BACKGROUND
BASICS OF AN ULTRASOUND
To understand how micro bubbles operate during an ultrasound, first one has to become familiar with the machine and the different variables attached. Sound is measured by frequency, meaning how often an object will vibrate every second. Using the unit of Hertz, frequencies can be measured, varying from different types of animals.
The piezoelectric crystal continuously contracts and
expands, and as a result receives and emits sound
waves, Sound waves that rebound result in the
compression of the crystal to enable a voltage.
Air will result in reflection of of ultrasound waves,
inhibiting a sharp image to form. In return, a jelly is
applied to the patient's skin to avoid contact with
air. Attenuation, refraction, or reflection may occur
once the patient is prepped. When energy from the
ultrasound is absorbed into one's body, attenuation occurs. Matter with varying acoustic impedance can result in refraction, interfering with the waves original path. Lastly, waves have the possibility to be reflected back.
Frequencies
Frequencies can vary vastly between different organisms. As an insight, humans can hear frequencies between 20 Hz to 20,000 Hz while on the other side of the spectrum, bats can hear over 20,000 Hz. Hertz or Hz is the unit of measurement used for frequencies and can be compared to how often an object vibrates every second.
ULTRASOUND READINGS
Fluid is always depicted as black while tissue is gray.
1.
The denser the substance, the lighter it would appear, bone being the brightest.
2.
Doppler flow machines display the direction and speed of blood in vessels, as tumors have an irregular blood flow.
3.
The presence, position, and size of the organ is evaluated.
4.
The contour, echo pattern, and lack of or abundance of echo (echo rich, echo poor) is examined.
5.
Figure HWP.1 displays many echo rich amyloid depositions (the buildup of the protein, created from bone marrow that can deposit in tissues) in the wall of a gallbladder.
Figure HWP.2 displays echo rich depositions of the amyloid protein in the lining of the abdomen.
MICROBUBBLE STRUCTURE
Microbubbles have an exterior composed of lipids, polymers, and proteins with an interior filled with air, nitrogen, perfluorobutane, perfluorohexane, and more. The thickness of the microbubble should also be considered, as experts have the ability to customize the exterior. Stiffer microbubbles account for more polymers and lipids while flexible bubbles equate to more phospholipids. Coaxial electrohydrodynamic atomisation and microfluidic (T-junction) processing are two techniques used to manufacture microbubbles to increase their stability. Microbubbles on their journey through the bloodstream encounter various obstacles such as fragmentation, oscillation, and the merging of two bubbles to form one.
SONOGRAPHY
Sonography: The use of sound to manipulate the permeability of a cell's membrane for drug/gene delivery.
If a cell's membrane is damaged, agents such as micro-bubbles have the opportunity to cross over. Once inside, their gas core dissolves and reflect in the ultrasound field to create a clearer, more precise image.
The image HWP. displays a prostate cancer cell exposed to ultrasound, as part of the cell membrane is damaged and allows entry for agents such as micro-bubbles.
MECHANISMS USED IN SONOGRAPHY
Microbubbles have to encounter many obstacles such as passing blood vessels and the extra vascular compartment to reach the targeted area. Cavitation is a mechanism used to to enable microbubbles to overcome these obstacles, more specific terms being stable or inertial cavitation.
INERTIAL CAVITATION
STABLE CAVITATION
PROCESS:
Micrbubbles push on the walls of blood vessels to create a gap large enough for agents to fit through for drug delivery. With micro bubbles increasing and decreasing in size rapidly, fluid is produced in the process called microstreaming.
PROCESS:
When microbubbles collapse, shock waves can be produced to allow for a greater gap in blood vessels. As microbubbles collapse, the gas core can increase in temperature and pressure, allowing for the release of photons, shock waves, and fluid microjets.
Another act of inertial cavitation is jetting. Jetting occurs when a microbubble nears a solid, causing the fluid on the opposite side of the bubble to become irregular. The irregular movement of the fluid generates fluid to shoot from the center of the bubble to the solid surface.
Figure HWP.6 depicts stable cavitation.
A: A microbubble pushing against the blood vessle
B. A microbubble pulling at the blood vessel
D: The act of micro-streaming to enlarge a gap in the blood vessel
Figure HWP.6 depicts inertital cavitation.
C: The microbubble jets fluid to create a gap for drug delivery