Creating a high-resolution spatial/symbolic model of the inner organs based on the Visible Human

Computerized three-dimensional models of the human body, based on the Visible Human Project of the National Library of Medicine, so far do not reflect the rich anatomical detail of the original cross-sectional images. In this paper, a spatial/symbolic model of the inner organs is developed, which is based on more than 1000 cryosections and congruent fresh and frozen CT images of the male Visible Human. The spatial description is created using color-space segmentation, graphic modeling, and a matched volume visualization with subvoxel resolution. It is linked to a symbolic knowledge base, providing an ontology of anatomical terms. With over 650 three-dimensional anatomical constituents, this model offers an unsurpassed photorealistic presentation and level of detail. A three-dimensional atlas of anatomy and radiology based on this model is available as a PC-based program.

Exploring the visible human's inner organs with the VOXEL-MAN 3D navigator

Improved rendering and segmentation techniques lead to a new quality of 3D reconstructions of the Visible Human. Using these we have implemented an interactive atlas of anatomy and radiology of the inner organs.

A realistic model of human structure from the visible human data

The computer-based 3D models of the human body reported to date suffer from poor spatial resolution. The Visible Human project has delivered high resolution cross-sectional images that are suited for generation of high-quality models. Yet none of the 3D models described to date reflect the quality of the original images. We present a method of segmentation and visualization which provides a new quality of realism and detail. Using the example of a 3D model of the inner organs, we demonstrate that such models, especially when combined with a knowledge base, open new possibilities for scientific, educational, and clinical work.

Exploring the Visible Human using the VOXEL-MAN framework

In principle the Visible Human data sets are an ideal basis for building electronic atlases. While it is easy to construct such atlases by just offering the possibility of browsing through the 2D slices, constructing realistic 3D models is a huge project. As one rather easy way to establish 3D use, we have registered the Visible Human data to the already existing 3D atlas VOXEL-MAN/brain. This procedure enables one to lookup anatomical detail in an atlas based on radiological images. Concerning the segmentation problem, which is the prerequisite for a real 3D atlas, we have developed an interactive classification method that delivers realistic perspective views of the Visible Human. As these volume based methods require high-end workstations, we finally have developed a multimedia program that runs on standard PCs and uses Quicktime VR movies.

[Ventricular fibrillation in intra-atrial cardioversion of atrial fibrillation]

Recently intra-atrial defibrillation has become an interesting alternative to external defibrillation and drug therapy for the treatment of atrial fibrillation. Low-energy intra-atrial defibrillation can be used to restore sinus rhythm f.ex. after a failed external cardioversion or during an electrophysiologic study when the administration of antiarrhythmic drugs should be avoided. Additionally this new technique has led to the development of implantable atrial defibrillators for the treatment of selected patients suffering from chronic atrial fibrillation. Intra-atrial defibrillation seems to be a highly effective and safe method, but little experience exists concerning the outcome so far. Especially the potential risk of inducing ventricular pro-arrhythmia is subject of current controversy. We report the case of a 79-year-old patient suffering from WPW syndrome with a concealed bypass tract who was subject to an intra-atrial defibrillation during an electrophysiologic study. At the beginning of the study atrial fibrillation could be converted to sinus rhythm by a single low-energy atrial defibrillation (3 J.). After a short period of time a second intra-atrial defibrillation had to be performed in the same way because of recurrent atrial fibrillation. By this atrial shock ventricular fibrillation was induced, so that high energy external defibrillation became necessary. Analyzing the ECG a correct R-wave synchronization was found, but a rather short preceding RR interval (252 ms). In conclusion, low energy atrial defibrillation is gaining importance as a highly effective new technique to restore sinus rhythm in patients suffering from atrial fibrillation resistant to conventional therapies. Nevertheless potential risks have to be considered such as the induction of ventricular pro-arrhythmia. Therefore, a correct R-wave synchronization is obligatory and shock delivery should be withheld after short RR intervals. Future prospective randomized studies will have to show whether this new technique is really safe enough and superior to the conventional methods for restoring sinus rhythm in patients suffering from atrial fibrillation.

Interactive volume visualization using "intelligent movies"

High quality visualization of medical volume models as performed by the VOXEL-MAN and similar systems is still too time consuming and the interaction complicated when sophisticated tools like dissection are used. We hence developed a new paradigm allowing to create simpler derivatives of the model, called "intelligent movies". These are in QuickTime or QuickTime VR format which allow interactive exploration with two degrees of freedom. As a decisive novelty, we extended it by a pixelwise link to the knowledge base which may be queried in the image context. Thus scenes emphasizing a selected aspect of the volume model may be created as intelligent movies, which a user (referring physician, student) can explore largely with the functionality of VOXEL-MAN, but in real time--on any standard PC--and also via a JAVA applet within web browsers. This is shown with the example of 3D interactive anatomical atlases and clinical cases.

[New kinds of 3-dimensional atlases of the anatomy and function of the human body]

It is a drawback of classical multimedia programs for the visualization of spatial knowledge, that they are based on a limited number of predefined views. This paper describes a model that combines pictorial and symbolic knowledge about spatial structures in a way that allows arbitrary views of the scene and the interrogation of the model in the context of the actual view. The style of the pictorial presentation only depends on the objective and the phantasy of the user. The functionality of the approach is demonstrated with the example of the human head. It is furthermore shown that the model potentially allows the simulation or generation of all classical visual teaching aids for anatomy.

A new representation of knowledge concerning human anatomy and function

By integrating concepts of computer graphics and artificial intelligence, novel ways of representing medical knowledge become possible. They allow unprecedented possibilities ranging from three-dimensional interactive atlases to systems for surgery rehearsal.

A new method for practicing exploration, dissection, and simulation with a complete computerized three-dimensional model of the brain and skull

In current practice, anatomical atlases are based on a collection of planar images presented in a book or, recently, stored on digital media. We present a new kind of interactive true three-dimensional (3D) anatomical atlases based on a volume model derived from MRI and CT. The model has a two-layer structure. The lower level is a volume model with a set of semantic attributes connected to each voxel. The semantic attributes are assigned by an anatomist using a volume editor. THe upper level represents a set of relations between these attributes. Interactive visualization tools such as multiple surface display, preparation of transparent material and cutting are provided. It is shown that the combination of this model with advanced tools for volume visualization provides the 'look and feel' of real dissection. The system therefore represents a bridge between real dissection of a cadaver and textbooks and classical atlases of anatomy. First tests have shown that the atlas system may be used successfully for teaching anatomy, but also as a reference for radiologists or surgeons. The powerful underlying data structure potentially includes all classical visual teaching aids. As a replacement of classical atlases, however, spatial resolution has still to be improved.

A new method for representing the human anatomy

In current practice, anatomical atlases are based on a collection of planar images presented in a book or, recently, stored on digital media. We present a new method for generating interactive true three-dimensional (3D) anatomical atlases based on a volume model derived from MRI and CT. The model has a two layer structure. The lower level is a volume model with a set of semantic attributes connected to each voxel. The semantic attributes are assigned by an anatomist using a volume editor. The upper level is a set of relations between these attributes. Interactive visualization tools such as multiple surface display, transparent rendering, and cutting are provided. It is shown that the combination of this data structure with advanced volume visualization tools provides the "look and feel" of real dissection. First tests show that the atlas system cannot only be used successfully for anatomy teaching, but also as a reference for radiologists or surgeons. As a replacement of classical atlases, however, the spatial resolution has still to be improved.

A computerized three-dimensional atlas of the human skull and brain

PURPOSE

To develop an anatomic atlas of the human head based on a volume model derived from MR and CT.

METHODS

Every voxel of this model was labeled by a neuroanatomist concerning its membership to a structural and/or functional region. A computer program was written that, instead of displaying precomputed images, allows the user to choose and compose arbitrary views.

RESULTS

The user can subtract parts and ask for annotations just by using the mouse. Conversely, one can compose images by choosing objects from the list of anatomical constituents which is displayed on the screen. A set of dissection tools allows a "look and feel" that comes near to a true dissection. Operations that are not possible in a real dissection, such as reassembly or filling cavities, can be performed.

CONCLUSION

The authors have developed a computerized model that can be used for anatomy teaching and also as a reference for radiologists or surgeons. To replace classical atlases, the spatial resolution must be improved and speed must approach real time. Functional imaging data (position emission tomography and single photon emission CT) can be added to the system. The system is mobile and can be situated in classrooms, operating rooms, reading rooms, and libraries.

Visualization of 3-D treatment plans with fast neutrons

The treatment planning for radiotherapy with fast neutrons requires modifications of the planning systems used for photons. The neutron- and photon-component of the treatment fields must be determined and can then be used for separate calculations. The corrections for inhomogeneities are performed by use of attenuation coefficients and the corresponding corrections for changes in the kerma. The treatment planning system MEVAPLAN (Siemens) was modified to follow these requirements. Thus treatment planning for 14 MeV DT-neutrons could be performed. The multiplanar option is used to calculate 3D-dose distributions based on up to 40 serial CT slices. The generated three-dimensional dose matrix and the CT data are transferred via magnetic tape to the visualization system VOXEL-MAN developed at the University Hospital of Hamburg. This system uses a ray casting algorithm based on the generalized Voxel-model to display detailed 3D-images of human anatomy together with the calculated dose distribution. Different treatment plans for neutrons and photons are calculated and visualized. Various manipulations of the data-sets are displayed to improve the critical examination of the simulated dose distribution and to discern the quality of treatment techniques.

[3-D visualization of dose distributions in CT image volumes]

The 3D-visualization of the entire spatial radiation dosage in cooperation with the 3D-radiation volume requires several data volumes. The structure of the interface between the 3D-treatment planning program "ProPlan" and the 3D-imaging system "VOXEL-MAN" is explained. The first results in the radiological application point out the possibilities of the complex registration of dose distributions and the critical examination of the irradiation technique.

3-D segmentation of MR images of the head for 3-D display

Algorithms for 3-D segmentation and reconstruction of anatomical surfaces from magnetic resonance imaging (MRI) data are presented. The 3-D extension of the Marr-Hildreth operator is described, and it is shown that its zero crossings are related to anatomical surfaces. For an improved surface definition, morphological filters-dilation and erosion-are applied. From these contours, 3-D reconstructions of skin, bone, brain, and the ventricular system can be generated. Results obtained with different segmentation parameters and surface rendering methods are presented. The fidelity of the generated images comes close to anatomical reality. It is noted that both the convolution and the morphological filtering are computationally expensive, and thus take a long time on a general-purpose computer. Another problem is assigning labels to the constituents of the head; in the current implementation, this is done interactively.

The use of the Fourier transform in cardiac digital angiography

Digital angiography has achieved broad clinical application as a morphological imaging modality through the technique of temporal subtraction known as digital subtraction angiography (DSA). After applying the Fourier transform to the intensity time curves (ITC) of an angiographic sequence, we are able to produce both morphological and functional images. The resulting pictures show an improved signal-to-noise ratio, reduction of motion artifacts, easy application of phase-synchronous subtraction, and integration and quantitative visualization of blood flow. The methods are demonstrated with nonselective angiograms and intravenous levocardiograms. Furthermore, when applied to angiographic sequences, the Fourier transform leads to a significant reduction in data without loss of important information.

[Classification of the germinal epithelium in Java monkeys (Macaca cynomolgus) using digital image processing]

Testicular tissue of two adult crab-eating macaques was used to investigate the distribution of the spermatids in the seminiferous tubules. For this purpose, morphological criteria for distinction among the various degrees of development of these cells were elaborated. Subsequently, based upon analyses of serial sections, three-dimensional reconstructions of the cellular distribution pattern were generated by means of digital image processing. In these reconstructions it became evident that the spatial extension of a single differentiation stage can vary considerably. Large tubular portions that contained a single differentiation stage alternated with those exhibiting several differentiation stages which occupied only small patch-like areas of the seminiferous epithelium. Particularly in the latter portions of the tubule a helical continuity of subsequent stages in the sense of a wave of spermatogenesis became immediately obvious. Transitory changes in the direction of the wave (modulations) occurred frequently. The present findings support the suggestion that an uniform kinetic principle of mammalian spermatogenesis exists, which is subjected to slight modifications during the evolution of primates.

Computer-aided three-dimensional reconstructions of the arrangement of primary spermatocytes in human seminiferous tubules

With the use of a digital image-processing method three-dimensional reconstructions of the arrangement of spermatocytes in human seminiferous tubules were performed. With this method it was possible to investigate the cellular distribution in the tubule in nearly any given perspective and projection. In addition, by means of simple mathematical procedures, such as by transformation of Cartesian coordinates into cylindrical coordinates, it was possible to vary the shape of a reconstruction, i.e., to convert the cylindrical image of a tubular portion into a right-angled r-phi-z-representation. The present work not only confirms the existence of a complex helical plan of organization of the human seminiferous epithelium but also provides further aspects of the phenomenon of physiological germ-cell loss and its integration into the kinetics of spermatogenesis.

[3-dimensional display of computed tomographic studies of craniofacial anomalies]

Craniofacial anomalies are conventionally investigated by cephalometry using ordinary radiographs and by computed tomography. Both methods have the major disadvantage of trying to demonstrate a complex three-dimensional structure, such as the skull, in two dimensions and they therefore cannot display a true spatial image. We present the principle underlying a three-dimensional display derived from computer tomographic studies and discuss the clinical application in the diagnosis of craniofacial anomalies.