Quantitative assessment of four-dimensional computed tomography image acquisition quality

Area of Science:

• Medical Imaging
• Radiation Oncology
• Image Quality Assessment

Background:

• Four-dimensional (4D) computed tomography (CT) is vital for radiation treatment planning, enabling visualization of tumor motion during respiration.
• Assessing the quality of 4D CT imaging is critical for accurate dose delivery and treatment efficacy.
• Current methods for 4D CT quality assurance require robust validation to ensure reliability.

Purpose of the Study:

• To develop and validate a comprehensive set of tests for evaluating the image quality of 4D CT scans used in radiation therapy.
• To assess key imaging parameters including phase-binning accuracy, geometric accuracy, volume accuracy, and CT number reproducibility.
• To compare the performance of different 4D CT reconstruction techniques.

Main Methods:

• Utilized a commercial respiratory motion phantom and a programmable moving platform with a CT phantom.
• Acquired 4D CT datasets on two different multislice helical CT scanners employing distinct 4D CT reconstruction approaches.
• Simulated breathing patterns by moving the platform and analyzed known inserts for contouring, phase-binning, shape, volume, and CT number accuracy.

Main Results:

• Phase-binning accuracy varied up to 5% depending on the reconstruction and binning order (pre- vs. post-reconstruction).
• Both CT scanner approaches demonstrated minimal geometric distortion and volume error.
• Partial-volume effects impacted volume accuracy, and 4D CT images showed increased CT number variation compared to static CT.

Conclusions:

• The developed tests provide a framework for characterizing 4D CT image quality relevant to radiation therapy.
• Understanding variations in phase-binning and CT number is essential for optimizing 4D CT acquisition and reconstruction parameters.
• Further optimization of 4D CT imaging protocols can enhance accuracy and reliability in radiation treatment planning.