Inadequate object positioning and improvement of automatic exposure control system calculations based on an empirical...

Area of Science:

• Medical Imaging
• Radiological Physics
• Diagnostic Radiology

Background:

• Automatic exposure control (AEC) in computed tomography (CT) can miscalculate tube current with patient off-center positioning.
• Existing positioning compensation mechanisms are not universally available on all CT systems.
• Empirical-based AEC systems require a method to address off-center patient positioning inaccuracies.

Purpose of the Study:

• To derive and verify a compensation process for empirical-based AEC systems.
• To achieve an equivalent effect to built-in positioning compensation mechanisms.
• To maintain consistent radiation dose and image quality despite patient table height variations.

Main Methods:

• Derived a relational equation to maintain constant tube current with varying table height and quality reference milliampere-seconds (QRmAs).
• Implemented this equation as a proposed compensation method for empirical-based AEC.
• Evaluated radiation dose and image quality using phantom imaging with and without the compensation method.

Main Results:

• The proposed compensation method significantly reduced variations in output radiation dose and noise level with changes in table height.
• Without the compensation method, table height variations led to substantial fluctuations in radiation dose and noise.
• Imaging an anthropomorphic chest phantom demonstrated a stable output radiation dose using the proposed method.

Conclusions:

• The derived compensation method effectively stabilizes radiation dose and image quality in CT scans with empirical-based AEC.
• This method provides a viable solution for CT systems lacking built-in patient positioning compensation.
• The findings support improved accuracy and patient safety in CT imaging through optimized AEC performance.