title: Visualization of multimodal polymer-shelled contrast agents using ultrasound contrast sequences: an experimental study in a tissue mimicking flow phantom.
abstract: BACKGROUND
  A multimodal polymer-shelled contrast agent (CA) with target specific potential was recently developed and tested for its acoustic properties in a single element transducer setup. Since the developed polymeric CA has different chemical composition than the commercially available CAs, there is an interest to study its acoustic response when using clinical ultrasound systems. The aim of this study was therefore to investigate the acoustic response by studying the visualization capability and shadowing effect of three polymer-shelled CAs when using optimized sequences for contrast imaging.
  
  
  METHODS
  The acoustic response of three types of the multimodal CA was evaluated in a tissue mimicking flow phantom setup by measuring contrast to tissue ratio (CTR) and acoustic shadowing using five image sequences optimized for contrast imaging. The measurements were performed over a mechanical index (MI) range of 0.2-1.2 at three CA concentrations (106, 105, 104 microbubbles/ml).
  
  
  RESULTS
  The CTR-values were found to vary with the applied contrast sequence, MI and CA. The highest CTR-values were obtained when a contrast sequence optimized for higher MI imaging was used. At a CA concentration of 106 microbubbles/ml, acoustic shadowing was observed for all contrast sequences and CAs.
  
  
  CONCLUSIONS
  The CAs showed the potential to enhance ultrasound images generated by available contrast sequences. A CA concentration of 106 MBs/ml implies a non-linear relation between MB concentration and image intensity.
authors.affiliation: Department of Medical Engineering, School of Technology and Health, KTH Royal Institute of Technology, Alfred Nobels Allé 10, 141 52, Huddinge, Stockholm, Sweden. malinl@sth.kth.se.
authors.forename: Malin
authors.initials: M
authors.lastname: Larsson
authors.forename: Matilda
authors.initials: M
authors.lastname: Larsson
authors.forename: Letizia
authors.initials: L
authors.lastname: Oddo
authors.forename: Silvia
authors.initials: S
authors.lastname: Margheritelli
authors.forename: Gaio
authors.initials: G
authors.lastname: Paradossi
authors.forename: Jacek
authors.initials: J
authors.lastname: Nowak
authors.forename: Lars-Åke
authors.initials: LÅ
authors.lastname: Brodin
authors.forename: Kenneth
authors.initials: K
authors.lastname: Caidahl
authors.forename: Anna
authors.initials: A
authors.lastname: Bjällmark
mesh_terms: D002339:Carotid Arteries / Q000000981:diagnostic imaging*; D003287:Contrast Media / Q000737:chemistry; D003911:Dextrans / Q000138:chemical synthesis; D004867:Equipment Design; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D058185:Magnetite Nanoparticles; D045423:Microbubbles; D019047:Phantoms, Imaging; D011108:Polymers / Q000737:chemistry*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014463:Ultrasonography / Q000295:instrumentation / Q000379:methods
chemical_list: D003287:Contrast Media; D003911:Dextrans; D058185:Magnetite Nanoparticles; D011108:Polymers; C097921:ferumoxtran-10