas it took less than 11 h with the suggested method. The validity of the suggested method was verified by gamma-ray spectroscopy.

Single nano particle collecting by using ultrasonic humidifier

The single nano particle state was obtained by using a ultrasonic humidifier. To control the surface tension, the concentration of methanol changed in the suspension of TiO2 nano particle. The collecting effect was investigated by measuring the particle size distribution. As the surface tension was decreased by increasing the concentration of methanol, the particle size at the peak of distribution was decreased and the number of particles per unit volume was increased. The nano particles with intended size could be collected by controlling the surface tension of the suspension.

Tissue Mimicking Phantom for Visualization of Temperature Elevation Caused by Ultrasound

To probe the temperature elevation effect caused by ultrasound, a tissue mimicking phantom was newly suggested. A carrageenan gel was adopted to realize not only the required transparency for visualization but also acoustic characteristics similar to human tissue. To visualize the temperature elevation inside phantom, thermochromic film with a critical temperature of discoloration was introduced. Acoustic characteristics of the tissue mimicking phantom were examined when the concentrations of carrageenan and sucrose changed. As the results, the attenuation coefficient of the phantom could be controlled in the range of 0.44~0.49 dB/cm/MHz, and the acoustic impedance in the range of 1.52~1.77 Mrayls. We could control the acoustic characteristics of the phantom by different concentration of carrageenan and sucrose, and it was possible to examine the temperature elevation caused by ultrasound in the phantom. The suggested method was verified by noninvasively visualizing the temperature elevation due to planar and focused ultrasound using the fabricated phantom.

Visualization of temperature elevation due to focused ultrasound generated by tone burst wave

The temperature elevation effect due to burst wave ultrasound was investigated experimentally. To observe the temperature distribution when focused ultrasound is radiated onto an acoustic dissipative medium of gelatin, a thermochromic film was used to perform a temperature visualization method. The discolored area on the thermochromic film caused by the ultrasound increased with different speeds depending on the duty cycle of the tone burst signal. Using the image process, the high-temperature region, the discolored region, caused by the focused ultrasound was measured. It is confirmed experimentally that the high-temperature area can be controlled by adjusting the duty cycle of the burst signal.

Experimental analysis of temperature elevation in ultrasonic beam from circular piston

The temperature distribution change due to plane ultrasound was analyzed experimentally with the ultrasonic visualization method. A thermochromic film inserted in the acoustic dissipative medium made of gelatin changed color because of the heat caused by the ultrasound propagation. From the image data of the discolored area on the film and the temperature change measured with a point-type thermal sensor, a temperature function of the value of the pixel data on the image was obtained. Using this function, the temperature distribution can be estimated noninvasively.

Visualization of temperature elevation in ultrasonic beam from circular piston

The temperature elevation due to ultrasound was investigated in a dissipative medium using gelatin with the thermochromic particle. As the ultrasonic source, a plane circular piezoelectric transducer was used. A thermochromism layer of 100 μm was inserted between two gelatin layers. The 670 kHz-ultrasound irradiated the medium for less than 1 min. The discolored area due to the ultrasound increased as the exposure time increases. Through the image processing, the temperature increasing tendency along the acoustic axis was confirmed experimentally.