intensifier tube face 24 is positioned approximately 147 cm from the x ray source 30 and the most vertical point of imaging extension 45 is approximately 8 5 cm above the image intensifier tube face 24 returning to fig1 the x ray normalization detector 66 is mounted to one side of the slit in the pre patient collimator 34 and provides readings of source intensity which are used to normalize x ray tube output variations during the scan the x ray normalization detector 66 measures the unattenuated x ray beam flux allowing the detector to sample quite a large solid angle of the beam x ray normalization detector 66 is formed by combining a scintillating cadmium tungstate cdwo 4 crystal with a silicon photodiode preferably the crystal measures 6 u00d7 6 mm by 3 mm thick additional details of the crystal material photodiode and construction are provided hereinbelow in the discussion of the imaging extension detector array 45 the 12 inch image intensifier tube iit 40 is a conventional medical image intensifier and serves as an x ray photon to visible light photon converter fig9 provides a cross sectional view of a typical image intensifier tube and the associated optics of the present invention incident x ray photons are absorbed by the thin 0 3 mm csi cesium iodide scintillator 78 on the image intensifier tube face 24 the csi crystal emits light photons which are converted to electrons by the attached photocathode 80 the electrons are accelerated and focused by focusing grids g1 g2 and g3 onto the output phosphor 82 for light conversion the quantum efficiency of this process is characterized by a 4 to 5 order.