On combining internal and external fiducials for liver motion compensation

Area of Science:

• Medical Imaging
• Surgical Navigation
• Biomedical Engineering

Background:

• Liver interventions require precise targeting, which is challenged by respiratory motion.
• Accurate motion compensation is crucial for improving the safety and efficacy of liver interventions.
• Current methods for motion compensation often involve external markers, which may have limitations.

Purpose of the Study:

• To evaluate the in-vivo accuracy of combining skin markers and fiducial needles for motion compensation during liver interventions.
• To compare the target registration error (TRE) using varying numbers of external skin markers and internal fiducial needles.
• To assess the impact of different transformation types on accuracy and the correlation between fiducial registration error (FRE) and TRE.

Main Methods:

• An in-vivo accuracy study was conducted in two swine.
• The study compared different combinations of skin markers (n(s)) and fiducial needles (n(f)).
• The tip of an additional tracked needle served as the target, and TRE was measured using various transformation types.

Main Results:

• Fiducial needles had the greatest effect on accuracy during continuous breathing.
• Mean RMS errors decreased from 4.8 mm (n(f)=0) to 2.0 mm (n(f)=1) and 1.7 mm (n(f)=2) with n(s)=4.
• Error reductions of up to 70% were achieved with two fiducial needles compared to no motion compensation.
• At expiration, mean RMS error ranged from 1.1 mm (n(f)=0) to 0.8 mm (n(f)=2).
• Fiducial registration error (FRE) strongly correlated with target registration error (TRE).

Conclusions:

• Combining skin markers and fiducial needles enhances motion compensation accuracy in liver interventions.
• The number of fiducial needles significantly impacts TRE, with two needles providing substantial error reduction.
• FRE can serve as a reliable intra-interventional measure of system accuracy, aiding in clinical decision-making.