Advanced Nanoparticles for Imaging

Modern imaging technologies allow for analysis of multi-dimensional and multi-parameter data.expecially on analyte presence, tissue properties and to collect additional information on a particular biological function. The most advanced imaging techniques include CT (Computed Tomography), MRI (Magnetic Resonance Imaging), and PET (Positron Emission Tomography).

Different materials (e.g. bone, fat, water, hair) absorb X-ray at a variance, inducing contrast in CT and allowing for the evaluation of possible tumor or lesions. Because of its relatively low soft tissue contrast between tumors and healthy tissues, a contrast agent is often required to obtain satisfactory results from a CT scan.

MRI is performed by submitting a subject in a strong magnetic field to align the hydrogen nuclei spins parallel to the field. When a radiofrequency current is pulsed through the under evaluation organisms, the protons are stimulated, and spin out of equilibrium, straining against the pull of the magnetic field. After the removal of the current, the spins come again parallel to the main magnetic field with a tissue dependent time constant. Near to its clinical use, MR is applied, in its microMR declination, in preclinical analysis but also to track stem cells, monitor immune cell response, and observe prenatal development.

In PET, radioactive probes (radionuclides) are used in conjunction with metabolically active substances or targeting molecules. Positrons are emitted by the breakdown of the radionuclide. Gamma rays are generated when positrons collide with electrons near the decay event. The scanner then detects the gamma rays, which arrive at the detectors in coincidence at 180° apart from one another. These signals are analyzed by a computer to create an image map of the organ or tissue object of the study.

• Kherlopian AR, Song T, Duan Q, Neimark MA, Po MJ, Gohagan JK, Laine AF. A review of imaging techniques for systems biology. BMC Syst Biol. 2008 Aug 12;2:74.