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

Advanced deep learning methodology for accurate, real-time segmentation of high-resolution intravascular ultrasound images

AIMS

The aim of this study is to develop and validate a deep learning (DL) methodology capable of automated and accurate segmentation of intravascular ultrasound (IVUS) image sequences in real-time.

METHODS AND RESULTS

IVUS segmentation was performed by two experts who manually annotated the external elastic membrane (EEM) and lumen borders in the end-diastolic frames of 197 IVUS sequences portraying the native coronary arteries of 65 patients. The IVUS sequences of 177 randomly-selected vessels were used to train and optimise a novel DL model for the segmentation of IVUS images. Validation of the developed methodology was performed in 20 vessels using the estimations of two expert analysts as the reference standard. The mean difference for the EEM, lumen and plaque area between the DL-methodology and the analysts was ≤0.23mm² (standard deviation ≤0.85mm²), while the Hausdorff and mean distance differences for the EEM and lumen borders was ≤0.19 mm (standard deviation≤0.17 mm). The agreement between DL and experts was similar to experts' agreement (Williams Index ranges: 0.754-1.061) with similar results in frames portraying calcific plaques or side branches.

CONCLUSIONS

The developed DL-methodology appears accurate and capable of segmenting high-resolution real-world IVUS datasets. These features are expected to facilitate its broad adoption and enhance the applications of IVUS in clinical practice and research.

A state-of-the-art review on segmentation algorithms in intravascular ultrasound (IVUS) images

Over the past two decades, intravascular ultrasound (IVUS) image segmentation has remained a challenge for researchers while the use of this imaging modality is rapidly growing in catheterization procedures and in research studies. IVUS provides cross-sectional grayscale images of the arterial wall and the extent of atherosclerotic plaques with high spatial resolution in real time. In this paper, we review recently developed image processing methods for the detection of media-adventitia and luminal borders in IVUS images acquired with different transducers operating at frequencies ranging from 20 to 45 MHz. We discuss methodological challenges, lack of diversity in reported datasets, and weaknesses of quantification metrics that make IVUS segmentation still an open problem despite all efforts. In conclusion, we call for a common reference database, validation metrics, and ground-truth definition with which new and existing algorithms could be benchmarked.

Coronary microvascular resistance: methods for its quantification in humans

Coronary microvascular dysfunction is a topic that has recently gained considerable interest in the medical community owing to the growing awareness that microvascular dysfunction occurs in a number of myocardial disease states and has important prognostic implications. With this growing awareness, comes the desire to accurately assess the functional capacity of the coronary microcirculation for diagnostic purposes as well as to monitor the effects of therapeutic interventions that are targeted at reversing the extent of coronary microvascular dysfunction. Measurements of coronary microvascular resistance play a pivotal role in achieving that goal and several invasive and noninvasive methods have been developed for its quantification. This review is intended to provide an update pertaining to the methodology of these different imaging techniques, including the discussion of their strengths and weaknesses.

Quantification of coronary plaque by 64-slice computed tomography: a comparison with quantitative intracoronary ultrasound

BACKGROUND

Noninvasive assessment of coronary atherosclerotic plaque may be useful for risk stratification and treatment of atherosclerosis.

MATERIALS AND METHODS

We studied 47 patients to investigate the accuracy of coronary plaque volume measurement acquired with 64-slice multislice computed tomography (MSCT), using newly developed quantification software, when compared with quantitative intracoronary ultrasound (QCU). Quantitative MSCT coronary angiography (QMSCT-CA) was performed to determine plaque volume for a matched region of interest (regional plaque burden) and in significant plaque defined as a plaque with > or =50% area obstruction in QCU, and compared with QCU. Dataset with image blurring and heavy calcification were excluded from analysis.

RESULTS

In 100 comparable regions of interest, regional plaque burden was highly correlated (coefficient r = 0.96; P < 0.001) between QCU and QMSCT-CA, but QMSCT-CA overestimated the plaque burden by a mean difference of 7 +/- 33 mm3 (P = 0.03). In 76 significant plaques detected within the regions of interest, plaque volume determined by QMSCT-CA was highly correlated (r = 0.98; P < 0.001) with a slight underestimation of 2 +/- 17 mm3 (P = not significant) when compared with QCU. Calcified and mixed plaque volume was slightly overestimated by 4 +/- 19 mm3 (P = ns) and noncalcified plaque volume was significantly underestimated by 9 +/- 11 mm3 (P < 0.001) with QMSCT-CA. Overall, the limits of agreement for plaque burden/volume measurement between QCU and QMSCT-CA were relatively large. Reproducibility for the measurements of regional plaque burden with QMSCT-CA was good, with a mean intraobserver and interobserver variability of 0% +/- 16% and 4% +/- 24%, respectively.

CONCLUSIONS

Quantification of coronary plaque within selected proximal or middle coronary segments without image blurring and heavy calcification with 64-slice CT was moderately accurate with respect to intravascular ultrasound and demonstrated good reproducibility. Further improvement in CT resolution is required for more reliable measurement of coronary plaques using quantification software.

Quantification of atherosclerotic coronary plaque components by submillimeter computed tomography

BACKGROUND

Although several investigations have shown that multi-detecor row computed tomography (MDCT) of the coronary arteries can detect noncalcified atherosclerotic plaque, it has remained unresolved if the method also determines features of a rupture-prone plaque. We set out to correlate the size of atherosclerotic plaque components with cardiac MDCT with histology.

METHODS AND RESULTS

In 30 autopsy cases, hearts were isolated, coronary arteries filled with contrast agent, and depicted with a clinical 16-row detector CT with a slice thickness of 0.63 mm. Transections of the three main coronary arteries were reconstructed and compared with histopathologic sections using light microscopy. MDCT measurements of total plaque area (r = 0.73, P < 0.0001) and calcified plaque area (r = 0.83, P < 0.0001) correlated well with histopathology, while measurements of non-calcified plaque area (r = 0.53, P < 0.0001) and lipid core size (r = 0.43; P < 0.0001) correlated less well. MDCT overestimated all plaque areas except lipid core size, which was underestimated.

CONCLUSIONS

Coronary CT provides an accurate and reproducible method for the quantitative assessment of total plaque and calcified plaque areas. However, the method is less accurate for the quantification of non-calcified plaque area and lipid core size, which is ascribed to limited spatial and contrast resolution. With the present technique, the detection of vulnerable plaques by MDCT remains uncertain.

Reproducible coronary plaque quantification by multislice computed tomography

BACKGROUND

The aim of this study was to investigate reproducibility and accuracy of computer-assisted coronary plaque measurements by multislice computed tomography coronary angiography (QMSCT-CA).

METHODS AND RESULTS

Forty-eight patients undergoing MSCT-CA and coronary arteriography for symptomatic coronary artery disease and quantitative intravascular ultrasound (IVUS, QCU) were examined. Two investigators performed the QMSCT-CA twice and a third investigator performed the QCU, all blinded for each other's results. There was no difference found for the matched region of interest (ROI) lengths (QCU 29.4 +/- 13 mm vs. QMSCT-CA 29.6 +/- 13 mm, P = 0.6; total length = 1,400 mm). The comparison of volumetric measurements showed (lumen QCU 267 +/- 139 mm(3) vs. mean QMSCT-CA 177 +/- 91 mm(3), P < 0.001; vessel 454 +/- 194 mm(3) vs. 398 +/- 187 mm(3), P <<0.001; and plaque 189 +/- 93 mm(3) vs. 222 +/- 121 mm(3); investigator 1, P = 0.02; and investigator 2, P = 0.07) significant differences. Automated lumen detection was also applied for QMSCT-CA (218 +/- 112 mm(3), P < 0.001 vs. QCU). The interinvestigator variability measurements for QMSCT-CA showed no significant differences.

CONCLUSION

QMSCT-CA systematically underestimates absolute coronary lumen- and vessel dimensions when compared with QCU. However, repeated measurements of coronary plaque by QMSCT-CA showed no statistically significant differences, although, the outcome showed a scattered result. Automated lumen detection for QMSCT-CA showed improved results when compared with those of human investigators.

Dedicated calibration formulas permit correction of differences between measurements by different IVUS devices as demonstrated in atherosclerotic human coronary arteries in vitro

Serial intravascular ultrasound (IVUS) measurements of coronary vessel dimensions are major endpoints of studies focusing on pharmacological interventions, efficiency of drug eluting stents, and vascular remodeling. In serial studies measurement variability among different IVUS devices may cause substantial misinterpretation and error. We analyzed 33 human coronary plaques in vitro using two different IVUS systems (mechanical IVUS system with a 40 MHz Atlantis SR catheter; solid-state electronic IVUS system with a 20 MHz Invision catheter) and repeatedly measured the total vessel, lumen, and plaque + media cross-sectional area and plaque burden (plaque + media area divided by total vessel area). Between the "raw" measurements made by the two devices, there was a significant difference for both plaque + media area (2.35+/-1.86 mm(2), P < 0.01) and plaque burden (5.39+/-3.68%, P < 0.05). Measurements were then corrected by use of recently introduced calibration formulas; as a result the differences decreased significantly for all IVUS parameters measured ( P < 0.0001). After correction, the remaining differences between the corrected mechanical and solid-state IVUS measurements similar to differences between repeated measurements with the same IVUS device (i.e., the intraobserver variability). Thus, in serial studies the use of different IVUS devices at index and follow-up procedure may introduce a substantial error as a result of system-related differences. The application of dedicated calibration formulas allows for correction for these differences by decreasing such differences to the level of intraobserver variability.

Volumetric Quantitative Analysis of Tissue Characteristics of Coronary Plaques After Statin Therapy Using Three-Dimensional Integrated Backscatter Intravascular Ultrasound

OBJECTIVES

The purpose of the present study was twofold: 1) to evaluate the usefulness of three-dimensional (3D) integrated backscatter (IB) intravascular ultrasound (IVUS) for quantitative tissue characterization of coronary plaques; and 2) to use this imaging technique to determine if six months of statin therapy alters the tissue characteristics of coronary plaques.

BACKGROUND

Three-dimensional IVUS techniques for quantitative tissue characterization of plaque composition have not been developed.

METHODS

Radiofrequency (RF) signals were obtained using an IVUS system with a 40-MHz catheter. The IB values of the RF signal were calculated and color-coded. The 3D reconstruction of the color-coded map was performed by computer software. A total of 18 IB IVUS images were captured at an interval of 1 mm in each plaque. A total of 52 patients with hyperlipidemia were randomized to treatment with pravastatin (20 mg/day, n = 17), atorvastatin (20 mg/day, n = 18), or diet (n = 17) for six months. The tissue characteristics of arterial plaque in each patient (one arterial segment per patient) were analyzed with 3D IB IVUS before and after treatment.

RESULTS

Significant increases of fibrous volume (pravastatin: 25.4 +/- 6.5% to 28.1 +/- 6.1%; atorvastatin: 26.2 +/- 5.7% to 30.1 +/- 5.5%) and mixed lesion volume (atorvastatin: 25.5 +/- 6.6% to 28.7 +/- 5.1%) and a reduction of lipid volume (pravastatin: 25.5 +/- 5.7% to 21.9 +/- 5.3%; atorvastatin: 26.5 +/- 5.2% to 19.9 +/- 5.5%) were observed after statin therapy.

CONCLUSIONS

Statin therapy reduced the lipid component in patients with stable angina without reducing the degree of stenosis. Three-dimensional IB IVUS offers the potential for quantitative volumetric tissue characterization of coronary atherosclerosis.

Non-invasive measures of pulse wave velocity correlate with coronary arterial plaque load in humans

OBJECTIVE

Arterial stiffness is an emerging major risk factor for cardiovascular morbidity and mortality. The aim of the present study was to assess if coronary artery plaque load correlates with non-invasive measures of arterial stiffness.

DESIGN

Prospective investigational study.

SETTING

Tertiary university hospital centre.

PATIENTS

Patients undergoing elective diagnostic coronary angiography.

INTERVENTIONS AND MAIN OUTCOME MEASURES

Coronary artery plaque burden was assessed using a 30 MHz intravascular ultrasound catheter during an automated pullback. Proximal coronary artery plaque volume was determined using a validated edge-detection algorithm following three-dimensional computerized reconstruction. Central arterial stiffness was assessed in each patient using applanation tonometry to radial, carotid and femoral pulses, with derivation of aortic pressure augmentation and pulse wave velocity using pulse wave analysis.

RESULTS

In 35 patients (61 +/- 2 years), proximal coronary arterial plaque volume was 5.9 +/- 0.6 mm3/mm of vessel. Plaque volume correlated positively with carotid-radial pulse wave velocity (r = 0.47, P = 0.008) and appeared to correlate with carotid-femoral pulse wave velocity (r = 0.34, P = 0.07). Aortic augmentation (r = 0.24, P = 0.16), augmentation index (r = 0.3, P = 0.08), and pulse pressure (r = 0.22, P = 0.2) did not correlate significantly with proximal coronary artery plaque volume.

CONCLUSIONS

Non-invasive measures of carotid-radial pulse wave velocity correlate with the extent of coronary artery plaque volume and may be a useful non-invasive surrogate marker for the extent of coronary atherosclerosis. Our findings are consistent with the suggestion that central aortic stiffness may promote the development of coronary atherosclerosis and ischaemic heart disease.

Angiographically silent left main disease detected by intravascular ultrasound: a marker for future adverse cardiac events

BACKGROUND

Concomitant moderate obstructive left main (LM) disease is associated with future cardiac events and poor prognosis in patients undergoing percutaneous intervention (PCI). Whether prognosis is similarly effected by LM disease not detected by angiography, but evident on intravascular ultrasound (IVUS) imaging, is not known. The purpose of this study was to evaluate the long-term prognosis of patients with angiographically insignificant LM coronary artery disease undergoing PCI.

METHODS AND RESULTS

One hundred and seven consecutive patients undergoing PCI with angiographically normal or mild LM disease had 2- and 3-dimensional IVUS imaging. IVUS images were digitized, and 3-dimensional reconstruction was performed. Percent diameter and area stenosis by angiography were 4.8% +/- 3.5% and 18.2% +/- 9.8%, respectively. IVUS mean luminal area and area stenosis were 17.9 +/- 5.6 mm2 and 30.2% +/- 14.7%, respectively. Long-term follow-up was available in 102 (95%) patients at a median of 29 (range 8-52) months. Major adverse cardiac events, defined as death (6), myocardial infarction (4), repeat PCI (13), or CABG (16), were associated with female sex (P =.04), diabetes (P =.02), angiographic minimum lumen diameter (P =.04), and IVUS minimum (P =.01) and mean (P =.01) lumen area. Multivariate predictors of late cardiac events were diabetes (hazard ratio 2.69, P =.014) and minimum lumen area by IVUS (hazard ratio 0.59, P =.015).

CONCLUSIONS

Despite being angiographically silent, LM disease detected by IVUS is an independent predictor of cardiac events and may serve as a marker for such events. These data extend the spectrum of LM disease severity and its relationship to cardiac prognosis in patients undergoing PCI.

Evaluation of vascular injury following percutaneous transluminal coronary angioplasty: a comparison of the accuracy of two- and three-dimensional intracoronary ultrasound imaging

BACKGROUND

Following percutaneous transluminal coronary angioplasty (PTCA), the extent of vascular injury is underestimated by angiographic assessment. Conventional intracoronary ultrasound (ICUS) imaging provides additional information with regard to the extent of dissections but requires mental reconstruction of consecutive images. Three-dimensional ICUS reconstruction overcomes this limitation and may provide more accurate assessment of the extent of vascular injury. This study compares conventional two-dimensional ICUS imaging to combined two- and three-dimensional ICUS information in the assessment of vascular injury following PTCA.

METHODS

Atherosclerotic, human coronary arteries (n=24) were studied in a specially constructed flow system. Balloon dilatation of significant stenoses was performed followed by assessment using two- and three-dimensional ICUS imaging methods. Treated arteries were submitted for histological assessment after pressure fixation. Dissection depth and length measurements were made from obtained images and compared to histomorphometric assessments.

RESULTS

Of the 20 arterial segments confirmed histologically to contain dissection, 11 (55%) and 18 (90%) were identified by two-dimensional ICUS and combined two- and three-dimensional ICUS respectively. The kappa values for correlation of dissection type were 0.29 (0.23-0.35) and 0.64 (0.57-0.71) respectively indicating better agreement using combined two- and three-dimensional ICUS. Two-dimensional ICUS consistently underestimated dissection length (3.52+/-1.75 mm compared with 6.54+/-2.42 mm, P<0.001) and depth (0.61+/-0.24 mm compared with 0.92+/-0.32 mm, P=0.001). Combined two- and three-dimensional ICUS produced accurate dissection length (6.13+/-2.29 mm compared with 6.54+/-2.42 mm, P=0.09) and depth (0.86+/-0.32 mm compared with 0.92+/-0.32 mm, P=0.28) estimations.

CONCLUSION

Computerized three-dimensional reconstruction of ICUS images provides improved accuracy compared to conventional ICUS imaging in the detection and quantitation of arterial dissection. This technique would be a useful adjunct to angiography for the precise assessment of vascular injury following PTCA.

Automated three-dimensional assessment of coronary artery anatomy with intravascular ultrasound scanning

BACKGROUND

Angiography allows the definition of advanced, severe stages of coronary artery disease, but early atherosclerotic lesions, which do not lead to luminal stenosis, are not identified reliably. In contrast, intravascular ultrasound scanning allows the precise characterization and quantification of a wide range of atherosclerotic lesions, independent of the severity of luminal stenosis.

METHODS

Three-dimensional (3-D) reconstruction of entire coronary segments is possible with the integration of sequential 2-dimensional tomographic images and allows volumetric analysis of coronary arteries.

RESULTS

Automated systems able to recognize lumen and vessel borders and to display 3-D images are becoming available.

CONCLUSION

These systems have the potential for on-line 3-D image reconstruction for clinical decision-making and fast routine volumetric analysis in research studies. This review describes 3-D intravascular ultrasound scanning acquisition, analysis, and processing, and the associated technical challenges.

Validation of an automated system for luminal and medial-adventitial border detection in three-dimensional intravascular ultrasound

The precise tomographic assessment of coronary artery disease by intravascular ultrasound (IVUS) is useful in quantitative studies. Such studies require identification of luminal and medial-adventitial (MA) borders in a sequence of IVUS images. We have developed a three-dimensional (3D) active-surface system for border detection that facilitates the analysis of many images with minimal user interaction. To assess the validity of the technique, luminal and MA borders in 529 end-diastolic images from nine coronary arterial segments (58.8 +/- 14.2 images per patient) were traced manually by four experienced observers. The computer-detected borders were compared with borders determined by the four observers using a modified Williams' index (WI), the ratio of inter-observer variability to computer-observer variability. While manual tracing required 49.2 +/- 12.1 min for analysis, the analysis system identified luminal (R2 = 0.92) and MA borders (R2 = 0.97) in 13.8 +/- 4.0 min, a decrease of 35.4 min (p < 0.000001). The computer minus observer differences in lumen area and MA area were -0.88 +/- 0.90 and -0.07 +/- 0.63 mm2. Therefore, the computer system underestimated both lumen and MA area, but this effect was very small in MA area. The WI values and 95% confidence intervals were 0.98 (0.89,1.06) for luminal border detection and 0.99 (0.95,1.04) for MA border detection. Plaque volume measurements, a common endpoint of clinical trials, also verified the accuracy of the technique (R2 = 0.98). The proposed 3D active-surface border detection system provides a faster and less-tedious alternative to manual tracing for assessment of coronary artery anatomy in vivo.

Time dependent changes of arterial distensibility induced by cholesterol and balloon injury in rabbits: an in vivo intravascular ultrasound study

The aim of this study was to validate in vivo measurement of intravascular ultrasound (IVUS) for the analysis of structural and functional vessel wall alterations in a chronic animal model. Furthermore, the relation between functional and structural alteration of the vessel wall should be investigated. Fifteen cholesterol-fed rabbits (1%) and 15 control rabbits underwent balloon injury of the abdominal aorta. Immediately before and after balloon traumatization as well as 2 and 6 weeks later IVUS depiction of 10 aortal vessel segments was performed (n = 1,100 measurements). In vivo IVUS measurements and morphometric analysis of the neointimal area of same aortal segments showed a high correlation (n = 148, r = 0.844, p < 0.001). Plaque area determined by morphometry revealed larger areas than the evaluation by IVUS (0.162 +/- 0.138 vs. 0.130 +/- 0.126 mm2, p < 0.001). Before balloon traumatization, pulsatility of the aortal vessel segments was less in cholesterol-fed rabbits (0.067 vs. 0.090, p < 0.01) and neointimal index higher (0.003 vs. 0). Investigation using IVUS 2 and 6 weeks after balloon traumatization demonstrated a continuous loss of arterial distensibility and an increase of neointimal index, being more pronounced in the cholesterol-fed group. As demonstrated by IVUS the loss of distensibility preceded the atherosclerotic alterations. Our investigation suggests using IVUS in this animal model is a reliable setting for long-term investigation of characteristics of the vessel wall. We could demonstrate that altered function of the vessel wall precedes the structural atherosclerotic vessel wall alterations.

Progression of coronary atherosclerosis quantified by analysis of 3-D reconstruction of left coronary arteries

OBJECTIVES

Quantitative measurements on three-dimensional (3-D) reconstructed coronary trees permit accurate evaluation of vascular volumes, lengths and diameters. We applied this technique to investigate diffuse luminal narrowing in patients with the clinical manifestation of progressive atherosclerosis.

METHODS

In 13 patients who presented repeatedly for coronary angioplasty (at least 4 years of invasive follow-up), left coronary arteries were reconstructed in 3-D from biplane coronary angiograms. Mean diameter, cross-sectional areas, total length, and volume were calculated for segments and branches. Five patients without coronary artery disease served as controls.

RESULTS

Patients with progressive coronary atherosclerosis demonstrated a significant reduction of total vascular volumes, mean diameters and cross-sectional areas at the initial investigation when compared with controls. Progressive luminal shrinkage occurred during follow-up (-0.04+/-0.13 mm per year and per segmental diameter). The progress of luminal narrowing in patients with coronary artery disease is related to the number of coronary risk factors and the duration of follow-up.

CONCLUSION

Quantitative measurements on 3-D reconstructed coronary trees are a useful investigative tool for the assessment of progression of coronary atherosclerosis.

Impact of nonmeasurable borders and variation in cross-section counts on intravascular ultrasound measurement of atherosclerotic plaque volume

The inability to measure borders and variation in the number of 1-mm cross sections acquired from an identical length of vessel in serial intravascular ultrasound (IVUS) pullbacks represents potential errors in calculating volumes by IVUS. In a clinical IVUS trial, the percentage of nonmeasurable lumen and external elastic membrane borders, and the percent variation in the number of 1-mm cross sections acquired from an identical vessel length at 2 separate time points, were determined. A statistical model that simulated the effect of varying the percentage of the total number of cross sections in a pullback (i.e., sample fraction) was developed using SAS software. Mean and maximum errors for calculation of atheroma volume for each sample fraction were determined. The mean percentage of nonmeasurable lumen and external elastic membrane borders in an individual patient was 8.4 +/- 8.4% and 17.4 +/- 18.4%, respectively. Mean variation in the number of 1-mm cross sections acquired in serial studies was 5.6 +/- 6.2%. A decrease in sample fraction from 95% to 50% was associated with a linear increase in the mean and maximum errors in atheroma volume, from 2.0 +/- 0.9% and 5.9 +/- 3.0%, to 7.1 +/- 2.8% and 23.4 +/- 10.3%, respectively. Thus, nonmeasurable borders and variation in the number of 1-mm cross sections acquired from an identical length of vessel in serial studies are real considerations in clinical IVUS trials. However, given the reported incidence of these considerations in this clinical trial, our statistical model suggests that the impact of each of these considerations on atheroma volume calculation is small.

Quantification of coronary artery lumen volume by digital angiography: in vivo validation

BACKGROUND

Coronary artery lumen volume may potentially have several advantages over the commonly used variables, such as percent stenosis or minimal lumen diameter, in the assessment of coronary artery disease. The goal of this study is to validate a quantitative assessment of lumen volume using a video densitometry technique.

METHODS AND RESULTS

Coronary arteriography was performed in 9 swine (body weight 20 to 55 kg) after power injection of contrast material (2 mL/s for 3 seconds) into the left main coronary artery. Phase-matched subtracted images were used to quantify regional lumen volume by a video densitometry technique. The in vivo volume measurements were validated by a polymer cast of the coronary arterial tree made at physiological pressure. The measured cast volume (V(C)) and video densitometric regional lumen volume (V(VD)) were related by V(VD)=1.06 V(C)-0.01 mL (r=0.99). The root mean square and systematic errors for these measurements were 17% and -3%, respectively.

CONCLUSIONS

A video densitometry technique for quantification of coronary lumen volume was validated both in vitro and in vivo in a swine animal model. The present results demonstrated the feasibility and potential utility of the video densitometry technique for accurate measurement of regional lumen volume in vivo. This study contributes to the understanding of the angiographic methods used for the assessment of coronary artery disease and indicates that this technique can potentially be used for quantification of diffuse coronary artery disease during routine coronary arteriography.

Intravascular ultrasound assessment of ambiguous coronary lesions

Accurate assessment of coronary lesions is essential for clinical decision-making. While angiography has long been accepted as the gold standard investigation, this technique provides only a planar 2-D silhouette of the arterial lumen and therefore has limited accuracy in the setting of vessel tortuosity or overlap, bifurcational and eccentric lesions, and diffusely diseased arteries. By providing high-resolution cross-sectional imaging through the arterial wall, intravascular ultrasound (IVUS) can overcome many of these limitations and accurately quantify angiographically indeterminate lesions. Angiographic evaluation of the left main coronary artery presents particular challenges that are ideally resolved with IVUS examination. The role of IVUS in the assessment of coronary stenoses of angiographically intermediate severity (50-70%) continues to evolve. Recent data correlating IVUS with intracoronary flow and pressure measurements suggest that epicardial coronary artery lesions with minimum lumen area of less than 3-4 mm2 may be haemodynamically significant. In addition to accurately quantifying minimum lumen diameter and area at the lesion site, IVUS can characterise coronary artery plaque morphology, and it may have the potential to predict plaque complications.

On the IVUS plaque volume error in coronary arteries when neglecting curvature

Plaque volume determined by common linear 3-D IVUS analysis systems will show under- or overestimation in curved vessel segments because these systems approximate the true 3-D transducer pull-back trajectory by a straight line. We developed a mathematical model that showed that the error is primarily dependent on the curvature of the pull-back trajectory and not on vessel tortuosity. Furthermore, we measured this error in vivo in the coronary arteries of 15 patients, comparing the plaque volume using a true 3-D reconstruction method with that of the linear approach. The in vivo plaque volume error ranged from 2.3% to -1.2% for 15 coronary segments with lengths ranging from 38.8 to 89.1 mm (62.2 +/- 13 mm). The volume error introduced by linear 3-D IVUS analysis systems is dependent on the curvature of the pull-back trajectory. The error measured in vivo was small and inversely related to segment length.

Evaluation of three-dimensional segmentation algorithms for the identification of luminal and medial-adventitial borders in intravascular ultrasound images

Intravascular ultrasound (IVUS) provides direct depiction of coronary artery anatomy, including plaque and vessel area, which is important in quantitative studies on the progression or regression of coronary artery disease. Traditionally, these studies have relied on manual evaluation, which is laborious, time consuming, and subject to large interobserver and intraobserver variability. A new technique, called active surface segmentation, alleviates these limitations and makes strides toward routine analyses. However, for three-dimensional (3-D) plaque assessment or 3-D reconstruction to become a clinical reality, methods must be developed which can analyze many images quickly. Presented is a comparison between two active surface techniques for three-dimensional segmentation of luminal and medial-adventitial borders. The force-acceleration technique and the neighborhood-search technique accurately detected both borders in vivo (r2 = 0.95 and 0.99, Williams' index = 0.67 and 0.65, and r2 = 0.95 and 0.99, WI = 0.67 and 0.70, respectively). However, the neighborhood-search technique was significantly faster and required less computation. Volume calculations for both techniques (r2 = 0.99 and r2 = 0.99) also agreed with a known-volume phantom. Active surface segmentation allows 3-D assessment of coronary morphology and further developments with this technology will provide clinical analysis tools.

Comparison of texture analysis methods for the characterization of coronary plaques in intravascular ultrasound images

Intravascular Ultrasound (IVUS) is a diagnostic imaging technique that provides tomographic visualization of coronary arteries. The aim of this study was to evaluate five texture analysis techniques and determine their ability to distinguish between plaque lesions of different composition. Using histological correlation, regions of calcified, fibrous, and necrotic core plaque were chosen from 27 coronary plaques. First-order statistics, Haralick's method, Laws' texture energy method, the neighborhood gray-tone difference matrix method, and texture spectrum features were examined using discriminant analysis. Self-validation indicated that Haralick's method yielded the most accurate results, with resubstitution and cross-validation error rates of 0.00 and 14.76%, respectively. Further optimization gave error rates of 6.67%, using only two discriminating features, IDM and entropy.

Three-dimensional automatic quantitative analysis of intravascular ultrasound images

Intravascular ultrasound (IVUS) has established itself as a useful tool for coronary assessment. The vast amount of data obtained by a single IVUS study renders manual analysis impractical for clinical use. A computerized method is needed to accelerate the process and eliminate user-dependency. In this study, a new algorithm is used to identify the lumen border and the media-adventitia border (the external elastic membrane). Setting an initial surface on the IVUS catheter perimeter and using active contour principles, the surface inflates until virtual force equilibrium defined by the surface geometry and image features is reached. The method extracts these features in three dimensions (3-D). Eight IVUS procedures were performed using an automatic pullback device. Using the ECG signal for synchronization, sets of images covering the entire studied region and corresponding to the same cardiac phase were sampled. Lumen and media-adventitia border contours were traced manually and compared to the automatic results obtained by the suggested method. Linear regression results for vessel area enclosed by the lumen and media-adventitia border indicate high correlation between manual vs. automatic tracings (y = 1.07 x -0.38; r = 0.98; SD = 0.112 mm(2); n = 88). These results indicate that the suggested algorithm may potentially provide a clinical tool for accurate lumen and plaque assessment.

Reproducibility of neointima quantification with motorized intravascular ultrasound pullback in stented coronary arteries

BACKGROUND

Intravascular ultrasound (IVUS) imaging has shown excellent reproducibility immediately after coronary stent implantation. However, the variability of measurements in lesions late after stent implantation, when neointima formation is present, has not been studied. Neointimal tissue is generally low echogenic and thus difficult to quantify. We therefore sought to analyze the reproducibility of morphometric measurements late after stent implantation.

METHODS AND RESULTS

Fifty consecutive patients were investigated 6 months after Palmaz-Schatz stent implantation (motorized catheter pullback 0.5 mm/s). Two experienced investigators independently identified the stent area, lumen area, and neointimal area at different sites within the stent. Planimetric measurements were performed with commercially available software. Correlation coefficient and mean difference for corresponding measurements were calculated for the intraobserver and interobserver comparisons. Variability for the intraobserver and interobserver comparisons was similar. Observer agreement regarding the presence of neointimal hyperplasia was as high as 71% (interobserver comparison 62%). The mean difference for neointima area was 0.06 +/- 1.5 mm(2) (-0.6 +/- 1.5 mm(2)); mean differences for lumen area were 0.02 +/- 0.19 mm(2) (0.03 +/- 0.17 mm(2)) and for stent area 0.01 +/- 0.09 mm(2) (-0.02 +/- 0.12 mm(2)) (values for interobserver comparison are given in parentheses). Correlation between measurements was high for all structures: correlation coefficients were 0.66 (0.69) for neointima, 0.94 (0.95) for lumen, and 0.95 (0. 91) for stent area.

CONCLUSIONS

Morphometric measurements of IVUS investigations with motorized IVUS pullback late after stent placement show good reproducibility. Intraobserver variability and interobserver variability are low. Differences for corresponding measurements were more pronounced for neointima area. Motorized catheter pullback guarantees high reliability of IVUS measurements and should be used routinely for clinical IVUS studies.

Three-dimensional reconstruction of the coronary artery wall by image fusion of intravascular ultrasound and bi-plane angiography

BACKGROUND

Intravascular ultrasound (IVUS) is becoming increasingly accepted for assessing coronary anatomy. However, its utility in visualizing and quantifying coronary morphology has been limited by its 2D tomographic nature. This study presents a 3D reconstruction technique that accurately preserves 3D geometric information.

METHODS AND RESULTS

Images obtained from manual IVUS pullbacks and continuous bi-plane angiography were fused, using angiography to reconstruct the transducer trajectory and aid in solving for the correct rotational orientation. A novel 3D active surface method automatically identified the luminal and medial-adventitial borders which, when superimposed on the transducer trajectory, could be surface-rendered for visualization and morphometry. Segmentation agreed well with manual assessment, and 3D luminal shape matched that of angiography when projected to 2D.

CONCLUSIONS

We conclude that this method provides an accurate reconstruction of the vessel's anatomy, which accounts for the true curvature of the vessel.

Reproducibility of volumetric quantification in intravascular ultrasound images

The reproducibility of volume measurements in intravascular ultrasound (IVUS) images derived from separate pull-back manoeuvres remains to be elucidated. Patients (n = 23) were imaged with IVUS prior to (first series) and following percutaneous transluminal angioplasty (PTA) (second series). In 15 patients, one matched vascular segment (3-4 cm in length), not subjected to PTA, was used for analysis of lumen, vessel and plaque volume using an automated contour analysis system. Volume measurements assessed by two independent observers and in the two separate series were compared. Interobserver differences in volume measurements were small (< or =0.4%), with low coefficients of variation (< or =1.7%) and high correlation coefficients (r = 1.00). Differences in volume measurements obtained in the two separate series were small (< or =2.6%), with low coefficients of variation (< or = 8.6%) and high correlation coefficients (r = 0.97-0.99). In conclusion, volume measurements derived from IVUS images are highly reproducible. Therefore, IVUS may be used to monitor the progression/regression of atherosclerotic plaque volume in a longitudinal study.

Preintervention lesion remodelling affects operative mechanisms of balloon optimised directional coronary atherectomy procedures: a volumetric study with three dimensional intravascular ultrasound

AIMS

To classify atherosclerotic coronary lesions on the basis of adequate or inadequate compensatory vascular enlargement, and to examine changes in lumen, plaque, and vessel volumes during balloon optimised directional coronary atherectomy procedures in relation to the state of adaptive remodelling before the intervention.

DESIGN

29 lesion segments in 29 patients were examined with intravascular ultrasound before and after successful balloon optimised directional coronary atherectomy procedures, and a validated volumetric intravascular ultrasound analysis was performed off-line to assess the atherosclerotic lesion remodelling and changes in plaque and vessel volumes that occurred during the intervention. Based on the intravascular ultrasound data, lesions were classified according to whether there was inadequate (group I) or adequate (group II) compensatory enlargement.

RESULTS

There was no significant difference in patient and lesion characteristics between groups I and II (n = 10 and 19), including lesion length and details of the intervention. Quantitative coronary angiographic data were similar for both groups. However, plaque and vessel volumes were significantly smaller in group I than in II. In group I, 9 (4)% (mean (SD)) of the plaque volume was ablated, while in group II 16 (11)% was ablated (p = 0.01). This difference was reflected in a lower lumen volume gain in group I than in group II (46 (18) mm(3) v 80 (49) mm(3) (p < 0.02)).

CONCLUSIONS

Preintervention lesion remodelling has an impact on the operative mechanisms of balloon optimised directional coronary atherectomy procedures. Plaque ablation was found to be particularly low in lesions with inadequate compensatory vascular enlargement.

Progression of atherosclerosis at one-year follow-up seen with volumetric intravascular ultrasound in femoropopliteal arteries

Volume measurements derived from intravascular ultrasound (IVUS) images assessed with an automated contour analysis system are accurate and reproducible. However, it is unknown to what extent plaque volume may change at follow-up. Therefore, the purpose of this longitudinal study is to examine whether IVUS is a sensitive means to identify progression of atherosclerosis and its derived primary end point plaque volume at 1-year follow-up. Patients (n = 11) undergoing percutaneous transluminal angioplasty (PTA) of the femoropopliteal artery were studied with IVUS immediately after PTA in the same session and at 1-year follow-up. Matched, well-identified vascular segments (3 to 4 cm in length), not subjected to PTA, imaged at baseline and after 1-year follow-up, were used for calculation of the longitudinal change in lumen, vessel and plaque volume, and mean plaque thickness. The median length of the selected vascular segments was 4 cm. At follow-up (12+/-2 months) a nonsignificant increase in lumen volume (2.3+/-11%), vessel volume (2.0+/-7.0%), and plaque volume (3.0+/-5.1%) was seen; the mean plaque thickness increase was 2.2+/-5.6%. In conclusion, progression of atherosclerosis implies changes in plaque and vessel volume, resulting in lumen volume change. This observation has important implications for future clinical trials aimed at monitoring the effect of pharmacologic agents on the progression and/or regression of atherosclerosis.

Serial volumetric intravascular ultrasound assessment of arterial remodeling in left main coronary artery disease

Serial volumetric intravascular ultrasound (IVUS) was used to study de novo, nontreated left main coronary arteries (LMCAs) in 31 patients. Using an automated contour detection algorithm, analysis of 7.2 +/- 2.5 mm long segments included arterial, lumen, and plaque volumes and plaque burden (plaque/arterial volumes). During follow-up (7.7 +/- 2.4 months), the percent change in lumen volume correlated with the percent change in arterial volume (r = 0.897, p <0.0001), but not with the percent change in plaque volume (r = 0.066, p = 0.7263). Percent changes in arterial volume correlated with percent changes in plaque + media volume (r = 0.448, p = 0.0115), indicating arterial remodeling. However, there was a spectrum of responses ranging from inadequate remodeling (decrease in lumen volume despite no increase or a decrease in plaque volume: i.e., arterial shrinkage) to overcompensation (an increase in lumen volume despite an increase in plaque volume). Serial volumetric IVUS (1) confirms the existence of both positive and negative remodeling in LMCA, and (2) shows that in moderate LMCA disease, luminal changes resulted primarily from positive versus negative remodeling, not plaque progression and/or regression.

Serial volumetric (three-dimensional) intravascular ultrasound analysis of restenosis after directional coronary atherectomy

OBJECTIVES

We report the use of three-dimensional (volumetric) intravascular ultrasound (IVUS) analysis to assess serial changes after directional coronary atherectomy (DCA).

BACKGROUND

Recent serial planar IVUS studies have described a decrease in external elastic membrane (EEM) area following catheter-based intervention as an important mechanism of late lumen renarrowing.

METHODS

Thirty-one patients with de novo native coronary lesions treated with DCA in the Serial Ultrasound Restenosis (SURE) Trial and in Optimal Atherectomy Restenosis Study (OARS) were enrolled in this study. Serial IVUS was performed before and after intervention and at 6 months' follow-up. In a subgroup of 18 patients from the SURE trial, IVUS was also performed at 24 h and at 1 month postintervention. Segments, 20-mm-long (200 image slices), were analyzed using a previously validated three-dimensional, computerized, automated edge-detection algorithm. The EEM, lumen, and plaque+media (P+M = EEM-lumen) volumes were calculated.

RESULTS

At follow-up, lumen volume was smaller than at postintervention (159+/-69 mm3 vs. 179+/-49 mm3, p = 0.0003). From postintervention to follow-up, there was a decrease in EEM volume (377+/-107 to 352+/-125 mm3, p < 0.0001), but no change in P+M volume (p = 0.52). The delta lumen volume correlated strongly with deltaEEM volume (r = 0.842, p < 0.0001), but not with deltaP+M volume. In the 18 patients from the SURE Trial, the decrease in lumen and EEM volumes occurred late, between 1 month and 6 months of follow-up.

CONCLUSIONS

Volumetric IVUS analysis demonstrated that late lumen volume loss following DCA was a result of a decrease in EEM volume. This was a late event, occurring between 1 and 6 months' postintervention.

Validation of the in vivo intravascular ultrasound measurement of in-stent neointimal hyperplasia volumes

OBJECTIVES

This study was undertaken to validate the in vivo intravascular ultrasound (IVUS) measurement of in-stent neointimal hyperplasia (IH) volumes.

BACKGROUND

Because stents reduce restenosis compared to balloon angioplasty, stent use has increased significantly. As a result, in-stent restenosis is now an important clinical problem. Serial IVUS studies have shown that in-stent restenosis is secondary to intimal hyperplasia. To evaluate strategies to reduce in-stent restenosis, accurate measurement of in-stent neointimal tissue is important.

METHODS

Using a porcine coronary artery model of in-stent restenosis, single Palmaz-Schatz stents were implanted into 16 animals with a stent:artery ratio of 1.3:1. Intravascular ultrasound imaging was performed at 1 month, immediately prior to animal sacrifice. In vivo IVUS and ex vivo histomorphometric measurements included stent, lumen and IH areas; IH volumes were calculated with Simpson's rule.

RESULTS

Intravascular ultrasound measurements of IH (30.4+/-11.0 mm3) volumes correlated strongly with histomorphometric measurements (26.7+/-8.5 mm3, r=0.965, p < 0.0001). The difference between the IVUS and the histomorphometric measurements of IVUS volume was 4.1+/-2.7 mm3 or 15.8+/-11% (standard error of the estimate=0.7). Both histomorphometry and IVUS showed that IH was concentric and uniformly distributed over the length of the stent. Intravascular ultrasound detected neointimal thickening of < or =0.2 mm in 5 of 16 stents. Sample size calculations based on the IVUS measurement of IH volumes showed that 12 stented lesions/arm would be required to show a 50% reduction in IVUS-measured IH volume and 44 stented lesions/arm would be required to show a 25% reduction in IH volume.

CONCLUSION

In vivo IVUS measurement of IH volumes correlated strongly with ex vivo histomorphometry. Using volumetric IVUS end points, small sample sizes should be necessary to demonstrate effectiveness of strategies to reduce in-stent restenosis.

Coronary wallstents show significant late, postprocedural expansion despite implantation with adjunct high-pressure balloon inflations

Adjunct high-pressure balloon inflations following the delivery of oversized self-expandable Wallstents may affect their implied late, postprocedural self-expansion. Consequently, we examined 15 "Magic" Wallstents, which were implanted following a strategy of stent oversizing and subsequent adjunct high-pressure balloon inflations (16 +/- 2 atm; all > or = 12 atm). The excellent radiographic visibility of this stent permitted reliable quantitative coronary angiographic measurement of both lumen and stent dimensions (before and after stenting, and at follow-up). At follow-up, extent and distribution of in-stent neointimal proliferation were evaluated with volumetric intravascular ultrasound. Between postintervention and follow-up examination, mean stent diameter increased from 3.7 +/- 0.4 to 4.2 +/- 0.4 mm (p <0.0001); there was no significant difference in late stent expansion between proximal, mid-, and distal stent subsegments. Late stent expansion showed a significant (reverse) relation to maximum balloon size (r = -0.56, p <0.04), but not with follow-up lumen size or late lumen loss. On average, 52 +/- 18% of the stent was filled with neointimal ingrowth; neointimal volume/cm stent length was 64 +/- 22 mm3. Both late stent expansion (r = 0.36, p <0.02) and maximum balloon pressure (r = 0.41, p <0.001) were related to neointimal volume/cm stent but not to follow-up lumen size. Thus, despite high-pressure implantation, Wallstents showed significant late self-expansion, which resulted in larger stent dimensions at follow-up that assisted in accommodating in-stent neointimal proliferation. Conversely, late stent expansion had a significant relation to the extent of in-stent neointimal ingrowth. Beneficial and disadvantageous effects of the late stent expansion appear to be balanced, because a relation to late lumen loss or follow-up lumen dimensions was not found to be present.

Developments in cardiovascular ultrasound. Part 2: Arterial applications

Many of the changes resulting from arterial disease can be measured, using Doppler ultrasound for measurement of blood velocity and B-scan imaging for measurement of tissue structure and composition. Wall thickness, the degree of arterial narrowing and plaque volume can be measured using B-scan imaging, and 3D ultrasound can be used to improve the accuracy of measurements of plaque volume and for improved visualisation of complex arterial geometries. Measurement of the dynamic properties of the arterial wall permits estimation of wall elasticity and plaque motion. From the Doppler signal, measurements of blood velocity are used to estimate the degree of arterial narrowing and volumetric flow, although measurement errors can be large. Wall shear stress can be estimated by measuring the velocity gradient at the vessel wall. The problems of inadequate spatial resolution and interference from overlying tissue are largely removed when intravascular systems are used, and these have superior capability in the assessment of arterial structure and tissue composition. However, measurement of quantities relating to blood flow is more difficult using the intravascular approach, as the indwelling cather disturbs the blood flow pattern, and currently, assessment of flow and vessel cross-section are not performed at the same site.

ECG-gated versus nongated three-dimensional intracoronary ultrasound analysis: implications for volumetric measurements

The quantitative analysis of a three-dimensional (3-D) intracoronary ultrasound (ICUS) image data set permits a more comprehensive assessment of coronary arterial segments. The 3-D image sets are generally acquired during continuous motorized pullbacks. However, the cyclic changes of vascular dimensions and the cyclic spatial displacement of the ICUS transducer relative to the vessel wall can result in characteristic image artifacts, which may limit the applicability of quantitative automated analysis systems. This limitation may be overcome by an ECG-gated image acquisition. In the present study we acquired in vivo (1) nongated and (2) ECG-gated 3-D ICUS image sets of 15 human atherosclerotic coronary arteries and performed a computer-assisted contour detection of the lumen and total vessel boundaries. Total vessel and lumen volumes measured significantly larger in the nongated versus ECG-gated end-diastolic image sets (753+/-307 mm3 vs. 705+/-305 mm3; 411+/-154 mm3 vs. 388+/-165 mm3, both: P < 0.05). Both end-diastolic and systolic measurements were available in nine arteries, showing a larger total vessel and lumen volume at systole (664+/-221 mm3 vs. 686+/-227 mm3, P=0.03; 384+/-164 mm3 vs. 393+/-170 mm3, P=0.08). The differences observed may be of particular interest for volumetric ICUS studies, addressing presumably small differences in vessel or lumen dimensions.

Atherosclerotic coronary lesions with inadequate compensatory enlargement have smaller plaque and vessel volumes: observations with three dimensional intravascular ultrasound in vivo

OBJECTIVE

To compare vessel, lumen, and plaque volumes in atherosclerotic coronary lesions with inadequate compensatory enlargement versus lesions with adequate compensatory enlargement.

DESIGN

35 angiographically significant coronary lesions were examined by intravascular ultrasound (IVUS) during motorised transducer pullback. Segments 20 mm in length were analysed using a validated automated three dimensional analysis system. IVUS was used to classify lesions as having inadequate (group I) or adequate (group II) compensatory enlargement.

RESULTS

There was no significant difference in quantitative angiographic measurements and the IVUS minimum lumen cross sectional area between groups I (n = 15) and II (n = 20). In group I, the vessel cross sectional area was 13.3 (3.0) mm2 at the lesion site and 14.4 (3.6) mm2 at the distal reference (p < 0.01), whereas in group II it was 17.5 (5.6) mm2 at the lesion site and 14.0 (6.0) mm2 at the distal reference (p < 0.001). Vessel and plaque cross sectional areas were significantly smaller in group I than in group II (13.3 (3.0) v 17.5 (5.6) mm2, p < 0.01; and 10.9 (2.8) v 15.2 (4.9) mm2; p < 0.005). Similarly, vessel and plaque volume were smaller in group I (291.0 (61.0) v 353.7 (110.0) mm3, and 177.5 (48.4) v 228.0 (92.8) mm3, p < 0.05 for both). Lumen areas and volumes were similar.

CONCLUSIONS

In lesions with inadequate compensatory enlargement, both vessel and plaque volume appear to be smaller than in lesions with adequate compensatory enlargement.

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.

Successful directional atherectomy of de novo coronary lesions assessed with three-dimensional intravascular ultrasound and angiographic follow-up

Recent histopathologic and intravascular ultrasound (IVUS) data indicate that inadequate compensatory enlargement of atherosclerotic lesions contributes to the development of significant arterial stenoses. Such lesions may contain less plaque, which may have implications for atheroablative interventions. In this study, we compared lesions with (group A, n = 16) and without inadequate compensatory enlargement (group B, n = 30) as determined by IVUS. The acute results and the follow-up lumen dimensions of angiographically successful directional coronary atherectomy procedures were compared. Inadequate compensatory enlargement was considered present when the preintervention arterial cross-sectional area at the target lesion site was smaller than that at the (distal) reference site. Three-dimensional IVUS analysis and quantitative angiography were performed in 46 patients before and after intervention. IVUS measurements included the arterial, lumen, and plaque (arterial minus lumen) cross-sectional areas at the target lesion site (i.e., smallest lumen site) and the (distal) reference site. Angiographic follow-up was performed in 42 patients. Preintervention and postintervention angiographic measurements and IVUS lumen cross-sectional area measurements were similar in both groups. However, at follow-up, the angiographic minimum lumen and reference diameters were significantly smaller in group A compared with group B (1.71 +/- 0.47 mm vs 2.14 +/- 0.73 mm, p <0.03, and 2.97 +/- 0.29 mm vs 3.39 +/- 0.76 mm, p <0.02; group A vs B). The data of this observational study suggest that lesions with inadequate compensatory enlargement, as determined by IVUS before intervention, may have less favorable long-term lumen dimensions after directional coronary atherectomy procedures.

Variations of remodeling in response to left main atherosclerosis assessed with intravascular ultrasound in vivo

Histopathologic studies have demonstrated that vessels enlarge to compensate for an increase in plaque burden; this has been confirmed in vivo using intravascular ultrasound (IVUS). The initial studies suggested a biphasic course of lesion formation with (1) preservation of lumen dimensions up to a plaque burden of approximately 40%, and (2) luminal narrowing as plaque burden further increases. In this study, we used IVUS and angiography to assess the extent of left main (LM) atherosclerosis in 107 patients undergoing catheter-based procedures of the left anterior descending or left circumflex coronary arteries. Using IVUS, atherosclerotic plaques were found in all LM arteries, but only 26 (24%) had varying degrees of luminal narrowing on the angiogram. Nevertheless, there was an inverse relation (r = -0.62, p <0.0001) between the minimal lumen area and the plaque burden (i.e., plaque + media divided by total vessel area) that was not restricted to plaque burden values >40% (or >30%), but persisted at plaque burden values of 20% to 40%. In addition, LM arteries with a plaque burden <40% had a similar total vessel area as did LM arteries with a plaque burden > or =40% (22.9 +/- 6.1 vs 21.8 +/- 4.8 mm2, p = 0.30). These data suggest that lumen dimensions may not be preserved even if plaque occupies no more than 20% to 40% of the total vessel area. Thus, there is more variation in remodeling response during earlier stages of plaque accumulation within the LM artery than is commonly suggested.

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.

ECG-gated three-dimensional intravascular ultrasound: feasibility and reproducibility of the automated analysis of coronary lumen and atherosclerotic plaque dimensions in humans

BACKGROUND

Automated systems for the quantitative analysis of three-dimensional (3D) sets of intravascular ultrasound (IVUS) images have been developed to reduce the time required to perform volumetric analyses; however, 3D image reconstruction by these nongated systems is frequently hampered by cyclic artifacts.

METHODS AND RESULTS

We used an ECG-gated 3D IVUS image acquisition workstation and a dedicated pullback device in atherosclerotic coronary segments of 30 patients to evaluate (1) the feasibility of this approach of image acquisition, (2) the reproducibility of an automated contour detection algorithm in measuring lumen, external elastic membrane, and plaque+media cross-sectional areas (CSAs) and volumes and the cross-sectional and volumetric plaque+media burden, and (3) the agreement between the automated area measurements and the results of manual tracing. The gated image acquisition took 3.9+/-1.5 minutes. The length of the segments analyzed was 9.6 to 40.0 mm, with 2.3+/-1.5 side branches per segment. The minimum lumen CSA measured 6.4+/-1.7 mm2, and the maximum and average CSA plaque+media burden measured 60.5+/-10.2% and 46.5+/-9.9%, respectively. The automated contour-detection required 34.3+/-7.3 minutes per segment. The differences between these measurements and manual tracing did not exceed 1.6% (SD<6.8%). Intraobserver and interobserver differences in area measurements (n=3421; r=.97 to.99) were <1.6% (SD<7.2%); intraobserver and interobserver differences in volumetric measurements (n=30; r=.99) were <0.4% (SD<3.2%).

CONCLUSIONS

ECG-gated acquisition of 3D IVUS image sets is feasible and permits the application of automated contour detection to provide reproducible measurements of the lumen and atherosclerotic plaque CSA and volume in a relatively short analysis time.

Electrocardiogram-gated intravascular ultrasound image acquisition after coronary stent deployment facilitates on-line three-dimensional reconstruction and automated lumen quantification

OBJECTIVE

This study evaluates the feasibility, reliability and reproducibility of electrocardiogram (ECG)-gated intravascular ultrasound (IVUS) image acquisition during automated transducer withdrawal and automated three-dimensional (3D) boundary detection for assessing on-line the result of coronary stenting.

BACKGROUND

Systolic-diastolic image artifacts frequently limit the clinical applicability of such automated analysis systems.

METHODS

In 30 patients, after successful angiography-guided implantation of 34 stents in 30 target lesions, we carried out IVUS examinations on-line with the use of ECG-gated automated 3D analyses and conventional manual analyses of two-dimensional images from continuous pullbacks. These on-line measurements were compared with off-line 3D reanalyses. The adequacy of stent deployment was determined by using ultrasound criteria for stent apposition, symmetry and expansion.

RESULTS

Gated image acquisition was successfully performed in all patients to allow on-line 3D analysis within 8.7 +/- 0.6 min (mean +/- SD). Measurements by on-line and off-line 3D analyses correlated closely (r > or = 0.95), and the minimal stent lumen differed only minimally (8.6 +/- 2.8 mm2 vs. 8.5 +/- 2.8 mm2, p = NS). The conventional analysis significantly overestimated the minimal stent lumen (9.0 +/- 2.7 mm2, p < 0.005) in comparison with results of both 3D analyses. Fourteen stents (41%) failed to meet the criteria by both 3D analyses, all of these not reaching optimal expansion, but only 7 (21%) were detected by conventional analysis (p < 0.02). Intraobserver and interobserver comparison of stent lumen measurements by the automated approach revealed minimal differences (0.0 +/- 0.2 mm2 and 0.0 +/- 0.3 mm2) and excellent correlations (r = 0.99 and 0.98, respectively).

CONCLUSIONS

ECG-gated image acquisition after coronary stent deployment is feasible, permits on-line automated 3D reconstruction and analysis and provides reliable and reproducible measurements; these factors facilitate detection of the minimal lumen site.