SPEEDING-UP RE-SAMPLED ALGORITHM IN RAY CASTING VOLUME RENDERING OF MEDICAL IMAGES

Ray casting algorithm can obtain a better quality image in volume rendering, however, it exists some problems, such as powerful computing capacity and slow rendering speed. How to improve the re-sampled speed is a key to speed up the ray casting algorithm. An algorithm is introduced to reduce matrix computation by matrix transformation characteristics of re-sampling points in a two coordinate system. The projection of 3-D datasets on image plane is adopted to reduce the number of rays. Utilizing boundary box technique avoids the sampling in empty voxel. By extending the Bresenham algorithm to three dimensions, each re-sampling point is calculated. Experimental results show that a two to three-fold improvement in rendering speed using the optimized algorithm, and the similar image quality to traditional algorithm can be achieved. The optimized algorithm can produce the required quality images, thus reducing the total operations and speeding up the volume rendering.

Analysis of Direct Volume Rendering in VTK

This paper introduces the techniques of direct volume rendering in VTK and discusses ray-casting--the most popular technique of direct volume rendering. The visualizations for medical volumetric data by three functions of raycasting are offered. Visualization effects prove that VTK is easy to get satisfied resuits with good quality in short time.

Evaluating the Growth of Pulmonary Nodular Ground-glass Opacity on CT: Comparison of Volume Rendering and Thin Slice Images

This study examined the value of volume rendering （VR） interpretation in assessing the growth of pulmonary nodular ground-glass opacity （nGGO）. A total of 47 nGGOs （average size, 9.5 mm; range, 5.7-20.6 mm） were observed by CT scanning at different time under identical parameter settings. The growth of nGGO was analyzed by three radiologists by comparing the thin slice （TS） CT images of initial and repeat scans with side-by-side cine mode. One week later synchronized VR images of the two scans were compared by side-by-side cine mode to evaluate the nGGO growth. The nodule growth was rated on a 5-degree scale： notable growth, slight growth, dubious growth, stagnant growth, shrinkage. Growth standard was defined as： Density increase 〉 30 HU and （or） diameter increase （by 20% in nodules 〉_10 mm, 30% in nodules of 5-9 mm）. Receiver operating characteristic （ROC） was performed. The results showed that 32 nGGOs met the growth criteria （29 nGGOs showed an increase in density; 1 nGGO showed an increase in diameter; 2 nGGOs showed an increase in both diameter and density）. Area under ROC curve revealed that the performance with VR interpretation was better than that with TS interpretation （P〈0.01, P〈0.05 and P〈0.05 for observers A, B and C respectively）. Consistency between different observers was excellent with both VR interpretation （κ=0.89 for observers A＆C A＆B, B＆C） and TS interpretation （κ=0.71 for A＆B, κ=0.68 for A＆C, κ=0.74 for B＆C）, but time spending was less with VR interpretation than with TS interpretation （P〈0.0001, P〈0.0001 and P〈0.05 for observers A, B and C, respectively）. It was concluded that VR is a useful technique for evaluating the growth of nGGO.

Fast interactive volume rendering method for adjustable vessel segmentation visualization

Medical diagnosis software and computer-assisted surgical systems often use segmented image data to help clinicians make decisions. The segmentation extracts the region of interest from the background, which makes the visualization clearer. However, no segmentation method can guarantee accurate results under all circumstances. As a result, the clinicians need a solution that enables them to check and validate the segmentation accuracy as well as displaying the segmented area without ambiguities. With the method presented in this paper, the real CT or MR image is displayed within the segmented region and the segmented boundaries can be expanded or contracted interactively. By this way, the clinicians are able to check and validate the segmentation visually and make more reliable decisions. After experiments with real data from a hospital, the presented method is proved to be suitable for efficiently detecting segmentation errors. The new algorithm uses new graphic processing uint （GPU） shading functions recently introduced in graphic cards and is fast enough to interact oil the segmented area, which was not possible with previous methods.

A Volume Rendering Algorithm for Sequential 2D Medical Images

Volume rendering of 3D data sets composed of sequential 2D medical images has become an important branch in image processing and computer graphics. To help physicians fully understand deep seated human organs and focuses ( e.g. a tumour) as 3D structures, in this paper, we present a modified volume rendering algorithm to render volumetric data. Using this method, the projection images of structures of interest from different viewing directions can be obtained satisfactorily. By rotating the light source and the observer eyepoint, this method avoids rotates the whole volumetric data in main memory and thus reduces computational complexity and rendering time. Experiments on CT images suggest that the proposed method is useful and efficient for rendering 3D data sets.

Value of helical CT volume rendering technique in post-operative evaluation of screw in screw fixation of axis fractures

To explore the value of helical CT volume rendering technique (VRT) in post-operative evaluation of screw fixation of axis fractures.Methods There were 21 cases of screw fixation of axis fractures between February 2002 and May 2004 in the study including six cases with fractures on axis body,five on odontoid process and 10 on axis body and odontoid process.All cases received X-ray plain film,helical CT scanning,multi-planar reformatting(MPR) and VRT.Results Screw fixation through axis body and massa lateralis atlantis was performed in 10 cases and that through axis body and odontoid process in 11.VRT could clearly display full aperture of screw orbit,location of screw and angle of fixation and hence was superior to X-ray plain film and MPR.Multi-angle VRT displayed asymmetrical space of odontoid process and massa lateralis atlantis in four cases and medial deviation of 2～5 mm of half screw in screw fixation through axis body and massa lateralis atlantis in six.Conclusion VRT can eliminate false shadow of fixation screw,clearly display full aperture of screw orbit and hence supply improtant imaging evidence for post-operative evaluation of screw fixation of axis fractures.7 refs,1 fig,1 tab.

An Improved HVQ Algorithm for Compression and Rendering of Space Environment Volume Data with Multi-correlated Variables

Volume visualization can not only illustrate overall distribution but also inner structure and it is an important approach for space environment research.Space environment simulation can produce several correlated variables at the same time.However,existing compressed volume rendering methods only consider reducing the redundant information in a single volume of a specific variable,not dealing with the redundant information among these variables.For space environment volume data with multi-correlated variables,based on the HVQ-1d method we propose a further improved HVQ method by compositing variable-specific levels to reduce the redundant information among these variables.The volume data associated with each variable is divided into disjoint blocks of size 43 initially.The blocks are represented as two levels,a mean level and a detail level.The variable-specific mean levels and detail levels are combined respectively to form a larger global mean level and a larger global detail level.To both global levels,a splitting based on a principal component analysis is applied to compute initial codebooks.Then,LBG algorithm is conducted for codebook refinement and quantization.We further take advantage of progressive rendering based on GPU for real-time interactive visualization.Our method has been tested along with HVQ and HVQ-1d on high-energy proton flux volume data,including>5,>10,>30 and>50 MeV integrated proton flux.The results of our experiments prove that the method proposed in this paper pays the least cost of quality at compression,achieves a higher decompression and rendering speed compared with HVQ and provides satisficed fidelity while ensuring interactive rendering speed.

Hardware Assisted Fast Volume Rendering with Boundary Enhancement

In this paper, a new volume rendering method with boundary enhancement is presented. The boundary is extracted and represented by surfaces explicitly. Then, using 3D texture mapping and graphics acceleration hardware, the volume data can be rendered with controllable boundary shading effect almost in real time. Test shows that this method is 4-5 times faster than the previous methods. Moreover, it can also be extended to render the surfaces and the volumetric data together interactively.

A cache-friendly sampling strategy for texture-based volume rendering on GPU

The texture-based volume rendering is a memory-intensive algorithm.Its performance relies heavily on the performance of the texture cache.However,most existing texture-based volume rendering methods blindly map computational resources to texture memory and result in incoherent memory access patterns,causing low cache hit rates in certain cases.The distance between samples taken by threads of an atomic scheduling unit(e.g.a warp of 32 threads in CUDA)of the GPU is a crucial factor that affects the texture cache performance.Based on this fact,we present a new sampling strategy,called Warp Marching,for the ray-casting algorithm of texture-based volume rendering.The effects of different sample organizations and different thread-pixel mappings in the ray-casting algorithm are thoroughly analyzed.Also,a pipeline manner color blending approach is introduced and the power of warp-level GPU operations is leveraged to improve the efficiency of parallel executions on the GPU.In addition,the rendering performance of the Warp Marching is view-independent,and it outperforms existing empty space skipping techniques in scenarios that need to render large dynamic volumes in a low resolution image.Through a series of micro-benchmarking and real-life data experiments,we rigorously analyze our sampling strategies and demonstrate significant performance enhancements over existing sampling methods.

Composed Scattering Model for Direct Volume Rendering

Based on the equation of transfer in transport theory of optical physics,a new volume rendering model, called composed scattering model (CSM), is presented. In calculating the scattering term of the equation, it is decomposed into volume scattering intensity and surface scattering intensity, and they are composed with the boundary detection operator as the weight function. This proposed model differs from the most current volume rendering models in the aspect that in CSM segmentation and illumination intensity calculation are taken as two coherent parts while in ekisting models they are regarded as two separate ones. This model has been applied to the direct volume rendering of 3D data sets obtained by CT and MRI. The resultant images show not only rich details but also clear boundary surfaces. CSM is demonstrated to be an accurate volume rendering model suitable for CT and MRI data sets.

Modeling and volume rendering approach of underwater three-dimensional acoustic energy field

The underwater acoustics is primary and most effective method for underwater object detection and the complex underwater acoustics battlefield environment can be visually described by the three-dimensional(3D)energy field.Through solving the 3D propagation models,the traditional underwater acoustics volume data can be obtained,but it is large amount of calculation.In this paper,a novel modeling approach,which transforms two-dimensional(2D)wave equation into 2D space and optimizes energy loss propagation model,is proposed.In this way,the information for the obtained volume data will not be lost too much.At the same time,it can meet the requirements of data processing for the real-time visualization.In the process of volume rendering,3D texture mapping methods is used.The experimental results are evaluated on data size and frame rate,showing that our approach outperforms other approaches and the approach can achieve better results in real time and visual effects.

A Scalable Data-Distributed Algorithm for Volume Rendering on Parallel Virtual Machines

An algorithm is presented for volume rendering in environments of parallel virtual machines. To reduce the communication cost, as well as to guarantee the locality of all subtasks, the volume data is divided into and organized as a series of slices. The task subdivision algorithm produces acceptable load balancing by maintaining and employing a database of performance indices. An asynchronous binary method merges all partial images in O(logn) time. An efficient development platform based on TCP/IP and Socket standards can help parallelize various rendering algorithms on virtual machines. Our algorithm was implemented on this platform using the classical client/server paradigm. The scalabilities of both task size and host number were tested experimentally.

Introducing Cinematic Rendering: A Novel Technique for Post-Processing Medical Imaging Data

Since the 1980s, various techniques have been used in the field of medicine for the post-processing of medical imaging data from computed tomography (CT) and magnetic resonance (MR). They include multiplanar reformations (MPR), maximum intensity projection (MIP) and Volume Rendering (VR). This paper presents the prototype of a new means of post-processing radiological examinations such as CT and MR, a technique that, for the first time, provides photorealistic visualizations of the human body. This new procedure was inspired by the quality of images achieved by animation software such as programs used in the entertainment industry, particularly to produce animated films. Thus, the name: Cinematic Rendering. It is already foreseeable that this new method of depiction will quickly be incorporated into the set of instruments employed in socalled virtual anatomy (teaching anatomy through the use of radiological depictions of the human body via X-ray, CT and MR in addition to the use of computer animation programs designed especially for human anatomy). Its potential for medical applications will have to be evaluated by future scientific investigations.

Fast B-spline surface extraction algorithm of seismic volume data on GPU

In the process of seismic data interpretation, the extraction of a horizon or a fault is generally needed. In this paper we present a fast extraction method. First select some feature points interactively, then reconstruct the surface according to the selected feature points by using B-spline interpolation curve or surface. In order to solve the error-drawing problem appeared in the process of interactive rendering, which is caused by the change of sampling interval as the view point changes, we combine shear-warp and splatting algorithm to render the surface. The rendering of seismic data and specific surface in our work are achieved on GPU platform using CUDA programming language, which make it able to meet the requirements of real-time rendering.

A Transfer Function Design for Medical Volume Data Using a Knowledge Database Based on Deep Image and Primitive Intensity Profile Features Retrieval

Direct volume rendering(DVR)is a technique that emphasizes structures of interest(SOIs)within a volume visually,while simultaneously depicting adjacent regional information,e.g.,the spatial location of a structure concerning its neighbors.In DVR,transfer function(TF)plays a key role by enabling accurate identification of SOIs interactively as well as ensuring appropriate visibility of them.TF generation typically involves non-intuitive trial-and-error optimization of rendering parameters,which is time-consuming and inefficient.Attempts at mitigating this manual process have led to approaches that make use of a knowledge database consisting of pre-designed TFs by domain experts.In these approaches,a user navigates the knowledge database to find the most suitable pre-designed TF for their input volume to visualize the SOIs.Although these approaches potentially reduce the workload to generate the TFs,they,however,require manual TF navigation of the knowledge database,as well as the likely fine tuning of the selected TF to suit the input.In this work,we propose a TF design approach,CBR-TF,where we introduce a new content-based retrieval(CBR)method to automatically navigate the knowledge database.Instead of pre-designed TFs,our knowledge database contains volumes with SOI labels.Given an input volume,our CBR-TF approach retrieves relevant volumes(with SOI labels)from the knowledge database;the retrieved labels are then used to generate and optimize TFs of the input.This approach largely reduces manual TF navigation and fine tuning.For our CBR-TF approach,we introduce a novel volumetric image feature which includes both a local primitive intensity profile along the SOIs and regional spatial semantics available from the co-planar images to the profile.For the regional spatial semantics,we adopt a convolutional neural network to obtain high-level image feature representations.For the intensity profile,we extend the dynamic time warping technique to address subtle alignment differences between similar profiles(SOIs).Finally,we propose a two-stage CBR scheme to enable the use of these two different feature representations in a complementary manner,thereby improving SOI retrieval performance.We demonstrate the capabilities of our CBR-TF approach with comparison with a conventional approach in visualization,where an intensity profile matching algorithm is used,and also with potential use-cases in medical volume visualization.

VolGraph-A PC-Based Visualization System for Three-Dimensional Medical Reconstructions

Three-dimensional reconstructions from tomography slices are paid great attention in medical applications nowadays. This paper introduces the design and the implement of VolGraph system: a new, inexpensive, PC-based visualization tool for three-dimensional medical reconstructions, which fully integrates the latest popular visualization algorithms ranging from classical surface rendering algorithm to volume rendering algorithms, such as Ray Casting, Splatting, and Shear-Warp.The input of VolGraph can be medical ima- ges including CT, MRI, etc, and the output can be in common image, VRML/XML or animation formats. Practice proves that the realization of a medical volume visualization system is now feasible on desktop PCs.

GPU-based multi-slice per pass algorithm in interactive volume illumination rendering

Volume rendering plays a significant role in medical imaging and engineering applications.To obtain an improved three-dimensional shape perception of volumetric datasets,realistic volume illumination has been considerably studied in recent years.However,the calculation overhead associated with interactive volume rendering is unusually high,and the solvability of the problem is adversely affected when the data size and algorithm complexity are increased.In this study,a scalable and GPU-based multi-slice per pass(MSPP)volume rendering algorithm is proposed which can quickly generate global volume shadow and achieve a translucent effect based on the transfer function,so as to improve perception of the shape and depth of volumetric datasets.In our real-world data tests,MSPP significantly outperforms some complex volume shadow algorithms without losing the illumination effects,for example,half-angle slicing.Furthermore,the MSPP can be easily integrated into the parallel rendering frameworks based on sort-first or sort-last algorithms to accelerate volume rendering.In addition,its scalable slice-based volume rendering framework can be combined with several traditional volume rendering frameworks.

Level-of-Detail Rendering of Large-Scale Irregular Volume Datasets Using Particles

This paper describes a level-of-detail rendering technique for large-scale irregular volume datasets.It is well known that the memory bandwidth consumed by visibility sorting becomes the limiting factor when carrying out volume rendering of such datasets.To develop a sorting-free volume rendering technique,we previously proposed a particle-based technique that generates opaque and emissive particles using a density function constant within an irregular volume cell and projects the particles onto an image plane with sub-pixels.When the density function changes significantly in an irregular volume cell,the cell boundary may become prominent,which can cause blocky noise.When the number of the sub-pixels increases,the required frame buffer tends to be large.To solve this problem,this work proposes a new particle-based volume rendering which generates particles using metropolis sampling and renders the particles using the ensemble average. To confirm the effectiveness of this method,we applied our proposed technique to several irregular volume datasets,with the result that the ensemble average outperforms the sub-pixel average in computational complexity and memory usage. In addition,the ensemble average technique allowed us to implement a level of detail in the interactive rendering of a 71-million-cell hexahedral volume dataset and a 26-million-cell quadratic tetrahedral volume dataset.

Overview of optical coherence tomography in neuro-ophthalmology

Optical coherence tomography(OCT)is a widely used non-invasive medical imaging technology that has revolutionized clinical care in ophthalmology.New developments,such as OCT angiography(OCTA)are expected to contribute even further to the widespread use of OCT-based imaging devices in the diagnosis and monitoring of patients with ophthalmic diseases.In recent years,many of the disadvantages such as limited field of view and imaging artefacts have been substantially reduced.Similar to the progress achieved in the assessment of retinal disorders,OCT is expected to change the approach to patients seen in the neuro-ophthalmology clinic.In this article,we review the technical features of OCT and OCT-based imaging techniques,highlighting the specific factors that should be taken into account when interpreting OCT in the field of neuro-ophthalmology.

Application of 3D Electrical Resistivity Tomography for Diagnosing Leakage in Earth Rock-Fill Dam

The leakage occurs during operation of the dam in Liuhuanggou reservoir. It’s a threat to the safety of the people’s lives and property in downstream. In order to eliminate the hidden danger of reservoir, ensure the safety of the dam, play better the function of flood control and water storage of the reservoir etc., we apply the 3D electrical resistivity tomography detecting technology and volume rendering image processing technology, make the measurement in field, process the data and combine the field survey to find out the leakage channels inside the dam. The results show that the 3D resistivity images appear the low resistivity zone corresponding with the leakage channels. There are two main leakage channels that come from different location inside the dam. It is feasible to diagnose the leakage in earth rock-fill dam by applying 3D electrical resistivity tomography.