Validation of a novel wire-type intravascular ultrasound imaging catheter.

Intravascular ultrasound can be used to characterize atherosclerotic plaques in arteries. This report describes the results of in vitro experiments with a novel wire-type intravascular ultrasound-imaging catheter developed in our laboratory. The ultrasound catheter comprises a 30-MHz transducer mounted on the tip of a wire-type catheter. The outer diameter of the catheter at the distal acoustic site was 0.025". Dimensional measurements of arteries obtained at the time of autopsy were acquired by intravascular ultrasound and direct planimetry. The luminal CSA (cross-sectional area), vessel CSA, and intima-media thickness for arterial samples (n = 22) acquired by ultrasound images and histopathologic microsections correlated closely (r = 0.99, 0.97, and 0.99, respectively). The histopathologic lumen CSA, vessel CSA, and intima-media thickness were less than those of corresponding ultrasound images in 43 of 54 samples (80%), 43 of 54 samples (80%), and 62 of 62 samples (80%), respectively. Intraobserver and interobserver variances of the luminal CSA vessel CSA and intima-media thickness by ultrasound images were excellence. This novel wire-type intravascular imaging catheter provides accurate vessel measurements and plaque thickness. Furthermore, this intravascular imaging catheter can be used in coronary arteries to assess the morphology of small distal coronary arteries.     

Update on Intravascular Ultrasound

Intravascular ultrasound (IVUS) has moved from being predominately a research tool at tertiary interventional centers to a clinical instrument used routinely to assess interventional success and resolve diagnostic challenges. Advances in instrumentation technology, along with emerging clinical data, have contributed to the wider application of IVUS. However, there are number of practical limitations that must be overcome to integrate intravascular ultrasound into the catheterization laboratory. It is novel to many experienced interventionalists and its use requires appropriate training and experience. This article reviews the technological advances in catheter, transducer, and imaging systems design and recent and emerging clinical trials.     

Future directions in intravascular ultrasound: from micro-motors to imaging guidewire systems

Intravascular ultrasound imaging requires both a small transducer assembly and catheter delivery system with optimal flexibil- ity and steerability. At this moment, multiele- ment electronic arrays provide an optimal catheter delivery system but the transducer assembly is both complicated and expensive while the image quality remains rather fair. Most intravascular ultrasound systems use mechanically rotated ultrasound beam generated by a single element. These systems provide good image quality but the need of a drive shaft restricts both the flexibility and steer ability of the catheter delivery system (Table I). In addition, the drive shaft behaves like spring and due to the curved trajectory of the catheter tube in the vascular system, a complicated frictional interaction will occur. The shaft will show a tendency to wind and unwind during one revolution, yielding a certain unpredictability of the angular position of the scanning head relative to that of the proximal system (Fig. 1).1     

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.     

Arterial wall characteristics determined by intravascular ultrasound imaging: an in vitro study

The feasibility of assessing arterial wall configuration with an intravascular 40 MHz ultrasound imaging device was investigated in an in vitro study of 11 autopsy specimens of human arteries. The system consists of a single element transducer, rotated with a motor mounted on an 8F catheter tip. Cross sections obtained with ultrasound were matched with the corresponding histologic sections. The arterial specimens were histologically classified as of the muscular or elastic type. Muscular arteries interrogated with ultrasound presented with a hypoechoic media, coinciding with the smooth muscle cells. In contrast, the media of an elastic artery densely packed with elastin fibers was as echogenic as the intima and the adventitia. On the basis of the cross-sectional image, it was possible to determine the nature of the atherosclerotic plaque. The location and thickness of the lesion measured from the histologic sections correlated well with the data derived from the corresponding ultrasound images. This study indicates that characterization of the type of artery and detection of arterial wall disease are possible with use of an intravascular ultrasound imaging technique.     

Intravascular ultrasound imaging in human peripheral and coronary arteries in vivo.

To determine the feasibility of intravascular ultrasound imaging in vivo, a miniaturized high frequency transducer catheter was introduced into human peripheral (n = 10) and coronary (n = 4) arteries. Cross-sectional ultrasound images were obtained from iliofemoral arteries in 10 patients using a 20 MHz transducer catheter (1.2 mm in diameter) and from coronary arteries in 4 patients using a 30 MHz transducer catheter 5 French size (Fr) following successful coronary angioplasty. Ultrasound images obtained from peripheral arteries showed a three-layered appearance (echo-reflective intima, echo-lucent media and echo-reflective adventitia) in the normal arteries. In diseased arteries, the location, amount and extent of atheromatous plaque were clearly documented. The arterial diameters measured by ultrasound closely correlated with the measurements by angiography (r = 0.91) in the peripheral arteries. Coronary angiograms obtained following balloon angioplasty revealed smooth edges at the dilatation sites without significant narrowing in all patients. However, a significant amount of residual atheromatous plaque was clearly observed on the ultrasound images at the previously dilated sites. Coronary dissection, which was identified as an echo-lucent area behind the plaque, was noted in 2 patients. Ultrasound images also revealed the presence of calcium in the plaque which was unrecognized on the angiograms in 3 patients. In addition, direct measurement of the lumen cross-sectional area was possible on the ultrasound images.(ABSTRACT TRUNCATED AT 250 WORDS)     

Transvascular Imaging: Feasibility Study Using a Vector Phased Array Ultrasound Catheter

Background: Transvascular imaging is defined as the acquisition of anatomic and functional information of structures lying beyond the confines of a vascular conduit within which the imaging device resides. Interrogating structures surrounding the vascular conduit is the subject of this feasibility study using a novel underblood, phased array ultrasound-tipped catheter. Methods: An intravascular catheter (10-F, 3.2-mm-diameter, four-way articulation) tipped with a 5.5- to 10-MHz frequency agile, vector phased array transducer with full Doppler capability (Sequoia, Acuson) was used. The imaging transducer has a wide range of tissue penetration (2 mm to >10 cm from the lens). The catheter was introduced via an 11-Fr femoral venous sheath into the inferior and superior vena cavae and right heart chambers. As the catheter was advanced, attention was directed to visualization of structures surrounding the vessel in which the catheter resided. Results: From the cavae and femoral vein the thoracic, abdominal and femoral arteries could be easily imaged. Anatomy that was visualized included the liver, hepatic veins, gallbladder, and mesenteric vessels. Normal and pathological anatomy and Doppler physiology could be readily appreciated. Doppler (i.e., pulsed- and continuous-wave, color flow, and tissue Doppler) fostered unique transvascular physiological hemo-dynamic and flow assessment. Conclusion: Transvascular imaging is feasible in human subjects using this 10-Fr catheter tipped with a 5.5- to 10 MHz vector phased array transducer. Intravascular navigation to a desired location within the body and the performance of diagnostic or therapeutic procedures at a remote site under direct ultrasound visualization are possible. Full Doppler capability extends the concept of transvascular hemodynamic and physiological assessment.     

Intravascular ultrasonic imaging

Because conventional imaging methods are inadequate for evaluating human coronary arteries in vivo, an intravascular ultrasonic imaging catheter was developed that allows the arterial wall to be studied in cross-section from within the artery. The catheter incorporates a mechanically rotating 20-MHz transducer, which is designed so that the ringdown occurs within the catheter and imaging is permitted up to the catheter's surface. The device rotates at 1800-rpm within a plastic sleeve and provides real-time cross-sectional images at 30 frames/sec. Preliminary experimental and clinical studies indicate that the intravascular ultrasonic imaging catheter could play a valuable role in providing preoperative information concerning arterial wall thickness and tissue characteristics, in distinguishing normal from diseased arterial wall structures during therapeutic intervention, and in assessing the results of intervention.     

Design characteristics for intravascular ultrasonic catheters

Several factors are important in the design of intracoronary ultrasonic imaging catheters. The mechanical considerations are first discussed and equations are developed for calculating the forces affecting catheter passage in a blood vessel. These equations are applied to the problem of Judkins (transfemoral) coronary artery catheterization, using previously described anatomical information and catheter moduli values. The introduction force is calculated for each position along the vessel for both a high and low value of estimated catheter-wall friction (coefficient values of 0.04 and 0.2, respectively). Next, the problem of catheter or transducer rotation is analytically described. The advantages of spiral drive cables with high torsional rigidity and low bending stiffness are numerically shown. Finally, several methods and considerations are given for electrical connection to the transducer. These results and equations should facilitate the design of intracoronary ultrasound imaging devices in the future.     

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.     

Assessment of normal and atherosclerotic arterial wall thickness with an intravascular ultrasound imaging catheter

A prototype intravascular ultrasound imaging catheter with a 20 MHz transducer was used to obtain 59 cross-sectional images in 14 segments of human atherosclerotic arteries. Three distinct components of the arterial wall were visualized on the ultrasound images: a highly reflective intima, an echolucent media, and a moderately reflective adventitia. Images were obtained at 1 mm increments in vitro and were compared with histologic sections at the same levels. Measurements of the arterial layers showed a close correlation between ultrasound images and histologic sections for the thickness of the intimal plaque (r = 0.91), the media (r = 0.83), and the total wall thickness (r = 0.85). The ultrasound images overestimated the mean intimal and total wall thickness by 0.3 mm and 0.7 mm compared to measurements in histologic sections (p less than 0.001). Intravascular imaging with high-frequency ultrasound is an accurate method for measuring microanatomic arterial dimensions and the extent of atheromatous involvement of the arterial wall. This method could represent an important adjunct to traditional angiographic techniques for assessing the severity of atherosclerosis.     

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.     

Percutaneous intravascular ultrasound imaging: validation of a real-time synthetic aperture array catheter

This study was designed to validate the dimensional accuracy and ability to characterize atherosclerotic vessel morphology of a new percutaneously passed ultrasound catheter. The 5.5F catheter used for this study has a synthetic aperture array transducer providing a radial field of view perpendicular to the catheter and can be passed over a standard 0.014-in guide wire. Initial in vitro studies were performed to assess accuracy of dimensional and morphologic information. In vitro images of fixed human vessels demonstrated good boundary definition, and dimensional measurements were closely correlated with histological samples (luminal area, r = .97; maximal lumen diameter, r = .95; maximal wall thickness, r = .83). Morphological subtypes were also closely correlated, with increasing severity of histological atherosclerosis characterized by predictable changes in the ultrasound images. Subsequently, the catheter was passed percutaneously in 28 patients to obtain images of coronary (n = 20) and pelvic (n = 12) vessels. Ultrasound images were compared with simultaneous digital angiograms. Correlation between ultrasonic and angiographic estimations of vessel diameters was good (r = .92). We conclude that intravascular ultrasound imaging will be useful for dimensional and morphological characterization of vascular disease, for the study of regression or progression of atherosclerosis, and, potentially, for guidance of therapeutic interventions such as atherectomy and angioplasty.     

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.     

Application of a new phased-array ultrasound imaging catheter in the assessment of vascular dimensions. In vivo comparison to cineangiography

Tomographic imaging techniques such as ultrasound can provide important information in the evaluation of vascular anatomy. Recent technical advances have permitted fabrication of a small (1.83 mm), phased-array, intravascular ultrasonic imaging catheter capable of continuous real-time, cross-sectional imaging of blood vessels. We used this imaging catheter to compare intraluminal ultrasound with cineangiography in the measurement of vascular dimensions in animals and to assess the intraobserver and interobserver variability of the technique. Segmental deformation of vessel anatomy was produced by stenoses created with a tissue ligature or by balloon dilation. The mean value for measurements of vessel diameter was 5.6 mm by cineangiography and 5.7 mm by intravascular ultrasound. The correlation between cineangiography and ultrasound was close (r = 0.98). Mean cross-sectional area by angiography was 28.8 mm2 and 29.6 mm2 (r = 0.96) by ultrasound. Percent diameter reduction produced by the stenoses averaged 48.4% by cineangiography and 40.1% by ultrasound, and the two methods correlated closely (r = 0.89). Correlation between cineangiography and ultrasound for vessel diameter and area before balloon dilation was closer (r = 0.92 and 0.88) than after balloon dilation (r = 0.86 and 0.81). This difference reflected an increase in measured vessel eccentricity following balloon dilation. These data demonstrate that intravascular ultrasound is an accurate and reproducible method for measurement of vascular diameter and cross-sectional area in vivo. Intravascular ultrasound is capable of accurately identifying and quantifying segmental deformation of vascular dimensions produced by either stenoses or balloon dilation.     

Balloon angioplasty of coarctation of the aorta evaluated with intravascular ultrasound imaging

Intravascular ultrasound images were employed to evaluate aortic coarctation before and after balloon angioplasty. Measurements obtained with use of an ultrasound imaging catheter correlated well with measurements made with digital aortography, both in the area of coarctation and in areas proximal and distal to it. The intravascular ultrasound images dramatically revealed dissection of the aortic wall and an intimal flap that was not appreciated on cineaortography or digital subtraction angiography. Intravascular ultrasound imaging may yield important morphologic information unavailable by other imaging techniques. Such information may allow more precise definition of the results of intravascular procedures and improve understanding of lesion characteristics predictive of a successful outcome.     

Intravascular ultrasound as a guiding modality for mechanical atherectomy and laser ablation

One of the most compelling practical applications for intravascular ultrasound imaging is in enhancing the safety and efficacy of the second-generation catheter devices designed to ablate or remove plaque. Initial studies have shown that intravascular ultrasound is well suited to demonstrate the amount of atheroma present in a vessel, and the distribution within the vessel wall at any given point. Further clinical studies are required to determine whether more complete debulking of atheroma, guided by ultrasound imaging, has a favorable impact in reducing the rates of acute closure and restenosis following the procedure.     

Validation of a Novel System for Co-Registration of Coronary Angiographic and Intravascular Ultrasound Imaging

IntroductionIntravascular ultrasound (IVUS) is a useful adjunct to guide percutaneous coronary intervention (PCI). Correlating IVUS images with angiographic findings can be challenging. We evaluated the utility of a novel co-registration system for IVUS and coronary angiography.Methods and resultsA 3-D virtual catheter trajectory was constructed from separate angiographic imaging runs using bespoke software. Intravascular ultrasound images were obtained using a commercially available mechanical rotational transducer with motorized pullback. Co-registration of ultrasound and angiographic images was then performed retrospectively based on the length of pullback, the 3-D trajectory and the start position of the catheter. Validation was performed in a spherical phantom model and in vivo in the coronary circulation of patients undergoing coronary angiography and intravascular imaging for clinical purposes. 111 paired angiographic and IVUS runs were performed in 3 phantom models. The differences between the reference length and the length measured on the 3D reconstructed path was −0.01 ± 0.40 mm. Intra-observer variability was 0.4%.We enrolled 25 patients in 3 European hospitals and performed 35 co-registration attempts with an 86% success rate. 71 landmarks were selected by the first operator, 68 by the second. Differences between angiographic and IVUS landmarks were −0.22 ± 0.72 mm and 0.05 ± 1.01 mm, respectively. Inter-observer variability was 0.23 ± 0.63 mm.ConclusionWe present a novel method for the co-registration of IVUS and coronary angiographic images. This system performed well in a phantom model and using images obtained from the human coronary circulation.ClassificationsInnovation, intravascular ultrasound, other technique