Depth Assessment in 2D Planar-Scanning Diffuse Optical Imaging.
Abstract: Methods for
depth assessment in planar-scanning diffuse optical imaging have been recently proposed
for the purpose of advancing optical mammography. The typical 2D planar-scanner includes
a collinear source-detector pair that scans the breast in the x-y plane and provides a
2D projection image. A second optical detector that is off-axis with respect to the
light source has been int... read moreroduced to determine the depth of a detected object from its
spatial shift between the on-axis and off-axis images. The spatial shift of the object
was associated to its depth through a theoretical depth-shift curve obtained with
diffusion theory. The theoretical depth-shift curve has been shown to be insensitive to
variations in sample thickness, background optical properties and inclusion size. In
this study, we have experimentally measured depth-shift curves to verify such
insensitivity and to confirm the validity of the theoretical predictions under practical
experimental conditions that do not match the ideal conditions used to derive the
theoretical depth-shift curves. We have experimentally confirmed the insensitivity of
the depth-shift curve to sample thickness, inclusion size, and background optical
properties for absorption coefficients > 0.09 cm -1. For lower values of the
background absorption coefficient, the experimental depth-shift curves deviate from the
reported theoretical curves resulting in depth assessment differences of 3-7 mm. We
assign this discrepancy to the effect of experimental boundary conditions, which becomes
more significant at low absorption values for which the optically probed volume becomes
larger. Considering the low absorption coefficient of breast tissue in the near-infrared
region (typically ~0.05 cm-1), the results of this thesis indicate that it is
appropriate to experimentally derive a depth-shift curve that is specific to the optical
mammography system to be used.
Thesis (M.S.)--Tufts University, 2013.
Submitted to the Dept. of Biomedical Engineering.
Advisor: Sergio Fantini.
Committee: Irene Georgakoudi, and Misha Kilmer.
Keywords: Biomedical engineering, Optics, and Medical imaging and radiology.read less