Three dimensional frameless fusion of ultrasound liver volumes

The authors have derived a "frameless fusion" technique to integrate volumetric images using internal vasculature as the fiducial markers. They demonstrate the feasibility of ultrasound (US to US) liver image fusion using internal vascular landmarks from in-vivo data obtained on separate scans taken minutes apart or weeks apart. The US volumes include scans from varying orientations on a single volunteer with a 5-8 MHz curvilinear transducer (GE Logiq 700 MR) attached to a motorized, hand-held track. Power Doppler US volumes were segmented to extract and reconstruct the portal vein structure as 1 mm cubed voxels. The vessel volumes were then rendered with commercial 3D software and correlated as a rigid body by a semi-automated, in-house program. After the vessel volumes were fused, the corresponding grayscale volumes were re-positioned and fused to create overlapping images. Volume registration was assessed in the grayscale data by measuring alignment of diaphragm and vessel walls (portal and hepatic vein) on 6 slices at 25-75% through the volumes. The fused data from the same day and after six weeks displayed an average 2 mm error centrally and 3-4 mm at the far field. Potential uses for merged or fused 3D images of the liver include the reconstruction of the whole organ for treatment planning, and lesion follow-up.