Intravascular and intracardiac ultrasound imaging: current research and future directions

Intravascular and intracardiac ultrasound imaging is a newly emerging catheter-based imaging modality with considerable promise. This review article presents the rationale behind attempts at developing intravascular imaging methods, the design features of intravascular instrumentation, the knowledge obtained with in vitro studies, the in vivo experience in humans, and the potential applications of intravascular imaging in arterial atherosclerosis. The feasibility of pulmonary artery imaging and the potential applications of intracardiac echocardiography are discussed. Finally, future directions in intravascular imaging are outlined.     

血管内影像技术的新进展

近年来血管内影像技术,特别是血管内超声领域的研究进展,主要包括:(1)对易损斑块认识的不断深入和检测率的逐步提高;(2)更有效地指导冠状动脉介入治疗,特别是指导药物洗脱支架的置入和随访。多种新型血管内影像技术日趋成熟,包括虚拟组织学血管内超声、整合背向散射血管内超声、光学相干断层成像术、近红外光谱仪、血管镜及血管内磁共振与传统的灰阶血管内超声一起,推动着血管内影像技术进入崭新的阶段。     

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.     

Current status of hybrid intravascular ultrasound and optical coherence tomography catheter for coronary imaging and percutaneous coronary intervention

Both intravascular ultrasound (IVUS) and optical coherence tomography (OCT) play a crucial role in elucidating the pathophysiology of coronary artery disease (CAD) with the goal to improve patient outcomes of medical and/or interventional CAD management. However, no single intravascular imaging technique has been proven to provide complete and detailed evaluation of all CAD lesions due to some limitations. Although sequential use of multiple modalities may sometimes be performed, there may be issues related to risk, time, and cost. To overcome these problems, several hybrids involving dual-probe combined IVUS-OCT catheters have been developed.The aim of this review article is to demonstrate some limitations of stand-alone imaging devices for evaluation of CAD, summarize the advances in hybrid IVUS-OCT imaging devices, discuss the technical challenges, and present the potential value in the clinical setting, especially in patients receiving medical or interventional CAD management.     

Coronary artery lumen volume measurement using three-dimensional intravascular ultrasound: Validation of a new technique

Objective: To validate an automated algorithm for the measurement of lumen volumes of coronary arteries. Background: Current intravascular ultrasound systems use absolute measurements of and changes in areas and diameters for the assessment of coronary artery disease. However, the coronary artery is a three-dimensional structure of complex geometry and volume. Methods: We used a comprehensive imaging system designed to reconstruct planar intravascular ultrasound images in three dimensions. This system consisted of a 25 MHz transducer-tipped rigid probe (for in vitro studies) or a 25 MHz transducer-tipped catheter within a 3.9F monorail imaging sheath (for in vivo studies), a motorized catheter pullback device that withdrew the transducer at 0.5 mm/sec, and an image processing computer that stacked 15 image slices/mm of vessel axial length and then performed thresholding-based three-dimensional image rendering and lumen volume measurement. We imaged 13 human coronary vessels (6 RCA, 6 LAD, 1 LCX) in vitro and 16 vessels (8 LAD, 6 RCA, 2 SVG) in vivo. Results: In vitro studies: Lumen volumes derived by three-dimensional intravascular ultrasound were 171 ± 121 mm³ and compared very well with those derived by histology (160 ± 109 mm³, r = 0.97, SEE = 29 mm³, P < 0.001) and with those derived by manual planimetry of planar intravascular ultrasound images (150 ± 106 mm³, r = 0.97, SEE = 30 mm³, P < 0.001). In vivo studies: Lumen volumes derived by three-dimensional intravascular ultrasound were 74 ± 35 mm³ and compared well with those derived by quantitative angiography (52 ± 20 mm³, r = 0.71, SEE = 25 mm³, P < 0.002). Conclusions: Three-dimensional intravascular ultrasound is a new technique that can accurately measure coronary artery lumen volumes. Further technical improvements may help to establish this technique as the new standard for lumen volume measurement. © Wiley-Liss, Inc.     

2011心血管影像回眸

基于影像学证据的诊断、治疗与干预措施越来越受到临床的重视。现以2011年国际发表的文献为基础,概述该年度在心血管影像领域包括超声心动图、核医学、磁共振成像、计算机断层成像、血管内超声及光学相干成像技术的最新进展与研究热点。     

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.     

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.     

Coronary angiogram classification of spontaneous coronary artery dissection

Spontaneous coronary artery dissection (SCAD) is under‐diagnosed and the true prevalence is underestimated. Unfortunately, SCAD is frequently missed on coronary angiogram since the arterial wall is not imaged with this test. Optical coherence tomography or intravascular ultrasound should be the true gold‐standard to diagnose SCAD. Given the elusive angiographic diagnosis of SCAD and the lack of familiarity with angiographic variants of SCAD, a diagnostic algorithm and angiographic classification for SCAD is proposed in this article. © 2013 Wiley Periodicals, Inc.     

Intravascular ultrasound evaluation of iliac stents one year following laser-assisted angioplasty

With the proliferation of sophisticated endovascular interventions, the need for more definitive assessment of preprocedural and postprocedural pathology and long-term outcome is acute. A new technique, intravascular ultrasound imaging, was used to provide a 1-year evaluation of iliac artery stents in a patient whose renal insufficiency contraindicated protocol-mandated arteriography. The sonogram provided adequate visualization of the functional status of the stents through cross-sectional measurements and the intimal response to the devices. This represents the first use of intravascular ultrasound imaging for long-term evaluation of iliac stents.     

Research and Clinical Applications of Optical Coherence Tomography in Invasive Cardiology: A Review

In cardiology, optical coherence tomography (OCT) is an invasive imaging technique based on the principle of light coherence. This system was developed to obtain three-dimensional high resolution images to examine coronary artery normal and/or pathological structure. This technique replaces the ultrasound used by its main alternative procedure, intravascular ultrasound, by a near-infrared light source. Acute coronary syndromes due to atherosclerotic vascular disease are the leading cause of mortality in developed and developing countries. As a consequence, intravascular imaging systems became an important area of research and 1991 marks the first use of OCT in coronary artery observations. Since its first appearance in invasive cardiology, OCT maintains a strong presence in the research environments for the identification of vulnerable plaques, as it is able to overcome difficulties presented by other techniques such as virtual intravascular ultrasound, near-infrared spectroscopy, and histology. Moreover, OCT is increasingly being used in the clinical practice as a guide during coronary interventions and in the assessment of vascular response after coronary stent implantation. This review focuses on the relevance of OCT in research and clinical applications in the field of invasive cardiology and discusses the future directions of the field.     

Intravascular ultrasound virtual histology imaging in acute ST-elevation myocardial infarction: A useful clinical tool during primary percutaneous coronary intervention

We described the novel use of intravascular ultrasound-virtual histology (IVUS-VH) imaging in two young adult male patients who presented with acute inferior ST-elevation myocardial infarction (STEMI) and we highlight the usefulness of this new invasive coronary imaging technique. Both patients had thrombotic occlusion of the right coronary arteries but the underlying pathophysiological mechanisms leading to acute thrombosis were different. The in vivo information obtained by IVUS-VH imaging was invaluable in pinpointing the likely etiology of STEMI and thus, guided our primary percutaneous coronary intervention strategy appropriately.     

Assessment of the results of percutaneous transluminal coronary angioplasty using an integrated ultrasound imaging-angioplasty Catheter

To evaluate the results percutaneous transluminal coronary angioplasty (PTCA), intra-vascular ultrasound imaging was performed in 32 proximal coronary arterial segments and in 16 atherosclerotic lesions after PTCA in 13 patients using a 5 Fr balloon catheter with an ultrasound transducer mounted just proximal to the balloon. Simultaneous angiographic measurements of vessel diameter were also performed using electronic calipers from contrast cine angiograms. There was good correlation between ultrasound and angiographic minimum luminal diameters of the normal proximal vessel (y = 0.59x + 1.49, r = 0.70, P<0.01, n = 32). However, the luminal diameter measured by intravascular ultrasound was significantly greater than when measured by contrast angiography (2.81±0.10 vs. 2.34±0.12mm, n = 16, P<0.001, mean ±SEM). Post-PTCA, there was good correlation between ultrasound and angiographic minimum luminal diameters of the lesion (y = 0.62x + 1.42, r=0.76, P<0.001, n = 16), but again luminal diameters were significantly greater when measured by intravascular ultrasound compared to contrast angiography (2.61±0.08 vs. 1.89 ± 0.10mm, n = 16, P<0.001). Furthermore, residual stenosis was significantly less when determined by intravascular ultrasound than by contrast angiography (7.3±2.0 vs. 18.1 ± 2.1%, n = 16, P<0.001). Intravascular ultrasound was able to detect coronary calcification that was not evident by contrast coronary angiography in 8 of 16 lesions. Post-PTCA, dissection was evident in four lesions by ultrasound, whereas dissection was appreciated in only three lesions by contrast angiography. We conclude that intravascular ultrasound can accurately measure the luminal diameter of coronary arteries both before and after PTCA and reveals more information about the lesion characteristics than does conventional contrast angiography.     

Comparison of effectiveness and safety of drug-eluting stents versus vascular brachytherapy for saphenous vein graft in-stent restenosis

We investigated the safety and efficacy of drug-eluting stents (DESs) for the treatment of patients who presented with in-stent restenosis (ISR) of saphenous vein grafts (SVGs) and compared the in-hospital and 6-month clinical outcomes of DESs with those of intravascular brachytherapy and balloon angioplasty alone. Records of 187 patients who presented with ISR of SVGs were analyzed. Of these, 34 consecutive patients were treated with DES implantation, 93 were treated with intravascular brachytherapy (n = 60 with gamma-radiation, n = 33 with beta-radiation), and 60 patients underwent conventional treatment with balloon angioplasty alone. Clinical and angiographic characteristics at baseline were comparable between groups. The DES group had less non-Q-wave myocardial infarction than did the intravascular brachytherapy and balloon angioplasty groups (0%, 20%, and 26%, p = 0.003 and <0.001, respectively). At 6 months, death occurred in 0% of the DES group, 2% of the intravascular brachytherapy group, and 5% of the balloon angioplasty group (p = 0.36 and <0.18, respectively). Target lesion revascularization/major adverse cardiac events were similar in the intravascular brachytherapy and DES groups (12% and 3%, p = 0.13) and significantly decreased compared with patients who were treated with balloon angioplasty alone (55%, p <0.001 for the 2 comparisons). The results of this retrospective analysis suggest that DES implantation is at least as effective and safe as intravascular brachytherapy for the treatment of SVG ISR and that these treatment modalities are superior to balloon angioplasty alone.     

Breaking the deadlock of calcified coronary artery lesions: A contemporary review

Percutaneous coronary intervention (PCI) of severely calcified lesions is known to result in lower procedural success rates, higher complication rates, and worse long-term clinical outcomes compared to noncalcified lesions. Adequate lesion preparation through calcium modification is crucial in ensuring procedural success and reducing adverse cardiovascular outcomes. There are numerous calcium modification devices currently available whose usefulness depends on the nature of the calcific disease and its anatomical distribution. It can be challenging for the interventionists to decide which device is best suited for their patient. There is also emerging evidence for intravascular imaging in guiding selection of calcium modification devices using parameters such as calcium distribution and depth that directly impact on procedural success and clinical outcomes. In this review we aim to discuss the pathophysiology of coronary calcification, evaluate strategies and technologies of calcium modification and propose an A-M-A-S-A algorithm in managing calcified coronary lesions.     

Intravascular ultrasound assessment of arterial dissection, intimal flaps, and intraarterial thrombi

Arterial dissection, intimal tears, and intraluminal thrombosis are common sequelae of catheter-based interventional procedures for coronary artery disease. These may not be recognized reliably by contrast angiography. Intravascular ultrasound imaging is an innovative method that allows visualization of the cross-sectional anatomy with high-resolution real-time images. This article presents the recent experience in arterial imaging with this method. Studies documenting the ability of intravascular ultrasound to demonstrate arterial atherosclerosis and to unmask some problems related to atherosclerotic disease and its treatment by catheter-based maneuvers are presented. Problems of arterial dissection, intimal flaps, and intravascular thrombosis are described with in vitro and in vivo documentation of the capability of intravascular ultrasound to visualize these abnormalities. The clinical implications of real-time imaging of intimal flaps and intraluminal clots, and the possible value of this imaging modality in the performance of catheter-based therapeutic procedures for coronary and peripheral arterial disorders are discussed.     

Esophageal Doppler: noninvasive cardiac output monitor

In this article we describe the esophageal Doppler, a noninvasive, instantaneous cardiac output monitor. Its reliability has been demonstrated to be comparable to that of other current techniques used in the clinical arena to measure cardiac output. It helps guiding intravascular fluid resuscitation by quantifying the increase in flow in response to fluid challenges and by indicating the plateau of the patient's cardiac function curve. When the plateau has been reached, further fluid loading may result in congestion without improvement in systemic flow. Thus, measuring cardiac output is the only way to determine the upper limit for fluid intake. In addition, a strategy based on cardiac output optimization has proven beneficial in high-risk surgical patients.     

Severe hemolysis and renal failure in glucose-6-phosphate dehydrogenase deficient patients with hepatitis E

Hemolytic anemia as a complication of acute hepatitis is not uncommon in patients with glucose-6-phosphate dehydrogenase deficiency. However, severe hemolysis in these patients is rare. We report a cohort of five patients with acute viral hepatitis E who developed severe intravascular hemolysis and unusually high levels of bilirubin. All five patients had severe, complicated, protracted courses of illness. Four patients developed acute renal failure, and two of these required hemodialysis. To the best of our knowledge this is the first report of a cohort of patients with glucose-6-phosphate dehydrogenase deficiency and acute viral hepatitis E with severe intravascular hemolysis. We emphasize the fact that intravascular hemolysis should be suspected in patients with acute viral hepatitis E with marked bilirubinemia and anemia. Measures to prevent renal failure should be taken in such cases.     

Milestones in cardiac ultrasound: echoes from the past History of cardiac ultrasound

Although the antecedents of cardiac ultrasound can be traced back to the 1870s, it was in 1954 that Edler and Hertz published their milestone paper. M-mode echocardiography reached its peak in the early 1970s, when the fibre-optic recorder made the method clinically viable. It was not long before real-time two-dimensional imaging was developed, however, and the invention of pulsed Doppler laid the foundation of duplex scanning. In 1985, colour flow imaging gave a fresh impetus to echocardiography. In parallel with the main developments, intravascular and transoesophageal scanning have gained clinical popularity within the last decade, together with techniques for the display of three-dimensional images. Other innovations include contrast agents, pressure gradient measurement and promising methods for tissue characterisation. It seems that current techniques are safe, but this needs to be kept continuously under review.     

Serial intravascular ultrasound assessment of the efficacy of intracoronary gamma radiation for preventing recurrent in-stent restenosis

Intracoronary stents reduce restenosis compared with balloon angioplasty. However, a major limitation of stenting is in-stent restenosis, which occurs in 10% to 40% of the patients depending upon risk factors. Serial intravascular ultrasound studies have shown that in-stent restenosis is primarily due to neointimal hyperplasia. Treatment of in-stent restenosis is challenging and recurrence rates are high regardless of interventional technique used. Several randomized clinical trials with intracoronary ionizing radiation using both beta (b) and gamma (g) emitters following primary catheter-based intervention have demonstrated a significant reduction in recurrence. The majority of these studies have used both serial angiographic and serial intravascular ultrasound endpoints to assess the efficacy of intracoronary radiation to prevent recurrence after the treatment of in-stent restenosis. As different mechanism of postradiation restenosis may operate in the original lesion segment, the ballooned segment and the actual irradiated segment, these imaging techniques have also helped to document any long-term affects of radiation including aneurysm formation, edge effects, geographical miss, and the presence or absence of remodeling. The angiographic results have correlated well with intravascular ultrasound results after radiation therapy and at follow-up. Thus, a combination of both serial intravascular ultrasound and careful angiography, which documents balloon, stent, and radiation source positioning, can fully assess the effectiveness of this modality of treatment.