Korean J Radiol.  2010 Feb;11(1):46-53. 10.3348/kjr.2010.11.1.46.

Is Weight-Based Adjustment of Automatic Exposure Control Necessary for the Reduction of Chest CT Radiation Dose?

• Prakash P
• Kalra MK
• Gilman MD
• Shepard JA
• Digumarthy SR

• KMID: 1787013
• DOI: http://doi.org/10.3348/kjr.2010.11.1.46

Abstract

OBJECTIVE
To assess the effects of radiation dose reduction in the chest CT using a weight-based adjustment of the automatic exposure control (AEC) technique.
MATERIALS AND METHODS
With Institutional Review Board Approval, 60 patients (mean age, 59.1 years; M:F = 35:25) and 57 weight-matched patients (mean age, 52.3 years, M:F = 25:32) were scanned using a weight-adjusted AEC and non-weight-adjusted AEC, respectively on a 64-slice multidetector CT with a 0.984:1 pitch, 0.5 second rotation time, 40 mm table feed/rotation, and 2.5 mm section thickness. Patients were categorized into 3 weight categories; < 60 kg (n = 17), 60-90 kg (n = 52), and > 90 kg (n = 48). Patient weights, scanning parameters, CT dose index volumes (CTDIvol) and dose length product (DLP) were recorded, while effective dose (ED) was estimated. Image noise was measured in the descending thoracic aorta. Data were analyzed using a standard statistical package (SAS/STAT) (Version 9.1, SAS institute Inc, Cary, NC).
RESULTS
Compared to the non-weight-adjusted AEC, the weight-adjusted AEC technique resulted in an average decrease of 29% in CTDIvol and a 27% effective dose reduction (p < 0.0001). With weight-adjusted AEC, the CTDIvol decreased to 15.8, 15.9, and 27.3 mGy for the < 60, 60-90 and > 91 kg weight groups, respectively, compared to 20.3, 27.9 and 32.8 mGy, with non-weight-adjusted AEC. No significant difference was observed for objective image noise between the chest CT acquired with the non-weight-adjusted (15.0 +/- 3.1) and weight-adjusted (16.1 +/- 5.6) AEC techniques (p > 0.05).
CONCLUSION
The results of this study suggest that AEC should be tailored according to patient weight. Without weight-based adjustment of AEC, patients are exposed to a 17 - 43% higher radiation-dose from a chest CT.

Keyword

Automatic exposure control (AEC); Chest CT; Weight based; Radiation dose

MeSH Terms

Adult
Aged
Aged, 80 and over
*Body Weight
Female
Humans
Male
Middle Aged
*Radiation Dosage
*Radiography, Thoracic
*Tomography, X-Ray Computed
Young Adult

Figure

• 

  Fig. 1 Scatter plot of radiation dose (CTDIvol-y-axis) versus patient transverse diameter (cm) (x-axis) showing moderate correlation for chest CT performed by non-weight-adjusted automatic exposure control technique (correlation coefficient = 0.61) (A). Strong correlation (correlation coefficient = 0.83) was observed for chest CT performed by weight-adjusted automatic exposure control technique (B).

• 

  Fig. 2 Scatter plot graph of radiation dose (CTDIvol - y-axis) versus patient weight (kg) (x-axis) shows moderate correlation for chest CT performed by non-weight-adjusted automatic exposure control technique (correlation coefficient = 0.66) (A). Strong correlation (correlation coefficient = 0.83) was observed for chest CT performed by weight-adjusted automatic exposure control technique (B).

• 

  Fig. 3 2.5 mm thick transverse chest CT performed by weight-adapted automatic exposure control technique in lung (A) and mediastinal (B) windows in 76-year-old female (weight 43 kg, objective noise 8.1, and CTDIvol 12.8 mGy). Chest CT examination with non-weight-adjusted automatic exposure control technique in 43-year-old female (weight 45 kg, objective noise 8.9, CTDIvol 18.0 mGy) in lung (C) and mediastinal (D) windows. At lower radiation dose, weight-adjusted automatic exposure control protocol provides acceptable image noise and diagnostic acceptability.

• 

  Fig. 4 2.5 mm thick transverse chest CT performed with weight-adapted automatic exposure control technique for lung (A) and mediastinal (B) windows in 46-year-old male (patient weight 107 kg, objective noise 10.5, and CTDIvol 28.0 mGy). Chest CT examinations using non-weight-adjusted automatic exposure control technique in 58-year-old male (patient weight 107 kg, objective noise 10.6, and CTDIvol 39.6 mGy) for lung (C) and mediastinal (D) windows. At lower radiation dose, weight-based automatic exposure control protocols provides acceptable image noise and diagnostic acceptability.

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