Consider Decreasing The Kv - GE Revolution CT User Manual

•
Recommended pediatric color coded protocols are installed on the system and are arranged
in colors according to height and weight for easy selection.
•
These protocols should be considered as a baseline. It is strongly encouraged that you work
with your radiologist and medical physicist to determine the lowest possible dose at the
image quality desired.
• Consider the diameter of the part being scanned as a final determination before scanning.
For instance, the part may be smaller or larger than what is indicated by the weight of the
patient.

3.5.2 Consider decreasing the kV

Decrease the kilovoltage to 70, 80 or 100 kV for smaller patients.
•
A decrease in kV should not be done without increasing the mA to maintain noise levels and
contrast to noise ratios.
•
Lower kV selections increase HU values. Therefore, increase the window width for viewing
images to maintain a similar appearance.
•
Since lower kV selections lower X-ray penetration, it is important to not use low kV
selections on too large of a patient, which can potentially result in compromised image
quality. Work with your radiologist and medical physicist to establish low kV protocols and
patient size limits.
• Refer to CTDI Dose Values and Adjustment Factors in the
Technical Reference Manual as a guide for making adjustments to mAs for changes
of the
in kV in a protocol.
•
For example, consider a protocol with a technique of 120 kV, 70 mA, Medium Body SFOV.
As a starting point, in order to maintain CTDI
be adjusted as follows for pediatric patients:
○
340 mA at 70 kV
○ 215 mA at 80 kV
○
110 mA at 100 kV
○
70 mA at 120 kV
○ 50 mA at 140 kV
•
To assure sufficient X-ray penetration, the following chart is intended as a relative guide to
the maximum patient diameter that can be scanned based on a kV and mA's selection. It
does not indicate a recommended technique factor (that is generally higher) since the
technique factor also depends on the image quality needed for the diagnostic task.
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Direction 5480385-1EN, Revision 1
Dose and Performance chapter
while changing the kV, the technique could
vol
3 Pediatric and small patient scans
Revolution CT User Manual