Virtual endoscopy

Cardiac applications of CT Interventional radiology Functional MRI and spectroscopy Interventionid MRI Cardiac MRI Radiation oncology Tissue oigineering" OR of the future Virtual endoscopy Virtual reality Therapeutic drug monitoring Telemedicine ... 

When compared to conventional endoscopy, virtual gastroscopy presents several advantages. 

Very high resolution systems (voxel diameters of 1 mm or less) may replace exploratory procedures such as endoscopy. The scan data can be processed interactively to give the physician views corresponding to a virtual endoscopic examination under his control. However, parallel studies in which hundreds of patients receive literal or virtual visualization procedures with comparison of diagnostic accuracy, and long term outcome will be necessary before virtual examinations can be accepted as the standard of medical care, see also Nuclear Magnetic Resonance Spectroscopy. 

Virtual Reality Diagnosis Systems. The third type of information-enhancing system is virtual reality diagnosis systems. These systems, typically used in diagnostic endoscopy and colonoscopy, replace an actual exploration on the patient with a virtual exploration on MRI images. A three-... 

FIGURE 29.18 Virtual endoscopy (a) three-dimensional reconstruction of structure to be viewed and (6) view from the inside fly-through. 

Auer, L. M. Virtual Endoscopy for Planning and Simulation of Minimally Invasive Neruosurgery, in Proc. First Joint Cottference qfCVRMed and MRCAS, 1997, Grenoble, France, Springer. 

The use of parallel projection rays implies that the virtual point of view is far from the reconstructed object. In some applications, such as virtual endoscopy, this simplified hypothesis does not hold, and a more complex perspective projection should be used. 

Virtual endoscopy is a computer-generated simulation of the endoscopic perspective obtained by processing computed tomography (CT) or magnetic resonance (MR) datasets (Rubin et al 1996 Yuh et al. 1999) and is one of the applications of virtual reality in medicine (Geiger and Kikinis 1994). 

The first presentations of virtual endoscopy in the radiological field were given by Vining in 1993 and 1994, who reported the application in the study of bronchi and colon, respectively. The idea to fly-through anatomical structures was followed by many investigators that had experienced the use of... 

Virtual endoscopy of the colon is a typical and probably the most important example of a dedicated study in the field of virtual endoscopy. The so-called virtual colonoscopy allows the evaluation of the internal surface of the colon in a minimally invasive manner, providing promising results for the diagnosis of cancer and clinically significant polyps (Fig. 7.1). 

The optimal MR angiography datasets for virtual endoscopy are those obtained with the contrast-enhanced technique. A bolus of i.v. gadolinium (0.1-0.2 ml/kg at 2-3 ml/s) is administered to the patient, and in the same fashion as CT angiography, the acquisition starts with the proper scan delay for... 

At our institution, as well as for other authors, biliary and urinary tract imaging with MR was used to generate virtual endoscopy of this anatomical district (Dubno et al. 1998 Neri et al. 1999a 2000a). 

To obtain virtual endoscopy of the larynx, the image acquisition is performed with the patient in the supine position on the CT table with moderate extension of the neck. The patient is asked to pho-nate the vocalic sounds ee or ay this allows the true vocal cords to be parallel and more clearly visible since they are aligned in the middle line of the glottis (Fig. 7.4). 

Fig. 7.5a,b. CT virtual endoscopy of the nasal cavity created with a perspective positioned in the rynopharynx (a). The arrow indicates the orientation of the virtual endoscope. The right superior (s), middle (M) and inferior (I) turbinates are shown (b)... 

Fig. 7.6. CT virtual endoscopy of the middle ear generated from a point of view located in the external auditory canal, shows the incus (/), malleus (M), promontory (P) and oval window (OVy)...

Fig. 7.7. Effects of conic view in virtual endoscopy of the colon. The exploration can be obscured by colonic folds if a restricted viewing angle is used some hidden corners ofthe colonic wall are not visualized...

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