Radiation dose reduction and image quality enhancement for patients unable to elevate their arms in chest CT: A comparative study.

Purpose: To propose a method to effectively reduce radiation dose while enhancing image quality in chest CT for patients unable to elevate their arms utilizing the air-gap technique.

Methods: Chest CT images were acquired in three positions: arms raised (control group, position A), arms lowered with the air-gap technique utilizing an in-house device (position B), and arms lowered without the device (position C). Data were categorized by body weight. Radiation dose was assessed using dose-length product (DLP) values, with quantitative analyses of image noise, contrast-to-noise ratio (CNR), and CNR-to-dose ratio (CNRDR). Qualitative assessment utilized a Likert scale.

Results: Average DLP was 473.7 ± 142.9 mGy × cm in position C, with the lowest in position A at 267.3 ± 93.3 mGy × cm. Position B had a DLP of 317.2 ± 121.4 mGy × cm, 18.7 % higher than position A but 33.0 % lower than position C. In patients over 70 kg, all positions exceeded the thoracic CT diagnostic reference level (DRL) (324.2 mGy × cm). For those under 70 kg (i.e., <50 kg, 50-70 kg), position B showed lower DLPs compared to the above DRL. Quantitative analysis indicated that position B maintained image quality similar to position A, with CNRDR of 30.2 ± 11.1 versus 26.6 ± 10.9 in position A, showing marginal significance (p = 0.046). The qualitative evaluation indicated that position A had the highest rating at 4.96, followed by position B at 4.51, and position C at 3.47.

Conclusion: The air-gap device with lowered arms during chest CT for patients unable to elevate their arms can reduce radiation dose while maintaining image quality. A custom-designed device facilitates safe and efficient procedures, especially for patients with higher body weight.