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patient dose reduction
patient dose reduction
The main dose impactors are;
kV (CarekV or Ref kV)
Rotation time
Pitch
mA (Qref)
Length of scan (z-axis)
1-4: is optimized in our RCH scan protocols to ensure lowest dose practical is given. For most patients these don't need to be changed however can be changed if necessary.
Pitch
Pitch: Table movement/ rotation speed
Increased pitch: Faster scan, lower dose, more interpolation
Decreased pitch: Slower scan, higher dose, less interpolation
The highest pitch we can achieve is 3.2 (6)
Rotation time
How long the tube/s take to complete a full 360 degrees of movement.
Less time = less photons to create images, shorter scan times, higher temporal resolution
More time = more photos to create images, longer scan time
The Force can have a rotation time as low as 0.25s in turbo flash mode (see above)
Dose optimisation at RCH
Exposure factors inbuilt into our protocols (see previous page on CareDose4D, Qref, Ref kV and CarekV)
Our scanning protocols all are designed to modulate and create the lowest possible dose scans whilst keeping our scans within diagnostic levels for RCH. They may appear nosier than what you may have seen in adult centers due to this reduced dose.
Case example: You can see the noise level is quite different in our RCH brain scan (left) compared to an adult CT brain (right)
Tin Filter (Sn Filter)
The Tin Filter absorbs lower energy photons provided to the patient. This changed the kV spectrum of photons contributing to the image (see graph below). This will reduce dose and optimize image quality for densities that have no use for the lower energy photons. We use the Sn filter mainly in bone and chest imaging.
Example of RCH facial bones cases with (above) and without Sn filter (below).
You can see the difference in soft tissue information (loss of grey/whit matter differentiation) in the Sn filter image due to the lack of lower energy photons. The bony detail remains unchanged
Tin Filter (above) and NO Tin Filter (below)
X-CARE + ADMIRE (see previous page CT Refresher for details)
practice makes perfect
practice makes perfect
We do not scan unless we believe the child will be capable of being able to complete the imaging. Where needed we will always perform practice imaging with the patient to ensure they are;
Holding still for required length of scan time
Capable of required breath holds where needed
Will cope with IV contrast
10 pearls of radiation saftey in ct
10 pearls of radiation saftey in ct
staff and parents dose reduction
staff and parents dose reduction
Scatter radiation in ct
Scatter radiation in ct
At RCH, we allow parents/guardians and staff to stay in the room for scans provided they are wearing lead. This has been based off scatter radiation mapping tests performed by our RCH Physics team that shows how low the scatter dose is.
Link to Teams: RS-IS-001 Scatter Radiation in CT.pdf
featal dose reduction
featal dose reduction
pregnancy in ct
pregnancy in ct
We must check pregnancy on patients above the age of 12 if the featal dose provided to the patient exceeds 1mSv. This does not include CT head, CT neck or CT face examinations.
If a parent/guardian or staff member is pregnant, where possible they can leave the room. If the circumstances require them to stay in the room, we must place them in appropriate lead and apply the time-distance-shielding principle to the best of our ability.
Link to Teams: Radiation and Pregnancy Procedure.pdf
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