How to reduce dose in Pediatric CT imaging

How to reduce dose
in Pediatric CT imaging
By C. Leidecker and T. Flohr
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Anatomical and physiological differences between
children and adults require special attention when
imaging pediatric patients. Image quality requirements
are different because of smaller structures as well as
higher heart rates and difficulties in cooperating during
the scan, to name a few. Adjusting imaging parameters
is important to meet image quality requirements and,
in addition, is essential to reduce dose as children are
more sensitive to radiation than adults.
The most important steps in reducing dose for pediatric patients are:
• to be sure that a CT scan is the most appropriate diagnostic test for
the clinical question at hand
• to scan only the regions that are indicated
• to optimize scan parameters to the diagnostic task
The dose for each individual scan should be carefully adjusted to achieve
the necessary image quality. Scans with lower radiation dose may have
higher image noise, but still deliver diagnostic image quality.
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Scan preparation
Warm surroundings and dimmed lighting are helpful to make children
more cooperative.
Patient sedation should be considered to avoid rescans due to patient
motion. Use fast rotation times and high pitches when possible.
Proper patient centering is always important to dose and image quality.
Double check and verify the patient’s position with the laser beams as
well as in the topogram.
If patients are not centered, dose can increase substantially or image
quality may be impaired.
The use of breast shields is not recommended. If you nevertheless
decide to use shielding with your Siemens scanner, it is important to
ensure that shields are removed during topogram acquisition. Otherwise
the system will increase the dose according to the additional attenuation
in the scan area and the potentially positive effect is negated. Always
follow the shield manufacturers’ instructions for proper use and
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Selecting protocols
Use Siemens’ default child protocols
As a starting point, Siemens provides default scan protocols for children,
tailored to various body regions and procedures.
You may customize and save these protocols according to your imaging
needs. Please ensure that your protocols are changed only by authorized
Always use a child protocol when imaging pediatric patients. As a
guideline, we recommend using pediatric protocols up to a weight of
55 kg (body imaging) or 6 years (head imaging). For body imaging
children heavier than 55 kg should be scanned with an adult protocol,
for head imaging children older than age 6 should be scanned with an
adult protocol.
Use Siemens’ CARE Dose4D
Child default protocols use CARE Dose4D, Siemens’ automated real-time
tube current modulation. Once the reference setting is defined,
CARE Dose4D automatically adjusts the tube current to the patient size
and anatomy to achieve the diagnostic image quality at lowest possible
dose. Once the reference for a protocol is set, do not change this value.
If you are using software version syngo CT 2010 or earlier, set the
reference value to the one you would choose for a 20 kg patient (see
example below). Once the reference is set, do not change this value.
CARE Dose4D adjusts the value to the individual patient.
If you are using syngo CT 2011 or later, set the reference to the value
you would choose for an adult. Do not change the reference value once
it has been set for a protocol. For further details on using CARE Dose4D
with syngo CT 2011, please refer to the Operator Manual.
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Example for Quality ref. mAs settings with CARE Dose4D
(SOMATOM Definition AS, syngo CT 2010)
Head Routine
Thorax Routine
350 eff. mAs
110 eff. mAs
210 eff. mAs
Typically reduce to
57% of
original value
Typically reduce to
45% of
original value
Typically reduce
to 43% of original
50 eff. mAs
90 eff. mAs
Child (Default:
200 eff. mAs
CARE Dose4D active)
The examples above use a default setting of 120 kV. If you choose to
change the kV-value, please adjust mAs-values as well, as described on
the next page.
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How to reduce dose
Avoid multiphase exams
Reduce the number of phases when appropriate. Campaigns such as
Image Gently ( urge clinicians to use single phase
scans whenever possible.
Use automatic exposure control
Always use CARE Dose4D. It adjusts the exposure to the size and
attenuation of the individual patient. Using an automatic adjustment
maintains uniform image quality for every patient while ensuring that
the minimum dose has been used.
Use low-kV scanning for contrast enhanced scans
For vascular exams, dose savings are possible by lowering the
kV-values. Choosing lower kV-settings requires an increase in mAs to
maintain image quality. However, even with such increased settings, the
dose can be reduced.
Low kV-settings for vascular exams
When changing kV-values
from 120 kV to 100 kV
from 120 kV to 80 kV
Increase eff. mAs-value by
a factor of 1.1
a factor of 1.5
Dose reduction
to 65% of value at 120 kV
to 50% of value at 120 kV
If you have been using
50 eff. mAs at 120 kV for
your CTA protocols, use
55 eff. mAs at 100 kV.
If you have been using
50 eff. mAs at 120 kV for
your CTA protocols, use
75 eff. mAs at 80 kV.
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Low kV-settings for other contrast enhanced exams, e.g. liver
When changing kV-values
from 120 kV to 100 kV
from 120 kV to 80 kV
Increase eff. mAs-value by
a factor of 1.2
a factor of 2.0
Dose reduction
to 75% of value at 120 kV
to 65% of value at 120 kV
80 kV can be also used for applications when the lowest achievable
mAs-value at 120 kV is still too high. When adjusting your mAs-value at
the lower kV-setting, monitor the CTDIvol until the desired value
is reached.
Use lower dose where low contrast resolution
is not required
Examples for scans that may not need optimal low contrast resolution
include lung and bone imaging as well as follow-up studies for shunt or
tube placement.
Use organ based dose modulation
If radiation sensitive organs are exposed during the scan, e.g. breast
tissue in thoracic exams, use X-CARE if available on your system.
X-CARE provides organ specific dose savings without the disadvantages
of in-plane shielding.
Use the appropriate reconstruction technique
Avoid sub-millimeter slices. Thicker slices, selection of a smoother kernel
and wider windowing reduce image noise, and, in return, help reduce
dose if scan parameters are changed for future exams. Use advanced
reconstruction techniques like Iterative Reconstruction, when available.
Thus, a dose reduction of up to 60% can be achieved.
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Dose reporting
Siemens provides all the necessary tools for efficient
dose management and monitoring.
Dose is reported in terms of CTDIvol and DLP, as required by IEC standards.
This represents the dose delivered to a reference phantom reported in a
standard way for all scanners and does not reflect actual exposure to
any given patient.
For all Siemens‘ protocols including pediatrics, as defined by the IEC, the
CTDIvol is measured in the 32 cm phantom for all body exams and in the
16 cm phantom for all head exams.
The CTDIvol is displayed prior to the exam and reflects changes in scan
parameters. Both CTDIvol and DLP are available after each individual
exam through either the Patient Protocol page or the Dose Structured
Report (Dose SR).
The Patient Protocol and Dose SR are automatically saved as separate
series at the end of the exam, and are available for viewing and
archiving as a series in the Patient Exam.
National organizations such as BfS and ACR provide recommendations
on reference dose levels in terms of CTDIvol and DLP. We recommend
including dose information in terms of CTDIvol and DLP in each patient
report for future reference and potential optimization of protocols.
Radiation risk associated with CT imaging is poorly understood. The
easiest way to reduce risk is by reducing patient dose according to the
ALARA principle (As Low As Reasonably Achievable) when optimizing
pediatric protocols.
IEC: International Electrotechnical Commission
BfS: Bundesamt für Strahlenschutz, Federal Office for Radiation Protection, Germany
ACR: American College of Radiology, USA
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seReduction_Glossary.indd 1
Observe patient reaction
carefully, because it is
important for your scan.
Have a careful look at the
ECG now – it may help you
in deciding the next step.
Be careful! Your contrast
protocol might be
By taking these points into
consideration you can
significantly reduce dose.
Action required by user.
Something needs to
be changed in the scan
This is a technical fact
with some extra
explanation here.
This is a special tip for
solving a difficult problem.
Carefully assure an
optimized patient
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seReduction_Glossary.indd 2
How to reduce dose?
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