Rationale and Objectives
The aim of this study was to assess the effects of radiation dose reduction on the assessment of the tracheal lumen on expiratory multidetector computed tomographic (MDCT) images of pediatric patients referred for evaluation for tracheomalacia (TM).
Materials and Methods
The hospital information system was used to retrospectively identify 20 standard-dose and 20 reduced-dose paired inspiratory and expiratory MDCT studies performed for the evaluation of suspected TM in pediatric patients (aged ≤ 18 years). The reduced-dose technique used a 50% reduction of the tube current for the expiratory portion of the study compared to the standard-dose technique. Two experienced pediatric radiologists, who were blinded to the tube current of the study, reported their levels of confidence for measuring the tracheal lumen using a four-point scale ranging from zero (no confidence) to three (highest level of confidence). The difference in confidence level between the two groups of studies was analyzed using the Mann-Whitney U test. The percentage of radiation dose reduction using the reduced-dose technique in comparison to the standard-dose technique was estimated using anthropomorphic thorax phantoms. The presence or absence of TM (≥50% expiratory reduction in tracheal cross-sectional luminal area) on MDCT imaging was compared to bronchoscopic results for the subset of 32 patients who underwent both procedures.
Results
A high level of confidence was reported for measuring the tracheal lumen on MDCT imaging for both standard-dose (median, 3.0) and reduced-dose (median, 3.0) expiratory sequences ( P = .80). The total radiation dose of the paired inspiratory-expiratory computed tomographic (CT) exam was decreased by 23% with the reduced-dose technique. TM was diagnosed by CT imaging in seven patients who underwent standard-dose and six patients who underwent reduced-dose paired inspiratory and expiratory MDCT studies. CT results for the presence or absence of TM were concordant with the results of bronchoscopy in all 32 patients who underwent both procedures.
Conclusion
The radiation dose of paired inspiratory-expiratory CT imaging can be reduced by 23% while maintaining similar diagnostic confidence for assessment of the tracheal lumen compared to a standard-dose technique in pediatric patients. Thus, a reduced-dose technique is recommended for evaluating TM in children.
Tracheomalacia (TM), a condition characterized by excessive expiratory collapse due to weakening of the tracheal wall and supporting cartilage, is the most common congenital anomaly of the central airways and a cause of potentially significant morbidity . Recently, paired inspiratory and expiratory multidetector computed tomographic (MDCT) imaging has been shown to be highly accurate in diagnosing TM in both children and adults . However, a potential disadvantage of this technique is that dual-phase (ie, inspiratory and expiratory phases) computed tomographic (CT) imaging is associated with up to twice as much radiation exposure as a single-phase CT acquisition. Such exposure is particularly concerning for pediatric patients, who are more susceptible than adults to the potentially harmful effects of ionizing radiation .
A previous study in adult patients showed that tube current can be reduced for the expiratory phase of MDCT studies while maintaining a high level of confidence in assessing the tracheal lumen for TM . However, to our knowledge, there is no published information regarding the use of a reduced-dose MDCT technique for the evaluation of TM in children. Because pediatric CT parameters are already routinely adjusted by patient age or weight, as well as by the use of automated tube current modulation, it is uncertain whether further dose reduction is possible while maintaining diagnostic confidence. Therefore, the purpose of this study was to evaluate the influence of a reduced-dose technique on the confidence levels of radiologists in assessing the tracheal lumen on paired inspiratory and expiratory MDCT exams of pediatric patients with clinically suspected TM.
Materials and methods
Patient Population
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MDCT Imaging Technique
Patient Preparation
Sedation and intubation
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Intravenous contrast material
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MDCT Technical Factors
Type of MDCT scanner
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MDCT parameters
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Table 1
Tube Voltage and Tube Current by Patient Weight
Weight (lb) Tube Voltage (kVp) Standard/Reduced Tube Current (mA) 10–19 80 60/30 20–39 90 70/35 40–59 100 80/40 60–79 100 100/50 80–99 120 120/60 100–150 120 140/70 >150 120 170/85
Table 2
Tube Voltage and Tube Current by Patient Age
Age (y) Tube Voltage (kVp) Standard/Reduced Tube Current (mA) Newborn to 1 80 60/30 1–3 100 80/40 3–6 120 80/40 >6 120 200/100
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CT Image Review and Evaluation
CT Image Review
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CT Image Evaluation
Quantitative measurement of tracheal luminal area
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Degree of confidence in measuring the tracheal luminal area
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Bronchoscopic Evaluation
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Radiation Dose
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Statistical Analysis
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Results
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Table 3
Patient Characteristics and Confidence Levels for Measurement of the Tracheal Lumen with Standard Versus Reduced Radiation Dose
Patient Characteristics Confidence Level Patient Age (mo) Gender Clinical Symptom Inspiration Expiration Standard radiation dose 1 1.5 M Stridor 3 3 2 52.3 F Stridor 3 3 3 141.6 M Cough 3 3 4 49.3 M Recurrent infection 3 3 5 5.8 M Stridor 3 3 6 6.5 M Cough 3 3 7 5.1 M Stridor 3 3 8 3.4 F Desaturation 3 3 9 5.4 M Desaturation 3 3 10 6.3 M Stridor 2 2 11 189.1 M Shortness of breath 3 3 12 15.3 M Stridor 2 3 13 73.1 F Recurrent infection 3 3 14 1.5 F Stridor 2 2 15 3.2 M Cough 2 3 16 3.9 M Stridor 2 2 17 7.9 M Recurrent infection 3 3 18 43.0 M Recurrent infection 3 3 19 0.9 M Stridor 3 3 20 4.4 M Stridor 3 3 Reduced radiation dose 1 2.5 M Cough 2 3 2 3.7 M Stridor 2 2 3 14.7 F Stridor 3 3 4 4.1 F Stridor 3 3 5 5.8 M Stridor 3 3 6 38.0 M Stridor 3 3 7 8.3 M Stridor 3 3 8 14.2 M Cough 3 3 9 50.8 M Cough 3 3 10 3.6 M Desaturation 3 3 11 143.7 M Cough 3 3 12 16.3 F Desaturation 3 3 13 6.9 F Stridor 3 3 14 2.0 F Desaturation 3 3 15 97.0 M Cough 2 2 16 45.2 M Stridor 3 3 17 58.0 F Recurrent infection 2 2 18 0.6 M Stridor 3 3 19 23.7 M Recurrent infection 3 3 20 25.5 M Shortness of breath 3 3
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Patient Characteristics
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MDCT Imaging Findings
Degree of Confidence in Measuring the Tracheal Luminal Area
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CT Diagnosis of TM
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Comparison Between CT Imaging and Bronchoscopy
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Radiation Doses
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Discussion
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