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Objectives. Balloon angioplasty of chronic coronary occlusions has a low procedural success and a high recurrence rate. Better tomographic insights into the lesion morphology may improve the interventional strategy and results. Methods. Intracoronary ultrasound was used during the recanalizaton procedure of 45 chronic coronary occlusions (2 weeks to 14 months; average 3.4 months) to determine the lesion morphology and to assess the angioplasty result. The luminal area and the plaque burden were measured proximal and distal to the occlusion, and within the occlusion. The ultrasonographic characteristics of the occlusive lesions were compared to 45 nonocclusive lesions of age-matched patients with stable angina pectoris. Results. Occlusive lesions were more often echodense as compared to nonocclusive lesions (35% vs. 20% p=0.10). In chronic occlusions a multi- layered plaque morphology was observed in 22%, and this morphology was not found in nonocclusive lesions. Angiographic characteristics were not related to the ultrasonographic morphology of the lesion. Despite similar vessel areas in occlusive and nonocclusive lesions, the balloon size selected according to the angiographic image was underestimated in occlusive lesions. Based on the quantitative ultrasound measurement the balloon size was increased from 2.6±0.3 mm to 3.3±0.5 mm in 53% of the lesions. This resulted in an increase of the luminal area from 3.51±0.92 to 5.08±1.43 mm2(p<0.001). The acute recoil after balloon angioplasty was similar (34±18%) in hypodense and echodense plaques, but was significantly higher in lesions with a multi-layered plaque morphology (49±22%; p<0.05). In 19 patients with severe dissections or extreme acute recoil (residual stenosis>50%) the use of a stent increased the luminal area from 3.94±0.81 to 7.51±1.71 mm2(p<0.001). Conclusion. Intracoronary ultrasound demonstrated a multi-layered plaque morphology in one fourth of the chronic occlusions. This type of plaque was associated with a significant acute recoil. The presence of diffuse atherosclerosis in neighbouring segments of chronic coronary occlusions leads to underestimation of the balloon size. Quantitative assessment by intracoronary ultrasound helped to optimize the balloon size leading to a significant luminal area gain. The detection of excessive acute recoil should be considered an indication for stent deployment.