Tomographic imaging with improved collimator

Abstract

Tomographic imaging is implemented by providing a source of penetrating radiation, means for forming a pencil beam and sweeping the pencil beam over a line in space, a radiation detector and a beam length collimator. The beam length collimator lies outside of the sweep plane defined by the sweeping motion of the pencil beam and has a plane of symmetry which intersects the sweep plane at an angle which may or may not be a right angle. The beam length collimator defines a sensitive volume which has a dimension along the length of the pencil beam where the selected slice is defined by (or partly by) a dimension of the pencil beam. The combination of the beam length collimator and the pencil beam define a sensitive volume from which scattered energy can pass the collimator and be detected. The beam length collimator preferentially detects energy scattered by the sensitive volume. The sweep of the pencil beam allows a line image representing a plurality of sensitive volumes within the sweep plane at a focal distance from the beam length collimator. By providing relative motion between the object and the source/detector/collimator arrangement, a tomographic image of the selected slice can be created. The beam length collimator allows the sensitivity of the imaging arrangement to be tailored to anomalies or cracks lying parallel to a surface of a longitudinally extending object or parallel to a circumference of a cylindrical object.