Molecular
imaging with magnetic resonance microsystems
Director:
Barjor Gimi, Ph.D. (PI)
David Gracias, Ph.D. (Co-PI)
Brief Discription and findings:
Our purpose in this project was to fabricate and demonstrate 3D
micropatterned encapsulation devices that are resonant at the frequencies used
in MRI, and design novel nested loop geometries for 2D microcoils designed to
provide high localized signal-to-noise ratio (SNR). We have made several
strides in our quest for 3D encapsulation devices for MRI. We
successfully demonstrated cell encapsulation, and stained cells with a
fluorescent marker for easy visualization within the device (Fig. 5). The
design and fabrication of the microcoils has been improved to include gold-coating
to render them bio-inert. We have optimized our acquisition protocols to
achieve images of high fidelity and obtained in vivo images of the
device (Fig. 5 d, e).
Figure 5: (a) SEM image of a microcontainer with open faces. (b) Optical microscopy image of the microdevice with cells encapsulated in an ECM gel, (c) corresponding fluorescence image showing cells stained with the viability stain, Calcein AM, In vivo MRI of the microdevice (with cells) both subcutaneously (d) and embedded in tumor tissue (e).
While negative contrast is valuable, there are several potential sources of
signal void in vivo. Therefore positive contrast obtained from
the device in the complete absence of background signal is desirable. Ni
microdevices, that have a high magnetic permeability, alter the magnetic field
in their immediate proximity and shift the resonance frequency of the adjacent
water. By suppressing the global on-resonance water signal, and by selective
excitation of the off-resonance water in proximity to the microdevice, the
device can be easily visualized with MRI in the absence of background
signal. We are also developing strategies to release drugs or contrast
agents from our encapsulation devices through focused inductive heating.
We have also made some advances in creating nanoporous surfaces for our 3D
microdevice to provide immunoprotection of the encapsulated cells. We
have fabricated 2D nested loop gold microcoils on a substrate of laboratory grade
glass, and characterized them electrically by measuring their inductance and
self-resonance. The self-resonance of the microcoils is in the 700-800
MHz range which is higher than the operating frequency of our MR scanners and
capacitance will be added to achieve resonance.
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Main publications: Gimi, B., Leong, T., Gu, Z., Yang, M., et al.,
Self-assembled three dimensional radio frequency (RF) shielded containers for
cell encapsulation. Biomed Microdevices, 2005. 7(4): p. 341-5.
Gimi, B., Artemov, D., Leong, T., Gracias, D.H., et al., Cell Viability and
Noninvasive In Vivo MRI Tracking of 3D Cell Encapsulating Self-Assembled
Microcontainers. Cell Transplantation, 2007. 16(4): p. 403-408.
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