Biomedical subjects
Publications and source records attributed to C Picard.
Papillomas of the choroid plexus arising in and occupying the cerebellopontine angle are rare. Such a case occurring in a 41-year-old woman is reported. The signs and symptoms are described. The literature is reviewed.
Preliminary results obtained with the new subcutaneous pH electrode confirm the reliability of this method as far as the purely technical aspects are concerned. The routine clinical use is still burdened with several unsolved problems which should be worked out as soon as possible.
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PURPOSE: To assess the clinical feasibility of an experimental modified angiographic system capable of real-time digital stereofluoroscopy and stereography in X-ray angiography, using a twin-focus tube and a stereoscopic monitor. METHODS: We report the experience obtained in 37 patients with a well-documented examination. The patients were examined for coronary angiography (11 cases), aortography (7 cases), pulmonary angiography (6 cases), inferior vena cava filter placement (2 cases), and cerebral angiography (11 cases). Six radiologists were asked to use stereoscopic features for fluoroscopy and angiography. A questionnaire was designed to record their subjective evaluation of stereoscopic image quality, ergonomics of the system, and its medical interest. RESULTS: Stereofluoroscopy was successfully used in 25 of 37 cases; diplopia and/or ghost images were reported in 6 cases. It was helpful for aortic catheterization in 10 cases and for selective catheterization in 5 cases. In stereoangiography, depth was easily and accurately perceived in 27 of 37 cases; diplopia and/or ghost images were reported in 4 cases. A certain gain in the three-dimensional evaluation of the anatomy and relation between vessels and lesions was noted. As regards ergonomic considerations, polarized spectacles were not considered cumbersome. Visual fatigue and additional work were variously reported. Stereoshift tuning before X-ray acquisition was not judged to be a limiting factor. CONCLUSION: A twin-focus X-ray tube and a polarized shutter for stereoscopic display allowed effective real-time three-dimensional perception of angiographic images. Our clinical study suggests no clear medical interest for diagnostic examinations, but the field of interventional radiology needs to be investigated.
Reconstructing a three-dimensional (3D) object from a set of its two-dimensional (2D) X-ray projections requires that the source position and image plane orientation in 3D space be obtained with high accuracy. We present a method for estimating the geometrical parameters of an X-ray imaging chain, based on the minimization of the reprojection mean quadratic error measured on reference points of a calibration phantom. This error is explicitly calculated with respect to the geometrical parameters of the conic projection, and a conjugate gradient technique is used for its minimization. By comparison to the classical unconstrained method, better results were obtained in simulation with our method, specially when only a few reference points are available. This method may be adapted to different X-ray systems and may also be extended to the estimation of the geometrical parameters of the imaging chain trajectory in the case of dynamic acquisitions.
The visual detection of fine structures and the accuracy of the quantitation of geometric and densitometric features, are closely related to the quality of the images available in two-dimensional (2D) and three-dimensional (3D) X-ray angiography. In this context, we propose to analyze all the parameters influencing this accuracy using an experimental design strategy. Preliminary tests of this procedure, applied to 2D and 3D angiographic data obtained from a dedicated phantom, yield encouraging results. We show that the detection of small arteries in a 3D angiogram is more sensitive to the number of projections than to the X-ray dose.
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