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Strategies for Formulating Appropriate MDCT Techniques When Imaging the Chest, Abdomen, and Pelvis in Pediatric Patients

¹ Division of Diagnostic Imaging, University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Blvd., Unit 56, Houston, TX 77030.
² Present address: Department of Radiology, The Toledo Hospital, 2142 N Cove Blvd., Toledo, OH 43606.
³ Department of Radiation Physics, University of Texas M. D. Anderson Cancer Center, Houston, TX 77030.
⁴ Department of Radiology, University of Texas Medical School, 6431 Fannin St., MSB 2.100, Houston, TX 77030.

View larger version (144K): [in a new window]   Fig. 1A. —Anthropomorphic phantoms used for this study. Photograph shows adult (A), 5-year-old (B), 10-year-old (C), and 1-year-old (D) phantoms.

View larger version (126K): [in a new window]   Fig. 1B. —Anthropomorphic phantoms used for this study. Photograph shows chest scanning setup with 1-year-old phantom. Note placement of skin dose monitors on anterior midline (three monitors) and lateral (two monitors) surfaces of chest. Only 1-year-old phantom included legs, which were used during dose measurements for convenience.

View larger version (132K): [in a new window]   Fig. 1C. —Anthropomorphic phantoms used for this study. Photograph shows abdominopelvic scanning setup with adult phantom. Note placement of skin dose monitors on anterior midline (three monitors) and lateral (two monitors) surfaces of abdominopelvic region.

View larger version (93K): [in a new window]   Fig. 2A. —Image-noise measurements. MDCT chest scan of 5-year-old phantom shows location of noise measurement region of interest. Area of sample was 557 mm2 for this phantom.

View larger version (96K): [in a new window]   Fig. 2B. —Image-noise measurements. MDCT abdominopelvic scan of 10-year-old phantom shows location of noise measurement region of interest. Area of sample was 565 mm2 for this phantom.

View larger version (13K): [in a new window]   Fig. 3. —Graph shows relationships between anterior surface midline chest dose and milliampere-seconds at 120 kVp for four anthropomorphic phantoms and two CT dose index phantoms. Peripheral chamber positions (1 cm below surface) were used in standard CT dose index phantoms. Sixteen-centimeter phantom CT dose indexp values underestimated entrance exposure measurements for pediatric phantoms by approximately 10%. Thirty-two-centimeter phantom CT dose indexp values underestimated entrance exposure measurements for adult phantom by approximately 20–35%. = adult phantom, = 10-year-old phantom, = 5-year-old phantom, = 1-year-old phantom, # = 16-cm CT dose index phantom, = 32-cm CT dose index phantom.

View larger version (13K): [in a new window]   Fig. 4. —Graph shows relationships between anterior surface midline abdominopelvic dose and milliampere-seconds at 120 kVp for four anthropomorphic phantoms and two CT dose index phantoms. Peripheral chamber positions (1 cm below surface) were used in standard CT dose index phantoms. Sixteen-centimeter phantom CT dose indexp values underestimated entrance exposure measurements for pediatric phantoms by approximately 10%. Thirty-two-centimeter phantom CT dose indexp values underestimated entrance exposure measurements for adult phantom by approximately 20–35%. = adult phantom, = 10-year-old phantom, = 5-year-old phantom, = 1-year-old phantom, # = 16-cm CT dose index phantom, = 32-cm CT dose index phantom.)

View larger version (15K): [in a new window]   Fig. 5. —Graph shows that increase in chest dose with decreasing patient size was largest for 120-kVp setting, commonly used for CT examinations. Two data points were obtained for each phantom (anterior surface midline and lateral surface). = adult phantom, = 10-year-old phantom, = 5-year-old phantom, = 1-year-old phantom.

View larger version (17K): [in a new window]   Fig. 6. —Graph shows that increase in abdominopelvic dose with decreasing patient size was largest for 140-kVp setting. Two data points were obtained for each phantom (anterior surface midline and lateral surface). = adult phantom, = 10-year-old phantom, = 5-year-old phantom, = 1-year-old phantom.

View larger version (34K): [in a new window]   Fig. 7. —Graph shows noise measurements from phantom chest and abdominopelvic images obtained at 200 mAs and varying peak kilovoltage. Image noise varied by as much as a factor of 3.3 among phantom images using identical scanning techniques. Black bar = 1-year-old phantom, bar with horizontal lines = 5-year-old phantom, bar with vertical lines = 10-year-old phantom, bar with cross-hatch lines = adult phantom. AbdPel = abdominopelvic image.

View larger version (14K): [in a new window]   Fig. 8. —Graph shows that chest image noise varied as function of surface anterior midline dose in similar manner for each phantom. We can decrease surface dose for pediatric CT examinations by matching image-noise values to those of acceptable adult technique. = adult phantom, = 10-year-old phantom, = 5-year-old phantom, = 1-year-old phantom.

View larger version (13K): [in a new window]   Fig. 9. —Graph shows that abdominopelvic image noise varied as function of surface anterior midline dose in similar manner for each phantom. We can decrease surface dose for pediatric CT examinations by matching image-noise values to those of acceptable adult technique. = adult phantom, = 10-year-old phantom, = 5-year-old phantom, = 1-year-old phantom.

View larger version (12K): [in a new window]   Fig. 10. —Graph shows that chest image noise varied as function of surface lateral dose in similar fashion to midline dose. = adult phantom, = 10-year-old phantom, = 5-year-old phantom, = 1-year-old phantom.

View larger version (12K): [in a new window]   Fig. 11. —Graph shows that abdominopelvic image noise varied as function of surface lateral dose in similar fashion to midline dose. = adult phantom, = 10-year-old phantom, = 5-year-old phantom, = 1-year-old phantom.

View larger version (80K): [in a new window]   Fig. 12. —21-month-old boy with cervical neuroblastoma. Chest CT image was obtained at 80 kVp and 160 mA with 0.5 sec per rotation, 4 x 5 mm detector configuration, pitch of 1.5, 5-mm thickness, and 21-cm field of view. Beam-hardening artifact (arrows) in bony shoulder region was considered sufficiently severe to remove this option from our pediatric protocol chart for chest CT.

View larger version (132K): [in a new window]   Fig. 13A. —4-year-old boy with stage V renal Wilms' tumor. All images were obtained with 23-cm display field of view. Note that although window width and window level settings on these three images are relatively consistent, the IV contrast timing is different among three image sets and results in various tissue contrast levels. Clinical abdominopelvic CT image was obtained before adjustment of CT for pediatric imaging. Technique parameters were 120 kVp, 128 mAs (160 mA and 0.8 sec), 4 x 3.75 mm detector configuration, and 1.5 pitch. This examination is associated with dose of approximately 29 mGy and is considered relatively free of artifact.

View larger version (131K): [in a new window]   Fig. 13B. —4-year-old boy with stage V renal Wilms' tumor. All images were obtained with 23-cm display field of view. Note that although window width and window level settings on these three images are relatively consistent, the IV contrast timing is different among three image sets and results in various tissue contrast levels. Clinical abdominopelvic CT image was obtained 2 months after A at 80 kVp, 120 mAs (150 mA and 0.8 sec), 4 x 5 mm detector configuration, 1.5 pitch. Beam-hardening artifacts (arrowheads) were considered sufficiently severe to remove this option from our pediatric protocol chart. This study was acquired with approximately 9 mGy, which is 70% reduction in dose relative to image shown in A.

View larger version (122K): [in a new window]   Fig. 13C. —4-year-old boy with stage V renal Wilms' tumor. All images were obtained with 23-cm display field of view. Note that although window width and window level settings on these three images are relatively consistent, the IV contrast timing is different among three image sets and results in various tissue contrast levels. Clinical abdominopelvic CT image was obtained 2 months after B using 100 kVp, 128 mAs (160 mA and 0.8 sec), 23-cm field of view, 4 x 5 mm detector configuration, and pitch of 1.5. Although beam-hardening artifacts are still present (arrow and arrowheads), their appearance is much less severe than that in 80-kVp image (B). This study was acquired with approximately 18 mGy, which is 40% reduction in dose relative to image shown in A.

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