4.4 IVUS ASSESSMENT IVUS assessment was performed using a commercially available IVUS system (Boston Scientific/ Scimed, Natick, MA). Studies were recorded on Index system (Echoplaque 2; INDEC Systems Inc, Mountain View, CA) for off-line analysis. Motorized transducer pullback permitted cross-sectional area measurements at 1mm axial increments throughout the length of the stent. All IVUS studies were performed after the intracoronary administration of 200 µg of nitroglycerin. The reference segment was the most visually normal cross section (largest lumen with least plaque burden) within 10mm proximal or distal to the lesion. Using the software, external elastic membrane (EEM) CSA (mm2), lumen CSA (mm2), minimal stent cross-sectional area (MSA); identified as the CSA at the tightest segment within stent, stent MLD were determined. The CSA at the proximal and the distal reference segments and at the most stenotic lesion as well as the CSA at the proximal and the distal stent edge was determined. A determination of the percent expansion was made by measuring the MSA and the average reference segment CSA. Average reference segment CSA is calculated as [Proximal Reference segment CSA +Distal Reference segment CSA)/2]. Plaque volume was calculated as vessel minus stent volume. Neointimal volume was calculated as stent minus lumen volume, and percentage (%) of neointimal obstruction was calculated as neointimal volume divided by stent volume. Neointimal coverage over stent surface and mean physical neointimal thickness were obtained by measuring circumferential stent length covered with neointimal hyperplasia (LN) and stent perimeter (LS) at every 1-mm cross-sectional image throughout the stented segment: (a) percentage of neointimal coverage over stent surface, calculated as total LN divided by total LS, and (b) mean physical neointimal thickness, calculated as mean neointimal area divided by mean LN for only the cross sections with detectable neointima.