Diagnostic Imaging

        

Body CT

We are currently updating our new protocols for our GE HD 750 64 Slice CT Scan.

Scan protocol

  1. The use of a non-enhanced scan prior to an enhanced sequence is rarely of diagnostic benefit in paediatric body CT. This is a simple way to achieve a dose reduction of 50 per cent.
  2. Dual or triple phase scanning is not appropriate in routine use. For specific indications such as investigation of focal hepatic lesions (eg suspicion of hemangioma, FNH) multi-phase scanning has a role if MR is not readily available. For the assessment of hepatoblastoma and other abdominal malignancies, we most often perform a portal venous phase alone (scanning the liver at 55 seconds for children under 30 kg, and 65 seconds for patients over 30 kg).
  3. Scanning the pelvis in addition to the abdomen (to the iliac crests) may not always be necessary, depending on clinical indication.
  4. Reducing coverage to a region of interest may be appropriate, especially in follow-up imaging

Technical parameters

Technical parameters should be adjusted for pediatric scanning. Routine use of adult protocols will increase dose exposure unnecessarily. The following adjustments are recommended to reduce dose while maintaining diagnostic image quality. They are intended as guidelines for the development of local protocols. Variability between CT manufacturers and scanner types means that one specific protocol will not be appropriate to optimize the performance characteristics of all scanners. This is affected by multiple factors including type and number of detectors, scanner geometry and filtration. Please contact your manufacturer for further advice regarding specific recommendations for your model.

Tube current (mAs) should be adjusted based on patient weight and anatomic region of interest. With all other factors held constant, patient radiation dose is directly proportional to x-ray tube current. For example, a 50 per cent reduction in tube current results in a 50 percent decrease in radiation dose. Weight-related reductions in mAs (tube current) are perhaps the most effective method of reducing dose to children. Smaller body size allows us to reduce this value considerably, sometimes up to five times less than a typical adult setting. For almost 10 years we have been using weight-adjusted protocols and, although the images are more grainy, there has been no significant loss of diagnostic quality. Noisier images don’t necessarily equate to non diagnostic images.

Typical Images using    

Dose chart below GE Light speed Ultra

8 Slice



Paediatric Body Exposure Chart (8 slice GE Lightspeed Ultra)

Below is the weight-adjusted settings we previously used with a single slice GE scanner, which may be helpful for those working with single slice technology.

References

Paediatric CT protocols

  • Donnelly LF, Frush DP (2003) Pediatric multidetector CT. Radiol Clin North Am 41: 637-655
  • Frush DP, Soden B, FrushKS, Lowry C (2002) Improved pediatric multidetector CT using a size-based color-coded format. Am J Roentgenol 178: 721-726
  • Donnelly LF, Emery KH, Brody AS, Laor T, Gylys-Morin VM, Anton CG, Thomas SR, Frush DP (2001) Minimizing radiation dose for pediatric body applications of single-detector helical CT: strategies at a large children’s hospital. American Journal of Radiology 176:303-306
  • Verdun FR, Lepori D, Monnin P, Valley JF, Schnyder P, Gudinchet F (2004). Management of patient dose and image noise in pediatric CT abdominal examinations. Eur Radiol 14: 835-841
  • CTisus  Johns Hopkins Web site giving adult and pediatric CT protocols.
  • Voch P (2005) CT dose reduction in children. Eur Radiol 15: 2330-2340
  • Cody DC, Moxley DM, Krugh KT, O’Daniel JC, Wagner LK, Eftekhari F (2004) Strategies for formulating appropriate MDCT techniques when imaging the Chest, Abdomen, and Pelvis in Pediatric Patients. AJR 182:849-859
  • FDA Public Health Notification(2001): Reducing radiation risk from computed tomography for pediatric and small adult patients.
  • PatersonA, Frush DP, Donnelly LF (2001) Helical CT of the body: are settings adjusted for pediatric patients? American Journal of Radiology 176:297-301

Parameters affecting CT dose

Malignancy risks associated with ionizing radiation

  • ICRP Publication no.60. 1990 recommendations of the International Commission on Radiological Protection. Oxford, England: Pergamon, 1991
  • BEIR VII – Phase 2 (2005) Health risks from exposure to low levels of ionizing radiation. National Academies Press.
  • Donnelly LF (2002) Lessons from history. Pediatr Radiol 32: 287-292

Risks associated with pediatric CT

  • Brenner DJ, Elliston CD, Hall EJ, Berdon WE (2001) Estimated risks of radiation-induced fatal cancer from pediatric CT. American Journal of Radiology 176:289-296
  • Pierce DA, Preston DL (2000) Radiation-related cancer risks at low doses among atomic bomb survivors. Radiation Research 154:178-186
  • Brenner DJ. Estimating cancer risks from pediatric CT: going from the qualitative to the quantitative. Pediatr Radiol 2002; 32: 228-231.
  • Conference on the ALARA concept in pediatric intelligent dose reduction (2002) Pediatr Radiol 32 (4): 217-313

Effective doses in CT examinations.

  • Picano E (2004) Sustainability of medical imaging. BMJ 328: 578-580
  • FDA website What are the radiation risks from CT?
  • Shrimpton PC, Hillier MC, Lewis MA, Dunn M (2005) Doses from Computed Tomography examinations in the UK – 2003 review. NRPB – W67, NRPB Publications.
  • Huda W. Effective doses to adult and pediatric patients. Pediatr Radiol 2002; 32: 272-279.

Useful articles for paediatricians

  • Frush DP, Donnelly LF and RosenNS (2004) Computed tomography and radiation risks: What pediatric health providers should know. Pediatrics 112(4): 951-957
  • Thomas KE, Parnell-Parmley JE, Haidar S, Moineddin R, Charkot E, BenDavid G and Krajewski C (2006) Assessment of radiation dose awareness among pediatricians. Pediatric Radiology 36: 823-832
  • American Academy of Pediatrics Grand Rounds8: 41-42 (2002) Think Twice before Ordering that CT.
  • Radiation Risks and Pediatric Computed Tomography (CT): A guide for health care providers. Published by the National Cancer Institute (2002). 

For more information click here.