Rationale and Objectives
Neonates are at increased risk for cold stress and hypothermia in cool environments. An infant transport mattress (ITM) is commonly used to increase neonate temperature during transport and has been used during CT scanning. This study determined the impact of an ITM on radiation dose and image artifacts during CT scanning.
Materials and Methods
CT images from a single clinical patient scanned with an ITM were reviewed, and observations of image artifacts were recorded. A phantom was scanned with and without the ITM while varying tube-current modulation, reconstruction method, slice thickness, metal reduction algorithm, tube voltage, and tube current. The effects of the ITM on computed tomography dose index (CTDI vol ), mean Hounsfield unit (HU), and HU standard deviation were recorded.
Results
The clinical patient scan demonstrated significantly decreased mean HU and increased HU standard deviation. In the phantom, the ITM increased CTDI vol 27% and induced an artifact that decreased the mean HU by 3.5 HU and increased HU standard deviation by 4.6 HU. Angular tube-current modulation, strong iterative reconstruction, thick slices, metal artifact reduction, and high mA reduced the artifact.
Conclusion s
Using ITM during CT scanning is not recommended given the relatively brief scanning time, increased dose, and induced image artifacts. Based on our results, several acquisition parameters may be altered to mitigate the image artifact if an ITM is required during scanning.
Introduction
Thermal maintenance of the patient is an essential aspect of neonatal care, especially in pre-term and low birth weight infants . Cold stress and possible hypothermia due to loss of thermal maintenance can contribute to increased morbidity and mortality . Previous studies have demonstrated that covering the patient with a polyethylene wrap immediately after birth reduces cold stress and rates of hypothermia among neonates in the delivery room . Similarly, a specially designed warming infant transport mattress (ITM) placed under the neonate during transport has been shown to increase admission temperature and decrease the incidence of hypothermia . The use of a polyethylene or a warming mattress has also been endorsed by the American Heart Association and American Academy of Pediatric . In a survey of English neonatal units, 25.2% of units employed a warming mattress either alone or in conjunction with a polyethylene wrap for premature infants .
Little information currently exists related to neonatal cold stress and hypothermia during imaging. One brief study from 1980 suggests using a warming mattress during computed tomography (CT) scanning to decrease cold stress and the chance of hypothermia; however, studies using modern CT technology do not exist. Modern CT scanners implement several automatic exposure control technologies to reduce patient radiation dose and improve image quality. Although these technologies typically lead to reduced patient radiation dose, it is possible that the presence of a foreign object could confuse the automatic exposure control algorithms leading to increased patient radiation dose. Further, a foreign object could alter beam characteristics and cause image artifacts .
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Materials and Methods
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Clinical Patient Scan
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Table 1
CT Scanning Protocol for Clinical Patient Scan
Patient (Baseline) Protocol Phantom Protocol Tube voltage (kVp) 100 80, 100, 120 Tube current (mA) Automatic (110 at kidneys) Automatic (140 average); fixed: 98, 110, 140, and 182 Rotation time (s) 0.4 0.4 Automatic tube-current selection? Yes Yes and no Tube-current modulation Longitudinal None, longitudinal, and angular Reconstruction kernel C B and C Slice thickness (mm) 3 1, 3, and 5 Statistical iterative reconstruction strength 3 0, 3, and 6 Pitch 0.891 0.891 CT localizer AP only AP only Collimation 64 × 0.625 64 × 0.625 Metal artifact compensation algorithm? No Yes and no
AP, anteroposterior; CT, computed tomography.
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Phantom Scans
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Results
Clinical Patient Scan
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Phantom Scans
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Table 2
Acquisition Parameter Impact on Image Artifact. P -Values are between Given Parameters with the ITM
Mean HU with ITM Mean HU without ITM Mean HU change HU Standard Deviation with ITM HU Standard Deviation without ITM HU Standard Deviation Change_P_ -Value (Mean HU/HU Standard Deviation) Baseline 114.0 ± 0.6 117.5 ± 0.5 −3.5 ± 0.8 15.4 ± 0.9 10.8 ± 0.5 4.6 ± 1.0 vs 140 mA: 0.26/ < 0.01 Shifted ITM 115.0 ± 0.4 117.5 ± 0.5 −2.5 ± 0.6 14.6 ± 0.5 10.8 ± 0.5 3.8 ± 0.7 vs Baseline: 0.03/0.01 Angular tube-current modulation 113.3 ± 0.8 117.8 ± 0.2 −4.5 ± 0.8 16.1 ± 0.9 11.2 ± 1.1 4.9 ± 1.4 vs Baseline: 0.52/0.79 vs 140 mA: 0.65/ < 0.01 Iterative reconstruction strength 0 114.1 ± 0.6 117.9 ± 0.3 −3.8 ± 0.7 19.5 ± 1.0 13.5 ± 0.5 6.0 ± 1.1 – Iterative reconstruction strength 6 113.7 ± 0.6 118.1 ± 0.3 −4.4 ± 0.7 11.6 ± 0.7 7.8 ± 0.3 3.8 ± 0.8 vs Strength 0: 0.02/ < 0.01 1 mm Slice thickness 113.4 ± 0.9 118.4 ± 0.2 −5.0 ± 0.9 27.1 ± 0.8 20.6 ± 1.0 6.5 ± 1.3 – 5 mm Slice thickness 113.6 ± 0.2 118.1 ± 0.3 −4.5 ± 0.4 12.2 ± 0.6 8.3 ± 0.6 3.9 ± 0.8 vs 1 mm: 0.42/ < 0.01 Metal artifact reduction algorithm 113.6 ± 0.6 118.1 ± 0.4 −4.5 ± 0.7 15.4 ± 0.8 10.6 ± 0.3 4.8 ± 0.9 vs Baseline: 0.26/0.69 80 kVp 101.7 ± 0.4 104.1 ± 0.3 −2.4 ± 0.5 18.3 ± 0.7 12.1 ± 0.6 6.2 ± 0.9 – 120 kVp 119.8 ± 0.4 124.3 ± 0.1 −4.5 ± 0.4 15.2 ± 0.6 12.0 ± 0.3 3.2 ± 0.7 vs. 80 kVp: 0.03/ < 0.01 80 kVp at 110 mA 102.1 ± 0.9 104.0 ± 0.2 −1.9 ± 0.9 33.7 ± 1.7 19.1 ± 1.2 14.7 ± 2.1 – 120 kVp at 110 mA 121.0 ± 0.6 124.8 ± 0.2 −3.8 ± 0.6 14.5 ± 0.9 10.1 ± 0.5 4.4 ± 1.1 vs 80 kVp at 110 mA: < 0.01/ < 0.01 98 mA 114.0 ± 1.1 118.1 ± 0.2 −4.1 ± 1.1 20.9 ± 1.7 12.7 ± 0.2 8.2 ± 1.7 – 110 mA 113.8 ± 0.3 117.7 ± 0.2 −3.9 ± 0.4 19.9 ± 1.7 12.0 ± 0.4 7.9 ± 1.7 – 140 mA 113.5 ± 0.5 117.8 ± 0.2 −4.3 ± 0.5 18.3 ± 1.1 11.2 ± 0.9 7.1 ± 1.4 – 182 mA 113.5 ± 0.5 117.7 ± 0.2 −4.2 ± 0.5 15.1 ± 1.0 9.9 ± 0.5 5.2 ± 1.1 vs 98 mA: 0.85/0.03 Kernel B 112.6 ± 0.5 116.8 ± 0.3 −4.2 ± 0.6 10.7 ± 0.7 7.3 ± 0.3 3.4 ± 0.8 vs Baseline: 0.27/ < 0.01
HU, Hounsfield units; ITM, infant transport mattress.
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Table 3
Acquisition Parameter Impact on Radiation Output
Slice mA with ITM Slice mA without ITM Slice mA change Slice CTDI vol with ITM (mGy) Slice CTDI vol without ITM (mGy) Slice CTDI vol change (mGy) Scan CTDI vol with ITM (mGy) Scan CTDI vol without ITM (mGy) Scan CTDI vol change Baseline 180 140 40 (28.6%) 6.6 5.2 1.4 (26.9%) 6.1 4.8 1.3 (27.1%) Shifted ITM 180 140 40 (28.6%) 6.5 5.2 1.3 (25.0%) 6.1 4.8 1.3 (27.1%) 80 kVp 342 269 96 (35.7%) 6.1 4.8 1.3 (27.1%) 5.7 4.4 1.3 (29.5%) 120 kVp 106 84 22 (26.2%) 6.2 5.1 1.1 (21.6%) 6.0 4.7 1.3 (27.7%) Angular tube-current modulation 162 140 22 (15.7%) 5.9 5.0 0.9 (18%) 5.8 5.0 0.8 (16.0%) 80 kVp with fixed 110 mA 110 110 – 2.0 2.0 – 2.0 2.0 – 120 kVp with fixed 110 mA 110 110 – 6.6 6.6 – 6.6 6.6 – 98 mA 98 98 – 3.6 3.6 – 3.6 3.6 – 110 mA 110 110 – 4.0 4.0 – 4.0 4.0 – 140 mA 140 140 – 5.1 5.1 – 5.1 5.1 – 182 mA 182 182 – 6.6 6.6 – 6.6 6.6 –
CTDI vol , volumetric computed tomography dose index; ITM, infant transport mattress.
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Discussion
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Conclusions
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