Three-dimensional intravascular ultrasonography: reconstruction of endovascular stents in vitro and in vivo.

Abstract

Intravascular ultrasonography displays an artery in loosely related cross-sectional images with limited axial information. However, intravascular ultrasound images are suited to three-dimensional reconstruction. A comprehensive intravascular ultrasound imaging system was used to reconstruct planar images in three-dimensions. This system consisted of a 25MHz transducer-tipped rigid probe (for in vitro studies) or a 25MHz transducer-tipped catheter within a 3.9F monorail imaging sheath (for in vivo studies), a motorized catheter pullback device that withdraws the transducer at 0.5mm/s, and an image processing computer that stacks 15 cross-sectional images/mm of stent axial length and then performs thresholding-based three-dimensional image rendering. We imaged 10 stents (4 Palmaz-Schatz, 3 Wiktor, 2 Strecker, and 1 Medinvent) in vitro after implantation in freshly harvested saphenous veins and 37 Palmaz-Schatz stents in vivo, 10 in native coronary arteries and 27 in vein grafts, 21 acutely and 18 on follow-up. Three-dimensional reconstruction of images obtained with this system reproduced the geometry of each stent design. In vitro, images of the Palmaz-Schatz stents showed the expanded diamonds, the central articulation, and flaring of both ends of both halves of the stents. Images of the Wiktor stents showed the sinusoidal wave-shaped coils in their helical configuration. Images of the Strecker stents showed the interlocking-loop design with gaps between the terminal loops at either end of the stent. Images of the Medivent stent reproduced the woven texture formed by braiding the stent wires. Three-dimensional reconstruction of images obtained in vivo also reproduced the spatial geometry of the Palmaz-Schatz stent. However, reconstruction of in vivo images was limited by cardiac-cycle-linked vessel motion and torsion and the presence of echo-dense tissue that could not be separated completely from the stent itself. Properly acquired intravascular ultrasound images can be used to reconstruct the spatial geometry of endovascular stents. Because stent spatial geometry is known and unambiguous, reconstruction of endovascular stents should be one of the tests of imaging systems designed to perform three-dimensional reconstruction of ultrasound images.