Intravascular ultrasound imaging of coronary arteries provides important information about coronary lumen, wall, and plaque characteristics. Quantitative studies of coronary atherosclerosis using intravascular ultrasound and manual identification of wall and plaque borders are limited by the need for observers with substantial experience and the tedious nature of manual border detection. We have developed a method for segmentation of intravascular ultrasound images that identifies the internal and external elastic laminae and the plaque-lumen interface. The border detection algorithm was evaluated in a set of 38 intravascular ultrasound images acquired from fresh cadaveric hearts using a 30 MHz imaging catheter. To assess the performance of our border detection method we compared five quantitative measures of arterial anatomy derived from computer-detected borders with measures derived from borders manually defined by expert observers. Computer-detected and observer-defined lumen areas correlated very well (r=0.96, y=1.02x+0.52), as did plaque areas (r=0.95, y=1.07x-0.48), and percent area stenosis (r=0.93, y=0.99x-1.34.) Computer-derived segmental plaque thickness measurements were highly accurate. Our knowledge-based intravascular ultrasound segmentation method shows substantial promise for the quantitative analysis of in vivo intravascular ultrasound image data.

Abstract-In the rapidly evolving field of intravascular ultrasound (IVUS), the assessment of vessel morphology still lacks a geometrically correct 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.

Magnesium attenuates AFR increase after an occlusion-reperfusion sequence. To our knowledge this is the first in vivo real-time demonstration of Mg's impact on free radicals.

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This article examines the effect of twist on flow through reversed vein segments in vitro and its effect on graft patency in vivo. Excised canine superficial femoral veins were perfused in vitro with normal saline solution or canine blood. Perfusion was carried out at five pressures and against three outflow resistances. Increasing increments of twist were applied to the outflow end of the vein. Flow was measured at each level of twist. With both saline solution and blood, flow was unaltered until twist reached 140 to 180 degrees. Flow then decreased sharply, stopping completely at 175 to 200 degrees of twist. In vivo experiments were then performed in 13 dogs. Reversed superficial femoral veins were used as end-to-end grafts to bypass the iliac arteries. Each graft was deliberately twisted 0, 45, 90, 135, or 200 degrees. All grafts were harvested 6 months after surgery. Eighteen of 20 grafts twisted 135 degrees or less remained patent. However, all five grafts twisted 200 degrees were thrombosed within 4 hours of surgery (p less than 0.05). These data suggest that in patients a slight amount of graft twist probably does not reduce flow; however, more than 135 degrees of twist will greatly reduce flow, leading to early graft thrombosis.

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JThe University of lo&. ~o w a City, IO&, U.S.A. Ab s t iract A n a u t o m a t e d m e t h o d f o r s e g m e n t a t i o n of Iepicardial and endocardial borders ,from intracardiac ultrasound (ICUS) i m a g e s is reported. O p t i m a l borders are dletected w i t h i n a single interactively defined elliptical region of interest u s i n g graph searching. A p r i o r i knowledge about t h e ultrasound echo r e s p o n s e s ariszng f r o m t h e m y o c a rdial borders as well a s i n f o r m a t i o n about heart w a i l m o rphology i s incorporated in o u r graph search. T h e detected epzcardzal borders serve a s t h e shape m o d e l during the detectzon of t h e endocardzal borders. T h e m e t h o d w a s appliea! t o 26 ICUS i m a g e s acquired in vivo in 2 dogs. T h e heart w a l l borders w e r e successfully detected in all i m a g e s . Good correlationwas obtained between computer-detected a n d observerdefined left v e n t r i c u l a r (LV) cavity areas a n d LV areas (r=O.99, y=O.98x+0.02; r=19.99, y=O.97~+0.86; respectively). Epicardial a n d endocardial borders w e r e correctly posztioned with a root-mean-square border positioning err o r of 0.96rt0.28 mm. Our results d e m o n s t r a t e t h e feasibility of a u t o m a t e d border detection in ICUS i m a g e s .