1. Image Gently, CT Imaging and Radiation Protection of Pediatric Patients
Kalpana Kanal, Ph.D., DABR
Associate Professor, Diagnostic Physics
Director, Diagnostic Physics Section
Director, Resident Physics Education
Dept. of Radiology
UW Medicine
a copy of this lecture may be found at:

2. Challenges of Pediatric Imaging
Little body fat compared to adults
Variations in normal growth and development
Small physical size present challenges
Lack of ability to breath hold, and potential need for sedation or other immobilization must be considered
Radiation doses - important due to the increased vulnerability (sensitivity) of tissues
Children have a longer lifetime in which to manifest stochastic (i.e. cancer) risks
Children incur a higher dose when identical CT settings are used
Ref: RSNA/AAPM module: Imaging Gently: CT Imaging and Radiation Protection of Pediatric Patients
© UW and Kalpana M. Kanal, PhD, DABR

3. Alliance for Radiation Safety Image Gently
The Alliance for Radiation Safety in Pediatric Imaging, the sponsors of the “Image Gently” campaign was formed in 2007
Fundamental principles of rad protection during ped imaging: justification, utilization and optimization
© UW and Kalpana M. Kanal, PhD, DABR

4. 5. Image Gently Website www.imagegently.org
© UW and Kalpana M. Kanal, PhD, DABR

5. 5. CT Procedure Checklist
Are additional modifications to the protocol warranted, i.e. follow-up examinations?
If multiphase scanning is indicated, the highest exposure should be for the phase that provides the most critical information. Consider lower doses for phases such as pre-contrast scanning if necessary or delayed images, such as with CT urography
Has appropriate use of sedation, and immobilization been implemented?
© UW and Kalpana M. Kanal, PhD, DABR

6. 5. Image Gently Website CT Procedure Checklist
Is CT the right test in this clinical situation? Is ultrasound or MR imaging more appropriate?
If CT is indicated, have appropriate adjustments based on size, scan indication, and region scanned been made?
Have general pediatric specific protocols been developed and uploaded to the scanner for common examinations?
© UW and Kalpana M. Kanal, PhD, DABR

7. 5. CT Procedure Checklist
Has the environment been made as child friendly as possible?
Is shielding being used when appropriate?
Have equipment and protocols been developed and reviewed periodically with qualified medical imaging physicists?
Has the pitch (in helical scanning) been adjusted to lower dose? (Between 1 and 1.5)
© UW and Kalpana M. Kanal, PhD, DABR

8. 5. CT Procedure Checklist
Has the appropriate scan field of view (bow tie filter) been selected?
Has patient positioning been optimized so that the patient is in the center of the gantry, the scan technique and length of the projection scout views have been minimized and only those phases necessary are being performed?
Have appropriate dose reduction technology such as tube current modulation been activated? Understand these technologies
© UW and Kalpana M. Kanal, PhD, DABR

9. 2. Interventional Fluoroscopy: Step Lightly
Treat kids with care: step lightly on the fluoroscopy pedal. Stop and child size the technique. Consider ultrasound or when applicable, MR guidance.”
© UW and Kalpana M. Kanal, PhD, DABR

10. 3. General Fluoroscopy: Pause and Pulse
Stop and child-size the technique. Use lowest pulse rate possible. Consider ultrasound or MRI when applicable.
© UW and Kalpana M. Kanal, PhD, DABR

11. 4. Nuclear Medicine
The pediatric nuclear medicine community has developed the Pediatric Radiopharmaceutical Administered Doses: 2010 North American Consensus Guidelines to directly address the need to lower radiation dose and standardize the radiopharmaceutical dose for children throughout the United States
© UW and Kalpana M. Kanal, PhD, DABR

12. 5. CR/DR Radiography
This group has sponsored a vendor summit to promote standardization of exposure index and to promote awareness of the need to optimize radiation exposure in routine radiographs in children
The group is working with digital radiography manufacturers to develop educational materials to promote appropriate use of their equipment in children
Recently, a digital radiography safety checklist was created for technologists to remind them of the critical steps needed when performing computed radiography or direct radiography in children
© UW and Kalpana M. Kanal, PhD, DABR

13. Image Wisely
The Image Wisely Campaign, the adult counterpart to the Image Gently Campaign, is based on the success of the Alliance for Radiation Safety in Pediatric Imaging.
The constituent founding organizations are AAPM, ACR, ASRT, and the Radiological Society of North America (RSNA), with individuals from the Alliance providing consultation.
© UW and Kalpana M. Kanal, PhD, DABR

14. CT Dose Indices CTDIvol and DLP
© UW and Kalpana M. Kanal, PhD, DABR
Ref: RSNA/AAPM module: Imaging Gently: CT Imaging and Radiation Protection of Pediatric Patients

15. CT Dose Indices CTDIvol
CTDIvol = [2/3 * surface dose + 1/3 * central dose] / Pitch
The original application of CTDIvol was to provide a standardized method to estimate and compare the radiation output of different CT scanners.
 CTDIvol was defined to be a dose index of CT scanners, not a patient dose index.
© UW and Kalpana M. Kanal, PhD, DABR
Ref: RSNA/AAPM module: Imaging Gently: CT Imaging and Radiation Protection of Pediatric Patients

16. DLP DLP = CTDIvol * Scan Length
DLP does not represent a patient dose index, but rather the energy deposited in a standard phantom
The risk to the patient from ionizing radiation associated with a CT examination is affected by the amount of radiation energy deposited in the tissue and the volume of the patient’s irradiated tissues
Therefore, the longer the length of patient that is scanned (along the z axis), all other factors remaining equal, the higher the radiation risk to the patient
© UW and Kalpana M. Kanal, PhD, DABR

17. DLP
© UW and Kalpana M. Kanal, PhD, DABR
Ref: RSNA/AAPM module: Imaging Gently: CT Imaging and Radiation Protection of Pediatric Patients

18. Patient Size Considerations Affect on Attenuation of Patient Size
Mass (kg)
PA (cm)
# HVL
LAT (cm)
Preterm 2 6
1.5
Newborn 3 9
2.2 10
2.5
1 yr 12 14
3.5
5 yr 19 16 4 22
5.5
12 yr 31 18
4.5 27
6.8
Adult 68 33
8.3
100+ 35
8.8 48
© UW and Kalpana M. Kanal, PhD, DABR
Ref: RSNA/AAPM module: Imaging Gently: CT Imaging and Radiation Protection of Pediatric Patients

19. Patient Size Considerations
© UW and Kalpana M. Kanal, PhD, DABR
Ref: RSNA/AAPM module: Imaging Gently: CT Imaging and Radiation Protection of Pediatric Patients

20. Why does patient dose decrease with increasing patient size?
Radiation output of the scanner in all three cases is identical
The entrance radiation dose to 32 cm phantom is 65% greater than the 10 cm phantom – closer to tube
The exit dose of the beam after traveling through 32 cm of plastic is far less than the exit dose after traveling through only 10 cm of plastic
The superficial layers of tissue of the patient’s body shield and reduce the patient’s core tissue dose. 
© UW and Kalpana M. Kanal, PhD, DABR
Ref: RSNA/AAPM module: Imaging Gently: CT Imaging and Radiation Protection of Pediatric Patients

21. Affect of Patient Size on CTDIvol and DLP
The under or over estimate of the patient dose by the displayed CTDIvol as a function of patient size depending on if the 16 or 32 cm CTDI phantom is used
The displayed CTDIvol underestimates the patient dose and misleads the radiologic technologist or radiologist if they assume CTDIvol represents the patient dose.
© UW and Kalpana M. Kanal, PhD, DABR
Ref: RSNA/AAPM module: Imaging Gently: CT Imaging and Radiation Protection of Pediatric Patients

22. Management of Image Quality and Radiation Dose for Pediatric Patients
Consultation between qualified medical physicist, radiologist and technologist is essential in IQ and dose management
© UW and Kalpana M. Kanal, PhD, DABR
Ref: RSNA/AAPM module: Imaging Gently: CT Imaging and Radiation Protection of Pediatric Patients

23. Recommended Adjustment of Tube Current Factors
A method to establish reduced mAs scan protocols for children that is independent of the manufacturer, model, and age of the CT scanner may be found at
© UW and Kalpana M. Kanal, PhD, DABR
Ref: RSNA/AAPM module: Imaging Gently: CT Imaging and Radiation Protection of Pediatric Patients

24. Recommended Adjustment of Tube Current Factors
When you fill in the baseline values, the table automatically calculates the mAs for the different ages.
© UW and Kalpana M. Kanal, PhD, DABR
Ref: RSNA/AAPM module: Imaging Gently: CT Imaging and Radiation Protection of Pediatric Patients

25. Recommended Adjustment of Kilovoltage (kV)
A lower kVp decreases patient dose and increases quantum mottle in the image while an increase in the kVp has the opposite effect, if mAs is unchanged.
The degree of change in radiation dose and quantum mottle caused by changes in high voltage is often reduced by changing the mAs in the opposite direction of the change in high voltage
© UW and Kalpana M. Kanal, PhD, DABR
Ref: RSNA/AAPM module: Imaging Gently: CT Imaging and Radiation Protection of Pediatric Patients

26. Recommended Adjustment of Kilovoltage (kV)
To improve contrast or to perform CT angiography, 100 kVp is reasonable for medium sized pediatric patients.
Neonates to small pediatric patients may be imaged as low as 80 kVp
80 kVp images at the maximum tube current of the CT scanner will not produce an adequate number of x-rays to avoid artifacts and maintain reasonable quantum mottle in the image for larger pediatric patients
© UW and Kalpana M. Kanal, PhD, DABR
Ref: RSNA/AAPM module: Imaging Gently: CT Imaging and Radiation Protection of Pediatric Patients

27. Recommended Adjustment of Kilovoltage (kV)
How does one practically adjust kVp for pediatric patients?
Lower kVp to improve contrast and adjust mAs to maintain radiation dose at original level
or reduce the radiation dose to maintain the contrast to noise ratio (CNR) in the original image. For example, 120 vs 80 kV
So now one can reduce mAs and patient dose until noise in the image increases up to 70% with no reduction in CNR compared to original image since the contrast in the image increased 70%
© UW and Kalpana M. Kanal, PhD, DABR
Ref: RSNA/AAPM module: Imaging Gently: CT Imaging and Radiation Protection of Pediatric Patients

28. Size Specific Dose (SSDE) for Pediatric Patients
CTDIvol displayed on console of CT scanner underestimates dose to pediatric patients
Task Group 204 of AAPM prepared a report that provides scaling factors as a function of patient size or age that can be used to estimate the dose to patient
CTDIvol displayed = 5.5, 32 cm phantom used. Lateral Diam = 15 cm
SSDE = CTDIvol * Correction Factor
SSDE = 5.5 * 2.29 mGy
SSDE = 13 mGy
© UW and Kalpana M. Kanal, PhD, DABR
Ref: RSNA/AAPM module: Imaging Gently: CT Imaging and Radiation Protection of Pediatric Patients

29. Recommendations for Clinical Protocols
Use alternate modalities such as US and MRI if possible
If possible, eliminate multiphase scans
Adjust CT scan parameters for individual patient indications – only cover area of interest and adjust techniques according to patient size
Shielding? – controversial
We use shielding for our patients at both UWMC and HMC
© UW and Kalpana M. Kanal, PhD, DABR

30. Review Question
Challenges presented during pediatric CT imaging include all except which one of the following?
Children are more apt to move during the scan
Children often require lower doses than the smallest radiation levels that can be set on state-of-the-art CT scanners
Children are more sensitive to radiation than adults
Children present different disorders than adults
© UW and Kalpana M. Kanal, PhD, DABR

31. Review Question
Which statement below is correct concerning CTDIvol, with all other parameters constant?
CTDIvol increases with a decrease in the tube current.
CTDIvol is unaffected by the composition and thickness of the bow-tie filter of the scanner.
CTDIvol increases as the pitch of the CT scanner increases.
CTDIvol typically does not represent the absorbed radiation dose to the pediatric patient.
© UW and Kalpana M. Kanal, PhD, DABR

32. Review Question Which statement below is true concerning DLP?
DLP cannot be used to estimate changes to patient dose from changes to CT scan parameters.
DLP decreases if CTDIvol during the examination increases.
DLP represents the energy deposited in the patient during the CT scan acquisition.
DLP is a less accurate estimation of patient dose than CTDIvol.
© UW and Kalpana M. Kanal, PhD, DABR

33. Review Question
Which one of the following statements is true concerning radiation dose to pediatric patients during CT scanning?
Dose reduction protocols for pediatric patients should be developed and implemented by a team consisting of a radiologist and technologist.
The dose reduction protocol on the Image Gently website can be used on multi detector or single detector CT scanners.
The dose reduction protocol on the Image Gently website reduces absorbed pediatric radiation dose estimates to values less than those the facility would use on its adult patients.
Pediatric dose reduction should be limited to adjustment of tube current (mA).
© UW and Kalpana M. Kanal, PhD, DABR

34. Review Question
With respect to the kVp in CT protocols for scanning children
The primary reason relatively high kVp is reduced is the reduction of patient dose.
If the kVp is reduced from 120 to 80 (66%), the mAs should be increased by 66%.
If the mAs is increased correctly with reduction in kVp, the CNR can be held constant in the image.
Pediatric CT protocols for infants and preschoolers are optimum if 120 kVp is typically used.
© UW and Kalpana M. Kanal, PhD, DABR

35. THANK YOU FOR YOUR ATTENTION
© UW and Kalpana M. Kanal, PhD, DABR
Cruise Ship docked in Skagway, Alaska - Image provided by Kanal