title: Localization of spherical lesions in tumor-mimicking phantoms by 3D sparse array photoacoustic imaging.
abstract: OBJECTIVE
  The authors have developed a sparse-array photoacoustic imaging (SPAI) system that is capable of mapping 3D distributions of optical absorption using a small number of laser pulses with no mechanical scanning needed. In previous studies, the authors have shown the localization accuracy and the high frame-rate image acquisition on simple phantoms with limited medical relevance. The purpose of this study was to test the imaging capabilities of SPAI in the context of breast tumor detection and localization.
  
  
  METHODS
  The authors constructed an array of phantoms that include spherical lesions of sizes 1.5-9 mm, buried in highly scattering tissue phantoms at depths of 3-30 mm. The authors investigated both homogeneous lesions made of blood at varying concentrations and heterogeneous lesions containing vessel-like structures. Volumetric images of the deeply buried lesions were taken at increasingly shallower depths and image-based localization was compared to measured depth.
  
  
  RESULTS
  The authors were able to detect and accurately localize homogeneous lesions having a realistic absorption coefficient of 0.2 cm(-1) down to depths of 9-20 mm, and heterogeneous lesions containing 0.5 mm diameter vessel-like structures down to depths of 13-20 mm. Image acquisition required 2.5 s for each volumetric lesion image.
  
  
  CONCLUSIONS
  These results suggest that 3D SPAI can detect highly vascularized lesions well below 1 cm in diameter and can overcome optical scatter of tissue to depths of 1-2 cm. With further improvement in the sensitivity and noise characteristics of the imaging system, similar imaging depths should be within reach in real breast tissue. The method, due to its optical contrast, 3D imaging, and fast acquisition, may prove useful in the clinic as an adjunct to existing breast screening tools.
authors.affiliation: Imaging Program, Lawson Health Research Institute, St. Joseph's Health Care, 268 Grosvenor Street, London, Ontario N6A 4V2, Canada.
authors.forename: Pinhas
authors.initials: P
authors.lastname: Ephrat
authors.forename: Genevieve C
authors.initials: GC
authors.lastname: Albert
authors.forename: Michael B
authors.initials: MB
authors.lastname: Roumeliotis
authors.forename: Michelle
authors.initials: M
authors.lastname: Belton
authors.forename: Frank S
authors.initials: FS
authors.lastname: Prato
authors.forename: Jeffrey J L
authors.initials: JJ
authors.lastname: Carson
mesh_terms: D000042:Absorption; D000162:Acoustics; D001943:Breast Neoplasms / Q000175:diagnosis* / Q000473:pathology*; D004867:Equipment Design; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional / Q000379:methods*; D055095:Optics and Photonics; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012984:Software; D013314:Stress, Mechanical