In recent years, as stereoscopic (also called stereoscopy or 3D imaging) display technology is applied more and more widely, more media tend to use it to provide the depth information that 2D images cannot bring. 3D stereoscopic display hardware has recently developed rapidly and made it possible to achieve high quality interactive volumetric rendering of diagnostic data on low-cost platforms [1]. 3D visualization for medical analysis is not yet widely accepted and applied, although most modern radiology workstations now start including 3D modules that can generate impressive virtual representations of the imaged structures. The possibility caused is medical data sets that contain many overlapping structures, leading volumetric techniques to generate cluttered images, which may become difficult to understand when projected onto a 2D screen.
Stereoscopy is a technique for creating or enhancing the illusion of depth in an image by means of stereopsis for binocular vision. Binocular vision is vision in which both eyes are used together [2]. It can give stereopsis in which parallax provided by the two eyes' different positions on the head give precise depth perception [3]. Binocular vision with volume perception of surrounding objects allows human beings to orient freely in the environment [4]. In volume space, projection plane represents to the retina of the human’s eye. The projection plane is able to perceive an object image in two different projections.
Each point in the space corresponds to specific physiological parallax in projection plane.
In our work, we present a stereoscopic image created by a standardized uptake value (SUV) calculation in positron emission tomography (PET) scans of lung and overlapped it with computer tomography (CT), showing it by 3D effects via shutter glasses. We apply stereoscopic technology to medical image processing to expend our vision from 2D to 3D and show that the biggest difference between them is the depth information. The advantage of depth in stereoscopic images built by computed tomography is helpful for diagnosis such as avoiding misdiagnosis or path planning.
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1.1. Related Works
De Silva et al. pointed out the most distinguishing feature of 3D display systems, compared to the traditional 2D counterparts, is their ability to provide an additional perception of depth to its viewers [5]. Thus, the mechanisms behind human depth perception play a significant role in 3D video systems. While there have been significant amounts of research carried out to understand human depth perception, in the areas of physiology and psychology, its applicability to 3D display systems is seldom spoken.
Understanding the mechanisms of depth perception is of utmost importance to the development of 3D video technologies that are heavily based on exploitation of human perception. It is explained with the aid of existing physiological and psychological models how humans perceive depth in 3D video displays. Based on these explanations a mathematical model is derived to explain the just noticeable difference in depth (JNDD) as perceived by a viewer, watching 3D video. The derived model is experimentally validated on an auto-stereoscopic display. This model is expected to be useful in both 3D content productions as well as in 3D content processing and compression.
An autostereoscopic display with image quality comparable to ordinary 2D displays has recently been developed [6]. Abildgaard et al. found with MIP models depth ambiguity is a problem [6]. When binocular stereoscopy with special glasses is used, the two images are not changed if the observer moves his or her head, apart from the obvious change in the viewing angle relative to the screen. In contrast to binocular stereoscopy, the prototype used in the present study produces a range of different views in different horizontal angles. The number of different views is configurable. Wang et al. used a fully crossed ROC paradigm in which eight radiologists interpreted chest CT examinations using each of three display modes, which included slice-by-slice, orthogonal MIP, and stereoscopic display [6, 7, 8]. There are a variety of compelling reasons to believe that stereographic display methods will provide considerable benefits for the display of 3D datasets, though the efficacy of these methods needs to be tested empirically. Santhanam et al. present a medical display and visualization framework for radiation therapy that couples a computer-based simulation of real-time lung tumor motion and its dose accumulation during treatment with an Augmented Reality Center (ARC) based display
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system [9]. Agus’s system allowed multiple untracked naked-eye users in a sufficiently large interaction area to coherently perceive rendered volumes as real objects, with stereo and motion parallax cues [1]. Nelson et al. proved stereoscopic viewing improved visualization of small structures when there were multiple overlapping structures.
Identification of high-contrast structures such as the fetal skull or spine showed improvements with stereoscopic viewing compared with conventional viewing [10]. They also noted that stereoscopic viewing enhanced visualization of structures near the observer compared with those that were far from the observer, some of which could be partially obscured by the nearer structure.
Beurden et al. reviewed empirical studies concerning the effectiveness of stereoscopic displays in medicine [11]. The review domains covered diagnosis, pre-operative planning, minimally invasive surgery (MIS) and training or teaching. Kickuth et al. compared the accuracy of stereoscopic and standard 3D CT in the classification of acetabular fractures [12]. Hernandez et al. presented a technique for stereoscopic visualization applied to three-dimensional (3D) ultrasonic breast data. Two conical transparent projections of the volume were computed from two slightly different viewpoints [13]. These two projections made up the stereoscopic pair. The pair was displayed on a stereoscopic monitor for the visualization of the 3D data with the depth dimension. Yamagishi found it is important task for medical school lecturers to teach thorough knowledge of the 3D extent of the vascular structure [14]. Recently, isotropic voxel data have been easily obtained by multi-detector CT (MD-CT). They made use of MD-CT data of clinical cases and created stereoscopic images for the purpose of practical education. Stereoscopic viewing yielded an exact 3D observation of the abdominal vascular structure. Real time rendering of the stereoscopic images could be performed by VOXEL-MAN. Using the data of clinical cases gave an impact on medical students.
1.2. Motivation
Lung cancer affects more than 100,000 Americans each year in all ages but particularly in the smoking population more than 50 years of age [8]. Most types of lung cancer can be effectively treated if they are detected early. Radiographic imaging plays an
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important role in the early detection and diagnosis of lung cancer. The primary radiographic imaging tools for lung nodule screening and early detection have shifted from film-based projection radiography to computed tomography (CT).
Maximum intensity projection (MIP) is the most common volumetric display method used for the task of lung nodule detection and allows thicker slabs comprised of multiple slices to be viewed. MIP projects the slab by taking the highest voxel value along a projection path as a final pixel value for display. In addition, MIP does not always correctly portray geometric structure and therefore may lead radiologists to misinterpret rendered images, especially images with small structures. In our preliminary study survey, we found that some of the radiologists spent most of their time viewing slabs comprised of a single slice in the stereographic display mode. The most likely explanation for this is that they were relatively more familiar with slice-by-slice display than with stereo display [6].
Wang et al. indicated that most of the radiologists preferred reading 3D images with a slab thickness equivalent to about five slices, and there was no difference in the time distribution patterns between the stereo and MIP modes [8].
An individual X-ray image alone fails to provide information about size, position, and shape of the object of interest [4]. A stereoroentgenographic image provides more complete information. 3D techniques for stereoscopic display of radiological images have been introduced for many years, but none of these have found wide uses [15, 16, 17]. A limitation with the majority of the stereoscopic techniques is the requirement of special viewing glasses. Fortunately, recent advances in computer hardware and software performance have made such stereoscopy affordable on desktop computers, facilitating viewing of volume data in offices as well as ultrasound equipment and laboratories. More powerful laptop computers make it possible to interactively display volume data in educational and scientific meetings, enhancing comprehension of anatomic structures [10].
Recently, several groups have begun to investigate the application of stereoscopic displays for radiological imaging [6, 18, 19]. Unlike other volumetric display methods, stereo display exploits visual stereopsis to avoid ambiguities associated with structure superimposition. Chan et al. had shown that stereo mammographic display improved detection and characterization performance compared to projection mammograms [18, 19].
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If we can implement stereoscopic technology with medical diagnosis, it may improve the efficiency of diagnosis with the depth information that 2D image cannot provide. Or it can be implemented in surgical simulation or education training. Agus et al. present a prototype medical data visualization system exploiting a light field display and custom direct volume rendering techniques to enhance understanding of massive volumetric data, such as CT, MRI, and PET scans [1]. Both the 3D complexity and the enormous size of medical data thus create a growing demand for interactive high quality 3D visualization.
Several researches have emphasized the potential benefits of stereoscopic display [20].
However, the usefulness of stereoscopic 3D CT must lie in the ability to classify them exactly. There is a clear need for more empirical evidence that quantifies the added value of stereoscopic displays in medical domains, and more and more researches are needed to assess the potential benefits of stereoscopic displays in those applications [11]. For those reasons, we compared stereoscopic and standard 2D image in the classification of in 2D MIP, perspective projection with mean volume rendering and perspective projection with bilinear interpolation stereoscopic images to show the improvement of our work.
1.3. Thesis Contribution
Many researches had been done the stereoscopic technique on medical domain before.
Abildgaard et al. used an autostereoscopic display in visualization of radiological anatomy from MR angiography [21]. Santhanam showed the display system to monitor the radiation dose delivery on the tumor [9]. Hernandez generated two conical transparent projections of high quality from an ultrasonic volume [13]. Those projections computed fewer than two slightly different viewing angles that represented a stereo pair. We use active shutter glasses that have better resolution with less expensive device. The display systems not only focus on lung but with entire chest and ribs will have more 3D effect of position depth relation. ARC display system needs one to wear a head mount, yet it makes one get more uncomfortable than shutter glasses. The stereoscopic display using CT and PET DICOM as a 3D display source data can have a better whole body structure rather than ultrasonic. In this thesis, we applied stereoscopic technology to medical image
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processing. We have SUV to help diagnose and ribs to judge the precise position of body and stereoscopic display’s depth information.
1.4. Thesis Layout
In section 2, we introduce fundamentals of medical image processing of this thesis.
Section 3 explains the methodology of calculation of SUV and other medical image analyzing and processing. In section 4, we describe the stereoscopic display principle and create 3D image of DICOM scans using perspective. In section 5, we demonstrate the results of the proposed perspective methods of stereo images and discuss with the 2D MIP image.
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