Abstract
We report on the design and first in vivo tests of a novel non-contact scanning imaging system for time-domain near-infrared spectroscopy. Our system is based on a null source-detector separation approach and utilizes polarization-selective detection and a fast-gated single-photon avalanche diode to record late photons only. The in-vivo tests included the recording of hemodynamics during arm occlusion and two brain activation tasks. Localized and non-localized changes in oxy- and deoxyhemoglobin concentration were detected for motor and cognitive tasks, respectively. The tests demonstrate the feasibility of non-contact imaging of absorption changes in deeper tissues.
Highlights
Near-infrared spectroscopy (NIRS) is a rapidly evolving non-invasive technique applied to study oxygenation-related processes in biological tissue [1,2,3] and to facilitate the diagnosis of diseases associated with abnormal oxygen supply to tissue, such as stroke [4], cancer [5], peripheral arterial disease [6], or traumatic brain injury [7]
Despite the recent impressive growth of NIRS applications - there are 42 NIRS clinical studies currently underway around the world [8] - there are still some drawbacks compared to other imaging modalities (e.g. Computed Tomography, Magnetic Resonance Imaging), i.e. inadequate spatial resolution, limited depth sensitivity, imprecise anatomical localization, contamination by superficial changes
Two-dimensional (2D) imaging approaches are realized in a variety of different methods, ranging from structured illumination combined with frequency-domain NIRS [10,11,12,13] to flying-spot scanning methods [14]
Summary
Near-infrared spectroscopy (NIRS) is a rapidly evolving non-invasive technique applied to study oxygenation-related processes in biological tissue [1,2,3] and to facilitate the diagnosis of diseases associated with abnormal oxygen supply to tissue, such as stroke [4], cancer [5], peripheral arterial disease [6], or traumatic brain injury [7]. Despite the recent impressive growth of NIRS applications - there are 42 NIRS clinical studies currently underway around the world [8] - there are still some drawbacks compared to other imaging modalities (e.g. Computed Tomography, Magnetic Resonance Imaging), i.e. inadequate spatial resolution, limited depth sensitivity, imprecise anatomical localization, contamination by superficial changes To improve on these shortcomings, NIRS undergoes a transition from a single-point technique employing one or several source-detector pairs towards an optical mapping technique by applying, first of all, large arrays of source-detector pairs [9]. Two-dimensional (2D) imaging approaches are realized in a variety of different methods, ranging from structured illumination combined with frequency-domain NIRS [10,11,12,13] to flying-spot scanning methods [14] These imaging approaches have already been applied to a variety of tasks, such as measuring optical properties of different types of phantoms and biological tissue [10,12,15,16]. Non-contact methods are useful where physical contact causes additional pain to the patient, as in the case of the diagnosis of burn wound severity [17]
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