Qualitative photoacoutics on contrast agent loaded polymeric microbubbles

Ultrasound mediated release of contrast agent loaded polymeric microbubbles

t.gans

Thesis GOAL To perform a feasibility study on contrast agent loaded polymeric microbubbles and their future role in photoacoustic imaging of tissues.

3Imaging of tumours

Microbubble destruction

5Principles of photoacoustic imaging

Gruneisen parameterAbsorbed optical energy

a photoacoustic image is related to the optical absorption in the tissue, as the incident photons must be absorbed to have any effect. Therefore,

a photoacoustic image IS an estimate of the destribution of acoustic pressure that arises following the absorption of a pulse of light.5

6Example of Photoacoustic Image

Source of contrast in a photoacoustic image is related to the optical absorption in the tissue.

The image itself is an estimate of the distribution of acoustic pressure that arises following the absorption of a pulse of light.6

The synthesis of contrast agent loaded microbubblesUSPIO (ultrasmall paramagnetic iron oxide particles)Rhodamine-BAurovist (commercially available gold nanospheres)peg-GNR-GNS (pegylated gold nanorods + gold nanospheres)

Comparing photoacoustic images pre and post microbubble destructionWhat is the best contrast agent?

Repeat step 2 with best contrast agent in a tomography set-up.The feasibility test

7Experimental procedure

7

8Microbubble loading and synthesis

9Microbubble characterisation

10Summary of characterisation

11Experimental set-up pre and post microbubble destruction

12Sample preparation

13Sample TreatmentControl settings: 3MHz, Focused Mode, 10V, 50Hz, 5 Cycles.Treatment settings: 3MHz, Focused Mode, 69V, 50Hz, 5 Cycles.Laser Settings: 532nm/780nm (3mJ/cm / 6.6mJ/cm), 10Hz, 10s.

1 PRE DESTRUCTIVE USUS properties (Frequency domain)PA properties2 POST DESTRUCTIVE USUS properties (Frequency domain)PA propertiesTreatment

We use the transducer to investigate how the sample interacts with transmitted ultrasound. Helps to determine whether microbubbles have been destroyed or not.13

14Results & Discussion

Regions at 6MHz, 9MHz, might be caused by MB explosions / eigenfrequency of microbubbles.

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15Results & discussion

Acoustic BackscatterRadiation ForcesLess attenuation of PA signals. More signals are able to reach the dectector.15

16Results & discussion

Redistribution of the medium.Less attenuation of PA signals. More singals able to reach the detectorRadiation forces on USPIO particles cause accumulation near interface layer

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17USPIO loaded mbs

US treatment appears to have a positive effect onPA signal contribution. Possibly due to 1) increased absorbed optical energy and 2) more PA signals being able to reach the detector.

Radiation forces cause signal shift to bottom of the bead

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18EMPTY Microbubbles

The polymer itself gives a very nominal PA signal

19Aurovist loaded MBs

The PA images contradict the results from the spectrophotometer, indicating the presence of Aurovist in the MB shell.

Radiation forces and accumulation of Aurovist results in increased concentration of gold which gives detectable PA signals.19

20Pegylated gold nanorods and gold nanospheres

PA images are similai to those of empty MBs. Results indicate that the payload was insufficient to generate a detectable PA signal.

21

Pegylated gold nanorods and gold nanospheres

The polymer is not generating detectable PA signals at a wavelength of 780nm.

22Rhodamine-B

Results follow a similar trend for USPIO and Aurovist loaded microbubbles.

23Summary

Contribution in PA signal after US treatment mainly attributed to:

Radiation forces causing a local re-distribution of the mediumReleased microbubble payloadLocal changes in the grunheisen parameterIncreased absorbance of optical energyLess attentuation of PA signals generated deeper down the bead because of MB destruction.

USPIO loaded MBs gave the best PA signal pre and post US treatment. Furthermore, USPIO has been FDA approved.

24conclusions

25Feasibility study

26Sample Treatment

Comparison of 2 beads based on 5 projections (both [0.09mg] USPIO).Bead 1: Plain USPIO. Bead 2: USPIO loaded MBs.

27PLAIN USPIO BEAD

28Features cross section PLAin USPIO BEAD

Negative photo with blue hueRegular photo

29BEAD containing USPIO LOADED Microbubbles

30USPIO loaded MBs post minus pre us treatment

31General conclusions and recommendationsWe were able to demonstrate an increase in the recorded PA signal after treating contrast agent loaded MBs with destructive US pulses.

The increase in PA signal after US treatment was mainly attributed to 1) radiation forces causing a local re-distribution of the medium 2) released MB payload 3) local changes in the Gruneisen parameter and 4) increased absorbance of optical energy. 5) Less attentuation of PA signals generated deeper down the bead.

In general, PA imaging based on the ultrasound triggered release of contrast agents is a viable modality, but there is room for improvements.

Finally, we showed that it is possible to locally release the MB payload.

======NOT EVERYTHING IS KNOWN =======

=======IMPROVEMENT IMAGE MODALITY======These improvements include, MBpayload optimisation, striving for MB monodispersity and lower MB rupture onsets.

========QUANTIFICATION=====The quantification of the released MB payload could possibly be done by employing the principle of acousto-optics

======USE IN THERAPEUTICS!!!======

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32gratitude

33Flythrough

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34Microbubble rupture onsets

35Bead alignement

36Microbubble treatment angles

37Slices us treatment