Localizing spherical fiducials in C-arm based cone-beam CT

Area of Science:

• Medical Imaging
• Image-Guided Interventions
• Cone-Beam CT

Background:

• C-arm cone-beam CT (CBCT) enables in situ 3D imaging, simplifying image-guided interventions by integrating imaging and intervention in the same location.
• Image-to-patient registration, crucial for interventions, commonly uses skin fiducials, but C-arm CBCT's limited reconstruction volume can exclude these markers and the organ of interest.

Purpose of the Study:

• To demonstrate that fiducial localization outside the reconstructed volume is achievable using projection images.
• To enable accurate fiducial coordinate determination even when markers are not within the reconstructed region.

Main Methods:

• Localization of fiducials was performed using the projection images from which the CBCT reconstruction was generated.
• This method replaces direct localization within volumetric images with localization in the 2D projection images.

Main Results:

• The proposed method successfully localized all tested fiducials, including those outside the reconstructed volume.
• Mean localization errors were 0.55 (0.22) mm for 4 mm markers and 0.51 (0.18) mm for 6 mm markers, demonstrating high accuracy.

Conclusions:

• The developed fiducial localization approach is accurate enough for thoracic-abdominal interventions.
• This method offers greater flexibility in fiducial placement, potentially replacing or augmenting direct volumetric localization.