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Primary radiation outside the imaged volume of a multislice helical CT scan

Department of Radiology, St Mary's Hospital, London W2 1PG, UK

View larger version (131K): [in a new window]   Figure 1. Kodak X-Omat V therapy verification film positioned within the aperture of the CT gantry.

View larger version (89K): [in a new window]   Figure 2. The pattern of film blackening from a helical scan of 5.2 cm length using the multislice scanner with 4 x 5 mm data acquisition (a) is contrasted with the pattern from a helical scan of 5.0 cm length and 5 mm data acquisition using the single slice scanner (b). The unmodulated region of each film lies along the CT scan axis.

View larger version (21K): [in a new window]   Figure 3. (a) Multislice scanner and (b) single slice scanner show the primary radiation energy deposited per unit length along the long axis of the patient as a percentage of the average primary radiation energy deposited per unit length within the reconstructed volume. Values are taken from optical density measurements along the scan axes of the films shown in Figure 1 for the multislice and single slice scanners, respectively.