A 3D reconstruction of vascular structures from two X-ray angiograms using an adapted simulated annealing algorithm.

A three-dimensional (3D) reconstruction of the vessel lumen from two angiographic views, based on the reconstruction of a series of cross-sections, is proposed. Assuming uniform mixing of contrast medium and background subtraction, the cross-section of each vessel is reconstructed through a binary representation. A priori information about both the slice to be reconstructed and the relationships between adjacent slices are incorporated to lessen ambiguities on the reconstruction. Taking into account the knowledge of normal vessel geometry, an initial solution of each slice is created using an elliptic model-based method. This initial solution is then deformed to be made consistent with projection data while being constrained into a connected realistic shape. For that purpose, properties on the expected optimal solution are described through a Markov random field. To find an optimal solution, a specific optimization algorithm based on simulated annealing is used. The method performs well both on single vessels and on branching vessels possessing an additional inherent ambiguity when viewed at oblique angles. Results on 2D slice independent reconstruction and 3D reconstruction of a stack of spatially continuous 2D slices are presented for single vessels and bifurcations.

Adaptive estimation of the mean frequency of a Doppler signal from short data windows.

The color Doppler estimator (CE1), which is calculated from the phase of the first correlation lag of the Doppler signal, is compared to the general mean frequency estimator (CEn), which is based on a weighted summation of all the available correlation lags, for long and short Doppler data sets (typically 48 and 8 Doppler samples). A new estimator of the Doppler signal mean frequency is derived from the results of this study. It optimizes the compromise between the range of analyzable frequencies and the estimation variance for the characteristics of the Doppler signal. Demonstration is provided that the behavior of this estimator shifts from that of CE1 to that of CEn, according to the setting of a single parameter. An adaptive version of this estimator is implemented and applied to Doppler recordings. Applications can be contemplated for color Doppler imaging.

Segmentation, modelling and reconstruction of arterial bifurcations in digital angiography.

The paper presents a method to model an arterial bifurcation from a pair of X-ray angiographic images. It is the initial step of a reconstruction process aiming at detecting and quantifying abnormal sites located on bifurcations. The method proposed consists of two steps. First, each image is independently segmented to extract the vessels in the images. The algorithm uses dynamic programming first to find the bifurcation centrelines from the original images, and secondly to extract vessel edges from the morphological gradient images, under a constraint of parallelism with the previously detected centrelines. Then, a three-dimensional bifurcation model is built by adapting cylinders around the three-dimensional bifurcation centrelines. These cylinders are obtained as a stack of binary orientable ellipses fitted to the projection densities in the corresponding cross-sections. Results obtained on simulated data, phantom and femoral bifurcations are displayed.

An attempt to 3D reconstruct vessel morphology from X-ray projections and intravascular ultrasounds modeling and fusion.

The emergency of interventional revascularization techniques in the treatment of atheromateous vascular diseases has resulted in the need for additional valuable diagnostic information about the 3D morphology and nature of the lesion. To overcome the limitations inherent to common vascular imaging techniques, such as Digital Angiography (DA) which only gives partial information on lumen narrowing or Intravascular Ultrasound (IVUS) which provides randomly oriented transversal images, a 3D reconstruction of the vessel by fusion of X-ray and IVUS images has been developed. For that purpose, X-ray and IVUS images are acquired according to a well-defined protocol and useful information to be fused is extracted. A geometric model then leads to the determination of the unknown parameters which allow the alignment of all data in a common reference frame. The registered data are then directly introduced into a probabilistic reconstruction process using a Markovian modeling associated with a simulated annealing-based optimization algorithm. Taking into account all the information available about the vessel, the method avoids the uncertainties and ambiguities of a reconstruction based only on one modality, and the probabilistic fusion solves the possible contradictions between both acquisitions. Results of vascular lumen 3D reconstruction are shown with data acquired on an excised dog aorta. The accuracy of reconstruction of the lumen by data fusion is significantly improved compared to results obtained with separate reconstruction from angiographic or ultrasonic data. Further work will include introduction of vessel wall texture elements into the probabilistic fusion process to increase the amount of information gained by intravascular ultrasonic tissue characterization.