KEYWORDS: Fluoroscopy, Image registration, Ultrasonography, Heart, Calibration, Visualization, Computed tomography, 3D modeling, In vivo imaging, Detection and tracking algorithms
This study assesses the accuracy of a new transesophageal (TEE) ultrasound (US) fluoroscopy registration
technique designed to guide percutaneous aortic valve replacement. In this minimally invasive procedure, a
valve is inserted into the aortic annulus via a catheter. Navigation and positioning of the valve is guided
primarily by intra-operative fluoroscopy. Poor anatomical visualization of the aortic root region can result in
incorrect positioning, leading to heart valve embolization, obstruction of the coronary ostia and acute kidney
injury. The use of TEE US images to augment intra-operative fluoroscopy provides significant improvements to
image-guidance.
Registration is achieved using an image-based TEE probe tracking technique and US calibration. TEE probe
tracking is accomplished using a single-perspective pose estimation algorithm. Pose estimation from a single
image allows registration to be achieved using only images collected in standard OR workflow. Accuracy of this
registration technique is assessed using three models: a point target phantom, a cadaveric porcine heart with
implanted fiducials, and in-vivo porcine images. Results demonstrate that registration can be achieved with
an RMS error of less than 1.5mm, which is within the clinical accuracy requirements of 5mm. US-fluoroscopy
registration based on single-perspective pose estimation demonstrates promise as a method for providing guidance
to percutaneous aortic valve replacement procedures. Future work will focus on real-time implementation and a
visualization system that can be used in the operating room.
KEYWORDS: Imaging systems, X-rays, 3D acquisition, X-ray imaging, 3D image processing, Image processing, Detection and tracking algorithms, Stereoscopy, 3D metrology, In vitro testing
Fluoroscopy is widely used for intra-procedure image guidance, however its planar images provide limited information
about the location of the surgical tools or targets in three-dimensional space. An iterative method based on the
projection-Procrustes technique can determine the three-dimensional positions and orientations of known sparse objects
from a single, perspective projection. We assess the feasibility of applying this technique to track surgical tools by
measuring its accuracy and precision through in vitro experiments. Two phantoms were fabricated to perform this
assessment: a grid plate phantom with numerous point-targets at regular distances from each other; and a sparse object
used as a surgical tool phantom. Two-dimensional projections of the phantoms were acquired using an image
intensifier-based C-arm x-ray unit. The locations of the markers projected onto the images were identified and measured
using an automated algorithm. The three-dimensional location of the phantom tool tip was identified from these images
using the projection-Procrustes technique. The accuracy and precision of the tip localization were used to assess our
technique. The average three-dimensional root-mean-square target registration error of the phantom tool tip was 1.8
mm. The average three-dimensional root-mean-square precision of localizing the tool tip was 0.5 mm.
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