Purpose: Conventional T2-weighted MRI produces a hypointense signal from iron-labeled cells, which renders quantification unfeasible. We tested a SWeep Imaging with Fourier Transformation (SWIFT) MRI pulse sequence to generate a quantifiable hyperintense signal from iron-labeled cells. Methods: Mesenchymal stem cells (MSCs) were labeled with different concentrations of iron oxide particles and examined for cell viability, proliferation, and differentiation. The SWIFT sequence was optimized to detect and quantify the amount of iron in the muscle tissue after injection of iron oxide solution and iron-labeled MSCs. Results: The incubation of MSCs with iron oxide and low concentration of poly-L-lysine mixture resulted in an internalization of up to 22 pg of iron per cell with no adverse effect on MSCs. Phantom experiments showed a dependence of SWIFT signal intensity on the excitation flip angle. The hyperintense signal from iron-labeled cells or solutions was detected, and an amount of the iron oxide in the tissue was quantified with the variable flip angle method. Conclusions: The SWIFT sequence can produce a quantifiable hyperintense MRI signal from iron-labeled cells. The graft of 18 x 106 cells was detectable for 19 days after injection and the amount of iron was quantifiable. The proposed protocol simplifies the detection and provides a means to quantify cell numbers. Magn Reson Med 78:1900–1910, 2017.
Bibliographical noteFunding Information:
1Musculoskeletal Quantitative Imaging Research, Department of Radiology and Biomedical Imaging, University of California, San Francisco, California, USA. 2Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minneapolis, Minnesota, USA. 3Center for Musculoskeletal Health, University of California at Davis School of Medicine, Sacramento, California, USA. Research reported in this publication was supported by the National Institute of Arthritis and Musculoskeletal and Skin Diseases of the National Institutes of Health under Award P50 AR060752, R01 AR043052, and 5K24AR048841-11 (NEL); R21 AR068507 (SM); and P41 EB015894. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. *Correspondence to: Sergey Magnitsky, Ph.D., Dept. of Radiology, University of California, San Francisco, 185 Berry St, Suite 350, San Francisco, CA 94107, USA. Tel: 415 514-8233; E-mail: email@example.com Received 15 July 2016; revised 18 November 2016; accepted 23 November 2016 DOI 10.1002/mrm.26585 Published online 17 January 2017 in Wiley Online Library (wileyonlinelibrary. com).
© 2017 International Society for Magnetic Resonance in Medicine
- cell tracking
- hypointense signal intensity
- iron oxide
- positive contrast