title: Imaging of pulmonary embolism and t-PA therapy effects using MDCT and liposomal iohexol blood pool agent: preliminary results in a rabbit model.
abstract: OBJECTIVE
  Polyethylene glycol-coated liposomal blood pool contrast agents maintain contrast enhancement over several hours. This study aimed to evaluate (long-term) imaging of pulmonary arteries, comparing conventional iodinated contrast with a liposomal blood pool contrast agent. Also, visualization of the (real-time) therapeutic effects of tissue plasminogen activator (t-PA) on pulmonary embolism (PE) was attempted.
  
  
  METHODS
  Six rabbits (weight approximately 4 kg) had autologous blood clots injected through the superior vena cava. Imaging was performed using conventional contrast (iohexol, 350 mg I/ml; GE HealthCare, Princeton, NJ) at a dose of 1400 mg I per animal, and after wash-out, animals were imaged using an iodinated liposomal blood pool agent (88 mg I/mL, dose 900 mg I/animal). Subsequently, five animals were injected with 2 mg of t-PA and imaging continued for up to 4(1/2) hours.
  
  
  RESULTS
  Both contrast agents identified PE in the pulmonary trunk and main pulmonary arteries in all rabbits. Liposomal blood pool agent yielded uniform enhancement, which remained relatively constant throughout the experiments. Conventional agents exhibited nonuniform opacification and rapid clearance postinjection. Three of six rabbits had mistimed bolus injections, requiring repeat injections. Following t-PA, pulmonary embolus volume (central to segmental) decreased in four of five treated rabbits (range 10-57%, mean 42%). One animal showed no response to t-PA.
  
  
  CONCLUSIONS
  Liposomal blood pool agents effectively identified acute PE without need for reinjection. PE resolution following t-PA was quantifiable over several hours. Blood pool agents offer the potential for repeated imaging procedures without need for repeated (nephrotoxic) contrast injections.
authors.affiliation: Department of Radiology, Carver College of Medicine, University of Iowa, 200 Hawkins Drive, Iowa City, IA, USA.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Burke
authors.forename: Ananth
authors.initials: A
authors.lastname: Annapragada
authors.forename: Eric A
authors.initials: EA
authors.lastname: Hoffman
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Chen
authors.forename: Ketan B
authors.initials: KB
authors.lastname: Ghaghada
authors.forename: Jered
authors.initials: J
authors.lastname: Sieren
authors.forename: Edwin J R
authors.initials: EJ
authors.lastname: van Beek
mesh_terms: D000818:Animals; D001769:Blood; D003287:Contrast Media; D005343:Fibrinolytic Agents / Q000627:therapeutic use*; D007472:Iohexol / Q000008:administration & dosage*; D008081:Liposomes; D008297:Male; D011651:Pulmonary Artery / Q000000981:diagnostic imaging; D011655:Pulmonary Embolism / Q000000981:diagnostic imaging* / Q000188:drug therapy*; D011817:Rabbits; D010959:Tissue Plasminogen Activator / Q000627:therapeutic use*; D014057:Tomography, X-Ray Computed
chemical_list: D003287:Contrast Media; D005343:Fibrinolytic Agents; D008081:Liposomes; D007472:Iohexol; D010959:Tissue Plasminogen Activator