Todd C. Soesbe1, Navin Bansal2,
Ananth V. Annapragada3, Ketan B. Ghaghada3, Zoltan
Kovacs1, A. Dean Sherry1,4
1Advanced Imaging Research Center,
University of Texas Southwestern Medical Center, Dallas, TX, United States; 2Department
of Radiology, Indiana University School of Medicine, Indianapolis, IN, United
States; 3School of Health Information Sciences, The University of
Texas at Houston, Houston, TX, United States; 4Department of
Chemistry, The University of Texas at Dallas, Dallas, TX, United States
Liposomal
delivery of MR contrast agents offers improved steady-state imaging and
signal-to-noise due to their long blood circulation life-time. Also, the
relative small size of the liposomes ( 100 nm in diameter) allows them to
have direct uptake in certain tumor lines that exhibit "leaky"
vasculature (e.g. MBA-MD-231 breast cancer cells). The 1H methyl group of
TmDOTMA has a chemical shift that is about -100 ppm away from bulk water.
This TmDOTMA peak can be imaged using chemical shift selective (CHESS)
techniques in which the water signal is completely absent. By using this
method we can obtain "waterless" MR images where the only signal is
due to the TmDOTMA filled liposomes. This is analogous to images obtained in
nuclear medicine where the only signal is from the radioactive isotope.
Liposomal TmDOTMA imaging has the potential to produce high resolution MR
angiograms and molecular targeted images that are not contaminated by the
bulk water signal. We explored this hypothesis by injecting a 5.8 mM solution
of TmDOTMA liposomes, both intravenously and intratumorally, into a
tumor-bearing mouse.