4 kV Assist Settings
4.1 Typical Clinical Tasks
To control the image contrast and noise for each scan, information regarding the diagnostic
intent must be included in the protocol. This is accomplished through clinical tasks.
Table 1: Typical Clinical Tasks
Typical Clinical Tasks
Scan Situation
Region of Primary Importance
CT Angiography
iodinated contrast agents are used
enhanced tissue regions
Bone, non-contrast
contrast agents are not used
bony regions
Soft Tissue, contrast-enhanced
iodinated contrast agents are used
both enhanced and non-enhanced tissue re‐
gions
Soft Tissue, non-contrast
contrast agents are not used
non-enhanced tissue regions
Cardiac
cardiac scans with iodinated contrast
agents
both enhanced and non-enhanced tissue re‐
gions
kV Assist recommendations for kV and NI/mA are optimized based upon typical clinical tasks or
scanning and imaging conditions.
4.2 Minimum and Maximum kV
In addition to the impact of a Clinical Task on kV selection, there may be clinical situations
where you wish to lock out a kV or range of kV stations. This can be accomplished using the
Minimum and Maximum kV Range
settings on the
kV Control
window during protocol setup.
For example, if the site does not want kV Assist to select 70 kV for head scans, the head
protocol can be constructed with kV min = 80 kV and kV max = 140 kV. In this case, the kV
Assist feature would only select kV settings of 80, 100, 120, or 140 kV.
4.3 Image Display
Images of the same anatomy scanned with different tube voltages display differently. This is
expected, due to Contrast-to-Noise Ratio changes. For example, images obtained with X-ray
scan technique factors set by kV Assist could be brighter in areas (due to increased contrast)
and noisier (due to increased noise). Even though similar information is present in the image,
the change to the image appearance could be distracting. In order to minimize this change, kV
Assist also provides the option for the system to modify the protocol’s reference WW and WL
(the WW and WL that would be used without kV Assist for an average patient). This can be
controlled through the
Auto Adjust
setting in the recon settings collection.
Adjustment of the WW and WL (if selected in the protocol or scan) is based on the Clinical Task,
as well as the reference WW and WL. In the case where image contrast is increased, the WL is
adjusted to compensate for the brighter pixels. In the case where image noise is increased, the
WW is adjusted to compensate for pixel variations.
Auto Adjust
updates the window width and
window level values entered by the user.
4.4 mA Limits
When a scan is prescribed using SmartmA, the scan setup uses limits for the min/max mA to
allow you to limit the range over which the system can modulate the mA. The maximum mA limit
allows the user to restrict the maximum amount of radiation emitted from the system during the
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4 kV Assist Settings
