Moo Ho Bae

P1C-6 Improved Ultrasonic Elasticity Imaging with Center Frequency Estimation and Global Shift Compensation

Ultrasonic elastography images the degree of hardness of a medium by estimating the displacement of ultrasonic signals before and after applying compression to the medium. The phase difference is first computed from the complex baseband signals using autocorrelation, and then the displacement is obtained from it. To obtain the displacement from the phase difference, one needs to know the center frequency of a wideband ultrasonic signal exactly, but it tends to change at every depth depending on the speckle and attenuation characteristics. Thus, accurate estimation of the displacement from the phase difference requires the knowledge of an exact center frequency. We show by simulation and experiment that the center frequency estimation combined with the global shift compensation greatly improves the strain image quality

Characterization of the Harmonic Generation from Cavitating Bubbles Interacted with a Diagnostic Ultrasound in the Focal Region of High Intensity Focused Ultrasound

Harmonic image (HI) has been proposed to be promising for visualizing lesions produced by therapeutic high intensity focused ultrasound (HIFU). The study characterizes harmonics generated from the bubble cavitating at the focal region of a therapeutic HIFU field in response to a typical diagnostic ultrasound. Based on Gilmore model, it was simulated the nonlinear dynamics of the bubble being resonated at 1 MHz of the therapeutic ultrasound and driven by a typical 3.5 MHz diagnostic pulse. It was shown that harmonic generation increased with MI in a sigmoid pattern where the rapid and transient changes occurred between 0.5 and 2 in MI. For whole ranges of MI (less than 8), the sub-harmonic was the predominant in magnitudes over other harmonic bands. This reveals that, if HI is considered for improving the detection of focal legion highly cavitating caused by a HIFU field, the sub-harmonic component would be a preferred parameter rather than the 2nd harmonic which has been commonly used in current harmonic imaging.

Ultrasonic Characterization of Thermal Distribution in Vicinity for a Cylindrical Thermal Lesion in a Biological Tissue

The study considers an ultrasonic characterization on the thermal distribution in vicinity for a cylindrical thermal lesion formed in a biological tissue. The cylindrical heat source is made of a standard nichrome wire with the diameter of 1 mm. The wire was inserted inside a pork muscle housed in a cuboidal container made of perspex. The heat is conducted radially outwards from the wire to the surrounding tissue. Thermal distribution near the heated wire was predicted by numerically solving a bioheat transfer function using FemLab (Comsol, Inc.). As the wire temperature was raised from the environmental temperature 20 °C to more than 80 °C in steps of 5 °C, ultrasonic B-scan images were acquired at each temperature. We assessed the feasibility of detecting the lesion boundary using changes in echogenicity, changes in centroid frequency due to attenuation, tissue moving characteristics resulting from changes in the speed of sound, and elastograms. These observations will be of use in improving ultrasonic monitoring and guiding in HIFU surgery and thermo-therapeutic process in general.