Intravascular ultrasound imaging of human coronary arteries in vivo. Analysis of tissue characterizations with comparison to in vitro histological specimens

Angiographic and physiologic assessment of coronary flow and myocardial perfusion in the cardiac catheterization laboratory

INTRODUCTION

For many years, coronary angiography has been used to define coronary artery lesions. Angiographic assessment of coronary flow using the TIMI flow grade system (TFG) and the TIMI frame count (TFC) methods have played a significant role in our understanding of coronary artery disease and they have proved useful in prediction of long-term clinical outcomes after myocardial infarction. The availability of invasive techniques to assess the physiological significance of coronary artery lesions allows a more rationale approach to the management of patients, particularly those with intermediate lesions. The TIMI scores and other angiographic parameters such as the TIMI myocardial perfusion grade (TMPG) are now integrated into clinical practice, as are the use of flow wires and pressure recording wires. Other angiographic techniques, (e.g. digital subtraction angiography), which at this time are predominantly research tools, will require software integration into the imaging chain to facilitate real-time analysis.

CONCLUSION

In this article, we provide a comprehensive descriptive review of the different means of assessment of coronary flow in the cardiac catheterization laboratory, focusing on scores deducted from angiography as well as invasive haemodynamic measurements of blood flow and pressure.

Flexible miniature compound lens design for high-resolution optical coherence tomography balloon imaging catheter

We report on a new optics design for an optical coherence tomography (OCT) balloon imaging catheter. The design involves a miniature compound gradient-index (GRIN) rod lens, which consists of a fiber optic mode-field reducer and relay rod lenses to achieve predictable high lateral resolution at a desired large working distance. The compound lens design significantly simplifies the engineering process for an OCT catheter and enables 3-D full circumferential cross sectional imaging of large luminal organs such as human esophagus. An as-designed OCT catheter is developed and demonstrated for real-time in vivo swine esophagus imaging in a 3-D spiral fashion.

Online PC-based integration of digital intracoronary ultrasound images into angiographic images during cardiac catheterization

In recent years, intravascular ultrasound (IVUS) has evolved as an important adjunct to angiography, providing insights that are significantly altering conventional paradigms in diagnosis and therapy. However, major drawbacks in the use of IVUS relied on the fact that a heavy console had to be moved from lab to lab, and extensive time for set up and image analysis. This additional time and the decrease in patients' through-put has not been applicable in clinical practice for many labs. Our manuscript concerns a novel PC-based platform for IVUS that enables the online intergration of digital intracoronary ultrasound images into angiographic images. This new technique offers remote operation, multiple control devices and custom viewing options. The PC-based platform enables IVUS images to be viewed simultaneously from multiple vantage points in the lab, and allows for multiple user interfaces.

Impact of intramural thrombus in coronary arteries on the accuracy of tissue characterization by in vivo intravascular ultrasound radiofrequency data analysis

Virtual Histology (VH) intravascular ultrasound (IVUS) allows differentiation between 4 different tissue phenotypes. However, the current classification tree for analysis cannot differentiate the presence of intramural thrombus. The aim of this study was to evaluate the impact of intramural thrombus for correlative accuracy between in vitro histopathology of coronary atherosclerotic plaque obtained by directional coronary atherectomy and corresponding in vivo tissue characterization obtained by VH IVUS. Coronary IVUS imaging of 30 coronary artery lesions was obtained using a 20-MHz phased-array IVUS catheter with a motorized pull-back system at set 0.5 mm/s. The debulking region of the in vivo histologic image was predicted from comparison between pre- and post-first debulking VH IVUS images. Cross-sectional histologic slices were cut every 0.5 mm starting from the most proximal part of the formalin-fixed debulking tissue. Histologic slices were divided into 2 groups by the presence or absence of pathologic thrombus. A total of 259 in vitro histologic slices were obtained, and pathologic thrombus was detected in 81 slices. Correlation was favorable, with high sensitivity for all plaque components, but specificities for fibrous (thrombus slices vs nonthrombus slices 36% vs 94%) and fibrofatty (9% vs 60%) tissue were lower in thrombus slices. Therefore, predictive accuracies for the 2 plaque components were lower in thrombus slices (fibrous tissue 78% vs 99%, fibrofatty tissue 68% vs 83%, respectively). In conclusion, intramural thrombus was colored as fibrous or fibrofatty by VH IVUS, reducing VH accuracy in these kinds of lesions.

Application of neural networks for the analysis of intravascular ultrasound and histological aortic wall appearance-an in vitro tissue characterization study

The role of tissue characterization by intravascular ultrasound (IVUS) imaging of the aortic wall has not been well established. The artificial neural networks (ANNs) are a promising tool for image classification. The aim of the study was to assess the texture correlation between matching IVUS and histologic images of the aortic wall. The computer-based discrimination of pathology within the data sets was also evaluated. In vitro IVUS images and histologic sections from 36 aortic segments were compared using texture parameters that produced the best correlation or the highest discriminative value. The images were classified as normal or abnormal with variable degrees of pathology. Tissue characterization was performed by a nearest neighbor classifier, linear discriminant analysis (LDA) and the ANN-based approach. Good agreement was observed between IVUS and the histologic reference with a correlation coefficient of r = 0.89, r = 0.76 and r = 0.71 for the three most successful texture parameters. The ANN-based approach was the most effective in discriminant analysis, with a correct classification rate of 87.5% for histologic images and 79.2% for IVUS data. The study shows that ANNs are a potentially effective tool for assessment of IVUS aortic images.

Imaging techniques for the vulnerable coronary plaque

The goal of this article is to illustrate the main invasive and noninvasive diagnostic modalities to image the vulnerable coronary plaque, which is responsible for acute coronary syndrome. The main epidemiologic and histological issues are briefly discussed in order to provide an adequate background. Comprehensive coronary atherosclerosis imaging should involve visualization of the entire coronary artery tree and plaque characterization, including three-dimensional morphology, relationship with the lumen, composition, vascular remodelling and presence of inflammation. No single technique provides such a comprehensive description, and no available modality extensively identifies the vulnerable plaque. In particular, we describe multislice computed tomography, which at present seems to be the most promising noninvasive tool for an exhaustive image-based quantification of coronary atherosclerosis.

Distinguishing characteristics of erythrocyte-rich and platelet-rich thrombus by intravascular ultrasound catheter system

BACKGROUND

Acute coronary syndromes are associated with platelet-rich, white thrombi (WT) and erythrocyte-rich, red thrombi (RT), but their ultrasonic characteristics are not well defined. To determine whether intravascular ultrasound (IVUS) could be used to detect specific characteristics of WT and RT, two experiments were performed.

METHODS

An in-vitro experiment evaluated five WT and five RT and an ex-vivo experiment evaluated thrombi from 17 atherosclerotic rabbits with disrupted plaques and overlying thrombi. Specimen were mounted flat, immersed in a saline bath and examined from the intimal surface. Thrombi were classified as WT (n = 69) or RT (n = 40) by gross inspection and histology. IVUS was performed using a 1 mm, 20 MHz transducer in a 4.8F catheter. Images were digitally converted and points integrated to account for angular and depth resolution. Sampling was performed at the water-tissue interface and four other sites at 0.3 mm radial depth increments. Signals from each depth were standardized by obtaining the ratio of each energy level to the level at the water-tissue interface.

RESULTS

The average energy ratio backscattered by RT was constant with increasing tissue depth while it attenuated for WT (P < 0.005; 2-way ANOVA). RT was less homogeneous and had more backscatter compared to WT. Light and electron microscopy corroborated these observations showing WT as densely homogenous and RT with loose cellular elements.

CONCLUSION

WT may be detected by its attenuated ultrasound pattern versus a non-attenuated pattern for RT by IVUS. This technique has potential for characterizing WT and RT.

Modeling Plaque Fissuring and Dissection during Balloon Angioplasty Intervention

Balloon angioplasty intervention is traumatic to arterial tissue. Fracture mechanisms such as plaque fissuring and/or dissection occur and constitute major contributions to the lumen enlargement. However, these types of mechanically-based traumatization of arterial tissue are also contributing factors to both acute procedural complications and chronic restenosis of the treatment site. We propose physical and finite element models, which are generally useable to trace fissuring and/or dissection in atherosclerotic plaques during balloon angioplasty interventions. The arterial wall is described as an anisotropic, heterogeneous, highly deformable, nearly incompressible body, whereas tissue failure is captured by a strong discontinuity kinematics and a novel cohesive zone model. The numerical implementation is based on the partition of unity finite element method and the interface element method. The later is used to link together meshes of the different tissue components. The balloon angioplasty-based failure mechanisms are numerically studied in 3D by means of an atherosclerotic-prone human external iliac artery, with a type V lesion. Image-based 3D geometry is generated and tissue-specific material properties are considered. Numerical results show that in a primary phase the plaque fissures at both shoulders of the fibrous cap and stops at the lamina elastica interna. In a secondary phase, local dissections between the intima and the media develop at the fibrous cap location with the smallest thickness. The predicted results indicate that plaque fissuring and dissection cause localized mechanical trauma, but prevent the main portion of the stenosis from high stress, and hence from continuous tissue damage.

Two-year serial coronary angiographic and intravascular ultrasound analysis of in-stent angiographic late lumen loss and ultrasonic neointimal volume from the TAXUS II trial

Late loss has been used as a reliable surrogate end point for evaluation and differentiation of short-term performance of drug-eluting stents. This study investigated the consistency between angiographic and intravascular ultrasound (IVUS) outcomes of late lumen loss (late loss) and neointimal growth to measure restenotic plaque load in TAXUS and bare metal stents. The randomized TAXUS II trial evaluates the polymer-based paclitaxel-eluting TAXUS stent in slow- and moderate-release formulations. Serial angiographic and IVUS analyses were available in 155 event-free patients (bare metal stent, 74; TAXUS stent, 81) after the procedure, at 6 months, and at 2 years. For this subanalysis, quantitative coronary angiographic (QCA) and IVUS measurements were used to derive late loss and neointimal volume. From after the procedure to 6 months, quantitative coronary angiography and IVUS showed matching results for the 2 groups with significant decreases in late loss and neointimal volume in the TAXUS versus the control group. From 6 months to 2 years, QCA and IVUS measurements also showed results similar to those in the control group, demonstrating neointimal compaction over time. However, in the TAXUS group, QCA late loss showed a nonsignificant decrease from 6 months to 2 years, whereas IVUS neointimal volume increased. In conclusion, although QCA and IVUS results were similar over the first 6 months, long-term assessment of changes in restenotic plaque load showed discrepant findings for the TAXUS. These findings suggest the need for critical reevaluation of current end points and the use of more precise techniques to detect lumen and stent boundaries.

Intravascular ultrasound for the evaluation of therapies targeting coronary atherosclerosis

Many cardiovascular events are clinical manifestations of underlying atherosclerotic disease. The progression of atherosclerosis, traditionally measured by angiography, is predictive of future clinical events and is a valid surrogate marker of cardiovascular (CV) disease. There is growing interest in using novel surrogate end points in clinical trials to expedite the development of new CV therapies. Innovative imaging technologies, such as intravascular ultrasound (IVUS), may carry advantages for the evaluation of coronary atherosclerotic burden and disease progression. Unlike angiography, which displays only the opacified luminal "silhouette," IVUS provides transmural imaging of the entire arterial wall and permits both detection of early-stage atherosclerosis and accurate cross-sectional and even 3-dimensional quantification of plaques. Intravascular ultrasound is now used to guide therapeutic interventions and for diagnostic purposes, primarily for the evaluation of ambiguous lesions and left main coronary artery disease. In addition, clinical studies are using IVUS serially to measure plaque progression, which appears to be related to future CV events. Although the probative force of clinical end point studies still is stronger, IVUS is catching up. Currently, several trials of CV therapies use IVUS-determined plaque progression as the end point. The rationale for using IVUS-based surrogate end points in clinical trials is discussed in the present review. Key advantages of using IVUS-based surrogate end points versus clinical outcome include smaller patient numbers and substantially shorter trial durations; this reduces costs and may expedite the development and testing of new drugs. We expect in the near future a further increase of the use of IVUS-based surrogate end points in trials that evaluate novel CV therapies targeting on coronary atherosclerosis.

Assessment of intermediate severity coronary lesions in the catheterization laboratory

The management of intermediate coronary lesions, defined by a diameter stenosis of 40% to 70%, continues to be a therapeutic dilemma for cardiologists. The 2-dimensional representation of the arterial lesion provided by angiography is limited in distinguishing intermediate lesions that require stenting from those that simply need appropriate medical therapy. In the era of drug-eluting stents, some might propose that stenting all intermediate coronary lesions is an appropriate solution. However, the possibility of procedural complications such as coronary dissection, no reflow phenomenon, in-stent restenosis, and stent thrombosis requires accurate stratification of patients with intermediate coronary lesions to appropriate therapy. Intravascular ultrasound (IVUS) and fractional flow reserve index (FFR) provide anatomic and functional information that can be used in the catheterization laboratory to designate patients to the most appropriate therapy. The purpose of this review is to discuss the critical information obtained from IVUS and FFR in guiding treatment of patients with intermediate coronary lesions. In addition, the importance of IVUS and FFR in the management of patients with serial stenosis, bifurcation lesions, left main disease, saphenous vein graft disease, and acute coronary syndrome will be discussed.

Comparison of nonuniform rotational distortion between mechanical IVUS and OCT using a phantom model

Optical coherence tomography (OCT) is an optical analog of mechanical intravascular ultrasound (M-IVUS) with much higher spatial resolution. However, no data exist regarding the nonuniform rotational distortion (NURD) with OCT. The aim of the study was to investigate whether OCT generates less NURD relative to M-IVUS. A coronary artery phantom model was constructed with a rubber ring (3.68 mm in diameter), located at the distal end of the phantom. This model was also composed of eight equally spaced steel wires and an additional marker-wire. Two types of vascular phantoms were used, mild curve (90 degrees ) and acute curve (near 180 degrees ). Subsequent M-IVUS (n = 6) and OCT (n = 6) imaging was performed. Eight angles between eight wires, except the marker-wire, were measured from each image. These angles, measured with M-IVUS and OCT, were compared with those of high-resolution optical photography as a gold standard. The average in angle differences was significantly smaller in OCT compared with M-IVUS in the mild curve model (3.2 +/- 1.0 degrees vs, 6.9 +/- 2.1 degrees , p < 0.01). Compared with the latter model, the average in angle differences was exaggerated in the acute curve model with M-IVUS (9.1 +/- 0.9 degrees vs. 6.9 +/- 2.1 degrees , p < 0.05) but not with OCT (3.5 +/- 0.8 degrees vs. 3.2 +/- 1.0 degrees , p= not significant). OCT generates significantly less NURD compared with M-IVUS, especially in tortuous situation.

Preintervention arterial remodeling as a predictor of intimal hyperplasia after intracoronary stenting: a serial intravascular ultrasound study

BACKGROUND

The impact of vascular remodeling pattern on intimal hyperplasia (IH) after coronary stenting is unknown.

HYPOTHESIS

The preintervention remodeling pattern of the lesion might be associated with IH after the coronary stenting procedure.

METHODS

Serial (pre-, post-stent implantation, and follow-up) intravascular ultrasound (IVUS) images were obtained in 58 patients with single-stent implantation (GFX stents in 41 and NIR in 17). The matching IVUS image slices at the preintervention lesion site were selected for serial comparisons. The remodeling index (RI) was defined as lesion/proximal reference external elastic membrane cross-sectional area (CSA) at preintervention lesion site. Adequate remodeling was defined as a RI > 0.95 and inadequate remodeling as a RI < or = 0.95. Vessel stretching, percent vessel stretching, and percent IH CSA, as well as pre- and postintervention IVUS variables were evaluated according to the remodeling pattern.

RESULTS

The percent IH CSA was 31% in adequate remodeling (n = 29, mean RI = 1.05) and 41% in inadequate remodeling (n = 29, mean RI = 0.88) (p = 0.049). Percent vessel stretching was 15% in adequate remodeling and 22% in inadequate remodeling (p = 0.007). The RI inversely correlated with percent vessel stretching (r = -0.435, p = 0.001).

CONCLUSIONS

Compared with preintervention adequate remodeling, inadequate remodeling was associated with increased percent IH CSA, which might be related with more vessel stretching.

Prospective comparison of coronary artery remodeling between acute coronary syndrome and stable angina in single-vessel disease: correlation between C-reactive protein and extent of arterial remodeling

BACKGROUND

Retrospective intravascular ultrasound (IVUS) studies showed that positive remodeling of coronary artery was associated with unstable clinical presentation. However, no prospective IVUS study has been performed to demonstrate such relationship. The relationship between C-reactive protein (CRP) and coronary artery remodeling is unknown.

HYPOTHESIS

Positive remodeling might be related with acute coronary syndrome in the prospective IVUS study. C-reactive protein levels might be associated with coronary artery remodeling.

METHODS

Preintervention IVUS images were prospectively obtained in 93 patients with single-vessel disease (30 for acute coronary syndrome and 63 for stable angina). Serum sample for CRP measurement was collected 24 h prior to coronary intervention. The remodeling index was defined as a ratio of (lesion/average reference) external elastic membrane area. Positive remodeling was defined as a remodeling index > 1.05 and negative remodeling as a remodeling index < 0.95.

RESULTS

The remodeling index was 0.99 +/- 0.13 in acute coronary syndrome versus 0.95 +/- 0.12 in stable angina (p = 0.048). Positive remodeling was associated with acute coronary syndrome (43 vs. 19%), whereas negative remodeling was more frequent in stable angina (49 vs. 33%) (p = 0.047). C-reactive protein levels were significantly higher in acute coronary syndrome than in stable angina (1.4 +/- 2.0 vs. 0.5 +/- 0.6 mg/dl, respectively, p = 0.002). However, there was no significant correlation between CRP levels and remodeling index (r = 0.078, p = 0.475).

CONCLUSIONS

Positive remodeling may be related with acute coronary syndrome in the prospective IVUS analysis. C-reactive protein levels may not predict the extent of arterial remodeling.

Elevated homocysteine levels might be associated with coronary artery remodeling in patients with stable angina: an intravascular ultrasound study

BACKGROUND

The relationship between plasma biologic markers and coronary artery remodeling is unknown.

HYPOTHESIS

Plasma biologic markers are associated with coronary artery remodeling.

METHODS

Preintervention intravascular ultrasound images were obtained in 44 patients with chronic stable angina. Plasma samples were collected 24 h before coronary intervention. The biologic markers included total cholesterol, low-density lipoprotein (LDL) cholesterol, triglyceride, high-density lipoprotein (HDL) cholesterol, lipoprotein(a) [LP(a)], C-reactive protein (CRP), and homocysteine. The remodeling index (RI) was defined as a ratio of the (lesion/proximal reference) external elastic membrane cross-sectional area. Positive remodeling was defined as an RI > 1.05, negative remodeling as an RI <0.95, and intermediate remodeling as an RI between 0.95 and 1.05.

RESULTS

Total cholesterol level (r = 0.092, p = 0.557), LDL cholesterol level (r = 0.123, p = 0.426), triglyceride level (r = 0.020, p = 0.901), HDL cholesterol level (r = 0.042, p = 0.789), LP(a) level (r = 0.062, p = 0.729), and CRP level (r = 0.266, p = 0.089) did not significantly correlate with the RI. However, the plasma homocysteine level positively correlated with the RI (r = 0.398, p = 0.008). The plasma homocysteine level was significantly lower in the lesions with negative remodeling and higher in the lesions with positive remodeling (10.8 +/- 0.7 micromol/l in negative remodeling, 13.1 +/- 0.6 micromol/l in intermediate remodeling, and 18.1 +/- 2.8 micromol/l in positive remodeling, p = 0.021).

CONCLUSIONS

Elevated homocysteine levels might be associated with coronary artery remodeling in patients with stable angina.

Association of angiotensin-converting enzyme inhibitors and serum lipids with plaque regression in cardiac allograft vasculopathy

We assessed clinical predictors of the process of cardiac allograft vasculopathy (CAV) in 39 consecutive patients (mean 49 years old) using three-dimensional intravascular ultrasound (3-D IVUS) examination of the left anterior descending coronary artery at 36 +/- 38 months and 47 +/- 40 months after cardiac allotransplantation (TX). Compared with 17 patients with plaque progression, 22 patients with plaque regression were more likely to be male (P < .01), to have a higher use of angiotensin-converting enzyme inhibitors (ACEI, P < .05), and to have a lower volumetric remodeling index (P < .001). The changes in plaque volume correlated with the changes in total cholesterol (P < .005) and low-density lipoprotein cholesterol (P < .02). Plaque progression of CAV was independently associated with time after TX, hypertension, nonuse of ACEI, donor age, and changes in total cholesterol and triglycerides. In conclusion, plaque progression is associated with positive vascular remodeling and plaque regression is associated with lower serum lipids and ACEI in patients after TX.

Diagnostic accuracy of optical coherence tomography and intravascular ultrasound for the detection and characterization of atherosclerotic plaque composition in ex-vivo coronary specimens: a comparison with histology

BACKGROUND

Both intravascular ultrasound and optical coherence tomography have been purported to accurately detect and characterize coronary atherosclerotic plaque composition. The aim of our study was to directly compare the reproducibility and diagnostic accuracy of optical coherence tomography and intravascular ultrasound for the detection and characterization of coronary plaque composition ex vivo as compared with histology.

METHODS AND RESULTS

Intravascular ultrasound (20 MHz) and optical coherence tomography imaging was performed in eight heart specimens using motorized pullback. Standard histology using hematoxylin-eosin and van Gieson staining was performed on 4 mum thick slices. Each slice was divided into quadrants and accurately matched cross-sections were analyzed for the presence of fibrous, lipid-rich, and calcified coronary plaque using standard definitions for both intravascular ultrasound and optical coherence tomography and correlated with histology. After exclusion of 145/468 quadrants, we analyzed the remaining 323 quadrants with excellent image quality in each procedure. Optical coherence tomography demonstrated a sensitivity and specificity of 91/88% for normal wall, 64/88% for fibrous plaque, 77/94% for lipid-rich plaque, and 67/97% for calcified plaque as compared with histology. Intravascular ultrasound demonstrated a sensitivity and specificity of 55/79% for normal wall, 63/59% for fibrous plaque, 10/96% for lipid-rich plaque, and 76/98% for calcified plaque. Both intravascular ultrasound and optical coherence tomography demonstrated excellent intraobserver and interobserver agreement (optical coherence tomography: kappa=0.90, kappa=0.82; intravascular ultrasound: kappa=0.87, kappa=0.86).

CONCLUSION

Optical coherence tomography is superior to intravascular ultrasound for the detection and characterization of coronary atherosclerotic plaque composition, specifically for the differentiation of noncalcified, lipid-rich, or fibrous plaque.

Impact of histological plaque characteristics on intravascular ultrasound parameters at culprit lesions in coronary artery disease

Prior intravascular ultrasound (IVUS) studies have demonstrated that a positive remodeling pattern of a culprit lesion is observed more frequently in acute coronary syndrome (ACS) than stable angina (SA). However, the relationship between the plaque morphology detected by IVUS and the histological type of atherosclerotic plaque has not been well defined. This is a prospective study on 37 consecutive patients who underwent directional coronary atherectomy. The 37 patients were divided into 2 groups; 21 patients with SA and 16 with ACS. Vessel and plaque cross sectional area were measured at the culprit lesion and the remodeling index (RI) was calculated by IVUS. The plaque tissue was assessed for the presence of inflammatory cells and lipids, and the presence of each was scored as 0 (absent), 1 (sparse), 2 (dense), or 3 (predominant). The RI of the patients with ACS was higher than that of SA. Inflammatory cells were present to a greater extent in patients with ACS. Inflammatory cells and lipids were significantly correlated with the RI (Inflammatory cell score grade > or = 2 patients; 1.14 +/- 0.13 versus grade 0 patients; 0.87 +/- 0.24, and grade 1 patients; 0.93 +/- 0.17, P < 0.01 and lipid score grade > or = 2 patients; 1.13 +/- 0.17 versus grade 0 patients; 0.85 +/- 0.18, P < 0.001 and grade 1 patients; 0.95 +/- 0.19, P < 0.05). The results clearly indicate that the evaluation of vessel morphology by vascular imaging is an important indicator of plaque instability.

Optical coherence tomography accurately identifies intermediate atherosclerotic lesions--an in vivo evaluation in the rabbit carotid artery

OBJECTIVE

We tested the ability of optical coherence tomography (OCT) to identify very early stages of atherosclerosis in vivo.

METHODS

Twelve New Zealand white male rabbits (weight 3.5-4.0 kg) underwent perivascular electrical injury of the common carotid arteries, and were then fed a cholesterol-rich diet. At 43+/-16 (range 27-63) days after injury, arteries were imaged by OCT, then rabbits were euthanized and vessels processed for histology.

RESULTS

A total of 14 carotid arteries were imaged by OCT and histology; 22 atherosclerotic lesions were identified, 16 (73%) occurring at the site of the electrical injury. At histology, 4 lesions were defined as Stary type I (isolated macrophages), 8 as type II (intracellular lipid accumulations), and 10 as type III (small extracellular lipid pools). No advanced (> or =type IV) lesions were documented. OCT failed to detect any type I lesions, but correctly defined a minority (2/8, 25%) of type II lesions and the majority (8/10, 80%) of type III lesions. For type III lesions, sensitivity, specificity and diagnostic accuracy of OCT were 80%, 95%, and 95%, respectively.

CONCLUSIONS

OCT can accurately detect intermediate (type-III) atherosclerotic lesions in vivo, but still fails to identify earlier stages of atherosclerosis.

Impact of vessel calcification on outcomes after coronary stenting

BACKGROUND

Calcified coronary arteries have few viable smooth muscle cells capable of proliferating, and, subsequently, might exhibit less in-stent restenosis. We therefore studied the outcome of stenting in patients with different amounts of coronary calcification.

METHODS

Six hundred twenty-one patients who underwent bare metal stenting of calcific native coronary arteries were studied retrospectively. Pre- and postinterventional intravascular ultrasound (IVUS) and qualitative and quantitative coronary angiography (QCA) were performed in 662 lesions. The arc of calcium was measured, and arteries were grouped (A, B, C, and D) according to the calcium arc in IVUS (0-90 degrees , 91-180 degrees , 181-270 degrees , and 271-360 degrees , respectively). Arteries with a superficial calcium arc of < or =270 degrees (Group E) were compared to arteries with >270 degrees calcification (Group F).

RESULTS

Clinical and lesion characteristics were similar, and the major complication rate was low (1.9%) in all groups. In Groups A, B, C, and D, patients with more calcific arteries had more non-Q-wave myocardial infarction (MI) (P=.04-.002). Patients in Group F (more extensive superficial calcification) had an increased frequency of non-Q-wave MI compared to Group E. Malapposition of stents to vessel wall and use of rotational atherectomy were more frequent in Group F (P=.001). Late events including death, MI, and revascularization with either coronary artery bypass grafting or percutaneous coronary intervention (PCI) were not different among the groups. Extensive calcification of coronary arteries is associated with more frequent peri-procedural non-Q-wave MI.

CONCLUSION

Despite the scarcity of viable cells, the late event rate in severely calcified arteries is not different from mildly calcified arteries. This may be due to more frequent malapposition of stents to vessel wall and augmented trauma during PCI in severely calcified arteries.

Assessment of coronary arterial plaque by optical coherence tomography

The purpose of this study was to analyze the ability of optical coherence tomography (OCT) to identify coronary arterial plaque diagnosed by histologic examination. We examined 166 sections from 108 coronary arterial segments of 40 consecutive human cadavers (24 men and 16 women; mean age 74 +/- 7 years). The plaque type was classified as fibrous (n = 43), fibrocalcific (n = 82), or lipid-rich (n = 41). The accuracy of OCT and intravascular ultrasound (IVUS) in characterizing the plaque type was studied, with the histologic consensus diagnosis serving as the gold standard. OCT, as well as IVUS, had high sensitivity and specificity for characterizing the different types of atherosclerotic plaque. OCT had a higher sensitivity for characterizing lipid-rich plaques than IVUS (85% vs 59%, p = 0.03). In conclusion, the high resolution of OCT permitted evaluation of lipid-rich plaques more accurately than IVUS.

Optical coherence tomography for imaging the vulnerable plaque

While our understanding of vulnerable coronary plaque is still at an early stage, the concept that certain types of plaques predispose patients to developing an acute myocardial infarction continues to be at the forefront of cardiology research. Intracoronary optical coherence tomography (OCT) has been developed to both identify and study these lesions due to its distinct resolution advantage over other imaging modalities. We review clinical research conducted at the Massachusetts General Hospital over the past five years to develop, validate, and utilize this technology to improve our understanding of vulnerable plaque. Our results show that intracoronary OCT may be safely conducted in patients and that it provides abundant information regarding plaque microscopic morphology, which is essential to the identification and study of high-risk lesions. Even though many basic biological, clinical, and technological challenges must be addressed prior to widespread use of this technology, the unique capabilities of OCT ensure that it will have a prominent role in shaping the future of cardiology.

Detection of cardiac cycle from intracoronary ultrasound

In this paper, we describe a method automatically to determine the phase of a cardiac cycle for each video frame of an intravascular ultrasound (IVUS) video recorded in vivo. We first review the principle of IVUS video and demonstrate the general applicability of our method. We show that the pulsating heart leads to phasic changes in image content of an IVUS video. With an image processing method, we can reverse this process and reliably extract the heart-beat phase directly from IVUS video. With the phase information, we demonstrate that we can build 3-D (3D) time-variant shapes and measure lumen volume changes within a cardiac cycle. We may also measure the changes of IVUS imaging probe off-center vector within a cardiac cycle, which serves as an indicator of vessel center-line curvature. The cardiac cycle extraction algorithm requires one scan of the IVUS video frames and takes O(n) time to complete, n being the total number of the video frames. The advantage of this method is that it requires no user interaction and no hardware set-up and can be applied to coronary scans of live beating hearts. The extracted heart-beat rate, compared with clinical recordings, has less than 1% error.

New techniques to evaluate esophageal function

Classical techniques like videofluoroscopy, stationary manometry and ambulatory 24-hour pH-metry are routinely used in the clinic to study patients with dysphagia, chest pain and reflux-related symptoms. Although many patients can be accurately diagnosed and their therapy successfully guided with these techniques, in many other patients, non-obstructive dysphagia or chest pain cannot be attributed to clear fluoroscopic or manometric abnormalities. Furthermore, ambulatory 24-hour pH-metry often shows a poor association between spontaneous acid reflux events and esophageal or extraesophageal symptoms, particularly in patients 'on' treatment. Non-obstructive dysphagia can be assessed with high-resolution manometry to detect segmental disturbances of peristalsis, increase in pressure gradient across the lower esophageal sphincter (LES) or abnormal axial movement of the LES during esophageal spasm. Impedance evaluation of bolus transit is a non-radiological method that can evaluate the functional relevance of manometric abnormalities. Patients with non-cardiac chest pain that do not respond to proton pump inhibitor therapy can be further assessed with intraluminal high-frequency ultrasound to detect sustained esophageal contractions of the longitudinal muscle layer. Impedance planimetry, with multimodal esophageal stimulation, may contribute to evaluate the sensitivity to mechanical, thermal and chemical stimuli. Finally, patients with persistent symptoms of gastroesophageal reflux in spite of adequate treatment with proton pump inhibitors may still have weakly acidic reflux and/or bile reflux associated with their symptoms. These types of refluxates can now be detected with combinations of pH-impedance or pH-Bilitec monitoring. This review will describe the available new techniques to evaluate patients with non-obstructive dysphagia, non-cardiac chest pain and persistent gastroesophageal reflux symptoms.

Regional material property alterations in porcine femoral arteries with atheroma development

We have developed a novel methodology that permits assessment of regional vascular mechanical property alterations in the presence of atheroma in vivo employing a Yucatan miniswine model with induced lesions. Femoral arteries were imaged with intravascular ultrasound. Image data were segmented and, following three-dimensional reconstruction, underwent finite element and sensitivity analysis with optimization to identify regions with altered vascular mechanical properties. All regions were compared to histological analysis. In 12 animals with 8 weeks of endothelial cell denudation and high cholesterol diet (induced atherosclerosis), the elastic modulus initially decreased with early lesion development and then increased with increasing fibrosis-(elastic modulus-all values x10(4)Pa-mean+/-SEM) histologically normal (non-denuded control segment) elements 9.73+/-0.01, fatty elements 9.53+/-0.01, fibrofatty elements 9.41+/-0.03, and fibrous elements 9.68+/-0.02 (all p<0.001 vs. normal elements). Wall thickness, however, increased with atheroma formation. These data demonstrate decreasing vascular material properties with early lesions, followed by an increase as lesions progress. This methodology permits determination of areas with early atheroma development, follow atheroma progression, and potentially evaluate interventions aimed at decreasing atheroma load and normalizing vascular material properties.

In vivo volumetric analysis of coronary stent using optical coherence tomography with a novel balloon occlusion-flushing catheter: a comparison with intravascular ultrasound

Optical coherence tomography (OCT) is limited as an intravascular imaging tool because of interference with blood. This study tested a new balloon occlusion-flushing catheter for OCT scanning of stented coronary arteries and compared stent measurements between OCT and intravascular ultrasound (IVUS). Motorized pullback with OCT and IVUS was examined in coronary stents deployed in swine. Quantitative measurements were obtained and compared between both groups. In addition, stent strut thickness was compared among OCT, IVUS and actual measurement. The occlusion catheter successfully provided motorized pullback OCT images in the stented coronary arteries without any complications. There were no differences in calculated lumen volume. However, stent volumes were significantly smaller with OCT than with IVUS (p < 0.05). OCT significantly underestimated the stent strut thickness compared with the actual measurement. Although OCT underestimates the stent strut thickness, motorized pullback OCT imaging with the occlusion catheter can provide appropriate in-stent images in the porcine coronary arteries.

Effectiveness of Sirolimus-Eluting Stent Implantation for the Treatment of Ostial Left Anterior Descending Artery Stenosis With Intravascular Ultrasound Guidance

OBJECTIVES

This study was designed to evaluate the clinical and angiographic outcomes of sirolimus-eluting stent (SES) implantation for ostial left anterior descending (LAD) lesions compared with bare-metal stent (BMS) implantation.

BACKGROUND

The effectiveness of SES implantation for ostial LAD lesions is currently unknown.

METHODS

Sirolimus-eluting stents were implanted in 68 consecutive patients with ostial LAD stenoses. The control group was composed of 77 patients treated with BMS during the preceding two years. In the SES group, for complete lesion coverage, stent positioning was intentionally extended into the distal left main coronary artery (LMCA) in 23 patients (34%) with intermediate LMCA narrowing.

RESULTS

Compared with the BMS group, the SES group had more multivessel involvement, received fewer debulking atherectomies, underwent more direct stenting, had a greater number of stents, and had more segments stented. The procedural success rate was 100% in both groups. The six-month angiographic restenosis rate was significantly lower in the SES group than in the BMS group (5.1% vs. 32.3%, p < 0.001). During the one-year follow-up period, neither death nor myocardial infarction occurred in either group, but target lesion revascularization was less frequent in the SES group than in the BMS group (0% vs. 17%, p < 0.001). In the SES group, there were no restenoses in cases with LMCA coverage, compared with three restenoses (7.9%) in cases with precise stent positioning (p = NS).

CONCLUSIONS

Sirolimus-eluting stent implantation in ostial LAD lesions achieved excellent results regarding restenosis and clinical outcomes compared with BMS implantation. This finding may be associated with reduced neointimal hyperplasia and complete lesion coverage.

Detection of Lipid-Laden Atherosclerotic Plaque by Wavelet Analysis of Radiofrequency Intravascular Ultrasound Signals

OBJECTIVES

This study examined the feasibility of using a wavelet analysis of radiofrequency (RF) intravascular ultrasound (IVUS) signals in detecting lipid-laden plaque.

BACKGROUND

Wavelet analysis is a new mathematical model for assessing local changes in a geometrical profile of time-series signals.

METHODS

Radiofrequency IVUS signals of 85 arbitrarily selected vectors were acquired from 27 formalin-fixed noncalcified atherosclerotic plaques from human necropsy with a digitizer at 500 MHz with 8-bit resolution by use of a 40-MHz IVUS catheter. Wavelet analysis of these RF signals was performed using a Daubechies-2 wavelet to obtain a color-coded map of the correlation coefficient with the wavelet reconstructed over the x-y plane of the wavelet scale and the distance from the IVUS catheter. The plaque segment was then examined histologically after being stained with Masson's trichrome stain. This technique also was applied in vivo in 29 human coronary plaque segments. These segments were excised subsequently by directional coronary atherectomy and processed for histologic analysis.

RESULTS

In the in vitro study, histologic examination revealed lipid-laden segments in 29 vectors. When performing a wavelet analysis with the Daubechies-2 wavelet, the color-coded mapping revealed a different pattern in lipid-laden plaques compared with other types of plaque. Using this wavelet analysis, lipid-laden plaque could be detected with a sensitivity of 83% (24 of 29) and a specificity of 82% (46 of 56). In the in vivo study, fatty plaque could be detected with a sensitivity of 81% (13 of 16) and a specificity of 85% (11 of 13) with this method.

CONCLUSIONS

Wavelet analysis of RF IVUS signals enabled in vitro as well as in vivo detection of lipid-laden plaque. This method may be useful in assessing plaque vulnerability in patients with coronary artery disease.

Porcine carotid arterial material property alterations with induced atheroma: an in vivo study

OBJECTIVE

A novel methodology has been developed to evaluate regional alterations in arterial wall material properties with induced atheroma in an animal model.

METHODS

Atheromatous lesions (fatty, fibro-fatty, and fibrous) were induced in the carotid arteries of a Yucatan miniswine model by endothelial cell denudation and high cholesterol diet. The images at base line and 8 weeks after denudation were obtained using intravascular ultrasound (IVUS) imaging along with hemodynamic data. Finite element analysis (FEA) along with optimization was employed to assess regional alterations in elastic modulus in the presence of atheroma confirmed by histology.

RESULTS

In animals with 8 weeks of induced atherosclerosis, the elastic modulus increased-(elastic modulus-all values x 10(4) Pa, mean+/-S.D.) normal elements (9.34+/-0.36) compared to abnormal elements (9.52+/-0.36) (p<0.05 versus normal elements). Wall thickness increased with atheroma formation. These data demonstrate stiffening vascular wall elastic modulus with lesion progression. This is different from the behavior of femoral arteries, where the elastic modulus decreases with early stages of atheroma development followed by an increase as lesions progress.

CONCLUSIONS

This methodology permits determination of areas with early atheroma development, follow atheroma progression, and potentially evaluate interventions aimed at decreasing atheroma load and normalizing vascular material properties.

Motor and sensory function of the esophagus: revelations through ultrasound imaging

Catheter based high frequency intraluminal ultrasound (HFIUS) imaging is a powerful tool to study esophageal sensory and motor function and dysfunction in vivo in humans. It has provided a number of important insights into the longitudinal muscle function of the esophagus. Based on the ultrasound images and intraluminal pressure recordings, it is clear that there is synchrony in the timing as well as the amplitude of contraction between the circular and the longitudinal muscle layers of the esophagus in normal subjects. On the other hand, in patients with spastic disorders of the esophagus, there is an asynchrony of contraction related to the timing and amplitude of contraction of the two muscle layers during peristalsis. Achalasia, diffuse esophageal spasm, and nutcracker esophagus (spastic motor disorders of the esophagus) are associated with hypertrophy of the circular as well as longitudinal muscle layers. A sustained contraction of the longitudinal muscle of the esophagus is temporally related to chest pain and heartburn and may very well be the cause of symptoms. Longitudinal muscle function of the esophagus can be studied in vivo in humans using dynamic ultrasound imaging. Longitudinal muscle dysfunction appears to be important in the motor and sensory disorders of the esophagus.

Protein kinase C regulation of GABAA receptors

Pharmacological studies with drugs that activate or inhibit several protein kinase C (PKC) isozymes have identified the PKC family of serine-threonine kinases as important in the regulation of gamma-aminobutyric acid type A (GABA(A)) receptor function. PKC modulates GABA(A) receptor surface density, chloride conductance and receptor sensitivity to positive allosteric modulators such as neurosteroids, ethanol, benzodiazepines and barbiturates. Recent studies using PKC isozyme-selective reagents and gene-targeted mice have begun to identify critical roles for three isozymes, PKCbetaII, PKCvarepsilon and PKCgamma, in various aspects of GABA(A) receptor regulation. Progress in this field touches upon therapeutic areas that are of great clinical importance such as anxiety and addiction. Increased understanding of how PKC regulates GABA(A) receptors and which PKC isozymes are involved holds promise for development of new treatments for diverse neuropsychiatric disorders.

Intravascular ultrasound: defining plaque regression

Intravascular ultrasound allows accurate assessment of the arterial vessel, including vessel luminal diameter and assessment of vessel disease in terms of plaque morphology, plaque volume and extent of calcification. Recently published trials highlight the role of intravascular ultrasound in monitoring disease progression in a clinical setting.

Sirolimus-eluting stent implantation for unprotected left main coronary artery stenosis

OBJECTIVES

This study was designed to compare the clinical and angiographic outcomes of sirolimus-eluting stent (SES) and bare metal stent (BMS) implantation for unprotected left main coronary artery (LMCA) stenosis.

BACKGROUND

The safety and effectiveness of SES implantation for unprotected LMCA stenosis have not been ascertained.

METHODS

Elective SES implantation for de novo unprotected LMCA stenosis was performed in 102 consecutive patients with preserved left ventricular function from March 2003 to March 2004. Data from this group were compared to those from 121 patients treated with BMS during the preceding two years.

RESULTS

Compared to the BMS group, the SES group received more direct stenting, had fewer debulking atherectomies, had a greater number of stents, had more segments stented, and underwent more bifurcation stenting. The procedural success rate was 100% for both groups. There were no incidents of death, stent thrombosis, Q-wave myocardial infarction (MI), or emergent bypass surgery during hospitalization in either group. Despite less acute gain (2.06 +/- 0.56 mm vs. 2.73 +/- 0.73 mm, p < 0.001) in the SES group, SES patients showed a lower late lumen loss (0.05 +/- 0.57 mm vs. 1.27 +/- 0.90 mm, p < 0.001) and a lower six-month angiographic restenosis rate (7.0% vs. 30.3%, p < 0.001) versus the BMS group. At 12 months, the rate of freedom from death, MI, and target lesion revascularization was 98.0 +/- 1.4% in the SES group and 81.4 +/- 3.7% in the BMS group (p = 0.0003).

CONCLUSIONS

Sirolimus-eluting stent implantation for unprotected LMCA stenosis appears safe with regard to acute and midterm complications and is more effective in preventing restenosis compared to BMS implantation.

Sensory and motor function of the esophagus: lessons from ultrasound imaging

Catheter-based high-frequency intraluminal ultrasound imaging is a powerful tool to study esophageal sensory and motor function and dysfunction in vivo in humans. It can be combined with manometry, pH, and impedance measurement techniques to determine the relationships between different physiologic parameters. High-frequency intraluminal ultrasound imaging has provided a number of important insights regarding the longitudinal muscle function of the esophagus. On the basis of the ultrasound images and intraluminal pressure recordings, it seems that there is synchrony in the timing and the amplitude of contraction between the circular and longitudinal muscle layers. A sustained contraction of the longitudinal muscle layer is temporally related to esophageal chest pain and heartburn. The biomechanics of the esophageal wall and its relationship to sensory and motor function can be studied in humans in vivo by using high-frequency intraluminal ultrasound much more precisely than has previously been possible. Achalasia, diffuse esophageal spasm, and nutcracker esophagus are associated with hypertrophy of circular and longitudinal muscle layers. Finally, high-frequency intraluminal ultrasound imaging is the only technique that can detect reflux-related distention of the esophagus and its role in esophageal symptoms. Future approaches to display and quantify ultrasound image data are discussed. The principles of high-frequency intraluminal ultrasound described here are also applicable to study of the motor and sensory function of the other regions of the gastrointestinal tract.

Assessment of Coronary Intima - Media Thickness by Optical Coherence Tomography Comparison With Intravascular Ultrasound

BACKGROUND

Optical coherence tomography (OCT) is a new imaging method. With a resolution of approximately 10-20 Em, which is approximately 10-fold higher than that of intravascular ultrasound (IVUS).

METHODS AND RESULTS

This study compared the coronary intima - media thickness (IMT) and the intimal thickness of 54 coronary arterial segments evaluated by histological examination with the results of OCT and IVUS. There was better agreement in IMT between OCT and histological examination than between IVUS and histological examination (r = 0.95, p < 0.001, mean difference = -0.01+/-0.07 mm for OCT; r = 0.88, p < 0.001, mean difference = -0.03+/-0.10 mm for IVUS). There was good agreement in the intimal thickness between OCT and histological examination (r = 0.98, p < 0.001, mean difference = 0.01+/-0.04 mm).

CONCLUSIONS

IMT could be measured more accurately by OCT than IVUS. In addition, the intimal thickness could be evaluated by OCT and correlated well with the histological examination.

Intravascular ultrasound evaluation of ruptured plaque in the left main coronary artery misinterpreted as an aneurysm by angiography

We report a patient who demonstrated a left main coronary aneurysm by angiography. Intravascular ultrasound (IVUS) revealed that it was in fact an ulceration, which indicated ruptured plaque. This case provides evidence that IVUS can permit a more powerful definition of ruptured plaque than angiography. On IVUS, ulceration exhibits significantly different characteristics from aneurysm.

Randomized comparison of debulking followed by stenting versus stenting alone for ostial left anterior descending artery stenosis: intravascular ultrasound guidance

BACKGROUND

Although directional coronary atherectomy (DCA) before stenting has the advantage of combining substantial removal of atheromatous plaque and prevention of elastic recoil, there has been no randomized study to investigate its efficacy in ostial left anterior descending artery (LAD) lesions. This study was aimed to evaluate the effect of DCA followed by stenting on ostial LAD stenosis under the guidance of intravascular ultrasound (IVUS).

METHODS

Eighty-six patients with ostial LAD stenoses were randomly assigned to DCA followed by stenting (group I) or stenting alone (group II). Aggressive DCA or optimal stenting was performed in both groups under the guidance of IVUS. The primary end point was angiographic restenosis at 6 months.

RESULTS

Baseline clinical and angiographic characteristics were similar between the 2 groups. The postprocedural minimal lumen diameter was larger in group I than group II (4.0 +/- 0.4 mm vs. 3.5 +/- 0.5 mm, P <.001). However, the angiographic restenosis rates were not significantly different between the 2 groups (9/32 [28.1%] in group I vs. 11/30 [36.7%] in group II, P =.472). The postprocedural IVUS stent area was the only independent determinant of restenosis by multivariate analysis (odds ratio.61, 95% CI 0.41-0.92, P =.018).

CONCLUSIONS

DCA followed by stenting achieved greater lumen gain than stenting alone for ostial LAD stenosis. However, DCA did not improve angiographic restenosis.

The salvage of graft occlusion in a maintenace hemodialysis patient with tuberous sclerosis by percutaneous transluminal angioplasty using intravascular ultrasound: case report

End-stage renal failure due to tuberous sclerosis is rare and there is no previous report of a patient with tuberous sclerosis undergoing long-term hemodialysis for over 18 years. The patency rate for a dialysis prosthetic graft is low, however, our patient's graft survived over 16 years. For thrombotic occlusion of a graft, we performed percutaneous thrombectomy and balloon angioplasty and salvaged graft occlusion. Moreover, this case is the first report in which the interventional procedure (mechanical thrombectomy and balloon angioplasty) could be observed by intravascular ultrasound in addition to angiography.

The decrease of plaque volume during percutaneous coronary intervention has a negative impact on coronary flow in acute myocardial infarction

OBJECTIVES

The aim of this study was to evaluate how decreased plaque volume during percutaneous coronary intervention (PCI) affects coronary flow in patients with acute myocardial infarction (AMI).

BACKGROUND

Coronary flow after reperfusion therapy is a major determinant of clinical outcomes in patients with AMI. However, little is still known about the changes in coronary flow that appear after PCI in response to the decreased plaque during the procedure.

METHODS

The study group comprised 60 patients with AMI who underwent pre- and post-PCI intravascular ultrasound (IVUS). Qualitative and quantitative analyses were performed on all IVUS procedures. External elastic membrane volume (EEMV), lumen volume (LV), and plaque volume (PV) were measured every 1.0 mm to include the lesion and reference segments 3.0 mm proximal and distal to the lesion. The difference between pre- and post-PCI PV was defined as the index of the decrease in plaque volume (DeltaPV). The corrected TIMI frame count (CTFC) was used to evaluate coronary flow after PCI.

RESULTS

Plaque volume was decreased at post-PCI IVUS in all 60 patients. Inadequate reflow (CTFC >40) was observed in 13 patients (21.7%). The decrease in PV was significantly larger in patients with inadequate reflow than in those with reflow (49.4 +/- 18.9 vs. 31.7 +/- 15.5 mm(3), p = 0.0010). Also, DeltaPV was significantly correlated with CTFC after PCI (r = 0.415, p = 0.0012).

CONCLUSIONS

The decrease in PV during PCI has a negative impact on coronary flow after PCI in patients with AMI. Embolization induced by PCI may occur in all patients with AMI.

A comparison of 10 MHz and 20 MHz ultrasound probes in imaging the eye and orbit

BACKGROUND

/aims: B-scan ultrasonography is an invaluable, versatile, non-invasive tool in ophthalmology. Recently, a "high frequency" contact 20 MHz probe has been introduced. B-scanning ultrasonography of orbital and ocular structures was performed with both a 10 MHz and the new 20 MHz probe, to evaluate what information was best obtained from each probe, and provide recommendations for the use of each.

METHODS

Patients were selected from routine ultrasound clinics at Aberdeen Royal Infirmary between 1 January 2002 and 1 August 2002. The vitreous, retina, choroid, sclera and, in the orbit, the extraocular muscles, optic nerve, and orbital fat were assessed with both the 10 MHz and 20 MHz probes. In the laboratory, using a "point target," the characteristics of the ultrasound beam at different distances from the probe were also assessed.

RESULTS

The point target showed that focus was deeper and that the lateral, and to a lesser degree the axial, resolution are sharper with the 20 MHz probe, compared with the 10 MHz probe. In patients' eyes, highly reflective structures are seen at higher resolution with the 20 MHz probe. Imaging of lower intensity reflectors such as the vitreous and particles within it are seen better with the 10 MHz probe. Increased tissue attenuation was evident with the 20 MHz probe.

CONCLUSION

The 20 MHz probe has a superior resolution and can be used to better detect details at the posterior pole and in the orbit. The 10 MHz probe can be used to examine low intensity scatterers, such as the vitreous humour, that cannot be seen using a higher frequency probe.

Routine intravascular ultrasound guidance of percutaneous coronary intervention

Intravascular ultrasound (IVUS) has played an integral role in the evolution of interventional cardiology. However, routine IVUS guidance of coronary stent implantation is not supported by a critical reappraisal of the available evidence. Although there is a trend toward a benefit with respect to target lumen revascularization favoring IVUS-guided coronary stent implantation, it is likely that this effect is driven by improved outcomes in small vessels, long coronary stenoses, and possibly saphenous vein graft interventions. No consistent trend in the incidence of death or myocardial infarction is apparent. Furthermore, the safety, efficacy, and effectiveness of IVUS should be taken into account when considering the goals, risks, benefits, and alternatives to such a treatment strategy.

Extra-stent vascular remodeling in in-stent restenosis after 188Re-MAG3 radiation therapy

BACKGROUND

The effect of beta-radiation on extra-stent vascular remodeling in patients with in-stent restenosis has not been studied. The correlation between the extent of extra-stent plaque proliferation and that of intimal hyperplasia (IH) in in-stent restenosis in patients who received beta-radiation therapy as well as conventional therapy has also not been studied.

METHODS

We evaluated the extra-stent remodeling in diffuse in-stent restenosis between a beta-radiation therapy patient group (188Re-MAG3, n=50) and a control group (n=9) by applying serial intravascular ultrasound (IVUS) analysis. Matching (post-intervention and follow-up) images were acquired at the follow-up lesion site and were available in 44 of 50 patients who received radiation therapy and in seven of nine control patients.

RESULTS

There was a significant increase of the external elastic membrane (EEM) area in both groups: 16.4 +/- 3.3 mm2 post-intervention to 17.1 +/- 3.3 mm2 at follow-up, P=0.001 in the radiation therapy group, and 16.8 +/- 4.0 mm2 post-intervention to 17.4 +/- 4.1 mm2 at follow-up, P=0.008 in the control group. There were no statistically significant differences of the Delta EEM area between the two groups: 0.7 +/- 0.4 mm2 in the radiation therapy group vs. 0.6 +/- 0.4 mm2 in the control group, P=0.389. The Delta IH area correlated with the Delta EEM area in the control group (r=0.826, P=0.022), but not in the radiation therapy group (r=0.016, P=0.919).

CONCLUSIONS

The findings of this IVUS study were that positive remodeling (increased EEM area) occurred equally in both control and irradiated patients with in-stent restenosis. The extent of remodeling was directly in proportion to IH in the control group, but no such relationship existed in the irradiated patient group.

Intravascular ultrasound assessment of patterns of arterial remodeling in the absence of significant reference segment plaque burden in patients with coronary artery disease

OBJECTIVES

We evaluated the impact of reference vessel segment plaque burden on lesion remodeling. Intravascular ultrasound (IVUS) assessment of lesion remodeling compares lesions to reference segments. However, reference segments are rarely disease-free and, therefore, have also undergone remodeling changes.

METHODS

Pre-intervention IVUS was obtained in 274 patients with right coronary artery lesions selected because the right coronary artery has less tapering and fewer side branches than the left anterior descending or left circumflex artery. Standard IVUS definitions were used. Patients were divided according to reference vessel segment plaque burden: group A (minimal reference disease, n = 91), both proximal and distal reference plaque burden <20%; group B (n = 91), either proximal or distal reference plaque burden 20% to 40% but both < or =40%; and group C (n = 92), either proximal or distal reference plaque burden >40%.

RESULTS

The remodeling index measured 0.98 +/- 0.16 in group A (range, 0.68 to 1.47), 1.04 +/- 0.18 in group B (range, 0.67 to 1.91), and 1.04 +/- 0.15 in group C (range, 0.74 to 1.70), analysis of variance p = 0.0208 (p = 0.0234 group A vs. group B and p = 0.0012 group A vs. group C, but p = 0.8 group B vs. group C). Positive, intermediate, and negative remodeling were observed in 24 (26%), 24 (26%), and 43 lesions (48%) in group A; 36 (40%), 28 (30%), and 27 lesions (30%) in group B; and 34 (37%), 39 (42%), and 19 lesions (21%) in group C, respectively (p = 0.0022).

CONCLUSIONS

Negative remodeling occurs commonly in coronary lesions with minimal reference segment disease. Negative remodeling is not just an "artifact" introduced by comparing lesions to diseased reference segments.