Intravascular Ultrasound Transducer Research Articles

Characterisation of red and white thrombus by intravascular ultrasound using radiofrequency and videodensitometric data-based texture analysis

Visual assessment of intravascular ultrasound (IVUS) video images cannot reliably identify thrombus. We examined if texture analysis of radiofrequency (r.f.) data or videodensitometric data (VD) could distinguish thrombi of different ages and cell compositions. Whole human blood (red clot = RC), platelet-rich plasma (white clot = WC) and plasma ( n = 6/group) were imaged at 4 and 24 h with 30 MHz IVUS transducers. At 4 h, VD- and r.f.-based analyses revealed significant differences between RC and WC with variance (VD red 26.4 ± 2.5, white 33.9 ± 7.8; r.f. red 1.4 ± 0.5, white 4.9 ± 1.3), kurtosis (VD red 0.29 ± 0.9, white 0.23 ± 0.3) and skewness (VD red 0.23 ± 0.13, white 0.35 ± 0.52; r.f. red 0.06 ± 0.01, white −0.06 ± 0.05). Also mean grey-level from both data sets was higher in RC (VD 134.8 ± 18.0; r.f. −13.3 ± 1.2) than in WC (VD 105.3 ± 17.4, r.f. 16.5 ± 2.2) ( p < 0.01). With increasing time, variance increased in WC (5.5 ± 1.5 at 24 h) and decreased in RC (0.9 ± 0.3.3 at 24 h). The more heterogeneous structure of WC may be distinguished from that of RC using texture analysis of either VD or r.f.-signals.

A study of the quantitative and qualitative impact of catheter shaft angulation in a mechanical intravascular ultrasound system

Nonuniform rotation of mechanical intravascular ultrasound transducers may give rise to a geometric distortion of the ultrasound image known as the rotation angle artefact. This investigation studied the influence of different degrees and combinations of catheter shaft angulation on image morphology and the quantitative impact of the artefact using a circular perspex phantom and 3.5 F, 30 MHz Boston Scientific “Sonicath” catheters connected to a Hewlett Packard Sonos intravascular scanner. Major and minor diameters, cross-sectional area and circumference of the phantom lumen were measured and a “distortion index” calculated. Visually apparent geometric distortion was graded from 1 (absent) to 4 (severe). As expected, eccentric transducer location was associated much more frequently with identifiable distortion (70%) than was a concentric location (6%). Greater distortion occurred with increasing degrees of catheter shaft angulation, and was more pronounced in images from older catheters. The lumen area measurements in images in which no artefact was identified were accurate to within ±10% in 97% of cases, compared to only 81% of cases when an artefact was noted. The quantitative accuracy of an image in which geometric distortion is identified is thus not reliable. The direction of the quantitative error cannot be confidently predicted in any given case, although the mean lumen area tends to increase as the grade of distortion increases.

Distortion of intravascular ultrasound images because of nonuniform angular velocity of mechanical-type transducers

The purpose of this study was to quantify nonuniform rotation in a current mechanical intravascular ultrasound (IVUS) instrument and its effect on arc, area, and diameter measurements. The accurate reconstruction of IVUS two-dimensional images is dependent on uniform rotation of the catheter tip. Prior investigations suggested that bends in the catheter driveshaft may be responsible for poor torque transmission, nonuniform rotation, and consequent errors in IVUS measurements. Eight 30 MHz mechanically driven IVUS catheters were evaluated in a model simulating the catheter course through the aorta and coronary ostium in a clinical study. Angular velocity and position profiles of the transducer, image angle, and diameter and area measurement errors were obtained from each catheter by imaging a vascular phantom with eight equispaced echogenic markers from concentric and eccentric positions. Six catheters also were tested for comparison in a simple curvature model. Rotational error was found in all catheters tested and worsened in the aortic model. Maximal angular error, defined as the largest angle between actual and presumed transducer direction, increased when measured in the aortic model as compared with the simple curvature model (17 ± 12 degrees to 45 ± 25 degrees; p < 0.05). Angles of 45 degrees were misrepresented with a mean range of values of 26 to 63 degrees. With eccentric catheter placement, area and diameters had average maximal absolute errors of 26% ± 7.8% and 23% ± 10%, respectively. In conclusion, nonuniform rotation of mechanical IVUS transducers constitutes a significant potential source of error in IVUS measurement of arcs of calcification, and lumen shape, area, and diameter.

High-frequency membrane hydrophone

A membrane hydrophone with a 37-/spl mu/m diameter spot poled electrode has been fabricated on a 4-/spl mu/m-thick film of the piezoelectric copolymer, polyvinylidene fluoride trifluoroethylene (PVDF-TrFE), and initially characterized. The hydrophone has an effective spot size of less than 100 /spl mu/m, an on-membrane +7-dB gain buffer amplifier, and a -3-dB bandwidth of 150 MHz. The acoustic properties of the hydrophone were investigated with a transducer equivalent circuit model, the electric fringe fields due to poling were characterized with a finite difference electrostatic field model, and the effective spot diameters 2a/sub 3/ and 2a/sub 6/ were estimated. Measurements on the bandwidth, effective spot size, and sensitivity are presented. This hydrophone appears suitable for the characterization of both the frequency and spatial parameters of high-frequency transducers such as intravascular ultrasound (IVUS) catheter transducers operating in the 10-40 MHz range.

In vivovalidation of lesion length measurements using motorized pullback of intravascular ultrasound transducers

In vivovalidation of lesion length measurements using motorized pullback of intravascular ultrasound transducers

734-6 ANGUS: A New Approach to Three-dimensional Reconstruction of Geometry and Orientation of Coronary Lumen and Plaque by Combined Use of Coronary Angiography and IVUS

Three-dimensional (3-D) vessel reconstruction using intravascular ultrasound (IVUS) is limited by the lack of information on the real vessel curvatures and the orientation of the IVUS catheter. To overcome these limitations a method was developed using data obtained from ANGiography and intravascular UltraSound (ANGUS). This technique provides real spatial geometry and orientation of coronary lumen and plaque. The artery is studied by IVUS during a pull-back (PB) of the IVUS catheter at a speed of 1 mm/s. Start and end of the PB are recorded by biplane fluoroscopy (BF) and finally biplane coronary angiography (BA) is performed without changes in geometrical X-ray settings. Using a new computer program the contours of the lumen-plaque and plaque-adventitia boundaries are semi-automatically detected at 0.5 mm intervals. BF allows geometrical reconstruction of the catheter trajectory, which is the path of the IVUS transducer during PB. Combined use of the IVUS data, the catheter trajectory and the lumen contours in the BA provides a unique 3-D reconstruction of coronary arteries without any evidence of an additional unknown geometric factor. Studying the trajectory in a vessel phantom of known dimensions a high accuracy was found (distance between reconstructed and real trajectory at any point &lt; 2 mm). First application in a human right coronary artery in-vivo (length: 75 mm) showed a difference of 2% between the length of the reconstructed trajectory and the PB distance. Checking the locations of the origin of side-branches in the 3-D reconstruction and BA differences of less than 2 mm were found. Location and shape of stenoses in simulated projections of the reconstructed lumen matched well with BA. However, at the site of a previous PTCA luminal haziness in angiography and dissection observed by IVUS may slightly reduce the accuracy of this technique. Thus combining ANGiography and intravascular UltraSound (ANGUS) is promising and provides a unique reconstruction of 3-D coronary geometry.

Prediction of mechanical properties of human atherosclerotic tissue by high-frequency intravascular ultrasound imaging. An in vitro study.

Intravascular ultrasound may be useful for studying the natural history of atherosclerotic lesions of different morphologies and for guiding interventional strategies. This study was designed to test the hypothesis that tissue appearance by intravascular ultrasound is related to the biomechanical properties of atheroma components. Forty-three atheroma caps were obtained from the abdominal aortas of 22 patients at autopsy and studied with an ultrasensitive, servo-controlled spectrometer. By measuring the static strain caused by increasing levels of compressive stress from 30 to 90 mm Hg, the uniaxial unconfined compression stiffness (ratio of stress to strain) was determined. After mechanical testing, specimens were imaged with a 6F, 20-MHz intravascular ultrasound transducer, and images were interpreted by an investigator who was unaware of the mechanical measurements. Specimens were classified as nonfibrous (n = 14), fibrous (n = 18), or calcified (n = 11) based on intravascular ultrasound appearance. The static stiffnesses of the nonfibrous, fibrous, and calcified ultrasound classes were 41.2 +/- 18.8 kPa, 81.7 +/- 33.2 kPa, and 354.5 +/- 245.4 kPa, respectively (p = 0.0002 by analysis of variance). The times to reach static equilibrium (creep time) for the nonfibrous, fibrous, and calcified classes were 79.6 +/- 26.5 minutes, 50.2 +/- 20.0 minutes, and 19.4 +/- 8.1 minutes, respectively (p = 0.0007). Intravascular ultrasound appearance was most significantly related to biomechanical behavior when calcium deposits were noted; the differences in biomechanical behavior between nonfibrous and fibrous tissue appearances were less apparent.(ABSTRACT TRUNCATED AT 250 WORDS)

Inferior vena caval filter thrombi: evaluation with intravascular US.

A 20-MHz intravascular ultrasound (US) transducer inside a percutaneously inserted catheter was used to evaluate inferior vena caval (IVC) filters for thrombi in vitro and in vivo. Six different IVC filters were studied with intravascular US in a saline-filled model. Each filter had a characteristic, recognizable US pattern. Experimental thrombi as small as 0.5 cm3 were easily detected. Intravascular US was used clinically 25 times to evaluate the IVC in 23 patients with 24 IVC filters. Positive-contrast cavograms were available for comparison in all 25 cases. In 13 cases, no thrombi were identified in the filter or IVC with either intravascular US or cavography; in five of 12 cases with thrombi, intravascular US and cavography demonstrated the thrombi equally well. In six cases, intravascular US was superior to cavography in detection or delineation of thrombus in the IVC or filter. Intravascular US was considered superior to external duplex US in evaluation of caval thrombi in all 21 cases available for comparison. No complications from intravascular US were noted.

Catheter-based intravascular ultrasound discriminates bicuspid from tricuspid valves in adults with calcific aortic stenosis

A catheter-based intravascular ultrasound transducer was used to study aortic valve morphology in adults with calcific aortic stenosis. Examination of 14 postmortem specimens disclosed that intravascular ultrasound consistently identified the number of cusps or the presence of a calcified median raphe in the conjoined cusp, or both, and thereby distinguished a calcified bicuspid from a calcified tricuspid aortic valve. These postmortem findings were then employed to identify valvular morphology in 15 patients undergoing diagnostic cardiac catheterization or balloon aortic valvuloplasty, or both. Reproduction of criteria established in vitro allowed discrimination of congenital valvular morphology in all 15 patients, including 7 in whom assessment by intravascular ultrasound was confirmed by subsequent pathologic examination. Identification of aortic valvular morphology by intravascular ultrasound has potential therapeutic implications for patients considered to be candidates for operative or nonoperative aortic valvuloplasty.