Preparation And Performance Of Multifuncational Contrast Agents Integrated With Fluorescence, Ultrasound And Magnetic Resonance Imaging

There is a variety of medical imaging modalities nowadays, includingultrasonography （US）, magnetic resonance imaging （MRI）, positron emissiontomography （PET） and single photon emission computed tomography （SPECT）. Dueto the inherent limitation of every imaging modality, we cann’t obtain complete andsufficient biological information with single modality. For example, ultrasonographyis capable of providing real-time image and cost-efficient whlie its resolution is low;MRI has high spatial resolution and excellent soft-tissue contrast while it is quiteexpensive and cannot provide real-time images; fluorescent imaging has highsensitivity and multicolor imaging abality while it has low spatial resolution andpoor tissue penetration depth. With the incorporation of the three imaging modalitiesto take advantage of the strengths of each modality, we can acquire relativelycomplete pathological information in the clinical diagnosis, which will greatlyimprove the accquracy and efficiency of diagnosis.The fabrication of novel multifuctional contrast agents is the foundation ofmultimodality imaging. In this paper, a multifunctional contrast agent by physicalincorporation of SPIO into PLA MBs as well as electrostatic adsorption of CdTeQDs onto the surface of the MBs shells is developed, and it is also a new contrastagent that supports tri-modal imaging, namely, ultrasonography, MRI andfluorescent imaging. The main results were as follows:1) The results of scanningelectron microscope and laser scattering particle size analyzer displayed that thediameter of major microbubbles ranged from700nm to5μm, which satisfied therequirement of ultrasound imaging.2) Fluorescence emission spectra andphotoluminescence spectroscopy confirmed that CdTe QDs were successfullydeposited onto the surface of the multimodal MBs, transmission electronmicroscopy （TEM） clearly showed the spherical structure and proved that the Fe₃O₄nanoparticles were well dispersed in the MBs.3) Ultrasound imaging experiments invivo and in vivo showed the good ultrasound contrast-enhancing ability of themultifunctional MBs.4) The in vivo MRI contrasting effect of the multimodalmicromubbles at various Fe concentrations was evaluated by T2-weighted MRI, andthe relaxation rate was60.5mM-1s-1.In conclusion, because that the layer by layer （LBL） and physical entrapmentmethods are simple and general, we can replace iron oxide and quantum dots withdrugs, target molecules, or other suitable nanoparticles for local drug delivery,targeted diagnosis and other multimodal imaging, providing a great prospect fordeveloping a new multifunctional diagnostic tool.