[Subtraction--its various methods, its relation to diagnosis in neuroradiology].
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Biomedical subjects
Publications and source records attributed to G Salamon.
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FMRI with standard 1.5 T scanners requires adapted algorithms because the time course of intensity signal showed a non-linearity of the baseline. The protocol contains sequential images covering periods of rest followed periods of stimulation. The images of each period of rest and stimulation were averaged, offering a series of averaged images. From this series, we conserved only the pixels which presented the alternated variations corresponding to the temporal pattern of the paradigm. A colour scale was used to present the average percentage of variations of each pixel selected. We have performed activation paradigms with a classical motor protocol. This simple "follow-up" method appears effective for the identification of activated areas.
The existence of individual variations in size and shape of the human brain constitutes a problem for the anatomical interpretation of brain reconstructed images obtained from scanning devices; it is, for example, responsible for most of the inaccuracies in reading CT scans. One way to account for these variations is to use a proportional localization system. In the 1960s a group of neurosurgeons developed such a system based on two pivotal intracerebral structures, the anterior and the posterior commissures; they published an atlas consisting of horizontal, coronal, and sagittal brain sections interpreted in the proportional system. The atlas also included standard proportional brain schemes based on anatomical and radiological studies on large numbers of individuals. In this article we report a target localization experiment that we carried out to determine if this atlas could be used as a reference for a more accurate interpretation of CT and, eventually, of positron emission tomography (PET) and nuclear magnetic resonance (NMR) scans. Ten radiopaque small targets were inserted through the skull in the cortex of three cadavers; head CT was performed, and the atlas was used for predicting the cortical location of the targets seen on the CT images: The predictions were confirmed. These results strongly support the use of the proportional atlas for the interpretation of CT as well as of PET and NMR scans.
In four human left cerebral hemispheres the cortical speech areas were identified, having been marked by differential color code before transverse sectioning. The results from the anatomic dissection specimens were compared with thin CT sections in normal individuals, the CT plane being aligned to the orbitomeatal plane as an external reference, and thus closely parallel to the bicommissural plane, as an internal reference. The same cortical structures were identified in the CT sections. A strategic approach to CT examination of the cortical speech areas is formulated, based on the external-internal system of reference.
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