Reconstruction Of Intravascular Ultrasound Images Research Articles

Automatic segmentation and 3D reconstruction of intravascular ultrasound images for a fast preliminar evaluation of vessel pathologies

Intravascular ultrasound (IVUS) imaging is used along with X-ray coronary angiography to detect vessel pathologies. Manual analysis of IVUS images is slow and time-consuming and it is not feasible for clinical purposes. A semi-automated method is proposed to generate 3D reconstructions from IVUS video sequences, so that a fast diagnose can be easily done, quantifying plaque length and severity as well as plaque volume of the vessels under study. The methodology described in this work has four steps: a pre-processing of IVUS images, a segmentation of media–adventitia contour, a detection of intima and plaque and a 3D reconstruction of the vessel. Preprocessing is intended to remove noise from the images without blurring the edges. Segmentation of media–adventitia contour is achieved using active contours (snakes). In particular, we use the gradient vector flow (GVF) as external force for the snakes. The detection of lumen border is obtained taking into account gray-level information of the inner part of the previously detected contours. A knowledge-based approach is used to determine which level of gray corresponds statistically to the different regions of interest: intima, plaque and lumen. The catheter region is automatically discarded. An estimate of plaque type is also given. Finally, 3D reconstruction of all detected regions is made. The suitability of this methodology has been verified for the analysis and visualization of plaque length, stenosis severity, automatic detection of the most problematic regions, calculus of plaque volumes and a preliminary estimation of plaque type obtaining for automatic measures of lumen and vessel area an average error smaller than 1 mm 2 (equivalent aproximately to 10% of the average measure), for calculus of plaque and lumen volume errors smaller than 0.5 mm 3 (equivalent approximately to 20% of the average measure) and for plaque type estimates a mismatch of less than 8% in the analysed frames.

Impact of Catheter Shaft Angulation on the Accuracy of Atherosclerotic Plaque Volume Measurement by Three-Dimensional Intravascular Ultrasound

Computerized three-dimensional reconstruction of intravascular ultrasound (IVUS) images is a relatively new imaging modality for the study of atheromatous coronary disease with particular use in serial study of atheroma regression. Distortion of the acquired IVUS images has an important influence on the quality and accuracy of volume measurements made from the 3-D reconstruction. We evaluated the impact of commonly encountered sources of image distortion, catheter shaft angulation and luminal transducer position, on the accuracy of plaque and vessel volume measurements. A segment of diseased post-mortem human coronary artery was studied in a specially designed water bath, which enabled IVUS examination. A number of angulations of the arterial segment and the IVUS catheter were made to reproduce the areas of tortuousity encountered in the in vivo setting. Nine conformations were made. Following acquisition of IVUS images the segment was fixed in formalin and sectioned. Vessel, lumen and plaque volumes were determined by histomorphometry. These were compared to volume measurements made from 3-D reconstruction of the IVUS images in each conformation. Minimal catheter angulation produced acceptable variability for vessel (–7.9%), lumen (–6.0%) and plaque volume (-8.5%). Proximal angulations significantly over-estimated vessel, lumen and plaque volumes. Variability was greatest when multiple, severe angulations were applied (–17.7 to –21.3%). Eccentric catheter tip positioning produced greater variability in vessel (mean 16.8 ± 2.6 v. 14.2 ± 3.1%, p < 0.01) and plaque volume (18.1 ± 2.8 v. 15.3 ± 3.5%, p < 0.01). Technical factors, such as catheter shaft angulation and transducer tip position, significantly influence the degree of image distortion and subsequent volume measurement by computerized three-dimensional reconstruction of IVUS images. Recognition of these factors is important particularly in longitudinal studies of atheroma regression.

Geometrically correct 3-D reconstruction of intravascular ultrasound images by fusion with biplane angiography--methods and validation.

In the rapidly evolving field of intravascular ultrasound (IVUS), the assessment of vessel morphology still lacks a geometrically correct three-dimensional (3-D) reconstruction. The IVUS frames are usually stacked up to form a straight vessel, neglecting curvature and the axial twisting of the catheter during the pullback. Our method combines the information about vessel cross-sections obtained from IVUS with the information about the vessel geometry derived from biplane angiography. First, the catheter path is reconstructed from its biplane projections, resulting in a spatial model. The locations of the IVUS frames are determined and their orientations relative to each other are calculated using a discrete approximation of the Frenet-Serret formulas known from differential geometry. The absolute orientation of the frame set is established, utilizing the imaging catheter itself as an artificial landmark. The IVUS images are segmented, using our previously developed algorithm. The fusion approach has been extensively validated in computer simulations, phantoms, and cadaveric pig hearts.

The effect of vascular curvature on three-dimensional reconstruction of intravascular ultrasound images.

To characterize the effect of vessel curvature on the geometric accuracy of conventional three-dimensional reconstruction (3DR) algorithms for intravascular ultrasound image data. A common method of 3DR for intravascular ultrasound image data involves geometric reassembly and volumetric interpolation of a spatially related sequence of tomographic cross sections generated by an ultrasound catheter withdrawn at a constant rate through a vascular segment of interest. The resulting 3DR is displayed as a straight segment, with inherent vascular curvature neglected. Most vascular structures, however, are not straight but curved to some degree. For this reason, vascular curvature may influence the accuracy of computer-generated 3DR. We collected image data using three different intravascular ultrasound catheters (2.9 Fr, 4.3 Fr, 8.0 Fr) during a constant-rate pullback of 1 mm/sec through tubing of known diameter with imposed radii of curvature ranging from 2 to 10 cm. Image data were also collected from straight tubing. Image data were digitized at 1.0-mm intervals through a length of 25 mm. Two passes through each radius of curvature were performed with each intravascular ultrasound catheter. 3DR lumen volume for each radius of curvature was compared to that theoretically expected from a straight cylindrical segment. Differences between 3DR lumen volume of theoretical versus curved (actual) tubes were quantified as absolute percentage error and categorized as a function of curvature. Tubing deformation error was quantified by quantitative coronary angiography (QCA). Volumetric errors ranged from 1% to 35%, with an inverse relationship demonstrated between 3DR lumen volume and segmental radius of curvature. Higher curvatures (r < 6.0 cm) induced greater lumen volume error when compared to lower curvatures (r > 6.0 cm). This trend was exhibited for all three catheters and was shown to be independent of tubing deformation artifacts. QCA-determined percentage diameter stenosis indicated no deformation error as a function of curvature. Total volumetric error contributed by tubing deformation was estimated to be 0.05%. Catheter-dependent geometrical error arises in three-dimensionally reconstructed timed linear pullbacks of intravascular ultrasound images due in part to uniplanar vascular curvature. Three-dimensional reconstruction of timed linear pullbacks is robust for vessels with low radii of curvature; however, careful interpretation of three-dimensional reconstructions from timed linear pullbacks for higher radii of curvature is warranted. These data suggest that methods of spatially correct three-dimensional reconstruction of intravascular ultrasound images should be considered when more pronounced vascular curvature is present.

In vitro validation of three-dimensional intravascular ultrasound for the evaluation of arterial injury after balloon angioplasty

Objectives. The hypothesis of this study was that threedimensional ultrasound imaging would facilitate the evaluation of arterial dissection after balloon angioplasty.Background. The presence and extent of arterial dissection occurring at the time of balloon angioplasty may be important predictors of abrupt vessel closure or late restenosis.Methods. Forty-one human arterial segments obtained after death were imaged in an in vitro system at physiologic pressure (80 to 100 mm Kg) before and after balloon angioplasty. Images were acquired with a 20- to 30-MHz mechanical intravascular ultrasound imaging system (Cardiovascular Imaging Systems) with a constant pullback technique (1 mm/s). Standard 0.5-in. (1.27-cm) video tapes were used for data storage and later playback for analog to digital conversion. Digitized data were reconstructed to three-dimensional images with use of voxel space modeling. The vessels were opened longitudinally and subjected to pathologic examination, photographed and classified histologically as normal, fibrous or calcified. Dissection was defined as a disruption and separation of components of the arterial wall. The length and depth of arterial dissection were evaluated grossly and microscopically.Results. Of the 41 arteries studied, 36 (88%) exhibited dissection on pathologic examination after balloon angioplasty. Three-dimensional reconstruction of intravascular ultrasound images identified dissection in 11 (92%) of 12 normal, 8 (100%) of 8 fibrous and 11 (69%) of 16 calcified arteries. Excellent agreement between ultrasound and pathologic findings was achieved in the evaluation of length and depth of dissection for histologically normal and fibrous arteries (kappa = 0.72 to 1.0). When the vessels were severely calcified, the agreement was not as good (kappa = 0.27 to 0.56), particularly in detection of small, nonraised intimai flaps.Conclusions. This histopathologic validation study suggests that three-dimensional intravascular ultrasound imaging facilitates the evaluation of both quantitative and morphologic features of arterial dissection induced by balloon angioplasty. The advantage of three-dimensional intravascular ultrasound is its ability to assess the length and morphology of arterial injury over an entire vessel segment.

Real-time three-dimensional reconstruction of intravascular ultrasound images of iliac arteries

Intravascular ultrasound (IU) imaging provides detailed tomographic images of the vascular wall and lumen. 1–3 One liability of this novel imaging modality, however, is the inability to view a given vascular segment in a composite format; detailed cross-sectional images are thus provided at the expense of a longitudinal perspective. The circumferential nature of a postangioplasty dissection may be well demonstrated by IU, for example, but the full longitudinal extent may not be readily apparent, even after repeated review of the videotaped images recorded over the length of the involved segment. Computer-based 3-dimensional (3-D) reconstruction (R) from serially recorded IU images offers a potential solution to this problem. By creating a longitudinal display of the entire vascular segment, 3-DR offers a composite format for presentation of detailed IU data, facilitating comparison of selected cross-sectional ullages with those that are proximal and distal. Previous studies from our laboratory have outlined the concepts, technique and instrumentation used for 3-DR, and demonstrated the feasibility and potential use of 3-DR. 4–6 Whereas off-line analysis of such 3-DRs has provided insight into mechanisms of recanalization, to be clinically useful during interventional procedures, 3-D image generation must be rapid, if not instantaneous. We report here the use of real-time 3-DR from IU images recorded during percutaneous iliac artery revascularization in 2 patients.

3D-surface reconstruction of intravascular ultrasound images using personal computer hardware and a motorized catheter control.

A system for three-dimensional (3D) presentation of intravascular ultrasound (US) images was designed. A standard hardware configuration based on personal computer equipment was used for acquisition and processing of image data. Pullback imaging with the US catheter was controlled by a specially designed motor assembly and performed either in equidistant 1-10 mm steps or at a constant retraction speed. Curvature of the vessel was documented on biplane digital subtraction angiograms and the US images were arranged according to the vessel shape in the angiograms. 3D reconstruction appears essential for spatial orientation of intravascular US and may be helpful in the planning of vascular interventions for a better appreciation of the extent and morphology of vascular lesions.