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International audience; This paper reports work in progress on X-ray angiography acquired under stereotactic conditions. The objective is to be able to match multimodality images (typically MRI and X-ray) without a stereotactic frame but with stereotactic precision. We have identified potential problems and have studied them in detail. We conclude that, although the overall application is feasible, much work remains to be done on the estimation of the X-ray system conic projection and on automatic matching based on vascular structures.

To evaluate the interest of 3D angiography in the diagnosis, treatment and follow-up of aneurysms with special regard with endovascular GDC treatment. Spin angiography with 44 subtracted views (512×512 image matrix) is first acquired with a rotation of a C-arm through 200 degrees at 40° per second in an angiographic room prototype LCV+ single plane (GEMS). 3D reconstruction ART (Algebraic Reconstruction Technique) is automatically applied and interactive visualisation of the 3D angiography is available on a workstation (UltraSparc 2, Sun microsystems) 10 minutes after the spin angiography acquisition. 3D angiography is displayed in MIP, surface rendering and endovascular views (virtual angioscopy). 52 2D and 3D angiographies were performed in 40 patients with 49 intracranial aneurysms whith the same protocol of acquisition (AP, lateral and spin angiography). Each 3D angiography (MIP and surface rendering) was analysed by 2 senior radiologists and compared with the corresponding 2D angiographies (AP, lateral and spin views). Artefacts due to GDC were present in 24 cases, but bothering in only 12 cases. Analysis of the aneurysm was better in MIP than in 2D in 32 cases, equivalent in 18 and worse in 2 due to patient movements during acquisition. Surface rendering gave additional information in 29 cases. The impact was judged important for decision making or choice of treatment in 25 cases. 3D angiography improves the analysis of the aneurysms, gives crucial information to make the decision for treatment and is now routinely used in our institution for the diagnosis of intracranial aneurysms and follow-up after GDC treatment.

A new method for stenosis quantification from 3D X-ray angiography images has been evaluated on both phantom and clinical data. On phantoms, for the parts larger or equal to 3 mm, the standard deviation of the measurement error has always found to be less or equal to 0.4 mm, and the maximum measurement error less than 0.17 mm. No clear relationship has been observed between the performances of the quantification method and the acquisition FoV. On clinical data, the 3D quantification method proved to be more robust to vessel bifurcations than its 3D equivalent. On a total of 15 clinical cases, the differences between 2D and 3D quantification were always less than 0.7 mm. The conclusion is that stenosis quantification from 3D X-4ay angiography images is an attractive alternative to quantification from 2D X-ray images.

Article dans revue scientifique avec comité de lecture.; PURPOSE: To evaluate three-dimensional (3D) digital subtraction angiography (DSA) as a supplement to two-dimensional (2D) DSA in the endovascular treatment (EVT) of intracranial aneurysms. MATERIALS AND METHODS: In 22 ruptured aneurysms, neck visualization, aneurysm shape, and EVT feasibility were analyzed at 2D DSA (anteroposterior, lateral, rotational views) and at maximum intensity projection (MIP) and surface shaded display (SSD) 3D DSA. The possibility of obtaining a working view for EVT at 3D DSA and the relevance of measurements in choosing the first coil also were assessed. RESULTS: Two-dimensional DSA images clearly depicted the aneurysm neck in four of 22 aneurysms; MIP images, in 10; and SSD images, in 21, but SSD led to overestimation of the neck size in one aneurysm. Aneurysm shape was precisely demonstrated in five of 22 aneurysms, EVT seemed to be nonfeasible at 2D DSA; however, SSD demonstrated feasibility and EVT was successfully performed. In one aneurysm, only SSD demonstrated the extension of the neck to a parent vessel, which was proved at surgery. Working views for EVT were deduced from 3D DSA findings in 20 of 21 aneurysms. The choice of the first coil was correct in 19 of 21 aneurysms. CONCLUSION: Three-dimensional DSA is valuable for evaluating the potential for EVT, finding a working view, and performing accurate measurements.

Colloque avec actes et comité de lecture.; Today, 3-D angiography volumes are routinely generated from rotational angiography sequences. In previous work \cite{Kerrien98}, we have studied the precision reached by registering such volumes with classical 2-D angiography images, inferring this matching only from the sensors of the angiography machine. The error led by such a registration can be described as a 3-D rigid motion composed of a large translation and a small rotation. This paper describes the strategy we followed to correct this error. The angiography image is compared in a two-step process to the Maximum Intensity Projection (MIP) of the angiography volume. The first step provides most of the translation by maximizing the cross-correlation. The second step recovers the residual rigid-body motion, thanks to a modified optical flow technique. A fine analysis of the equations encountered in both steps allows for a speed-up of the calculations. This algorithm was validated on 17 images of a phantom, and 5 patients. The residual error was determined by manually indicating points of interest and was found to be around 1 mm.

During an interventional neuroradiology exam, knowing the exact location of the catheter tip with respect to the patient can dramatically help the physician. An image registration between digital subtracted angiography (DSA) images and a volumic pre-operative image (magnetic resonance or computed tomography volumes) is a way to infer this important information. This mono-patient multimodality matching can be reduced to finding the projection matrix that transforms any voxel of the volume onto the DSA image plane. This modelization is unfortunately not valid in the case of distorted images, which is the case for DSA images. A classical angiography room can now generate 3D X-ray angiography volumes (3DXA). Since the DSA images are obtained with the same machine, it should be possible to deduce the projection matrix from the sensor data indicating the current machine position. We propose an interpolation scheme, associated to a pre-operative calibration of the machine that allows us to correct the distortions in the image at any position used during the exam with a precision of one pixel. Thereafter, we describe some calibration procedures and an associated model of the machine that can provide us with a projection matrix at any position of the machine. Thus, we obtain a machine-based 2D DSA/3DXA registration. The misregistration error can be limited to 2.5 mm if the patient is well centered within the system. This error is confirmed by a validation on a phantom of the vascular tree. This validation also yields that the residual error is a translation in the 3D space. As a consequence, the registration method presented in this paper can be used as an initial guess to an iterative refining algorithm.