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We have developed a novel 3D visualization and guidance system for handheld optical imaging
devices. In this paper, the system is applied to measurements of breast/cancerous tissue optical
properties using a handheld diffuse optical spectroscopy (DOS) instrument. The combined
guidance system/DOS instrument becomes particularly useful for monitoring neoadjuvant
chemotherapy in breast cancer patients and for longitudinal studies where measurement
reproducibility is critical. The system uses relatively inexpensive hardware components and
comprises a 6 degrees-of-freedom (DOF) magnetic tracking device including a DC field generator,
three sensors, and a PCI card running on a PC workstation. A custom-built virtual environment
combined with a well-defined workflow provide the means for image-guided measurements,
improved longitudinal studies of breast optical properties, 3D reconstruction of optical properties
within the anatomical map, and serial data registration. The DOS instrument characterizes tissue
function such as water, lipid and total hemoglobin concentration. The patient lies on her back at a
45-degrees angle. Each spectral measurement requires consistent contact with the skin, and lasts
about 5-10 seconds. Therefore a limited number of positions may be studied. In a reference
measurement session, the physician acquires surface points on the breast. A Delaunay-based
triangulation algorithm is used to build the virtual breast surface from the acquired points. 3D
locations of all DOS measurements are recorded. All subsequently acquired surfaces are
automatically registered to the reference surface, thus allowing measurement reproducibility
through image guidance using the reference measurements.
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