Significance: Speckle noise is an inherent limitation of optical coherence tomography (OCT) images that makes clinical interpretation challenging. The recent emergence of deep learning could offer a reliable method to reduce noise in OCT images.
Aim: We sought to investigate the use of deep features (VGG) to limit the effect of blurriness and increase perceptual sharpness and to evaluate its impact on the performance of OCT image denoising (DnCNN).
Approach: Fifty-one macula-centered OCT pairs were used in training of the network. Another set of 20 OCT pair was used for testing. The DnCNN model was cascaded with a VGG network that acted as a perceptual loss function instead of the traditional losses of L1 and L2. The VGG network remains fixed during the training process. We focused on the individual layers of the VGG-16 network to decipher the contribution of each distinctive layer as a loss function to produce denoised OCT images that were perceptually sharp and that preserved the faint features (retinal layer boundaries) essential for interpretation. The peak signal-to-noise ratio (PSNR), edge-preserving index, and no-reference image sharpness/blurriness [perceptual sharpness index (PSI), just noticeable blur (JNB), and spectral and spatial sharpness measure (S3)] metrics were used to compare deep feature losses with the traditional losses.
Results: The deep feature loss produced images with high perceptual sharpness measures at the cost of less smoothness (PSNR) in OCT images. The deep feature loss outperformed the traditional losses (L1 and L2) for all of the evaluation metrics except for PSNR. The PSI, S3, and JNB estimates of deep feature loss performance were 0.31, 0.30, and 16.53, respectively. For L1 and L2 losses performance, the PSI, S3, and JNB were 0.21 and 0.21, 0.17 and 0.16, and 14.46 and 14.34, respectively.
Conclusions: We demonstrate the potential of deep feature loss in denoising OCT images. Our preliminary findings suggest research directions for further investigation.
Retinal photography is a non-invasive and well-accepted clinical diagnosis of ocular diseases. Qualitative and quantitative assessment of retinal images is crucial in ocular diseases related clinical application. Pulsatile properties caused by cardiac rhythm, such as spontaneous venous pulsation (SVP) and pulsatile motion of small arterioles, can be visualized by dynamic retinal imaging techniques and provide clinical significance. In this paper, we aim at vessel pulsatile motion detection and measurement. We proposed a novel approach for pulsatile motion measurement of retinal blood vessels by applying retinal image registration, blood vessel detection and blood vessel motion detection and measurement on infrared retinal image sequences. The performance of the proposed methods was evaluated on 8 image sequences with 240 images. A preliminary result has demonstrated the good performance of the method for blood vessel pulsatile motion observation and measurement.
Retinal photography is a non-invasive and well-accepted clinical diagnosis of ocular diseases. Qualitative and quantitative assessment of retinal images is crucial in ocular diseases related clinical application. In this paper, we proposed approaches for improving the quality of blood vessel detection based on our initial blood vessel detection methods. A blood vessel spur pruning method has been developed for removing the blood vessel spurs both on vessel medial lines and binary vessel masks, which are caused by artifacts and side-effect of Gaussian matched vessel enhancement. A Gaussian matched filtering compensation method has been developed for removing incorrect vessel branches in the areas of low illumination. The proposed approaches were applied and tested on the color fundus images from one publicly available database and our diabetic retinopathy screening dataset. A preliminary result has demonstrated the robustness and good performance of the proposed approaches and their potential application for improving retinal blood vessel detection.
Retinal optic cup-disk-ratio (CDR) is a one of important indicators of glaucomatous neuropathy. In this paper, we
propose a novel multi-step 4-quadrant thresholding method for optic disk segmentation and a multi-step temporal-nasal segmenting method for optic cup segmentation based on blood vessel inpainted HSL lightness images and green images. The performance of the proposed methods was evaluated on a group of color fundus images and compared with the manual outlining results from two experts. Dice scores of detected disk and cup regions between the auto and manual results were computed and compared. Vertical CDRs were also compared among the three results. The preliminary experiment has demonstrated the robustness of the method for automatic optic disk and cup segmentation and its potential value for clinical application.
Retinal images are long-accepted clinical diagnostic method for ocular diseases. Of late, automated assessment of retinal
images has proven to be a useful adjunct in clinical decision support systems. In this paper, we propose a retinal image
registration method, which combine retinal image enhancement and non-rigid image registration methods, for
longitudinal retinal image alignment. A further illumination correction and gray value matching methods are applied for
the longitudinal image comparison and subtraction. The solution can enhance the assessment of longitudinal changes of
retinal images and image subtraction in a clinical application system. The performance of the proposed solution has been
tested on longitudinal retinal images. Preliminary results have demonstrated the accuracy and robustness of the solutions
and their potential application in a clinical environment.
Small animal image registration is challenging because of its joint structure, and posture and position difference in each
acquisition without a standard scan protocol. In this paper, we face the issue of mouse whole-body skeleton registration
from CT images. A novel method is developed for analyzing mouse hind-limb and fore-limb postures based on geodesic
path descriptor and then registering the major skeletons and fore limb skeletons initially by thin-plate spline (TPS)
transform based on the obtained geodesic paths and their enhanced correspondence fields. A target landmark correction
method is proposed for improving the registration accuracy of the improved 3D shape context non-rigid registration
method we previously proposed. A novel non-rigid registration framework, combining the skeleton posture analysis,
geodesic path based initial alignment and 3D shape context model, is proposed for mouse whole-body skeleton
registration. The performance of the proposed methods and framework was tested on 12 pairs of mouse whole-body
skeletons. The experimental results demonstrated the flexibility, stability and accuracy of the proposed framework for
automatic mouse whole body skeleton registration.
Automatic small animal whole-body organ registration is challenging because of subject's joint structure, posture and
position difference and loss of reference features. In this paper, an improved 3D shape context based non-rigid
registration method is applied for mouse whole-body skeleton registration and lung registration. A geodesic path based
non-rigid registration method is proposed for mouse torso skin registration. Based on the above registration methods, a
novel non-rigid registration framework is proposed for mouse whole-body organ mapping from an atlas to new scanned
CT data. A preliminary experiment was performed to test the method on lung and skin registration. A whole-body organ
mapping was performed on three target data and the selected organs were compared with the manual outlining results.
The robust of the method has been demonstrated.
3D shape context is a method to define matching points between similar shapes as a pre-processing step to non-rigid
registration. The main limitation of the approach is point mismatching, which includes long geodesic distance mismatch
and neighbors crossing mismatch. In this paper, we propose a topological structure verification method to correct the
long geodesic distance mismatch and a correspondence field smoothing method to correct the neighbors crossing
mismatch. A robust 3D shape context model is proposed and further combined with thin-plate spline model for non-rigid
surface registration. The method was tested on phantoms and rat hind limb skeletons from micro CT images. The results
from experiments on mouse hind limb skeletons indicate that the approach is robust.
Micro-CT/PET imaging scanner provides a powerful tool to study tumor in small rodents in response to therapy.
Accurate image registration is a necessary step to quantify the characteristics of images acquired in longitudinal studies.
Small animal registration is challenging because of the very deformable body of the animal often resulting in different
postures despite physical restraints. In this paper, we propose a non-rigid registration approach for the automatic
registration of mouse whole body skeletons, which is based on our improved 3D shape context non-rigid registration
method. The whole body skeleton registration approach has been tested on 21 pairs of mouse CT images with variations
of individuals and time-instances. The experimental results demonstrated the stability and accuracy of the proposed
method for automatic mouse whole body skeleton registration.
Small animal registration is an important step for molecular image analysis. Skeleton registration from whole-body or
only partial micro Computerized Tomography (CT) image is often performed to match individual rats to atlases and
templates, for example to identify organs in positron emission tomography (PET). In this paper, we extend the shape
context matching technique for 3D surface registration and apply it for rat hind limb skeleton registration from CT
images. Using the proposed method, after standard affine iterative closest point (ICP) registration, correspondences
between the 3D points from sour and target objects were robustly found and used to deform the limb skeleton surface
with thin-plate-spline (TPS). Experiments are described using phantoms and actual rat hind limb skeletons. On animals,
mean square errors were decreased by the proposed registration compared to that of its initial alignment. Visually,
skeletons were successfully registered even in cases of very different animal poses.
KEYWORDS: Optic nerve, Magnetic resonance imaging, Retina, Manganese, Visualization, Image segmentation, Signal detection, Animal model studies, Interference (communication), 3D modeling
Investigating whether manganese transport is impaired in the optic nerve of small animal model is a new approach for
evaluating optic neuritis. One needs to quantify signal intensity enhancement due to Mn2+ after intra-orbital injection,
along the optic nerve from MR images. Quantification is very challenging as the optic nerve (ON) is not straight, its
location does not correspond to standard slice orientation, the noise is substantial, and the signal is subject to
inhomogeneity from the coil sensitivity. In this paper, we propose a semi-automatic method whereby 1) the retina point
and the start of the chiasm in a mouse brain MR image are defined manually in a 3D visualization environment, 2) optic
nerve in reformatted slices perpendicular to the optic nerve segment is semi-manually selected, 3) an automatic
algorithm extracts the intensities along the optic nerve while correcting for intensity inhomogeneity, and 4) a model for
the Mn2+ diffusion with a exponential decay function is fitted to the intensity profile. Results for the study of
experimental autoimmune encephalomyelitis (EAE) are reported whereby statistically significant differences were found
between the EAE and the control group.
Extraction and reconstruction of rectal wall structures from an ultrasound image is helpful for surgeons in rectal clinical diagnosis and 3-D reconstruction of rectal structures from ultrasound images. The primary task is to extract the boundary of the muscular layers on the rectal wall. However, due to the low SNR from ultrasound imaging and the thin muscular layer structure of the rectum, this boundary detection task remains a challenge. An active contour model is an effective high-level model, which has been used successfully to aid the tasks of object representation and recognition in many image-processing applications. We present a novel multigradient field active contour algorithm with an extended ability for multiple-object detection, which overcomes some limitations of ordinary active contour models—"snakes." The core part in the algorithm is the proposal of multigradient vector fields, which are used to replace image forces in kinetic function for alternative constraints on the deformation of active contour, thereby partially solving the initialization limitation of active contour for rectal wall boundary detection. An adaptive expanding force is also added to the model to help the active contour go through the homogenous region in the image. The efficacy of the model is explained and tested on the boundary detection of a ring-shaped image, a synthetic image, and an ultrasound image. The experimental results show that the proposed multigradient field-active contour is feasible for multilayer boundary detection of rectal wall.
KEYWORDS: 3D image processing, 3D displays, Image processing, 3D visualizations, Tumors, Ultrasonography, Image display, Detection and tracking algorithms, Java, 3D modeling
This paper presents a software system prototype for rectal wall ultrasound image processing, image display and 3D reconstruction and visualization of the rectal wall structure, which is aimed to help surgeons cope with large quantities of rectal wall ultrasound images. On the core image processing algorithm part, a novel multigradient field active contour model proposed by authors is used to complete the multi-layer boundary detection of the rectal wall. A novel unifying active contour model, which combines region information, gradient information and contour's internal constraint, is developed for tumor boundary detection. The region statistical information is described accurately by Gaussian Mixture Model, whose parameter solution is computed by Expectation-Maximization algorithm. The whole system is set up on Java platform. Java JAI technology is used for 2D image display, Java3D technology is employed for 3D reconstruction and visualization. The system prototype is currently composed of three main modules: image processing, image display and 3D visualization.
The Project of 3D reconstruction of rectal wall structure aims at developing an analysis system to help surgeons cope with a large quantities of rectal ultrasound images, involving muscular layer detection, rectal tumor detection, and 3D reconstruction, etc. In the procedure of tumor detection, a traditional active contour model suffers some difficulties for finding the boundary of tumor when it deforms from the seed in the interior of a tumor. In this paper, we proposed a novel united active contour model with the information of image region feature and image gradient feature for the purpose of tumor detection. Region-based method added in the model, however, introduces a statistical method into the segmentation of the image and hence becomes less sensitive to noise. The originality in this algorithm is that we introduce a Gaussian Mixture Model (GMM) into the statistical model description of seed region. This model can perform more accurate and optimal statistical description than a single Gaussian model. A K-means algorithm and an Expectation Maximization (EM) algorithm are used for optimal parameter estimation of GMM. The experimental results show the new model has more optimal performance for image segmentation and boundary finding than classical active contour model.
This paper is devoted to the control problem of a robot manipulator for a class of constrained motions in an unknown environment. To accomplish a task in the presence of uncertainties, we propose a new guidance and control strategy based on multisensor fusion. Three different sensors-robot joint encoders, a wrist force-torque sensor and a vision system--are utilized for our task. First of all, a sensor-based hybrid position/force control scheme is proposed for an unknown contact surface. Secondly, a new multisensor fusion scheme is utilized to handle an uncalibrated workcell, wherein the surface on which there is a path to be followed by a robot is assumed to be unknown but visible by the vision system and the precise position and orientation of camera(s) with respect to the base frame of the robot is also assumed to be unknown. Our work is related with areas such as visual servoing, multisensor fusion and robot control for constrained motion. The main features of the proposed approach are: (1) multi-sensor fusion is used both for two disparate sensors (i.e. force- torque and visual sensors) and for complementary observed data rather than redundant ones as in traditional way; (2) visual servoing is realized on the tangent space of the unknown surface; (3) calibration of the camera with respect to the robot is not needed.
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