title: Susceptibility-weighted imaging for stem cell visualization in a rat photothrombotic cerebral infarction model.
abstract: BACKGROUND
  In cell therapy, magnetic resonance imaging (MRI) has been used to visualize superparamagnetic iron oxide (SPIO)-labeled stem cells homing to a lesion. Improving traceability is to utilize the sequence that maximizes sensitivity to the susceptibility effect of SPIO.
  
  
  OBJECTIVE
  To explore the best method by comparing the MRI sequences to visualize mesenchymal stem cells (MSCs) labeled with SPIO.
  
  
  METHODS
  Human bone marrow (hBM)-derived MSCs were labeled by internalization of SPIO nanoparticles. In vitro MRI was performed for the SPIO-labeled hBM-MSCs in tubes with T2-weighted (T2W), T2*-weighted (T2*W), and susceptibility-weighted images (SWI). Contrast-to-noise ratio (CNR) and volumes of dark signal of SPIO-labeled hBM-MSCs were obtained on images of each sequence. Photothrombotic cerebral infarction (PTCI) was induced in eight rats, and 2.5 × 10(5) SPIO-labeled hBM-MSCs were infused through the tail vein on the third day. In vivo MRI of the rat brain was performed using a 3.0 T MRI on the first, third, seventh, and 14th days. CNRspio was obtained on T2W imaging, T2*W imaging, and SWI. The dark signals were compared with the SPIO-positive cells of Prussian blue staining.
  
  
  RESULTS
  In vitro MRI of 5 × 10(5) SPIO-labeled hBM-MSCs showed the CNR and volume of dark signal to be 63, 517 mm(3) in SWI, 41, 228 mm(3) in T2*W imaging, and 56, 41 mm(3) in T2W imaging, respectively. In vivo MRI showed a dark signal surrounding the high signal intensity of PTCI. Pathologically, the dark signals were matched with SPIO-labeled hBM-MSC in the corresponding rat. The dark signal was most prominent in SWI, then T2*W imaging, and finally in T2W imaging (P <0.05). In SWI, other causes of dark signals were matched with the veins and the choroid plexuses on histopathology.
  
  
  CONCLUSIONS
  SWI can visualize SPIO-labeled hBM-MSCs more sensitively, earlier, and with larger size and greater contrast than T2W imaging and T2*W imaging.
authors.affiliation: Department of Radiology, Chung-Ang University Hospital, Seoul, Republic of Korea.
authors.forename: Bon Chul
authors.initials: BC
authors.lastname: Ha
authors.affiliation: Department of Radiology, Chung-Ang University Hospital, Seoul, Republic of Korea.
authors.forename: Jisung
authors.initials: J
authors.lastname: Jung
authors.affiliation: Department of Radiology, Chung-Ang University Hospital, Seoul, Republic of Korea kwakbk@cau.ac.kr.
authors.forename: Byung Kook
authors.initials: BK
authors.lastname: Kwak
mesh_terms: D000818:Animals; D058948:Cell Tracking / Q000379:methods*; D002478:Cells, Cultured; D002544:Cerebral Infarction / Q000473:pathology* / Q000628:therapy*; D003287:Contrast Media; D003911:Dextrans; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D004195:Disease Models, Animal; D006801:Humans; D020767:Intracranial Thrombosis / Q000473:pathology* / Q000628:therapy*; D008027:Light; D058185:Magnetite Nanoparticles; D008297:Male; D045164:Mesenchymal Stem Cell Transplantation / Q000379:methods; D059630:Mesenchymal Stem Cells / Q000166:cytology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013194:Staining and Labeling / Q000379:methods
chemical_list: D003287:Contrast Media; D003911:Dextrans; D058185:Magnetite Nanoparticles; C097921:ferumoxtran-10
keywords: Susceptibility-weighted imaging (SWI); magnetic resonance imaging (MRI); photothrombotic cerebral infarction; rat; stem cell; superparamagnetic iron oxide (SPIO)