5th EuropEan MolEcular IMagIng MEEtIng - ESMI

5th EuropEan MolEcular IMagIng MEEtIng – EMIM2010
Standardization of molecular PBCA-microbubbles for routine use
Fokong S. , Liu Z. , Gätjens J. , Kiessling F. .
Helmholtz Institute, Aachen, Germany
sfokong@ukaachen.de
Introduction: To develop standardized highly monodisperse
targeted polybutylcyanoacrylate (PBCA)microbubbles
for contrast enhanced molecular
ultrasound imaging.
Methods: PBCA-microbubbles were produced by
mechanical agitation and size isolated by centrifugation.
Physical parameters of the size optimized
microbubbles and regular (Sonovist) microbubbles
were compared. Targeting of the microbubbles for
molecular imaging was achieved by covalently binding
streptavidin molecules onto the shell of surface
activated PBCA-microbubbles and the subsequent
attachment of biotinylated markers. The amount of
targeting ligands on the surface of the microbubbles
was quantified using a fluorescence activated cell
sorter (FACS). The suitability of these microbubbles
for destructive imaging methods like power Doppler
ultrasound, used for the evaluation of the degree of
angiogenesis and the effect of antiangiogenic therapy,
was investigated in gelatin phantoms.
Results: Following a new protocol for the synthesis
of PBCA microbubbles, highly monodisperse populations
could be isolated. Curves obtained from
particle sizer measurements showed size isolated
microbubbles which are normally distributed with
a narrower standard deviation (> 97% ± 1.0-3.0 µm)
in comparison to regular Sonovist microbubbles
(> 97% ± 0.2–10 µm). The high monodispersity was
also confirmed by SEM (scanning electron microscopy)
pictures. The population distribution remained
constant even with prolonged storage in solution
(over 4 months), indicating high stability. Comparison
of the resonance frequencies and the persistence
in an ultrasound field showed a significantly lower
resonance frequency and a lower persistence in the
ultrasound field for the monodispersed microbubbles
compared to the polydispersed microbubbles.
The high monodispersity was maintained even with
covalent coupling of streptavidin molecules onto the
shell of the microbubbles. A quantification of the
number of streptavidin molecules on the surface by
the use of a FACS gave approximately 2 x 10 4 streptavidin
molecules per microbubble. This number can
be tuned according to the degree of surface activation
of the microbubbles. Destructive imaging using
SPAQ (Sensitive Particle Acoustic Quantification)
[1] was also possible with these monodispersed microbubbles
showing a highly reproducible destruction
with high mechanical index ultrasound waves.
Conclusions: Size optimized non modified PBCAmicrobubbles
are more suitable for use as ultrasound
contrast agents in comparison to regular Sonovist
microbubbles. The simplified synthetic protocol allows
for a speed up in the synthesis and purification
process (6 days vs. 3 h). The low resonance frequency
and persistence lead to more efficient detection using
power Doppler techniques. Also, given the relative
high number of targeting ligands which can be
easily attached to their surface, and the possibility to
efficiently quantify their amounts in a region of interest,
they are very suitable for molecular imaging of
intravascular targets. In summary, the tuned properties
of the microbubbles presented in this study, will
make them very interesting as building blocks for
tailoring of specific contrast agents for ultrasound.
Acknowledgement: This work is supported by the
German Federal Ministry of Education and Research
(BMBF-0315017).
References:
1. M. Reinhardt, P. Hauff, A. Briel, V. Uhlendorf, M. Schirner,
Sensitive particle acoustic quantification (SPAQ),
Investigative Radiology 40 (2005) 2-7.
EuropEan SocIEty for MolEcular IMagIng – ESMI
P-062
poStEr
PROBE DESIGN