194 research outputs found
MMFNet: A Multi-modality MRI Fusion Network for Segmentation of Nasopharyngeal Carcinoma
Segmentation of nasopharyngeal carcinoma (NPC) from Magnetic Resonance Images
(MRI) is a crucial prerequisite for NPC radiotherapy. However, manually
segmenting of NPC is time-consuming and labor-intensive. Additionally,
single-modality MRI generally cannot provide enough information for its
accurate delineation. Therefore, a multi-modality MRI fusion network (MMFNet)
based on three modalities of MRI (T1, T2 and contrast-enhanced T1) is proposed
to complete accurate segmentation of NPC. The backbone of MMFNet is designed as
a multi-encoder-based network, consisting of several encoders to capture
modality-specific features and one single decoder to fuse them and obtain
high-level features for NPC segmentation. A fusion block is presented to
effectively fuse features from multi-modality MRI. It firstly recalibrates
low-level features captured from modality-specific encoders to highlight both
informative features and regions of interest, then fuses weighted features by a
residual fusion block to keep balance between fused ones and high-level
features from decoder. Moreover, a training strategy named self-transfer, which
utilizes pre-trained modality-specific encoders to initialize
multi-encoder-based network, is proposed to make full mining of information
from different modalities of MRI. The proposed method based on multi-modality
MRI can effectively segment NPC and its advantages are validated by extensive
experiments.Comment: 34 pages, 12 figure
Direct Counterfactual Communication with Single Photons
Intuition from our everyday lives gives rise to the belief that information
exchanged between remote parties is carried by physical particles.
Surprisingly, in a recent theoretical study [Salih H, Li ZH, Al-Amri M, Zubairy
MS (2013) Phys Rev Lett 110:170502], quantum mechanics was found to allow for
communication, even without the actual transmission of physical particles. From
the viewpoint of communication, this mystery stems from a (nonintuitive)
fundamental concept in quantum mechanics wave-particle duality. All particles
can be described fully by wave functions. To determine whether light appears in
a channel, one refers to the amplitude of its wave function. However, in
counterfactual communication, information is carried by the phase part of the
wave function. Using a single-photon source, we experimentally demonstrate the
counterfactual communication and successfully transfer a monochrome bitmap from
one location to another by using a nested version of the quantum Zeno effect.Comment: 13 pages, 3 figure
Multi-level Cross-modal Interaction Network for RGB-D Salient Object Detection
Depth cues with affluent spatial information have been proven beneficial in
boosting salient object detection (SOD), while the depth quality directly
affects the subsequent SOD performance. However, it is inevitable to obtain
some low-quality depth cues due to limitations of its acquisition devices,
which can inhibit the SOD performance. Besides, existing methods tend to
combine RGB images and depth cues in a direct fusion or a simple fusion module,
which makes they can not effectively exploit the complex correlations between
the two sources. Moreover, few methods design an appropriate module to fully
fuse multi-level features, resulting in cross-level feature interaction
insufficient. To address these issues, we propose a novel Multi-level
Cross-modal Interaction Network (MCINet) for RGB-D based SOD. Our MCI-Net
includes two key components: 1) a cross-modal feature learning network, which
is used to learn the high-level features for the RGB images and depth cues,
effectively enabling the correlations between the two sources to be exploited;
and 2) a multi-level interactive integration network, which integrates
multi-level cross-modal features to boost the SOD performance. Extensive
experiments on six benchmark datasets demonstrate the superiority of our
MCI-Net over 14 state-of-the-art methods, and validate the effectiveness of
different components in our MCI-Net. More important, our MCI-Net significantly
improves the SOD performance as well as has a higher FPS
COVID-MTL: Multitask Learning with Shift3D and Random-weighted Loss for Automated Diagnosis and Severity Assessment of COVID-19
There is an urgent need for automated methods to assist accurate and
effective assessment of COVID-19. Radiology and nucleic acid test (NAT) are
complementary COVID-19 diagnosis methods. In this paper, we present an
end-to-end multitask learning (MTL) framework (COVID-MTL) that is capable of
automated and simultaneous detection (against both radiology and NAT) and
severity assessment of COVID-19. COVID-MTL learns different COVID-19 tasks in
parallel through our novel random-weighted loss function, which assigns
learning weights under Dirichlet distribution to prevent task dominance; our
new 3D real-time augmentation algorithm (Shift3D) introduces space variances
for 3D CNN components by shifting low-level feature representations of
volumetric inputs in three dimensions; thereby, the MTL framework is able to
accelerate convergence and improve joint learning performance compared to
single-task models. By only using chest CT scans, COVID-MTL was trained on 930
CT scans and tested on separate 399 cases. COVID-MTL achieved AUCs of 0.939 and
0.846, and accuracies of 90.23% and 79.20% for detection of COVID-19 against
radiology and NAT, respectively, which outperformed the state-of-the-art
models. Meanwhile, COVID-MTL yielded AUC of 0.800 0.020 and 0.813
0.021 (with transfer learning) for classifying control/suspected, mild/regular,
and severe/critically-ill cases. To decipher the recognition mechanism, we also
identified high-throughput lung features that were significantly related (P <
0.001) to the positivity and severity of COVID-19.Comment: COVID-19 research; computer vision and pattern recognition; 13 pages,
10 figures and 5 table
Extra-cavity-enhanced difference-frequency generation at 1.63 {\mu}m
A 1632-nm laser has highly important applications in interfacing the
wavelength of rubidium-based quantum memories (795 nm) and the telecom band
(typically 1550 nm) by frequency conversion in three-wave mixing processes. A
1632-nm laser source based on pump-enhanced difference frequency generation is
demonstrated. It has 300 mW of output power, in agreement with simulations, and
a 55% quantum efficiency. An average power fluctuation of 0.51% over one hour
was observed, and 200-kHz linewidth was measured using a delayed
self-heterodyne method.Comment: 7 pages, 5 figures, accepted by Journal of the Optical Society of
America
Nonlinear frequency conversion and manipulation of vector beams in a Sagnac loop
Vector beams (VBs) are widely investigated for its special intensity and
polarization distributions, which is useful for optical micromanipulation,
optical micro-fabrication, optical communication, and single molecule imaging.
To date, it is still a challenge to realize nonlinear frequency conversion
(NFC) and manipulation of such VBs because of the polarization sensitivity in
most of nonlinear processes. Here, we report an experimental realization of NFC
and manipulation of VBs which can be used to expand the available frequency
band. The main idea of our scheme is to introduce a Sagnac loop to solve the
polarization dependence of NFC in nonlinear crystals. Furthermore, we find that
a linearly polarized vector beam should be transformed to an exponential form
before performing the NFC. The experimental results are well agree with our
theoretical model. The present method is also applicable to other wave bands
and second order nonlinear processes, and may also be generalized to the
quantum regime for single photons.Comment: 8 pages, 3 figure
Revealing photons behaviors in a birefringent interferometer
The interferometer is one of the most important devices for revealing the
nature of light and for precision optical metrology. Though lots of experiments
were performed for probing photons behaviors in various configurations, a
complete study of photons behavior in a birefringent interferometer has not
ever been performed. Based on an environmental turbulence immune Mach-Zehnder
interferometer, tunable photonic beatings by rotating a birefringent crystal
versus the temperature of the crystal for both single-photon and two-photon are
observed. Furthermore, the two-photon interference fringes beat two times
faster than the single-photon interference fringes. This beating effect is used
to determine the thermal dispersion coefficients of the two principal
refractive axes with a single measurement, the two-photon interference shows
super-resolution and high sensitivity. Obvious differences between two-photon
and single photon interference are also revealed in an unbalanced situations.
In addition, influences of the photon bandwidth to the beating behaviors that
come from polarization-dependent decoherence are also investigated. Our
findings will be important for better understanding the behavior of two-photon
interference in a birefringent interferometer and for precision optical
metrology with quantum enhancement.Comment: 13 pages, 5 figures. accepted in PR
Topological charge independent frequency conversion of twisted light
Light with orbital angular momentum (OAM), or twisted light, is widely
investigated in the fields of optical communications, quantum information
science and nonlinear optics by harnessing its unbounded dimension. For
light-matter interacting with twisted light like quantum memory and nonlinear
frequency conversion, efficiencies in these processes are usually decreasing
exponentially with topological charges, which severely degrades the fidelity of
the output states. Here we conceive and develop a method to eliminate the
dependence of conversion efficiency on topological charges in second harmonic
generation (SHG) process by utilizing a special designed image technique. The
independence of SHG conversion efficiency on topological charge is verified for
different topological charges, this independence is valid for various pump
power. This method can be generalized to other light matter interaction
processes and will revolute the field of light matter interaction with twisted
light to achieve higher efficiency and higher fidelity.Comment: 5 pages, 3 figures, comments are welcom
Up-conversion imaging processing with field-of-view and edge enhancement
Spiral phase contrast is an important and convenient imaging processing
technology in edge detection, and a broader field-of-view (FOV) of imaging is a
long-pursuing aim to see more regions of the illumination objects. Compared
with near-infrared (NIR) spectrum, the up-conversion imaging in visible
spectrum benefits from the advantages of higher efficiency detection and lower
potential speckle. FOV enhanced and spiral phase contrast up-conversion imaging
processing methods by using second order nonlinear frequency up-conversion from
NIR spectrum to visible spectrum in two different configurations are presented
in this work. By changing the temperature of crystal, controllable spatial
patterns of imaging with more than 4.5 times enhancement of FOV is realized in
both configurations. Additionally, we present numerical simulations of the
phenomenon, which agree well with the experimental observations. Our results
provide a very promising way in imaging processing, which may be widely used in
biomedicine, remote sensing and up-conversion monitoring.Comment: 11 pages,5 figures,22 reference
Contrast-weighted Dictionary Learning Based Saliency Detection for Remote Sensing Images
Object detection is an important task in remote sensing image analysis. To
reduce the computational complexity of redundant information and improve the
efficiency of image processing, visual saliency models have been widely applied
in this field. In this paper, a novel saliency detection model based on
Contrast-weighted Dictionary Learning (CDL) is proposed for remote sensing
images. Specifically, the proposed CDL learns salient and non-salient atoms
from positive and negative samples to construct a discriminant dictionary, in
which a contrast-weighted term is proposed to encourage the contrast-weighted
patterns to be present in the learned salient dictionary while discouraging
them from being present in the non-salient dictionary. Then, we measure the
saliency by combining the coefficients of the sparse representation (SR) and
reconstruction errors. Furthermore, by using the proposed joint saliency
measure, a variety of saliency maps are generated based on the discriminant
dictionary. Finally, a fusion method based on global gradient optimization is
proposed to integrate multiple saliency maps. Experimental results on four
datasets demonstrate that the proposed model outperforms other state-of-the-art
methods
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