title: Development and characterization of an omnidirectional photoacoustic point source for calibration of a staring 3D photoacoustic imaging system.
abstract: Photoacoustic imaging is a modality which makes use of the contrast provided by optical imaging techniques and the spatial resolution and penetration depth similar to acoustic imaging modalities. We have developed a method for fast 3D photoacoustic imaging using a sparse hemispherical array of transducers. Such a system requires characterization of the transducer's response to an ideal point source in order to accurately reconstruct objects in the imaging volume. First, an attempt was made to design an ideal photoacoustic point source via a combination of liquids which would appropriately scatter and absorb the light such that a spherical distribution was achieved. Methylene blue (MB(+)) was used as the primary optical absorber while Intralipid (IL) was used as the liquid responsible for the optical scatter. A multitude of combinations were tested and the signal uniformity was characterized. The combination of 200 microM MB(+) and 0.09% IL was found to produce the most uniform signal over the range of transducers in the hemispherical array. The liquid source was then characterized over a broader range of azimuthal and zenith angles where it was shown the azimuthal consistency was much greater than the stability seen in different zenith elevations. The source was then used in a calibration scan for an imaging volume of 40 x 40 x 40 mm(3). At 216 points evenly spaced in the imaging volume, parameters were recorded for signal amplitude, width, and time-of-flight. These calibration parameters could then be applied to an iterative reconstruction algorithm in an attempt to more accurately produce images.
authors.affiliation: Imaging Program, Lawson Health Research Institute, St. Joseph's Health Care, 268 Grosvenor St., London, Ontario, N6A 4V2, Canada.
authors.forename: Michael
authors.initials: M
authors.lastname: Roumeliotis
authors.forename: Pinhas
authors.initials: P
authors.lastname: Ephrat
authors.forename: John
authors.initials: J
authors.lastname: Patrick
authors.forename: Jeffrey J L
authors.initials: JJ
authors.lastname: Carson
mesh_terms: D000162:Acoustics; D000465:Algorithms; D002138:Calibration; D003952:Diagnostic Imaging / Q000379:methods*; D004867:Equipment Design; D005336:Fiber Optic Technology; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008027:Light; D008055:Lipids / Q000737:chemistry; D008751:Methylene Blue / Q000737:chemistry; D055100:Optical Fibers; D055095:Optics and Photonics; D015203:Reproducibility of Results; D012542:Scattering, Radiation
chemical_list: D008055:Lipids; D008751:Methylene Blue