Various multi-center trials have shown that cardiac resynchronization therapy (CRT) is an effective procedure
for patients with end-stage drug invariable heart failure (HF). Despite the encouraging results of CRT, at least
30% of patients do not respond to the treatment. Detailed knowledge of the cardiac anatomy (coronary
venous tree, left ventricle), functional parameters (i.e. ventricular synchronicity) is supposed to improve
CRT patient selection and interventional lead placement for reduction of the number of non-responders.
As a pre-interventional imaging modality, cardiac magnetic resonance (CMR) imaging has the potential
to provide all relevant information. With functional information from CMR optimal implantation target
sites may be better identified. Pre-operative CMR could also help to determine whether useful vein target
segments are available for lead placement. Fused with X-ray, the mainstay interventional modality, improved
interventional guidance for lead-placement could further help to increase procedure outcome.
In this contribution, we present novel and practicable methods for a) pre-operative functional and anatomical
imaging of relevant cardiac structures to CRT using CMR, b) 2D-3D registration of CMR anatomy and
functional meshes with X-ray vein angiograms and c) real-time capable breathing motion compensation for
improved fluoroscopy mesh overlay during the intervention based on right ventricular pacer lead tracking.
With these methods, enhanced interventional guidance for left ventricular lead placement is provided.
KEYWORDS: 3D image processing, Detection and tracking algorithms, 3D acquisition, Fluoroscopy, Reconstruction algorithms, X-rays, X-ray imaging, 3D modeling, Visualization, 3D image reconstruction
Minimally invasive catheter ablation procedures are guided by biplane fluoroscopy images visualising the interventional
scene from two different orientations. However, these images do not provide direct access to their
inherent spatial information. A three-dimensional reconstruction and visualisation of the catheters from such
projections has the potential to support quick and precise catheter navigation. It enhances the perception of
the interventional situation and provides means of three-dimensional catheter pose documentation. In this contribution
we develop an algorithm for tracking the three-dimensional pose of electro-physiological catheters in
biplane fluoroscopy images. It is based on the B-Snake algorithm which had to be adapted to the biplane and
in particular the asynchronous image acquisition situation. A three-dimensional B-spline curve is transformed
so that its projections are consistent with the catheter path enhancing feature images, while the information
from the missing image caused by the asynchronous acquisition is interpolated from its sequence neighbours. In
order to analyse the three-dimensional precision, virtual images were created from patient data sets and threedimensional
ground truth catheter paths. The evaluation of the three-dimensional catheter pose reconstruction
by means of our algorithm on 33 of such virtual image sets indicated a mean catheter pose error of 1.26 mm and
a mean tip deviation of 3.28 mm. The tracking capability of the algorithm was evaluated on 10 patient data
sets. In 94 % of all images our algorithm followed the catheter projections.
KEYWORDS: Arteries, Angiography, X-rays, 3D image processing, 3D image reconstruction, 3D acquisition, Data acquisition, X-ray imaging, Sensors, Imaging systems
A method is proposed that allows for a fully automated computation of a series of high-resolution volumetric reconstructions
of a patient's coronary arteries based on a single rotational acquisition. During the 7.2 second acquisition
the coronary arteries are injected with contrast material while the imaging system rotates around the patient to obtain a
series of X-ray projection images over an angular range of 180 degrees. Based on the simultaneously recorded ECG-signal
the projection images corresponding to the same cardiac cycle can be utilized to reconstruct three-dimensional
(3D) high-spatial-resolution angiograms of the coronary arteries in multiple (3D+t) cardiac phases within the cardiac
cycle. The proposed acquisition protocol has been applied to 22 patients and the tomograpic reconstructions depicted
the main arteries as well as the main bifurcations in multiple cardiac phases in all enrolled patients. For the first
time, this feasibility study shows that a three-dimensional description of the coronary arteries can be obtained intraprocedurally
in a conventional interventional suite by means of tomographic reconstruction from projection images without any user interaction.
A fully automated 3D centerline modeling algorithm for coronary arteries is presented. It utilizes a subset of standard rotational X-Ray angiography projections that correspond to a single cardiac phase. The projection selection is based on a simultaneously recorded electrocardiogram (ECG). The algorithm utilizes a region growing approach, which selects voxels in 3D space that most probably belong to the vascular structure. The local growing speed is controlled by a 3D response computation algorithm. This algorithm calculates a measure for the probability of a point in 3D to belong to a vessel or not.
Centerlines of all detected vessels are extracted from the 3D representation built during the region growing and linked in a hierarchical manner. The centerlines representing the most significant vessels are selected by a geometry-based weighting criterion.
The theoretically achievable accuracy of the algorithm is evaluated on simulated projections of a virtual heart phantom. It is capable of extracting coronary centerlines with an accuracy that is mainly limited by projection and volume quantization (0.25 mm). The algorithm needs at least 3 projections for modeling, while in the phantom study, 5 projections are sufficient to achieve the best possible accuracy. It is shown that the algorithm is reasonably insensitive to residual motion, which means that it is able to cope with inconsistencies within the projection data set caused by finite gating accuracy, respiration or irregular heart beats. Its practical feasibility is demonstrated on clinical cases showing automatically generated models of left and right coronary arteries (LCA/RCA).
A novel approach is presented which combines rotational X-ray imaging, real-time fluoroscopic X-ray imaging and real-time catheter tracking for improved guidance in interventional electrophysiology procedures. Rotational X-ray data and real-time fluoroscopy data obtained from a Philips FD10 flat detector X-ray system and are registered with real-time localization data from catheter tracking equipment. The visualization and registration of rotational X-ray data with catheter location data enables the physician to better appreciate the underlying anatomy of interest in three dimensions and to navigate the interventional or mapping device more effectively. Furthermore, the fused information streams from rotational X-ray, real-time X-ray fluoroscopy and real-time three-dimensional catheter locations offer a direct imaging feedback during interventions, facilitating navigation and potentially improving clinical outcome. With the technique one is able to reduce the fluoroscopic time required in a procedure, since the catheter is registered and visualized with off-line projection data from various view angles. We show a demonstrator which integrates, registers, and visualizes the various data streams. It can be implemented in the clinical work-flow with reasonable effort. Results are presented based on an experimental setup. Furthermore, the robustness and the accuracy of this technique have been determined based on phantom studies.
In carotid plaque imaging, MRI provides exquisite soft-tissue characterization, but lacks the temporal resolution for tissue strain imaging that real-time 3D ultrasound (3DUS) can provide. On the other hand, real-time 3DUS currently lacks the spatial resolution of carotid MRI. Non-rigid alignment of ultrasound and MRI data is essential for integrating complementary morphology and biomechanical information for carotid vascular assessment. We assessed non-rigid registration for fusion of 3DUS and MRI carotid data based on deformable models which are warped to maximize voxel similarity. We performed validation in vitro using isolated carotid artery imaging. These samples were subjected to soft-tissue deformations during 3DUS and were imaged in a static configuration with standard MR carotid pulse sequences. Registration of the source ultrasound sequences to the target MR volume was performed and the mean absolute distance between fiducials within the ultrasound and MR datasets was measured to determine inter-modality alignment quality. Our results indicate that registration errors on the order of 1mm are possible in vitro despite the low-resolution of current generation 3DUS transducers. Registration performance should be further improved with the use of higher frequency 3DUS prototypes and efforts are underway to test those probes for in vivo 3DUS carotid imaging.
KEYWORDS: 3D image processing, 3D image reconstruction, Heart, 3D modeling, Angiography, 3D acquisition, Image segmentation, Arteries, Electrocardiography, 3D metrology
Three-dimensional rotational coronary angiography (3DRCA) is a new
technique for imaging coronary vessels in the human body. Due to
the residual cardiac motion, projections being in the same cardiac
motion state are extracted from the acquired series using
electrocardiogram (ECG) information. A gating window is determined
at a pre-defined trigger delay relative to the R-peaks with a
constant width. In order to achieve the best possible image
quality, cardiac phases must be found during which the heart is
nearly stationary. However, the (ECG) signal represents the
electrical activity of the heart and corresponds to the heart
movement only approximately. Currently, the optimum gating window
positioning is based on values derived by experience. It is
difficult to determine where the heart is most stable in the cycle
due to a high patient variability. Furthermore, the optimal gating
window position is depending on the coronary vessel segment. The
purpose of this work is to introduce a simple and efficient image
based technique, which is able to determine the optimal gating
window position fully automatically. The measurements in this
paper are based on the analysis of two-dimensional X-ray
projection data of the coronary arteries in an animal (pig) model.
KEYWORDS: 3D modeling, Calibration, 3D image processing, Arteries, Data acquisition, Angiography, Data modeling, Image segmentation, X-rays, Systems modeling
For the diagnosis of ischemic heart disease, accurate quantitative analysis of the coronary arteries is important. In coronary angiography, a number of projections is acquired from which 3D models of the coronaries can be reconstructed. A signifcant limitation of the current 3D modeling procedures is the required user interaction
for defining the centerlines of the vessel structures in the 2D projections. Currently, the 3D centerlines of the coronary tree structure are calculated based on the interactively determined centerlines in two projections. For every interactively selected centerline point in a first projection the corresponding point in a second projection has to be determined interactively by the user. The correspondence is obtained based on the epipolar-geometry. In this paper a method is proposed to retrieve all the information required for the modeling procedure, by the interactive determination of the 2D centerline-points in only one projection. For every determined 2D centerline-point the corresponding 3D centerline-point is calculated by the analysis of the 1D gray value functions of the corresponding epipolarlines in space for all available 2D projections. This information is then used to build a 3D representation of the coronary arteries using coronary modeling techniques. The approach is illustrated on the analysis of calibrated phantom and calibrated coronary projection data.
KEYWORDS: Heart, 3D image processing, 3D modeling, 3D image reconstruction, Calibration, Motion models, 3D acquisition, Angiography, Animal model studies, Data modeling
3D rotational coronary angiography (3DRCA) is one of the
application areas of 3D rotational X-Ray imaging. In this
application a sequence of projection images is acquired when the
C-arm is rotated around the patient. Since the heart is a moving
object, only projections can be used which correspond to the same
phase of the cardiac cycle. This significantly limits the number
of projections available for reconstruction causing streaking
artefacts in the reconstructed image due to angular undersampling.
The involvement of additional projections in the reconstruction
procedure from different viewing angles would increase the quality
of the volume data. Each successive acquired projection is
slightly different compared with the previous one due to two
reasons: First, there is a motion to the deformation of the heart,
second there is an induced deformation owing to the change in the
projection angle. The purpose of this work is to determine the
motion owing to the heart deformation, so as to compensate for
this motion in projection images in a different heart phase.
Hereto we propose to use concepts from coronary modeling in
combination of conventional reconstruction procedures. The
proposed method facilitates the use of additional projections in
the reconstruction. Motion-compensated reconstructed volume data
are presented for coronary arteries in an animal (pig) model.
We present results on 3D image quality in terms of spatial resolution (MTF) and low contrast detectability, obtained on a flat dynamic X-ray detector (FD) based cone-beam CT (CB-CT) setup. Experiments have been performed on a high precision bench-top system with rotating object table, fixed X-ray tube and 176 x 176 mm2 active detector area (Trixell Pixium 4800). Several objects, including CT performance-, MTF- and pelvis phantoms, have been scanned under various conditions, including a high dose setup in order to explore the 3D performance limits. Under these optimal conditions, the system is capable of resolving less than 1% (~10 HU) contrast in a water background. Within a pelvis phantom, even inserts of muscle and fat equivalent are clearly distinguishable. This also holds for fast acquisitions of up to 40 fps. Focusing on the spatial resolution, we obtain an almost isotropic three-dimensional resolution of up to 30 lp/cm at 10% modulation.
A new approach for 3D vessel centreline extraction using multiple, ECG-gated, calibrated X-ray angiographic projections of the coronary arteries is described. The proposed method performs direct extraction of 3D vessel centrelines, without the requirement to either first compute prior 2D centreline estimates, or perform a complete volume reconstruction. A front propagation-based algorithm, initialised with one or more 3D seed points, is used to explore a volume of interest centred on the projection geometry's isocentre. The expansion of a 3D region is controlled by forward projecting boundary points into all projection images to compute vessel response measurements, which are combined into a 3D propagation speed so that the front expands rapidly when all projection images yield high vessel responses. Vessel centrelines are obtained by reconstructing the paths of fastest propagation. Based on these axes, a volume model of the coronaries can be constructed by forward projecting axis points into the 2D images where the borders are detected. The accuracy of the method was demonstrated via a comparison of automatically extracted centrelines with 3D centrelines derived from manually segmented projection data.
During the last years, three-dimensional X-ray imaging has become a well-established imaging modality, setting the golden standard for spatial resolution in three-dimensional X-ray imaging. Firstly introduced on a motorized C-arm system, it gained benefit from the high spatial resolution of the image intensifier. Using cone-beam reconstruction, it provided fast access to truly three-dimensional imaging with isotropic voxel dimensions. However, the non-rigid mechanics and the image distortion in the image intensifier required dedicated calibration processes and obligated the developers to use the most stable and reliable system in the C-arm device family. The need for system calibration also required the system to be able to reproducibly adjust the C-arm to the pre-calibrated positions, which seemed only possible with the motorized movement of a high-end system. On mobile, non-motorized C-arm systems, which are often used for guiding surgical procedures, however, 3D application has not been feasible due to the non-reproducibility of the mechanical movement. In this paper, first results regarding the feasibility of this approach are presented. The data were acquired on a Philips BV 26 surgical C-arm. This device is fully movable. The C arc is adjusted manually.
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