Page 21 - Cellular Imaging in Regenerative Medicine, Cancer and Osteoarthritis

which all scatter and reflect high-frequency sound waves differently resulting in intensity differences in an ultrasound image. Compared to MRI, SPECT, PET and CT imaging ultrasound imaging has some advantages such as price, convenience, and fast real-time imaging, but it has poor penetration through bone or air (74, 75). The sound waves can also be used for site-specific cell labelling. This can be achieved with the use of ultrasound contrast agents like microbubbles. The microbubbles change their size under influence of the generated waves. The vibration of the microbubbles that arises can change the structure of cell membrane and enhance its permeation. Through sonoporation reversible or non-reversible cell membrane pores are generated upon microbubble oscillations (76, 77).
SPECT
Single-photon emission computed tomography (SPECT) is a nuclear imaging technique just like positron emission tomography (PET). SPECT is widely used in (pre)clinical studies and is an advanced radionuclide molecular imaging technique that is able to evaluate biochemical changes and levels of molecular targets in vivo (78). It enables whole body imaging of molecular targets/processes with high sensitivity. Since biochemical changes often occur before anatomical changes in disease, SPECT has clear diagnostic strength (79). However SPECT has a key weakness, which is, showing poor anatomical information. This weakness may be eliminated through the combination of instruments with either CT or MRI, producing a single scanner capable of accurately identifying molecular events with precise correlation to anatomical findings (80, 81).
SPECT can measure the biodistribution of extremely small (<10−10 molar) concentrations of radiolabelled biomolecules/nanoparticles in vivo with, when using a pre-clinical system, sub-millimetre resolution and quantify the molecular kinetic processes in which they participate. Its capabilities include:
(i) the ability to image radiolabelled biomolecules/nanoparticles
(ii) compared to PET, SPECT has the ability to measure relatively slow kinetic processes due to the relatively long half-life of the commonly used radionuclides
(iii) the ability to probe two or more molecular pathways simultaneously by detecting radionuclides with different emission energies (82).
Introduction
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