title: An optimized ultrasound detector for photoacoustic breast tomography.
abstract: OBJECTIVE
  Photoacoustic imaging has proven to be able to detect vascularization-driven optical absorption contrast associated with tumors. In order to detect breast tumors located a few centimeter deep in tissue, a sensitive ultrasound detector is of crucial importance for photoacoustic mammography. Further, because the expected photoacoustic frequency bandwidth (a few MHz to tens of kHz) is inversely proportional to the dimensions of light absorbing structures (0.5-10+ mm), proper choices of materials and their geometries and proper considerations in design have to be made to implement optimal photoacoustic detectors. In this study, we design and evaluate a specialized ultrasound detector for photoacoustic mammography.
  
  
  METHODS
  Based on the required detector sensitivity and its frequency response, a selection of active material and matching layers and their geometries is made leading to functional detector models. By iteration between simulation of detector performances, fabrication and experimental characterization of functional models an optimized implementation is made and evaluated. For computer simulation, we use 1D Krimholtz-Leedom-Matthaei and 3D finite-element based models.
  
  
  RESULTS
  The experimental results of the designed first and second functional detectors matched with the simulations. In subsequent bare piezoelectric samples the effect of lateral resonances was addressed and their influence minimized by subdicing the samples. Consequently, using simulations, a final optimized detector was designed, with a center frequency of 1 MHz and a -6 dB bandwidth of 0.4-1.25 MHz (fractional bandwidth of ~80%). The minimum detectable pressure was measured to be 0.5 Pa.
  
  
  CONCLUSIONS
  A single-element, large-aperture, sensitive, and broadband detector is designed and developed for photoacoustic tomography of the breast. The detector should be capable of detecting vascularized tumors with 1-2 mm resolution. The minimum detectable pressure is 0.5 Pa, which will facilitate deeper imaging compared to the current systems. Further improvements by proper electrical grounding and shielding and implementation of this design into an arrayed detector will pave the way for clinical applications of photoacoustic mammography.
authors: Biomedical Photonic Imaging Group, Mira Institute for Biomedical Technology and Technical Medicine, University of Twente, Enschede, The Netherlands.
authors: Wenfeng
authors: W
authors: Xia
authors: Daniele
authors: D
authors: Piras
authors: Johan C G
authors: JC
authors: van Hespen
authors: Spiridon
authors: S
authors: van Veldhoven
authors: Christian
authors: C
authors: Prins
authors: Ton G
authors: TG
authors: van Leeuwen
authors: Wiendelt
authors: W
authors: Steenbergen
authors: Srirang
authors: S
authors: Manohar
mesh_terms: D017097:Electric Impedance; D004867:Equipment Design; D020342:Finite Element Analysis; D061088:Photoacoustic Techniques / Q000295:instrumentation*; D014054:Tomography / Q000295:instrumentation*; D016217:Ultrasonography, Mammary / Q000295:instrumentation*