Imaging Depths of Near-Infrared Quantum Dots in First and Second Optical Windows

Abstract

Potential advantages of quantum dot (QD) imaging in the second optical window (SOW) at 1,000 to 1,400 nm over the first optical window (FOW) at 700 to 900 nm have attracted much interest. QDs that emit at 800 nm (800QDs) and QDs that emit at 1,300 nm (1,300QDs) are used to investigate the imaging depths at the FOW and SOW. QD images in biologic tissues are processed binarized via global thresholding method, and the imaging depths are determined using the criteria of contrast to noise ratio and relative apparent size. Owing to the reduced scattering in the SOW, imaging depth in skin can be extended by approximately three times for 1,300QD/SOW over 800QD/FOW. In liver, excitation of 1,300QD/SOW can be shifted to longer wavelengths; thus, the imaging depth can be extended by 1.4 times. Effects of quantum yield (QY), concentration, incidence angle, polarization, and fluence rate F on imaging depth are comprehensively studied. Under F approved by the Food and Drug Administration, 1,300QDs with 50% QY can reach imaging depths of 29.7 mm in liver and 17.5 mm in skin. A time-gated excitation using 1,000 times higher F pulses can obtain the imaging depth of < 5 cm. To validate our estimates, in vivo whole-body imaging experiments are performed using small-animal models.

Cyto/hemocompatible magnetic hybrid nanoparticles (Ag2S–Fe3O4) with luminescence in the near-infrared region as promising theranostic materials

“…To the best of our knowledge, this is the highest QY reported for Ag 2 S QDs until now and therefore offers a great advantage in deep tissue imaging. As reported by Won et al, improvement of QY is much more efficient than increased concentration in enhancing the signal/noise ratio and the imaging depth [36].…”

Nanotechnologies for Noninvasive Measurement of Drug Release

“…With optical techniques in tissue imaging, viable wavelengths are generally restricted to the “biological window,” a range of wavelengths from 650 to 1400 nm; we will refer to the spectral region from 650 to 1000 nm as the first optical window, and the region from 1000 to 1400 nm as the second optical window. 42,82,131-134 Wavelengths < 650 nm are strongly absorbed by hemoglobin, and those >950 nm light begin to be absorbed by water. 131,135 In addition to probe brightness and tissue penetration depth, optical signal must be larger compared to the background, especially if the background is large and variable.…”

“…Single-walled carbon nanotubes are capable of sensitive in vivo imaging in the second optical window, and QDs which emit within the second optical window showed significant improvement compared to imaging in the first optical window. 41,42,134 Alternatively, upconversion NPs for deep tissue imaging have been developed which are capable of imaging as deep as 3.2 cm through tissue.83 However, approaches to image drug release in the biological window must rely on drugs and NPs that are either photoactive or absorb within this range of wavelengths. In the previously stated examples of NP systems that measure drug release based upon fluorescent resonance energy transfer, the NPs must be excited by a light which can penetrate deep into tissue.…”

Advanced NIR‐II Fluorescence Imaging Technology for In Vivo Precision Tumor Theranostics

“…[3] Besides these conventional imaging modalities, fluorescence imaging is now gaining tremendous attention for its real-time feedback, multiple signals acquirement, high sensitivity, and high spatial resolution, as well as its nonionizing radiation property. [5][6][7][8][9] Benefiting from these unique capabilities, the NIR-II fluorescence imaging is expected to become the next generation intravital imaging technique. Due to the strong photon absorption and scattering as well as tissue autofluorescence, fluorophores emitted in the visible range (400-650 nm) and the first near-infrared (NIR-I, 650-950 nm) spectral windows can only achieve tissue penetration depths within several millimeters, [4] which greatly compromises their applications in animal studies and clinical practices.…”