The destruction experiments & Introduction to cavitation

Sheng-Chieh Lu () and Chih-Kuang Yeh ()

Ultrasound Imaging LaboratoryDepartment of Biomedical Engineering and Environmental

Sciences, National Tsing Hua University

OUTLINE

Review for molecular imageDestruction experiments of liposomesIntroduction to cavitationApplications of cavitationDiscussions & ConclusionsFuture worksReference

Molecular imaging by ultrasound

Molecular imaging is to SEE the specific tissue at molecular level

Red blood cell

Specific molecule

Ultrasound transducer

Targeted agent

Too tiny to see

Small vessel or capillary

Liposomes as UCAscz = Mismatch impedance

11c22c echo signal

incident ultrasound

hydrophile side

anti-hydrophile side

Lipid-dissolved

Lipid-dissolvedBi-layer structure

Diameter of Liposomes< 1 um

B-scan setup

A 25-MHz transducer (13-mm focal length, 0.5-inch aperture) was aligned at a motion stage and focused on a vessel in phantom

B-mode scan, sample rate 120-MHz, width 4-mm, depth 4-mm

Motion Controller

5900PR

PCI-6602

Trigger

Position

A/D

Clock

RF

Diameter = 2.4 mm

TransducerB-modescan

Diplexer

Properties of air liposomes

Low buffer temperature Proper vortex time (~120 seconds)Effective working time is about 10 min

Destruction experiments of liposomes

Setup for destruction

Motion Controller

5900PR

PCI-6602

Trigger

Position

A/D

Clock

RFCase 1Pressure: No

Case 2Sine wave 5 cyclesPressure: 0.4 MPa

Case 3Sine wave 5 cyclesPressure: 1.8 MPa

25 MHz transducer

B-modescan

WaveGenerator

33120

Diameter = 2.4 mm

PowerAmplifier

Trigger

Sine wave

Pulse

2.25 MHz transducer

Diplexer

Results of destruction

Images of dstructionNon-pressure 0.4 MPa 1.8 MPa

1st min

110th sec

3rd min

10th min

SpectrumNon-pressure 0.4 MPa 1.8 MPa

Spectrum

Short conclusions & discussions

The acoustic pressure threshold of destruction of liposomes is below 0.4 MPa at 2.25 MHz central-frequency.It is observed that some broadband signals in high frequency.

Introduction to cavitation

Cavitation phenomenon

Inertial cavitation was first studied by Lord Rayleigh in the late 19th century.

When a volume of liquid is subjected to a sufficiently low pressure it may rupture and form a cavity. This phenomenon is termed cavitation inception.

May occur behind the blade of a rapidly rotating propeller or on any surface vibrating underwater with sufficient amplitude and acceleration.

Cavitation phenomenon

Shrimp light phenomenon Francis turbine, cavitation damage

Animation of cavitation

High Pressure

Low Pressure

Acoustic shock wave

Acoustic shock wave

High Temperature, several thousand kelvins

Two types of cavitation

Cavitation is generally classified into two typesstable cavitation and inertial cavitation

stable cavitation inertial cavitation

Setup for detecting IC & SC

Signals of SC & IC

(a) typical background noise level

(b) stable cavitation. (c) inertial

cavitation. (d) both inertial and

stable cavitation.

Broadband signal of liposomes

Non-pressure 0.4 MPa 1.8 MPa

Applications of cavitation

Gene transfection with ultrasound

Micro bubblePlasmid DNA

Exterior

Interior

Plasmid DNA

Exterior

Interior

Cell membrane

Cell membrane

Other applicationsAlthough cavitation is undesirable in many circumstances, but not always the case.

Supercavitating torpedoes the torpedo in a large bubble of cavitation. By greatly reducing contact with water, these torpedoes can go faster.

Ultrasonic cleaning.

Water purification

In industry, cavitation is often used to homogenize.

Discussions & Conclusions

Threshold of the experiment to induce cavitation?It is almost sure that liposomes will be destructed under burst pulses at 1.8 MPa in pressure.From spectrum, broadband was found and as well a peak at 12.5 MHz. Is that peak a sub-harmonic of 25 MHz pulse?From destruction, we observe the broadband noise caused by inertial cavitation.

Future works

Substitute microbubble UCAs with liposomes to produce cavitationexperiment includes:Determine the threshold Gene transfection experiment

Reference

O. Couture et al. (2006) Ultrasound in Med. & Biol., 32:73-82

S. H. Huang et al. (2001) Journal of Pharmaceutical Sciences, 90:1917-1926.

C. K. Yeh et al. (2006),9th Western Pacific Acoustics Conference, Seoul, Korea.

Paul A. Dayton et al. (2002) Journal of magnetic resonance imaging 16:362377.

THANK YOU!

The destruction experiments & Introduction to cavitationOUTLINEMolecular imaging by ultrasoundLiposomes as UCAsB-scan setupProperties of air liposomesDestruction experiments of liposomesSetup for destructionResults of destructionImages of dstructionSpectrumSpectrumShort conclusions & discussionsIntroduction to cavitationCavitation phenomenonCavitation phenomenonAnimation of cavitationTwo types of cavitationSetup for detecting IC & SCSignals of SC & ICBroadband signal of liposomesApplications of cavitationGene transfection with ultrasoundOther applicationsDiscussions & ConclusionsFuture worksReferenceTHANK YOU!