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possibly a major concern regarding the delivery of adequate number of stem cells to
the injured myocardium with only a small fraction of stem cells remaining within
the heart after injection [ 25 ]. Considering variable cardiac outcomes it is imperative
that better methods of tracking stem cells and imaging are developed to determine
the fate of these cells after transplantation.
8.3 Cardiac Imaging in Stem Cell Therapy
Imaging modalities that have been validated for stem cells tracking include fluores-
cence imaging (FI), bioluminescence imaging (BLI), positron emission tomography
(PET), single-photon emission computed tomography (SPECT), magnetic reso-
nance imaging (MRI) and computed tomography (CT) (Table 8.1). Each of these
techniques has its own strengths and weaknesses with respect to the use in animal
and human studies. BLI has been the most popular imaging modality for small ani-
mal studies [ 26 ] while planar FI has been limited to proof-of-principle studies [ 27 ].
Imaging modalities such as PET, SPECT, and MRI allow tomographic assessment
of cells in both animals as well as humans. PET and SPECT, when combined with
CT, have been particularly useful in quantifying the whole-body distribution of cells
after delivery, whereas MRI has seen more utility in determining the transmural
location of stem cells due to its superb spatial resolution [ 26 , 28 – 32 ].
8.4 Non-invasive Methods of Cardiac Imaging Post Stem
Cell Therapy
The ideal cardiac imaging modality should provide integrated information related to
the entire process of cell engraftment, survival, and functional outcome following
stem cell therapy. Established parameters of noninvasive imaging, such as contrac-
tile function, perfusion, and viability of the myocardium, do not provide direct visu-
alization of transplanted cells, their biology or function [ 33 ] leading to use of
contrast agents and detectors for noninvasive visualization of therapeutic cells
in vivo. Ideal imaging technique for stem cell tracking should be biocompatible and
safe with no genetic modification or perturbation to the stem cell. Techniques should
allow cell quantification at any anatomic location with minimal or no dilution with
cell division. Ideally these techniques should cause minimal or no transfer of con-
trast agent to non-stem cells [ 34 ]. Such imaging approaches may help understand
the logistics in preclinical studies and may also have direct clinical applications.
Multiple imaging techniques have been used for in vivo imaging of labeled trans-
planted cells. Magnetic resonance imaging (MRI) uses super-paramagnetic iron
oxide (SPIO) while radionuclide technology involves agents like In-111 oxin, F18-
FDG and Tc-99m HMPAO to meet the broad objectives of stem cell tracking. MRI
S. Raina et al.