Nanotechnology and medical image enhancement

Nanoparticles can be designed so that they can enhance the contrast for different imaging modalities. For example they can have attached to their surface a molecule that binds to a specific disease state and thus hold the nanoparticle onto the cells and tissue of interest. So, one can enhance X-ray contrast using nanoparticles made from high atomic number material; MRI contrast can be enhanced using superparamagnetic particles; optical imaging can be enhanced either by luminescent nanoparticles or surface plasmon resonance particles; ultrasound imaging can be enhanced using nano/microbubbles. The building blocks to achieve the aforementioned are to make the particles under well-controlled conditions and to design, or have available, the appropriate linker between the nanoparticle and the disease state of interest.

Nuclear and radiology image enhancement

This requires nanoparticles to be created that have a radioactive component added to give some form of specialized image enhancement or a high atomic number to absorb X-rays to give additional contrast on X-ray images. For the former, it is possible to attach particles containing a radioactive gamma-emitting tracer to give single-photon emission computed tomography (SPECT) images, or Flourine-18 to give positrons for the positron emission tomography (which is detected by having two gamma rays emerging in opposite directions) that is becoming more widely used for neuroimaging of the brain.

MRI image enhancement

The most widely used image enhancers for MRI have been based on gadolinium compounds, either chelates or oxide nanoparticles. These give a positive T1 contrast (white on grey) in images. But there is increasing use of superparamagnetic iron oxide nanoparticles (SPIONs) which give a black on grey T2 image contrast. These have an advantage in being less toxic than gadolinium but also lend themselves more readily to being used in combination with image enhancers based on complementary techniques, such as radio-labelled, luminescent labelling and so forth.

Luminescence enhancement

Traditionally there are a number of approved dyes that have been used, especially during surgery to identify diseased tissue. However these dyes can suffer from bleaching and changes due to the chemistry in the local environment. There is increasing use being made of highly luminescent quantum dots, nanodiamonds and other nanoparticles because these can be designed to be not so dependent on local chemistry, but they can be functionalized to detect particular disease states.

Plasmonic effects

Gold and silver particles of sizes in the range 20–40 nm can give a large enhanced optical scattering caused by the excitation of surface plasmons. These two metals show particularly sharp and optically intense surface plasmon effects (surface plasmons result from an oscillation of the conduction electrons in small particles of these two metals). While these particles could be used in the body, they are currently used mainly for in vitro studies especially for some forms of widely adopted biosensors.

Ultrasound enhancement

Bubbles are the main agent for introducing additional contrast for ultrasound, and these are in the form of liposomes filled with a gas such as argon. The outer surface of the liposome is usually functionalized so that the bubbles preferentially attach to the target that is being investigated. Generally these are larger than the usual definition of nanoparticles, that is they are larger than 100 nm diameter.

This is an excerpt from the white paper "Nanotechnology: What does the future look like for the medical devices industry?". To download our other medical device white papers, please visit the Insight page on the Compliance Navigator website.