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host. Labeling efficiencies are closely dependent on the type of stem cell, the
radionuclide and its concentration, and incubation time.
To localize the stem cells in target tissues, a dual-isotope study is usually
performed to overlay the signals from labeled stem cells to tissue anatomies
delineated by the second isotope [15-17]. As shown in Figure 12.1A, 111 In sig-
nals from cells were overlaid on myocardial wall anatomy delineated by [ 99m Tc]
sestamibi [18]. The autoradiographic confirmation of 111 In signal with the his-
tological staining of stem cells is presented in Figure  12.1B-D. To facilitate
the localization of stem cells in tissue anatomies, the SPECT or PET signals
from labeled cells can be fused with high-resolution anatomical images from
computed tomography (CT) [19] when a SPECT/CT or PET/CT hybrid scanner
is available or coregistered with magnetic resonance (MR) images acquired
sequentially from a stand-alone MR scanner as shown in Figure 12.1A.
A high intracellular concentration of the radionuclide can be obtained
by adjusting the incubation time and concentration of the radionuclide in
the labeling media. As such, the direct labeling method can achieve high
detection sensitivity. A phantom study suggested that 10,000, 5,000, and
Rat 2
(A) Dual-isotope SPECT images and coregistration with MR images: 111 In-labeled stem cells
were implanted in the infarcted rat heart; a dual-energy window detects simultaneously [ 99m Tc]
sestamibi (pseudocolored in yellow) and [ 111 In] (blue) signals; the SPECT images were coregis-
tered on MRI image (gray). (B) Autoradiographs of heart sections obtained after transplanta-
tion of 111 In and Feridex double-labeled stem cells in the infarcted myocardium of a rat. (C), (D)
Prussian blue staining of iron for localization of the stem cells. LV, left ventricle; RV, right ven-
tricle. (Reprinted from Zhou R, Acton PD, Ferrari VA. Journal of American College of Cardiology
2006;48:2094-2106 with permission.) (E)-(G) Homing of [ 111 In]-labeled BMSCs to the infarcted
heart (in dogs) after intravenous injection at day 1 (E), day 2 (F), and day 7 (G) by SPECT imag-
ing. For each panel, sagittal (left) and coronal (right) view of fused SPECT (color) and CT (gray)
images are shown. Initial retention of cells in the lung is indicated by strong 111 In signal in
the lung. (Reprinted from (Kraitchman DL, Tatsumi M, Gilson WD, Ishimori T, Kedziorek D,
Walczak P, Segars WP, Chen H,  et. al. Dynamic imaging of allogeneic mesenchymal stem cells
trafficking to myocardial infarction, Circulation, 2005 112: 1454-1464.)
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