Interventional applications of intravascular ultrasound imaging: initial experience and future perspectives

Intravascular ultrasound imaging offers the potential to provide more detailed information about vessel and lesion morphology and physiology than is currently available from angiography. The greatest impact of intravascular ultrasound upon clinical decisions may be in the area of cardiac and vascular interventions. To evaluate the utility of intravascular ultrasound, we prospectively studied 45 patients, 11 of whom underwent interventional procedures. Intravascular ultrasound imaging was performed before and after interventions using a 20 MHz, mechanically rotating transducer on either 6.5 Fr or 8.0 Fr catheter systems. Interventions included seven peripheral vessel balloon angioplasties (Femoral artery-two, Renal artery-two, Arteriovenous fistula-two, Aortic coarctation-one), two Femoral artery rotational atherectomies, and two balloon valvuloplasties (Pulmonic valve-1, Mitral valve-1). Intravascular ultrasound and digital angiography provided similar information about vessel size. However, morphological information about the vessel wall, plaque composition, plaque topography, luminal thrombus, and vessel dissections was better appreciated by intravascular ultrasound. Intravascular ultrasound was determined to have provided unique and clinically useful information in 10/11 (91%) interventions. These preliminary data illustrate the potential value of intravascular ultrasound for the evaluation of the vascular system and in particular its value in interventional procedures.     

Clinical indications for intravascular ultrasound imaging

Intravascular ultrasound (IVUS) is a catheter-based imaging modality, which provides high resolution cross-sectional images of the coronary arteries. Unlike angiography, which displays only the opacified luminal silhouette, IVUS permits imaging of both the lumen and vessel wall and allows characterization of the type of the plaque. Although IVUS provides accurate quantitative and qualitative information regarding the lumen and outer vessel wall, it is not routinely used during coronary angiography or in angioplasty procedures because the risk to benefit ratio (additional expense, procedural time, certain degree of risk, and complication versus improvement in the outcome) does not justify routine utilization. Nevertheless, there are situations where IVUS is extremely useful tool both for diagnosis and management so the aim of this review is to summarize the indications for IVUS imaging in the contemporary clinical practice.     

血管内超声表现不同的冠状动脉斑块临床特点比较

目的 采用血管内超声（IVUS）分析冠心病患者冠状动脉内斑块的临床特点。方法 入选2010年1月至2013年12月在沈阳军区总医院心内科住院并经冠状动脉造影证实的冠心病患者220例,根据IVUS斑块回声强弱分为3组：衰减斑块组（n＝42）,钙化斑块组（n＝63）和纤维斑块组（n＝115）。对此220例患者的基线资料和斑块特点进行比较分析。根据IVUS检查结果,确定需行经皮冠状动脉介入治疗（PCI）术的患者有140例（全部成功）,其中衰减斑块组26例（PCI比率62%）,钙化斑块组41例（PCI比率65%）、纤维斑块组73例（PCI比率63%）。对此140例患者的斑块特点、PCI术特点以及随访情况进行比较分析。结果 钙化斑块组患者年龄较其余两组大（P＜0.05）,总胆固醇（TC）和低密度脂蛋白胆固醇（LDL-C）均显著低于其余两组（P＜0.05）;衰减斑块组患者的既往心肌梗死或冠状动脉搭桥术（CABG）以及吸烟史均显著高于其余两组（P＜0.05）。钙化斑块组的最小管腔面积和病变血管直径显著低于其余两组（P＜0.05);与其他两组患者相比,衰减斑块组患者的斑块负荷较重、病变血管面积较大（P＜0.05）。在行PCI术的患者中：与其他两组患者相比,衰减斑块组患者的斑块负荷较重（P＜0.05）。行PCI术的各组患者在1年内发生死亡、心肌梗死和再次血运重建的概率间无统计学差异（P＞0.05）。结论 吸烟、既往心肌梗死或CABG史与衰减斑块的发生有关;与钙化斑块组及纤维斑块组相比,衰减斑块组具有较大的斑块负荷;PCI对IVUS证实的不稳定斑块具有较好的治疗效果。     

Clinical perspectives of intravascular ultrasound

The history of intravascular ultrasound imaging, recent developments in catheter technology, and the initial in vivo experience are reviewed. Additionally, the article also discusses the potential applications of intravascular ultrasound imaging in coronary and peripheral arterial atherosclerosis, hypertension, pulmonary arterial disorders, valvular heart disease, aortic abnormalities, and in congenital heart disorders. Possible future directions are outlined.     

Feasibility of intravascular ultrasound studies: Predictors of imaging success before coronary interventions

Background: Intravascular ultrasound (IVUS) is currently used to study lesions during transcatheter coronary therapy. However, before dilation some lesions cannot be reached or crossed with the imaging catheter. Hypothesis: This study seeks to elucidate which factors determine the feasibility of IVUS examination before coronary interventions. Methods: Accordingly, 100 consecutive patients undergoing IVUS examination before coronary angioplasty were prospectively studied. The clinical and angiographic characteristics of 77 patients with a successful IVUS study (Group A) were compared with those of 23 patients in whom IVUS was attempted but the target lesion could not be interrogated (Group B). The echogenic characteristics of the target lesion [before (n = 77) or after intervention (in 18 patients in Group B)] were also studied. Results: Patients in Group B were significantly older (62 ± 7 vs. 57 ± 10 years, p < 0.05) and more frequently had stable angina [8 (35%) vs. 9 (11%), p < 0.05]. The distribution of lesions within the coronary tree and angiographic lesion characteristics including length, eccentricity, calcification, bend location, and the American College of Cardiology/American Heart Association classification were similar in both groups. However, proximal tortuosities (>45° at end diastole) were more frequently found in Group B [20 (87%) vs. 47 (61%), p < 0.05]. In addition, by quantitative angiography, patients in Group B had smaller arteries (reference diameter 2.8 ± 0.4 vs. 3.1 ± 0.4 mm, p < 0.05) and more severe lesions (minimal lumen diameter 0.46 ± 0.24 vs. 0.65 ± 0.34 mm, p < 0.05). On IVUS, calcified lesions were more frequently visualized in Group B (61 vs. 38%, p < 0.05). On multivariate analysis, catheter size, baseline minimal lumen diameter, angiographic proximal tortuosities, and lesion calcification on imaging were independent predictors of the feasibility of IVUS studies. Conclusions: Unsuccessful IVUS studies before intervention occur more frequently (1) in vessels with proximal tortuosities or severe lumen narrowing, (2) in lesions that are calcified on IVUS, and (3) when large imaging catheters are used.     

The potential value of intravascular ultrasound imaging in diagnosis of aortic intramural hematoma

Objective To evaluate the potential value of intravascular ultrasound (IVUS) imaging in the diagnosis of aortic intramural hematoma (AIH). Methods From September 2002 to May 2005, a consecutive series of 15 patients with suspected aortic dissection (AD) underwent both IVUS imaging and spiral computed tomography (CT). Six patients diagnosed as acute type B AIH by CT or IVUS composed the present study group. Results The study group consisted of five males and one female with mean age of 66 years old. All of them had chest or back pain. In one patient, CT omitted a localized AIH and an associated penetrating atherosclerotic ulcer (PAU), which were detected by IVUS. In another patient, CT mistaken a partly thrombosed false lumen as an AIH, whereas IVUS detected a subtle intimal tear and slow moving blood in the false lumen. In the four rest patients, both CT and IVUS made the diagnosis of AIH, however, IVUS detected three PAUs in three of them, only one of them was also detected by CT, and two of them escaped initial CT and were confirmed by follow up CT or magnetic resonance imaging. Conclusions IVUS imaging is a safe examination and has high accuracy in the diagnosis of AIH, particularly for diagnosing localized AIH, distinguishing AIH with thrombosed classic AD and detecting accompanied small PAUs.     

Lesion characteristics of acute myocardial infarction: an investigation with intravascular ultrasound

OBJECTIVE—To use intravascular ultrasound (IVUS) to compare plaque morphology in acute myocardial infarction and stable angina pectoris.
DESIGN—Retrospective study.
SETTING—Primary care hospital.
PATIENTS—59 consecutive cases of acute myocardial infarction and 50 consecutive cases of stable angina pectoris.
METHODS—IVUS was used before coronary intervention.
MAIN OUTCOME MEASURES—Plaque morphology (incidence of eccentric plaque, subtle dissections, low echoic thrombus, calcification, echolucent areas, and bright speckled echo material), assessed visually using IVUS.
RESULTS—There were no significant differences in plaque eccentricity or calcification between the two groups, but low echoic thrombus (acute myocardial infarction 15% v stable angina pectoris 0%), subtle dissections (37% v 4%), echolucent areas (31% v 0%), and bright speckled echo material (90% v 0%) were more common in the infarction group than in the stable angina group (p < 0.001 for all). There was a longer time between the onset of symptoms and the IVUS examination in patients with low echoic thrombus than in those without (p < 0.03).
CONCLUSIONS—Low echoic thrombus, subtle dissections, echolucent areas, and bright speckled echo material are morphological characteristics associated with plaque at the time of acute myocardial infarction. These findings correspond pathologically to ruptured plaque.


Keywords: intravascular ultrasound; acute myocardial infarction; plaque morphology     

Validation of quantitative analysis of intravascular ultrasound images

This study investigated the accuracy and reproducibility of a computer-aided method for quantification of intravascular ultrasound. The computer analysis system was developed on an IBM compatible PC/AT equipped with a framegrabber. The quantitative assessment of lumen area, lesion area and percent area obstruction was performed by tracing the boundaries of the free lumen and original lumen.Accuracy of the analysis system was tested in a phantom study. Echographic measurements of lumen and lesion area derived from 16 arterial specimens were compared with data obtained by histology. The differences in lesion area measurements between histology and ultrasound were minimal (mean ± SD: –0.27±1.79 mm², p>0.05). Lumen area measurements from histology were significantly smaller than those with ultrasound due to mechanical deformation of histologic specimens (–5.38±5.09 mm², p<0.05). For comparison with angiography, 18 ultrasound cross-sections were obtainedin vivo from 8 healthy peripheral arteries. Luminal areas obtained by angiography were similar to those by ultrasound (–0.52±5.15 mm², p>0.05). Finally, intra- and interobserver variability of our quantitative method was evaluated in measurements of 100in vivo ultrasound images. The results showed that variations in lumen area measurements were low (5%) whereas variations in lesion area and percent area obstruction were relatively high (13%, 10%, respectively).Results of this study indicate that our quantitative method provides accurate and reproducible measurements of lumen and lesion area. Thus, intravascular ultrasound can be used for clinical investigation, including assessment of vascular stenosis and evaluation of therapeutic intervention.Dr. C.D. Mario, Div. of Cardiology, Vicenza, Italy, is the recipient of the E.S.C. Research Fellowship 1991.     

Imaging of pulmonary vascular disease by intravascular ultrasound

To assess the ability of intravascular ultrasound (IVUS) to image changes in the pulmonary arterial wall associated with pulmonary hypertension (PHT), 10 subjects requiring diagnostic right and left heart catheterization were studied. In addition to measurements of pulmonary artery pressure and pulmonary vascular resistance and pulmonary angiography, when indicated, all underwent simultaneous IVUS imaging in the pulmonary arterial system using a 20 MHz ultrasound transducer mounted on a 2 mm diameter catheter. Four patients had normal pulmonary artery pressures and 6 had varying degrees of PHT. Satisfactory ultrasound images were obtained in 9 out of the 10 patients. In those with normal pulmonary artery pressures ultrasound showed a thin vessel wall with no destinction between separate layers. In patients with systemic PHT, a threelayered vessel wall was apparent and areas compatible with intimai proliferation were seen. In a patient with pulmonary embolic disease areas consistent with mural thrombus were detected at sites of luminal narrowing on the pulmonary angiogram. IVUS is capable of imaging some of the morphological changes in the wall of the pulmonary artery known to occur in longstanding PHT and may therefore become a useful adjunct to haemodynamic measurements and pulmonary angiography for thein vivo assessement of pulmonary vascular disease.Abbreviations IVUS intravascular ultrasound - PHT pulmonary hypertension     

In vitro and in vivo intravascular ultrasound imaging.

This paper presents our experience with intravascular ultrasound imaging of animal and human arteries in vitro and in vivo using a high-frequency (20 M Hz) ultrasound transducer. In vitro, 32 human coronary artery segments were imaged with intravascular ultrasound and compared with corresponding histological sections. Ultrasound and histology measurements correlated significantly (P less than 0.0001) for coronary artery cross-sectional area (r = 0.94), lumen cross-sectional area (r = 0.85) and wall thickness (r = 0.92). In vivo, 19 sheep and eight human common femoral arteries were imaged and the angiographic lumen diameter of 14 animal and six human arteries was compared to the diameter of the corresponding ultrasound images. Significant correlations were found for lumen diameter in animals and humans (P less than 0.001, r = 0.91 and P less than 0.0001, r = 0.96, respectively). These studies demonstrate that this technique can provide high resolution images of arterial vessels and may have unique advantages in diagnosing atherosclerotic vascular disease and in catheter based therapies.     

Intravascular ultrasound cross-sectional arterial imaging

In this paper we review the current status of intravascular ultrasound. Data from qualitative and quantitative studies is presented. Our experimental findings and those of other investigators are reviewed. Intravascular ultrasound has been shown to delineate normal and abnormal arterial morphology as well as to identify and differentiate fibrous, lipid-rich, calcified plaques and complicated plaques. Quantitative studies show strong correlations between ultrasound and histology for lumen area, wall thickness, and plaque area. In vivo studies from our experimental work and clinical laboratory as well as the work of other researchers is presented. This data supports the potential of ultrasound imaging for guidance of intravascular intervention. The potential advantages and limitations of this new technology are discussed. This methodology shows promise for the assessment of the extent and severity of atherosclerosis, monitoring its progression and regression and guiding intravascular plaque ablation technologies.     

Ambiguous coronary angiography: Clinical utility of intravascular ultrasound

We report the use of intravascular ultrasound (IVUS) in situations where angiography was ambiguous or uncertain in assessing the significance of coronary stenoses. The indications for performing intravascular ultrasound were (1) angiographic findings did not correlate with the clinical presentation (n = 5) and (2) the lesion was not seen well by angiography because of overlapping vessels at the site of suspected stenosis (n=3). We studied eight lesions in seven patients. Six nonobstructive stenoses on angiography were shown by IVUS to be significant. In two patients, stenoses were thought to be significant on angiography, but, due to overlapping of the vessels, there was doubt regarding the severity of the narrowing. In these two patients, IVUS clearly showed that the lesions were nonobstructive. As seen from the above results, angiography underestimated 6/8 stenoses and overestimated in 2/8 stenoses when compared to IVUS. We conclude that IVUS can be used to clarify ambiguous angiographic findings which can have a major impact on the clinical decision making. © 1992 Wiley-Liss, Inc.     

Application of intravascular ultrasound for detection and quantitation of coronary atherosclerosis

Although angiography is widely utilized to assess the extent and severity of coronary artery disease (CAD), arteriography yields only a silhouette of the vessel lumen. Coronary intravascular ultrasound supplements angiography by providing a tomographic perspective of lumen geometry and vessel wall structure. Intracoronary ultrasound can now be performedin vivo utilizing small, flexible probes capable of negotiating tortuous vessles. We have performed coronary ultrasound in more than 100 patients, including a group of normal subjects, with no serious complications. Measurements of coronary lumen dimensions by angiography and ultrasound correlated closely for normal vessels (r=0.92) and for concentrically narrowed atherosclerotic vessels (r=0.90). However, the correlation between angiography and ultrasound was only fair for eccentrically narrowed arteries (r=0.79) and was poor following angioplasty (r=0.30). Coronary artery wall motion was measured by intravascular ultrasound and demonstrated significant differences between normal arteries (18% lumen area change) and atherosclerotic vessels (11% change). Coronary ultrasound demonstrated important differences in the structure of normal and altherosclerotic vessel walls. Arteries in normal subjects exhibited a thin intimal leading-edge echo (mean 0.20 mm) and subadjacent sonolucent zone (mean 0.12 mm). Atherosclerotic vessels typically demonstrated increased thickness of both structures and often exhibited dense fibrocalcific plaques that shadowed underlying anatomy. These ultrasound abnormalities were often present at angiographically normal sites. Several limitations of coronary intravascular ultrasound were apparent, including echo dropout, distortions produced by non-coaxial imaging, and inability to image small or severely narrowed vessels. Coronary intravascular ultrasound holds great promise for the detection and quantification of CAD in the clinical setting.     

Assessment of contemporary stent deployment using intravascular ultrasound.

Four second- and third-generation coronary stents were evaluated using QCA and intravascular ultrasound for adequacy of stent expansion, the influence of disease burden on adequacy of deployment, and postdeployment structural effects on the artery. Despite satisfactory stent deployment rates on angiography of 92 %, adequate stent deployment by IVUS ranged from 38% to 55%. There was no significant difference in deployment success across the four stent types. Lesions with significant plaque burden were associated with a lower rate of deployment success (P = 0.04). Twenty-one edge dissections were demonstrated by IVUS; only six were detected by angiography. Observations made on first-generation stents regarding adequacy of deployment still hold true for newer-generation stents. Significant plaque burden is an independent negative predictor of stent deployment success. The presence of IVUS-detected edge dissections indicates that the extent of injury during PCI extends beyond the physical length of the stent.     

Importance of calibration for diameter and area determination by intravascular ultrasound

Background: Intravascular ultrasound (IVUS) permits quantitative assessment of the lumen diameter and area of coronary arteries. The experimental study was performed to evaluate the accuracy of diameter and area measurements.Methods and results: Lumen quantitation (lumen diameter D and cross-sectional area A) in lucite tubes (lumen diameter 2.5 to 5.7 mm, Plexiglas) was performed using a mechanical IVUS system (HP console, 3.5F catheter, Boston Scientific, 30 MHz). The influence of fluid type (blood, water and saline solution), fluid temperature (20°C/37°C), catheter to catheter variation, gain setting and ultrasound frequency (12, 20 and 30 MHz) was determined. In blood at 20°C there was a constant deviation of the measured diameter from the true luminal diameter of –0.29 ± –0.04 mm (p<0.06). In water and saline solution at 20°C the mean deviation from true diameter was –0.21 ± –0.06 mm (p<0.06). At 37°C, the deviation in blood was greater than at 20° (–0.34 ± –0.02 mm) which is >10% in a 3mm tube (p<0.06). Three of the ten catheters tested in water at 20°C underestimated true diameter by more than –0.3 mm. The deviation from true diameter (5mm tube) with varying gain settings was –0.14 mm to –0.23 mm compared to –0.19 mm at standard settings (p>0.288). At 12 MHz diameter measured was over-estimated. The error in absolute area estimation increased with increasing diameter tested in blood at 37°C (–1.21 to –2,72mm²), whereas the relative error ([Measured Area-True Area]/True Area × 100 [%]) was more striking at smaller diameters (up to –25% in the 2.5 mm tube).Conclusion: Luminal diameters and areas are underestimated by this particular IVUS system. When IVUS imaging and measurements are made during coronary interventions this error should be taken into account with regard to appropriate sizing of the device and the assessment of the postprocedure result. Because systematic errors might also occur in other IVUS systems (not tested in this study), it is advisable to ensure that each system is validated prior to clinical use, especially when exact measurements are required.This paper is followed by an Editorial Comment written by V. Bhargava et al. (see pp. 231–232).     

稳定型心绞痛患者与不稳定心绞痛患者冠状动脉血管内超声特点的比较

目的:通过对稳定型心绞痛（SAP）与不稳定心绞痛（UAP）患者冠状动脉血管内超声（IVUS）测定,进行斑块定性及定量分析,比较不同心绞痛患者冠状动脉斑块影像学特征性改变。方法:分别对37例SAP患者与34例UAP患者行冠状动脉造影及IVUS影像学检查;分析冠状动脉斑块性质,测定最小面积处外弹力膜面积（EEMA）、管腔横截面积、斑块面积（PA）、斑块负荷、重构指数等指标,并对各指标进行统计学分析。结果:UAP患者冠状动脉病变脂质斑块数明显多于SAP患者（P＜0.05）,而钙化斑块例数在两组间未见显著性差异;定量分析显示两组患者EEMA未见显著差异,而斑块负荷（PA/EEMA）的比较中两组间有显著性差异（P＜0.01）。UAP患者病变处倾向于表现为正性重构,而SAP患者多为负性重构。结论:SAP与UAP冠状动脉病变斑块性质及血管重构存在差异,IVUS能有效反映冠状动脉病变斑块特点。     

In vitro and in vivo comparison of three different intravascular ultrasound catheter designs.

Intravascular ultrasound (IVUS) is an invasive imaging modality, which provides detailed two-dimensional images of blood vessels. There are currently two different types of IVUS catheters available, namely, the phased-array and the mechanical designs. The operating ultrasound frequency of these catheters ranges from 20 to 40 MHz. This study sought to evaluate the image quality, accuracy of diameter and pullback length measurements, and catheter handling characteristics of three different IVUS catheters currently available for clinical use using both in vitro phantom models and in patients undergoing percutaneous coronary intervention (PCI). In gelatin phantom models, image quality assessed on a semiquantitative scale was significantly different between the three IVUS catheters (P = 0.01) with the 40-MHz catheter providing the best images. Accuracy of lumen diameter measurements, when compared to optical microscopy, were similar between the three IVUS catheter designs (all R(2) = 0.99). There were no significant differences in accuracy of pullback length measurements in vitro between the three designs. However, there were differences in the performance of the three IVUS catheters when used for preinterventional imaging in patients undergoing PCI. Both mechanical IVUS catheters were associated with lower procedural, fluoroscopy, and lesion crossing times compared to the phased-array catheter (all P < 0.05). There were no significant differences between the catheters during postinterventional IVUS imaging. There were also small but potentially important differences with regards to clinical events and complications associated with the use of the different IVUS catheters during the PCI procedures, reflecting differences in catheter design.     

Value of intravascular ultrasound in the assessment of coronary pseudostenosis during coronary interventions

Coronary pseudostenosis (PS) are increasingly visualized during coronary interventions. In many patients PS are readily recognized by a characteristic angiographic pattern, but in other cases the diagnosis remains difficult. The value of intravascular ultrasound (IVUS) in the study of PS remains unknown. In this study, IVUS was used to assess the morphologic appearance of the vessel wall in 10 consecutive patients showing images of PS during coronary interventions. Mean age of the group was 60 ± 12 years and two patients were female. IVUS was performed with a motorized pullback system to assess lumen, plaque, and total vessel cross-sectional areas. Measurements were performed both at the site of PS and at the distal reference segment. PS were always located on angled coronary segments. In one patient no lumen narrowing was detected with IVUS at the site of PS. In the remaining nine patients, however, a very localized elliptic-shaped lumen narrowing was demonstrated. As compared with the distal reference segment, coronary lumen (6.3 ± 2.2 vs. 12.7 ± 4.8 mm², P < 0.001) and total vessel area (11.9 ± 3.3 vs. 16.1 ± 6.1 mm², P < 0.05) were smaller at the site of PS. Severe lumen asymmetry was also documented at this site. In addition, a characteristic image of a flattened, three-layered wall, overlying a hypoechogenic space, was visualized in five patients. This unique pattern was considered the correlate of a partial coronary intussusception. PS induced some resistance to the advancement of catheters in two patients and temporary flow impairment in two additional patients. However, in every case, the image of PS disappeared once the guidewire was removed. Thus, at sites with PS, IVUS allows ruling out severe atherosclerosis and coronary dissections. In addition, IVUS also provides important diagnostic clues, including the image of intussusception, for making the correct diagnosis of this benign entity. Cathet. Cardiovasc. Intervent. 46:327–332, 1999. © 1999 Wiley-Liss, Inc.