title: Sentinel lymph nodes in the rat: noninvasive photoacoustic and US imaging with a clinical US system.
abstract: OBJECTIVE
  To evaluate in vivo sentinel lymph node (SLN) mapping by using photoacoustic and ultrasonographic (US) imaging with a modified clinical US imaging system.
  
  
  METHODS
  Animal protocols were approved by the Animal Studies Committee. Methylene blue dye accumulation in axillary lymph nodes of seven healthy Sprague-Dawley rats was imaged by using a photoacoustic imaging system adapted from a clinical US imaging system. To investigate clinical translation, the imaging depth was extended up to 2.5 cm by adding chicken or turkey breast on top of the rat skin surface. Three-dimensional photoacoustic images were acquired by mechanically scanning the US transducer and light delivery fiber bundle along the elevational direction.
  
  
  RESULTS
  Photoacoustic images of rat SLNs clearly help visualization of methylene blue accumulation, whereas coregistered photoacoustic/US images depict lymph node positions relative to surrounding anatomy. Twenty minutes following methylene blue injection, photoacoustic signals from SLN regions increased nearly 33-fold from baseline signals in preinjection images, and mean contrast between SLNs and background tissue was 76.0 +/- 23.7 (standard deviation). Methylene blue accumulation in SLNs was confirmed photoacoustically by using the optical absorption spectrum of the dye. Three-dimensional photoacoustic images demonstrate dynamic accumulation of methylene blue in SLNs after traveling through lymph vessels.
  
  
  CONCLUSIONS
  In vivo photoacoustic and US mapping of SLNs was successfully demonstrated with a modified clinical US scanner. These results raise confidence that photoacoustic and US imaging can be used clinically for accurate, noninvasive imaging of SLNs for axillary lymph node staging in breast cancer patients.
authors.affiliation: Philips Research North America, Briarcliff Manor, NY, USA.
authors.forename: Todd N
authors.initials: TN
authors.lastname: Erpelding
authors.forename: Chulhong
authors.initials: C
authors.lastname: Kim
authors.forename: Manojit
authors.initials: M
authors.lastname: Pramanik
authors.forename: Ladislav
authors.initials: L
authors.lastname: Jankovic
authors.forename: Konstantin
authors.initials: K
authors.lastname: Maslov
authors.forename: Zijian
authors.initials: Z
authors.lastname: Guo
authors.forename: Julie A
authors.initials: JA
authors.lastname: Margenthaler
authors.forename: Michael D
authors.initials: MD
authors.lastname: Pashley
authors.forename: Lihong V
authors.initials: LV
authors.lastname: Wang
mesh_terms: D000818:Animals; D001365:Axilla; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D007834:Lasers; D008198:Lymph Nodes / Q000000981:diagnostic imaging* / Q000473:pathology; D008751:Methylene Blue; D055095:Optics and Photonics / Q000295:instrumentation / Q000379:methods*; D051381:Rats; D017207:Rats, Sprague-Dawley; D021701:Sentinel Lymph Node Biopsy; D018709:Statistics, Nonparametric; D014463:Ultrasonography / Q000295:instrumentation / Q000379:methods*
chemical_list: D008751:Methylene Blue