Technical Note: Investigating internal-external motion correlation using fast helical CT

Area of Science:

• Medical Imaging
• Respiratory Physiology
• Biomedical Engineering

Background:

• Breathing motion significantly impacts medical imaging quality, especially in thoracic and abdominal scans.
• Accurate surrogates for respiratory motion are crucial for image-guided interventions and motion artifact reduction.
• Non-invasive external surrogates are desirable for ease of use and patient comfort.

Purpose of the Study:

• To quantify the accuracy of anterior torso skin surface position measurements as a surrogate for breathing motion.
• To evaluate the reliability of external surface landmarks for real-time respiratory monitoring during CT scans.

Main Methods:

• Fourteen patients underwent free-breathing helical CT scans with simultaneous abdominal pneumatic bellows monitoring.
• Diaphragm dome position served as the gold standard, correlated with bellows data to establish a breathing model.
• Anterior torso surface positions were measured from CT scans and correlated against the diaphragm position model.

Main Results:

• A strong correlation (average residual error 9.21%) was found between diaphragm motion and the abdominal bellows signal.
• Correlations between surface positions and diaphragm motion varied across the torso and between patients.
• A consistently high correlation was observed near the abdomen, with an average minimum residual error of 11.8% for skin surface surrogates.

Conclusions:

• The thoracic patient surface can be an accurate breathing surrogate, but its reliability varies geographically.
• Careful selection of surface landmarks is necessary for accurate and dependable use of skin surface surrogates.
• Future research will focus on developing surface imaging algorithms for comprehensive chest and torso motion analysis.