Eric Maurincomme

Artifacts in intravascular ultrasound imaging during coronary artery stent implantation

Intravascular ultrasound imaging is able to provide direct images of the stent meshwork. However, a paradoxical question remains unanswered: Why is it not possible to correct or prevent implantation defects by ultrasound-guided implantation? We postulate that these discrepancies are due to image artifacts. We performed an in vitro experiment allowing detection, physical characterization, and computerized simulations of the various aspects of these artifacts. The width of the echo of a strut is variable, dependent on its distance from the transducer. The stent strut echo orientation is variable, and depends on the position of the transducer inside the stent. The stent contour image depends on the position of the transducer. In conclusion, knowledge of these stent intravascular ultrasound image artifacts enabled us to discriminate accurately between artifacts and real stent implantation defects, and are indispensable for accurate qualitative and quantitative analyses of stents.

Three-Layer Appearance of the Arterial Wall in Intravascular Ultrasound Imaging:

A three‐layer appearance of the arterial wall in intravascular ultrasound imaging has been described, but its correspondence with a characteristic histologic structure is still controversial. Some studies emphasize the imprecision of vessel‐wall measurements carried out on the intravascular ultrasound image, while other studies cast doubt upon the reality of the three‐layer appearance and its correspondence with a characteristic histologic structure. The consequences of this disputed point are important with respect to the interpretation of such images. We performed an in vitro study using phantoms and heighty postnecroptic arteries to determine the relations existing between histology, acoustic properties of arterial wall tissue, and intravascular ultrasound image formation. Measurements carried out on phantoms showed a significant overestimation of wall thickness, equal to axial resolution and due to the radial impulse response of the imaging system. Measurements performed on normal arterial walls of muscular arteries with a three‐layer appearance or normal arterial walls of elastic arteries with a single‐layer appearance showed very clearly that there was no correlation with histologic measurements of the thickness of intima and media taken individually. However, measurements (n = 53), which include the intima plus the media, exhibit excellent correlation with histologic measurements: r = 0.95 ± 0.03, y = 1.02 + 11.2. The shiny internal ring of the muscular artery wall on the image corresponded always to the internal elastic lamina (IEL). Thus, the three‐layer appearance is not an artifact. However, specific alterations, which this appearance may undergo during image formation such as beam incidence angle, lateral and radial impulse responses, and the effects of proximity of the transducer to the arterial wall, modified the shape and sizes characterizing the IEL on intravascular ultrasound images. The description and understanding of such image alterations are necessary for both interpreting them and determining which are the only reliable measurements that can be performed.

3D display of high resolution vertebral structure images.

A methodology for three-dimensional (3D) representation of vertebral trabecular structures was proposed. A set of X-ray CT images was obtained using a specific high resolution acquisition system. The images were then segmented in order to separate trabecular and cortical bone structures. Finally, the complex 3D surfaces were visualized using a volume rendering technique.

Methodology for three-dimensional reconstruction of intravascular ultrasound images

Intravascular ultrasound imaging is a new method for obtaining high resolution images of sections of the arterial wall. It is particularly interesting for detecting features of vascular pathology that are inaccessible by other conventional techniques. We propose a methodology for acquiring image sequences, that allows us to reconstruct a three-dimensional image of the vessels. The various positions of the catheter within the artery lead to geometric distortions of the ultrasound image. First, we have observed, analyzed, and interpreted the most specific reasons for intravascular image artefacts, using calibrated phantoms. Second, sequences of in- vitro pathological segments are acquired. Some pre-filtering methods are tested, in order to ease the segmentation step. Finally, the corresponding 3-D image is reconstructed and visualized, using various volume rendering techniques.

What are the advantages and limitations of three-dimensional intracoronary ultrasound imaging?

Intracoronary ultrasound imaging is able to provide real-time high resolution images of sections of the arterial wall. It is particularly interesting for analyzing, both qualitatively and quantitatively, features of vascular pathology that are inaccessible to other modalities. However, this analysis is still based on two-dimensional images, whereas the structure and the extent of atherosclerotic lesions are three-dimensional.