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A generation-2 (Gen-2) handheld optical imager capable of two-dimensional surface and three-dimensional tomographic imaging has recently been developed. Herein, the ability of the handheld imager to detect and resolve two targets under diffuse and fluorescence imaging conditions has been demonstrated via tissue phantom studies. Two-dimensional surface imaging studies demonstrated that two 0.96 cm diameter Indocyannine Green targets were detected and resolved ~0.5  cm apart (between edges) at a target depth of 1 cm during diffuse imaging and up to 2 cm depth during fluorescence imaging. Preliminary 3D tomographic imaging capability to resolve the two targets was also demonstrated, but requires extensive future studies.

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Fiber-free non-contact near-infrared (NIR) imaging devices using wide-field detectors are emerging apart from the contact and fiber-based NIR devices. Unlike the fiber-based devices that can image deep tissues, the fiber-free noncontact devices have been used only for subsurface imaging (≤1 cm) to date. A new compact (7 × 8 × 12 cm 3) handheld Near-Infrared. Optical Scanner (NIROS) has been developed for fiber-free non-contact imaging of deep tissues in both reflectance and transmittance modes. Absorption-contrasted diffuse imaging studies were performed on tissue mimicking cubical phantoms (5.5 × 5.5 × 5.5 cm 3 volume) using India. Ink based targets located at various depths (0.5 to 4 cm) in both reflectance and transmittance modes. Preliminary in vivo breast imaging studies in transmittance mode were also performed to determine the deep target detectability of NIROS. The hand-held NIROS could detect targets up to 1.5 cm in reflectance mode and across the entire depth of the phantom (4 cm deep) in transmittance mode, as observed from phantom studies. Absorption-contrasted targets placed as deep as 6 cm were detectable in vivo breast tissues during transmittance imaging, when comfortable pressure was applied via compression. The non-contact hand-held NIROS demonstrated the ability to detect targets deeper than 1 cm (which was the limit attempted to date using other non-contact NIR devices in phantoms or in vivo). The ability of the portable handheld NIROS to perform deep tissue imaging can allow for in vivo breast imaging studies in the future, with a potential as an initial assessment tool for breast cancer pre-screening.

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