Dual-high-frequency ultrasound excitation on microbubble destruction volume.
OBJECTIVE
The goal of this work was to test experimentally that exposing air bubbles or ultrasound contrast agents in water to amplitude modulated wave allows control of inertial cavitation affected volume and hence could limit the undesirable bioeffects.


METHODS
Focused transducer operating at the center frequency of 10 MHz and having about 65% fractional bandwidth was excited by 3 micros 8.5 and 11.5 MHz tone-bursts to produce 3 MHz envelope signal. The 3 MHz frequency was selected because it corresponds to the resonance frequency of the microbubbles used in the experiment. Another 5 MHz transducer was used as a receiver to produce B-mode image. Peak negative acoustic pressure was adjusted in the range from 0.5 to 3.5 MPa. The spectrum amplitudes obtained from the imaging of SonoVue contrast agent when using the envelope and a separate 3 MHz transducer were compared to determine their cross-section at the -6 dB level.


RESULTS
The conventional 3 MHz tone-burst excitation resulted in the region of interest (ROI) cross-section of 2.47 mm while amplitude modulated, dual-frequency excitation with difference frequency of 3 MHz produced cross-section equal to 1.2mm.


CONCLUSIONS
These results corroborate our hypothesis that, in addition to the considerably higher penetration depth of dual-frequency excitation due to the lower attenuation at 3 MHz than that at 8.5 and 11.5 MHz, the sample volume of dual-frequency excitation is also smaller than that of linear 3-MHz method for more spatially confined destruction of microbubbles.
Shen
Che-Chou
CC
Department of Electrical Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan.
Su
Shin-Yuan
SY
Cheng
Chih-Hao
CH
Yeh
Chih-Kuang
CK
D003287:Contrast Media / Q000737:chemistry*; D045423:Microbubbles; D019047:Phantoms, Imaging; D010743:Phospholipids / Q000737:chemistry*; D013459:Sulfur Hexafluoride / Q000737:chemistry*; D014159:Transducers; D014463:Ultrasonography / Q000379:methods*
D003287:Contrast Media; D010743:Phospholipids; C420843:contrast agent BR1; D013459:Sulfur Hexafluoride