We studied 12 patients undergoing elective coronary stent implantation for either recurrent restenosis or adverse lesion appearance. By use of a 4.8F 20 MHz intravascular ultrasound catheter, the conventional angioplasty site was examined before and after coronary stent implantation. Quantitative angiographic analysis revealed the expected excellent final result with a group mean poststent diameter reduction of 14 +/- 9% and a cross-sectional area reduction of 22 +/- 13%. Angiographic analysis also indicated an increase in minimum stenosis diameter from 1.8 +/- 0.6 mm after conventional balloon angioplasty to 2.8 +/- 0.3 mm after coronary stent implantation. Quantitative analysis of the corresponding intravascular ultrasound images, however, revealed significant residual endoluminal obstruction. Fractional plaque area remained unchanged from 30 +/- 12% after conventional balloon angioplasty to 32 +/- 11% after stent implantation. The circumferential distribution of plaque increased significantly from 0.44 +/- 0.17 to 0.55 +/- 0.15 (p = 0.03) after stent implantation. Despite the lack of significant change in the ultrasound-determined minimum stenosis diameter after stent placement, there was a borderline significant increase in the plaque-free lumen area (before stent, 6.35 +/- 1.55 mm2; after stent, 7.25 +/- 1.6 mm2; p = 0.06). Thus, in contrast to the substantial improvement in the angiographically assessed residual luminal obstruction after stent implantation compared with the prestent condition, considerably less improvement was found by intravascular ultrasound-assessed examination. Morphometric analysis indicated a tendency toward circumferential remodeling of plaque. The inherently different approaches to vascular imaging represented by contrast angiography and intravascular ultrasound techniques appear to provide complementary information.(ABSTRACT TRUNCATED AT 250 WORDS)