A multiresolution image segmentation technique based on pyramidal segmentation and fuzzy clustering

In this paper, an unsupervised image segmentation technique is presented, which combines pyramidal image segmentation with the fuzzy c-means clustering algorithm. Each layer of the pyramid is split into a number of regions by a root labeling technique, and then fuzzy c-means is used to merge the regions of the layer with the highest image resolution. A cluster validity functional is used to find the optimal number of objects automatically. Segmentation of a number of synthetic as well as clinical images is illustrated and two fully automatic segmentation approaches are evaluated, which determine the left ventricular volume (LV) in 140 cardiovascular magnetic resonance (MR) images. First fuzzy c-means is applied without pyramids. In the second approach the regions generated by pyramidal segmentation are merged by fuzzy c-means. The correlation coefficients of manually and automatically defined LV lumen of all 140 and 20 end-diastolic images were equal to 0.86 and 0.79, respectively, when images were segmented with fuzzy c-means alone. These coefficients increased to 0.90 and 0.93 when the pyramidal segmentation was combined with fuzzy c-means. This method can be applied to any dimensional representation and at any resolution level of an image series. The evaluation study shows good performance in detecting LV lumen in MR images.

Quantitative measurements in IVUS images

IntraVascular UltraSound (IVUS) is a catheter-based technique which provides real-time high resolution tomographic images of both the lumen and arterial wall of a coronary segment, this in contrast to X-ray arteriography that provides a shadow image (luminogram) of the entire lumen. Nowadays the lumen and vessel parameters are measured manually, which is very time consuming and suffers from high inter- and intra-obser variability. With the continuing improvement in IVUS imaging, it is now feasible to develop and clinically apply automated methods of three-dimensional quantitative analysis of the coronary vessel morphology in an objective and reproducible way with automated contour detection techniques (QCU). Quantification, in 2D and 3D, as well as volume rendering for visualization of the IVUS images requires segmentation of the images (contour detection). The 3D contour detection system described in this article is based on the combination of contour detection in the transversal and sagital view. This article provides some of the basic principles of IVUS, the IVUS image quantification, the three-dimensional reconstruction and the contour detection and quantification in three-dimensional IVUS images.

Stenosis quantification from post-stenotic signal loss in phase-contrast MRA datasets of flow phantoms and renal arteries

In this study a semi-automated and observer-independent algorithm for quantifying post-stenotic signal loss (PSL) in 3D phase-contrast (PC) magnetic resonance angiography (MRA) of patients with renal artery stenosis is presented. This algorithm was developed on MRA datasets of stenotic phantoms, which were included in a flow circuit with stationary flows. The length and the severity of the PSL (incorporating both length and degree of PSL) in the maximum intensity projections (MIPs) of MRA datasets were proposed for quantifying stenoses. The algorithm was tested in renal arteries of ten patients with renal artery stenosis and seven healthy volunteers. Digital subtraction angiography (DSA) was performed in the patients and served as the gold standard. Stenosis severity showed better correlation with the severity of the PSL than with the length, both for in vitro as in vivo. Spearman correlation coefficients (rS) showed statistically significant correlations between the severity of the PSL and parameters determined by DSA, i.e. percent diameter stenosis (rS = 0.90). The length of the PSL showed no correlation with the diameter stenosis (rS = 0.37).

A randomized clinical trial of alpha(1)-antitrypsin augmentation therapy

We have investigated whether restoration of the balance between neutrophil elastase and its inhibitor, alpha(1)-antitrypsin, can prevent the progression of pulmonary emphysema in patients with alpha(1)-antitrypsin deficiency. Twenty-six Danish and 30 Dutch ex-smokers with alpha(1)-antitrypsin deficiency of PI*ZZ phenotype and moderate emphysema (FEV(1) between 30% and 80% of predicted) participated in a double-blind trial of alpha(1)-antitrypsin augmentation therapy. The patients were randomized to either alpha(1)-antitrypsin (250 mg/kg) or albumin (625 mg/kg) infusions at 4-wk intervals for at least 3 yr. Self-administered spirometry performed every morning and evening at home showed no significant difference in decline of FEV(1) between treatment and placebo. Each year, the degree of emphysema was quantified by the 15th percentile point of the lung density histogram derived from computed tomography (CT). The loss of lung tissue measured by CT (mean +/- SEM) was 2.6 +/- 0.41 g/L/yr for placebo as compared with 1.5 +/- 0.41 g/L/yr for alpha(1)-antitrypsin infusion (p = 0.07). Power analysis showed that this protective effect would be significant in a similar trial with 130 patients. This is in contrast to calculations based on annual decline of FEV(1) showing that 550 patients would be needed to show a 50% reduction of annual decline. We conclude that lung density measurements by CT may facilitate future randomized clinical trials of investigational drugs for a disease in which little progress in therapy has been made in the past 30 yr.

Quantification in cardiac MRI

Magnetic resonance imaging (MRI) offers several acquisition techniques for precise and highly reproducible assessment of global and regional ventricular function, flow, and perfusion at rest and under pharmacological or physical stress conditions. Recent advances in hardware and software have resulted in strong improvement of image quality and in a significant decrease in the required imaging time for each of these acquisitions. Several aspects of heart disease can be studied by combining multiple MRI techniques in a single examination. Such a comprehensive examination could replace a number of other imaging procedures, such as diagnostic X-ray angiography, echocardiography, and scintigraphy, which would be beneficial for the patient and cost effective. Despite the advances in MRI, quantitative image analysis often still relies on manual tracing of contours in the images, which is a time-consuming and tedious procedure that limits the clinical applicability of cardiovascular MRI. Reliable automated or semi-automated image analysis software would be very helpful to overcome the limitations associated with manual image processing. In this paper the developments directed toward automated quantitative image analysis and semi-automated contour detection for cardiovascular MR imaging are reviewed. J. Magn. Reson. Imaging 1999; 10:602-608.

Stenting of long coronary artery lesions: initial angiographic results and 6-month clinical outcome of the micro stent II-XL

To evaluate the results of long Micro Stent II (MS-XL) implantations, 119 MS-XLs were implanted in 102 patients (age, 62.83 years). Nineteen stents (16%) were implanted in saphenous vein grafts; 100 stents (84%) were implanted in native coronary arteries. Twenty-five patients (25%) were treated because of acute myocardial infarction (AMI); 30 patients (29%) because of unstable angina or angina class IV, and 47 patients (46%) because of stable angina. Eighty-six de novo lesions (84%) and 16 restenotic lesions (16%) were treated. Indications for stent implantation include elective, 61 patients (60%); suboptimal balloon angioplasty result, 22 patients (21%); and bailout after balloon angioplasty, 19 patients (19%). Because of residual thrombus after stenting, 27 patients (26%) received abciximab. All patients received ticlopidin for 28 days and acetylsalicylic acid. One hundred and seventeen MS-XLs (98%) were implanted successfully. Additional (shorter) MS-II were implanted in 40 patients (39%). The stented segment length was 45 +/- 20 mm. The minimum lumen diameter increased from 0.5 +/- 0.5 mm before to 2.7 +/- 0.5 mm after stent implantation. The acute gain was 2.2 +/- 0.4 mm. Early clinical events (<4 weeks) include death, 3 (3%); subacute stent thrombosis, 1 (1%); non-Q-wave infarction, 2 (2%); CABG, 1 (1%); vascular complications, 2 (2%). Late clinical events (<6 months) include acute myocardial infarction, 5 (5%); reintervention, 6 (6%); CABG, 1 (1%). The procedural success rate was 88%, and the event free survival at 6 months was 76%. Stenting of long lesions with the MS-XL was successful and associated with an acceptable complication rate. Cathet. Cardiovasc. Intervent. 48:105-112, 1999.

Gadolinium contrast-enhanced three-dimensional MRA of peripheral arteries with multiple bolus injection: scan optimization in vitro and in vivo

In this study, a scanning protocol was developed to image the arterial bed of the pelvis and both legs along their entire length in patients with peripheral arterial disease, using standard hard- and software. Three adjacent stations are acquired consecutively, with some small overlap; per station; one Gadolinium contrast bolus is administered. The scanning protocol was optimized in an in vitro phantom study. The optimal flip angle was found to be 50 degrees. Also, the optimal scan delay was chosen to be equal to the arrival time of the contrast bolus thereby minimizing artifacts. Three contrast bolus injections showed sufficient enhancement of the vessels after image subtraction. Finally, stenosis quantification by manual caliper was performed by five observers in the MRA images and correlated with the percent diameter reduction determined by quantitative angiography from corresponding X-ray images. The results of the MRA measurements were reproducible and intra- and inter-observer variabilities were statistically non-significant (p = 0.54 and p = 0.12, respectively). Stenosis quantification performed by four observers showed a good correlation with the X-ray derived values (rp > 0.90, p < 0.02); the results from one observer were not significantly correlated. Five patients with proven peripheral disease were investigated with this new MRA scanning protocol. The images were of good quality which allowed adequate clinical evaluation; the original diagnoses obtained from X-ray examinations, were confirmed with MRA. In conclusion, peripheral arterial disease can be evaluated adequately with this MR scanning protocol.

Sources of error in lung densitometry with CT

RATIONALE AND OBJECTIVES

To determine and analyze the most important error sources in lung CT densitometry in vivo.

METHODS

The authors examined the influences of CT acquisition errors, physiologic changes, and image segmentation errors on lung densitometry. Among others, spatial dependency and long-term reproducibility of the density measurements of blood and air were examined over a period of 4 years in a group of 28 patients with pulmonary emphysema. These results were related to the measured lung densities in this group.

RESULTS

The density measurement of blood and air is strongly dependent on the position in the thorax. Despite full-scanner calibrations, x-ray tube replacement can induce a significant increase in measured blood density.

CONCLUSIONS

A change in a lung density parameter over time can actually be the result of tube replacement or changing blood density. A simple postprocessing technique can correct for these changes.

The effect of DICOM on QCA and clinical trials

Almost without any exemption, new cardiac catheterization laboratories are entirely digital without 35 mm cinefilm as the storage medium. In addition, existing laboratories are increasingly converting to the digital world. Aside from the organizational aspects, this has significant implications for the daily diagnostic review process of the procedures, and for the quantitative analysis of selected frames by QCA. The DICOM standard has now been well accepted in the catheterization laboratories. In stead of mechanical cine projectors, a department must decide on so-called DICOM-Viewers or 'digital Tagarno's'. In this paper the effects of DICOM on image quality and therefore on the visual interpretation of these images, as well as on QCA are discussed. Since the digital images can be enhanced, these look sharper than the conventional cinefilm images. However, edge enhancement has an effect on QCA, reason why the digital data must be stored in raw format. With the enormous amounts of digital data produced in a catheterization laboratory, image compression is of great importance. Currently, an international study is being carried out to determine which compression level is still acceptable from a visual interpretation and QCA point of view. Finally, the implications of the digital era on clinical trials are discussed. One of the important conclusions is that one should be encouraged not to switch from cinefilm to digital in the course of a trial, while a mixed population from the beginning is no problem, as long as the proper statistical calculations are carried out. In conclusion, despite the fact that there are still a number of items to be checked and possibly modified in the standard, the existing DICOM standard has succeeded in bringing widespread utilization of QCA in cardiac angiography closer than ever.

Anatomical model matching with fuzzy implicit surfaces for segmentation of thoracic volume scans

Many segmentation methods for thoracic volume data require manual input in the form of a seed point, initial contour, volume of interest etc. The aim of the work presented here is to further automate this segmentation initialization step. In this paper an anatomical modeling and matching method is proposed to coarsely segment thoracic volume data into anatomically labeled regions. An anatomical model of the thorax is constructed in two steps: 1) individual organs are modeled with blended fuzzy implicit surfaces and 2) the single organ models are grouped into a tree structure with a solid modeling technique named constructive solid geometry (CSG). The combination of CSG with fuzzy implicit surfaces allows a hierarchical scene description by means of a boundary model, which characterizes the scene volume as a boundary potential function. From this boundary potential, an energy function is defined which is minimal when the model is registered to the tissue-air transitions in thoracic magnetic resonance imaging (MRI) data. This allows automatic registration in three steps: feature detection, initial positioning and energy minimization. The model matching has been validated in phantom simulations and on 15 clinical thoracic volume scans from different subjects. In 13 of these sets the matching method accurately partitioned the image volumes into a set of volumes of interest for the heart, lungs, cardiac ventricles, and thorax outlines. The method is applicable to segmentation of various types of thoracic MR-images, provided that a large part of the thorax is contained in the image volume.

Scan optimization of gadolinium contrast-enhanced three-dimensional MRA of peripheral arteries with multiple bolus injections and in vitro validation of stenosis quantification

In this study, a T1-weighted three-dimensional (3D) spoiled gradient-echo scanning protocol was developed to image the complete arterial system of the pelvis and both legs along their entire length in patients with peripheral arterial disease. Three adjacent stations were to be acquired consecutively, with some overlap, to image the entire area of interest; per station one gadolinium (Gd) contrast bolus would be administered. In an in vitro phantom study, the scanning protocol was optimized. The optimal flip angle was found to be 50 degrees. Also, the optimal scan delay was chosen to be equal to the arrival time of the contrast bolus, thereby minimizing artifacts. Three contrast bolus injections showed sufficient enhancement of the vessels after image subtraction. Finally, stenosis quantification by manual caliper was performed by five observers in the magnetic resonance angiography (MRA) images and correlated with the percent diameter reduction determined by quantitative angiography from corresponding X-ray images. The MRA measurements were reproducible, and intra- and interobserver variabilities were statistically non-significant (p=0.54 and p=0.12, respectively). Stenosis quantification performed by four observers showed a good correlation with the X-ray-derived values (rp > 0.90, p < 0.02); the results from one observer were not significantly correlated. Five patients with proven peripheral disease were investigated with this new MRA scanning protocol, using standard hardware and software. The images were of good quality, which allowed adequate clinical evaluation; the original diagnoses obtained from X-ray examinations, were confirmed with MRA. In conclusion, peripheral arterial disease can be evaluated adequately with this magnetic resonance scanning protocol.

Automated measurement of volume flow in the ascending aorta using MR velocity maps: evaluation of inter- and intraobserver variability in healthy volunteers

PURPOSE

An automated contour detection algorithm was developed for the objective and reproducible quantitative analysis of velocity-encoded MR studies of the ascending aorta.

METHOD

The only user interaction required is the manual definition of a center point inside the cross-section of the aorta in one of the available images. The automated contour detection algorithm detects an initial model contour in this image and subsequently corrects for motion and deformation of the aortic cross-section in each of the acquired images over the complete cardiac cycle using dynamic programming techniques. Integrating the flow velocity values for each pixel within the detected contour results in an instantaneous flow value. Next, by integrating the instantaneous flow values for each acquired phase over the complete cardiac cycle, left ventricular stroke volume measurement could be obtained. The results of the automated method were compared with results derived from manually traced contours in MR studies from 11 healthy volunteers.

RESULTS

An excellent agreement in stroke volume measurements was observed: signed difference 0.61+/-1.15%. Inter- and intraobserver variabilities were <2% for both manual and automated image analysis methods. Manual tracing of contours required on the order of 10 min; the analysis time for automated contour detection was <6 s/study.

CONCLUSION

The present contour detection allows fast and reliable left ventricular stroke volume measurements from aortic flow studies using velocity-encoded MR studies in healthy volunteers. Further study is required to assess the accuracy and reproducibility of the algorithm in patients with aortic and aortic valve disease.

The DICOM review stations: are they truly different?

Digital acquisition systems are widely used nowadays. The digitization of the cath lab environment is now directed towards the change in the exchange media from an analog (i.e. cinefilm) to a digital (i.e. CD-R) medium. An important consequence of this development is the need for another type of review system. This article focuses on the replacement of the cineprojector by a digital equivalent: the DICOM review station. Since the technologies differ fundamentally, the DICOM review station has very little in common with its analog predecessor. This article explains the basics of DICOM review stations. Different approaches, both in hardware and in software, are possible, each showing their advantages and drawbacks. The impact of choices made by the industry will be illustrated by a number of commercially available DICOM review stations. Further, the article discusses the topics of diagnostic image quality and performance. In our opinion, these are the major topics when it comes to an objective comparison of the capabilities of DICOM review stations. The relation of these subjects with design choices in terms of hardware and software are discussed.

Fast and accurate automated measurements in digitized stereophotogrammetric radiographs

Until recently, Roentgen Stereophotogrammetric Analysis (RSA) required the manual definition of all markers using a high-resolution measurement table. To automate this tedious and time-consuming process and to eliminate observer variabilities, an analytical software package has been developed and validated for the detection, identification, and matching of markers in RSA radiographs. The digital analysis procedure consisted of the following steps: (1) the detection of markers using a variant of the Hough circle-finder technique; (2) the identification and labeling of the detected markers; (3) the reconstruction of the three-dimensional position of the bone markers and the prosthetic markers; and (4) the computation of micromotion. To assess the influence of film digitization, the measurements obtained from nine phantom radiographs using two different film scanners were compared with the results obtained by manual processing. All markers in the phantom radiographs were automatically detected and correctly labeled. The best results were obtained with a Vidar VXR-12 CCD scanner, for which the measurement errors were comparable to the errors associated with the manual approach. To assess the in vivo reproducibility, 30 patient radiographs were analyzed twice with the manual as well as with the automated procedure. Approximately, 85% of all calibration markers and bone markers were automatically detected and correctly matched. The calibration errors and the rigid-body errors show that the accuracy of the automated procedure is comparable to the accuracy of the manual procedure. The rigid-body errors had comparable mean values for both techniques: 0.05 mm for the tibia and 0.06 mm for the prosthesis. The reproducibility of the automated procedure showed to be slightly better than that of the manual procedure. The maximum errors in the computed translation and rotation of the tibial component were 0.11 mm and 0.24, compared to 0.13 mm and 0.27 for the manual RSA procedure. The total processing time is less than 10 min per radiograph, including interactive corrections, compared to approximately 1 h for the manual approach. In conclusion, a new and widely applicable, computer-assisted technique has become available to detect, identify, and match markers in RSA radiographs and to assess the micromotion of endoprostheses. This new technique will be used in our clinic for our hip, knee, and elbow studies.

MR of the heart under pharmacologic stress

Magnetic resonance imaging is one method for assessing cardiac function and perfusion at rest and under stress conditions. In this article, the potential of stress magnetic resonance imaging for evaluating ischemic heart disease is reviewed, and technical aspects of some developments that may contribute to comprehensive magnetic resonance imaging assessment of heart disease under rest and stress are discussed.

Variations in blood flow waveforms in stenotic renal arteries by 2D phase-contrast cine MRI

Waveform variations in blood flow measurements through stenotic renal arteries have been reported already with echo Doppler studies. We studied these variations with MRI in 14 patients (mean age, 60 years) with suspected renal arterial stenosis (24 patent arteries, four occluded). Flow measurements were successful in 15 arteries and unsuccessful in nine, due to practical limitations. Seven healthy younger volunteers (mean age, 28 years) and five healthy older volunteers (mean age, 58 years) were recruited for comparison purposes. In patients, the severity of stenoses was also assessed by digital subtraction angiography and intraarterially measured transstenotic pressure drops. We found flow patterns to be statistically significantly (P < 0.01) age-related. Younger healthy subjects showed shorter wave duration, higher diastolic flow, and total blood flow per minute. Also, with increasing stenosis severity, the systolic wave became more damped and the systolic wave duration became statistically significantly (P = .03) longer.

Objective stenosis quantification from post-stenotic signal loss in phase-contrast magnetic resonance angiographic datasets of flow phantoms and renal arteries

In this study a semi-automated and observer-independent algorithm for quantifying post-stenotic signal loss (PSL) in three-dimensional phase-contrast (PC) magnetic resonance angiography (MRA) of patients with renal artery stenosis is presented. This algorithm was developed on MRA datasets of stenotic phantoms, included in a flow circuit with stationary flows. The length and the severity of the PSL (incorporating both the length and the degree of PSL) in the MRA datasets were proposed for quantifying the stenoses. The algorithm was tested in renal arteries; ten patients with renal artery stenosis and seven healthy volunteers were investigated. Digital subtraction angiography was performed in the patients and served as the gold standard. Stenosis severity showed better correlation with the severity of the PSL than with the length, both for in vitro and in vivo measurements. Spearman correlation coefficients (rs) showed statistically significant correlations between the severity of the PSL and parameters determined by digital subtraction angiography, i.e., percent diameter stenosis (rs = 0.90). The length of the PSL showed no correlation with the diameter stenosis (rs = 0.37). In conclusion, this study presents a semi-automated and observer-independent way of quantifying signal loss, and the severity of the PSL is proposed for quantifying stenoses, rather than the length of PSL.

Quantitative coronary arteriography: current status and future

Quantitative coronary arteriography (QCA) has been accepted as a means for the objective assessment of vessel sizing. Gradient field transform (GFT) is now available as a third generation QCA approach for the quantification of complex morphology. In the meantime the DICOM-3 (DICOM: Digital Imaging and Communications in Medicine) standard has been accepted for the exchange of digital data acquired in a catheterization laboratory. Issues to be resolved in digital imaging include the basic question of whether the commonly used matrix size of 512 x 512 pixels and 8 bits of density resolution is really sufficient to appreciate the same fine details as are visible on cinefilm. Other major issues of differences between the conventional cinefilm and the modern digital approach are edge enhancement and image compression. We believe that digital imaging and the DICOM-3 standard are here to stay; although the transition period may take longer and be hampered in practice by more hurdles than were originally anticipated, in a few years' time, 35-mm film will be an exception.

Evaluation of an automatic intraluminal edge detection technique for intravascular ultrasound images

Intravascular ultrasound (IVUS) imaging enables detailed analysis and precise measurements of vascular cross-sections. However, to achieve a reduction in the existing level of observer variability requires the development of quantitative IVUS. We have developed a fully automatic intraluminal edge detection technique, based on adaptive active contour models and called ADDER (adaptive damping dependent on echographic regions) that allows the quantitation of the intraluminal cross-sectional area (ICSA). Using a 30-MHz mechanically rotated transducer mounted at the tip of a 3.5-F catheter, 58 normal and pathologic arterial segments (from coronary, renal, splenic, iliac, and carotid arteries) were imaged in vitro. These images were analyzed by 2 experts, E1 and E2, who manually traced the intraluminal contour twice for each image, as well as with ADDER. Intra-observer variabilities for ICSAs were found to be excellent (-1.454 +/- 3.51% for E1, 0.96 +/- 5.4% for E2). The inter-observer variability was 2.1 +/- 4.3%. The success factor for ADDER was 89%. Its intra-observer variability was null, as the method always finds a unique contour. The correlation between the automatically detected ICSA and the manual ICSA was: r = 0.99 (y = 1.03x + 0.89 mm2). Morphometric variations between manually and automatically traced contours, analyzed by the centerline method, were 100 +/- 140 mm on average. In conclusion, the ADDER automatic contour detection applied to IVUS images is robust and characterized by small systematic and random errors; therefore, quantitative IVUS is a useful tool in clinical research trials.

Derivation of optimal filters for the detection of coronary arteries

In this paper optimal filters for the detection of coronary arteries with a diameter range of 0.5-6.0 mm in digital X-ray images are derived using a computational approach. This approach is based on the two requirements for optimal detection. First, the filter should maximize the number of detected true edges and minimize the number of detected false edges. Second, if an edge has been detected, its position should be as close as possible to the true edge position in the image. Since the grey value profile in a digital X-ray image associated with an arterial vessel is asymmetric, the theory on edge detection derived by Canny has been expanded with two additional boundary constraints to make it suitable for the derivation of filters for asymmetric edges. It is demonstrated that it is possible to derive optimal filters for coronary segments. The localization error, defined by the square root of the sum of the squared systematic and random errors in the assessment of the arterial diameter, depends on the size of the coronary artery and the amount of noise in the image. In this paper, an evaluation study is described to assess the relationship between localization error and the amount of noise upon the vessel profile. For that purpose, an analytical description of the vessel profile in an angiographic image was derived. For the larger arteries the relation between noise and localization error was found to be linear and no systematic over- or underestimations were observed, even if the noise level was very high. However, it can be shown that the smallest diameter that can be measured depends on the amount of noise present in the data. Even for images that contain only a low amount of noise, arterial diameters below 0.7 mm cannot be measured accurately. If the noise in the image increases, the lowest measurable arterial diameter value also increases. Also the random error increases rapidly for vessel diameters below 1.2 mm, but with a limited amount of noise and a diameter value above 0.7 mm the random error is still acceptable [0.15 mm (21%) for 0.7-mm vessels, 0.06 mm (6%) for 1-mm vessels].

Clinical and angiographic outcome of Micro Stent II implantation in native coronary arteries

To evaluate immediate success and 6-month restenosis rate, 70 Micro Stents II were implanted for 65 stenoses in 63 patients (age 59+/-9 years). Stable angina pectoris was present in 47% of the patients (38% class I to III; 9% class IV), whereas 32% had postinfarction angina and 21% had unstable angina. Indications for stent implantation were elective in 62% and semi-elective in 38% of the patients. Sixty-two percent of the patients received ticlopidin and acetylsalicylic acid for 28 days, whereas 38% of the patients received only acetylsalicylic acid. All stents were deployed successfully at the target site. Subacute closure occurred in 2 patients (3%), both of whom were not treated with ticlopidin. Two other patients (3%) developed non-Q-wave infarction after side branch occlusion during the procedure. The minimum lumen diameter increased from 1.0+/-0.5 mm to 2.8+/-0.4 mm after stent implantation. At follow-up the loss in diameter was 0.9+/-0.6 mm, indicating a net gain of 0.9+/-0.8 mm. Late clinical events (4 weeks to 6 months) were coronary angioplasty of a stented segment (3%), coronary angioplasty of a nonstented segment (10%), and coronary artery bypass grafting (2%). No deaths or myocardial infarction occurred. The procedural success rate was 94% and the event-free survival at 6-month follow-up was 79%. Micro Stent II implantation can be done with a high rate of immediate success and good 6-month outcome. The Micro Stent II has proven to be a versatile device that can also be used in patients with less favorable coronary anatomy or lesion characteristics.

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.

Micro stent I, initial results, and six months follow-up by quantitative coronary angiography

The Micro stent (MS) is a balloon expandable stent that allows the treatment of stenoses in distal and tortuous coronary arteries. This prospective study was performed to evaluate initial and late results of MS implantations. A total of 127 MS (101 in native coronary arteries and 26 in saphenous vein grafts) were implanted in 85 patients (1.5 stents/pt, 65 male, and 20 female, age 62, +/-10 yr) with angina pectoris class II-III: 21 (25%), angina pectoris class IV: 41(48%), and acute myocardial infarction: 23 (27%). Indications per segment treated (n=93): elective: 49 (53%); suboptimal balloon angioplasty (PTCA) result: 33 (35%); bailout: 11 (12%). The patients were discharged with 100 mg of aspirin daily unless other indications for oral anticoagulants were present. Procedural success (diameter stenosis of 30% without the occurrence of clinical events within 3 wk) was 85%. Early clinical events (<3 wk included: death:1%; subacute closure: 5%; coronary artery bypass surgery (CABG): 1%; vascular complications: 4%. Late clinical events (3 wk-6 mo) included: acute myocardial infarction:3%, PTCA 5%, CABG 3%, angina class Ill-IV: 4%. Quantitative angiographic results were: the minimum lumen diameter increased from 0.90+/-0.72 before to 3.05+/-0.48 mm (<P0.001) after stent implantation. At follow-up, which was 5.5 mo +/-1.1 mo, 61/79 pts (77%), the loss in diameter was 0.90+/-0.68 mm. The net gain was 1.26+/-0.90 mm. The restenosis rate (diameter stenosis > 50% at FU) was 13%. This study demonstrates high procedural and late success rates of Micro stent implantations.