Two systems that independently allow the investigation of the response of individual unattached and attached microbubbles have previously been described. Both offered methods of studying the acoustic response of single microbubbles; in well defined acoustic fields. The aim of the work described here was to investigate the responses of single attached microbubbles for a range of acoustic pressures and to compare these to the backscatter from unattached single microbubbles subjected to the same acoustic fields.
Single attached BiSphere (TM) (Point Biomedical) microbubbles were attached to polyester with poly-L-lysine. Individual attached microbubbles were insonated at 1.6 MHz for acoustic pressures ranging from 300 to 1000 kPa using a Sonos5500 (Philips Medical Systems) research ultrasound scanner. Each microbubble was aligned to 6 cycle pulse, M-mode ultrasound beams, and unprocessed backscattered RIP data captured using proprietary hardware and software. The backscatter from these microbubbles was compared to that of single unattached microbubbles subjected to the same acoustic parameters. microbubbles were insonated several times to determine possible differences in rate of decrease of backscatter between attached and unattached microbubbles.
In total over 100 single attached microbubbles have been insonated. At 550kPa an acoustic signal was detected for 20% of the attached microbubbles and at 1000kPa for 63%. At acoustic pressures of 300kPa no signal was detected. Mean RMS fundamental pressure from attached and unattached microbubbles insonated at 800 kPa was 9.7 Pa and 8.7 Pa respectively. The ratio between the first two backscattered pulses decreased with increasing pressure. However, for unattached microbubbles the magnitude of the ratio was less than that of attached (at 550kPa mean ratio attached: 0.92 +/- 0.1, unattached: 0.28 +/- 0.2). There was no significant difference in the peak amplitude of the backscattered signal for unattached and attached microbubbles.
BiSphere (TM) microbubbles comprise an internal polymer shell with an albumin coating, resulting in a stiff shell. BiSphere (TM) microbubbles do not oscillate in the same manner as a softer shelled microbubble, but allow gas leakage which then performs free bubble oscillations. The results here agree with previous acoustic and optical microscopy measurements which show that a proportion of microbubbles will scatter and this number increases with acoustic pressure. The lack of difference in scatter between the unattached and attached microbubbles; may be attributed to the free microbubble oscillation being in the vicinity of the stiff shell, which may provide the same motion damping to a wall. Second pulse exposure shows that the wall becomes important in the survival of the free gas. These high quality measurements can be further improved by incorporating microbubble sizing to increase the specificity of the comparisons between unattached and attached microbubbles.
|Title of host publication||2008 IEEE ULTRASONICS SYMPOSIUM, VOLS 1-4 AND APPENDIX|
|Place of Publication||NEW YORK|
|Publisher||Institute of Electrical and Electronics Engineers (IEEE)|
|Number of pages||3|
|Publication status||Published - 2008|
|Event||IEEE Ultrasonics Symposium - Bejing, China|
Duration: 2 Nov 2008 → 5 Nov 2008
|Conference||IEEE Ultrasonics Symposium|
|Period||2/11/08 → 5/11/08|