Figure 5. Transaxial CT images obtained at the top of the iliac crest in two single volunteers. The scans were performed with reduced radiation dose to each volunteer with the CT_a system using patient-specific scan parameters (Table 3). (a) Image of a slim volunteer(31 cm greater diameter) obtained with the optimum radiation dose. The image noise is high but does not exceed the specified level of 30 Hounsfield units (HU). (b) Image of a corpulent volunteer (47 cm greater diameter). The image noise (approximately 10 HU) is much lower than the required level of 30 HU, indicating that a further substantial dose reduction is possible.