Pediatric CT and Image Gently

The utility of CT in patients of all ages is undeniable [1-4], and its use expanded markedly over the last decades of the 20th and early 21st centuries  [5, 6].  By 2000 and 2007, approximately 11% of the estimated 69 million CT scans performed annually in the US were in children [5–7]. This widespread adoption obviated the need for many invasive diagnostic procedures, such as exploratory laparotomies [8], but also contributed to a substantial rise in medical radiation exposure. Indeed, the NCRP Report No. 160 documented a sevenfold increase in radiation exposure from medical imaging between 1980 and 2006, largely attributable to  CT and nuclear medicine[7, 9].

In response to these concerns, professional initiatives such as the Image Gently Alliance, focusing on children, and the Image Wisely campaign, focusing on adults, emphasized justification and optimization. Their shared message: “the right patient, the right exam, at the right time, done the right way”, has been instrumental in educating radiologists, technologists, referring providers, and the public, with the goal of reducing unnecessary radiation exposure through evidence-based imaging.

As a result of these efforts, utilization patterns have shifted in pediatric imaging. While CT remains a valuable diagnostic tool that has replaced more invasive procedures in many scenarios, recent data demonstrate a decline in pediatric CT use, particularly in emergency departments. For example, the proportion of ED encounters involving CT decreased from 3.9% in 2009 to 2.9% in 2018, while ultrasonography increased from 2.5% to 5.8% and MRI from 0.3% to 0.6% during the same period [10]. This trend reflects both heightened awareness of radiation risks and the successful implementation of advocacy campaigns and clinical decision support tools [10–12].

The child could be considered the paradigm underscoring the importance of this process. Why is this so? What makes children different? Children differ from adults in a number of important ways relevant to radiation exposure and potential stochastic risks. Compared to adults, (1) children are smaller, (2) they are growing, and (3) they have longer remaining lifespans.

1. Children are smaller than adults. For any given set of CT scanning parameters, the effective dose is higher for smaller cross-sectional areas. This is because dose is defined as absorbed energy per unit mass, and therefore the same energy in a smaller mass will result in a higher dose per unit mass. In addition, in the case of CT, where the beam is applied circumferentially, dose in the center of a small patient will be higher than in the center of a large patient, due to the lesser attenuation of the surrounding tissue in a small patient. These effects will be most pronounced in the youngest patients with smaller body mass and radius. Calculated dose parameters that are displayed in current CT scanners are based on data obtained from the 32 cm phantom. In an average adult, whose size is equivalent to 29 cm, the 32 cm acrylic phantom will underestimate the dose to that average adult by approximately 30% [10]. This, of course, would be compounded in pediatric patients. In an analysis of effective dose by body mass, effective dose in pediatric patients was increased by 50% compared to adult patients despite a reduction of approximately 25% in scanning parameters in that series. The increase was most marked in the infants, in whom effective dose increased 100% [10]. It is therefore very important to realize that, for a given set of CT scanning parameters, we must CHILD-SIZE the scanning parameters just to maintain the same image noise that is acceptable in the CT images of our adult patients.
2. Children are growing. Stochastic risk, particularly the risk of future cancer, is higher in children due to longer post-exposure life expectancy and greater tissue sensitivity. Large cohort studies estimate that annual pediatric CT imaging in the United States may induce thousands of future cancers, with risk proportional to dose and age at exposure [14]. Dose-reduction strategies, including standardization of pediatric CT protocols and focusing on reducing the highest quartile of exposures, could prevent up to 43% of projected radiation-induced cancers in children [14,15].
3. Children have longer remaining life spans. Potentially induced cancers do not become manifest until after a latency period, which varies with the type of cancer and age of the patient. The longer life expectancy of the pediatric patient allows sufficient time for a latency period to occur. Further, with a longer life, the chances of repeated and increased cumulative doses are increased.

Strategies to reduce radiation dose follow the ALARA principle (As Low As Reasonably Achievable); i.e., obtaining diagnostic examinations at the lowest possible dose. At all ages, CT examinations should only be performed when indicated, and consideration should be given to alternative modalities, such as Ultrasound and MRI, as appropriate. Multiphase examinations double or triple the radiation dose, are rarely indicated in pediatrics, and should only be used when absolutely necessary, with adjustment of parameters as possible. For example, if pre-contrast images are necessary to assess for calcifications within a tumor, the pre-contrast scan should be restricted to the site of the tumor, and can be done with much lower scanning parameters, as image noise would not interfere with detection of calcifications. By the same token, follow-up examinations to assess changes in size of a large tumor, or renal calculus burden, can be done with limited scanning field and much lower scanning parameters and exposure [13]. Institutions should be accredited by an organization that evaluates image quality and radiation dose indices and documents that CT doses are “child-sized.”

Significant inroads have been made in reducing radiation exposure to the pediatric patient since the launch of the Image Gently and Image Wisely campaigns. There have been over 50,000 pledges to the Image Gently website, and a similar number to Image Wisely by the end of 2016 (with 20,000 new pledges in the first month of 2017 alone). Beginning in 2007-2008, a decreasing trend in the number of CT scan examinations for pediatric patients has been observed [17]. The most significant recent advances in reducing radiation exposure to pediatric patients undergoing CT scans include the widespread adoption of iterative reconstruction (IR) algorithms, model-based IR, and deep learning-based reconstruction (DLR), as well as the use of low tube voltage protocols and photon-counting detector CT. These technologies have enabled substantial dose reductions (often exceeding 50%) while maintaining or improving diagnostic image quality, particularly in small children where lower tube voltage is feasible due to smaller body size and less photon attenuation[18-24].

Iterative and model-based IR algorithms (such as ASIR, SAFIRE, MBIR, and AIDR-3D) reduce image noise and allow for lower tube current and voltage settings, directly translating to lower radiation doses. Deep learning-based reconstruction further improves noise suppression and image quality, enabling even greater dose reductions compared to conventional IR, especially at 80 kVp in pediatric CT. Photon-counting detector CT represents a newer advance, providing high-resolution images at lower doses, which is particularly advantageous for children requiring repeated imaging.[19-20]

In summary, the principles of justification and optimization underlie both the request and the performance of diagnostic imaging examinations. CT is a valuable tool, which helps us save lives and avoid more invasive procedures. As other imaging modalities, it needs to be used judiciously, with understanding of potential risk factors, and the relationship of these risk factors to the age and size of our patients.

Cross links:

https://www.cancer.gov/about-cancer/causes-prevention/risk/radiation/pediatric-ct-scans

http://www.imagegently.org/

http://www.radiologyinfo.org/

http://www.pedrad.org

http://www.eurosafeimaging.org/

http://www.wfpiweb.org/

References

1. Brink M, et al., Added value of routine chest MDCT after blunt trauma: evaluation of additional findings and impact on patient management. AJR 2008. 190(6): p. 1591-8.
2. Federle MP, Abdominal trauma: the role and impact of computed tomography. Invest Radiol 1981. 16(4): 260-8.
3. Salim A, et al., Whole body imaging in blunt multisystem trauma patients without obvious signs of injury: results of a prospective study. Arch Surg, 2006. 141(5): 468-73; discussion 473-5.
4. Awasthi, S., et al., Is hospital admission and observation required after a normal abdominal computed tomography scan in children with blunt abdominal trauma? Acad Emerg Med 2008. 15(10): 895-9.
5. Mettler FA, Jr., et al., CT scanning: patterns of use and dose. J Radiol Prot 2000. 20(4): 353-9.
6. Broder J., Fordham LA, and Warshauer DM, Increasing utilization of computed tomography in the pediatric emergency department, 2000-2006. Emerg Radiol 2007. 14(4): 227-32.
7. Mettler FA, Jr, et al., Radiologic and nuclear medicine studies in the United States and worldwide: frequency, radiation dose, and comparison with other radiation sources-1950-2007. Radiology 2009. 253(2): 520-31.
8. Faget C, et al., Value of CT to predict surgically important bowel and/or mesenteric injury in blunt trauma: performance of a preliminary scoring system. Eur Radiol 2015. 25(12): 3620-8.
9. NCRP. NCRP Report No 160. [cited 2010; Available from: http://ncrponline.org/publications/reports/ncrp-report-160/.
10. Impact of Iterative Model Reconstruction Combined With Dose Reduction on the Image Quality of Head and Neck CTA in Children.Cheng B, Xing H, Lei D, et al.Scientific Reports. 2018;8(1):12613. doi:10.1038/s41598-018-30300-4
11. Impact of Iterative Model Reconstruction Combined With Dose Reduction on the Image Quality of Head and Neck CTA in Children.Cheng B, Xing H, Lei D, et al.Scientific Reports. 2018;8(1):12613. doi:10.1038/s41598-018-30300-4.
12. Impact of Iterative Model Reconstruction Combined With Dose Reduction on the Image Quality of Head and Neck CTA in Children.Cheng B, Xing H, Lei D, et al.Scientific Reports. 2018;8(1):12613. doi:10.1038/s41598-018-30300-4
13. Ware DE, et al., Radiation effective doses to patients undergoing abdominal CT examinations. Radiology 1999. 210(3): 645-50.
14. The Use of Computed Tomography in Pediatrics and the Associated Radiation Exposure and Estimated Cancer Risk.Miglioretti DL, Johnson E, Williams A, et al. JAMA logoJAMA Pediatrics. 2013;167(8):700-7. doi:10.1001/jamapediatrics.2013.311.
15. ICRP, 1990 Recommendations of the International Commission on Radiological Protection. ICRP Publication 60, 1991. Annex B Biological effects of ionizing radiation.
16. Strauss, K.J., et al., Image gently: Ten steps you can take to optimize image quality and lower CT dose for pediatric patients. AJR 2010. 194(4): 868-73.
17. Miglioretti DL, et al., The use of computed tomography in pediatrics and the associated radiation exposure and estimated cancer risk. JAMA Pediatr 2013. 167(8): 700-7.
18. Radiation Dose Reduction at Pediatric CT: Use of Low Tube Voltage and Iterative Reconstruction.Nagayama Y, Oda S, Nakaura T, et al. Radiographics : A Review Publication of the Radiological Society of North America, Inc. 2018 Sep-Oct;38(5):1421-1440. doi:10.1148/rg.2018180041.
19. Innovative Advances in Pediatric Radiology: Computed Tomography Reconstruction Techniques, Photon-Counting Detector Computed Tomography, and Beyond.Mese I, Altintas Mese C, Demirsoy U, Anik Y.Pediatric Radiology. 2024;54(1):1-11. doi:10.1007/s00247-023-05823-2.
20. Radiation Dose Reduction for 80-kVp Pediatric CT Using Deep Learning-Based Reconstruction: A Clinical and Phantom Study. Nagayama Y, Goto M, Sakabe D, et al. AJR. American Journal of Roentgenology. 2022;219(2):315-324. doi:10.2214/AJR.21.27255.
21. Advanced CT Techniques for Decreasing Radiation Dose, Reducing Sedation Requirements, and Optimizing Image Quality in Children.Gottumukkala RV, Kalra MK, Tabari A, Otrakji A, Gee MS.Radiographics : A Review Publication of the Radiological Society of North America, Inc. 2019 May-Jun;39(3):709-726. doi:10.1148/rg.2019180082.
22. Feasibility Study of Using One-Tenth mSv Radiation Dose in Young Children Chest CT With 80 kVp and Model-Based Iterative Reconstruction.Sun J, Zhang Q, Hu D, et al.Scientific Reports. 2019;9(1):12481. doi:10.1038/s41598-019-48946-z.
23. Impact of Iterative Model Reconstruction Combined With Dose Reduction on the Image Quality of Head and Neck CTA in Children.Cheng B, Xing H, Lei D, et al.Scientific Reports. 2018;8(1):12613. doi:10.1038/s41598-018-30300-4.
24. (10)Ultra-Low-Dose Lung Multidetector Computed Tomography in Children - Approaching 0.2 Millisievert. Tschauner S, Zellner M, Pistorius S, et al. European Journal of Radiology. 2021;139:109699. doi:10.1016/j.ejrad.2021.109699.