Dara Kraitchman

Guan Wang

Judy A Cook

Steven Shea

Yingli Fu

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POSTER PRESENTATION Open Access
CT and quantitative 19F MRI tracking of
encapsulated mesenchymal stem cells in a
peripheral arterial disease rabbit model
Guan Wang1,2*, Yingli Fu1, Steven Shea4, Judy A Cook1, Dara Kraitchman1,3
From 16th Annual SCMR Scientific Sessions
San Francisco, CA, USA. 31 January - 3 February 2013
Background
Nearly 12% of Americans suffer from peripheral arterial
disease (PAD) and many are not eligible for conventional
angioplasty or surgical bypass. Microencapsulated stem
cell (SC) therapy offers a novel means to transplant
allogeneic SCs to avoid immunorejection and enable
image tracking. However, quantitative evaluation of cap-
sule fate is elusive. Here we explore c-arm CT and
19F-MRI for serial evaluation of dual X-ray/MR-visible SC
microcapsules (XMRCaps) in a rabbit PAD model.
Methods
XMRCaps were produced using a modified alginate micro-
encapsulation method impregnating perfluorooctylbro-
mine (PFOB) and human or rabbit SCs. In vitro validation
studies were performed in a phantom consisting of known
quantities of XMRCaps. C-arm CT images (dynaCT, Sie-
mens Artis Zee) were acquired and reconstructed at 0.46
mm3 voxel size. 19F MRI was acquired with a flexible,
4-channel Tx/Rx 19F coil (3D TrueFISP, Siemens Tim
Trio, 4.1 ms TR; 2.0 ms TE; 32 averages) in the coronal
plane. 1H MRI was acquired with the system body or
body matrix coil.
For in vivo studies, c-arm CTs and MRIs were acquired
at one, two, and three weeks after human SC (XenoSC) or
rabbit SC (AlloSC) XMRCap intramuscular administration
in the hindlimb of a PAD rabbit (n=4) using identical ima-
ging parameters as the in vitro studies. To test the repeat-
ability of 19F MRI, imaging sets were acquired twice on
the same day in one rabbit with the 19F coil repositioned
in between. To enhance repeatability, the fluorine coil was
constrained to a fixed geometry. Reference PFOB markers
were placed within the imaging field to enable quantitation
of XMRCaps.
Segmentation of the injections sites in c-arm CT and
19F MRI was performed with a thresholding algorithm.
Relative fluorine concentration was determined by aver-
aging the integrated 19F signal intensity over the segmen-
ted volume after normalization to the 19F standards.
Results
Calculated XMRCap volumes in CT and MRIs were highly
concordant in vitro (Figure 1a). 19F MRI repeatability stu-
dies showed the volume and concentration errors of <3%
and <6%, respectively. For the AlloSC rabbits, in vivo injec-
tion volume decreased 5±1% each week and concentration
increased 12 ± 9% each week, while the XenoSC rabbits
had volume and concentration decreases of 30 ± 2% and
35 ± 17%, respectively, each week (Figure 1b and c).
Conclusions
MRI provides accurate assessment of XMRCap volumes
with increased MRI volumes due to partial volume
effects of the larger MRI voxel. In vivo volume changes
of XMRCaps injection sites in the ischemic environment
of the PAD rabbit could be quantified on MRI and CT.
However, only MRI was able to demonstrate alterations
in the fluorine concentration. In particular, decreases in
XMRCap volumes with stable or increasing fluorine
concentrations in animals that received allogeneic stem
cells suggest better tolerance of allogenic microencap-
suled cells than xenogenic stem cells.
Funding
a grant from Siemens AG, NIH R33-HL089029, and the
Maryland Stem Cell Research Foundation (2008-
MDSCRFII-0399).
1Radiology and Radiological Science, Johns Hopkins University, Baltimore,
MD, USA
Full list of author information is available at the end of the article
Wang et al. Journal of Cardiovascular Magnetic
Resonance 2013, 15(Suppl 1):P24
http://www.jcmr-online.com/content/15/S1/P24
© 2013 Wang et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons
Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in
any medium, provided the original work is properly cited.
Author details
1Radiology and Radiological Science, Johns Hopkins University, Baltimore,
MD, USA. 2Electrical and Computer Engineering, Johns Hopkins University,
Baltimore, MD, USA. 3Molecular and Comparative Pathobiology, Johns
Hopkins University, Baltimore, MD, USA. 4Center for Applied Medical
Imaging, Siemens Corporation, Corporate Research and Technology,
Baltimore, MD, USA.
Published: 30 January 2013
doi:10.1186/1532-429X-15-S1-P24
Cite this article as: Wang et al.: CT and quantitative 19F MRI tracking of
encapsulated mesenchymal stem cells in a peripheral arterial disease
rabbit model. Journal of Cardiovascular Magnetic Resonance 2013 15(Suppl
1):P24.
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Figure 1 a) Correlation between MRI and CT volume of the 200 (blue), 100 (red) and 50 (green) XMRCaps. b) The XMRCaps injection volume in
19F MRI images at one, two and three weeks after delivery. The AlloSC rabbits have rabbit SCs and XenoSC rabbits has human SCs. c) Relative
normalized fluorine concentration corresponding to the segmented volumes.
Wang et al. Journal of Cardiovascular Magnetic
Resonance 2013, 15(Suppl 1):P24
http://www.jcmr-online.com/content/15/S1/P24
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CT and quantitative 19F MRI tracking of encapsulated mesenchymal stem cells in a peripheral arterial disease rabbit model

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CT and quantitative 19F MRI tracking of encapsulated mesenchymal stem cells in a peripheral arterial disease rabbit model

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