Gamma camera-mounted anatomical X-ray tomography: technology, system characteristics and first images

Scintigraphic diagnosis, based on functional image interpretation, becomes more accurate and meaningful when supported by corresponding anatomical dat a. In order to produce anatomical images that are inherently registered wit h images of emission computerised tomography acquired with a gamma camera, an X-ray transmission system was mounted on the slip-ring gantry of a GEMS Millennium VG gamma camera. The X-ray imaging system is composed of an X-ra y tube and a set of detectors located on opposite sides of the gantry rotor that moves around the patient along with the nuclear detectors. A cross-se ctional anatomical transmission map is acquired as the system rotates aroun d the patient in a manner similar to a third-generation computerised tomogr aphy (CT) system. Following transmission, single-photon emission tomography (SPET) or positron emission tomography (PET) coincidence detection images are acquired and the resultant emission images are thus inherently register ed to the anatomical maps. Attenuation correction of the emission images is performed with the same anatomical maps to generate transmission maps. Pha ntom experiments of system performance and examples of first SPET and coinc idence detection patient images are presented. Despite limitations of the s ystem when compared with a state of the art CT scanner, the transmission an atomical maps allow for precise anatomical localisation and for attenuation correction of the emission images.