Computed Tomography/Fluoroscopy Fusion and 3D Transesophageal Echocardiography-Guided Percutaneous Paravalvular Leak Closure.

Percutaneous paravalvular leak closure seems a safe alternative to surgery in frail patients. However, it is a challenging procedure that should be tailored to each patient with optimal imaging guidance. Transesophageal echocardiography during the procedure and computed tomography scan/fluoroscopy fusion provide guidance for critical steps, such as PVL localization and crossing. (Level of Difficulty: Advanced.).

Scale-space for empty catheter segmentation in PCI fluoroscopic images.

PURPOSE: In this article, we present a method for empty guiding catheter segmentation in fluoroscopic X-ray images. The guiding catheter, being a commonly visible landmark, its segmentation is an important and a difficult brick for Percutaneous Coronary Intervention (PCI) procedure modeling. METHODS: In number of clinical situations, the catheter is empty and appears as a low contrasted structure with two parallel and partially disconnected edges. To segment it, we work on the level-set scale-space of image, the min tree, to extract curve blobs. We then propose a novel structural scale-space, a hierarchy built on these curve blobs. The deep connected component, i.e. the cluster of curve blobs on this hierarchy, that maximizes the likelihood to be an empty catheter is retained as final segmentation. RESULTS: We evaluate the performance of the algorithm on a database of 1250 fluoroscopic images from 6 patients. As a result, we obtain very good qualitative and quantitative segmentation performance, with mean precision and recall of 80.48 and 63.04% respectively. CONCLUSIONS: We develop a novel structural scale-space to segment a structured object, the empty catheter, in challenging situations where the information content is very sparse in the images. Fully-automatic empty catheter segmentation in X-ray fluoroscopic images is an important and preliminary step in PCI procedure modeling, as it aids in tagging the arrival and removal location of other interventional tools.

A tree-topology preserving pairing for 3D/2D registration.

PURPOSE: Fusing preoperative and intra-operative information into a single space aims at taking advantage of two complementary modalities and necessitates a step of registration that must provide good alignment and relevant correspondences. This paper addresses both purposes in the case of 3D/2D vessel tree matching. METHOD: We propose a registration algorithm endorsing this vascular tree nature by providing a pairing procedure that preserves the tree topology and by integrating this pairing into an iterative algorithm maintaining pairing coherence. In addition, we define two complementary error measures quantifying the resulting alignment error and pairing error, and both are based on manual ground-truth that is independent of the type of transformation to retrieve. RESULTS: Experiments were conducted on a database of 63 clinical cases, evaluating robustness and accuracy of our approach with respect to the iterative closest point algorithm. CONCLUSION: The proposed method exhibits good results in terms of both pairing and alignment as well as low sensitivity to rotations to be compensated (up to 30°).

Clinical apparatus for the reduction of dose area product for patients undergoing x-ray catheterization.

PURPOSE: The authors describe a design for prepatient region of interest attenuators (ROIAs) to reduce dose area product (DAP) for clinical use. The authors describe a model to predict DAP values from x-ray technique parameters recorded during a clinical procedure for image sequences obtained in the presence or absence of ROIAs. The model was developed primarily to determine what the DAP to a patient undergoing cardiac catheterization with a ROIA would have been if no ROIA had been used allowing a determination of DAP reduction. METHODS: Copper ROIAs with thicknesses that vary gradually so as not to cause significant image artifacts were constructed. X-ray image sequences were acquired on a clinical catheterization system with and without ROIAs with varying x-ray technique parameters. DAP values were measured for all said exposures using an ionization chamber and compared to a model the authors developed. RESULTS: The model can predict DAP values within 3.5% on average with or without ROIAs when compared to ionization chamber measurements. CONCLUSIONS: The proposed experimental design is adequate for measuring DAP reductions on the order of 1.5-3.5 that are expected when introducing a ROIA during patient catheterization imaging.

Quantitative assessment of myocardial perfusion using time-density curve analysis after elective percutaneous coronary intervention.

UNLABELLED: The aim of this study was to assess myocardial blush (MB) using a novel software algorithm that quantifies time-density curves (TDC) after percutaneous coronary intervention (PCI). METHODS: Thirty-two patients referred for elective PCI were enrolled. TDC curves were generated and mean maximal myocardial contrast density (Dmax) was calculated from 5 regions of interest in the PCI territory. Dmax was normalized to contrast injected in the proximal coronary artery (DI). RESULTS: Mean DI significantly increased after PCI in all subjects. Dmax correlated directly with subjective grading of Thrombolysis in Myocardial Infarction (TIMI) myocardial blush (R=0.47; P<.01). In 7 subjects referred for PCI of a chronic total occlusion (CTO), mean DI remained increased after PCI. Mean DI was lower in CTO versus non-CTO subjects; however, fold-improvement was higher after PCI of CTO lesions. CONCLUSION: Quantifying MB using TDC analysis is feasible and correlates with subjective MB grading. The clinical utility of MB quantitation after PCI requires further study.

Iterative closest curve: a framework for curvilinear structure registration application to 2D/3D coronary arteries registration.

Treatment coronary arteries endovascular involves catheter navigation through patient vasculature. The projective angiography guidance is limited in the case of chronic total occlusion where occluded vessel can not be seen. Integrating standard preoperative CT angiography information with live fluoroscopic images addresses this limitation but requires alignment of both modalities. This article proposes a structure-based registration method that intrinsically preserves both the geometrical and topological coherencies of the vascular centrelines to be registered, by the means of a dedicated curve-to-curve distance pairs of closest curves are identified, while pairing their points. Preliminary experiments demonstrate that the proposed approach performs better than the standard Iterative Closest Point method giving a wider attraction basin and improved accuracy.

Curvilinear structure enhancement with the polygonal path image--application to guide-wire segmentation in X-ray fluoroscopy.

Curvilinear structures are common in medical imaging, which typically require dedicated processing techniques. We present a new structure to process these, that we call the polygonal path image, denoted (see text for symbol). We derive from (see text for symbol) some curvilinear structure enhancement and analysis algorithms. We show that (see text for symbol) has some interesting properties: it generalizes several concepts found in other methods; it makes it possible to control the smoothness and length of the structures under study; and it can be computed efficiently. We estimate quantitatively its performance in the context of interventional cardiology for the detection of guide-wires in Xray images. We show that (see text for symbol) is particularly well suited for this task where it appears to outperform previous state of the art techniques.

Graph-based geometric-iconic guide-wire tracking.

In this paper we introduce a novel hybrid graph-based approach for Guide-wire tracking. The image support is captured by steerable filters and improved through tensor voting. Then, a graphical model is considered that represents guide-wire extraction/tracking through a B-spline control-point model. Points with strong geometric interest (landmarks) are automatically determined and anchored to such a representation. Tracking is then performed through discrete MRFs that optimize the spatio-temporal positions of the control points while establishing landmark temporal correspondences. Promising results demonstrate the potentials of our method.

A comprehensive study of stent visualization enhancement in X-ray images by image processing means.

In this work we propose a comprehensive study of Digital Stent Enhancement (DSE), from the analysis of the requirements to the validation of the proposed solution. First, we derive the stent visualization requirements in the context of the clinical application and workflow. Then, we propose a DSE algorithm combining automatic detection, tracking, registration and contrast enhancement. The most original parts of our solution: landmark segmentation and non-linear image registration are detailed. Finally, we validate the algorithm on a large number of synthetic and clinical cases. Performance is characterized in terms of automation, image quality and execution time. This work is, to the best of our knowledge, the first comprehensive article on DSE, covering problem statement, proposed solution, and validation strategies.

Cardiac Image Registration: Rotational Error Correction and Gated Stabilization for Cardiac Motion.

Background: Dynamic motion of the heart due to cardiac and respiratory cycles, and rotation from varying patient positions between imaging modalities, can cause errors during cardiac image registration. This study used phantom, patient and animal models to assess and correct these errors. Methods and Results: Rotational errors were identified and corrected using different phantom orientations. ECG-gated fluoro images were aligned with similarly gated CT images in 9 patients, and accuracy assessed during atrial fibrillation (AF) and sinus rhythm. A tracking algorithm corrected errors due to respiration; 4 independent observers compared 25 respiration sequences to an automated method. Following correction of these errors, target registration error was assessed. At 20 mm and 30 mm from the phantom model's center point with an in-plane rotation of 8 degrees, measured error was 2.94 mm and 5.60 mm, respectively, and the main error identified. A priori method accurately predicted ECG location in only 38% (p=0.0003) of 313 R-R intervals in AF. A posteriori method accurately gated the ECG during AF and sinus rhythm in 97% and 98% of 375 beats evaluated, respectively (p=NS). Tracking algorithm for ECG-gated motion compensation was identified as good or fair 96% of the time, with no difference between observers and automated method (chi-square=25; p=NS). Target registration error in phantom and animal models was 1.75±1.03 mm and 0 to 0.5 mm, respectively. Conclusions: Errors during cardiac image registration can be identified and corrected. Cardiac image stabilization can be achieved using ECG gating and respiration.

Guide-wire extraction through perceptual organization of local segments in fluoroscopic images.

Segmentation of surgical devices in fluoroscopic images and in particular of guide-wires is a valuable element during surgery. In cardiac angioplasty, the problem is particularly challenging due to the following reasons: (i) low signal to noise ratio, (ii) the use of 2D images that accumulate information from the whole volume, and (iii) the similarity between the structure of interest and adjacent anatomical structures. In this paper we propose a novel approach to address these challenges, that combines efficiently low-level detection using machine learning techniques, local unsupervised clustering detections and finally high-level perceptual organization of these segments towards its complete reconstruction. The latter handles miss-detections and is based on a local search algorithm. Very promising results were obtained.

Accuracy and usefulness of fusion imaging between three-dimensional coronary sinus and coronary veins computed tomographic images with projection images obtained using fluoroscopy.

AIMS: Coronary sinus (CS) and coronary veins are not delineated by fluoroscopy. The study evaluates the feasibility and accuracy of cardiac tomography (CT) image registration of CS anatomy on fluoroscopic image. METHODS AND RESULTS: Eighteen consecutive patients underwent contrast-enhanced, ECG-gated CT scanning. Coronary sinus, coronary veins, superior vena cava, the distal portion of the trachea, and of the two main bronchi were reconstructed. These images were then fused over the CS fluoroscopic angiogram. Registration accuracy was verified by assessing the overlap of CS borders both in the CT- and in the fluoroscopy-derived images. The mean distance between the centrelines of the CS was 0.73 mm, with a maximum distance of 2.22 mm. For the first-order branches, mean distance was 0.80 mm with a maximum distance of 2.64 mm. High Lin concordance correlation coefficients were computed (>0.95) for the CS and first-order branch diameters, although the Bland and Altman limits were large. The agreement between the number of vessels identified was moderate with kappa = 0.43. CONCLUSION: Fusion imaging processing of two different imaging modalities (CT and fluoroscopy) may be feasible and accurate for guiding CRT implantation as it allows constant comprehensive display of CS body and branches. Prospective studies are needed for assessing clinical implications.

Quantitative automated assessment of myocardial perfusion at cardiac catheterization.

Perfusion assessed in the cardiac catheterization laboratory predicts outcomes after myocardial infarction. The aim of this study was to investigate a novel method of assessing perfusion using digital subtraction angiography to generate a time-density curve (TDC) of myocardial blush, incorporating epicardial and myocardial perfusion. Seven pigs underwent temporary occlusion of the left anterior descending coronary artery for 60 minutes. Angiography was performed in the same projections before, during, and after occlusion. Perfusion parameters were obtained from the TDC and compared with Thrombolysis In Myocardial Infarction (TIMI) frame count and myocardial perfusion grade. In addition, safety and feasibility were tested in 8 patients after primary percutaneous coronary intervention. The contrast density differential between the proximal artery and the myocardium derived from the TDC correlated well with TIMI myocardial perfusion grade (R = 0.54, p <0.001). The arterial transit time derived from the TDC correlated with TIMI frame count (R = 0.435, p = 0.011). Using a cutoff of 2.4, the density/time ratio, a ratio of density differential to transit time, had sensitivity and specificity of 100% for coronary arterial occlusion. The positive and negative predictive values were 100%. The generation of a TDC was safe and feasible in 7 patients after acute myocardial infarctions, but the correlation between TDC-derived parameters and TIMI parameters did not reach statistical significance. In conclusion, this novel method of digital subtraction angiography with rapid, automated, quantitative assessment of myocardial perfusion in the cardiac catheterization laboratory correlates well with established angiographic measures of perfusion. Further studies to assess the prognostic value of this technique are warranted.

Motion correction for coronary stent reconstruction from rotational X-ray projection sequences.

This paper presents a new method for 3-D tomographic reconstruction of stent in X-ray cardiac rotational angiography. The method relies on 2-D motion correction from two radiopaque markerballs located on each side of the stent. The two markerballs are on a guidewire and linked to the balloon, which is introduced into the artery. Once the balloon has been inflated, deflated, and the stent deployed, a rotational sequence around the patient is acquired. Under the assumption that the guidewire and the stent have the same 3-D motion during rotational acquisition, we developed an algorithm to correct cardiac stent motion on the 2-D X-ray projection images. The 3-D image of the deployed stent is then reconstructed with the Feldkamp algorithm using all the available projections. Although the correction is an approximation, we show that the intrinsic geometrical error of our method has no visual impact on the reconstruction when the 2-D markerball centers are exactly detected and the markerballs have the same 3-D motion as the stent. Qualitative and quantitative results on simulated sequences under different realistic conditions demonstrate the robustness of the method. Finally, results from animal data acquired on a rotational angiography device are presented.

Assessment of a novel angiographic image stabilization system for percutaneous coronary intervention.

BACKGROUND: Optimization of coronary images for percutaneous coronary intervention (PCI) remains difficult due to cardiac motion throughout the respiratory and cardiac cycles. We tested a novel system to stabilize angiographic images at the region of interest in order to assist during PCI. METHODS: Patients undergoing PCI to the right coronary artery (RCA) (group 1, n = 22) or complex PCI (group 2, n = 16) were prospectively enrolled and the angiographic image sequences of patients who died suddenly of confirmed or presumed stent thrombosis following PCI (group 3, n = 16) were retrospectively reviewed. All image sequences were analyzed off-line by three cardiologists before and after image stabilization for accuracy of stent placement, presence of residual edge dissection, and adequacy of procedural outcome. RESULTS: Image stabilization was successful in 100% of cases in a mean time of 95 +/- 71 seconds and was considered to be helpful in 13.6% of group 1, in 18.3% of group 2, and in 10% of group 3 cases. There was good correlation between observers with a kappa statistic of 0.85 to 1.0 for all observations. However, there was no difference in the reviewers' opinions of stent placement, presence of edge dissection, or adequacy of procedural result when comparing the standard angiographic views and the stabilized images. In particular, no previously unrecognized edge dissections were apparent in group 3 with stabilized display. CONCLUSION: Image stabilization centered on the region of interest was considered helpful in a small subset of patients, particularly the complex PCI patients. However, no differences in objective parameters could be demonstrated.

Reconstruction of coronary arteries from a single rotational X-ray projection sequence.

Cardiovascular diseases remain the primary cause of death in developed countries. In most cases, exploration of possibly underlying coronary artery pathologies is performed using X-ray coronary angiography. Current clinical routine in coronary angiography is directly conducted in two-dimensional projection images from several static viewing angles. However, for diagnosis and treatment purposes, coronary artery reconstruction is highly suitable. The purpose of this study is to provide physicians with a three-dimensional (3-D) model of coronary arteries, e.g., for absolute 3-D measures for lesion assessment, instead of direct projective measures deduced from the images, which are highly dependent on the viewing angle. In this paper, we propose a novel method to reconstruct coronary arteries from one single rotational X-ray projection sequence. As a side result, we also obtain an estimation of the coronary artery motion. Our method consists of three main consecutive steps: 1) 3-D reconstruction of coronary artery centerlines, including respiratory motion compensation; 2) coronary artery four-dimensional motion computation; 3) 3-D tomographic reconstruction of coronary arteries, involving compensation for respiratory and cardiac motions. We present some experiments on clinical datasets, and the feasibility of a true 3-D Quantitative Coronary Analysis is demonstrated.

Registration of three-dimensional left atrial computed tomographic images with projection images obtained using fluoroscopy.

BACKGROUND: Anatomic structures such as the left atrium and the pulmonary veins (PVs) are not delineated by fluoroscopy because there is no contrast differentiation between them and the surrounding anatomy. Representation of an anatomic structure via a 3D model obtained from computed tomography (CT) imaging and subsequent projection of these images over the fluoroscopy system may help in navigation of the mapping and ablation catheter to the appropriate sites during electrophysiology procedures. METHODS AND RESULTS: In this feasibility study, in vitro experiments were performed with a plastic heart model (phantom) with 2 catheters or radiopaque platinum beads placed in the phantom at the time of CT imaging and fluoroscopy. Subsequently, 20 consecutive patients underwent contrast-enhanced, ECG-gated CT scanning. Left atrial volumes were generated from the reconstructed data at &75% of the R-R interval during the cardiac cycle. Similarly, the superior vena cava and the coronary sinus were also reconstructed from these images. During the electrophysiology procedure, digital records (cine sequences) were obtained. Using predetermined algorithms, both the phantom model and the patients' 3D left atrial models derived from the CT were registered with projection images of fluoroscopy. Registration was performed with a transformation that linked the superior vena cava and the coronary sinus from the CT model with a catheter placed inside the coronary sinus via the superior vena cava. Registration was successfully accomplished with the plastic phantom and in all 20 patients. Registration accuracy was assessed in the phantom by assessing the overlapping beads seen both in the CT and the fluoroscopy images. The mean registration error was 1.4 mm (range 0.9 to 2.3 mm). Accuracy of the registered images was assessed in patients with recordings from a basket catheter placed sequentially in the superior PVs and by injecting contrast into the PVs to assess overlapping of contrast-filled PVs with the corresponding vessels on the registered images. The images could be calibrated quite accurately. Any rotational error, which was usually minor, could be corrected by rotating the images as needed. CONCLUSIONS: Registration of 3D models of the left atrium and PVs with fluoroscopic images of the same is feasible and could enable appropriate navigation and localization of the mapping and ablation catheter during procedures such as atrial fibrillation ablation.

3D tomographic reconstruction of coronary arteries using a precomputed 4D motion field.

In this paper, we present a new method to perform 3D tomographic reconstruction of coronary arteries from cone-beam rotational x-ray angiography acquisitions. We take advantage of the precomputation of the coronary artery motion, modelled as a parametric 4D motion field. Contrary to data gating or data triggering approaches, we homogeneously use all available frames, independently of the cardiac phase. In addition, we artificially subtract angiograms from their background structures. Our method significantly improves the reconstruction, by removing both motion and background artefacts. We have successfully tested it on the datasets from a synthetic phantom and 10 patients.