Imaging Microbubbles Antony Hsu Shanti Bansal Daniel Handwerker Richard Lee Cory Piette.
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Transcript of Imaging Microbubbles Antony Hsu Shanti Bansal Daniel Handwerker Richard Lee Cory Piette.
Imaging Microbubbles
Antony Hsu
Shanti Bansal
Daniel Handwerker
Richard Lee
Cory Piette
Topics of Discussion
Brownian Motion What are these bubbles and why do we
use them? Following the Great Perrin - Diffusion and
Gravitational Motion of Microbubbles Optical Imaging of Microbubbles
What is ultrasound?
Ultrasound uses high frequency sound waves to image internal structures
The wave reflect off different density liquids and tissues at different rates and magnitudes
It is harmless, but not very accurate
Ultrasound and Microbubbles
Air in microbubbles in the blood stream have almost 0 density and have a distinct reflection in ultrasound
The bubbles must be able to fit through all capillaries and remain stable
We must examine the properties of microbubbles before using this technique
What is Brownian Motion?
Small particles are effected by so many different factors in a solution that they move around at in a random walk
Even if a solution seems stagnate, the microbubbles will still move
What is a Random Walk?
After every seconds, a particle moves in a direction at a velocity v
There is an equal probability that the particle will move in any direction no matter what its past direction was
Each particle is independent of all other particles
Characteristics of Random Walks
Particles have a net displacement of 0 (after time)
Particles usually remain in one region and then wander to other regions
1-m
Shell
Air or High Molecular Weight Gases
We’re all about Microbubbles (1)
We’re all about Microbubbles (4)
Used with ultrasound echocardiography and magnetic resonance imaging (MRI)
Diagnostic imaging - Traces blood flow and outlines images
Drug Delivery and Cancer Therapy
Left Arrow: Lipid-Coated MicrobubbleRight Arrow: Saline Microbubble
We’re all about Microbubbles (2)
We’re all about Microbubbles (3)
We’re all about Microbubbles (5)
Small (1-7 m) bubbles of air (CO2, Helium) or high molecular weight gases (perfluorocarbon).
Enveloped by a shell (proteins, fatty acid esters).
Exist - For a limited time only! 4 minutes-24 hours; gases diffuse into liquid medium after use.
Size varies according to Ideal Gas Law (PV=nRT) and thickness of shell.
How Bubbles Separate
Given a volume filled with different sizes of microbubbles, which bubbles move toward which end due to gravity?
Following Perrin, we look at the characteristic length (lambda) which will tell us about the motion of the bubble.
G = -c(x,t) D
T = D + G
How Bubbles Separate(2)
How do we get lambda()?
= k Tmeff g
K =Boltzman’s constant (1.38x10-23 J/K)T = Temperature in Kelvin (300K)g = gravity(9.81 m/s2)meff = effective mass
meff = (4/3) r3 (p - w)p = density of particlew = density of water(1g/cm3)r = radius of bubble(cm)
The size of of microbubbles is known(1-7mm). Therefore, the only factor to be determined is the density of the microbubble.With gas-filled bubbles, the thickness and density of the shell gives the bubble its mass.
How Bubbles Separate(3)
Why is all this important?Well, we want a bubble that will not “float” or “sink.”
By adjusting the shell thickness to the force of gravity,
we can achieve “neutral buoyancy.” Basically, by designing the bubble such that
the density as a whole has the density of water, then the bubble will undergo only diffusion flux.
Perrin’s light microscope
Perrin did research on diffusion and brownian motion He conducted experiments to examine diffusion
through emulsions He built used a light microscope to visualize emulsions
at different depths Perrin determined depth of pictures by the following
formula: H=CH’. C = relative refractive index of the two media which the cover-glass separates. H’ = height of microscope.
Perrin’s Light Microscope
Optical target trackingon image sequences
Computer equipment improvement has lead to higher resolution optical imaging
Most computerized optical pattern recognition filters today have been designed to process one image at a time. (isolated images)
These filters would prove ineffective in recording microbubbles moving through the blood stream (image sequencing).
Isolated images do not deal with changes in background, sequential imaging does
this problem leads to the development of the “two image system”--a model that takes into account two successive frames
this model is based on the maximum-likelihood (ML) estimation The ML estimation takes into account the continuity between two
successive frames
Optical target tracking (cont.)
One frame is taken at a known location, one at an “estimated” location
This estimated location will depend on location and size of the object
In this case, the size of microbubble will remain constant (approximately the size of a red blood cell). However, the location will vary.
Idle time between frames depends directly on probability factors.
The two frames are correlated, forming a clear and concise picture of the object’s movement.
A Novel Technique to Visualize Microbubbles
An optical tracking system is placed on Perrin’s light microscope
Allow easy visualization of microbubbles and analysis
A Novel Method of Microbubble Visualization
Future of Microbubbles
Using microbubbles as a pressure sensitive gauge (especially important for heart)
Enhancing ultrasound/ MR images. Novel gasses used for microbubbles.
Drug delivery