Response of renal and femoropopliteal arteries to Palmaz stent implantation assessed with intravascular ultrasound

PURPOSE

To establish the processes responsible for late lumen loss in renal and femoropopliteal Palmaz stents using intravascular ultrasound (IVUS).

METHODS

The first 7 consecutive patients treated with stents for renal (n = 4) and femoropopliteal (n = 3) arterial occlusive disease were studied with IVUS immediately after angiographically successful stent placement (< 10% residual stenosis) and periodically during follow-up. Images of both stent edges and the most stenotic site inside the stent at followup were matched to the same cross sections captured immediately after stent placement for quantitative analysis.

RESULTS

Late lumen loss in renal artery stents at 5 to 34 months was considerably less than in femoropopliteal stents (17% versus 62%, respectively). In the renal location, late lumen loss (3.0 +/- 1.3 mm2) was due to neointimal hyperplasia, whereas stent area remained unchanged (3% decrease). Late lumen loss (7.4 +/- 8.2 mm2) in femoropopliteal stents was due to neointimal hyperplasia and stent area reduction (26%). Overall, in both types of arteries, neointimal development and stent area reduction were larger at the most stenotic site than at the stent edges.

CONCLUSIONS

These data suggest that there may be differences between renal and femoropopliteal arteries in the extent of hyperplastic response to stents.

Intravascular ultrasound evidence for coarctation causing symptomatic renal artery stenosis

BACKGROUND

A recent study of human cadaveric renal arteries revealed that renal artery narrowing could be due not only to atherosclerotic plaque compensated for by adaptive remodeling, but also to hitherto undescribed focal narrowing of an otherwise normal renal arterial wall (ie, coarctation). The present study investigated whether vessel coarctation could be identified in patients with symptomatic renal artery stenosis (RAS).

METHODS AND RESULTS

Consecutive symptomatic patients with angiographically proven atherosclerotic RAS who were referred for stent placement were studied by 30-MHz intravascular ultrasound before intervention (n=18) or after predilatation (n=18). Analysis included assessment of the media-bounded area and plaque area (PLA) at the most stenotic site and at a distal reference site (most distal cross-section in the main renal artery with normal appearance). Coarctation was considered present whenever the target/reference media-bounded area was </=85%. Before intervention, coarctation was observed in 9 of 18 patients and adaptive remodeling in 9 of 18 patients. Coarctation lesions had a significantly smaller PLA than adaptive remodeled lesions (P=0.001). Similarly, despite predilatation, coarctation was seen in 8 of 18 patients who had significantly smaller PLAs (P=0. 008) when compared with those patients who had adaptive remodeled lesions. No differences in severity of RAS or angiographic or clinical parameters were observed.

CONCLUSIONS

Low-plaque coarctation may cause a considerable proportion of symptomatic RAS, which is angiographically and clinically indistinguishable from plaque-rich RAS.

Endovascular stent-grafts for aneurysms of the femoral and popliteal arteries

Our objective was to investigate the preliminary use of endovascular stent-grafts for the treatment of femoropopliteal artery aneurysm. Ten patients with an aneurysm of the femoropopliteal artery referred for endovascular treatment were investigated. The series consisted of patients with a true aneurysm of the superficial femoral artery (n = 2); a true aneurysm of the popliteal artery (n = 4); an aneurysmal dilatation of a Biograft bypass (n = 2); a false aneurysm of the superficial femoral aneurysm (n = 1); and a false aneurysm of a composite bypass (n = 1). In 8 of the 10 patients the stent-graft was composed of one or more Palmaz stents sutured to an ePTFE tube graft; in the other 2 patients a venous covering was used in combination with Palmaz stents. The procedure was guided by angiography and intravascular ultrasound. The results of our investigation showed that endovascular stent-grafting of aneurysms of the femoropopliteal artery is a feasible but experimental technique that should be restricted to a selected group of patients.

Accurate assessment of abdominal aortic aneurysm with intravascular ultrasound scanning: validation with computed tomographic angiography

PURPOSE

The purpose of this study was to assess the accuracy of intravascular ultrasound (IVUS) parameters of abdominal aortic aneurysm, used for endovascular grafting, in comparison with computed tomographic angiography (CTA).

METHODS

This study was designed as a descriptive study. Between March 1997 and March 1998, 16 patients with abdominal aortic aneurysms were studied with angiography, IVUS (12.5 MHz), and CTA. The length of the aneurysm and the length and lumen diameter of the proximal and distal neck obtained with IVUS were compared with the data obtained with CTA. The measurements with IVUS were repeated by a second observer to assess the reproducibility. Tomographic IVUS images were reconstructed into a longitudinal format.

RESULTS

IVUS results identified 31 of 32 renal arteries and four of five accessory renal arteries. A comparison of the length measurements of the aneurysm and the proximal and distal neck obtained with IVUS and CTA revealed a correlation of 0.99 (P <.001), with a coefficient of variation of 9%. IVUS results tended to underestimate the length as compared with the CTA results (0.48 +/- 0.52 cm; P <.001). A comparison of the lumen diameter measurements of the proximal and distal neck derived from IVUS and CTA showed a correlation of 0.93 (P <.001), with a coefficient of variation of 9%. IVUS results tended to underestimate aneurysm neck diameter as compared with CTA results (0.68 +/- 1.76 mm; P =.006). Interobserver agreement of IVUS length and diameter measurements showed a good correlation (r = 1.0; P <.001), with coefficients of variation of 3% and 2%, respectively, and no significant differences (0.0 +/- 0.16 cm and 0.06 +/- 0.36 mm, respectively). The longitudinal IVUS images displayed the important vascular structures and improved the spatial insight in aneurysmal anatomy.

CONCLUSION

Intravascular ultrasound scanning results provided accurate and reproducible measurements of abdominal aortic aneurysm. The longitudinal reconstruction of IVUS images provided additional knowledge on the anatomy of the aneurysm and its proximal and distal neck.

Plaque area increase and vascular remodeling contribute to lumen area change after percutaneous transluminal angioplasty of the femoropopliteal artery: an intravascular ultrasound study

OBJECTIVE

The aim of the study was to assess the change in lumen area (LA), plaque area (PLA), and vessel area (VA) after percutaneous transluminal angioplasty (PTA) of the femoropopliteal artery.

METHODS

This was a prospective study. Twenty patients were studied with intravascular ultrasound (IVUS) immediately after PTA and at follow-up examination. Multiple corresponding IVUS cross-sections were analyzed at the segments that were dilated by PTA (ie, treated sites; n = 168), including the most stenotic site (n = 20) and the nondilated segments (ie, reference sites; n = 77).

RESULTS

At follow-up examination, both the PLA increase (13%) and the VA decrease (9%) resulted in a significant LA decrease (43%) at the most stenotic sites (P =.001). At the treated sites, the LA decrease (15%) was smaller and was caused by the PLA increase (15%). At the reference sites, the PLA increase (15%) and the VA increase (6%) resulted in a slight LA decrease (3%). An analysis of the IVUS cross-sections that were grouped according to LA change (difference >/=10%) revealed a similar PLA increase in all the groups: the type of vascular remodeling (VA decrease, no change, or increase) determined the LA change. At the treated sites, the LA change and the VA change correlated closely (r = 0.77, P <.001). At the treated sites, significantly more PLA increase was seen in the IVUS cross-sections that showed hard lesion or media rupture (P <.05). No relationship was found between the presence of dissection and the quantitative changes.

CONCLUSION

At the most stenotic sites, lumen narrowing was caused by plaque increase and vessel shrinkage. Both the treated sites and the reference sites showed a significant PLA increase: the type of vascular remodeling determined the LA change at follow-up examination. The extent of the PLA increase was significantly larger in the IVUS cross-sections that showed hard lesion or media rupture.

Conductance method for the measurement of cross-sectional areas of the aorta

A modified conductance method to determine the cross-sectional areas (CSAs) of arteries in piglets was evaluated in vivo. The method utilized a conductance catheter having four electrodes. Between the outer electrodes an alternating current was applied and between the inner electrodes the induced voltage difference was measured and converted into a conductance. CSA was determined from measured conductance minus parallel conductance, which is the conductance of the tissues surrounding the vessel times the length between the measuring electrodes of the conductance catheter divided by the conductivity of blood. The parallel conductance was determined by injecting hypertonic saline to change blood conductivity. The conductivity of blood was calculated from temperature and hematocrit and corrected for maximal deformation and changes in orientation of the erythrocytes under shear stress conditions. The equations to calculate the conductivity of blood were obtained from in vitro experiments. In vivo average aortic CSAs. determined with the conductance method CSA(G) in five piglets, were compared to those determined with the intravascular ultrasound method CSA(IVUS). The regression equation between both values was CSA(G)=-0.09+1.00 x CSA(IVUS), r=0.97, n=53. The mean difference between the values was -0.29%+/-5.57% (2 standard deviations). We conclude that the modified conductance method is a reliable technique to estimate the average cross-sectional areas of the aorta in piglets.

In-vitro validation, with histology, of intravascular ultrasound in renal arteries

OBJECTIVE

To investigate the feasibility of using intravascular ultrasound to characterize normal and diseased renal arteries.

MATERIALS AND METHODS

Forty-four renal artery specimens from 21 humans, removed at autopsy, were studied with intravascular ultrasound in vitro. From each vascular specimen, two to four sets of corresponding intravascular ultrasound images and histologic sections were subjected to qualitative analysis. The renal arterial wall was considered normal by intravascular ultrasound when the wall thickness (intima and media) was 0.5 mm or less. On intravascular ultrasound imaging, a distinction was made between bright lesions with or without peripheral shadowing (i.e. calcification). Histological sections were examined and fibromuscular lesions were scored with or without calcifications. Quantitative analysis of a multitude of intravascular ultrasound cross-sections (interval 5 mm) included assessment of the lumen area, vessel area, plaque area and percentage area obstructed. The target site (smallest lumen area) was compared with a reference site (largest lumen area before the first major side branch).

RESULTS

Of the 130 corresponding intravascular ultrasound images and histologic sections analysed, 55 were normal and 75 presented a bright lesion on ultrasound; in 31 lesions, peripheral shadowing was involved. The sensitivity of the intravascular ultrasound in detecting calcifications was 87%, and the specificity was 89%. Lumen area reduction at the target site was associated with vessel and plaque area enlargement in eight specimens, with plaque area enlargement in 12 specimens and with a vessel area reduction in 21 specimens.

CONCLUSIONS

Intravascular ultrasound is a reliable technique for distinguishing renal arteries with or without a lesion. Both plaque development and local vessel narrowing may result in renal artery stenosis.

Intravascular ultrasound and histology in in vitro assessment of iliac artery angioplasty

PURPOSE

Intravascular ultrasound (IVUS) was used to assess in vitro the morphologic and quantitative effects of balloon angioplasty (PTA) of the iliac artery.

METHODS

Forty human iliac arteries (>/= 30% area stenosis) were studied with IVUS in vitro before and after PTA and the findings were validated with histology.

RESULTS

The sensitivity of IVUS for dissection was 74% and for media rupture 59%. The incidence of vascular damage was higher when the whole segment was analyzed rather than the target site alone. Dissections occurred at the thinnest region of the plaque, unrelated to plaque calcification. Following PTA, quantitative changes at the target site were greater compared with the overall data derived from all cross-sections. The increase in lumen area was caused solely by an increase in vessel area.

CONCLUSIONS

IVUS is sensitive in detecting dissections, which occurred irrespective of calcification at the thinnest region of the plaque. The increase in lumen area after PTA was caused by stretching of the vessel.

Stent placement for treatment of renal artery stenosis guided by intravascular ultrasound

PURPOSE

To study the impact of intravascular ultrasound (IVUS) during renal artery stent placement.

MATERIALS AND METHODS

Patients (n = 22) with atherosclerotic renal artery stenosis were studied with IVUS after predilation and after angiographically successful stent deployment (diameter stenosis < 10%). After predilation, IVUS was used to assess whether the balloon size selected angiographically was correct (discrepancy balloon-reference lumen diameter < 20%). After stent placement, IVUS images were assessed for (i) complete stent-vessel wall apposition; (ii) complete stent expansion (discrepancy stent-reference lumen diameter < 20%), and (iii) complete lesion covering by the stent. Modification based on IVUS included selection of a larger balloon, additional dilation, and placement of a second stent. Clinical outcome was based on blood pressure, amount of antihypertensive drugs, and glomerular filtration rate during follow-up of 3 months.

RESULTS

Stent placement and ultrasound imaging were completed successfully in 18 patients. After predilation, IVUS warranted the use of a larger balloon in five patients. After stent placement, incomplete stent apposition (n = 1), discrepancy between stent and reference lumen diameter (n = 3), and lesion distal to the stent (n = 2) seen on IVUS were treated with additional dilation in five patients and with a second stent in one patient. A larger balloon was used in three patients. Mean blood pressure and amount of antihypertensive drugs decreased (P < .05).

CONCLUSIONS

In a number of patients, IVUS monitoring during renal artery stent placement resulted in additional lumen enlargement not considered necessary at angiography.

Comparison of angiography and intravascular ultrasound before and after balloon angioplasty of the femoropopliteal artery

PURPOSE

To compare angiographic and intravascular ultrasound (IVUS) data before and after balloon angioplasty (PTA) of the femoropopliteal artery.

METHODS

Qualitative and quantitative analyses were performed on corresponding angiographic and IVUS levels obtained from 135 patients.

RESULTS

IVUS detected more lesions, calcified lesions, and vascular damage than angiography. Sensitivity of angiography was good for the presence of a lesion (84%), moderate for eccentric lesions (53%) and for vascular damage (52%), and poor for calcified lesions (30%). The increase in angiographic diameter stenosis was associated with a decrease in lumen area and increase in percentage area stenosis on IVUS.

CONCLUSIONS

Angiography is less sensitive than IVUS for detecting lesion eccentricity, calcified lesions, and vascular damage. Presence of a lesion and amount of plaque were underestimated angiographically. Only before PTA was good agreement found between angiographic diameter stenosis and lumen size on IVUS.

Intravascular ultrasound predictors of restenosis after balloon angioplasty of the femoropopliteal artery

OBJECTIVES

To determine intravascular ultrasound parameters related to restenosis following percutaneous transluminal balloon angioplasty (PTA) of the femoropopliteal artery.

DESIGN

Prospective study.

MATERIALS AND METHODS

Patients were studies with intravascular ultrasound before and after angiographic successful PTA (n = 114). Intravascular ultrasound cross-sections obtained with 1 cm interval in the dilated segment were analysed. A distinction was made between anatomic (duplex scanning) and clinical (Rutherford criteria) restenosis assessed within 1 month and at 6 months after PTA.

RESULTS

Intravascular ultrasound predictors of 1 month anatomic outcome were lumen area stenosis after PTA, lumen area increase, plaque area decrease, and area stenosis decrease; predictor of 6 months anatomic outcome was area stenosis after PTA. Multivariate analysis revealed that area stenosis after PTA was the only independent predictor of both 1 and 6 months anatomic outcome. Intravascular ultrasound predictors of 1 month clinical outcome were the presence of hard lesion and the mean arc of hard lesion. Multivariate analysis revealed that the mean arc of hard lesion was the only independent predictor of 1 month clinical outcome. No predictors for 6 months clinical outcome were found.

CONCLUSIONS

Intravascular ultrasound can elucidate parameters predictive of restonosis after PTA. The strongest intravascular ultrasound parameter predictive of anatomic restenosis was a large area stenosis after PTA.

Intravascular ultrasound in endovascular stent-grafts for peripheral aneurysm: a clinical study

PURPOSE

To evaluate the potential diagnostic information of intraprocedural intravascular ultrasound (IVUS) in patients undergoing endovascular stent-grafting for peripheral aneurysm.

METHODS

IVUS was used in 17 patients preprocedurally to measure the diameter of the proximal and distal neck and the length of the aneurysm. Balloon and stent-graft sizes were selected based on these measurements. Following stent-graft deployment, angiography and IVUS were used to document stent apposition and the configuration and diameter of the stent-graft.

RESULTS

Stent-graft insertion was considered successful in 8 patients based on angiography and IVUS images. In 9 others, both imaging modalities showed inadequate results, necessitating 12 additional procedures: balloon angioplasty for stent-graft stenosis (2) and inadequate stent-graft apposition (1); an additional stent-graft (4); an extra stent (1); thrombectomy (2); and conversion (2) for inadequate stent-graft position and a graft rupture. In these patients, intraprocedural IVUS was superiorto angiography in contributing vital information to aid in the selection of the additional interventions.

CONCLUSIONS

During management of peripheral aneurysms with endovascular stent-grafts, IVUS monitoring was a useful adjunct when the initial procedure was unsatisfactory and/ or when intraprocedural angiographic studies were inconclusive.

Validation of automated contour analysis of intravascular ultrasound images after vascular intervention

PURPOSE

The purpose of this study was to determine the feasibility of automated contour analysis of intravascular ultrasound images obtained after vascular intervention.

STUDY DESIGN

This was a descriptive study.

METHODS

Intravascular ultrasound images obtained from patients after balloon angioplasty (n = 10), stent (n = 10), or stent graft placement (n = 10) were analyzed. A comparison was made between lumen area measured with an automated and a manual system. The location showing the smallest lumen area derived from the automated system was compared with the smallest lumen area selected by visual estimation.

RESULTS

Images containing a dissection as a result of balloon angioplasty could not be analyzed by the automated system. The coefficient of variation between the lumen area measurements obtained with the automated system and the manual tracing system of images with a stent (n = 76) or stent graft (n = 79) was 2.7% and 2.1%, respectively. Correlation between the two systems was high (r = 1.00, p < 0.01) both for images containing stents or stent grafts. Minimum lumen area measured with the automated analysis system was smaller than minimum lumen area selected by visual estimation (mean difference 0.8 mm2 (4.9%) for stents and 2.4 mm2 (10.9%) for stent grafts). The location of the smallest lumen area determined with both systems was the same (<1 cm) in 16 cases and differed more than 1 cm in 4 other cases.

CONCLUSIONS

The automated analysis system shows good agreement with manual contour analysis of lumen area in images with a stent or stent graft and is a reliable tool for determination of the smallest lumen area. The system is not able to analyze an irregular-shaped lumen area caused by a dissection.

Intravascular ultrasonography allows accurate assessment of abdominal aortic aneurysm: an in vitro validation study

OBJECTIVE

The objective of this study was to acquire insight into the interpretation of intravascular ultrasound images of the abdominal aorta and to assess to what extent this technique can provide useful parameters for the endovascular treatment of patients with abdominal aortic aneurysm.

STUDY DESIGN

This was a descriptive study.

METHODS

Fifteen abdominal aortic specimens (normal, atherosclerotic, or aneurysmal) were studied. Ultrasonic images and corresponding histologic sections were compared for vessel wall characteristics, lesion morphologic characteristics, and lumen diameter. The length of the aneurysm and the length of the proximal and distal neck were measured and compared with external measurements. Tomographic images were reconstructed to a three-dimensional format.

RESULTS

Normal aortic wall was seen as a two- or three-layered structure corresponding with intima, media, and adventitia. A distinction could be made among fibrous lesion, calcified lesion, and thrombus and between normal and aneurysmal aorta. Correlation between the histologic specimens and intravascular ultrasonography for lumen diameter measurements was high (r = 0.93; p < 0.001). In a similar fashion, correlation between external measurements and intravascular ultrasound measurements on the length of the aneurysm and its proximal and distal neck was high (r = 0.99; p < 0.001). Three-dimensional analysis enhanced interpretation of the tomographic images by visualizing the spatial position of anatomic structures and contributed to understanding the shape and dimensions of the aneurysm.

CONCLUSIONS

Intravascular ultrasonography provides accurate information on the vessel wall, lesion morphologic characteristics, and quantitative parameters of the abdominal aorta. Spatial information supplied by three-dimensional analysis contributes to a more realistic interpretation of the tomographic images.

Reliability and reproducibility of automated contour analysis in intravascular ultrasound images of femoropopliteal arteries

An automated contour analysis system was previously developed to increase reproducibility and facilitate quantitative analyses of intravascular ultrasound (IVUS) images. The aim of this study was to compare measurements by this automated system with those obtained by conventional manual tracing, and to determine the intra- and interobserver variability of the automated system. IVUS images obtained in the femoropopliteal artery (n = 12) were analyzed with both systems. Area measurements by the automated system agreed well with the results obtained by manual tracing, displaying low coefficients of variation (8.5 to 15.7%) and high correlation coefficients (r = 0.92 to 0.98). Intra- and interobserver comparison of lumen area, vessel area, plaque area and percentage area stenosis showed low coefficients of variation (6.0 to 15.3% and 5.7 to 14.0%, respectively) and high correlation coefficients (both: r = 0.93 to 0.99). These data indicate that the automated analysis system is a reliable tool for the quantitative assessment of vessel dimensions in IVUS images obtained during clinical examination of peripheral arteries.

Discrepancy between stent deployment and balloon size used assessed by intravascular ultrasound

OBJECTIVES

This study was designed to assess the discrepancy in stent deployment seen on intravascular ultrasound and its relation to the balloon size selected for stent delivery.

DESIGN

Prospective study.

MATERIALS AND METHODS

The study group comprised 27 patients treated using a stent (n = 18) or stent-graft combination (n = 9). Following angiographically optimal stent deployment (< 10% residual stenosis) intravascular ultrasound was used to compare the smallest intra-stent lumen area with measurements at both stent edges and the lumen area of the proximal and distal reference sites.

RESULTS

In 14 of the 27 stents the intra-stent dimension was the same as the dimension of the stent edge (difference < or = +/- 10%). Of the remaining stents the intra-stent dimension was smaller (difference > 10%) than the proximal stent edge in seven stents (range 11-39%), smaller than the distal stent edge in three stents (range 11-20%) and smaller than both stent edges in three stents (range 12-37%). Both in patients treated with a stent or stent-graft combination, the resulting smallest intra-stent lumen area was smaller than the balloon size used (mean difference 32% and 42%, respectively) and smaller than the mean lumen area of the reference sites (mean difference 25% and 23%, respectively).

CONCLUSION

This intravascular ultrasound study shows a discrepancy between intra-stent lumen area, the area of the stent edges and the balloon size used.

Failure of intravascular ultrasound to predict dissection after balloon angioplasty by using plaque characteristics

Intravascular ultrasound (IVUS) is more sensitive than angiography in the assessment of plaque characteristics before intervention and vascular damage after balloon angioplasty. On the basis of IVUS data, this finding may improve clinical treatment by reducing the incidence of severe dissections after balloon angioplasty. We therefore studied the relation between plaque characteristics and dissections after balloon angioplasty. First, an in vitro study on atherosclerotic arteries (n = 42) was performed in which IVUS images were compared with histologic sections to validate the IVUS technique; second, the in vitro findings were compared with IVUS findings obtained in vivo (n = 73). Dissections were observed in 37 histologic sections and visualized on IVUS in 22 (59%) of the corresponding ultrasonic cross-sections; in vivo dissections were demonstrated by IVUS in 46 (63%) cases. Dissections were generally seen at the thinnest region of the plaque on both histologic sections (92%) and IVUS cross-sections (in vitro 83%; in vivo 93%). No significant relation was found between pre-interventional plaque characteristics such as composition features and eccentricity and the incidence, location, and extent of postinterventional dissections. Thus IVUS is able to identify dissections after balloon angioplasty, generally occurring at the site of the thinnest plaque diameter. However, neither the incidence nor the severity of these dissections was related to any of the preinterventional plaque characteristics.

Evaluation of directional atherectomy studied by intravascular ultrasound in femoropopliteal artery stenosis

PURPOSE

To evaluate the role of intravascular ultrasound (IVUS) before and after directional atherectomy (DA) in the treatment of femoropopliteal artery stenosis.

METHODS

In 12 patients with 16 stenoses IVUS was performed before and immediately after an angiographically successful DA. This was defined as a diameter reduction (DR) < or = 50%, which was calculated using the minimal lumen diameter compared with the diameter of a nearby "normal" segment. In the presence of residual plaque on IVUS an additional DA was performed. Endpoints studied were DR < or = 30% on IVUS compared with the IVUS findings of the angiographically normal reference segment, or when no additional atherosclerotic material could be removed by further DA passages.

RESULTS

Additional DA (mean 1.6 per lesion) had to be performed in all patients. Initial DA increased the cross-sectional free lumen area (FLA) from 3.8 +/- 2.0 mm2 to 8.1 +/- 2.7 mm2 (p = 0.0004). Additional DA increased FLA to 9.3 +/- 2.3 mm2 (p = 0.002) after the second passage and to 9.8 +/- 2.4 mm2 (p = 0.09) after the final DA run. The plaque area (PLA) before DA decreased from 18.1 +/- 4.2 mm2 to 15.4 +/- 4.8 mm2 (p = 0.002) after the first passage, and to 13.5 +/- 5.0 mm2 (p = 0.004) and 12. 8 +/- 4.4 mm2 (p = 0.07) after the second and final DA runs, respectively. PLA of the reference segment (9.5 +/- 5.7 mm2) was significantly smaller (p = 0.006) than the final PLA of the treated lesion, indicating a large amount of retained plaque. As a result of DA there was an increase in the area bordered by the medial layer, i. e., the total vessel area (from 21.9 +/- 4.7 mm2 to 23.0 +/- 4.7 mm2), significantly in eccentric and soft lesions. On IVUS, dissection and plaque rupture after the final passage was seen in 12 of 16 stenoses; two dissections were seen on the completion angiogram. After the final passage in all stenoses except three, the DR with IVUS was < or = 30%.

CONCLUSION

Lumen enlargement following DA is predominantly due to plaque excision. Vessel expansion combined with plaque excision varies in different stenoses and is an important factor in eccentric and soft lesions. Despite additional DA considerable plaque remains.

Automated lumen definition from 30 MHz intravascular ultrasound images

One prerequisite for standard clinical use of intravascular ultrasound imaging is rapid evaluation of the data. The main quantities to be extracted from the data are the size and the shape of the lumen. Until now, no accurate, robust and reproducible method to obtain the lumen boundaries from intravascular ultrasound images has been described. In this study, 21 different (semi-)automated binary-segmentation methods for determining the lumen are compared with manual segmentation to find an alternative for the laborious and subjective procedure of manual editing. After a preprocessing step in which the catheter area is filled with lumen-like grey values, all approaches consist of two steps: (i) smoothing the images with different filtering methods and (ii) extracting the lumen by an object definition method. The combination of different filtering methods and object definition methods results in a total of 21 methods and 80 experiments. The results are compared with a reference image, obtained from manual editing, by use of four different quality parameters--two based on squared distances and two based on Mahalanobis distances. The evaluation has been carried out on 15 images, of which seven are obtained before balloon dilation and eight after balloon dilation. While for the post-dilation images no definite conclusions can be drawn, an automated contour model applied to images smoothed with a large kernel appears to be a good alternative to manual contouring. For pre-dilation images a fully automated active contour model, initialized by thresholding, preceded by filtering with a small-scale median filter is the best alternative for manual delineation. The results of this method are even better than manual segmentation, i.e. they are consistently closer to the reference image than the average distance of all individual manual segmentations.

Effect of balloon angioplasty in femoropopliteal arteries assessed by intravascular ultrasound

OBJECTIVE

To study the effects of balloon angioplasty (PTA) of the femoropopliteal artery with intravascular ultrasound (IVUS).

MATERIALS AND METHODS

Corresponding IVUS cross-sections (n = 1033) obtained before and after PTA from 115 procedures were analysed. Vascular damage including plaque rupture, dissection and media rupture was assessed. Free lumen area (FLA), media-bounded area (MBA) and plaque area (PLA) were measured.

RESULTS

After PTA vascular damage was seen at the target site in 83 (72%) arteries: plaque rupture in 30 (26%), dissection in 66 (57%) and media rupture in 20 (17%) arteries. The FLA increased from 5.4 +/- 3.4 mm2 to 14.1 +/- 5.0 mm2 (p < 0.001), MBA increased from 26.9 +/- 10.0 mm2 to 32.9 +/- 10.7 mm2 (p < 0.001) and PLA decreased from 21.6 +/- 8.5 mm2 to 18.8 +/- 8.0 mm2 (p < 0.001). The increase in MBA accounted for 68% of lumen gain. The frequency of vascular damage and the relative contribution of MBA increase and PLA decrease to luminal gain were not different in procedures with balloon diameter < or = 5 mm and > or = 6 mm.

CONCLUSIONS

Vascular damage is common following PTA. Lumen gain is mainly due to vessel expansion and, to a lesser extent, to a decrease in plaque area.

Stent remodeling contributes to femoropopliteal artery restenosis: an intravascular ultrasound study

This case report describes the status of femoropopliteal artery stents after intervention documented with intravascular ultrasound compared with the changes seen at follow-up. To treat an extensive dissection after balloon angioplasty, a 57-year-old man underwent placement of seven adjacent Palmaz stents. At 5-month follow-up, an angiographic and intravascular ultrasound examination revealed four distinct stenotic lesions (> or = 50%) at stent junctions. Intravascular ultrasound images obtained during the initial stent placement were compared with the corresponding images obtained at follow-up. A distinction was made between changes seen at stent junctions and stent edges (n = 8), those seen within each stent (n = 7), and those in the nonstented sections proximally and distally (n = 3). Intravascular ultrasound examination established that both intimal hyperplasia and stent area reduction (stent remodeling) resulted in lumen area reduction. The extent of the changes seen at the stent junctions were greater than that of changes seen within the stents: lumen area reduction, 67% versus 23%; stent area reduction, 26% versus 11%; and intimal hyperplasia, 10.8 versus 3.3 mm2; respectively. Changes in the nonstented sections were minimal (< 2%). The stent edge seen at the adductor canal showed elliptical deformation. Thus there is a higher risk of restenosis at the stent junctions. In addition to intimal hyperplasia, stent remodeling contributes to restenosis.

Remodeling of atherosclerotic coronary arteries assessed with intravascular ultrasound in vitro

This study investigated remodeling in human coronary arteries with intravascular ultrasound. We conclude that regression analysis performed by Glagov et al and adopted by others is reproducible but is unable to discern shrinkage of the vessel area.

Potentials of volumetric blood-flow measurement

Current intravascular ultrasound techniques produce real-time imaging of a vessel cross-section with a scan plane normal to blood flow. When randomly distributed blood particles travel through this ultrasound imaging plane, the received echo signals decorrelate as a function of time. The speed of such a decorrelation procedure is proportional to the flow velocity. This phenomenon provides a potential to estimate blood velocities by means of decorrelation analysis. In this paper, we present a method for measuring local blood velocity and quantifying volume flow directly from cross-sectional intravascular ultrasound data. This method is based on multiple decorrelation assessments with a sequence of radio frequency echo signals. The velocity measurement is obtained by comparing the measured decorrelation value with the prior knowledge of the beam characteristics of an intravascular ultrasound transducer. Volume flow is derived by integrating the cross-sectional area and its corresponding velocity vector over the vessel lumen. The decorrelation-based method was tested in vitro with a flow phantom. Measurements were also carried out in vivo in pig experiments to determine the usefulness of this method in clinical settings. Preliminary results of these experiments indicate that the proposed decorrelation method is able to extract cross-sectional velocity profiles and volumetric flow both in vitro and in vivo.

Computerized assessment of coronary lumen and atherosclerotic plaque dimensions in three-dimensional intravascular ultrasound correlated with histomorphometry

Intravascular ultrasound (IVUS), which depicts both lumen and plaque, offers the potential to improve on the limitations of angiography for the assessment of the natural history of atherosclerosis and progression or regression of the disease. To facilitate measurements and increase the reproducibility of quantitative IVUS analyses, a computerized contour detection system was developed that detects both the luminal and external vessel boundaries in 3-dimensional sets of IVUS images. To validate this system, atherosclerotic human coronary segments (n = 13) with an area obstruction > or = 40% (40% to 61%) were studied in vitro by IVUS. The computerized IVUS measurements (areas and volumes) of the lumen, total vessel, plaque-media complex, and percent obstruction were compared with findings by manual tracing of the IVUS images and of the corresponding histologic cross sections obtained at 2-mm increments (n = 100). Both area and volume measurements by the contour detection system agreed well with the results obtained by manual tracing, showing low mean between-method differences (-3.7% to 0.3%) with SDs not exceeding 6% and high correlation coefficients (r = 0.97 to 0.99). Measurements of the lumen, total vessel, plaque-media complex, and percent obstruction by the contour detection system correlated well with histomorphometry of areas (r = 0.94, 0.88, 0.80, and 0.88) and volumes (r = 0.98, 0.91, 0.83, and 0.91). Systematic differences between the results by the contour detection system and histomorphometry (29%, 13%, -9%, and -22%, respectively) were found, most likely resulting from shrinkage during tissue fixation. The results of this study indicate that this computerized IVUS analysis system is reliable for the assessment of coronary atherosclerosis in vivo.