Nanotechnology is currently being applied to innovative methods of medical imaging. The development of imaging at the nanoscale has the ability to enhance the field of medicine by providing more detailed images of cellular processes. Current methods of medical imaging are being adapted to increase their potential at the nanoscale as well as being used as contrast agents for tracking injected nanoparticles in the body.
Research is currently underway in applying the technology to stem cell transplants and for the diagnostic imaging of early stage diseases.
Nanotechnology and Nuclear Magnetic Resonance (NMR)
Nuclear Magnetic Resonance (NMR) is a technique which exploits the magnetic properties of atomic nuclei to form medical images through Magnetic Resonance Imaging (MRI). Atomic nuclei in a magnetic field absorb and emit electromagnetic radiation, with the resonance frequency of a substance being directly proportional to the strength of the magnetic field.
Medical images are therefore produced as the resonance frequencies are dependent on location. MRI is frequently used to obtain images of various organs in the body. Nanotechnology provides the potential for medical imaging through NMR at the nanoscale.
More detailed images can be produced by aligning the atomic nuclei in an nanostructure which supplies a large magnetic field that is 10,000 times bigger than the magnetic field of Earth. In order to control and manipulate the large magnetic field produced, radio frequencies are pulsed on a micro second time scale. Research is currently developing practical technology utilizing NMR at the nanoscale.
A diamond chip which contains high density nitrogen-vacancy centers, or defect areas in the diamond, provides magnetic field sensitivity and nanoscale spatial resolution to samples placed on the diamond chip before performing NMR-based MRI scans. The diamond chip was able to provide submicrometer resolution allowing for new applications of MRI, including imaging biomolecules at the cellular level.
Nanotechnology and Stem Cell Imaging
Medical imaging through nanotechnology is also being applied to tracking transplanted stem cells. Medical imaging of stem cells requires added contrast agents. However, current contrast agents present problems such as metabolic degradation within the body and photobleaching, when photochemical destruction occurs. Current research is focused on evaluating various nanoparticles with unique optical and magnetic properties that can provide real-time tracking of transplanted stem cells.
Along with traditional fluorescent imaging and MRI, nanoparticles have also been used to develop another method of nanoscale medical imaging, photoacoustic imaging. The technique works by the application of a photoacoustic wave, formed from the thermal tissue expansion caused by a laser pulse. The resulting ultrasound emission has been employed for imaging single nanoparticles in tissue. Gold nanoparticles are particularly well suited as high contrast agents for photoacoustic imaging of stem cells but other plasmonic nanoparticles have been tested successfully.
A practical example of nanotechnology being employed for stem cell imaging is the use of iron oxide nanoparticles for tracking neural stem cells in patients with brain trauma. Stem cells have the potential for regenerating damaged brain tissue, but research progress requires careful tracking of the stem cells in the body. An injection of neural stem cells was tracked to the brain lesion of a patient through the use of MRI and iron oxide nanoparticles as a contrast agent. The signal detected through MRI changed as the stem cells accumulated around the brain lesion, showing successful migration of the stem cells from the injection site.
The Use of Nanotechnology for Diagnostic Imaging of Alzheimer's Disease
Nanotechnology is also being employed for non-invasive diagnostic imaging of medical conditions such as Alzheimer's disease. Amyloid fybrils form plaques in the brain which cause the neurodegeneration associated with the disease. Though they can be imaged using current methods, amyloid fybrils are not closely associated with the development of the disease. Instead the smaller peptides Aβ oligomers, which form amyloid fybrils, are more promising biomarkers for the early stages of the condition.
A probe for Aβ oligomers was formed by attaching oligomer-specific antibodies onto magnetic nanostructures. When Aβ oligomers are present a stable complex is formed on the probe. A magnetic resonance imaging signal is then produced which can be utilized for diagnostic imaging of early-stage Alzheimer's disease.
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- New research offers breakthrough in nanotechnology https://www.sheffield.ac.uk/news/nr/nanotechnology-nuclear-magnetic-resonance-1.174327
- Jenson, H.A. et al. 2017. Nanotechnology-based stem cell transplant and cell-based therapy, Imaging in Stem Cell Transplant and Cell-Based Therapy, 2, pp. 17-35. https://link.springer.com/chapter/10.1007/978-3-319-51833-6_2
- Zhu, J. et al. 2006. Tracking neural stem cells in patients with brain trauma, The New England Journal of Medicine, 355, pp. 2376-2378. http://www.nejm.org/doi/full/10.1056/NEJMc055304#t=article
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