MRI technology may non-invasively locate, quantify specific cells in the body

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MRI can be used to visualize cell populations of interest in the living body utilizing fluorocarbon labeling, according to research that will be presented Aug. 21 by Carnegie Mellon University scientist Eric Ahrens, at the 236th national meeting of the American Chemical Society in Philadelphia.

The ability to non-invasively locate and track cells, such as immune cells, will aid the study and treatment of cancer, inflammation and autoimmune diseases, as well as provide a tool for advancing clinical translation of the field of cellular regenerative medicine, by tracking stem cells for example, according to the Pittsburgh-based Carnegie researcher.

“With our technology we can image specific cells in real-time with exquisite selectivity, which allows us to track their location and movement and to count the apparent number of cells present. We then use conventional MRI to obtain a high-resolution image that places the labeled cells in their anatomical context,” said Ahrens, an associate professor of biological sciences at the Mellon College of Science.

"The large background signal from mobile water and intrinsic tissue contrast differences can often make it challenging to unambiguously identify regions containing these metal-ion labeled cells throughout the body, which is the current state of the art," Ahrens said.

Ahrens said his new approach—fluorocarbon labeling—solved the problem by producing images that show the labeled cells at their precise location in the body. Cells of interest were labeled with a perfluoropolyether (PFPE) nanoemulsion, which is a colloidal suspension of tiny fluorocarbon droplets. Then, the labeled cells were introduced into an animal subject and tracks the cells in vivo, using 19F MRI.

The new 19F MRI detects the signal from the nucleus of the fluorine atom. Fluorine is not normally present in the body at sufficient concentrations to detect, so when the PFPE-labeled cells are transplanted into the body, MRI is used to detect the fluorine tracer.

Ahrens' team said they have recently used the PFPE technology to label and track dendritic cells and T cells in a mouse model of type I diabetes.
Cellular MRI agents also can be adapted to label other cell types, including cells from bone marrow and stem cells, according to Ahrens.

Recent advances in cell-based therapeutics research have focused on training immune cells to counteract diseases including cancer and diabetes and on directing stem cells to regenerate damaged tissues. Non-invasively visualizing the therapeutic cells in patients after transfer can be a vexing problem, according to Ahrens, and any approach that can speed up the testing of these treatments will be extremely useful.

“Ideally we would label therapeutic cells with our cellular MRI agents before they are implanted into a patient. In this way, we could use MRI to visualize the movement of the therapeutic cells in the patient to monitor whether they migrate to and remain in the desired tissues,” Ahrens explained.