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Full-field optical angiography (FFOA) has considerable potential for clinical applications in the prevention and diagnosis of various diseases. However, owing to the limited depth of focus attainable using optical lenses, only information about blood flow in the plane within the depth of field can be acquired using existing FFOA imaging techniques, resulting in partially unclear images. To produce fully focused FFOA images, an FFOA image fusion method based on the nonsubsampled contourlet transform and contrast spatial frequency is proposed. Firstly, an imaging system is constructed, and the FFOA images are acquired by intensity-fluctuation modulation effect. Secondly, we decompose the source images into low-pass and bandpass images by performing nonsubsampled contourlet transform. A sparse representation-based rule is introduced to fuse the lowpass images to effectively retain the useful energy information. Meanwhile, a contrast spatial frequency rule is proposed to fuse bandpass images, which considers the neighborhood correlation and gradient relationships of pixels. Finally, the fully focused image is produced by reconstruction. The proposed method significantly expands the range of focus of optical angiography and can be effectively extended to public multi-focused datasets. Experimental results confirm that the proposed method outperformed some state-of-the-art methods in both qualitative and quantitative evaluations.

Human early visual cortex response amplitudes monotonically increase with numerosity (object number), regardless of object size and spacing. However, numerosity is typically considered a high-level visual or cognitive feature, while early visual responses follow image contrast in the spatial frequency domain. We find that, at fixed contrast, aggregate Fourier power (at all orientations and spatial frequencies) follows numerosity closely but nonlinearly with little effect of object size, spacing or shape. This would allow straightforward numerosity estimation from spatial frequency domain image representations. Using 7T fMRI, we show monotonic responses originate in primary visual cortex (V1) at the stimulus’s retinotopic location. Responses here and in neural network models follow aggregate Fourier power more closely than numerosity. Truly numerosity tuned responses emerge after lateral occipital cortex and are independent of retinotopic location. We propose numerosity’s straightforward perception and neural responses may result from the pervasive spatial frequency analyses of early visual processing. The authors show that spatial frequency domain Fourier power closely but nonlinearly follows numerosity, simplifying computing numerosity from early visual responses. Monotonic early visual cortex and neural network responses follow Fourier power, while later tuned responses follow numerosity.

Molecular imaging is a crucial technique in clinical diagnostics but it relies on radioactive tracers or strong magnetic fields that are unsuitable for many patients, particularly infants and pregnant women. Ultra-high-frequency radio-frequency acoustic (UHF-RF-acoustic) imaging using non-ionizing RF pulses allows deep-tissue imaging with sub-millimetre spatial resolution. However, lack of biocompatible and targetable contrast agents has prevented the successful in vivo application of UHF-RF-acoustic imaging. Here we report our development of targetable nanodroplets for UHF-RF-acoustic molecular imaging of cancers. We synthesize all-liquid nanodroplets containing hypertonic saline that are stable for at least 2 weeks and can produce high-intensity UHF-RF-acoustic signals. Compared with concentration-matched iron oxide nanoparticles, our nanodroplets produce at least 1,600 times higher UHF-RF-acoustic signals at the same imaging depth. We demonstrate in vivo imaging using the targeted nanodroplets in a prostate cancer xenograft mouse model expressing gastrin release protein receptor (GRPR), and show that targeting specificity is increased by more than 2-fold compared with untargeted nanodroplets or prostate cancer cells not expressing this receptor. Ultra-high-frequency radio-frequency acoustic molecular imaging is a safe molecular imaging diagnostic option because it does not require radioactive probes or high magnetic fields, but lack of biocompatible targeted contrast agents has so far limited its in vivo application. In this paper the authors present perfluorocarbon nanodroplets containing hypertonic saline solution for targeted molecular imaging of prostate cancer in animal models.

Imaging Cherenkov emission during radiotherapy permits real-time visualization of external beam delivery on superficial tissue. This signal is linear with absorbed dose in homogeneous media, indicating potential for quantitative dosimetry. In humans, the inherent heterogeneity of tissue optical properties (primarily from blood and skin pigment) distorts the linearity between detected Cherenkov signal and absorbed dose. We examine the potential to correct for superficial vasculature using spatial frequency domain imaging (SFDI) to map tissue optical properties for large fields of view. In phantoms, applying intensity corrections to simulate blood vessels improves Cherenkov image (CI) negative contrast by 24% for a vessel 1.9-mm-in diameter. In human trials, SFDI and CI are acquired for women undergoing whole breast radiotherapy. Applied corrections reduce heterogeneity due to vasculature within the sampling limits of the SFDI from a 22% difference as compared to the treatment plan, down to 6% in one region and from 14% down to 4% in another region. The optimal use for this combined imaging system approach is to correct for small heterogeneities such as superficial blood vessels or for interpatient variations in blood/melanin content such that the corrected CI more closely represents the surface dose delivered.

Recent advances in high-field (≥7 T) MRI have made it possible to study the fine structure of the human brain at the level of fiber bundles and cortical layers. In particular, techniques aimed at detecting MRI resonance frequency shifts originating from local variation in magnetic susceptibility and other sources have greatly improved the visualization of these structures. A recent theoretical study [He X, Yablonskiy DA (2009) Proc Natl Acad Sci USA 106:13558–13563] suggests that MRI resonance frequency may report not only on tissue composition, but also on microscopic compartmentalization of susceptibility inclusions and their orientation relative to the magnetic field. The proposed sensitivity to tissue structure may greatly expand the information available with conventional MRI techniques. To investigate this possibility, we studied postmortem tissue samples from human corpus callosum with an experimental design that allowed separation of microstructural effects from confounding macrostructural effects. The results show that MRI resonance frequency does depend on microstructural orientation. Furthermore, the spatial distribution of the resonance frequency shift suggests an origin related to anisotropic susceptibility effects rather than microscopic compartmentalization. This anisotropy, which has been shown to depend on molecular ordering, may provide valuable information about tissue molecular structure.

Focal defects are one of the important features for the diagnosis of lymph node (LN) metastasis. In our previous study, an accurate method for detecting contrast agents was proposed. However, conventional B-mode and contrast-enhanced images via ultrasound contrast agents (UCAs) have the limitations of contrast and spatial resolution to visualize the microcirculation, such as focal defects to distinguish between benign and malignant LN. In the present study, we have developed a novel method based on clutter filtering with singular value decomposition (SVD) analysis using time-integrated amplitude envelope (TIAE) in high-frequency 40 MHz ultrasound for high contrast resolution of the microcirculation in LN tissue. A mouse LN was visualized in vivo without and with UCA to compare the contrast enhancement. A metastatic LN model was established with LM8-luc cells of C3H/HeJ- lpr / lpr and MXH54/Mo- lpr / lpr mice. Bioluminescence imaging and pathological observations were also conducted to evaluate tumor growth. It was found that clutter-filtered contrast-enhanced images with UCA could visualize the feature of the microcirculation in the control LN and focal defects in the metastatic LN. Consistent with histological findings of disrupted architecture and cellular heterogeneity, whereas clutter-filtered B-mode images without UCA failed to visualize the vascular circulation. TIAE provided images with high noise resistance, and the calculated vascular area in the LN showed a decreasing trend in the metastatic group compared to the control group. Our framework enables robust visualization and quantification of LN heterogeneity in microcirculation.

The Tropical Rainfall Measurement Mission (TRMM) satellite is the first to be designed to measure precipitation, and its precipitation products have been assessed in a variety of ways. Data for its post-real-time level 2 product (3B42) performed well in terms of the precipitation amount at the monthly scale because they were corrected by a precipitation dataset that was gauged every month. However, the performance of this dataset in terms of precipitation frequency and intensity is still not ideal. To this end, TRMM 3B42 products were evaluated using precipitation data from 747 meteorological stations over mainland China in this study. The Pearson’s correlation coefficient (CC), relative bias (RB), and relative error (RE) were used to assess the capability of TRMM products in terms of estimating the frequency, intensity, and amount of precipitation for different categories of precipitation during nighttime and daytime in a multiscale analysis (including interannual variation, seasonal cycles, and spatial distribution). Our results showed the following: (1) The 3B42 products reproduced interannual trends of the frequency and amount of precipitation (except for trace precipitation) with an average correlation coefficient of 0.84. (2) 3B42 performed well at calculating the annual and monthly precipitation amount, but performed poorly for frequency and even worse for intensity. The biases in these two properties canceled out, however, which led to a better estimate of the amount. (3) 3B42 represented the distribution of the subdaily amount of precipitation over a majority of the regions in the east, but did not perform well on the Tibetan Plateau or in northwest China. The performance of 3B42, as detailed in this study, can serve as valuable guidance to data users and algorithm developers.

Scene-selective regions were shown to be significantly affected by spatial frequencies (SF) and have different sensitivities to low spatial frequencies (LSF) and high spatial frequencies (HSF). However, previous studies mainly focused on the neural activations or the neural patterns in a single SF band. To investigate the extent to which the information of a single SF is used in scene category representations, we not only decoded the scene categories in each SF, but also used the neural patterns to LSF or HSF to decode the patterns to non-filtered (NF) scenes based on fMRI data using multivoxel pattern analysis (MVPA). As luminance contrast was shown to follow statistical regularities along with SF, we performed the decoding analyses separately in two conditions of contrast where the contrast of LSF and HSF was unmodified or equalized. The results showed distinct SF preferences in the two contrast conditions, showing that luminance contrast has a significant role in SF processing. In addition, we also performed the above analyses only within natural and indoor scenes, respectively. The results showed the scene-selective regions were more efficient in distinguishing natural scene categories in LSF, and the LSF was preferentially used along with high luminance contrast in recognition of natural scenes. On the other hand, humans preferentially used HSF information in distinguishing indoor scenes. This distinct SF preferences maybe caused by the different aspects of information conveyed by LSF and HSF, as well as the different strategies of spatial perception in natural and indoor scenes recognition.

PurposeThis study is to investigate the contrast sensitivity function (CSF) using the quick CSF (qCSF) test in Chinese adults with myopia.MethodsThis case series study included 320 myopic eyes of 160 patients (mean age 27.75 ± 5.99 years) who underwent a qCSF test for acuity, area under log CSF (AULCSF), and mean contrast sensitivity (CS) at 1.0, 1.5, 3.0, 6.0, 12.0, and 18.0 cycle per degree (cpd). Spherical equivalent, corrected-distant visual acuity (CDVA), and pupil size were recorded.ResultsThe spherical equivalent, CDVA (LogMAR), spherical refraction, cylindrical refraction, and the scotopic pupil size of the included eyes were − 6.30 ± 2.27 D (− 14.25 to − 0.88 D), 0 ± 0.02, − 5.74 ± 2.18 D, − 1.11 ± 0.86 D, and 6.77 ± 0.73 mm, respectively. The AULCSF and CSF acuity were 1.01 ± 0.21 and 18.45 ± 5.39 cpd, respectively. The mean CS (log units) at six different spatial frequencies were 1.25 ± 0.14, 1.29 ± 0.14, 1.25 ± 0.14, 0.98 ± 0.26, 0.45 ± 0.28, and 0.13 ± 0.17, respectively. A mixed effect model showed significant correlations between age and acuity, AULCSF, and CSF at 1.0, 12.0, and 18.0 cpd. Interocular CSF differences were correlated with the interocular difference of spherical equivalent, spherical refraction (at 1.0 cpd, 1.5 cpd), and cylindrical refraction (at 12.0 cpd, 18.0 cpd). The lower cylindrical refraction eye had higher CSF compared with the higher cylindrical refraction eye (0.48 ± 0.29 vs. 0.42 ± 0.27 at 12.0 cpd and 0.15 ± 0.19 vs. 0.12 ± 0.15 at 18.0 cpd).ConclusionsThe age-related decrease in contrast sensitivity is at low and high spatial frequencies. Higher-degree myopia may show a decrease in CSF acuity. Low astigmatism was noted to affect the contrast sensitivity significantly.

Exploration of the deep sea and ocean in the marine industry has continued to gain interest in recent years. To get the detailed imaging of deep sea layers, marine vessels and robots are fitted with advanced imaging technologies. There are certain factors like water properties and impurities that affect the quality of the photographs captured by the underwater imaging devices. As sea water absorbs colors, so processing of sea imaging data becomes more challenging. Water light attenuation is a phenomenon that is caused by the absorbance and scattering factors. Certain studies showed that the existence of certain intrinsic shortcomings are attributed to the appearance of objects and ambient noise in underwater images. As a result, it is difficult in a real-time system to distinguish objects from their surroundings in these images. We measures the algorithms performance with respect to various aspects, effect of the hardware and software parts for underwater images and critical review of different underwater image enhancement algorithms. First, we describe some well-known techniques of spatial and frequency domains. Then, we list the existing quantitative measurements which are required to measure the quality of the enhanced image. Finally, the performance of various up-to-date existing methods is compared based on the outcomes of standard quantitative measurements, and factors such as requirements/suitability, and technical aspects, are included. Furthermore, a variety of image databases used for image contrast enhancement is discussed in detail. This study expands the scope for other researchers to understand the important characteristics of different underwater image contrast enhancement methods, and also provides future research directions.