Operating instructions

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Dose Information
100kV-Protocols
The system offers a spectrum of four kV settings (80
kV, 100 kV, 120 kV and 140 kV) for individual adapta-
tion of the patient dose in pediatric scans and for opti-
mization of the contrast-to-noise ratio in contrast-
enhanced CT angiographic studies.
In contrast enhanced studies, such as CT angiographic
examinations, the contrast-to-noise ratio for fixed
patient dose increases with decreasing tube voltage.
As a consequence, to obtain a given contrast-to-noise
ratio, patient dose can be reduced by choosing lower
kV-settings. This effect is even more pronounced for
smaller patient diameters. It can be demonstrated by
phantom measurements using small tubes filled with
diluted contrast agent embedded in plastic phantoms
with different diameters. The iodine contrast-to-noise
ratio for various kV-settings is depicted in fig. 1 as a
function of the phantom diameter. Compared to a
standard scan with 120 kV, the same contrast-to-noise
ratio in a 24 cm phantom, corresponding to a slim
adult, is obtained with 0.5 times the dose for 80 kV
(1.5 times the mAs) and 0.7 times the dose (1.1 times
the mAs) for 100 kV. Ideally, 80 kV should be used for
lowest patient dose. In practice, however, the use of
80 kV for larger patients is limited by the available mA-
reserves of the X-ray generator.
In these patients, 100 kV is a good compromise and
the preferable choice for CTA examinations.