KEYWORDS: Visualization, Image registration, Liver, Radiofrequency ablation, 3D acquisition, 3D image processing, Matrices, 3D displays, 3D vision, Computed tomography
Interventional procedures on deformable organs pose difficulties for the radiologists when inserting the probe
towards a lesion. The deformation due to the breathing makes a reliable and automated alignment of the
interventional 2D CT-Fluoro to the pre-interventional 3D CT-Volume very challenging. Such alignment is highly
desirable since, during the intervention, the CT-Volume brings more information as it is enhanced with contrast
agent and has a higher resolution than the CT-Fluoro slice. A reasonable solution for the alignment is obtained
by employing a robust optimization technique. However, since we would like to help the needle guidance towards
the lesion, due to the involved deformation, a single slice of the 3D CT-Volume is not satisfactory.
The main contribution of this paper consists in visualizing slices of the 3D CT-Volume that are resulting
from the out-of-plane motion parameters along weighted isosurfaces in the convergence basin of the similarity
function used during the alignment. This visualization copes with the uncertainty in estimating the deformation
and brings much more information than a single registered slice. Three experienced interventional radiologists
were consulted and their evaluation clearly highlighted that such visualization unfolding the neighborhood with
the belonging structures, like vessels and lesion spread, will help the needle guidance.
In this paper we present four visualization modes based on piecewise and global registration. These visualization
modes are evaluated by two interventional radiologists. We are using three routinely acquired datasets from
three patients who underwent RF Liver Ablation procedure. Piecewise 2D-3D registration is applied to define
a subvolume in the preinterventional dataset that compensates for tissue deformation. The liver in the CT-Fluoroscopy
(CT-Fluoro) slice is respectively divided into four and six rectangles. Every single rectangle is
independently registered and the intersection of the resulting planes, define a subvolume. This subvolume is
minimally traversed in an animation sequence. The visualizations are evaluated qualitatively with regard to
the information displayed. Two alternative visualization approaches are also evaluated. The first alternative
approach is to display axial slices around the global registered slice, since the interventional radiologists are used
to evaluate axial slices. The second alternative approach is to define two envelope planes of the previously defined
subvolume and display this envelope volume. The evaluation results show that the visualization of the minimum
volume comprised in the registered four and six planes is preferred over the axial visualization or the envelope
planes since it shows the lesion from different angles and follows the breathing movement. The interventional
radiologists also appreciated the facilitated assessment of the neighborhood of the lesion.
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