Scanning Parameters

what parameters do the technologist control

umA

uScan time

uSlice thickness

uField of view (FOV)

uReconstruction algorithm

ukVp

uPitch (helical)

what is the kVp for adults and pediatrics

120/80

what is the con of increasing mA

produces more heat and thus longer delay between scans

what kind of movement can parameters not stop

involuntary movement

what is step and shoot

• CT table moves in and then stays until the exact position and tube rotates around it

• there is a slight delay in between = interscan delay

• images are parallel to eachother

• usually done for head

what is a pro about conventional CT

1. can be angled

2. highest image quality

3. contiguous or non-contiguous (reduces patient dose)

4. dynamic or cine mode

when do we usually use conventional CT

head

conventional CT

what does conventional CT do to decrease scan time

clustering

what is the disadvantage of conventional CT

1. interscan delay

2. limited to how data can be reconstructed

what is dynamic or cine mode mean

constant imaging to find out where biopsy needs to be

what can helical scanning not do and why

helical scanning can not have an angle. The computer will get overwhelmed and images will come out distorted and wrong values (contrast). It is because it is not getting a complete 360 image

pros on helical scanning

1. single breath hold acquisitions = decrease scan time, less motion artifacts, higher patient output

2. slip ring technology = no interscan delay

3. greater data manipulation and reconstruction

x refers to the size shape motion and path of the beam

beam geometry