scan. Because of the interaction between tube voltage and tube current, however, the scanner
output at a fixed mA value is very different between kV stations. This is especially important for
kV Assist, since the scan kV may be different from the baseline kV in the protocol. This could
result in very different behavior if the same mA limits are used.
For example, if you select a maximum mA limit of 440 mA at 120 kV, and then perform a scan at
80 kV (with the same 440 mA limit), the maximum X-ray output during the scan (at the
maximum mA limit) could be 2-3 times lower than expected. This is equivalent in terms of
maximum output to a scan at 120 kV with a mA limit of ~150-220 mA, which may not be the
desired behavior. To prevent you from having to perform this type of calculation manually to
update mA limits when a new kV is used, kV Assist automatically updates the mA limits for the
kV selected. The mA limits are set to achieve the same minimum / maximum scanner radiation
output as at the baseline kV (up to the system limits).
4.5 Build a protocol with kV Assist
Use this procedure to build a kV Assist enabled protocol and define the baseline Manual kV,
Noise Index, or Manual mA values in the protocol.
1. From the image monitor, click .
2. Click
Protocol Management
, then click
Protocol Management
again.
3. From the
CT Login
authentication window, enter your
Log On Name
and
Password
.
4. From the
Protocol Selection
window, create a new protocol or select a protocol to edit.
5. Click [Edit] if you are making changes to an existing protocol.
6. Set the Scout parameters.
7. Set the Axial scan parameters.
a. From the
Scan Settings
window, set the baseline parameters for
Noise Index
,
Mode
,
Slice Thickness
,
Rotation Time
,
Pitch
and
SFOV
.
NOTE:
Once kV Assist is selected, you are not able to change these settings until kV
Assist is turned off.
b. From the
Scan Settings
window, open the
kV and mA Control
collection and then click
[kV] and set the baseline
Manual kV
value.
c. From the
kV Mode
area, select [kV Assist].
d. Select a
Clinical Task
.
e. Select a minimum and maximum kV value to define the kV range.
This selection allows the user to avoid using too low or too high of tube voltages.
f. Select [Auto Adjust].
8. Continue with specifying the parameters for the series.
9. Verify the remaining parameters for the subsequent series in the protocol.
10. Save the protocol.
Revolution CT User Manual
Direction 5480385-1EN, Revision 1
Chapter 18 Protocols
589
