title: Echographic detectability of optoacoustic signals from low-concentration PEG-coated gold nanorods.
abstract: OBJECTIVE
  To evaluate the diagnostic performance of gold nanorod (GNR)-enhanced optoacoustic imaging employing a conventional echographic device and to determine the most effective operative configuration in order to assure optoacoustic effectiveness, nanoparticle stability, and imaging procedure safety.
  
  
  METHODS
  The most suitable laser parameters were experimentally determined in order to assure nanoparticle stability during the optoacoustic imaging procedures. The selected configuration was then applied to a novel tissue-mimicking phantom, in which GNR solutions covering a wide range of low concentrations (25-200 pM) and different sample volumes (50-200 μL) were exposed to pulsed laser irradiation. GNR-emitted optoacoustic signals were acquired either by a couple of single-element ultrasound probes or by an echographic transducer. Off-line analysis included: (a) quantitative evaluation of the relationships between GNR concentration, sample volume, phantom geometry, and amplitude of optoacoustic signals propagating along different directions; (b) echographic detection of "optoacoustic spots," analyzing their intensity, spatial distribution, and clinical exploitability. MTT measurements performed on two different cell lines were also used to quantify biocompatibility of the synthesized GNRs in the adopted doses.
  
  
  RESULTS
  Laser irradiation at 30 mJ/cm(2) for 20 seconds resulted in the best compromise among the requirements of effectiveness, safety, and nanoparticle stability. Amplitude of GNR-emitted optoacoustic pulses was proportional to both sample volume and concentration along each considered propagation direction for all the tested boundary conditions, providing an experimental confirmation of isotropic optoacoustic emission. Average intensity of echographically detected spots showed similar behavior, emphasizing the presence of an "ideal" GNR concentration (100 pM) that optimized optoacoustic effectiveness. The tested GNRs also exhibited high biocompatibility over the entire considered concentration range.
  
  
  CONCLUSIONS
  An optimal configuration for GNR-enhanced optoacoustic imaging was experimentally determined, demonstrating in particular its feasibility with a conventional echographic device. The proposed approach can be easily extended to quantitative performance evaluation of different contrast agents for optoacoustic imaging.
authors.affiliation: National Research Council, Institute of Clinical Physiology, Lecce, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Conversano
authors.forename: Giulia
authors.initials: G
authors.lastname: Soloperto
authors.forename: Antonio
authors.initials: A
authors.lastname: Greco
authors.forename: Andrea
authors.initials: A
authors.lastname: Ragusa
authors.forename: Ernesto
authors.initials: E
authors.lastname: Casciaro
authors.forename: Fernanda
authors.initials: F
authors.lastname: Chiriacò
authors.forename: Christian
authors.initials: C
authors.lastname: Demitri
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Gigli
authors.forename: Alfonso
authors.initials: A
authors.lastname: Maffezzoli
authors.forename: Sergio
authors.initials: S
authors.lastname: Casciaro
mesh_terms: D002470:Cell Survival / Q000187:drug effects; D006046:Gold / Q000737:chemistry* / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D007834:Lasers; D061986:MCF-7 Cells; D008422:Materials Testing; D043942:Nanotubes / Q000737:chemistry*; D010316:Particle Size; D019047:Phantoms, Imaging; D061088:Photoacoustic Techniques / Q000295:instrumentation / Q000379:methods*; D011092:Polyethylene Glycols / Q000737:chemistry* / Q000494:pharmacology; D012815:Signal Processing, Computer-Assisted; D014159:Transducers; D014463:Ultrasonography / Q000295:instrumentation / Q000379:methods*
chemical_list: D011092:Polyethylene Glycols; D006046:Gold