Angular Modulation
The angular-modulation technique
was introduced in 1994 for a single– detector
row helical CT scanner (Smart-
Scan; GE Medical Systems, Waukesha,
Wis) (13–15). This software-based technique
modulated tube current on the basis
of the measured density of regional
structures and the absorption values of
the object of interest. This information
was obtained by measuring local x-ray
beam absorption in 100 central channels
on two localizer radiographs (lateral and
anteroposterior views). Preprogrammed
sinusoidal modulation of tube current
was achieved during 360° rotation for
equalization of local differences in beam
absorption to obtain relatively constant
noise content and reduce radiation exposure.
A radiation dose reduction of up to
20%, depending on patient geometry
(asymmetry), has been reported (14). A
recent refinement of the angular-modulation
approach is an online, real-time,
anatomy-adapted, attenuation-based tube
current modulation technique (CARE
Dose; Siemens Medical Solutions, Forchheim,
Germany) that does not need the
information of radiographic localizer images
to achieve ATCM (1–3,16–20
Angular Modulation
The angular-modulation technique
was introduced in 1994 for a single– detector
row helical CT scanner (Smart-
Scan; GE Medical Systems, Waukesha,
Wis) (13–15). This software-based technique
modulated tube current on the basis
of the measured density of regional
structures and the absorption values of
the object of interest. This information
was obtained by measuring local x-ray
beam absorption in 100 central channels
on two localizer radiographs (lateral and
anteroposterior views). Preprogrammed
sinusoidal modulation of tube current
was achieved during 360° rotation for
equalization of local differences in beam
absorption to obtain relatively constant
noise content and reduce radiation exposure.
A radiation dose reduction of up to
20%, depending on patient geometry
(asymmetry), has been reported (14). A
recent refinement of the angular-modulation
approach is an online, real-time,
anatomy-adapted, attenuation-based tube
current modulation technique (CARE
Dose; Siemens Medical Solutions, Forchheim,
Germany) that does not need the
information of radiographic localizer images
to achieve ATCM (1–3,16–20
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