Arterial spin labeling (ASL) MRI is a non-invasive technique for the quantification of cerebral perfusion, and pseudo-continuous arterial spin labeling (PCASL) has been recommended as the standard implementation by a recent consensus of the community. Due to the low spatial resolution of ASL images, perfusion quantification is biased by partial volume effects. Consequently, several partial volume correction (PVEc) methods have been developed to reduce the bias in gray matter (GM) perfusion quantification. The efficacy of these methods relies on both the quality of the ASL data and the accuracy of partial volume estimates. Here we systematically investigate the sensitivity of different PVEc methods to variability in both the ASL data and partial volume estimates using simulated PCASL data and in vivo PCASL data from a reproducibility study. We examined the PVEc methods in two ways: the ability to preserve spatial details and the accuracy of GM perfusion estimation. Judging by the root-mean-square error (RMSE) between simulated and estimated GM CBF, the spatially regularized method was superior in preserving spatial details compared to the linear regression method (RMSE of 1.2 vs 5.1 in simulation of GM CBF with short scale spatial variations). The linear regression method was generally less sensitive than the spatially regularized method to noise in data and errors in the partial volume estimates (RMSE 6.3 vs 23.4 for SNR = 5 simulated data), but this could be attributed to the greater smoothing introduced by the method. Analysis of a healthy cohort dataset indicates that PVEc, using either method, improves the repeatability of perfusion quantification (within-subject coefficient of variation reduced by 5% after PVEc).

Black phosphorus surface plasmon (BPSP) is a new promising candidate material for electromagnetic field confinement at the subwavelength scale. Here, we theoretically investigated the light confinement, second-order nonlinearity and lifetimes of tunable surface plasmons in nanostructured black phosphorus nanoflakes with superstrates. The grating structure can enhance the local optical field of the fundamental wave (FW) and second harmonic wave (SHW) due to the surface plasmon resonance. Based on the coupled mode theory (CMT), a theoretical model for the nanostructured black phosphorus was established to study the spectrum features of FW. The lifetimes of the plasmonic resonant modes were investigated with the finite difference time domain (FDTD) simulations and CMT. Since the permittivity of black phosphorus depends on its Fermi energy and electron scattering rate, the lifetimes of plasmonic absorption modes are tunable with both the Fermi energy and scattering rate. The intensity, wavelengths and spectral width of BPSP resonance modes and their lifetimes can be precisely controlled with the Fermi energy, scattering rate, side length and refractive index of the superstrate. The sensitivity is described by varying the refractive index of the superstrate such as an aqueous solution. We have introduced a secondorder nonlinear source to investigate the SHW of nanostructured black phosphorus. This paper presents the corner/edge energy distribution and the tunable lifetime of BPSP as well as their unprecedented capability of photon manipulation for second-order nonlinearity within the deep subwavelength scale. The configuration and method are useful for research of the absorption, lifetime of light and nonlinear optical processes in black phosphorus-based optoelectronic devices, especially the modulation and sensing applications.

early detection of compromised circulation is essential for postoperative monitoring of free flap. Hourly clinical checkups such as inspection and palpation still result in a delay in detection. Conversely, optical reflection and temperature measurement are useful alternatives for detecting blood circulation. However, conventional methods that verify ischemia and congestion within a short period have not been reported. In this study, we measured short-term changes in optical reflection and temperature in a rat flap using a wearable flexible sensor probe previously developed in our laboratory. Five ischemia and five congestion groin flap models were measured using a sensor probe and reference devices. Curve fitting was performed on transition signals to evaluate changes in signals and their time constants. The optical reflection signal decreased after venous ligation and increased after arterial ligation. The parameters of the fitted curves indicate a significant difference between congestion and ischemia at p < 0.01 (probability value), which was detected within a few minutes after ligation. However, insufficient significance was observed in the temperature signal. Our method gives supporting information to verify ischemia and congestion, and has the potential to rapidly detect compromised circulation. Tissue transplantation involves surgery to recover tissue defects after cancer excision or injury. Tissue including vasculature is lifted from its original healthy body location and transplanted to the defect location. The tissue, termed a free flap, receives blood supply by anastomosis of arteries and veins at the defect location, restoring circulation to the free flap. As the expected quality of life of patients has been increasing recently, tissue transplantation is more commonly performed in hospitals. However, although the technique has advanced, the risk of flap failure remains 1-9%, depending on the position of the reconstruction 1,2,3,4,5. The key reason for flap failure is compromised circulation in the blood vessels due to thrombosis 1,6,7 , which occurs in one week after the surgery in most cases. Early salvage surgery soon after the compromised circulation event is essential to increase the rescue rate of tissue 8,9. Thus, real time detection of tissue circulation is necessary. Regular postoperative checkups in hospital involve manual checkups such as pin prick tests, inspection, and palpation. Pin prick tests monitor blood circulation by examining bleeding from the skin surface. Slow or absent bleeding occurs with arterial occlusion (ischemia), whereas darker bleeding is observed with venous occlusion (congestion). During inspection, a pale flap colour indicates an ischemia event, whereas a cyanotic purple colour represents a congestion event. During palpation, a decrease in skin temperature may suggest ischemia, but temperature change is not significant during congestion 10. Some groups have reported that hourly checkups of transplanted tissue are required during the first two postoperative days 7,11,...