title: X-ray fused with magnetic resonance imaging (XFM) to target endomyocardial injections: validation in a swine model of myocardial infarction.
abstract: BACKGROUND
  Magnetic resonance imaging (MRI) permits 3-dimensional (3D) cardiac imaging with high soft tissue contrast. X-ray fluoroscopy provides high-resolution, 2-dimensional (2D) projection imaging. We have developed real-time x-ray fused with MRI (XFM) to guide invasive procedures that combines the best features of both imaging modalities. We tested the accuracy of XFM using external fiducial markers to guide endomyocardial cell injections in infarcted swine hearts.
  
  
  RESULTS
  Endomyocardial injections of iron-labeled mesenchymal stromal cells admixed with tissue dye were performed in previously infarcted hearts of 12 Yucatan miniswine (weight, 33 to 67 kg). Features from cardiac MRI were displayed combined with x-ray in real time to guide injections. During 130 injections, operators were provided with 3D surfaces of endocardium, epicardium, myocardial wall thickness (range, 2.6 to 17.7 mm), and infarct registered with live x-ray images to facilitate device navigation and choice of injection location. XFM-guided injections were compared with postinjection MRI and with necropsy specimens obtained 24 hours later. Visual inspection of the pattern of dye staining on 2,3,5-triphenyltetrazolium chloride-stained heart slices agreed (kappa=0.69) with XFM-derived injection locations mapped onto delayed hyperenhancement MRI and the susceptibility artifacts seen on the postinjection T2*-weighted gradient echo MRI. The distance between the predicted and actual injection locations in vivo was 3.2+/-2.6 mm (n=64), and 75% of injections were within 4.1 mm of the predicted location.
  
  
  CONCLUSIONS
  Three-dimensional to two-dimensional registration of x-ray and MR images with the use of external fiducial markers accurately targets endomyocardial injection in a swine model of myocardial infarction.
authors.affiliation: Cardiovascular Branch, Division of Intramural Research, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892-1538, USA.
authors.forename: Ranil
authors.initials: R
authors.lastname: de Silva
authors.forename: Luis F
authors.initials: LF
authors.lastname: Gutiérrez
authors.forename: Amish N
authors.initials: AN
authors.lastname: Raval
authors.forename: Elliot R
authors.initials: ER
authors.lastname: McVeigh
authors.forename: Cengizhan
authors.initials: C
authors.lastname: Ozturk
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Lederman
mesh_terms: D000818:Animals; D004396:Coloring Agents; D007267:Injections; D007501:Iron / Q000008:administration & dosage; D018810:Magnetic Resonance Angiography; D023421:Models, Animal; D009203:Myocardial Infarction / Q000000981:diagnostic imaging*; D011859:Radiography; D033581:Stem Cell Transplantation / Q000379:methods; D013552:Swine
chemical_list: D004396:Coloring Agents; D007501:Iron