Читать книгу Leksell Radiosurgery - Группа авторов - Страница 92

The ICON treatment unit has the availability of stereotactic cone-beam computed tomography (CBCT). The stereotactic component comes from the fact that the voxels of the CBCT are in Leksell stereotactic coordinates. The CBCT system consists of a compact X-ray tube with a flat panel detector [17]. The C-arm, which is attached to the unit, holds the X-ray source and detector. A typical scan time from initiation of C-arm movements to full CBCT acquisition is approximately 5 min. Two modes are available for imaging, one is a low-dose mode of 2.5 mGy per scan and a high-dose mode of 6.3 mGy per scan in terms of CTDI (CT Dose Index). These CBCTs are non-diagnostic quality [18, 19]. The similarities of these two modes are the energy (90 kVp), the number of projections (332), the volume size (448 × 448 × 448 voxels), the voxel size (0.5 mm), the X-ray spot focal size (0.6 mm), the pulse length (40 ms), the detector pixel size (0.368 mm), and the filter (Hamming Window). The differences between these two modes (2.5 vs. 6.3) are the charge per projection (0.4 vs. 1.0 mAs), tube current (0.1 vs. 0.25 mA), resolution (7 vs. 8 lp/cm), and the contrast to noise ratio (1 vs. 1.5).