Tomographic scanning apparatus with ionization detector means

An axial tomography system is disclosed which includes an assembly rotatable about an axis extending along a central opening defined therein, and means for positioning the body portion to be examined within the central opening so that the axis of assembly rotation is perpendicular to a plane passing through the bodily structures to be examined. A source of penetrating radiation is mounted on the assembly toward one side thereof and provides radiation in the form of a fan beam. Means are provided for rotating the assembly so that the fan beam impinges upon said body portion at a plurality of incident directions. Detector means for the radiation are positioned on the assembly opposite the source, enabling detection of radiation which traverses laterally and is not absorbed in the thin body section in which the aforementioned plane resides. The detector means is preferably of the ionization type, and may comprise an array of side-by-side mutually insulated strip electrodes, spaced from a common high voltage electrode. The principal axis of each electrode is oriented along a radius extending toward the radiation source, and the ionization space between such strip and the common electrode can be regarded as defining a cell the principal axis of which is similarly oriented. Collimating means overlie the detector means and serve to assure that the radiation incident on each such cell is only that which has passed through an appropriate element of the body portion being examined