In this section we are going to explain and clarify some terms that every radiologist wanting to keep up pace with the applications of nanotechnology in imaging should know in the year 2015.
What do we mean by the term nanotechnology?
Nanotechnology is a relatively elastic term that has been used through time to describe many different things.
For the layman nanotechnology describes more or less everything that has to do with the “magical” world of the very small things.
In a more scientific context “nanotechnology” refers to the science,
engineering and technology conducted at the nanoscale,
which is about 1 to 100 nanometers.
It is worth mentioning at this point that x-rays have wave lengths roughly between 0,01 njm and 10nm.
What is different at the nanoscale?
What makes the nanoscale so unique is that the physical phenomena that dominate on this scale are the quantum effects.
This means for example that certain physical properties of the materials may take only discrete values like 1,2,3 rather than values from a continous spectrum of numbers like anything between 1 and 3.
On the nanoscale these properties are also size dependent and not (necessarily) the same as on the macroscale.
What are the main advantages of nanobased contrast agents over traditional contrast agents?
a)Longer circulation time
b)Targeted delivery
c)Multimodal use
d)Reduction of the rate of renal clearance
e)Leakage through the walls of the capillary vessels due to the small size of the nanoparticles
Some important terms found in the imaging with nanotechnology literature:
a)Biofunctionalization:
The modification of a material in such a way that it attains a desired biological property.
One example is the biofuntionalization of surfaces so that they entrap specific substances.
b)Enhance Permeability and Retention effect
What is understood by this term is the increased retention of nanoparticles in the tumor microenvironment.
The classical explanation is the leaking pattern of tumor vasculature as opposed to normal vasculature.
c)PEGylation:
PET=polyethylene glycol
Hydrophylic polymer used for the biofunctionalization of the surface of nanoparticles.
PEG increases their water solubility and decreases their uptake by the reticuloendothelial system resulting in a longer circulation time.
It also decreases the aggregation of the different nanoparticles.
d)Blood pool agents: Contrast media exhibiting long blood circulation times
How can we directly visualize nanoparticles?
Atomic Force Microscope:
It is a kind of microscope that can provide a picture of the surface of nanoscaled objects.
The reason it is called AFM is that it uses interactions=forces at the atomic level in order to depict the surfaces.
How can we evaluate the mechanical surface properties of materials and why is this relevant to nanobased imaging?:
There are two things one always has to remember when thinking of nanoparticles.
First of all they posess a high surface to volume ratio and secondly their surface properties have a great influence on their interactions with other substances,
as is observed in imaging.
The main tool used in this context is a method called nanoindentation.
This method takes advantage of the changes that occur on a material surface when touched by a very sharp tip like a pencil that is writing upon a paper on the macroscale.
How did nanotechnology evolve throughout the years?
Nanotechnology dates back to as early as the year 1959 when the physicist Richard Feynman (nobel prize 1965) gave his famous lecture “There is plenty of room at the bottom”.
In this lecture he talked about the possibility of manipulating and controlling things on a small scale.
“The principles of physics,
as far as I can see do not speak against the possibility of maneuvering things atom by atom.
It is not an attempt to violate any laws; it is something,
in principle,
that can be done; but in practice,
it has not been done because we are too big.”
Nowadays,
nanotechnology is considered to be one of the key enabling technologies with significant impact on many different medical technologies.