In this paper, we propose an efficient image fusion algorithm using multiple salient features with guided image filter to prevent the problem of low contrast detail. First, we employ the guided image filter to decompose the input images into a series of smoothed and detailed images at different scales. Second, the salient features are extracted from the decomposed smoothed images and detailed images using two different algorithms: the spectral residual (SR) algorithm for extracting mainframe information and the graphbased visual saliency (GBVS) model for extracting gradient saliency information to construct the fusion rules. In addition, generalized intensity-hue-saturation (GIHS) is adopted to combine the decomposition coefficients. Finally, the fused image is reconstructed by the fused smoothed and fused detailed images. The experimental results demonstrate that the proposed algorithm can achieve better performance than other fusion methods in the domains of MRI-PET and MRI-SPECT fusion.

Introduction

With the development of medical imaging technology, modern medical imaging provides multiple diagnostic images for clinical diagnosis, such as computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET), and single-photon emission computed tomography (SPECT) images. They focus on various aspects to provide information. CT and MRI images are anatomical images with a high spatial resolution that provide body contours and soft tissue information. PET and SPECT images are functional images with lower spatial resolution that contain color information that reflects the body’s metabolic level. To overcome the limitations of single medical image information expression and to provide more comprehensive and complementary information for medical diagnosis and treatment, multimodal medical image fusion has been proposed. Multimodal medical image fusion obtains a single fused image in terms of human visual perception to increase the clinical applicability of medical images for the diagnosis and assessment of medical problems [1]. Brain diseases have a high incidence and present a high risk to people’s lives. To provide additional auxiliary information for such diseases, this paper focuses on the fusion of anatomical images and functional images of brain diseases.

I. INTRODUCTION

II. PREPARE-AND-MEASURE PHOTON SUBTRACTION-BASED MDI CV-QKD SCHEME

III. THE EQUIVALENT ENTANGLEMENT ASSISTED PHOTON SUBTRACTION-BASED MDI CV-QKD SCHEME AND CORRESPONDING COVARIANCE MATRICIES

IV. THE SECRET-KEY RATE CALCULATIO

V. ILLUSTRATIVE SECRET-KEY RATE RESULT

VI. CONCLUDING REMARKS

REFERENCES

To potentially overcome the practical security loopholes of CV-QKD protocols, in this paper, we propose to use the optimized eight-state measurement-device-independent (MDI) protocol and demonstrate that it can significantly outperform corresponding Gaussian modulation-based MDI and virtual photon subtraction-based MDI CV-QKD protocols in terms of both secret-key rate and achievable transmission distance. Contrary to the common belief that virtual photon subtraction method can extend the distance of MDI CV-QKD protocols, we show that this is not true for fully optimized MDI CV-QKD protocols and realistic system parameters.

INTRODUCTION

The quantum key distribution (QKD) leverages the principles of quantum mechanics to realize the distribution of keys with security that can be verified [1]–[8]. Various QKD schemes can be placed into two broad categories: discrete variable (DV) and continuous variable (CV) QKD schemes. DV-QKD employs the photon counting, followed by the postelection to identify signaling intervals when the detection takes place [7]. These schemes are affected by the long dead time of the single-photon detectors (SPDs), high dark current rate, and insufficient quantum efficiency. In contrast, the CV-QKD employs either homodyne or heterodyne detection. The long deadtime of SPDs, used in DV-QKD schemes, limits the baud rate and consequently the secret-key rate (SKR). Given that CV-QKD schemes employ the homodyne/heterodyne detection instead, they do not exhibit the deadtime problem. The CV-QKD protocols are typically implemented based on Gaussian modulation (GM) [9]–[14] or discrete modulation (DM) [15]–[19]. (An interested reader interested in differences between GM-based and DM-based CV-QKD schemes is referred to refs. [6] and [7].) The security analysis of CV-QKD schemes typically relies on idealized assumptions, which are very difficult to satisfy in practice. Any imperfection in practical devices yields to the security loophole that can be exploited by Eve to compromise security.

The purpose of this study is to review and compare simulation methods for describing the transport of charge clouds in silicon based semiconductor detectors and investigate the effects on energy spectrum for silicon based photon counting strip detectors. Charge clouds and detailed carrier transport are sim ulated and compared using two different approaches including analytical and Monte Carlo schema. The results of the simulations are evaluated using pulse height spectra (PHS) for a silicon strip detector with edge on geometry at two energies (25 and 75 keV) at various x-ray absorption locations relative to the pixel boundary and detector depth. The findings confirm carrier diffusion plays a large role in the charge sharing effect in photon counting detectors, in particular when the photon is absorbed near the pixel boundary far away from the pixel electrode. The results are further compared in terms of the doublecounting probability for x-ray photons absorbed near the pixel boundary as a function of the threshold energy. Monte Carlo and analytical models show reasonable agreement (2% relative error in swank factor) for charge sharing effects for a silicon strip detector with edge-on geometry. For 25 keV mono-energetic photons absorbed at 5 µm from the pixel boundary, the theoretical threshold energy at 10% double-counting probability based on charge sharing is 5.5, 8.5 and 9.2 keV for absorption depths of 50, 250 and 450 µm from the electrode, respectively. The transport of charge clouds affects the spectral characteristics of photon counting detectors and the double-counting probability results show the theoretical threshold energy to avoid double-counting as a function of x23 ray energy and x-ray interaction locations for silicon and can be considered for future studies of charge sharing effects.

Introduction

Photon-counting detectors with energy discrimination capabilities have been recently developed for many medical x-ray imaging applications[1, 2] promising several advances including the ability to estimate the energy of transmitted photons at each pixel location. This technological development could enable improved material decomposition, higher spatial resolution, and implementa tion of beam hardening corrections.In most cases, photon counting detectors with energy discrimination can achieve higher signal-to-noise ratio[3] leading to improvements in existing modalities or allowing novel applications.[1, 4–8] In addition, photon-counting detectors can be used in spectral CT applications.[9– 15] One major challenge for photon-counting detectors is a phenomenon gen erally known as charge sharing. Under an externally applied bias, a cloud of charge carriers created by the energy imparted by an absorbed x-ray photon travels within the semiconductor and reaches the detector electrode. Near a pixel boundary, the cloud may be divided and detected simultaneously by multiple pixels recording energies lower than the energy carried by the x-ray quantum. The distribution of energy causes distortions in the spectral response. The significance of this effect depend on the detection material, charge carrier mobil ity, pixel size, absorption location with respect to the pixel boundary, depth of interaction within the active detector layer, temperature, applied bias (including non-uniform electric field affects due to Frisch grid structures).

The first two-photon entanglement experiment performed 50 years ago by Kocher and Commins (KC) provided isolated pairs of entangled photons from an atomic three-state fluorescence cascade. In view of questioning of Bell’s theorem, data from these experiments are re-analyzed and shown sufficiently precise to confirm quantum mechanical and dismiss semi-classical theory without need for Bell’s inequalities. Polarization photon correlation anisotropy (A) is useful: A is near unity as predicted quantum mechanically and well above the semi-classic range, 0 6 A 6 1=2. Although yet to be found, one may envisage a three-state molecule emitting entangled photon pairs, in analogy with the KC atomic system. Antibunching in fluorescence from single molecules in matrix and entangled photons from quantum dots promise it be possible. Molecules can have advantages to parametric down-conversion as the latter photon distribution is Poissonian and unsuitable for producing isolated pairs of entangled photons. Analytical molecular applications of entangled light are also envisaged.

Introduction

Statistical characterization of quantum correlations has been guided for half a century by Bell’s inequalities [10,11]. In 1935, in a provocative paper, Einstein, Podolsky and Rosen suggested a hypothetical experiment capable of testing some apparently paradoxical predictions of quantum theory, the EPR paradox [12]. Einstein believed quantum mechanical descriptions of physical systems to be correct only if supplemented with statistical distributions involving certain hidden variables but von Neumann [13] presented a mathematical proof that any hidden-variable theory must be in conflict with quantum mechanics. Bell argued that the proofs, although mathematically correct, rested upon physically unrealistic assumptions and showed that regardless of choice of hidden-parameter framework expectation values will obey certain inequalities [10,11]. The EPR paradox is philosophically interesting and has led also to a paradigmatic concept: ‘‘entanglement” (Schrödinger: ‘‘Verschränkung”) [14] with roots in the wave-particle duality, today finding spreading applicability as briefly reviewed here. In 1950 Wu and Shaknow [15], based on a suggestion by Wheeler [16], demonstrated that the angular correlation of annihilation radiation from positron-electron pairs quantitatively fulfills the asymmetry predicted by quantum pair theory. I will along similar lines consider the asymmetry of the first polarized photon correlation experiments with visible light and show that these are sufficiently precise to rule out local hidden-variable theories with reasonable statistical accuracy, and useful in general (e.g., molecular) contexts. Today’s quantum photon theory and technology follows in my view from mainly two strands of seminal experiments: 1. The discovery by Hanbury Brown and Twiss [17,18] that photons from a thermal source have a tendency to arrive in bunches – an effect characteristic of thermal bosons which can be explained in terms of classical fields. 2. Photon bunching studies by Mandel and coworkers [19,20] with the discovery of photon antibunching by Kimble, Dagenais and Mandel [21], predicted by Fano [22], Glauber [23] and Stoler [24] as a purely quantum field phenomenon. A seminal experiment by Kocher and Commins [1] demonstrated the generation of isolated pairs of entangled photons by an atomic fluorescence cascade and is the focus of this communication. In its wake followed several studies using this technique combined with a suggestion by Clauser, Horne, Shimony and Holt how to test Bell’s inequality by measuring at four combinations of orientations of the polarizers [25–27]. Also two-photon correlation experiments using laser parametric down-conversion technique were reported strongly violating the Bell inequality, however, also substantially the classical probability [28].

ABSTRACT

A transmittance monitor has been developed for the second tagged-photon beamline at the Research Center for Electron Photon Science, Tohoku University, Japan. In this beamline, an internal radiator is employed to produce the bremsstrahlung photon beam out of circulating electrons in a synchrotron. The transmittance, which is defined as the probability of finding a photon coming to the target position when an electron is detected with a photon-tagging counter, should be determined to deduce cross sections for photo-induced reactions. The developed monitor consists of a telescope of thin plastic scintillators with a positron and electron converter, and a dedicated circuit implemented in a field-programmable gate array chip. The transmittance can be measured with this monitor for high-intensity photon beams corresponding to 20 MHz tagging signals. The measured transmittance is found to be constant with respect to the photon intensity for each photon-tagging channel.

Introduction

Photo-induced reactions with the incident energy ranging from several hundred MeV to a few GeV are important to study the structure of hadrons in detail. A hadron is a color-neutral object, and described in principle by quark and gluon dynamics as a solution of the fundamental theory of the strong interaction, quantum chromodynamics (QCD). At low energies, little is known for the solution owing to the large running QCD coupling constant. What are the effective degrees of freedom describing hadrons is a subject of interest associated with the color confinement problem. Meson photoproduction experiments have been conducted [1–5] to give information on the subject with an electromagnetic-calorimeter (EMC) system, FOREST [6], on the second photon beamline [7] at the Research Center for Electron Photon Science (ELPH), Tohoku University, Japan. Fig. 1 shows a schematic view of the second photon beamline at ELPH. Bremsstrahlung photons are generated by inserting a thin carbon fiber (radiator) with a diameter of 11 μm into circulating electrons [7] in the electron synchrotron called Booster STorage (BST) ring (previously known as the STB ring) [8]. The energy of each photon is determined by measuring the momentum of its corresponding post-bremsstrahlung electron with a tagging detector system, STB-Tagger II [7], having 116 photon-tagging channels. Each tagging signal is produced from a telescope of two scintillating fibers with a cross section of 4 × 4 mm2 , covering a photon energy with a width of 0.5–2.8 MeV (?). The tagging signal does not always correspond to a photon arriving at the target. Some of the tagged photons may be converted into a positron and electron (? +? −) pair owing to the material on the photon beamline. These undesirable ? +? − pairs are swept out with a dipole magnet, TAGX [9], which is placed in front of FOREST. Furthermore, a photon is not generated when Møller scattering or Coulomb multiple scattering takes place at the radiator, but the scattered electron might hit a tagging detector. Therefore, the photon transmittance (so called the tagging efficiency), which is defined as the probability of finding a photon coming to the target position when an electron is detected with a tagging detector, should be determined to deduce cross sections for photoinduced reactions. The transmittance is experimentally measured since it is difficult to incorporate all the conditions of circulating electrons in the calculation. So far, we have measured the transmittance, ?? , using an EMC module on the photon beamline. The energy of a photon is measured with the module in response to the tagging signal. The singles rate of the module should be reduced so that it could work, namely the photonbeam intensity should be much lowered. Thus, we make the circulating current in the BST ring very low during the transmittance measurement. We describe a photon beam in this condition as a faint beam.

ORBITAL radiation environments can strongly limit the performance and reliability of spacecraft payloads. Mitigation techniques are typically put in place to prolong the lifetime of these systems. Throughout the duration of a mission, however, single-event transients (SETs) generated by energized particles can still penetrate spacecraft shielding, potentially disrupting the proper operation of circuits. The circuits receiving messages from a ground station are particularly sensitive to these events, since they carry the weakest signals due to long transmission distances and atmospheric attenuation. Therefore, detecting single-event effects is of importance for the proper operation of these systems. The previous work has shown that it is possible to design analog circuits to sense SETs by monitoring changes in voltage or currents in a circuit [1], [2]. In addition, several methods for transient detection in the digital domain have been proposed [3]. However, no methods for sensing SETs in RF systems were found in the literature. RF power detectors are typically used in a variety of applications, including millimeter-wave radiometry [4], envelope detection [5], and built-in-self-testing of RF systems [6], [7]. Silicon–germanium heterojunction bipolar transistors (SiGe HBTs) are excellent candidates to fabricate detectors for space applications, since their performance improves at low temperatures and they exhibit a built-in tolerance to total ionizing dose (TID) up to several Mrad(SiO2) [8]. This paper proposes the use of RF power detectors to sense the occurrence of an SET in RF communications systems. By sampling a small fraction of the signal from the main data path into a power detector, information about the signal-tonoise and distortion ratio can be obtained. This information can be used by the digital subsystem to implement detectiondriven data correction protocols. The proposed concept is illustrated in Fig. 1, which depicts a simplified schematic of a direct-conversion RF receiver. The RF receiver uses several directional couplers between each stage that direct a small fraction of the main signal to the input of an RF power detector.