GE Revolution CT User Manual page 238

each reconstruction algorithm and is especially apparent with higher resolution algorithms such
as bone and edge. The change in kernel is required when the DFOV selection makes the pixel
size too large to support the intended spatial resolution. This characteristic is independent of
SmartmA. In this system, the AEC feature has been characterized to automatically adjust the
exposure according to the user-prescribed DFOV of the primary image reconstruction.
Does SmartmA require two scout images in order to function correctly?
No, all AEC features (SmartmA, ODM, and kV Assist) are designed to require only one scout
acquisition.
How is the SmartmA mA determined when NI and ASiR-V interact?
To determine the SmartmA mA value required to achieve the prescribed NI, the effect of the
prescribed ASiR-V percentage on the level of noise in the primary reconstructed image is
considered. The effect of increasing ASiR-V percentage in SmartmA is to lower the mA value
required to achieve the prescribed NI.
What affects the SmartmA mA value?
SmartmA mA values are dependent on three categories of inputs: patient-dependent, scan
technique and primary image reconstruction parameters.
Patient-dependent: Attenuation size and shape of the anatomy being scanned determined from
the scout.
Scan Technique:
•
Scan type (Axial, Cine, Helical, Cardiac)
• kV
•
SFOV
•
Rotation time
•
Detector Coverage (Helical only)
•
Standard or High-Definition mode
Primary Reconstruction Parameters:
• Noise index
•
Slice thickness
• DFOV
•
ASiR-V percentage
• Reconstruction Type (HD or non-HD kernel)
What is the recommended range of NI for different anatomical regions?
The recommended range of NI for different anatomical regions is contained in the
Values table, in the Slice Thickness Reference Noise Index and Noise Index Values section of
this manual.
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Revolution CT User Manual
Direction 5480385-1EN, Revision 1
Noise Index
2 Scan Theory